INTRODUCTION TO GRQUNDWATER INVESTIGATIONS QSHEBL 9285..9-15B
540/R-95-091
PB95-963217
FOREWORD
This manual is for reference use of students enrolled in scheduled training courses of the U.S.
Environmental Protection Agency (EPA). While it will be useful to anyone who needs information
on the subjects covered, it will have its greatest value as an adjunct to classroom presentations
involving discussions among the students and the instructional staff.
This manual has been developed with a goal of providing the best available current information;
however, individual instructors may provide additional material to cover special aspects of their
presentations.
Because of the limited availability of the manual, it should not be cited in bibliographies or other
publications.
References to products and manufacturers are for illustration only; they do not imply endorsement
by EPA.
Constructive suggestions for improvement of the content and format of the manual are welcome.
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INTRODUCTION TO GROUNDWATER INVESTIGATIONS
(165.7)
3 Days
This introductory course is designed to provide participants with information concerning
hydrogeological processes and the necessary elements of a sound groundwater site investigation. It
is intended for personnel who are involved in groundwater contamination investigations but have
little prior hydrogeological experience. This course is not designed for geologists or
hydrogeologists.
Topics that are discussed include hydrogeological definitions and concepts; basic geology and
geochemistry; drilling, construction, and placement of monitoring wells; groundwater sampling
considerations; groundwater flow rates; and groundwater modeling.
Instructional methods include lectures, group discussions, case studies, and class problem-solving
exercises.
After completing the course, participants will be able to:
• Identify the components of a groundwater system.
• List the primary hydrogeological factors to be considered in a site investigation.
• Construct a flow net and calculate the hydraulic gradient of a simple system.
• Discuss the primary advantages and disadvantages of the most common geophysical
survey methods.
• Identify the different types of pumping tests and the information that can be obtained
from each.
• Describe monitoring well drilling and sampling techniques.
U.S. Environmental Protection Agency
Office of Emergency and Remedial Response
Environmental Response Team
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CONTENTS
Acronyms and Abbreviations
Glossary
SECTION 1
SECTION 2
SECTION 3
SECTION 4
SECTION 5
SECTION 6
SECTION 7
SECTION 8
SECTION 9
SECTION 10
GEOLOGY
Article: Geometry of Sandstone Reservoir Bodies
HYDROGEOLOGY
THE HYDROGEOLOGICAL INVESTIGATION
Checklist for a Hydrogeological Investigation
GEOPHYSICAL METHODS
MONITORING THE VADOSE ZONE
WELL CONSTRUCTION
HYDROGEOCHEMISTRY
Article: Migration of Chlorophenolic Compounds at the Chemical Waste
Disposal Site at Alkali Lake, Oregon—1. Site Description and
Ground-Water Flow
Article: Migration of Chlorophenolic Compounds at the Chemical Waste
Disposal Site at Alkali Lake, Oregon—2. Contaminant
Distributions, Transport, and Retardation
Article: Using the Properties of Organic Compounds to Help Design a
Treatment System
GROUNDWATER FLOW RATES AND MODELING
PROBLEM EXERCISES
Problem 1—Flow Net Construction
Problem 2—Geologic Cross-Section Construction
Problem 3—Aquifer Tests
Problem 4—Groundwater Investigation
Problem 5—Nomograph
APPENDICES
Appendix A—Sampling Protocols
Appendix B—References
Appendix C—Sources of Information
9/93
Contents
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ACRONYMS AND ABBREVIATIONS
ACS American Chemical Society
AGI American Geological Institute
ARAR applicable or relevant and
appropriate requirement
ASTM American Society for Testing
and Materials
ATSDR Agency for Toxic Substances
and Disease Registry
atm atmosphere
BDAT best demonstrated available
technology
BM Bureau of Mines
BNA base/neutral/acid extractables
BOD biochemical oxygen demand
BTEX benzene, toluene, ethylbenzene,
and xylenes
CAA Clean Air Act
CDC Centers for Disease Control
CE current electrode
CERCLA Comprehensive Environmental
Response, Compensation and
Liability Act of 1980
CERCLIS CERCLA Information System
CERI Center for Environmental
Research Information
CFR Code of Federal Regulations
CLP Contract Laboratory Program
9/93
CFA continuous flight auger
COC chain of custody
COD chemical oxygen demand
COE U.S. Army Corps of Engineers
CWA Clean Water Act
DO dissolved oxygen
DOJ U.S. Department of Justice
DOT U.S. Department of
Transportation
DQO data quality objectives
DRI direct-reading instruments
DNAPL dense, nonaqueous phase liquid
Eh oxygen-reduction potential
EM electromagnetic
EMSL-LV Environmental Monitoring
Systems Laboratory - Las
Vegas
EP,OX toxicity-extraction procedure
toxicity
EPA U.S. Environmental Protection
Agency
EPIC Environmental Photographic
Interpretation Center
ER electrical resistivity
ERP Emergency Response Plan
Acronyms and Abbreviations
-------
ERT EPA Emergency Response
Team
ERTS Earth Resources Technology
Satellite
EROS Earth Resources Observation
Systems
ESB EPA Environmental Services
Branch
ESD Environmental Services
Division
eV electron volt
FIFRA Federal Insecticide, Fungicide,
and Rodenticide Act
FIT field investigation team
FRP fiberglass reinforced plastic
FS feasibility study
FSP field sampling plan
GAC granular activated carbon
GC gas chromatograph
GC/MS gas chromatography/mass
spectrometry
gpm gallons per minute
GPR ground-penetrating radar
GWA Ground Water Act of 1987
HASP health and safety plan (see also
site safety plan)
HAZMAT hazardous materials team
HRS
hazard ranking system
HSL hazardous substance list
(previous term for target
compound list)
HSA hollow-stem auger
HSO health and safety officer (see
also SSC, SSHO, and SSO)
HSWA Hazardous and Solid Waste
Amendments (to RCRA, 1984)
HWS hazardous waste site
ICS incident command system
IDL instrument detection limit
IDLH immediately dangerous to life
and health
IP ionization potential
IR infrared (spectroscopy)
K hydraulic conductivity
LEL lower explosive limit
LNAPL light, nonaqueous phase liquid
LUST leaking underground storage
tank
MCL maximum contaminant level
MCLG maximum contaminant level
goal
MDL method detection limit
MSL mean sea level
m/sec meters per second
MHz megahertz
Acronyms and Abbreviations
9/93
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MS/MS mass spectrometry/mass
spectrometry
NEAR nonbinding preliminary
allocation of responsibility
NCIC National Cartographic
Information Center
NCP National Oil and Hazardous
Substances Pollution
Contingency Plan
NEIC National Enforcement
Investigation Center
NIOSH National Institute of
Occupational Safety and Health
NIPDWR National Interim Primary
Drinking Water Regulations
NOAA National Oceanic and
Atmospheric Administration
n.o.s. not otherwise specified (used
in shipping hazardous material)
NPDES National Pollutant Discharge
Elimination System
NPL National Priorities List
NRC Nuclear Regulatory
Commission
NSF National Sanitation Foundation
NTIS National Technical Information
Service
NWS National Weather Service
OERR EPA Office of Emergency and
Remedial Response
OHMTADS Oil and Hazardous Materials
Technical Assistance Data
System
OSHA Occupational Safety and Health
Administration
OSWER EPA Office of Solid Waste and
Emergency Response
OVA organic vapor analyzer (onsite
organic vapor monitoring
device)
OWPE EPA Office of Waste Programs
Enforcement
PAC powdered activated carbon
PAH polycyclic aromatic
hydrocarbons
PCB polychlorinated biphenyls
PCDD polychlorinated dibenzo-/>-
dioxin
PCDF polychlorinated dibenzofuran
PCP pentachlorophenol
PE potential electrode
PEL permissible exposure limit
PID photoionization detector
PO project officer (EPA)
POHC principle organic hazardous
constituent
POM polycyclic organic matter
POTWs publicly owned treatment
works
ppb parts per billion
9/93
Acronyms and Abbreviations
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PPE personal protective equipment
ppm parts per million
PRP potentially responsible party
psig pounds per square inch gauge
PVC polyvinyl chloride
QA quality assurance
QA/QC quality assurance and quality
control
QAMS quality assurance management
staff
QC quality control
RA remedial action
RAS routine analytical services
RCRA Resource Conservation and
Recovery Act of 1978
RD remedial design
REM remedial planning
REM/FIT remedial planning/field
investigation team
RI/FS remedial investigation and
feasibility study
ROD record of decision
RPM EPA remedial project manager
RQ reportable quantity
RSPO remedial site project officer
RSCC Regional Sample Control
Center
SARA Superfund Amendments and
Reauthorization Act of 1986
SAS special analytical services
SCBA self-contained breathing
apparatus
SCS Soil Conservation Service
SDL sample detection limit
SDWA Safe Drinking Water Act
SI site inspection
SITE Superfund Innovative
Technology Evaluation
SM site manager
SOP standard operating procedure
SP spontaneous potential
SQG small quantity generator
SSC site safety coordinator
SVOC semivolatile organic
compound
SWDA Solid Waste Disposal Act
TAT technical assistance team
TCLP toxicity characteristic leaching
procedure
TEGD Technical Enforcement
Guidance Document
TDS total dissolved solids
TLV threshold limit value
TOC total organic carbon
Acronyms and Abbreviations
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TOH total organic halogen
TOX total organic halides
TSCA Toxic Substances Control Act
TSDF treatment, storage, and disposal
facility
TUHC total unburned hydrocarbons
UEL upper explosive limit
UMTRCA Uranium Mill Tailing Radiation
Control Act
USCG United States Coast Guard
USCS Unified Soil Classification
System
USDI U.S. Department of the Interior
USGS U.S. Geological Survey
UST underground storage tank
UV ultraviolet
VOA volatile organic analysis
VOC volatile organic compound
9/93 5 Acronyms and Abbreviations
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GLOSSARY
acre-foot
adsorption
advection
alluvium
anisotropic
aquifer
aquifer test
aquitard
artesian
artificial recharge
artesian aquifer
bedload
enough water to cover 1 acre to a depth of 1 foot; equal to 43,560
cubic feet or 325,851 gallons
the attraction and adhesion of a layer of ions from an aqueous solution
to the solid mineral surfaces with which it is in contact
the process by which solutes are transported by the bulk motion of the
flowing groundwater
a general term for clay, silt, sand, gravel, or similar unconsolidated
material deposited during comparatively recent geologic time by a
stream or other body of running water as a sorted or semisorted
sediment in the bed of the stream or on its floodplain or delta, or as
a cone or fan at the base of a mountain slope
hydraulic conductivity ("K"), differing with direction
a geologic formation, group of formations, or a part of a formation
that contains sufficient permeable material to yield significant
quantities of groundwater to wells and springs. Use of the term
should be restricted to classifying water bodies in accordance with
stratigraphy or rock types. In describing hydraulic characteristics such
as transmissivity and storage coefficient, be careful to refer those
parameters to the saturated part of the aquifer only.
a test involving the withdrawal of measured quantities of water from,
or the addition of water to, a well (or wells) and the measurement of
resulting changes in head (water level) in the aquifer both during and
after the period of discharge or addition
a saturated, but poorly permeable bed, formation, or group of
formations that does not yield water freely to a well or spring
confined; under pressure sufficient to raise the water level in a well
above the top of the aquifer
recharge at a rate greater than natural, resulting from deliberate or
incidental actions of man
see confined aquifer
the part of the total stream load that is moved on or immediately above
the stream bed, such as the larger or heavier particles (boulders,
pebbles, gravel) transported by traction or saltation along the bottom;
the part of the load that is not continuously in suspension or solution
9/93
1
Glossary
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capillary zone
capture
coefficient of storage
cone of depression
confined
confined aquifer
confining bed
diffusion
discharge area
discharge velocity
dispersion
drawdown
effective porosity
negative pressure zone just above the water table where water is drawn
up from saturated zone into soil pores due to cohesion of water
molecules and adhesion of these molecules to soil particles. Zone
thickness may be several inches to several feet depending on porosity
and pore size.
