Structural Geology (Geol 305) Semester (071) · (structural relationships): An igneous body or any structure (fold or fault) must be younger than the rocks it cuts ( the rocks contain

Structural Geology(Geol 305)

Semester (071)

Dr. Mustafa M. HaririDr. Mustafa M. Hariri

NonNon--Tectonic StructuresTectonic Structures

Objectives

By the end of this unit you will be able to know:By the end of this unit you will be able to know:The Fundamental Concepts in Geology and their The Fundamental Concepts in Geology and their importanceimportanceWhat is the NonWhat is the Non--Tectonic Structures and how they Tectonic Structures and how they formed?formed?The difference between Tectonic and NonThe difference between Tectonic and Non--Tectonic Tectonic StructuresStructuresThe different types of NonThe different types of Non--Tectonic Structures Tectonic Structures

FUNDAMENTAL CONCEPTSFUNDAMENTAL CONCEPTSThese concepts are very important to study These concepts are very important to study

structural geology and they help in solving the structural geology and they help in solving the structural problemsstructural problems

1)1) Doctrine of Doctrine of uniformitarianismuniformitarianism::The present is the key to the past (Processes are

taking place today within the earth are similar to the ones took place in the past and to that will take place in the future) example example sand bars and beachessand bars and beaches

Can't be applied to: Iron to iron formation in lake superior Can't be applied to: Iron to iron formation in lake superior (different atmospheric composition)(different atmospheric composition)

Contrast in nature of Contrast in nature of ArcheanArchean and and proterozoicproterozoic crusts (differences crusts (differences in processes)in processes)

2) Law of superposition:2) Law of superposition:Within layered sequence oldest rocks occur at the

base of sequence and younger rocks toward top unless the sequence is inverted

3) Law of original horizontally:3) Law of original horizontally:Sediments and Sedimentary rocks form in

horizontal to nearly horizontal orientation at the time of deposition.

FUNDAMENTAL CONCEPTSFUNDAMENTAL CONCEPTS4) Law of crosscutting relationships 4) Law of crosscutting relationships

(structural relationships):(structural relationships):An igneous body or any structure (fold or

fault) must be younger than the rocks it cuts ( the rocks contain the igneous body or structure must have been there before the structures or the igneous body)

5) Law of faunal succession:5) Law of faunal succession:The fossil organisms should be

systematically changed, possibly more advanced toward the top of the sequence (Permits determination of whether the sequences is upright or overturned)

6) Multiple working hypotheses:6) Multiple working hypotheses:Consider more than one assumptions and

test them until you are sure from one of them.

FUNDAMENTAL CONCEPTSFUNDAMENTAL CONCEPTS

7) Outrageous hypothesis:7) Outrageous hypothesis:Consider the data to reach to

solution and illuminate other hypothesis

8)Pumpelly8)Pumpelly’’s rule:s rule:Small structures are a key to

and mimic the styles and orientation of larger structures of the same generation within a particular area.

NONTECTONIC STRUCTURESNONTECTONIC STRUCTURES

Those structures include the primary sedimentary Those structures include the primary sedimentary and volcanic structures. They are useful in and volcanic structures. They are useful in determining the facing direction in a sequence determining the facing direction in a sequence of rocks of rocks

Examples of these structures are:Examples of these structures are:Bedding featuresBedding featuresmud cracksmud cracksripples marksripples markssole markssole marksvesiclesvesicles

Bedding Planes

Nontectonic Structures can be distinguished from Tectonic Structures by the following:

1)Nontectonic structures 1)Nontectonic structures usually older than usually older than the tectonic structuresthe tectonic structures

2)Tectonic structures 2)Tectonic structures usually show a usually show a parallel orientation over wide areaparallel orientation over wide areacompare to the compare to the nontectonicnontectonic ones.ones.

3) Small structures in tectonic 3) Small structures in tectonic mimic large mimic large size ones.size ones.

NonNon--Tectonic StructuresTectonic StructuresPrimary Sedimentary StructuresPrimary Sedimentary StructuresBEDDING BEDDING

Bedding Planes

Bedding planesBedding planes represents represents mechanical zones of weakness mechanical zones of weakness and they form when there is a and they form when there is a compositional or textural compositional or textural difference is exist between two difference is exist between two beds.beds.

Examples are:Examples are:Different grain sizes Different grain sizes Different compaction Different compaction Discontinuity of deposition Discontinuity of deposition . .

Graded beddingGraded bedding contain a range of contain a range of particle sizes from large at the particle sizes from large at the base to small at the top. base to small at the top. (boulder(boulder………… toto………….clay) .clay)

Graded bedding is important in Graded bedding is important in determining the facing directiondetermining the facing direction

They are useful in determining the They are useful in determining the facing directionfacing direction.

Graded Bedding

.

