Sedimentary GeologySedimentary Geology •"The scientific study of sedimentary rocks and of the...

Sedimentary Geology

Dr. Abdullah I. NabhanSenior GeologistHead of Sedimentary Geology Dep.P.O. Box 54141 Jeddah, 21514Kingdom of Saudi ArabiaTel. : +966 12 6195000 Ext. 4191Fax: +966 12 6196000Mob. +966500062245E-mail: [email protected]: [email protected]

mailto:[email protected]

mailto:[email protected]

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• How to identify the sediments and sedimentary rocks and their

depositional environments.

• Scientific thinking and procedures in interpreting sedimentary and

stratigraphic records.

Course Goal

Sedimentary Geology

Dr. Abdullah I. Nabhan

General Review and IntroductionSEDIMENTARY GEOLOGY

Nonmarinedepositional environments

and systems.

Marginal marinedepositional environments

and systems

.

Marinedepositional environments

and systems .

Course PlanOnly major environments can be covered, emphasizing the principles in environmental interpretation.


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Sedimentary Geology

• "The scientific study of sedimentary rocks and of the processes by

which they were formed; the description, classification, origin and

interpretation of sediments" (Glossary of Geology, AGI, 1974)

• The products of mechanical and chemical weathering.


Accommodation Space

General Review

SEMENTRAY PROCESSES Type of processes

1 2

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chemical precipitation and dissolution

Chemical Processes

burrowing, binding, baffling, etc..

Biological Processes

Wind, current flow, gravity flow, glaciers

Physical Processes

compaction, cementation, precipitation and

dissolution, etc.

Diagenetic Processes


General Review

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Facies analysis

Lithologic and biologic characteristics of a stratigraphic

unit, and its interpretative attributes of depositional environments

and conditions.

Climate

Stratigraphy


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Facies analysis

Lithofacies – A rock body characterized by specific

lithological characteristics, including those of

composition, texture, sedimentary structure, color,

geometry, type of contacts, thickness, trend of

thickness etc.

Biofacies – A rock body characterized by specific

paleontological characteristics, including those of

biological composition, istribution of species, etc.


Walther’s Law of Correlation of Facies

Stratigraphy

Lateral variations are expressed in the

vertical due to the succession of facies

Relationship between vertical and lateral

variations

Stack them together in strat column

for modern analysis

Walther’s Law of Correlation of Facies

Stratigraphy

No significant erosion and nondeposition.

The present is the key to the past” is valid.

There is a limited number of associations

of lithology.

Grain type (mineral grains, matrix, lithoclasts),

grain size, grain sorting, grain shape, porosity,

cements.

Diagrammatic illustration of principal kinds of grain contacts (Based on Taylor,

J. M., 1950)

Texture

Sediment analysis

Classification by grain size

Sediment analysis

Gravel > 2mm Sand >1/16 mm < 2 mm Mud <1/16 mm

Classifying carbonates:

Based on presence of mud matrix, & grain/mud support

Mudstone - less than 10% grains Wackestone, Packstone, etc - more than 10% grains

Sediment analysis

Dunham Folk

Scanning Electron

Microscope (SEM)

characterizing

mineral and material

with surface

features.

X-ray Diffraction

(XRD)XRD is used to

identify the minerals

based on their

crystalline structural

properties

Sediment analysis

Sedimentary Rocks

Carbonate rocksPrecipitated by a variety of

organic and inorganic processes

Siliciclastic rocks(Silicate Minerals)

weathering and erosion of precursor rocks

Evaporite rocks

Form from evaporating saline waters

BENJAMIN VEGA

Manager

Classification of Sedimentary Rocks

Sedimentary Structures

cements in cavities, etc.burrows, trace and tracks,

rootlets, etc.)

Beddings, desiccation

cracks, geometry of

sedimentary rock bodies

Biogenic Structures Physical Structures Late Diagenetic Structures

Facies


• Ripples

• Wave ripple lamination

• Dunes (including sand waves, bars eyc)

• Hummocky

• Lamination

• Cross-bedding

Current ripple cross-lamination Climbing ripple cross lamination

Facies

Sedimentary Structures Graded bedding

Interference ripples

Skolithos burrows Fossils

Hummocky

Facies


• Planar cross beds in modern and ancient sand dunes.

Facies

Mineral and Chemical Composition

Quartz sandstone ("clean sandstone").

Arkose – terrestrial, > 25% feldspar grains

Facies

Mineral and Chemical Composition

Graywacke ("dirty sandstone") quartz, feldspar, and lithic fragments

lithic sandstone - typical of deltaic deposits

Facies

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Nonmarine Environment

Characteristics of Nonmarine

Environment

Alluvial fan

Fluvial

Lacustrine

Glacial

Eolian

(those may have a marginal marine or marine

influence, not a clear cut in some cases).

Nonmar ine foss i l s

Alluvial Fan Depositional Systems

Alluvial fans are generally located in the lower part of the lower slope of mountain belts.

Types:

• Debris-flow-dominated fans

• Braided fluvial fans, and

• Meandering fluvial fans

No sea-level controles (except fan deltas)

• Arid alluvial fans

• humid alluvial fans


Arid alluvial fans


• located in regions with an arid or semiarid climate.

• Tectonically-controlled in high-relief area.

• Facies type: Debris and mud flows.

• Several 100s sq. meters to 100s of sq. km.

Schematic diagram showing major sedimentary environments of the depositional system (After Friedman and sanders, 1978).