the decrease in water discharge naturally from a ground-water
reservoir plus any increase in water recharged to the reservoir
resulting from pumping
the volume of water an aquifer releases from or takes into storage per
unit surface area of the aquifer per unit change in head
depression of heads surrounding a well caused by withdrawal of water
(larger cone for confined aquifer than for unconfmed)
under pressure significantly greater than atmospheric throughout and
its upper limit is the bottom of a bed of distinctly lower hydraulic
conductivity than that of the material in which the confined water
occurs
geological formation capable of storing and transmitting water in
usable quantities overlain by a less permeable or .impermeable
formation (confining layer) placing the aquifer under pressure
a body of "impermeable" material stratigraphically adjacent to one or
more aquifers
the process whereby particles of liquids, gases, or solids intermingle
as a result of their spontaneous movement caused by thermal agitation
an area in which subsurface water, including both groundwater and
water in the unsaturated zone, is discharged to the land surface, to
surface water, or to the atmosphere
an apparent velocity, calculated from Darcy's law, which represents
the flow rate at which water would move through the aquifer if it were
an open conduit (also called specific discharge)
the spreading and mixing of chemical constituents in groundwater
caused by diffusion and by mixing due to microscopic variations in
velocities within and between pores
the vertical distance through which the water level in a well is lowered
by pumping from the well or a nearby well
the amount of interconnected pore space through which fluids can
pass, expressed as a percent of bulk volume. Part of the total porosity
Glossary
9/93
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evapotranspiration
flow line
fluid potential
gaining stream
groundwater
groundwater divide
groundwater model
groundwater reservoir
groundwater system
head
heterogeneous/geological
formation
homogeneous
will be occupied by static fluid being held to the mineral surface by
surface tension, so effective porosity will be less than total porosity.
the combined loss of water from direct evaporation and through the
use of water by vegetation (transpiration)
the path that a particle of water follows in its movement through
saturated, permeable rocks (synonym: streamline)
the mechanical energy per unit mass of water or other fluid at any
given point in space and time, with respect to an arbitrary state of
datum
a stream or reach of a stream whose flow is being increased by inflow
of groundwater (also called an effluent stream)
water in the zone of saturation
a ridge in the water table or other potentiometric surface from which
groundwater moves away in both directions normal to the ridge line
simulated representation of a groundwater system to aid definition of
behavior and decision-making
all rocks in the zone of saturation (see also aquifer)
a groundwater reservoir and its contained water; includes hydraulic
and geochemical features
combination of elevation above datum and pressure energy imparted
to a column of water (velocity energy is ignored because of low
velocities of groundwater). Measured in lengtii units (i.e., feet or
meters).
characteristics varying aerially or vertically in a given system
geology of the aquifer is consistent; not changing with direction or
depth
hydraulic conductivity "K" volume flow through a unit cross-section area per unit decline in head
(measured in velocity units and dependent on formation characteristics
and fluid characteristics)
9/93
Glossary
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hydraulic gradient
change of head values over a distance
hydrograph
impermeable
infiltration
interface
intrinsic permeability
isotropic
laminar flow
losing stream
mining
nonsteady state-nonsteady
shape
where:
H = head
L = distance between head measurement points
graph that shows some property of groundwater or surface water as a
function of time
having a texture that does not permit water to move through it
perceptibly under the head difference that commonly occurs in nature
the flow or movement of water through the land surface into the
ground
in hydrology, the contact zone between two different fluids
pertaining to the relative ease with which a porous medium can
transmit a liquid under a hydrostatic or potential gradient. It is a
property of the porous medium and is independent of the nature of the
liquid or the potential field.
hydraulic conductivity ("K") is the same regardless of direction
low velocity flow with no mixing (i.e., no turbulence)
a stream or reach of a stream that is losing water to the subsurface
(also called an influent stream)
in reference to groundwater, withdrawals in excess of natural
replenishment and capture. Commonly applied to heavily pumped
areas in semiarid and arid regions, where opportunity for natural
replenishment and capture is small. The term is hydrologic and
excludes any connotation of unsatisfactory water-management practice
(see, however, overdraft).
(also called unsteady state-nonsteady shape) the condition when the
rate of flow through the aquifer is changing and water levels are
declining. It exists during the early stage of withdrawal when the
water level throughout the cone of depression is declining and the
shape of the cone is changing at a relatively rapid rate.
Glossary
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nonsteady state-steady
shape
optimum yield
overdraft
pellicular water
perched
permeability
permeameter
piezometer
porosity
potentiometric surface
recharge
recharge area
safe yield
saturated zone
is the condition that exists during the intermediate stage of withdrawals
when the water level is still declining but the shape of the central part
of the cone is essentially constant
the best use of groundwater that can be made under the circumstances;
a use dependent not only on hydrologic factors but also on legal,
social, and economic factors
withdrawals of groundwater at rates perceived to be excessive and,
therefore, an unsatisfactory water-management practice (see also
mining)
water adhering as films to the surfaces of openings and occurring as
wedge-shaped bodies at junctures of interstices in the zone of aeration
above the capillary fringe
unconfined groundwater separated from an underlying body of
groundwater by an unsaturated zone
the property of the aquifer allowing for transmission of fluid through
pores (i.e., connection of pores)
a laboratory device used to measure the intrinsic permeability and
hydraulic conductivity of a soil or rock sample
a nonpumping well, generally of small diameter, that is used to
measure the elevation of the water table or potentiometric surface. A
piezometer generally has a short well screen through which water can
enter.
the ratio of the volume of the interstices or voids in a rock or soil to
the total volume
imaginary saturated surface (potential head of confined aquifer); a
surface that represents the static head; the levels to which water will
rise in tightly cased wells
the processes of addition of water to the zone of saturation
an area in which water that is absorbed eventually reaches the zone of
saturation
magnitude of yield that can be relied upon over a long period of time
(similar to sustained yield)
zone in which all voids are filled with water (the water table is the
upper limit)
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Glossary
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slug-test
specific capacity
specific yield
steady-state
storage
storage coefficient "S"
storativity
sustained yield
transmissivity
vadose zone
an aquifer test made by either pouring a small instantaneous charge of
water into a well or by withdrawing a slug of water from the well
(when a slug of water is removed from the well, it is also called a
bail-down test)
the rate of discharge from a well divided by the drawdown in it. The
rate varies slowly with the duration of pumping, which should be
stated when known.
ratio of volume of water released under gravity to total volume of
saturated rock
the condition when the rate of flow is steady and water levels have
ceased to decline. It exists in the final stage of withdrawals when
neither the water level nor the shape of the cone is changing.
in groundwater hydrology, refers to 1) water naturally detained in a
groundwater reservoir, 2) artificial impoundment of water in
groundwater reservoirs, and 3) the water so impounded
volume of water taken into or released from aquifer storage per unit
surface area per unit change in head (dimensionless) (for confined,
S = 0.0001 to 0.001; for unconfmed, S = 0.2 to 0.3)
the volume of water an aquifer releases from or takes into storage per
unit surface area of the aquifer per unit change in head (also called
coefficient of storage)
continuous long-term groundwater production without progressive
storage depletion (see also safe yield)
the rate at which water is transmitted through a unit width of an
aquifer under a unit hydraulic gradient
the zone containing water under pressure less than that of the
atmosphere, including soil water, intermediate vadose water, and
capillary water. Some references include the capillary water in the
saturated zone. This zone is limited above by the land surface and
below by the surface of the zone of saturation (i.e., the water table).
Also called the unsaturated zone or zone of aeration. According to
Freeze and Cherry (1979):
1. It occurs above the water table and above the capillary fringe.
2. The soil pores are only partially filled with water; the moisture
content 6 is less than the porosity n.
3. The fluid pressure p is less than atmospheric; the pressure head ^
is less than zero.
4. The hydraulic head h must be measured with a tensiometer.
Glossary
9/93
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5. The hydraulic conductivity K and the moisture content 6 are both
functions of the pressure head ^.
water table surface of saturated zone area at atmospheric pressure; that surface in
an unconfined water body at which the pressure is atmospheric.
Defined by the levels at which water stands in wells that penetrate the
water body just far enough to hold standing water.
9/93 7 Glossary
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GEOLOGY
PERFORMANCE OBJECTIVES
At the end of this lesson, participants will be able to:
• Define the Doctrine of Uniformitarianism
• Describe the three basic rock types and evaluate each as
aquifers
• Describe the rock forming processes found on the Rock
Cycle diagram
• Identify the medium responsible for the erosion and transport
of sediments
• Describe the following depositional environments:
Alluvial fans
Braided streams
Meandering streams
Coastal (deltaic, interdeltaic, barrier island complexes)
Wind-blown deposits
Carbonates.
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GEOLOGY
NOTES
MW1
720ft
MW3
718.25ft
9/93
Geology
-------
NOTES
Doctrine
of
Uniformitarianism
"The Present is the
Key to the Past"
James Mutton, 1785
THE ROCK CYCLE
Deposition •
Transport
LJthification
\
Sedimentary rocks
>|
Metamorphism
X
Metamorphic rocks
Melting
Geology
9/93
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NOTES
SEDIMENTATION
• Erosion processes (weathering)
• Transport agents
• Deposition
• Lithification
EROSION PROCESSES
• Wind
• Ice
• Water
• Biology
• Gravity
TRANSPORT AGENTS
• Wind
• Ice
• Water
• Biology
• Gravity
9/93
Geology
-------
NOTES
DEPOSITION
• Wind
• Ice
• Water
• Gravity
LITHIFICATION
Cementation
Diagenesis
TYPES OF CEMENT
• Silica
• Iron oxides
• Kaolinite
• Montmorillonite
• Illite
• Calcite (aragonite)
Geology
9/93
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SEDIMENTARY ROCKS
Composed of particles of any rock type
- "Pores" form during deposition
Most aquifers are sedimentary rocks
SEDIMENTARY ROCKS
NOTES
Limestone
Shale
Sandstone
Coal
Dolomite
Siltstone
Conglomerate
Evaporite
METAMORPHISM
• Recrystallization
• "Earth's sweat"
9/93
Geology
-------
NOTES
METAMORPHIC ROCKS
PRESSURE
METAMORPHIC ROCKS
Marble Slate
Quartzite Phyllite
Gneiss Schist
"EARTH"S SWEAT"
Geology
9/93
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MELTING/MAGMA
NOTES
IGNEOUS ROCKS
Intrusive
e.g., granite
• Extrusive
e.g., basalt
IGNEOUS ROCKS
Gabbro Basalt
Granite Rhyolite
9/93
Geology
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NOTES
INTRUSIVE IGNEOUS
ROCK BODIES
Adapted from General Biology by Robert Foster. 1969. p 63.
SEDIMENTARY ROCKS
Composed of particles of any rock type
- "Pores" form during deposition
Most aquifers are sedimentary rocks
ROCK TYPE ENVIRONMENT
Conglomerate
Sandstone
Clay/shale
Limestone
Landslide, alluvial fan
Rivers, streams, beaches,
deltas, dunes, sand bars
Lagoon, lake, flood plain,
deeper ocean
Coral reef, atoll,
deeper ocean
Geology
9/93
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CRITERIA TO DEFINE
"DEPOSITIONS.
ENVIRONMENTS
NOTES
LONGITUDINAL PROFILE
A Alluvial and landslide
B Braided stream
M Meandering stream
C Coastal
• Stream headwaters
<• L (length)-
t
I (height)
4.
Mouth of
0/0?
Geology
-------
NOTES
CRITERIA
Longitudinal channel profile
Median channel-grain size
Sphericity/sorting
CRITERIA
• Penetration of stream
• Width-to-depth ratio
• Degree of sinuosity
LONGITUDINAL
CHANNEL PROFILE
Geology
10
9/93
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NOTES
LONGITUDINAL PROFILE
A Alluvial and landslide
B Braided stream
M Meandering stream
C Coastal
rx j/ Stream headwaters
: : : A : i^:S^9^tf/na/ H
t
(height)
1 Mouth of
"T^Ocean
STREAM GRADIENTS
High'
-* Low
MEDIAN
CHANNEL-GRAIN SIZE
9/93
11
Geology
-------
NOTES
MEDIAN CHANNEL-GRAIN SIZE
1 r^rnp < **
* *
PV )
:::: A "^%.
'•'•'•'•'•'•'•'•'•'•'•'•'•'• ' W'^SSM-:^
D • • ^^^^
Small
'•fste*.
