GRAPHIC PROBLEMS IN
PHYSICAL STRATIGRAPHY
It is well known that all graphic expressions such as geologic maps, columnar
sections, cross sections.... etc. of any geologic phenomena are made for one or both
of two purposes; The first is to aid the geologist in resolving complex relationships,
and the second is to enable the geologist to express his ideas and conclusions. Only
the first purpose is considered in the present problems.
PROBLEM 1
DRAFTING OF COLUMNAR SECTION IN GRAPHIC SYMBOLS
(Outcrop section)
Columnar sections illustrate stratigraphic data obtained from measured surface and
subsurface rock sequences. These sections are the basis for the construction of
many types of stratigraphic maps and cross sections; therefore, they should be
prepared accurately and systematically.
The following figure show five forms of graphic columnar sections:
1
2
3
4
5
Figure 1. Forms of graphic columnar sections.
Type 1, commonly used in many early geologic reports and still used by some
geologists, is a simple parallel-line form.
-1-
Type 2, is now preferred by most geologists and stratigraphers, as it expresses the
stratigraphic sequence and relations of outcropped rock units more clearly.
Type 3 and type 4, are prepared in conjunction with electrical log curves, and are
adaptable for special problems of correlation.
Type 5, is not too frequently used; however, there is one advantage of this type,
that the structural attitudes of the strata may be shown.
Graphic black-line symbols representing rock lithologies have been more or less
standardized (the attached lithologic symbols). However, in the event a lithology
is to be plotted for which there is no standard symbol, the geologist must invent one
and then identify it in the legend. If a new symbol is introduced, care should be
taken that it does not conflict with any other symbol.
Lithologies may also be represented by colors. Color symbols are used by
geologists for representing lithologies of well cuttings and surface samples.
Frequently, a combination of graphic symbols and color is used to emphasize the
stratal subdivisions of the section.
Columnar sections should be plotted as soon as possible after recording the field
data. Some companies make it mandatory for the geologist to prepare a temporary
or progress graphic section during the course of his field observations. This practice
permits him to, constantly, retain stratigraphic orientation and to compile
stratigraphic information more readily in the office.
Materials required:
1- Gridded drawing paper or tracing paper.
2- India ink (black).
3- Straightedge.
4- Colored pencils.
Data provided:
The lithologic descriptions and unit thicknesses are given for a subsurface
stratigraphic section.
Requirements and procedure:
A lithologic well log is to be drafted by means of black-line symbols.
-2-
Age
Lithologic description
Thickness
(ft.)
1- Interbedded fine-grained sandstone, few
lignites in lower part.
200
2- Essentially medium to fine grained, buff
sandstone.
70
3- Dark gray arenaceous shale and mudstone,
common laminae of fine grained sand and silt.
8000
4- Dark gray foraminiferal, calcareous shale.
400
5- Thin bedded, light gray foraminiferal
limestone with thin beds of dark gray calcareous
shale, limestone-shale ratio 20:1.
15
Cretaceous
-------------- Unconformity -------------6- Light gray medium grained, friable, slightly
calcareous sandstone.
7- Dark gray slightly silty, calcareous shale,
occasional thin purple limestone layers in lower
part.
8- Alternating fine-crystalline, light bluishgray argillaceous limestone and dark gray
foraminiferal shale, limestone-shale ratio 1:5.
25
40
20
9- Dark gray thin-bedded, slightly silty shale,
thin bentonite streaks.
45
10- Gray medium grained friable sandstone.
50
11- Dark gray fissile, carbonaceous shale.
100
12- Coarse-grained to conglomeratic, gray friable
sandstone.
50
-------------- Unconformity --------------
-3-
Jurassic
1- Light gray shale, marlstone, sandstone,
sandstones rarely exceed 10% of formation.
25
2- Light gray mudstone, fine-grained yellowish
sandstone.
80
3- Red, medium-grained, friable sandstone.
30
Pennsylvanian
-Permian
Permian
Triassic
-------------- Unconformity (?) -------------1- Red medium-grained, cross-bedded sandstone.
20
-------------- Unconformity (?) -------------2- Red thin-bedded siltstone.
300
1- Gray to pink laminated silty limestone; top is
Triassic-Permian boundary.
10
2- Thin bedded red siltstone.
60
3- Pink to gray laminated silty limestone.
4
4- Red thin-bedded siltstone; few thin white
limestone layers near base, local gypsum at base.
90
5- Gray to pinkish-red medium to coarse-grained
sandstone, cross-bedded, ridge former.
305
6- Red siltstone and fine-grained sandstone;
grades into basal of unit no.5.
150
Interbedded, fine-grained, red friable
sandstones.
450
-4-
Pennsylvanian
Mississippian
1- Thick bedded, red conglomeratic sandstones and
red siltstones.