NonNon--Tectonic StructuresTectonic StructuresPrimary Sedimentary StructuresPrimary Sedimentary StructuresBEDDINGBEDDING

Cross beddingCross bedding forms in sediments forms in sediments transported by water or windtransported by water or wind

Types:Types:tangential tangential planarplanartroughtroughfestoonfestoonFor finer sediments and small scaleFor finer sediments and small scaleripple ripple HummockyHummockyMud cracksMud cracks form by extensional form by extensional

cracks due to drying of fine grain cracks due to drying of fine grain sediments deposited by water.sediments deposited by water.

Cross Bedding

Mud Cracks

NonNon--Tectonic StructuresTectonic StructuresPrimary Sedimentary StructuresPrimary Sedimentary StructuresBEDDING BEDDING

Ripple MarksRipple Marks form where sediments is moved by a current. They are very common along beaches and streams as well as deeper water, where bottom currents or surface waves interact with bottom sediments.

Types:1) current1) current they are asymmetric, their

steep sides face downstream in the direction of transport. They are not useful in determining the facing direction

2) 2) oscillatoryoscillatory they are symmetrical and consist of high and low crests

They form by back and forth motion of water (such as lake)

They are useful in determining the facing direction as the crests have sharp peaks separated by

rounded trough.

Ripple Marks


Rain-imprint

Rain ImprintsRain Imprints form where rain falls on fine sediment and preserved in sedimentary record by another layer of sediment. They are used also to determine facing direction.

Tracks and TrailsTracks and Trails left by organisms, used also in determining the facing direction of beds.

Sole Marks, Scour Marks, Flute CastsSole Marks, Scour Marks, Flute CastsMarks formed as an object moves across a bedding surface or as currents scour a bedding surface. Flute molds consist of scoop-shaped structures formed when the currents scour and erode a surface. Flute casts form when these molds filled with sediment.

All these features are used to determine the top of the bed.

Fossils Track

Dewatering Structures (Load Cast)Dewatering Structures (Load Cast) form after deposition and dewatering of sediments as a result of gravitational instability at the interface between a layer of water saturated sand and underlying mud. The weight of the newly deposited overlying sediment forces out the interstitial water. They can also be used in determining the facing direction by usiThey can also be used in determining the facing direction by using the ng the

broadly convex bottom side of the cast that face the toward the broadly convex bottom side of the cast that face the toward the bottom.bottom.

FossilsFossils they are useful in determining the relative age and facing direction by studying the relative position in sequence.

They are also useful strain indicators.They are also useful strain indicators.

Reduction SpotsReduction Spots are sedimentary structures produced by a small grain or fragment that is chemically different from the surrounding.

They are useful as strain indicators. They are useful as strain indicators.


Sedimentary Sedimentary FaciesFaciesThe vertical and lateral variation in sedimentary The vertical and lateral variation in sedimentary

rocks due to the rocks due to the paleoenvirnomentspaleoenvirnoments change. change. Each sediment (rock) type is called a Each sediment (rock) type is called a faciesfaciesor lithesome. One or lithesome. One faciesfacies is separated from is separated from others by particular characteristicsothers by particular characteristics(composition, texture, sorting, physical (composition, texture, sorting, physical and biogenic sedimentary structures)and biogenic sedimentary structures)

NonNon--Tectonic StructuresTectonic StructuresPrimary Sedimentary StructuresPrimary Sedimentary StructuresSedimentary Sedimentary FaciesFacies

NonNon--Tectonic StructuresTectonic StructuresPrimary Sedimentary StructuresPrimary Sedimentary StructuresUnconformitiesUnconformities

UnconformitiesUnconformitiesA break in the sedimentary record, where A break in the sedimentary record, where

part of a part of a stratigraphicstratigraphic succession and succession and history is missing. Unconformities are history is missing. Unconformities are produced by erosion or nonproduced by erosion or non--depostiondepostion(or both).(or both).

Types of unconformities:Types of unconformities:

DisconformityDisconformity::Is produced by deposition of a sequences Is produced by deposition of a sequences

followed by erosion without tilting or followed by erosion without tilting or deformation, then comes subsidence deformation, then comes subsidence and renewed depositionand renewed deposition. Beds above . Beds above and below unconformity remain parallel. and below unconformity remain parallel. Topographic relief along the Topographic relief along the unconformity may be present. unconformity may be present.

ParaconformityParaconformity is in places where there is is in places where there is little relief on an unconformity.little relief on an unconformity.

DisconformityDisconformity

AngularAngular

NonNon--conformityconformity

NonNon--Tectonic StructuresTectonic StructuresPrimary Sedimentary StructuresPrimary Sedimentary StructuresUnconformitiesUnconformities

Angular unconformityAngular unconformity:Is produced where a sequence has Is produced where a sequence has

been tilted as a result of been tilted as a result of slumming or tectonic slumming or tectonic processes, and followed by processes, and followed by deposition of new sedimentary deposition of new sedimentary strata.strata.