V.V» -
\
:::::: pi^sOc630
RELATIONSHIP OF STREAM VELOCITY
/ •
-3- ///// : Eros
Q) 100 - '///••:•.•.•.:
\ /Xx//x
^
^ 10 Transportation
'o
o /
J"- J
01 , 1 /VJ^il
°n;;p/^
/7^M,
^\\\\y-.\\\\\\\
:; Deposition ;;
: :i :::::: 1 :::::::
Size 0.001 0.01 0.1 1.0 10 100
(mm) Clay Silt Sand Gravel
SPHERICITY/SORTING
Geology
12
9/93
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SPHERICITY
Rounded
SORTING
Poor
Well
PENETRATION OF
STREAM
NOTES
9/93
13
Geology
-------
NOTES
STREAM CHANNEL
Penetration
Shallow «-
Deep
WIDTH-TO-DEPTH RATIO
STREAM CHANNEL
Width-to-Depth Ratio
High^
-> Low
Geology
14
-------
NOTES
DEGREE OF SINUOSITY
STREAM CHANNEL
Sinuosity
Low
DEPOSITIONAL
ENVIRONMENTS
9/93
15
Geology
-------
NOTES
DEPOSITIONAL
ENVIRONMENTS
• Alluvial fan
• Braided stream
• Meandering stream
• Coastal deposits
• Wind-blown deposits
ALLUVIAL FAN
Geology
16
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NOTES
BRAIDED STREAM
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17
Geology
-------
NOTES
MEANDERING STREAM
COASTAL DEPOSITS
Geology
18
9/93
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WIND-BLOWN DEPOSITS
NOTES
9/93
19
Geology
-------
NOTES
CARBONATES
• Limestones
• Dolomites
EVAPORITES
• Carbonates
• Sulfates
• Chlorides
GLACIATION
Geology
20
9/93
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NOTES
GLACERS/FREEZE-THAW
• Weathering and transport
• Large scale changes
• Poor to excellent sorting
(e.g., glacial till and outwash)
PROCESSES OF GLACIATION
• Erosion
• Transportation
• Deposition
9/93
21
Geology
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Geometry of Sandstone Reservoir Bodies1
Abstract Natural underground re»ervoiri capable of
containing water, petroleum, ond goiei include sond-
stonei, limeitonei, dolomilei. ond fractured rock) ol vari-
ou> typei. Comprehensive reieorch ond exploration el-
lorti by the petroleum industry hove revealed much about
the character ond diitribution ol corbonole rocks (lime-
itonei ond dolomitei) ond tondilonei. Poroiity and per-
meability cf the depoiili ore criteria for determining
Iheir efficiency 01 reservoirs for fluid). Trend) of certain
sandstones ore predictable. Furthermore, londilone rei-
ervoiri hove been leu oflecled Ihon corbonole reservoirs
by postdeposilionol cementation ond compaction, Froc-
lure porosity has received lets concentrated itudy; hence,
we know leu about Ihii type of reservoir. The discuisioni
in this paper ore confined to sandstone reservoirs.
The principal sondstone-generoting environment! ore
(1) fluvial environments luch os olluviol tons, braided
streams, ond meandering streams; (2) distributary-channel
ond delta-front environment) of various type) of delta);
(3) cooilol barrier islands, tidal channels, ond chenier
plains; (X) desert and cooslol eolion plains; end (5)
deeper marine environment), where the sands are dis-
tributed by both normal ond density current).
The alluvial-fan environment is characterized by flash
floods ond mudfiowi or debris flows which deposit the
coarsest and most irregular sand bodies. Braided streams
hove numerous shcllow channels separated by brood
sondbors; lateral channel migration results in the deposi-
tion of thin, lenticular sond bodies. Meandering streams
migrate within belts 20 lime) the channel width and
deposit two very common types of sand bodies. The
processes of bank-coving ond point-bar accretion result
in lateral channel migration ond the formation of sand
bodies (point bars) within each meander loop. Natural
cut-ofis ond channel diversions result in the abandon-
ment of individual meanders ond long channel seg-
ments, respectively. Rapidly abandoned channel) ore
filled with some sond but predominantly with fine-groined
sediment) (cloy plugs), whereos gradually abandoned
channels ore filled mainly with sands ond silts.
The most common sandstone reservoirs are of deltaic
origin. They ore laterally equivalent to fluviol sands ond
prodelto ond marine cloys, ond they consist of two types:
delta-front or fringe sond) ond abandoned dislribulory-
chonnel sends. Fringe sands ore sheetlike, and their hind-
word margins ore abrupt (against organic cloys of Ihe
delloic plain). Seaward, these sands grade into fhe
finer prodelto ond marine sediment). Distributary-channel
sandstone bodies ore narrow, Ihey hove abrupt bosol
contacts, ond Ihey decrease in groin size upward. They
cut into, or completely through, Ihe fringe sends, ond
also connect with Ihe upstream fluvial sond) or braided
or meandering streams.
Some of Ihe more porous ond permeable sandstone
reservoirs ore deposited in the cooslol interdeltoic reolm
ol sedimentation. They consist of well-sorted beach and
shorefoce sands associated with barrier islands ond tidal
channels which occur between barriers. Barrier sond
bodies ore long and narrow, are aligned parallel with
RUFUS J. L.BLANC1
Houston, Texas 77001
the coastline, ond are characterized by on upward in-
crease in groin size. They ore flanked on the landward
side by logoonol cloy) ond on the opposite side by
marine cloyi. Tidal-channel sond bodie) hove abrupt
bosol contacts and range in grain size from coarse at
the base to fine ot the lop. Laterally, they merge with
barrier sond) and grade into the finer sediment) of
(idol delta) ond mud flat).
The most poroui and permeable sandstone reservoirs
are product) of wind activity in coa>lol and deserl re-
gions. Wind-laid (eolion) sands ore typically very well
sorted and highly crossbedded, ond they occur o ex-
teniive sheets.
Marine sandstone! are those associated with normal-
marine processes of the continental shell, slope, ond
deep ond those due to density-current origin (turbidile)).
An important type of normal-marine sond i> formed
during marine transgression). Although these sends are
extremely thin, Ihey ore very distinctive and widespread,
hove sharp updip limits, ond grade seaward into marine
shales. Delta-fringe and borrier-shorefoce sands are two
other types of (hollow-marine sands.
Turbidile) have been interpreted to be associated
with submarine canyons. These sond) ore transported
from nearshore environments seaward through canyons
ond ore deposited on submarine fans in deep marine
basins. Other lurbidiles form as o result of slumping of
deltaic focies ot shelf edges. Turbidile sands ore usually
associated with thick marine ihole>.
' Manuscript received, March 17, 1972.
'Shell Oil Company. This paper is based on the
writer's 30 years of experience in studies of modem
and ancient clastic sedimenls—from 1941 to 194S. with
the Mississippi River Commission, under the guidance
of H. N. Fisk, and, since August 1948, with Shell
Development Company and Shell Oil Company.
The writer is grateful to Shell Oil Company for per-
mission to publish this paper, and he is deeply indebted
to Alan Thomson for his critical review of the manu-
script; he is also grateful to Nick W. Kusakis, John
Bush, Dave C. Fogt. Gil C. Flanagan, and George F.
Korenek for assistance in Ihe preparation of illustra-
tions and reference material; to Aphrodite Mamoulides
and Bernice Melde for their library assistance; to Dar-
leen Vanderford for typing the manuscript, and to Judy
Breeding for her editorial assistance.
Numerous stimulating discussions of models of das-
tic sedimentation and the relationship of sedimentary
sequences to depositions! processes were held with
Hugh A. Bernard and Robert H. Nanz, Jr., during the
late 1940s and 1950s, when we were closely associated
with Shell's early -exploration research efiort. The
writer is particularly indebted to these two men for
their numerous contributions, many of which are in-
cluded in this paper.
The writer also wishes to thank W. B. Bull, Univer-
sity of Arizona, for his'valuable suggestions concerning
the alluvial-fan model of clastic sedimentation.
133
Reproduced by Permission
-------
134
Rufus J. LeBlanc
INTRODUCTION
Important natural resources such as water,
oil, gas, and brines are found in underground
reservoirs which are composed principally of
the following types of rocks: (1) porous sands,
sandstones, and gravels; (2) porous limestones
and dolomites; and (3) fractured rocks of vari-
ous types. According to the 1971 American Pe-
troleum Institute report on reserves of crude oil
and natural gas, sandstones are the reservoirs
for about 75 percent of the recoverable oil and
65 percent of the recoverable gas in the United
States. It is also estimated that approximately
90 percent of our underground water supply
comes from sand and gravel (Walton, 1970).
Sandstone and carbonate (limestone and do-
lomite) reservoirs have been intensively studied
during the past 2 decades; consequently, the
general characteristics and subsurface distribu-
tion of these two important types of reservoirs
are relatively well known in numerous sedimen-
tary basins. The factors which control the ori-
gin and occurrence of fracture porosity have
received less attention; thus, our knowledge
and understanding of this type of reservoir are
more limited.
The detection of subsurface porosity trends
within sedimentary basins was recognized by the
petroleum industry as one of its most signifi-
cant problems, and for the past 2 decades it has
addressed itself to a solution through extensive
research. Largely as a result of this research,
which is summarized below, our ability to de-
termine trends of porous sedimentary rocks has
progressed noticeably, especially during the
past 10 years.
The amount of porosity and permeability
present within sedimentary rocks and the ge-
ometry of porous rock bodies are controlled
mainly by two important factors: (1) the envi-
ronmental conditions under which the sedi-
ments were deposited and (2) the postdeposi-
tional changes within the rocks as a result of
burial, compaction, and cementation. Postde-
positional diagenetic processes have less effect
on the porosity and permeability of sands and
sandstones than they have on carbonate sedi-
ments; consequently, porosity trends are signifi-
cantly more predictable for sandstones than for
limestones and dolomites.
Organization of paper—The following two
parts of this paper give a brief historical sum-
mary of the early research on clastic sediments
and present a classification of environments of
deposition and models of clastic sedimentation.
A resum£ of significant studies of modern clas-
tic sediments—mainly by the petroleum indus-
try, government agencies, and universities—
follows. The main part of the paper concerns
the sedimentary processes, sequences, and ge-
ometry of sand bodies which characterize each
of the following models of clastic sedimenta-
tion: alluvial fan, braided stream, meandering
stream, deltaic (birdfoot-lobate and cuspate-
arcuate), coastal interdeltaic (barrier island
and chenier plain), and marine (transgressive,
submarine canyon, and fan).
HISTORICAL SUMMARY or EARLY RESEARCH ON
MODERN CLASTIC SEDIMENTS
Geologists are now capable of interpreting
the depositional environments of ancient sedi-
mentary facies and of predicting clastic poros-
ity trends with a reasonable degree of accuracy
(Peterson and Osmond, 1961; Potter, 1967;
Rigby and Hamblin, 1972; Shelton, 1972).
This capability stems from the extensive re-
search conducted on Holocene sediments by
several groups of geologists during the past 3
decades. Conditions which led to this research,
and the most significant studies of clastic sedi-
mentation which provided the models, criteria,
and concepts necessary to make environmental
interpretations, are summarized below.
During the late 1930s and early 1940s, pe-
troleum geologists became aware that improved
methods of stratigraphic interpretations were
badly needed, and that knowledge and geologic
tools necessary to explore for stratigraphic
traps were inadequate. A detailed study made
by the Research Committee of The American
Association of Petroleum Geologists on the re-
search needs of the industry ultimately led to
the establishment of geologic research depart-
ments by major oil companies. By 1948, explo-
ration research by the oil industry was io—its
early stages, and expansion proceeded /rapidly
thereafter.
Meanwhile, some very significant develop-
ments were occurring at Louisiana State Uni-
versity. H. V. Howe and R. J. Russell, together
with their graduate students, had already pub-
lished several Louisiana Geological Survey bul-
letins summarizing their pioneer work on the
late Quaternary geology of southern Louisiana
(Howe and Moresi, 1931, 1933; Howe et al.,
1935; Russell, 1936). Their early work on the
Mississippi deltaic plain and the chenier plain
of southwestern Louisiana is considered to be
the beginning of the modern environmental ap-
proach to stratigraphy. Fisk became fascinated
-------
Geometry of Sandstone Reservoir Bodies
135
with the Howe and Russell approach, and he
applied results of their research to his study of
Tertiary sediments. The work of Fisk (1940)
in central Louisiana, which included a study of
the lower Red River Valley and part of the
Mississippi Valley, attracted the attention of
General Max Tyler, president of the Mississippi
River Commission in Vicksburg. General Tyler
engaged Fisk as a consultant and provided him
with a staff of geologists to conduct a geologic
investigation of the lower Mississippi River al-
luvial valley.
The Fisk (1944) report on the Mississippi
Valley, which now has become a classic geo-
logic document, established the relations be-
tween alluvial environments, processes, and
character of sediments. The AAPG, recogniz-
ing the significance of this contribution, re-
tained Fisk as Distinguished Lecturer, and the
results and significance of his work became
•widely known. One of his most significant con-
tributions came when, as the petroleum indus-
try was getting geologic research under way, he
was selected by a major oil company to direct
its geologic research effort in Houston.