720
2- Thin bedded red .and green sandstones; few
thin, fine-crystalline sandy limestone containing
a few fossils.
200
-------------- Unconformity -------------1- Fine-crystalline, sandy, Micro-oolitic limestone.
50
2- Hard, dense, gray limestone; breccia at base, ridge
former, some chert.
125
-------------- Unconformity -------------3- Thin bedded, sandy, gray to pink, mottled limestone.
-------------- Unconformity --------------
Ordovician
1- Massive-bedded, buff Medium-crystalline, limestone and
dolomitic limestone, highly jointed, few scattered chert
nodules, cliff former.
270
-------------- Unconformity -------------2- Fine-grained, will sorted. White friable sandstone;
locally conglomeratic at base, generally a slope former,
fossiliferous.
150
-------------- Unconformity -------------3- Red to brownish- red fine-crystalline, dolomitic
limestone and dolomite, chert nodules in lower part,
locally arenaceous in basal part, escarpment former,
fossiliferous.
Cambrian
50
190
1-Red coarse-crystalline, sandy, glauconitic dolomite and
dolomitic sandstone.
14
2- Coarse-grained, friable, conglomeratic sandstone; gray
to white, locally cross-bedded, conglomerates best
developed in basal part
90
-------------- Unconformity --------------
-5-
PreCambrian
Gneiss, Schist and Granite.
Best wishes.
PROBLEM 2
DRAFTING OF COLUMNAR SECTION
IN
GRAPHIC SYMBOLS (Lithologic well log) & COLORS
Well logs generally are represented by narrow columns between straight vertical
lines. They may reproduce a driller's log, be based on studies of well cuttings or
cores, or by interpretations of electric logs (See Fig.1. no. 4).
Graphic well logs should be accompanied by notations regarding the kind of data
upon which they are based because different types of logs vary considerably in
their accuracy and details. Most of them are based on samples collected at more or
less regular intervals that come from several different strata and consequently the
logs are somewhat generalized. Some driller's logs are misleading because different
kinds of rock were not carefully identified.
Materials required:
1- Gridded drawing paper or tracing paper.
2- India ink (black).
3- Straightedge.
4- Colored pencils.
Data provided:
The lithologic descriptions and unit thicknesses are given for a subsurface
stratigraphic section at Marsa Matruh area, north Western Desert, Egypt.
-6-
Requirements and procedure:
A lithologic well log is to be drafted. The student should follow as shown in
problem1. In order to emphasize the rock units of the section, colors may be
applied to the graphic column. This part of problem is designed to familiarize the
student with a systematic scheme of representing many kinds of lithologies by
means of a few colors and black-line symbols.
The colors used for representing the basic lithologic groups are:
Yellow: for coarse clastics (grain size more than 0.1 mm).
Gray: Shales.
Sky blue: Carbonates of all kinds (generally limestones), in case of dolomite, the
same as limestones with the dolomite diagonal blue-line ruling.
Red: Igneous rocks.
Black-line pattern: Evaporites (sulphates and chlorides).
Questions:
1) What lithologies characterize the Lower Miocene sediments?
2) What lithology is particularly characteristic of the Middle Eocene deposits?
3) How are the Albian and Aptian deposits differentiated lithologically?
4) What is the purpose of plotting a stratigraphic section in color?
5) What are the advantages of the colored section over the black-line type?
Disadvantages?
6) What are the symbols for oolite, pyrite, mica, chert, macro and microfossil,
glauconite, carbonaceous materiel and nodules?
7) What colors represent the basic lithologic groups?
-7-
8) Is it possible to separate, lithologically, some specific units? Give example.
Upper
Cretace
ous
Santonian
Middle Eocene
Lower Miocene
Middle
Miocene
Age
Lithologic description
Thickness
(m)
Limestone, gray, dense with shale intercalations.
600
Shales, slightly calcareous, sandy near top.
300
Sandstone, medium grained, weakly consolidated,
calcareous.
200
Shale, dark gray, medium hard, micaceous.
40
Sand, clayey, medium grained.
40
Limestone, coarsely granular, slightly argillaceous
at the middle of the unit.
200
Dolomite, finely sucrosic.
1050
Dolomite, medium sucrosic, with chert concretions.
250
Dolomite, dens to medium sucrosic.
70
Shale, gray, slightly silty.
20
Dolomite, calcareous, dense, finely granular.
400
Limestone, fractured, clayey materials in
fractures.
150
35
Limestone, microcrystalline, dense.
-8-
Turonian
Limestone, coarsely granular.
100
Dolomite, calcareous with chert nodules.
350
Limestone, microcrystalline, dense, slightly
pyritic.
60
15
Shale, light-gray.
