Practical Exercises in Basin Analysis

Practical Exercises in Basin Analysis
For 4th Year Students

Prepared and Compiled
By
Dr. Mohamed Elhossainy

Geology Department
Faculty of Science
Kafrelsheikh University
Depositional Sedimentary
Environments
WHAT IS A SEDIMENTARY ENVIRONMENT?

A sedimentary environment is an area of the Earth's surface where sediment is deposited. It
can be distinguished from other areas on the basis of its physical, chemical, and biological
characteristics. Before studying ancient sedimentary environments, it is helpful to consider the
types of sedimentary environments present on the Earth today.
CONTINENTAL ENVIRONMENTS
Continental environments are those environments which are present on the continents, such
as alluvial fans, fluvial environments (rivers), lacustrine environments (lakes), aeolian or eolian
environments (deserts), and paludal environments (swamps).
Continental Sedimentary Environments
Dr. Mohamed M. Elhossainy 2|Page

1. Alluvial fans are fan-shaped
deposits formed at the base of
mountains. Alluvial fans are most
common in arid and semi-arid
regions where rainfall is infrequent
but torrential, and erosion is rapid.
Alluvial fan sediment is typically
coarse, poorly- sorted gravel and
sand.
2. Fluvial environments include braided and meandering river and

stream systems. River channels,
bars, levees, and floodplains are
parts (or sub-environments) of the
fluvial environment. Channel deposits
consist of coarse, rounded gravel,
and sand. Bars are made of sand or
gravel. Levees are made of fine sand
or silt. Floodplains are covered by silt
and clay. This photo shows the Sand along the Oconee River, Sandersville, GA.
Photo by Pamela Gore, 2009

3. Lakes (lacustrine environments) are diverse. They may be large or
small, shallow or deep, fresh water or salt water, and filled with
terrigenous, carbonate, or evaporite sediments. Mud cracks, wave
ripples, laminations, and varves may be present in lakes. Fine sediment
and organic matter settling in some lakes produced laminated oil
shales.
4. Deserts (aeolian or eolian

environments) are areas with little
or no rainfall during the year. Deserts
usually contain vast areas where
sand is deposited in dunes. Dune
sands are well sorted, well rounded,
and frosted or polished, without
associated gravel or clay. Cross-bedding is common.
5. Swamps (paludal environments) are areas of standing water with

trees. Decaying plant matter accumulates to form peat, which may
eventually become coal.

TRANSITIONAL ENVIRONMENTS
Transitional environments are those environments at or near where the land meets the sea.
Transitional sedimentary environments include deltas, beaches and barrier islands, lagoons, salt
marshes, and tidal flats. Tidal flats are low-lying areas that are alternately covered by water and
exposed to the air each day.
1. Deltas are fan-shaped deposits of sediment, formed where a river flows

into a standing body of water, such as a lake or sea. Coarser sediment
(sand) tends to be deposited near the mouth of the river; finer sediment
is carried seaward and deposited in deeper water. Some well known
deltas include the Mississippi River delta and the Nile River delta.

2. Beaches and barrier islands are shoreline deposits exposed to wave
energy and dominated by sand with a marine fauna. Barrier islands are
separated from the mainland by a lagoon. They are commonly
associated with tidal flat deposits.
3. Lagoons are bodies of water on the landward side of barrier islands.

They are protected from the pounding of the ocean waves by the barrier
islands, and contain finer sediment than the beaches (usually silt and
mud). Lagoons are also present behind reefs, or in the center of atolls.
4. Tidal flats are areas that are periodically flooded and drained by the
tides (usually twice each day). Tidal flats are areas of low relief,
commonly cut by meandering tidal channels. Laminated or rippled clay,
silt, and fine sand (either terrigenous or carbonate) may be deposited.
Intense burrowing is common. Stromatolites may be present on
carbonate tidal flats, if conditions are appropriate (high salinity). Salt
marshes are associated with tidal flats behind barrier islands in Georgia
and in other areas.

Tidal flat with ripples at low tide, Wassaw Island, Georgia coast Salt marsh at high tide behind Jekyll Island, GA
MARINE ENVIRONMENTS
Marine environments are in the seas or oceans. Marine environments include reefs, the
continental shelf, slope, rise, and abyssal plain.
1. Reefs are wave-resistant, mound-like structures made of the calcareous

skeletons of organisms such as corals and certain types of algae. Most
modern reefs are in warm, clear, shallow, tropical seas, between the
latitudes of 30°N and 30°S of the equator. Atolls are ring-like reefs
surrounding a central lagoon.
2. The continental shelf is the flooded edge of the continent. It is

relatively flat (with a slope of less than 0.1°), shallow (less than 200 m
or 600 ft deep), and may be up to hundreds of miles wide. Continental
shelves are exposed to waves, tides, and currents, and are covered by
sand, silt, mud, and gravel. The flooding of the edges of the continents
occurred when the glaciers melted at the end of the last Ice Age, about
10,000 years ago.