By 1950, a few major oil companies were
deeply involved in studies of recent sediments.
However, the small companies did not have
staff and facilities to conduct this type of re-
search, and American Petroleum Institute Proj-
ect 51 was established for the purpose of con-
ducting research on recent sediments of the
Gulf Coast. Scripps Institution of Oceanogra-
phy was in charge of the project, which contin-
ued for 8 years. Results of this research were
available to all companies (Sbepard el al,
1960).
While the petroleum industry was conduct-
ing "in-house" research and supporting the API
project, some significant research was being
done by the U.S. Waterways Experiment Sta-
tion in Vicksburg, Mississippi, and by the new
Coastal Studies Institute at Louisiana State Uni-
versity under the direction of R. J. Russell.
These two groups conducted detailed studies of
recent sediments for many years, and results
were made available to the petroleum industry.
By 1955, a fairly good understanding of pro-
cesses of sedimentation and character of related
sediments in several depositional environments
had been acquired. Although the applicau'on of
this wealth of knowledge to operational prob-
lems was very difficult, some useful applica-
tions nevertheless had been made by the middle .
1950s, and it was generally agreed that the ini-
tial research effort was successful.
Since 1955, geologists all over the world
have become involved in studying recent sedi-
ments and applying the results to research on
older rocks. Geologists with the U.S. Geologi-
cal Survey and several universities have con-
ducted studies of alluvial fans, braided streams,
and eolian deposits; and the oceanographic in-
stitutions, such as Scripps, Woods Hole, and
Lam on I, have investigated deep-marine • sedi-
ments on a worldwide basis. Publication of pa-
pers on clastic sedimentation has been increas-
ing rapidly. The first textbook on the geology
of recent sediments cites more than 700 refer-
ences, 75 percent of which have appeared since
1955 (Kukal, 1971). Many of these contribu-
tions, considered to be most significant to the
current understanding of clastic sediments, are
cited in this paper.
MODELS AND ENVIRONMENTS OF
CLASTIC SEDIMENTATION
The realm of clastic sedimentation can be di-
vided into several conceptual models, each of
which is characterized by certain depositional
environments, sedimentary processes, se-
quences, and patterns. What are considered to
be some of the most common and basic models
and environments' of clastic sedimentation, ar-
ranged in order from the periphery to the cen-
ter of a depositional basin, are listed below and
are shown on Figures 1—4.
Continental
Alluvial (fluvial) models
Alluvial Ian
Braided stream
Meandering stream (includes flood basins be-
tween meander belts)
Eolian (can occur al various positions within con-
tinental and transitional models)
Transitional
Deltaic models
Birdfoot-lobate (fluvial dominated)
Cuspate-ajcuale (wave and current dominated)
Estuarine (with strong tidal influence)
Coasial-inierdcllaic models
Barrier-island model (includes barrier islands,
lagoons behind barriers, tidal channels, and
tidal deltas)
Cbenier-plain model (includes mud fiats and
cbeniers)
Marine
(Note: Sediments deposited in shallow-marine en-
vironments, such as deltas and barrier islands, are
•The classification of depositional environments pre-
sented herein was initially developed by the writer and
his colleague, Hugh A. Bernard, during the early 1950s
(LeBlanc and Bernard, 1954) and was recently modi-
fied (Bernard and LeBlanc. 1965). For other classifi-
cations, refer to Laporte (1968), Sclley (1970), Crosby
(1972). and KuluU (1971).
-------
136
Rufus J. LeBlonc
Fio. 1—Some common models of clastic sedimentation. See Figures 2—4 for details.
included under the transitional group of environ-
ments.)
Transgressive-marine model
Submarine-canyon and submarine-fan model
RESUME OF SIGNIFICANT STUDIES OF
MODERN CLASTIC SEDIMENTATION
Alluvial Fans
Although much work has been done on allu-
vial fans, only a few papers discuss the relation
of sedimentary sequences to depositional pro-
cesses. Some of the more important contribu-
tions are by Rickmers (1913), Pack (1923),
Blackwelder (1928), Eckis (1928), Blissen-
bach (1954), McKee (1957), Beaty (1963),
Bull (1962, 1963, 1964, 1968, 1969, 1971),
Hoppe and Ekman (1964), Wind;r (1965),
Anstey (1965), Denny (1965, 1967), Legget
ei al. (1966), and Hooke (1967).
Braided Streams
Early papers on braided streams concerned
channel patterns, origin of braiding, and physi-
cal characteristics of braided streams. Signifi-
cant studies of this type were conducted by
Lane (1957), Leopold and Wolraan (1957),
Cbein (1961), Krigstrom (1962), Fahnestock
(1963), andBrice (1964).
The relatively few papers on the relation of
braided-stream deposits to depositional pro-
cesses did not appear until the 1960s. Doeglas
(1962) discussed braided-stream sequences of
the Rhone River of France, and Ore (1963,
1965) presented some criteria for recognition
of braided-stream deposits, based on the study
of several braided streams in Wyoming, Colo-
rado, and Nebraska. Fahnestock (1963) de-
scribed braided streams associated with a gla-
cial outwash plain in Washington. More re-
cently, Williams and Rust (1969) discussed the
sedimentology of a degrading braided river in
the Yukon Territory, Canada. Coleman (1969)
presented results of a study of the processes
and sedimentary characteristics of one of the
largest braided rivers, the Brahmaputra of
Bangla Desh (formerly East Pakistan). N.
Sroitb (1970) studied the Platte River from
Denver, Colorado, to Omaha, Nebraska, and
used the Platte model to interpret Silurian
braided-stream deposits of the Appalachian re-
giOD. Waechter (1970) has recently studied the
braided Red River in the Texas Panhandle, and
Kessler (1970, 1971) has-investigated the Ca-
nadian River in Texas. Boothroyd (1970) stud-
ied braided streams associated with glacial out-
wash plains in Alaska.
-------
ENVIRONMENTS
DEPOSITIONAl MODELS
AUUVIAl
(FLUVIAL)
z
UJ
Z
»—
Z
o
u
AUUVIAl
f ANS
(APEX. MIDDLE
& BASE OF FAN)
BRAIDED
STREAMS
MEANDERING
STREAMS
| AUUVIAl
VAUEY)
STREAM
FIOWS
VISCOUS
FIOWS
MEANDER
BEITS
FIOODBASINS
CHANNELS
SHEETFIOODS
"SIEVE DEPOSITS-
DEBRIS FIOWS
MUDFIOWS
CHANNELS
(VARYING SIZES)
LONGITUDINAl
TRANSVERSE
CHANNELS
NATURAL LEVEES
POINT BARS
STREAMS. LAKES
& SWAMPS
O
II
o
3
it
in
Q
3
O.
w
O
3
It
It
2
o
o
Q.
EOUAN
COASTAL DUNES
DUNES
DESERT DUNES
OTHER DUNES
TYPES:
TRANSVERSE
SEIF
(LONGITUDINAL)
BARCHAN
PARABOLIC
DOME-SHAPED
Tio. 2—Alluvial (fluvial) and eolinn environments and models of clastic sedimentation.
CO
-------
ENVIRONMENTS
DEPOSITIONS MODELS
Z
O
DEITAIC
UPPER
DELTAIC
PIAIN
LOWER
DEITAIC
PLAIN
FRINGE
DISTAL
MEANDER
BELTS
FIOODBASINS
DISTRIBUTARY
CHANNELS
INTER-
DISTRIBUTARY
AREAS
INNER
OUTER
CHANNELS
NATURAL LEVEES
POINT BARS
STREAMS,
LAKES
& SWAMPS
CHANNELS
NATURAL LEVEES
MARSH.
LAKES,
TIDAL CHANNELS
4 TIDAL FLATS
RIVER-MOUTH
BARS
BEACHES 4
BEACH RIDGES
TIDAL FLATS
ItlUAIIHf OflTA
WIOI tANCI »H IIOII
OI1MIIVI4IIII IMMt
IN fllUAIIII.
BIRDFOOT-LOBATE
DELTA
CUSPATE-ARCUATE
DELTA
C
•*»
D>
5"
n
ESTUARINE DELTA
Fic. 3—Deltaic environments and modek of clastic sedimentation.
-------
Geometry of Sandstone Reservoir Bodies
139
Meandering Streams
H. N. Fisk's studies of the Mississippi allu-
vial valley, conducted for the Mississippi River
Commission during the period 1941—48, repre-
sent the first significant contribution on mean-
dering stream environments and deposits. This
pioneer effort provided geologists with knowl-
edge of the fundamental processes of alluvial-
valley sedimentation. Another study of a mean-
dering stream, the Connecticut River, and its
valley was made by Jahns (1947). Important
work on alluvial sediments deposited by mean-
dering streams was also done. by Sundborg
(1956) in Sweden, and by Frazier and Osanik
(1961), Bernard and Major (1963), and
Harms et al. (1963) on the Mississippi, Brazos,
and Red River point bars, respectively. Thus,
by 1963 the general characteristics of point-bar
sequences, and the closely related abandoned-
channel and flood-basin sequences, were suffi-
ciently well established to permit geologists to
recognize this type of sedimentary deposit in
outcrops and in the subsurface.
Other important contributions were made by
Allen (1965a) on the origin and characteristics
of alluvial sediments, by Simons et al (1965)
on the flow regime in alluvial channels, by Ber-
nard et al. (1970) on the relation of sedimen-
tary structures to bed form in the Brazos valley
deposits, and by McGowen and Garner (1970)
on coarse-grained point-bar deposits.
Deltas
The early work by W. Johnson (1921, 1922)
on the Fraser delta, Russell (1936) on the Mis-
sissippi delta, Sykes (1937) on the Colorado
delta, and Fisk (1944) on the Mississippi delta
provided a firm basis for subsequent studies of
more than 25 modern deltas during the late
1950s and the 1960s.
Fisk continued his studies of the Mississippi
delta for more than 20 years. His greatest con-
tributions were concerned with the delta frame-
work, the origin and character of delta-front
sheet sands, and the development of bar-finger
sands by seaward-migrating rivermouth bars.
Scruton's (1960) paper on delta building
and the deltaic sequence represents results of
API Project 51 on the Mississippi delta. Addi-
tional research on Mississippi delta sedimenta-
tion, sedimentary structures, and mudlumps
was reported by Welder (1959), Morgan
(1961), Morgan el al. (1968), Coleman et al.
(1964), Coleman (1966b), Coleman and Gagli-
ano (1964, 1965), and also by Kolb and Van
Lopik (1966). Coleman and Gagliano (1964)
also discussed and illustrated processes of
cyclic sedimentation. The most recent papers
on the Mississippi delta are by Frazier (1967),
Frazier and Osanik (1969), and Gould
(1970).
Studies of three small birdfoot deltas of
Texas—the Trinity, Colorado, and Guadaiupe
—were made by McEwen (1969), Kanes
(1970), and Donaldson (1966), respectively.
In addition, Donaldson et al. (1970) presented
a summary paper on the Guadaiupe delta.
These four contributions are valuable because
each one presents photographs and logs of
cores of complete deltaic sequences.
European geologists associated with the pe-
troleum industry and universities also have
made valuable contributions to our understand-
ing of deltas. Kruit (1955) and Lagaaij and
Kopstein (1964) discussed their research on
the Rhone delta of southern France, Allen
(1965c, 1970) summarized the geology of the
Niger delta of western Africa, ^and van Andel
(1967) presented a resume^ of the work done on
the Orinoco delta of eastern Venezuela. More
recently, the Po delta of Italy was studied by B.
Nelson (1970) and the Rhone delta of southern
France by Oomkens (1970).
Other recent contributions on modern deltas
are by Coleman et al. (1970) on a Malaysian
delta, by R. Thompson (1968) on the Colo-
rado delta in Mexico, and by Bernard et al.
(1970) on the Brazos delta of Texas.
The deltaic model is probably the most com-
plex of the clastic models. Although additional
research is needed on this aspect of sedimenta-
tion, the studies listed have provided some
valuable concepts and criteria for recognition
of ancient deltaic facies.
Coastal-Interdeltaic Sediments
Valuable contributions to our knowledge of
this important type of sedimentation have been
made by several groups of geologists. In the
Gulf Coast region, the extensive Padre Island-
Laguna Madre complex was studied by Fisk
(1959), and the chenier plain of southwestern
Louisiana was studied by Gould and McFarlan
(1959) and Byrne et al. (1959). The Galves-
ton barrier-island complex of the upper Texas
coast was investigated mainly by LeBlanc and
Hodgson (1959), Bernard et al. (1959, 1962),
and Bernard and LeBlanc (1965).