200
Albian
Lower
Cretaceous
Cenomanian
Dolomite, with chert nodules, thin intercalations
of argillaceous limestone.
Limestone, microcrystalline, argillaceous.
80
Dolomite, coarsely sucrosic, white.
100
Limestone, argillaceous, microcrystalline.
100
Limestone, sandy with macrofossils.
50
Limestone, argillaceous, slightly sandy near base.
500
Sandstone, slightly argillaceous.
260
Sandstone, calcareous, medium grained.
250
Sandstone, argillaceous, weakly consolidated, fine
grained.
270
Limestone, microcrystalline, clayey, fossiliferous.
65
Shale, gray.
10
Sandstone, clayey, medium to fine grained.
40
Dolomite, argillaceous, fractured.
120
Sandstone, calcareous, medium grained.
150
Intercalations of limestone and calcareous shale.
220
Interbedded sandstone and shale in 50" to 30"
units, shale intercalations increase near base.
2000
Dolomite, finely sucrosic, cherty.
150
Sandstone and shale intercalations.
70
-9-
Aptian
Dolomite, white, coarsely sucrosic.
180
Shale with thin intercalations of dolomite.
300
Shale, slightly arenaceous, calcareous.
180
Shale, calcareous.
100
Dolomite, finely sucrosic.
200
Shale with thin dolomite intercalations,
calcareous.
510
Sandstone, slightly argillaceous, medium to fine
grained.
70
180
Shale, variegated, slightly calcareous.
250
Shale, sandy, calcareous.
130
Jurassic
Dolomite and shale intercalations.
Limestone, slightly argillaceous, fossiliferous.
310
Shale, sandy.
112
Limestone.
50
Shale, arenaceous.
70
Limestone, microcrystalline, argillaceous.
50
Dolomite, medium to coarse sucrosic, white.
250
Sandstone, clayey, medium grained.
70
Limestone, slightly sandy.
300
Shale, gray, calcareous.
40
Sandstone, medium grained, dolomitic.
40
Limestone, argillaceous, slightly arenaceous, the
sand content increases near the base.
Best wishes.
- 10 -
1000
Problem 3
CONSTRUCTION OF A SEDIMENT MAP
Stratigraphers are increasingly in need for a better understanding of the numerous
processes which control the distribution of modern sediments and the environments
under which they accumulate. These processes, including weathering,
transportation, deposition and lithification, are intimately related and complex and
a modification in any one of them may drastically affect the sedimentation pattern.
Knowledge of particle settling rates, fluid flow, turbidity, selective transportation
and precipitation of materials by chemical and biological agencies assists the
stratigrapher in his evaluation studies of ancient sediments.
It is the objective of this problem to demonstrate that several types of deposits,
differing in texture and composition, may accumulate contemporaneously on the
same time surface. The sedimentationist is concerned with the depositional
variables as they occur in space and in time before accurate correlations of the
deposits can be determined.
Materials required:
1. Colored pencils.
2. India ink (black).
Data provided:
The attached figure is a base map showing the distribution of various types of
sediments accumulating simultaneously in a modern depositional marine area. The
symbols on the map represent the type of bottom sediment at each locality.
Requirements and procedure:
Prepare a colored map showing the subsea distribution and lateral relationships of
five contemporaneous deposits. Analyze the distribution of the sediment symbols
and enclose each deposit with a dashed boundary line. The shapes and sizes of
these sediment areas will vary according to the interpretation of the data; however,
- 11 -
these discrepancies will be limited to only minor details if the analysis is carefully
performed.
Color the various sediment areas as follows:
Sand ---- yellow.
Gravel ---- orange.
Mud ---- gray.
Calcareous deposits ----blue.
Sandy calcareous deposits ---- red.
Each of these areas in which sedimentation is relatively uniform constitutes a
lithotope. A constant environment may persist in the same area over an appreciable
length of time, thus giving rise to thick deposits of similar lithology. Conversely,
two or more different environments of sedimentation may exist adjacent to each
other, and result in several lithotopes. Fluctuations of sea level are commonly
responsible for the lateral intertonguing of lithotopes.
Questions:
1) Describe the character of the land surface which could produce the sedimentary
pattern developed.
2) Should the lines drawn between the various lithotopes be interpreted as sharp
lithologic demarcations or should they be considered as representing transitional
boundaries?
3) Would it be possible for the calcareous deposits to overlap the coarser clastics
formed near shore? What factors could account for this shifting?
4) What adjustments would cause the gravel and sand lithotopes to blanket the
calcareous deposits? How do you explain the presence of gravels far off shore?
5) Discuss the causes for variations in sedimentary patterns within an open sea
environment.