Nonconformity:Nonconformity:Is an unconformity in which igneous Is an unconformity in which igneous

or metamorphic rocks (or both) or metamorphic rocks (or both) occur below the erosion surface, occur below the erosion surface, and sedimentary rocks occur and sedimentary rocks occur above. It indicates that a long time above. It indicates that a long time interval passed between formation interval passed between formation of the igneous and metamorphic of the igneous and metamorphic rocks at great depths in the Earth rocks at great depths in the Earth and deposition of sediment. and deposition of sediment.

The three types of unconformities may be The three types of unconformities may be present in one area.present in one area.

Non-conformity and Angular Unconformity

Foliation,Foliation,Pillow Pillow structuresstructuresPhenocrystsPhenocrysts, , CrossCross--cutting,cutting,

NonNon--Tectonic StructuresTectonic StructuresPrimary Igneous StructuresPrimary Igneous Structures

Foliation and LineationFoliation and Lineation

CrossCross--cuttingcutting

Pillow LavaPillow Lava

NonNon--Tectonic StructuresTectonic StructuresPrimary Igneous StructuresPrimary Igneous Structures

--Xenoliths, Xenoliths, -- PyroclasticPyroclastic rock rock

structuresstructures--Compositional banding Compositional banding -- Contact metamorphic Contact metamorphic

zoneszones--Vesicles.Vesicles.Some of these structures are useful Some of these structures are useful

in determining the facing direction in determining the facing direction and top positionand top position

BrecciaBreccia

Landslide and Submarine Landslide and Submarine FlowsFlows:

They form above and below They form above and below sea level and triggered bysea level and triggered byearthquakes (tectonic) overloading of slopeshigh precipitationoversteeping of slopeshuman activities

NonNon--Tectonic StructuresTectonic StructuresGravity Related FeaturesGravity Related Features

Turbidities are deposits by rapid flow of sediments driven by

turbidity current down a slope turbidity current down a slope onto sea floor or lake flooronto sea floor or lake floor. They

consist of unsorted mass of sediments called

BOUMA SEQUENCEBOUMA SEQUENCE



BOUMA SEQUENCE OF BOUMA SEQUENCE OF TURBIDITESTURBIDITESShale (pelite)Silt (pelite)Rippled or cross-bedded sandstoneLaminated sandstone (well sorted)Graded bedding of poorly sorted sandstone

These are useful in determining the These are useful in determining the facing direction and the top of facing direction and the top of the sedimentary sequence.the sedimentary sequence.

SALT STRUCTURESSALT STRUCTURESEvaporiteEvaporite deposits occur in sedimentary sequences at deposits occur in sedimentary sequences at

shallow shallow crustalcrustal levels. Rock salt deposits formed by levels. Rock salt deposits formed by evaporation of sea water and composed mostly of halite. evaporation of sea water and composed mostly of halite. These rocks flow more readily than does any other rock These rocks flow more readily than does any other rock type.type.



Salt flows at surface conditions by Salt flows at surface conditions by the force of gravitythe force of gravity. The . The salt salt density contrasts with the greater density contrasts with the greater density and strength of the density and strength of the sediments surrounding them.sediments surrounding them.This produces a variety of This produces a variety of structures ranging form glacier structures ranging form glacier on the surface to salt pillow and on the surface to salt pillow and stocks and domes at depth.stocks and domes at depth. The The internal structure of these salt internal structure of these salt features features indicates a plastic flow indicates a plastic flow ““with folds, foliation, and other with folds, foliation, and other structures similar to the ones structures similar to the ones form under high pressure and form under high pressure and temperature in metamorphic temperature in metamorphic rocksrocks. .


SALT STRUCTURESSALT STRUCTURESDiapirsDiapirs:: are salt or other material that move upward and are salt or other material that move upward and

gravitationally gravitationally intrude the above sediments. They serve in many places of the world as hydrocarbon traps.

Locations of diapirs and geometry of the structures produced within the sediments are controlled by:

extensional process in cover sediments related to the flow of thextensional process in cover sediments related to the flow of the e salt by gravity underneath.salt by gravity underneath.


IMPACT STRUCTURESThese structures are formed by These structures are formed by meteoritic impact and are meteoritic impact and are

usually have a circular or elliptical outlines.usually have a circular or elliptical outlines. They are They are characterized by shatter cones structures (characterized by shatter cones structures (cone shape cone shape fractures with epics at the point of force and the base is fractures with epics at the point of force and the base is away from it)away from it)

Documents

Structural Geology (Geol 305) Semester (071) · (structural relationships): An igneous body or any structure (fold or fault) must be younger than the rocks it cuts ( the rocks contain