Among the impressive studies made by Euro-
peans during the past 15 years are those by van
Straaten (1954), who presented results of very
-------
2
o
z
<
ex.
COASTAL
INTER-
OEITAIC
ENVIRONMENTS
DEPOSITIONAL MODELS
COASTAl
PLAIN
(SUBAERIAL)
SUBAQUEOUS
BARRIER
ISLANDS
CHENIER
PLAINS
TIDAL
LAGOONS
TIDAL
CHANNELS
SMALL
ESTUARIES
BACK BAR.
BARRIER,
BEACH.
BARRIER FACE,
SPITS 4 FLATS.
WASHOVER FANS
BEACH
* RIDGES
TIDAL FLATS
TIDAL FLATS
TIDAL DELTAS
SHOALS
& REEFS
BARRIER IS.
COMPLEX
CHENIER
PLAIN
jo
c
0
o>
a
3
uj
Z
SHALLOW
MARINE
DEEP
MARINE
INNER
SHELF.
(NERITIC)
MIDDLE
SHOALS
4 BANKS
OUTER
CANYONS
FANS (DELTAS)
SLOPE &
ABYSSAL
TRENCHES 4
TROUGHS
SHALLOW
MARINE
DEEP
MARINE
Fic. 4—Coaslal-interdeltaic and marine environmenU and models of clastic sedimentation.
-------
Geometry of Sandstone Reservoir Bodies
141
significant work on tidal flats, tidal channels,
and tidal deltas of the northern Dutch coast,
and by Horn (1965) and H. £. Rebeck
(1967), who reported on the barrier islands and
tidal flats of northern Germany.
During the past several years, a group of ge-
ologists has conducted interesting research on
the coastal-interdeltaic complexes which char-
acterize much of the U.S. Atlantic Coast re-
gion. Hoyt and Henry (1965, 1967) published
several papers on barriers and related features
of Georgia. More recently, results of studies at
the University of Massachusetts on recent
coastal environments of New England were re-
ported by Daboll (1969) and by the Coastal
Research Group (1969).
In addition, Curray et at. (1969) described
sediments associated with a strand-plain barrier
in Mexico, and Potter (1967) summarized the
characteristics of barrier-island sand bodies.
Eolian Sand Dunes
Prior to the middle 1950s, eolian deposi-
tional environments were studied principally by
European geologists (Cooper, 1958). Since
that time, the coastal sand dunes of the Pacific,
Atlantic, and Gulf coasts of the United States,
as well as the desert dunes of the United States
and other countries, have been investigated by
university professors and by geologists with the
U.S. Geological Survey. Some of the most sig-
nificant contributions, especially those con-
cerned with dune stratification, are discussed in
the section on the eolian model of clastic sedi-
mentation.
Marine Sediments
Early work on modern marine sands, exclu-
sive of those deposited adjacent to and related
to interdeltaic and deltaic depositional environ-
ments, was conducted largely by scientists asso-
ciated with Scripps, Woods Hole, and Lament
oceanographic departments. Several aspects of
marine sediments were discussed by Trask et al.
(1955), and the recent sands of the Pacific
Ocean off California were studied by Revelle
and Shepard (1939), Emery et al (1952), and
Emery (1960a). Stetson (1953) described the
northwestern Gulf of Mexico sediments, and
Ericson et al. (1952, 1955)-and Heezen et al.
(1959) investigated the Atlantic Ocean sedi-
ments. Later, Curray (1960), van Andel
(1960), and van Andel and Curray (1960) re-
ported results of the API project on the Gulf of
Mexico. A few years later, results of the API
project studies on the Gulf of California were
reported by van Andel (1964) and van Andel
and Shor (1964). Menard (1964) discussed
sediments of the Pacific Ocean. For a more
complete list of references to studies of recent
marine sands, the reader is referred to Kuenen
(1950). Guilcher (1958), Shepard et al.
(1963), and Kukal (1971).
Much of the early research on modern ma-
rine environments was devoted to submarine
canyons, fans, and basins considered by the in-
vestigators to be characterized mainly by tur-
bidity-current sedimentation. Several scientists
affiliated with Scripps and the University of
Southern California published numerous papers
on turbidites which occur in deep marine ba-
sins.
It is extremely difficult to observe the pro-
cesses of turbidity-current sedimentation under
natural conditions; consequently, the relations
between sedimentary sequences and processes
are still relatively poorly understood. Much of
the research dealing with turbidity currents has
been concerned with theory, laboratory models,
and cores of deep-water sediments deposited by
processes which have not been observed.
ALLUVIAL-FAN MODEL OF CLASTIC
S EDIMENT ATI OK
Occurrence and General Characteristics
Alluvial fans occur throughout the world,
adjacent to mountain ranges or high hills. Al-
though they form under practically all types of
climatic conditions, they are more common and
best developed along mountains of bold relief
in arid and semi-arid regions (Figs. 5, 6).
The alluvial-fan model has the following
characteristics: (1) sediment transport occurs
under some of the highest energy conditions
within the entire realm of clastic sedimentation,
(2) deposition of clastic sediment occurs di-
rectly adjacent to the areas of erosion which
provide the sediments, and (3) deposits are of
maximum possible range in size of clastic parti-
cles (from the largest boulders to clays) and
are commonly very poorly sorted compared
with other types of alluvial sediments (Fig. 5).
The size of individual alluvial fans is con-
trolled by drainage-basin area, slope, climate,
and character of rocks within the mountain
range. Individual fans range in radius from sev-
eral hundred feet to several tens of miles. Co-
alescing fans can occur in linear belts that are
hundreds of miles long. Fan deposits usually at-
tain their maximum thicknesses and grain size
near the mountain base (apex of fan) and
-------
142
Rufus J. LeBlanc
StCtlON I-C
Fie. S—Alluvial-fan model of clastic sedimentation.
gradually decrease in thickness away from.the
apex.
The alluvial-fan environments commonly
grade downstream into braided-stream or
playa-lake environments. In some areas, where
mountains are adjacent to oceans or large in-
land lakes, alluvial fans are formed under both
subaerial and submerged conditions. Such fans
are now referred to as "Gilbert-type" deltas.
Alluvial-fan deposits form important reser-
voirs for groundwater in many areas, and adja-
cent groundwater basins are recharged through
the fan deposits which fringe these basins.
Source, Transportation, and Deposition
of Sediments
Tectonic activity and climate have a pro-
found influence on the source, transportation,
and deposition of alluvial-fan deposits. Uplift
of mountain ranges results in very intensive
erosion of rocks and development of a very
high-gradient drainage system. The rate of
weathering and production of clastic material is
controlled mainly by rock characteristics and
climate (temperature and rainfall).
Clastic materials are transported from source
areas in mountains or high hills to alluvial fans
-------
Geometry of Sandstone Reservoir Bodies
143
by several types of flows: stream flows and
sbeetfloods and debris flows or mudflows. Sedi-
ment transport by streams is usually character-
istic of large fans in regions of high to moder-
ate rainfall. Mudflows or debris flows are more
common on small fans in regions of low rain-
fall characterized by sudden and brief periods
of heavy downpours.
Stream deposits—Streams which drain rela-
tively small segments of steep mountain ranges
have steep gradients; they may erode deep can-
yons and transport very large quantities of
coarse debris. The typical overall stream gra-
dient is concave upward, and the lowest gra-
dient occurs at the toe of the fan (Fig. 5).
Hooke (1967) described a special type of
stream-flow deposit, which be called "sieve de-
posits," on fans which are deficient in fine sedi-
ments. These gravel deposits are formed when
water infiltrates completely into the fan. Bull
(1969) described three types of water-laid sedi-
ments on alluvial fans: channel, sheetflood, and
sieve deposits. Stream channels radiate outward
from the fan apex and commonly are braided.
The processes of channel migration, diversion,
abandonment and filling, and development of
new main channels and smaller distributary
channels on the lower part of the fan surface
are characteristic features. Most fan surfaces
are characterized by one or a few active chan-
nels and numerous abandoned channels. De-
posits on abandoned portions of gravelly and
weathered fan surfaces are referred to as
"pavement."
Alluvial-fan channel deposits have abrupt
basal contacts and channel geometry; they are
generally coarse. Bull (1972) described chan-
nel deposits as imbricated and massive or thick-
bedded.
Heavy rainfall in mountainous source areas
can result in floods on alluvial fans. The rela-
tively shallow and wide fan channels are not
capable of carrying the sudden influx of large
volumes of water; consequently, the streams
overtop their banks and flood part of the fan
surface. The result is the deposition of thin lay-
ers of clastic material between channels. Bull
(1969) reported sheetflood deposits to be finer
grained than channel deposits, cross-bedded,
and massive or thinly bedded.
Debris-1lo\v deposits—Some workers refer to
both fine-grained and coarse-grained types of
plastic flowage in stream channels as mudflows,
but others consider mudfiows to be fine-grained
debris flows. Examples of transportation and
deposition of clastic sediments by mudflows
Fio. 6—Stratigraphic geometry of BO alluvial fan.
Alier Bull (1972).
were first described by Rickmers (1913) and
Blackwelder (1928). The following conditions
favor the development of mudflows: presence
of unconsolidated material with enough clay, to
make it slippery when wet, steep gradients,
short periods of abundant water, and sparse
vegetation.
Pack (1923) discussed debris-flow deposi-
tion on alluvial-fan surfaces. Debris flows occur
as a result of very sudden, severe flooding of
short duration. Beaty (1963) described eye-
witness accounts of debris flows on the west
flank of the White Mountains of California and
Nevada. Debris flows follow channels, overtop
the channel banks, and form lobate tongues of
debris along channels. Debris-flow deposits are
very poorly sorted, fine- to coarse-grained, and
unstratified; they have abrupt margins. This
type of deposit is probably most common on
the upper parts of the fans between the apex
and midfan areas.
Summary: Character and Geometry of
Alluvial-Fan Deposits
Most of the alluvial-fan studies conducted
thus far have been concerned primarily with
the origin and general characteristics of fans
and the distribution of sediments on the sur-
faces of fans. An exception is Bull's excellent
summary paper (Bull, 1972), which contains
significant data on the geometry of channel,
sheetflood, debris-flow, mudflow, and sieve de-
posits. The abstract of Bull's paper is quoted
below:
-------
144
Rufus J. LeBlanc
Alluvial fans commonly are thick, oxidized, erogenic
deposits whose geometry is influenced by the rate and
duration of uplift of the adjacent mountains and by
climatic factors.
Fans consist of water-laid sediments, debris-flow de-
posits, or both. Water-laid sediments occur as channel,
sheelnood, or sieve deposits. Entrenched stream chan-
nels commonly are backfilled with gravel that may be
imbricated, massive, or thick bedded. Braided sheets of
finer-grained sediments deposited downslope from the
channel may be cross-bedded, massive, laminated, or
thick bedded. Sieve deposits are overlapping lobes of
permeable gravel.
Debris-flow deposits generally consist of cobbles and
boulders in a poorly sorted matrix. Mudflows are fine-
grained debris flows. Fluid debris flows have graded
bedding and horizontal orientation of tabular particles.
Viscous flows have uniform particle distribution and
vertical preferred orientation that may be normal to
the flow direction.
Logarithmic plots of the coarsest one percenlile ver-
sus median particle size may make patterns distinctive
of depositional environments. Sinuous patterns indicate
shallow ephemeral stream environments. Rectilinear
patterns indicate debhs flow environments.
Fans consist of lenticular sheets of debris (length/
width ratio generally 5 to 20) and abundant channel
fills near the apex. Adjacent beds commonly vary
greatly in particle size, sorting, and thickness. Beds ex-
tend for long distances along, radial sections and chan-
nel deposits are rare. Cross-fan sections reveal beds of
limited extent that are interrupted by cut-and-fill struc-
tures.
Three longitudinal shapes are common in cross sec-
tion. A fan may be lenticular, or a wedge that is either
thickest, or thinnest, near the mountains.
Ancient Alluvial-Fan Deposits
Some examples of ancient alluvial-fan depos-
its which have been reported from the United
States, Canada, Norway, and the British Isles
are summarized in Table 1, together with other
types of alluvial deposits.