Best wishes
- 12 -
Sediments location map
• Gravel
O Sand
∆ Mud
X Sandy calcareous deposits
- 13 -
□ Calcareous deposits
PREPARATION
OF
A STRATIGRAPHIC CROSS SECTION
Stratigraphic cross sections are prepared for the purpose of illustrating correlations,
formation thicknesses, lithologic sequences, extent and interrelationships of
unconformities, positions of peleontologic zones, and geologic distribution of
stratigraphic units. They are an indispensable part of many geologic projects, for
they present details of stratigraphy and structure which are difficult to illustrate by
maps alone.
The datum of the stratigraphic section is a horizontal line representing a definite
stratigraphic horizon. The structural elevations are ignored and the datum horizon
is shown as if no structure existed. Formation boundaries are plotted above or
below the datum by scaling vertically according to the thicknesses of the
formations.
The first consideration in the construction of a cross section is the graphic scale.
Commonly, the vertical scale is made larger than the horizontal in order to show
details of stratigraphy or structure. It should be pointed out however, that
exaggeration of the vertical scale distorts actual relationships. This distortion is
especially objectionable in structural sections where measured dips constitute part
of the basic data, because angular values must be converted into difference of
elevation per unit of horizontal distance before they can be plotted on the section.
When plotting a cross section on an enlarged vertical scale all measurements of
thickness or elevation must made vertically in order to avoid horizontal
displacement of various features. This procedure results in apparent thinning of
formations where dips are steep, for in such regions a stronger component of the
horizontal scale enters the picture.
Figure A is a stratigraphic cross section whose datum is the top of unit 1. Vertical
and horizontal scales are equal. In figure B the vertical scale is doubled. Units 1
and 4 are of the same thickness and the thickness is constant. Where units 2 and 3
wedge out, a strong dip is introduced in unit 4. There is no apparent distortion of
unit 4 in figure A, but there is marked attention in figure B, in which the vertical
scale is doubled. This effect is magnified as the vertical scale is increased.
- 14 -
A
B
Figures A&B. Effect of vertical scale exaggeration.
The example discussed illustrates the effects of exaggerating vertical scale;
however, it is not to be construe as admonishment against the practice of increasing
the vertical scale, but rather to call attention to the defects. It is often necessary to
use large vertical scales in cross sections in order to emphasize significant details,
but the exaggeration should be no greater than necessary to accomplish this
objective.
Much time and effort will be spent to little advantage if cross sections are made
larger than need be. When the scale of a drawing is doubled, the area over which
one must work is quadrupled. The area of a drawing becomes an important
consideration if the sections are to be hand-colored. Before starting to draw a
section (or map) carefully consider the following suggestions:
1. Select a minimum scale that will permit plotting the essential details of
stratigraphy.
2. Select a minimum scale that will make important structural features apparent.
3. Determine the smallest space that will accommodate legible lettering.
4. Consider the over-all size of the finished drawing. Extremely large drawings are
unwieldy, and often fail to show comprehensive relationships as effectively as
smaller ones.
- 15 -
5. Investigate the limiting sizes of the various reproduction machines available. It is
unfortunate to have drawn a section or map one inch too large to pass through the
machine.
6. Where practicable make the horizontal scale of the cross sections the same as
that of maps of the region. This practice greatly facilitates construction and
checking the sections and makes correlation of the various presentations easier for
the reader.
7. The cost of materials and printing increases with the size of the drawing. It is
more economical to make small drawings.
- 16 -
PROBLEM 4
Materials required:
1. One sheet of 30 cm x 6O cm.
2. Engineer's scale.
3. Additional materials as in Problem 2.
Data provided:
1. Lithologic information on seven stratigraphic sections containing thirteen rock
units. The basic lithologies of individual units from youngest to oldest are as
follows:
Unit
no.
Lithology
13
12
11
10
9
8
7
6
5
4
3
2
1
Hard, black, thin-bedded shale.
Gray fine-crystalline, fossiliferous limestone.
Gray sandy shale.
Hard, calcareous sandstone.
Red shale with interbeds of anhydrite.
Massive, gray to tan, firm conglomerate.
Dark gray shale.
Buff medium-grained sandstone.
Red silty to sandy shale.
White to tan, coarse-crystalline dolomite.
Firm, conspicuously cross-bedded sandstone.
Gray fine-crystalline limestone with chert nodules.
Black thin-bedded shale.
- 17 -
2. Thickness in meters of each rock unit within the sections.
Section
no.
1
2
3
4
5
6
7
Unit thickness
1
130
65
-
2
125
115
55
-
3
180
150
235
256
100
65
65
4
100
50
85
100
170
270
320
5
250
210
195
200
185
180
170
6
55
60
63
55
50
40
13
7
90
280
330
280
415
590
115
8
300
110
90
95
60
20
20
9
160
200
180
195
185
115
-
10
30
40
50
65
20
-
11
180
160
160
180
125
130
40
12
208
270
387
200
65
22
15
13
165
120
150
300
400
430
415
3. Three major time units:
- Pennsylvanian (units 13 to 8 inclusive).
