3 Objectives By the end of this unit you will be able to know: The Fundamental Concepts in Geology and their importanceWhat is the Non-Tectonic Structures and how they formed?The difference between Tectonic and Non-Tectonic StructuresThe different types of Non-Tectonic Structures
4 FUNDAMENTAL CONCEPTSThese concepts are very important to study structural geology and they help in solving the structural problemsDoctrine of uniformitarianism: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 sand bars and beachesCan't be applied to: Iron to iron formation in lake superior (different atmospheric composition)Contrast in nature of Archean and proterozoic crusts (differences in processes)2) Law of superposition:Within layered sequence oldest rocks occur at the base of sequence and younger rocks toward top unless the sequence is inverted3) Law of original horizontally:Sediments and Sedimentary rocks form in horizontal to nearly horizontal orientation at the time of deposition.
5 FUNDAMENTAL CONCEPTS4) Law of crosscutting 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: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:Consider more than one assumptions and test them until you are sure from one of them.
6 FUNDAMENTAL CONCEPTS 7) Outrageous hypothesis: Consider the data to reach to solution and illuminate other hypothesis8)Pumpelly’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.
7 NONTECTONIC STRUCTURES Those structures include the primary sedimentary and volcanic structures. They are useful in determining the facing direction in a sequence of rocksExamples of these structures are:Bedding featuresmud cracksripples markssole marksvesiclesBedding Planes
8 Nontectonic Structures can be distinguished from Tectonic Structures by the following: 1)Nontectonic structures usually older than the tectonic structures2)Tectonic structures usually show a parallel orientation over wide area compare to the nontectonic ones.3) Small structures in tectonic mimic large size ones.
9 Non-Tectonic Structures Primary Sedimentary Structures BEDDING Bedding planes represents mechanical zones of weakness and they form when there is a compositional or textural difference is exist between two beds.Examples are:Different grain sizesDifferent compactionDiscontinuity of deposition.Graded bedding contain a range of particle sizes from large at the base to small at the top. (boulder…… to…….clay)Graded bedding is important in determining the facing directionThey are useful in determining the facing direction.Bedding PlanesGraded Bedding
10 Non-Tectonic Structures Primary Sedimentary Structures BEDDING Cross bedding forms in sediments transported by water or windTypes:tangentialplanartroughfestoonFor finer sediments and small scalerippleHummockyMud cracks form by extensional cracks due to drying of fine grain sediments deposited by water.Cross BeddingMud Cracks
11 Non-Tectonic Structures Primary Sedimentary Structures BEDDING Ripple 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) current they are asymmetric, their steep sides face downstream in the direction of transport. They are not useful in determining the facing direction2) oscillatory they are symmetrical and consist of high and low crestsThey 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
12 Non-Tectonic Structures Primary Sedimentary Structures BEDDING Rain 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 Trails left by organisms, used also in determining the facing direction of beds.Sole Marks, Scour Marks, Flute Casts Marks 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.Rain-imprintFossils Track
13 Non-Tectonic Structures Primary Sedimentary Structures BEDDING 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 using the broadly convex bottom side of the cast that face the toward the bottom.Fossils they are useful in determining the relative age and facing direction by studying the relative position in sequence.They are also useful strain indicators.Reduction Spots are sedimentary structures produced by a small grain or fragment that is chemically different from the surrounding.They are useful as strain indicators.
14 Non-Tectonic Structures Primary Sedimentary Structures Sedimentary Facies The vertical and lateral variation in sedimentary rocks due to the paleoenvirnoments change. Each sediment (rock) type is called a facies or lithesome. One facies is separated from others by particular characteristics (composition, texture, sorting, physical and biogenic sedimentary structures)
15 Non-Tectonic Structures Primary Sedimentary Structures Unconformities DisconformityUnconformitiesA break in the sedimentary record, where part of a stratigraphic succession and history is missing. Unconformities are produced by erosion or non-depostion (or both).Types of unconformities:Disconformity:Is produced by deposition of a sequences followed by erosion without tilting or deformation, then comes subsidence and renewed deposition. Beds above and below unconformity remain parallel. Topographic relief along the unconformity may be present.Paraconformity is in places where there is little relief on an unconformity.AngularNon-conformity
16 Non-Tectonic Structures Primary Sedimentary Structures Unconformities Angular unconformity:Is produced where a sequence has been tilted as a result of slumming or tectonic processes, and followed by deposition of new sedimentary strata.Nonconformity:Is an unconformity in which igneous or metamorphic rocks (or both) occur below the erosion surface, and sedimentary rocks occur above. It indicates that a long time interval passed between formation of the igneous and metamorphic rocks at great depths in the Earth and deposition of sediment.The three types of unconformities may be present in one area.
19 Non-Tectonic Structures Primary Igneous Structures -Xenoliths,- Pyroclastic rock structures-Compositional banding- Contact metamorphic zones-Vesicles.Some of these structures are useful in determining the facing direction and top positionBreccia
20 Non-Tectonic Structures Gravity Related Features Landslide and Submarine Flows:They form above and below sea level and triggered byearthquakes (tectonic)overloading of slopeshigh precipitationoversteeping of slopeshuman activities
21 Non-Tectonic Structures Gravity Related Features Turbidities are deposits by rapid flow of sediments driven by turbidity current down a slope onto sea floor or lake floor. They consist of unsorted mass of sediments calledBOUMA SEQUENCE
22 Non-Tectonic Structures Gravity Related Features BOUMA SEQUENCE OF TURBIDITESShale (pelite)Silt (pelite)Rippled or cross-bedded sandstoneLaminated sandstone (well sorted)Graded bedding of poorly sorted sandstoneThese are useful in determining the facing direction and the top of the sedimentary sequence.Bouma Sequence
23 Non-Tectonic Structures Gravity Related Features SALT STRUCTURESEvaporite deposits occur in sedimentary sequences at shallow crustal levels. Rock salt deposits formed by evaporation of sea water and composed mostly of halite. These rocks flow more readily than does any other rock type.
24 Non-Tectonic Structures Gravity Related Features Salt flows at surface conditions by the force of gravity. The salt density contrasts with the greater density and strength of the sediments surrounding them. This produces a variety of structures ranging form glacier on the surface to salt pillow and stocks and domes at depth. The internal structure of these salt features indicates a plastic flow “with folds, foliation, and other structures similar to the ones form under high pressure and temperature in metamorphic rocks.
25 Non-Tectonic Structures Gravity Related Features SALT STRUCTURESDiapirs: are salt or other material that move upward and 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 the salt by gravity underneath.
26 Non-Tectonic Structures Gravity Related Features IMPACT STRUCTURESThese structures are formed by meteoritic impact and are usually have a circular or elliptical outlines. They are characterized by shatter cones structures (cone shape fractures with epics at the point of force and the base is away from it)