Humid alluvial fans


• Associated with humid climate

• High water and moisture supply and high-energy

current flow

• Facies type: Inter bedding of fine and coarse-

grained sediments

• 100 to 10,000 sq. km.

Meandering stream:

• Single

• Point bars attached to inside of bends Channel

• overbank areas clearly differentiated

Erosion

Channel

migration

Braided stream:

• Multiple, numerous mid-channel bars little differentiated than overbank

• near source at change in gradient

• Gravel near fans, sandy more distal, few fines

• sheet sands, or elongate lenticular


Fluvial Depositional Systems


Meandering stream

Braided Stream


Paleozoic systems of Saudi Arabia

Summary vertical profile model showing shallow-braided stream channel and bar sub-environments (Abdulkadir et al. 2013)

Debsiah

Wajid Basin

Khusayyayn (Alam)

Al Ula

Shiqri

Ash Shiq(Siq)

Skolithos burrows

Paleozoic systems of Saudi Arabia

Tabuk Basin

(Memesh, Nabhan and Dini, 2018)

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Calcium Carbonate deposits

• Calcium carbonate is a chemical composited with the formulaCaCO3.

• Composed of more than 50% carbonate

• Mainly calcite (CaCO3) – LIMESTONES

• Mainly dolomite CaMg(CO3)2 – DOLOSTONES

• if calcite > dolomite, but dolomite >10% - DOLOMITIC LIMESTONE

• Most are biochemical, but can be inorganic.

• Chemical alteration of limestone in Mg-rich water solutions canproduce dolomite.

Lacustrine


Lacustrine deposits are sedimentary rock

formations which formed in the bottom

of ancient lakes.

Playa lake

Playa lake: a transitional category

between lakes and playas.

Calcium Carbonate deposits

calcium carbonate deposited by evaporation

Lacustrine tufas formed at the periphery of lakes (freshwater reefs)

Lacustrine tufas Calcrete deposits

Lacustrine deposits Playa lake deposits

U/Th


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Marginal Marine Environments

Delta

Beach

Tidal flats

Lagoon

Between continental nonmarine environments and normal marine

environments.

Processes related to alluvial, river, eolian, freshwater, glacial,

wave, tide, and oceanic currents.


Delta

Beach

Tidal flats

Lagoon


DeltaDelta Classification

River-dominated deltas

Tide-dominated deltasWave-dominated Deltas

Controlling factors

• The balance between sediment supply at the river mouth

and the energy flux at the site of accumulation.

• Sediment supply > sediment dispersal by tide, wave,

longshore current.

• Sediment redistribution


Delta

1. Upward coarsening

2. Upward thickening

3. Fine grained

4. Extensive, geometry

5. Presence of marine fossils and

marine burrows

6. High organic contents

7. Sedimentary structures

Deltas in Rock Record


BeachBarriers are elongate accumulations of sediment parallel to the coast • Backshore• foreshore


Sothern part: wider with low topography (0.3 m). Crabs mixed sediments in fore and back beaches.

Marine processes

Wind processes

Foreshore

Berm

Northern part: high topography (2-3m) ,narrow and high energy processes

North-central part

(Nabhan, 2015)


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Evaporite deposits

• Evaporite rocks form when sea water or lake water dries up and

precipitates gypsum (CaSO4·2H2O), halite (NaCl), or other

minerals.

• Gypsum is hydrated calcium sulphate; the sulphates are the

second major group to form as sea water evaporates.

• Anhydrite is calcium sulphate without the bound molecular water

that defines gypsum

•Vegetated sabkha

Quartz, feldspar and opaque

minerals

Vertically oriented halite crystal

•Sabkhas are characterized by evaporate-saline tidal-flood and eolian deposits (Renfor, 1974).

• Bare sabkha

Sabkha

(Nabhan and Yang, 2018)


The sequence of precipitates derived from the seawater is calcium carbonate first, then gypsum, halite and finally potassium and magnesium salts.

Siliciclastic sand

Sabkha


Reefs

Continental shelf

Slope

Abyssal plain

Marine Environments

Middle to Upper Jurassic Carbonate deposits

Modern reefs are in warm, clear, shallow and tropical

Red Sea coral reefs Carbonate deposits

Reefs• Calcium carbonate and organic reefs usually prevails and grow right along the coastline and shallow marine

waters.

Marine Environments

Representative foraminiferal types in the ocean today

Foraminifera

Benthic Foraminifera • One of the most common microfossils groups in deep oceans and nearshore environment is foraminifera.

Marine Environments

Khabra Sinkhole in Roadcut Sinkholes in Riyadh region

Carbonate Dissolution• Limestones are dissolves easily in weak acids.

Carbonates as geohazards


Sediment analysis

sieve analysis is a practice or procedure used to assess the particle size distribution of a granular material.

Petrography is the microscopic identification and interrelationships of mineral grains in the fabric of a rock.

For the characterization of

sediments of different forms

and sizes

Wet and dry sieving

To identify rocks and

minerals in thin sections

Petrographic microscope

>4 phi sizes analyzed using

the pipette method.

Hydrometer MethodParticle mass is measured using

the sedimentation method and

via X-ray absorption.

SediGraph

Textbook

An excellent reference books for your future career

as a sedimentologist.

SEDIMENTARY and STRATIGRAPHY

GARY NICHOLS

PRINCIPLES OF SEQUENCE STRATIGRAPHY

O. Catuneanu

[email protected]

Sedimentary GeologySedimentary Geology •"The scientific study of sedimentary rocks and of the...

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