- Mississippian (units 7 to 3 inclusive).
- Ordovician (units 2 and 1).
*Unconformity at base of units 8 and 3; unit 1 was incompletely measured.
4. Spacing of section along a west to east line:
1-2 = 700 m
2-3 = 680 m
3-4 = 660 m
4-5 = 900 m
5-6 = 850 m
6-7 = 1000 m
Requirements and procedure:
Plot on a scale of 1 cm = 100 m the relative location of the sections along a base
line (stratigraphic datum) which is to represent the bottom of unit 4. This line is to
be placed 24 cm below the top of the sheet. Section 1 should be placed on the left
side of the sheet and section 7 on the right side. Arrange the age, and lithologic unit
classification to the left of section 1.
Plot on a scale of 1 cm = 100 m the lithologic units of each section above and
below the datum of the cross section. The columns are to be drawn in relief style
- 18 -
and should not exceed 1.5 cm in width. Use the lithologic line symbols given in
problem 1.
Draw all correlation and unconformity lines and qualify each. Unreliable
correlations are to be represented by dotted lines, fair correlations by dashed lines,
and good correlations by solid lines.
Connect the tope of the sections with a heavy line. Place a title block in the lower
right-hand corner. Near the title block show the vertical scale and the legend of
lithologies. Color the lithologic units on the sections.
Questions:
1. Does this alignment of sections show structural relationships? Discuss.
2. What conditions could account for the variation in thickness of unit 7?
3. What does the line connecting the tops of the sections represent? Does it have
structural significance?
4. What is the evidence for an unconformity at the base of unit 3?
5. Does the absence of unit 10 in section 6 necessarily indicate the presence of an
unconformity between units 9 and 11 in the section? Discuss.
6. Unit 12 in section 3 exhibits considerable thickness. What conditions could
account for such a thickness compared to that in sections 5, 6 and 7?
7. What sedimentational processes could account for the absence of units 9 and 10
in section 7?
8. Could unit 6 be termed "blanket sand"?
Best wishes
- 19 -
INTERTONGUING DEPOSITS
PART I
Correlation of intertongued rock units
A rock unit, as defined by the American Commission of Stratigraphic
Nomenclature, is a division of rocks segregated on the basis of objective characters
deemed to have significance in classification. A rock unit's identity is not based on
time relations. The formation is the basic rock unit with which geologists are most
concerned. Differentiation of rock units is required for geological mapping,
description, establishing structural relations, and deciphering geologic processes
and history. The boundaries of any given rock unit are surfaces marking the
lithologic changes from units above and below. The character of these surfaces is
extremely variable and ranges from sharp to transitional.
The lateral intertonguing (wedging) of rock units of different texture and
composition has been demonstrated in many areas and in many parts of the
geologic column. Limestone may intertongue with a sand and shale sequence, or
dolomites, anhydrites and shales may wedge laterally into a massive homogenous
sandstone section.
The intertonguing of deposits is commonly produced by oscillations of sea level.
These oscillations result from unstable tectonic conditions within both the source
and depositional areas, and result in lithologic and paleontologic boundaries which
transect time surfaces.
The rate, extent, and character of intertonguing vary considerably, and give rise to
many complex stratigraphic relationships which must be clarified before the
geologic history of an area can be interpreted.
To establish lateral relationships of sedimentary wedges, the following procedure is
suggested:
1- Outline the broad, regional stratigraphic and structural aspects of the area.
2- Map the areal extent of all major lithologic units.
3- Select, describe, measure and collect samples from stratigraphic sections.
4- Correlate the sections by all possible means (lithology, paleontology, mineralogy,
etc.).
5- Assemble all data for final analysis.
- 20 -
* The study of intertongued deposits must take into account, not only the thickness
and areal extent of deposits, but also the time relationships of one rock unit to
another.
PROBLEM 5
Materials required:
1. Colored pencils.
2. India ink (black).
3. Artist’s blending stumps.
4. Straightedge.
Data provided:
Six stratigraphic sections containing seven intertonguing rock units are shown in
the attached figure.
Requirements and procedure:
Study the vertical and lateral distribution of the rock units represented in the
sections, and then draw the lithologic boundaries keeping in mined the principle of
intertonguing. Ink the boundaries and color each lithologic unit to more clearly
demonstrate its lateral relationship to other units.
Questions:
1- Discuss the factors controlling the intertonguing of deposits.
2- What effect does vertical migration of a lithologic boundary have on structural
interpretations?
3- Would you expect to find many depositional diastems in a sequence of
intertongued sediments? Discuss.
4- What criteria could be employed to prove the time equivalency of dissimilar
deposits?