3. The continental slope and continental rise are located seaward of
the continental shelf. The continental slope is the steep (5- 25°) "drop-
off" at the edge of the continent. The continental slope passes seaward
into the continental rise, which has a more gradual slope.
The continental rise is at the base of the continental slope, where thick
accumulations of sediment are deposited. Large landslides have
occurred down the continental slope, and landslide deposits at the base
of the slope are part of the continental rise. Such a landslide could
trigger a tsunami.
During the Ice Ages, when sea level was much lower than today, the
continental shelves were exposed as dry land and cut by river channels.
In some places, the catastrophic flow of meltwater from glacial lakes
carved deep submarine canyons into the edge of the continental slope.
Turbidity currents flowing down these canyons deposited their
sediment to form huge submarine fans at the base of the slope, as
part of the continental rise. Turbidity current deposits or turbidites are
characterized by graded bedding.

4. The abyssal plain is the deep ocean floor. It is basically flat, and is
covered by very fine-grained sediment, consisting primarily of clay and
the shells of microscopic organisms (such as foraminifera,
radiolarians, and diatoms). Abyssal plain sediments may include chalk,
diatomite, and shale, deposited over the basaltic ocean crust.
WHAT KINDS OF FEATURES HELP US TO IDENTIFY ANCIENT

SEDIMENTARY ENVIRONMENTS?
Sedimentary rocks, which are exposed in many areas, contain clues that help us to determine
the sedimentary environment in which they were deposited millions of years ago. By an
examination of the physical, chemical, and biological characteristics of the rock, we can
determine the environment of deposition. Each sedimentary environment has its unique
combination of physical, chemical, and biological features. These features help us to identify
the sedimentary environment in which a rock was deposited.
In lab, you will be examining hand specimens of sedimentary rocks, describing their physical,
chemical, and biological features, and then, interpreting their possible sedimentary
environments of deposition. Geologists consider the characteristics that we will study in lab
(see outline below), but they also study the geometry of the sedimentary deposits, the vertical
sequence in which the rocks occur, and the paleocurrent directions.

Certain generalizations can be made, which help in identifying the depositional environment.
For example, fluvial sequences become finer upward, whereas delta and lacustrine sequences
coarsen upward. These predictable changes occur because the environments migrate over one
another as sea level changes, or as a basin fills with sediment.
As a general rule, grain size is coarser in shallow water "high energy" environments where
waves or currents are present. Waves and currents transport finer sediment offshore into "low
energy" environments, generally in deep, quiet water. Fine grain size indicates deposition in a
"low energy", quiet water environment.
Dr. Mohamed M. Elhossainy 10 | P a g e

Techniques of Basin Analysis
A. Preparation of Stratigraphic Maps and Cross Sections
1. Stratigraphic Cross Sections
2. Structure-Contour Maps
3. Isopach Maps
4. Paleogeologic Maps
5. Lithofacies Maps
6. Computer-generated Maps
7. Paleocurrent Analysis and Paleocurrent Maps
B. Siliciclastic petrofacies (Provenance) Studies
C. Geophysical Studies

Sheet No. 1 is represented
Faculty of Science
in pages from 15 to18
Geology Department
Sedimentary Basin Analysis

Answer of Sheet No. 1

Faculty of Science Sheet No. 2
Geology Department

The following lithological log represents a pure siliciclastic succession deposited during a
change in the sea level.
1. Determine the FUS and CUS between the different formations. Write the transgressive –
regressive trends in the column “T or R?”.
2. In the column labeled “relative sea level” draw a sea level curve based on your
environmental interpretation.
3. Compare the T-R based on FUS/CUS with that based on sea level curve.
4. What is the possible cause of the sea level in the section?


Geology Department

The following lithological log represents a pure carbonate succession deposited during a change
in the sea level.
3. Compare the T-R based on FUS/CUS with that based on sea level curve.


Geology Department

The following lithological log represents a mixed siliciclastic-carbonate succession deposited
during a change in the sea level.
2. Determine for each formation present in the section the shoreline dominance as in the
following:
a. Siliciclastic dominated
b. Carbonate dominated
c. Siliciclastic-carbonate dominated
4. Compare the T-R based on FUS/CUS and the shoreline dominance with that based on sea
level curve.


Geology Department
Geology Department

Geology Department

Sheet No. 7

Sheet No. 8

Sheet No.9

Sheet No.10

Sheet No.11

Sheet No.12
The map show the dispersion of boulders of mica – slate encountered in a glacial
deposit.
Requirements:
1. Determine the general direction of ice movement.