BRAZDED-STREAM MODEL or CLASTIC
SEDIMENTATION
Occurrence and General Characteristics
Braided streams occur throughout the world
under a very wide range of physiographic and
climatic conditions. They are common features
on extensive alluvial plains which occupy a po-
sition in the clastic realm of sedimentation be-
tween the high-gradient alluvial-fan environ-
ment at the base of mountain ranges and the
low-gradient meandering-stream model of sedi-
mentation (downstream). In physiographic
provinces characterized by mountainous areas
adjacent to the sea, the braided-stream environ-
ment can extend directly to the coastline and
thus constitute the predominant environment of
alluvial deposition. In this type of situation,
meandering streams do not exist (Fig. 7). The
braided stream is also a common feature of gla-
cial outwash-plains associated with the fluvio-
glacial environment.
The braided-stream model is characterized
by extremely variable rates of sedimentation in
multiple-channel streams (Fig. 8), the patterns
of which vary widely compared with meander-
ing channels. Braided channels are usually wide
and shallow; they contain numerous bars, are
slightly sinuous or straight, and migrate at
rapid rates. Stream gradients are high, are quite
variable, and are less than those of alluvial fans
but generally greater than those of meandering
streams. Large fluctuations in discharge occur-
ring over short periods of time are also com-
mon. The combination of steep gradients and
high discharge rates results in the transporta-
MOUNTAINS OR HILLS
AP • AUUV1AI f*
US • M(AMI
0 "Oil I*
Fie. 7—B raided-stream model of clastic sedimentation.
-------
Geometry of Sandstone Reservoir Bodies
145
tion and deposition of large amounts of coarse
material, ranging from boulders to sand.
Braided-stream deposits overall are finer than
those of alluvial fans, coarser than those of
meandering streams, and quite varied in stratifi-
cation.
Source, Transportation, and Deposition
of Sediments
Aggrading braided streams transport very
large quantities of clastic material derived from
a variety of sources, such as outwash plains, al-
luvial fans, mountainous areas, and broad
plains. Unlike that of meandering streams, the
bulk of the sedimentary load of most braided
streams is transported as bed load. Rates of
sediment transport and deposition are ex-
tremely variable, the maximum rate occurring
during severe floods of short duration. High-
gradient upstream segments of braided streams
close to source areas are characterized by depo-
sition of poorly sorted clastic sediments which
Table 1. Examples of Ajicient Alluvial-Fan, Braiderl-Stream, and Meandering-Stream Deposits
Jltutlal Fan
Arizona
California
California
Colorado
Colorado
Colorado
Conneclkul Valley
Massachusetts
Massachusetts
Montana
Montana
Montana
S.W. USA
Texas
Wyoming
Northeastern Canada
Northwest Territories
Wales and Scotland
Norway
BtaUed Slrtam
Llano Enacado
Maryland
Mississippi
Montana
New York
New Jersey. New York
Pennsylvania
Wyoming
Nonhwelt Territories
Scotland
Spain
Spitsbergen
Meandering Stream
Colorado
Illinois
Illinois
Kansas
Maryland
Michigan
Montana
Mississippi
New York
Pennsylvania
Pennsylvania
Texas
Wen Virginia
Wyoming
No vi Scotia
Northwest Territories
England
South Wales
Spitsbergen
Nc»- South W.lci
Comptaile
Arizona
California
California
Colorado
Colo. Plateau
Colo. Plateau
Kansas
Massachusetts
Montana
Nebraska
Nebraska
North Dakota
Oklahoma
Rhode Island
Texas
Alberta
Quebec
Aulrar
Melton. 1965
Crowell. 1954
Flemal. 1967
Gatehouse. 1967
Boggs. 1966
Bolyard. 1959
Brady. 1969
Finch. 1959
Stokes, 1961
Howard, 1966
Hubert, I960
Klein. 1968
Hewitt el al.. 1965
Shelion. 1972
Lins. 1950
Shelion. 1971
Bretz 4. Horberg, 1949
Hansen. 1969
Wesiel. 1969
Stanley. 1968
Mutch. 1966
Shideler. 1969
Cwinn. 1964
Ecrg & Cook. I96S
Gwinn & Mutch, 1965
Shelion. 1967
Wilson. 1967. 1970
Bcaiy. 1961
Exum & Harms, 1968
Harms, 1966
Butlner. 1968
Smith. 1970: Shelion, 1972
Royse. 1970
Visher. I965b
Beutner fl cl.. 1967
Smith. 1970
Ryan. 1965
Mutch. 1968
Bull. 1972
Fisher & McGowcn. 1969
McCowen & Croat. 1971
McCowen & Gamer. I96S: Shelion, 1971
Beerbower. 1964, 1969
Berg. I96S
Spearing. 1969
Byen. 1966
Oineley & Williams, 1968
Klein, 1962
Way. 1968
Mia II. 1970
Allen. 1964: Laming. 1966
Bluck. 1965. 1967
Kelling. 196S
Nilsen. 1969
Williams. 1966. 1969
Naglcgaal. 1966
Moody-Sluart. 19(6
Conolly. 1965
-------
146
Rufui J. LeBlanc
FIG. 8—Types of braided-slream chancels and ban.
range in size from boulder to sand. Farther
downstream, there is a gradual decrease in
grain size and an increase in sorting.
The bed-load materials are transported under
varying bed-form conditions, depending upon
river stage. Coleman (1969) reported ripple
and dune migration in the Brahmaputra River
of Bangla Desh ranging from 100 ft to 2,000 ft
(30-610 m) per day. Chein (1961) reported
downstream movement of sandbars in the Yel-
low River of China to be as great as 180-360
ft (55-110 m) per day. (For comparison, the
rate of bed-load movement in the meandering
Mississippi is about 40 ft [12 m] per day.)
Process of channel division (braiding) by de-
velopment of bars—The exact causes of chan-
nel division which results in the development of
the braided pattern are not very well under-
stood. Two methods in which channel division
takes place have been described by Ore (1963)
as follows:
Leopold and Wolman (1957, p. 43-44), using re-
sulis of both stream-table studies and observation] of
natural braided streams, discuss in some detail bow
channel division may take place. At any time, the
stream is carrying coarser fractions along the channel
center than at the margins, and due to some local hy-
draulic condition, pan of the coarsest fraction is depos-
ited. Finer material is, in part, trapped by coarser par-
ticles, initiating a central ridge in the channel. Progres-
sive additions to the top and downstream end of the
incipient bar build the surface toward water level. As
progressively more water is forced into lateral channels
beside the growing bar, the channels become unstable
and widen. The bar may then emerge as an island due
to downcutling in lateral channels, and eventually may
become stabilized by vegetation. New bars may then
form by the same process in lateral channels. These
authors stress that braiding is not developed by the
stream's inability to move the total quinuty of sedi-
ment provided to it; as incapacity lead: merely to ag-
gradation without braiding. The condition requisite to
braiding is that the stream cannot move certain sizes
provided; that is, the stream is incompetent to trans-
port the coarsest fraction furnished to a given reach.
Observations for the present study substantiate the
braiding process of Leopold and Wolman.
Many features of streams, bars, and braided reaches
result from changes in regimen (e.g., discharge, load,
gradient), to a large extent representing seasonal fluc-
tuations. Other features of ban result from normal
evolution, and represent no change in regimen.
The incipient longitudinal bar formed in a channel
commonly has an asymmetric, downstream-pointing,
crescenlic shape. This coarse part is the "nucleus" of
the bar, is coarser than successive additions to the
downstream end, and largely retains its position and
configuration as long as any part of the bar remains.
During longitudinal bar evolution downstream of this
incipient bar the water and its sediment load com-
monly sweep from one lateral channel diagonally
across the downstream end of the bar, forming a
wedge of sediment with an advancing front at its
downstream edge. This wedge of sediment is higher at
its downstream edge, both on the longitudinal bars de-
scribed here, and where found as transverse bars to be
considered later. The latter build up the channel floor,
independent of longitudinal bar development, simply
by moving downstream.
After a certain evolutionary stage, bar height stops
increasing because insufficient water for sediment
transport is flowing over its surface, and deepening and
widening of lateral channels slowly lower water level.
From then on, the bar may be either stabilized by veg-
etation or dissected.
Widening of a reach after bar deposition is in some
cases associated with lateral dissection of the newly
formed bar. Most erosion, however, apparently occurs
on the outer channel margin* If water level remains
essentially constant for long periods of time, lateral
dissection may establish terraces along bar margins. A
compound terrace etfect may be established during
falling water stages. The constant tendency of the
stream to establish a cross-sectional profile of equilib-
rium is the basic cause of lateral cutting by the stream.
Longitudinal bars which become awash during high-
water stages may be dissected by small streams flowing
transversely over their surfaces. In stream-table experi-
ments, sediment added to a system eroding transverse
channels on bar surfaces is first transported along lat-
eral channels beside the bars. Eventually, these chan-
nels fill to an extent that sediment starts moving trans-
versely over bar surfaces, and fills bar-lop, transverse
channels. The addition of sufficient sediment to fill lat-
eral and bar-top channels often culminates in a trans-
verse bar covering the whole bar surface evenly.
Another process of braiding, in addition to that de-
scribed by Leopold and Wolman, takes place in well
sorted sediments, and involves dissection of transverse
bars. This is in opposition to construction of longitudi-
nal bars in poorly sorted sediment, the type of braiding
discussed above. Both types may occur together geo-
graphically and temporally. During extended periods of
high discharge, aggradation is by large tabular bodies
of sediment with laterally sinuous fronts at the angle
of repose migrating downstream.- Stabilization of dis-
charge or decrease in load after establishment of these
transverse ban results in their dissection by anastomos-
ing channels; bars in this case form as residual ele-
ments of the aggradational pattern.
The transient nature of braided stream depositional
surfaces is characteristic of the environment The
streams and deposilional areas within the stream exhibit
profound lateral-migration tendencies, especially during
-------
Geometry of Sandstone Reservoir Bodies
147
periods of high discharge. Channel migration lakes
place on several scales. Individual channels erode later-
ally, removing previously deposited bars. They divide
and coalesce, and several are usually flowing adjacent
to one another concurrently within the main channel
system. The whole channel system, composed of sev-
eral flowing channels with bars between, also exhibits
migrating tendencies.
Braided-stream deposits—Our knowledge of
modern braided-stream deposits has increased
substantially during the past several years as a
result of studies' of several rivers in Wyoming,
Colorado, and Nebraska by Ore (1963, 1965);
the Brahmaputra River of Bangla Desb (for-
merly East Pakistan) by Coleman (1969); the
Platte River of Colorado and Nebraska by N.
Smith (1970); the Red River of the Texas pan-
handle by Waechter (1970); the Canadian
River of northwest Texas by Kessler (1970,
1971); and the Copper River of Alaska by
Boothroyd (1970). These studies revealed that
braided-stream deposits are laid down princi-
pally in channels as longitudinal bars and trans-
verse bars. Abandoned-channel deposits (chan-
nel fills) have been reported by Doeglas
(1962) and Williams and Rust (1969).
According to Ore (1963, 1965), longitudi-
nal-bar deposits occur mainly in upstream
channel segments and transverse bars are more
common in downstream segments; however, in
some places these two types of bars occur to-
gether (Fig. 8). Longitudinal-bar deposits are
lens-shaped and elongated in the downstream
direction. Grain size decreases downstream
from coarse to fine in an individual bar; depos-
its are poorly sorted and mainly horizontally
stratified but laterally discontinuous. Trans-
verse-bar deposits occur as long thin wedges
and are highly dissected by channels. The
downstream edges of transverse bars migrate to
produce planar cross-stratification and some
festoon crossbedding. Sediments of transverse
bars are generally finer and better sorted than
those of longitudinal bars.
N. Smith (1970) described some very signifi-
cant relations between types of bars, straiifica-
tion, and grain size in the Platte River. In the
upstream segment in Colorado, the deposits
consist mainly of longitudinal bars character-
ized by low-relief stratification, generally hori-
zontally bedded but including some festoon
crossbedding. The downstream channel seg-
ment in Nebraska is characterized by trans-
verse-bar deposits consisting of better sorted,
fine-grained sand with abundant tabular cross-
stratification and some festoon crossbedding.
The Red River braided-stream sediments of
West Texas consist of longitudinal-bar deposits
with low-angle or horizontal stratification; they
are deposited during waning flood stages
(Waechter, 1970). Low-river-stage deposits
consist mainly of migrating transverse-bar de-
posits (in channels) with tabular cross-stratifica-
tion and some festoon crossbedding. The migra-
tion of very shallow channels results in stratifica-
tion sets that are horizontal, tabular or lentic-
ular, and laterally discontinuous.