5- How does intertonguing introduce complexities in stratigraphic nomenclature?
6- What is the relation of the base of the Creek anhydrite to sea level in wells 1, 2,
3, and 4? Is this difference, due entirely to structural conditions? Discuss.
7- What conditions would account for the change in thickness of the Doline
limestone between wells 3 and 6?
- 21 -
Limestone
Shale
Conglomerate
- 22 -
Anhydrite
Sandstone
PART ІІ
CORRELATION OF INTERTONGUING DEPOSITS
WITHIN A TIME-ROCK UNIT
A time-rock unit is defined as a sequence of strata included between two time
surfaces. The time-rock unit, unlike a rock unit, need not be delineated by
lithologic boundaries.
PROBLEM 6
This problem differs from problem 5 by involving the correlation of four
intertonguing sedimentary types (facies) within a time-rock unit.
Materials required:
1. One sheet of 50 cm x 65 cm white drawing paper.
2. Colored pencils.
3. Engineer's scale.
4. Ruling pen.
5. Large triangle.
6. India ink (black).
7. Artist's blending stumps.
Data provided:
1. Locations of 14 stratigraphic sections spaced along a west - east line as follows:
Well no.
1-2
2-3
3-4
4-5
5-6
6-7
7-8
Distance (m)
330
330
450
450
450
360
390
Well no.
8-9
9-10
10-11
11-12
12-13
13-14
Distance (m)
540
560
335
455
550
330
2. Data in the following table include the well numbers and depth intervals (in feet)
in which facies, A, B, C and D were penetrated:
- 25 -
Well no.
Facies (A)
Facies (B)
Facies (C)
2400-3450
4300-6500
2
2350-3050
4270-6400
450-2400
3450-4300
6500-6800
410-2350
3050-4270
6400-6700
350-2680
2950-4260
4620-4900
6360-6900
300-4900
6120-6800
350-720
1150-4880
5500-5900
6130-6600
1260-3480
3600-4900
5300-6000
1300-3350
3800-6100
1350-3220
3800-6500
1200-1970
2670-3020
3800-6800
1200-1500
3800-4750
4900-6000
3900-4600
4950-5180
5320-6300
0-450
1
3
2680-2950
4260-4620
4900-6360
4
4900-6120
5
4880-5500
5900-6130
4900-5300
6
7
8
9
10
11
12
4020-4220
5420-6200
5610-6900
13
14
5700-6800
26
Facies (D)
0-410
0-350
0-300
0-350
720-1150
0-1260
3480-3600
0-1300
3350-3800
0-1350
3220-3800
0-1200
1970-2670
3020-3800
0-1200
1500-3800
4750-4900
0-1900
2300-3900
4600-4950
5180-5320
0-450
620-1620
2280-4020
4220-5420
720-820
2300-2560
2780-4620
5000-5610
2800-4500
5020-5700
1900-2300
450-620
1620-2280
0-720
820-2300
2560-2780
4620-5000
0-2800
4500-5020
* Note: all depths are in feet, convert them into meters.
Facies A, conglomerates and coarse-grained sandstones.
Facies B, medium-grained sandstones with shale interbeds.
Facies C, essentially shales and sandy shales.
Facies D, limestones and dolomites.
Requirements and procedure:
Plot the 14 sections according to their spacing on a vertical and horizontal scale
1 cm = 100 m. Consider the tops of the sections as the upper time surface and the bases of
the sections as the lower time surface of the time-rock unit.
Plot the various facies intervals occurring in each well and indicate by correlation lines
the most plausible lateral intertonguing of the units. Ink the lithologic boundaries. Label
and color each facies. Prepare a legend and title block.
Questions:
1. Is it possible for a lithologic boundary to migrate stratigraphically within a time-rock
unit? Discuss.
2. What procedure or procedures could be followed in acquiring basic data for the
purpose of establishing intertonguing relationships?
3. What may be some of the results of interpretation of a composite geologic section
where abrupt facies changes are present relative to (a) stratigraphic thickness, (b)
formational names, (c) correlations?
4. What is the importance of intertongued deposits in the accumulation of oil and gas?
Best wishes
- 27 -
PROBLEM 7
The following data represent 5 stratigraphic surface sections were measured along the
Cairo - Suez district. These sections were arranged from East to West direction as follows:
- Section І (South of Gebel Ataqa):
Thickness
(m)
Base
Lithologic characteristics
Fossil content
Not exposed
-
250
Chalky limestone, which alternates with limestones near
the top of the unit.
Nummulites gizehensis
Cerithium giganteum
Gisortia gigantea
Spondylus sp.
Natica longa
Carolia placunoides
Ostrea clot-beyi
Ostrea multicostata
Spondylus aegyptiacus
Plicatula polymorpha
Nummulites contortusstriatus
30
Calcareous shales and shales at the lower and middle
intervals, being sandstones at the top.