2. Comment on the dispersion of boulders.

Sheet No.13

Sheet No.14

Sheet No.15

Analysis of sedimentary structures
❖ Paleocurrent analysis
Directional properties of sedimentary structures are important in paleoenvironmental
interpretation. Generally, they indicate the current flow direction at the time of deposition
and provide an important key for evaluating paleogeography. In fluvial, deltaic, and most
turbidite deposits, paleocurrent patterns indicate paleoslope. Paleocurrent studies may
also provide important information regarding the geometry (e.g. elongation) of particular
lithic units. Some of the most important structures which provide direction of movement
data are cross bedding, current crescents, flute casts, and asymmetrical ripples. Those that
indicate only the line of movement include parting lineation, groove casts, and
symmetrical ripples.
If the structural dip is less than 25°, the measured azimuth of linear structures needs no
correction (Potter & Pettijohn 1963). If the dip exceeds 25°, the effects of tilting must be
removed. This can be done with a stereonet, as illustrated in Figure 1.
Figure 1: The correction of a linear structure for tectonic tilt using stereographic
projection.
(1) Plot the plane of the bedding and linear structure (as a line) on the stereogram. In this
example the bedding has a dip of 50° and a dip direction of 320° (strike N50°E, dip

50°W). The rake of the linear structure is 40°; the azimuth of a vertical plane, which
passes through the linear structure, is 260°.
(2) Restore the bedding to horizontal (point A to point B). Move the intersection point of
the linear structure with the great circle projection of the bedding point (point C)
along the nearest small circle (dotted line) to the edge of the stereogram. Read the
azimuth of the linear structure. In this example it is 270° (due west).
❖ Graphic presentation of directional data
A popular device for presenting directional data is the current rose, which is a histogram
converted to a circular distribution. Various class intervals are used, but a 30° interval
will meet most needs. It is better to plot the percentage of observations in each class than
to plot the total number of observations (Fig. 2a). The class interval with the most
observations is the modal class. When measurements of structures which show direction
of movement are plotted (e.g. cross beds and flute casts), the rose diagram indicates the
direction toward which the current moved. Most distributions produce a single dominant
mode (unimodal), although some have two or more subequal modes (bimodal,
polymodal). In the case of structures which show line of movement, each measurement is
represented by two opposite azimuth values (e.g. 30 and 210°). The resulting current rose
consists of two reflected halves (Fig. 2b). Measurements made from several different
structures may be plotted on a single composite rose diagram (also called a composite ray
diagram, radial line diagram, or spoke diagram) (Fig. 2c).

Figure 2: Rose diagrams. The diagrams may utilize (a) direction of movement data, (b) line of
movement data, or (c) data from several different structures. Data plotted: (a) twelve cross-bed
dip azimuths (in degrees) - 10, 80, 112, 71, 130,42, 58, 72, 67,74, 99, 102; (b) compass bearing
of eight groove casts (in degrees) - 20(200), 331(151), 340(160), 305(125), 15(195), 18(198),
39(219), 6(186); (c) compass bearing of four groove casts - 60(240), 71(251), 20(200), 39(219),
three flute casts - 42, 37, 50, and six cross-bed dip azimuths - 17, 55, 33, 78, 10, 43.

❖ Vector mean and vector magnitude
➢ Direction of movement data

Although the current rose gives a general idea of the paleocurrent direction, a more rigorous
approach is needed. The vector mean is the most commonly used measure of the average flow
direction. Strongly bimodal distributions may produce a vector mean that has little geologic
significance.
The vector mean can be determined graphically (Reiche 1938) by assigning a vector of unit
length to each measured value (Fig. 3b). The first observation is plotted as a vector starting at an
arbitrary point of origin. The second is then plotted at the end of the first, and so on until
all have been plotted. The line which connects the point of origin with the end of the last vector
is the graphical vector mean.
Another method, involving summation of the sine and cosine for each direction of movement
azimuth (e.g. cross bedding), is shown in Figure 2.5a. The vector mean is the arctan of the
resulting tangent. It is important to keep in mind that in a 360° distribution any value of the
tangent will have two possible azimuths that differ by 180°. For example, the tangent for a 10°
angle and a 190° angle is 0.176. They are distinguished by the sign of the sine and cosine. In the
first quadrant (azimuth = 10°) both will be positive and in the third quadrant
(azimuth = 190°) they will be negative. These relationships are summarized in Figure 3a.
Programs for use with programmable calculators are also available (Lindholm 1979a, Freeman &
Pierce 1979).