Kessler (1970) reported longitudinal-bar de-
posits consisting mainly of fine sand in up-
stream reaches of the Canadian River in West
Texas. Transverse-bar deposits are predominant
in the downstream part of the area studied.
Kessler (1971) also discussed individual flood
sequences of deposits which contain parallel
bedding and tabular and small-ripple cross-lam-
inations. These sequences are covered by clay
drapes and are laterally discontinuous.
Coleman (1969) presented the results of a
significant study of one of the largest braided
rivers of the world, the Brahmaputra in Bangla
Desh. This river is 2-6 mi (3-9.5 km) wide
and migrates laterally as much as 2,600 ft (790
m) per year; deposition of sediments in its
channels during a single flood occurs in a defi-
nite sequence of change, ranging from ripples
up to 5 ft (1.5 m) high that migrate down-
stream 400 ft (120 m) per day to sand waves
50 ft (15 m) high that migrate up to 2,000 ft
(610 m) per day.
Williams and Rust (1969) presented results
of a very detailed study of a 4-mi (6.5 km)
segment of a degrading braided stream, the
Donjek River of the Yukon Territory, Canada.
They divided the bar and channel deposits,
which range from coarse gravels to clays, into
seven facies. Ninety-five percent of the bar de-
posits are of the longitudinal type and consist
of gravel, sand, and some finer sediments.
Abandoned-channel deposits consist of grada-
tional sequences of gravels, sand, and clays that
become finer upward.
Summary: Braided-Stream Deposits
Most of the sediments of modern braided
streams studied during the past decade have
been referred to by authors as transverse- or
longitudinal-bar deposits. These sediments were
deposited within braided channels during vary-
ing discharge conditions ranging from low wa-
ter to flood stage. Thus, all longitudinal and
transverse bars should be considered as a spe-
cial type of bed form occurring within active
braided channels.
-------
148
Rufus J. LeBlanc
MARINE
C - CHANKId
0 - DlltA
I) • I1AIDID 111! AM
MIW-MEAN LOW WA1EK
irt- IMtf IMf OlATf MOOD ilACI
rt • ro>Ni IAI
*•••"- - '» ^ VJ^rv ". •, '«^>Tv *on •! 1 ——•
MAI MOOD JtAGI
FIOOOIASIN
MATU'Al
llVtl
7I-OX3-7
Pic. 9—Selling and general • characteristics of meandering-stream model of clastic sedimentation.
Studies by Doeglas (1962) and Williams
and Rust (1969) are significant because they
describe abandoned-channel deposits. Doeglas
discussed the methods of channel abandonment
and described the channel-fill deposits as coarse
grained, with channel or festoon laminations, in
the upstream portions of abandoned channels,
and as fine grained, silty, and rippled in the
downstream porticos of abandoned channels.
Ancient Braided-Stream Deposits
Some examples of ancient braided-stream de-
posits which have been reported from the
United States, Spitsbergen, and Spain are sum-
marized in Table 1.
MEANDEHINC-STREAM MODEL OF
CLASTIC SEDIMENTATION
Occurrence and General Characteristics
Meandering streams generally occur in
coastal-plain areas updip from deltas and
downdip from the braided streams. The axis of
sedimentation is usually perpendicular to the
shoreline (Fig. 9).
This model is characterized by a single-chan-
nel stream which is deeper than the multichan-
nel braided stream. Meandering streams usually
have a wide range in discharge (cu ft/sec)
which varies from extended periods of low-wa-
ter flow to flood stages of shorter duration.
Flooding can occur one or more times per year
and major flooding once every several years.
The meandering channel is flanked by natural
levees and point bars, and it migrates within a
zone (meander belt) about 15 to 20 times the
channel width. Channel segments are aban-
doned and filled with fines as new channels de-
velop.
Source, Transportation, and Deposition
of Sediments
Sediments are derived from whatever type of
deposit occurs in the drainage area. Clays and
fine silts are transported in suspension (sus-
pended load), and coarser sediments such as
sand, gravel, and pebbles are transported as bed
load. Sediment transport and deposition during
extended low-water stages are confined to the
chancel and can be nil or very slow. Maximum
sediment transport occurs during rising flood
stage when the bed of the channel is scoured.
The maximum rate of sediment deposition
occurs during falling flood stages. Grain size
depends on the type of sediment available to .
the channel; the coarsest sediments are depos-
ited in the deepest part of the channel, and the
finest sediments accumulate in floodbasins and
in some parts of the abandoned channels.
Channel migration and deposition of point-
bar sediments—The most important processes
of sedimentation in the meandering-stream
model are related to channel migration which
occurs as a result of bank caving and point-bar
accretion (Fig. 10). The process of bank cav-
ing occurs most rapidly during falling flood
-------
Geometry of Sandstone Reservoir Bodies
149
I IANK CAVING
roml-iAi ACCIIIION
Fic. 10—Areas of bank caving and point-bar accretion along a meandering channel.
stage, when currents of maximum velocities are
directed against the concave bank. Bank caving
occurs at maximum rates in bends where the
bed and bank materials are very sandy. Rates
are much slower in areas where banks are char-
acterized by clayey sediments (Fisk, 1947).
Deposition occurs on the convex bar (point
bar) simultaneously with bank caving on the
concave bank.
Bank caving and point-bar accretion result in
channel migration and the development of the
point-bar sequence of sediments (Fig. 11). The
point bar is probably the most common and
significant environment of sand deposition. The
thickness of this sequence is governed by chan-
nel depths. Point-bar sequences along the Mis-
sissippi River attain thicknesses in excess of
150 ft (45 m). Medium-size rivers like the Bra-
zos of Texas produce point-bar sequences that
are 50 ft (15 m) thick (Bernard et at., 1970).
Channel diversions and filling of abandoned
channels—The process of channel diversion
and channel abandonment is another character-
istic feature of meandering streams. There are
two basic types of diversion and abandonment:
(1) the neck or chute cutoff of a single mean-
der loop and (2) the abandonment of a long
channel segment as a result of a major stream
diversion (Fisk, 1947).
Meander loops which are abandoned as a re-
sult of neck or chute cutoffs become filled with
sediment (Fig. 12A). The character of the
channel fill depends on the orientation of the
abandoned loop with respect to the direction of
flow in the new channel. Meanders oriented
with their cutoff ends pointing downstream
•(Fig. 12B) are filled predominantly with clays
(clay plugs); those oriented with the cutoff
ends pointing upstream are filled principally
with sands and silts.
A major channel diversion is one which re-
sults in the abandonment of a long channel seg-
ment or meander belt, as shown in Figure 13.
Channeling of flood water in a topographically
low place along the bank of the active channel
can rapidly erode unconsolidated sediments
and create a new channel. This process can
happen during a single flood or as a result of
several floods. The newly established channel
has a gradient advantage across the topographi-
cally lower fioodbasin. A diversion can occur at
any point along the channel.
FOINT'iAl DIFOSMl
Fic. 11—Development of point-bar sequence of sediments.
-------
150
Rufus J. LeBlanc
CHUTE CUTOFF
TYPES OF CHANNEL FILLS
Fio. 12—Channel diversion, abandonment, and filling u a result of neck and chute cutoffs.
The character of the sediments which fill
long channel segments is governed by the man-
ner of channel diversion. Abrupt abandonment
(during a single flood or a few floods) results
in the very rapid filling of only the upstream
end of the old channel, thus creating a long sin-
uous lake. These long, abandoned channels
(lakes) fill very slowly with clays and silts
transported by flood waters (Fig. 14, left).
Gradual channel abandonment (over a long
period) results in very gradual channel deterio-
ration. Diminishing flow transports and depos-
its progressively smaller amounts of finer sands
and silts (Fig. 14, right).
Summary: Characteristics of Meander-Belt
and Fioodbasin Deposits
The meandering-stream model of sedimenta-
tion is characterized by four types of sedi-
ments: the point bar, abandoned channel, natu-
ral levee, and fioodbasin. The nature of each of
these four types of sediments and their interre-
lations are summarized in Figure 15.
Only two main types of sand bodies are asso-
ciated with a meandering stream: the point-bar
-AlAMOOMtO MtAMDt* Mil
sands and the abandoned-channel fills. The for-
mer, which are much more abundant than the
latter, occur in the lower portion of the point-
bar sequence and constitute at least 75 percent
of the sand deposited by a meandering stream.
Coalescing point-bar sands can actually form a
"blanketlike" sand body of very large regional
extent. The continuity of sand is interrupted
only by the "clay plugs" which occur in aban-
doned meander loops or in the last channel po-
sition of meander belts which have been aban-
doned abruptly.
Examples of ancient alluvial deposits of
meandering-stream origin which have been re-
ported in the Literature are summarized in
Table 1.
DELTAIC MODELS OF CLASTIC SEDIMENTATION
Occurrence and General Characteristics
Deltaic sedimentation occurs in the transi-
tional zone between continental and marine (or
inland seas and lakes) realms of deposition.
Deltas are formed under subaerial and suba-
queous conditions by a combination of fluvial
and marine processes which prevail in an area
where a fluvial system introduces land-derived
sediments into a standing body of water.
Flc. 13—Major channel diversion and abandonment
of a meander belt.
Fio. 14—Variations in character of abandoned channel
nil typical of meander belts.
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-------
152
Rufus J. LeBlonc
FIG. 16—Occurrence of deltaic models of
clastic sedimentation.
Large deltas usually are associated with ex-
tensive coastal plains; however, all coastal
plains do not include large deltas. The deltaic
environment occurs downstream from the
meandering-stream environment and is directly
adjacent to, and updip (landward) from, the
marine environment; it is flanked by the
coastal-interdeltaic environment. Most large
deltas occur on the margins of marine basins,
but smaller deltas also form in inland lakes,
seas, and coastal lagoons and estuaries (Fig.
16).
That portion of a delta which is constructed
under subaerial conditions is called the "deltaic
plain"; that portion which forms under water is
called the "delta front," "delta platform," and
"prodelta." The bulk of the deltaic mass is de-
posited under water.
Deltas are considered to be extremely impor-
tant because they are the sites of deposition of
sand much father downdip than the interdeltaic
environment, as well as being tilt sites where
clastic deposition occurred at maximum rates.
Source and Transportation
of Sediments
Sediments deposited in large deltas are de-
rived from extensive continental regions which
are usually composed of rock types of varied
compositions and geologic ages. Thus, the com-
position of deltaic sediments can be quite var-
ied.
The sediment load of rivers consists of two
parts: (1) the clays and fine silts transported in
suspension and (2) the coarser silts and sands,
and in some cases gravels, transported as bed
load. The ratio of suspended load to bed load
varies considerably, depending upon the rock
types and climatic conditions of the sediment-
source areas. The suspended load is generally
much greater than the bed load.
The transportation of sediment to a delta is
an intermittent process. Most rivers transport
the bulk of their sediments during flood stages.
During extended periods of low discharge, riv-
ers contribute very little sediment to their del-
tas.
The extent to which deltaic sediments are
dispersed into the marine environment is de-
pendent upon the magnitude of the marine pro-
cesses during the period that a river is in flood
stage. Maximum sediment dispersal occurs
when a river with a large suspended load
reaches flood stage at the time the marine envi-
ronment is most active (season of maximum
currents and wave action). Minimum dispersal
occurs when a river with a small suspended
load (high bed load) reaches flood stage at a
time when the marine environment is relatively
calm.
Size of deltas—There is an extremely wide
range in the size of deltas;1 modern deltas
range in area from less than 1 sq mi (2.6 sq
km) to several hundreds of square miles. Some
large deltaic-plain complexes are several thou-
sand square miles in area. Delta size is depen-
dent upon several factors, but_ the three most
important are the sediment load of the river;
the intensity of marine currents, waves, and
tides; and the rate of subsidence. For a given
rate of subsidence, the ideal condition for the
construction of a large delta is the sudden large
influx of sediments in a calm body of water
with a small tidal range. An equally large sedi-
ment influx into a highly disturbed body of wa-
ter with a high tidal range results in the forma-
tion of a smaller delta, because a large amount
of sediment is dispersed beyond the limits of
what can reasonably be recognized as a delta.
Rapid subsidence enhances the possibility for a
large fluvial system to construct a large delta.
Types of deltas—A study of modem deltas
of the world reveals numerous types. Bernard
' Published figures on area! extent of deltas are based
on size of the deltaic plain and do not include sub-
merged portions of the delta, which in many cases are
as large as or larger than tic deltaic plains.