30
Sands, gravels and sandstones, with basaltic extrusions.
Silicified wood
70
Argillaceous limestones, rich in sand content at the
middle of the unit.
Clypeaster sp.
Ostrea frondosa
Operculina complanata
90
This unit is characterized by an argillaceous limestone
facies at the lower half of it, being highly argillaceous
and sandy limestone with thin shale intercalations at the
upper half of it.
Chlamys submalvinae
Ostrea crassissima
Placuna miocenica
Turetella terebralis
Scutella sp.
35
Sandy limestone with about 10 m of sandstone at the
lower part of the bed.
Planorbis sp.
Lanistes carinatus
15 (top)
Gravels, sands and sandstones.
- 28 -
--- Rare ---
- Section ІІ (Gebel Homeyira):
Thickness
(m)
Lithologic characteristics
Fossil content
Base
Unexposed
-
100
Chalky limestone being limestone at the top.
45
Sandy limestone with some argillaceous Carolia placunoides
intercalations at the middle part, being Ostrea clot-beyi
limestone at the top. At the lower part, there is Ostrea mu11icostata
an Ostrea bank of about 3 m.
Plicatula polymorpha
Spondylus aegyptiacus
Nummulites contortusstriatus
35
Gravels, sands and sandstones.
Silicified wood
45
Sandstone and shale intercalations at the lower
10 meters, which became sandy limestone at the
middle part with an Ostrea bank at the top 8
meters.
Oysters
Scutella zitteli
Cibicides aknerianus
Cibicides lobatulus
Miogypsina sp.
Nonion scaphum
Operculina complanata
95
Shales at the lower 10 meters, overlained by 20
m of sandstone, being limestone and sandy
limestone with intercalations of shales and about
5 m Ostrea bank, overlained by 15 m shales.
Miogypsina sp.
Bolivina hebes
Amphistegina radiata
Ostrea gigensis
Ostrea frondosa
Ostrea plicatula
Ostrea virleti
Gravels, sands and sandstones.
Small Silicified wood
20 (top)
- 29 -
Serpula sp.
Lucina mokattamensis
Gisortia gigantea
Natica aegyptiacum
Natica longa
Rimella dublicucostata
- Section ІІІ (Gebel Aweibid):
Thickness
(m)
Lithologic characteristics
Fossil content
Base
Unexposed
-
200
Chalky limestone being argillaceous limestone at Anisaster sp.
the upper 30 meters.
Sismondea sp.
Natica longa
Gisortia gigantea
65
Limestone with shale intercalations, this unit Anisaster gibberulus
intercalated with 4 Oyster banks with 4 m thick. Carolia placunoides
for each bank.
Ostrea clot-beyi
Ostrea multicostata
Sismondea sp.
Turitella sp.
Nummulites
contortusStriatus
45
Sands, gravels, and sandstones with volcanic Silicified wood
extrusions.
80
Sands and sandstones at the base, overlained with
13 meters argillaceous limestone, in the middle
and upper parts, there are limestone with sandy
and argillaceous intercalations.
Flabellipecten sp.
Ostrea gigensis
Ostrea lamellosa
Ostrea frondosa
Balanus sp.
Echinolampas sp.
Venus burdigalensis
20
Gravels, sands and sandstones.
Small silicified wood
30 (top)
Limestone overlained in the uppermost 8 meters
by gravely sands and sandstones.
- 30 -
--- Rare ---
- SECTION IV (Gabel Abou – Treifiya):
Thickness
(m)
Lithologic characteristics
Fossil content
Base
Unexposed
-
21
Chalky limestone.
185
Limestone, chalky at the lower third, being Nummulites gizehensis
argillaceous and chalky dolomitic at the upper Nummulites sp.
third.
Textularia sp.
Lucina sp.
Gisortia gigantea
Natica longa
Vulsella crispata
25
Sandy limestone, intercalated with sandstone Carolia placunoides
and Ostrea bank.
Ostrea clot-beyi
Ostrea multicostata
Spondylus aegyptiacus
40
Gravels, sands and sandstones with volcanic Silicified wood
rocks.
20
Sandy limestone with 3 m Ostrea bank in the
middle part of the unit.
Ostrea gigensis
Ostrea frondosa
Ostrea plicatula
Gravels, sands and sandstones.
Silicified wood of small
size
20 (top)
Alveolina
frumentiformis
Nummulites praecursor
- 31 -
- SECTION V (Gebel Mokattam and Gebel Ahmer):
Thickness
(m)
Lithologic characteristics
Fossil content
Base
Unexposed
-
41
Limestone.