Figure 3: Methods for calculating the vector mean and vector magnitude.
(a) Trigonometric method. The tangent of the mean vector is calculated by dividing the sum of the sines
by the sum of the cosines. The vector mean is the arctan of this value. It is critical that the signs of the
trigonometric functions be accurately recorded. In this example the negative tangent (positive sine and
negative cosine) lies in the 2nd quadrant, and the resultant azimuth (-74°) is plotted counterclockwise from
zero at the bottom of the circle (see illustration to the right of the tabulated sines and cosines). According
to standard geologic usage, this equals 106° (measured clockwise from zero (due north) or S74°E in the
parlance of many geologists in the United States. The vector magnitude in percent (L) is determined by
dividing R (11.8) by the number of measurements (15) multiplied by 100.
(b) Graphical method. Each measured azimuth is plotted as a unit vector. One unit of length can be 1 cm,
1 in. or whatever is convenient. In this illustration the unit vectors are labeled 1 to 15 (azimuths given in
(a) above). The resultant vector, the line which connects the origin with the end of the last unit vector, is
the vector mean. The vector magnitude is obtained by dividing the length of the resultant vector (12 units)
by the total length of the unit vectors (15 units) multiplied by 100.

Sheet No.16

Sheet No.16
Continued sheet no.16

Answer of sheet no.16

Sheet No.17

Continued sheet no.17


Sheet No.18


Sheet No.19


Sheet No.20


Sheet No.21


Sheet No.22


Practical Exercises in Basin Analysis

Uploaded by

Copyright:

Available Formats

Practical Exercises in Basin Analysis

Uploaded by

Document Information

Original Description:

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Practical Exercises in Basin Analysis

Uploaded by

Copyright:

Available Formats

Practical Exercises in Basin Analysis

For 4th Year Students

Dr. Mohamed Elhossainy

WHAT IS A SEDIMENTARY ENVIRONMENT?

Continental Sedimentary Environments

Dr. Mohamed M. Elhossainy 2|Page

2. Fluvial environments include braided and meandering river and

Photo by Pamela Gore, 2009

Dr. Mohamed M. Elhossainy 3|Page

4. Deserts (aeolian or eolian

5. Swamps (paludal environments) are areas of standing water with

Dr. Mohamed M. Elhossainy 4|Page

1. Deltas are fan-shaped deposits of sediment, formed where a river flows

Dr. Mohamed M. Elhossainy 5|Page

3. Lagoons are bodies of water on the landward side of barrier islands.

Dr. Mohamed M. Elhossainy 6|Page

1. Reefs are wave-resistant, mound-like structures made of the calcareous

2. The continental shelf is the flooded edge of the continent. It is

Dr. Mohamed M. Elhossainy 7|Page

Dr. Mohamed M. Elhossainy 8|Page

WHAT KINDS OF FEATURES HELP US TO IDENTIFY ANCIENT

Dr. Mohamed M. Elhossainy 9|Page

Dr. Mohamed M. Elhossainy 10 | P a g e

B. Siliciclastic petrofacies (Provenance) Studies

Dr. Mohamed M. Elhossainy 14 | P a g e

Sedimentary Basin Analysis

Dr. Mohamed M. Elhossainy 15 | P a g e

Dr. Mohamed M. Elhossainy 19 | P a g e

Sedimentary Basin Analysis

Dr. Mohamed M. Elhossainy 20 | P a g e

Dr. Mohamed M. Elhossainy 22 | P a g e

Sedimentary Basin Analysis

Dr. Mohamed M. Elhossainy 23 | P a g e

Dr. Mohamed M. Elhossainy 25 | P a g e

Sedimentary Basin Analysis

Dr. Mohamed M. Elhossainy 26 | P a g e

Dr. Mohamed M. Elhossainy 28 | P a g e

Sedimentary Basin Analysis

Dr. Mohamed M. Elhossainy 29 | P a g e

Sedimentary Basin Analysis

Dr. Mohamed M. Elhossainy 30 | P a g e

Dr. Mohamed M. Elhossainy 31 | P a g e

Dr. Mohamed M. Elhossainy 32 | P a g e

Dr. Mohamed M. Elhossainy 33 | P a g e

Dr. Mohamed M. Elhossainy 34 | P a g e

Dr. Mohamed M. Elhossainy 35 | P a g e

1. Determine the general direction of ice movement.

Dr. Mohamed M. Elhossainy 36 | P a g e

Dr. Mohamed M. Elhossainy 37 | P a g e

Dr. Mohamed M. Elhossainy 38 | P a g e

Dr. Mohamed M. Elhossainy 39 | P a g e

Dr. Mohamed M. Elhossainy 40 | P a g e

Dr. Mohamed M. Elhossainy 41 | P a g e

Dr. Mohamed M. Elhossainy 42 | P a g e

➢ Direction of movement data

Dr. Mohamed M. Elhossainy 43 | P a g e

Dr. Mohamed M. Elhossainy 44 | P a g e

Dr. Mohamed M. Elhossainy 45 | P a g e

Continued sheet no.16