-------
Geometry of Sondstone Reservoir Bodies
153
(1965) summarized some of the factors which
control delta types as follows:
Delias and dchaic sediments are produced by the
rapid deposition of stream-borne materials in relatively
still-standing bodies of water. Notwithstanding the
effects of subsidence and water level movements, mosl
deltaic sediments are deposited off the delta shoreline
in the proximity of the river's mouth. As these materi-
als build upward to the level of the still-standing body
of water, the remainder of deltaic sediments are depos-
ited onshore, within the delta's flood plains, lakes,
bays, and channels.
Nearly 2,500 years ago, Herodotus, using the Nile as
an example, stated that the land area reclaimed from
the sea by deposition of river sediments is generally
deltoid in shape. The buildup and progradation of del-
taic sediments produces a distinct change in stream
gradient from the fluvial or alluvial plain to the deltaic
plain. Near the point of gradient change the major
courses of rivers generally begin to iranspon much
finer materials, to bifurcate into major distributaries,
and to form subaerial deltaic plains. The boundaries of
the subaerial plain of an individual delta are the lat-
eral-most distributaries, including their related sedi-
ments, and the coast line. Successively smaller distribu-
taries form sub-deltas of progressively smaller magni-
tudes.
Deltas may be classified on the basis of the nature of
their associated water bodies, such as lalce, bay, inland
sea, and marine deltas. Other classifications may be
based on the depth of the water bodies into which they
prograde, or on basin structure.
Many delta types have been described previously.
Most of these have been related to the vicissitudes of
sedimentary processes by which they form. Names
were derived largely from the shapes of the delta
shorelines. The configuration of the delta shores and
many other deposilional forms expressed by different
sedimentary facies appear to be directly proportional
to the relative relationship of the amount or rale of
river sediment influx with the nature and energy of the
coastal processes. The more common and better under-
stood types, listed in order of decreasing sediment in-
flux and increasing energy of coastal processes (waves,
currents, and tides), are: birdfoot, lobate, cuspate, ar-
cuate, and estuarine. The subdeltas of the Colorado
River in Texas illustrate this relationship. During the
first part of this century, the river, transporting ap-
proximately the same yearly load, built a birdfoot-lo-
bate type delta in Matagorda Bay, a low-energy water
body, and began to form a cuspate delta in the Gulf of
Mexico, a comparatively high-energy water body.
Many deltas are compounded; their subdeltas may be
representative of two or more types of deltas! such as
birdfoot, lobate, and arcuate. Less-known deltas, such
as the Irrawaddy, Ganges, and Mekong, are probably
mature esluarine types. Others, located very near major
scarps, are referred to the "Gilbert type," which is sim-
ilar to an alluvial fan.
Additional studies of modern deltas are re-
quired before a more suitable classification of
delta types can be established. J. M. Coleman
(personal commun.) and bis associates, to-
gether with the Coastal Studies Institute at
Louisiana State University, are presently con-
ducting a comprehensive investigation of more
than 40 modern dehas. Results of their studies
undoubtedly will be a significant contribution
toward the solution to this problem.
Only three types of deltas will be considered
in this report: the birdfoot-lobate, the cuspate-
arcuate, and the esluarine.
Sedimentary Processes and Deposits of
the Bird/oot-Type Delta
The processes of sedimentation within a
delta are much more complex and variable
than those which occur in the meandering-
stream and coastal-inierdeltaic environment of
sedimentation. It is impossible to discuss these
deltaic processes in detail in a short summary
paper such as this; therefore, only a brief sum-
mary of the following significant processes is
presented.
1. Dispersal of sediment in the submerged parts of
the delta (from river mouths seaward);
2. Formation of rivermouth bars, processes of chan-
nel bifurcation, and development of distributary chan-
nels;
3. Seaward progradation of delta, deposition of the
deltaic sequence of sediments, and abandonment and
filling of distributary channels; and
4. Major river diversions, abandonment of deltas,
and development of new deltas.
Dispersal and deposition of sediments—Riv-
erborne sediments which are introduced in z
standing body of water (a marine body or in-
land lakes and seas) are transported in suspen-
sion (clays and fine silts) and as bed load
(coarse silts, sands, and coarser sediments).
Most of the sands and coarse silts are deposited
in the immediate delta-front environment as
rivermouth bars and slightly beyond the bar-
front zone. The degree of sand dispersal is, of
course, controlled by the level of marine en-
ergy; however, in most birdfoot deltas, sands
are not transported beyond 50-ft (15 m) water
depths. Fisk (1955) referred to the sands de-
posited around (he margins of the subaerial del-
taic plain as "delta-front sands," and they are
called "delta-fringe sands" herein.
The finer sediments (clays and fine silts),
which are transported in suspension, are dis-
persed over a much broader area than the
fringe sands and silts. The degree of dispersal is
governed by current intensity and behavior.
Accumulations of clays seaward of the delta-
fringe sands are referred to as "prodelta" or
"distal clays" (Fig. 17).
Channel bifurcation and development of dis-
tributary channels—Some of the most signifi-
cant deltaic processes are those which result in
the origin and development of distributary
-------
154
Rufus J. LeBlonc
FIG. 17—Distribution of distributary-channel and fringe sands in a birdfoot-lobate delta.
channels. Welder (1959) conducted a detailed
study of these processes in a part of the Missis-
sippi delta, and Russell (1967a) summarized
the origin of branching channels, as follows:
The creation of branching channels is determined by
the fact that threads of maximum turbulence and tur-
bulent interchange (Austausch; 1.2.3; 3.5) lie deep and
well toward the sides of channels, particularly if they
have fiat bed: (typical of clay and fine sediments in
many delta regions). These threads are associated with
maximum scour and from them, sediment is expelled
toward areas of less turbulence and Austauscb. Signifi-
cant load is propelled toward mid-channel, where
shoals are most likely to form.
OIICINAl MAMCHING OF A MITA CHAKMfl
Fio. 18—Stages in development of channel bifurcation.
After Russell (1967).
At its mouth, the current of a delta channel contin-
ues forward (as a result of momentum) and creates jet
flow into the lake or sea it enters. After leaving the
confinement imposed by fixed banks, however, the cur-
rent flares marginally to some extent (widening the jet,
reducing its velocity, and eventually dissipating its fiow
energy). Near the termination of confining banks the
jet fiow is concentrated and moves ahead into relatively
quiet water. With flaring of jet flow comes an increase
in spacing between threads of most intense turbulence
and exchange. There is a tendency toward scour below
each thread, but the exchange prpcess sends most of
the entrained material toward marginal quiet water on
both sides (Fig. 8 [Fig. 18 of this paper]). Deposition
creates a submarine natural levee on the outer side of
each thread. Sediment is also attracted toward and de-
posited in the widening area of mid-channel water,
where it builds a shoal. The channel divides around the
shoal, creating two distributaries, each of which devel-
ops its own marginal threads of maximum turbulence,
perpetuating conditions for other divisions below each
new channel mouth. If not opposed by wave erosion
and longshore currents, the subdivision continues in
geometric progression (2, 4, 8, 16, etc.) as the delta
deposit grows forward. >'„
The marginal natural levees are submarine features
at first and fish may swim across their crests. Later
they grow upward, and for awhile become areas where
logs and other flotsam accumulate and where birds
walk with talons hardly submerged. Salt- or fresb-wa-
ter-tolerant grasses invade the shallow water and newly
created land, first along levee crests, later to widen as
the levees grow larger. Salicornia and other plants be-
come established pioneer trees such as willows, and
eventually in the plant succession comes the whole
complex characteristic of natural levees upstream. In
tropical areas mangroves are likely to become the
dominant trees.
-------
Geometry of Sandstone Reservoir Bodies
155
A similar conversion exists in mid-channel, where
the original ihoaJ becomes land and cither develops
into a lenticular or irregular island or becomes the
point of land at the bead of two branching distributar-
ies.
Progradation of delta and deposition oj del-
taic sequence—Fisk's discussion of the process
of distributary-channel lengthening (prograda-
tion of delta seaward) is probably one of the
most significant of bis many contributions on
deltaic sedimentation (Fisk, 1958). His de-
scription of this important aspect of delta de-
velopment is presented below. (Stages in the
development of a birdfoot-type delta are shown
in Figure 19.)
Each of the prc-modern Mississippi River courses
was initiated by an upstream diversion, similar to the
one presently affecting the Mississippi as the Atchafa-
laya River enlarges (Fisk, 1952). Stream capture was a
gradual process involving increasing Sow through a
diversional arm which offered a gradient advantage to
the gulf. After capture was effected, each new course
lengthened seaward by building a shallow-water delta
and extending it gulfward. Successive stages in course
lengthening are shown djagrammalically on Figure 2
[Fig. 19, this paper]. The onshore portion of the delta
surface ... is composed of distributaries which are
flanked by low natural levees, and interdistributary
troughs holding near-sea-level marshes and shallow wa-
ter bodies. Channels of the principal distributaries ex-
tend for some distance across the gently sloping offshore
surface of the delta to the inner margin of the sleeper
delta front where the distributary-mouth bars are situ-
ated. The offshore channels are bordered by submarine
levees which rise slightly above the offshore extensions
of the interdistributary troughs.
In the process of course lengthening, the river occu-
pies a succession of distributaries, each of which is fa-
vorably aligned to receive increasing flow from up-
stream. . . . The favored distributary gradually widens
and deepens to become the main stream . . . ; its natural
levees increase in height and width and adjacent inter-
distributary troughs fill, permitting marshland develop-
ment. Levees along the main channel are built largely
during floodslagc; along the distal ends of distributar-
ies, however, levee construction is facilitated by cre-
vasses . . . which breach the low levees and permit
water and sediment to be discharged into adjacent
troughs during intermediate river stages as well as dur-
ing fioodslage. Abnormally wide sections of the levee
and of adjacent mudflats and marshes are created in
this manner, and some of the crevasses continue to re-
main open and serve as minor distributaries while the
levees increase in height. Crevasses also occur along
the main stream during floodstages . . . and permit
tongues of sediment to extend into the swamps and
marshes for considerable distances beyond the normal
toe position of the levee.
Distributaries with less favorable alignment are
abandoned during the course-lengthening process, and
their channels are filled with sandy sediment. Aban-
doned distributaries associated with the development of
the present course below New Orleans vein the marsh-
lands. . . . Above the birdJoot delta, the pattern is simi-
lar to that of the older courses . . . ; numerous long,
branching distributaries diverge at a low angle.
Stream diversions, abandonment of deltas,
and development oj new deltas—Deltas pro-
grade seaward but they do not migrate later-
ally, as a point bar does, for example. A delta
shifts position laterally if a major stream diver-
sion occurs upstream in the alluvial environ-
ment or in the upper deltaic-plain region (Fig.
20). Channel diversions were discussed in the
section on the meandering-stream model.
Deltas, like meander belts, can be abandoned
abruptly or gradually, depending upon the time
required for channel diversion to occur. Once a
delta is completely abandoned, all processes of
deltaic sedimentation cease to exist in that par-
ticular delta. With a standing sea level, the sedi-
ments of the abandoned delta compact, and
subsidence probably continues. The net result is
the encroachment of the marine environment
over the abandoned delta. This process bas er-
roneously been referred to by some authors
as "the destructive phase of deltaic sedi-
mentation." The author maintains that the
proper terminology for this process is "trans-
gressive marine sedimentation." The two pro-
cesses and their related sediments are signifi-
cantly different, as the discussion of the trans-
gressive marine model of sedimentation demon-
strates (see the succeeding section on this
model).
As the marine environment advances land-
ward over an abandoned subaqueous delta
front and the margins of the deltaic plain, the
upp:r portion of the deltaic sequence of sedi-
ment is removed by wave action. The amount
of sediment removed depends on the inland ex-
tent qf the transgression and on the rate of sub-
sidence. The front of the transgression is usu-
ally characterized by deposition of thin marine
sand units. Seaward, sediments become finer
and grade into clays. Thus, local marine trans-
gressions which occur because of delta shifts
result in the deposition of a very distinctive
marine sedimentary sequence which is easily
distinguished from the underlying deltaic se-
quence.
Concurrent with marine transgression over
an abandoned delta, a new delta will develop on
the flanks of the abandoned delta. Sedimentary
processes in the new delta are similar to those
described under the discussion of progradation
of deltas.
Repeated occurrences of river diversions re-
sult in the deposition of several discrete deltaic
masses which are separated by thin transgres-
sive marine sequences (Fig. 20). Under ideal
conditions, deltaic fades can attain thicknesses
-------
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