Nummulites gizehensis
Nummulites corvispira
Echinolampas africanus
Schizaster
mokattamensis
Turbinella frequens
65
Sandy limestone, argillaceous near the lower Nummulites contortus part.
striatus
Anisaster gibberulus
Carolia placunoides
Spondylus aegyptiacus
Ostrea clot-beyi
Ostrea multicostata
50
Gravels, sands and siliceous ferruginated Silicified wood
sandstones, with hydrothermal tubes (tuber
structures of Gebel Ahmer).
* It must be noted that:
1- The characteristic fauna of the Lower Middle Eocene (Lower Lutitian) are:
Alveolina frumentiformis and Nummulites praecursor.
2- The characteristic fauna of the Upper Middle Eocene (Upper Lutitian) are:
Nummulites gizehensis, Gisortia gigantea, Natica longa, Vulsella crispata,
Natica aegyptiacum, Cerithium giganteum and Nummulites corvispira.
3- Upper Eocene fauna are:
Nummulites contortus-striatus, Spondylus aegyptiacus, Carolia placunoides,
Ostrea clot-beyi, Ostrea multicostata, Spondylus aegyptiacus, and Plicatula
polymorpha.
4- The Oligocene is characterized by volcanic eruptions represented by volcanic
rocks hydrothermal solutions causing silicification of woods.
- 32 -
5-The characteristic fauna of the Lower Miocene are:
Operculina complanata and Scutella zitteli.
6- The Middle Miocene is characterized by marine facies having the following
fauna:
Ostrea gigensis, Ostrea frondosa, Ostrea plicatula, Ostrea lamellosa, Placuna
miocenica, Ostrea crassissima and Turitella terebralis.
7- The Upper Miocene is characterized by non-marine facies especially in the
west.
8- The Pliocene is characterized by the rarity in fossil content.
Requirements:
It is required to:
1- Draw a columnar section for each of the above mentioned sections.
2- Determine the time rock units using the characteristic faunal content for each
time unit.
3- Illustrate the relationships between the exposed formations in the different
sections using the unconformity surface between the Upper Eocene and the
Oligocene as a base line, and using the following scales:
- Horizontal scale 1: 200000
- Vertical scale 1: 10000
4- Write down your interpretations concerning the depositional environment.
Location map of the measured stratigraphic sections
- 33 -
PROBLEM 8
DEVELOPMENT OF A PANEL DIAGRAM
Panel or "fence" diagrams are used for representing stratigraphic data in three
dimensions. They are effective in demonstrating changes in lithologic facies,
pinchouts, truncations, unconformities, and other stratigraphic conditions
occurring in a region.
Sections used in the panel diagram should be selected on the basis of their
relative locations and their lithologic and stratigraphic variations.
Materials required:
1- Straightedge.
2- Engineer's scale.
3- Colored pencils.
4- Artist's blending stumps.
Data provided:
The attached table shows 18 well sections which penetrate ten formations.
Formation 10 is the oldest. Numbers in the columns represent the depths at
which the top of each formation was encountered. Certain formations are absent
in some wells. There is no faulting in the region.
Requirements and procedure:
Construct a colored stratigraphic panel diagram on a vertical scale of 1 = 100000
showing the distribution and relationships of the formations penetrated in the
wells. On the attached location map, scale and plot the total depth of each well.
Plot the formation depths on the vertical lines and then connect formation tops
to develop a panel system according to the pattern shown on the base map.
Label and color each formational unit. The panel boundaries should be inked
before coloring in order to obtain greater contrast between the stratigraphic units.
Unconformities are to be shown as black wavy lines.
- 34 -
Depths to Formation tops
Well
no.
Formation
1
2
3
4
5
1
X
2
X
150
3
X
1100
4
X
5
X
6
X
7
X
8
X
450
9
X
10
X
650
11
X
400 2650 3250
12
X 600 1100 2400 2700
13
X
750
14
X
15
X
16
X
17
X
550
18
X
* X = Formation in which the well started.
6
7
8
600
9
10
1800
900
520
2100 2750 3650
950 1000
550
1100
2020
800 1700 2200
1200
800 1450
1400
3800
3500
1220 1800
1100 1500
900
700 2100
2100 3100 3900
1100 1600
Total
depth
2010
1120
4500
1720
625
2040
2320
1850
2320
1950
4600
4020
2000
2500
1550
2370
3940
2700
Questions:
1- What formational unit is bounded at its base by a regional unconformity?
2- Is there more than unconformity? If so, compare or contrast with the
unconformity in question 1.
3- What evidence is there of onlap? What formations are involved?
4- Briefly outline the geologic history of the area.
5- What conditions could account for the decrease in section thickness between
wells 3 and 2?
6- Is there any evidence to suggest an unconformity between wells 13 and 8?
- 35 -
- 36 -
Location map