Lecture 8 - Stratigraphy PDF

Stratigraphy Correlations 1: Basic Geology Correlations 1: Basic Geology / HDAR It all started here ➢ Siccar Point - a rocky promontory in the county of Berwickshire on the east coast of Scotland. 1788 Source: https://www.pinte rest.ph/pin/48885 1734547761318/ Correlations 1: Basic Geology / HD...

Stratigraphy Correlations 1: Basic Geology Correlations 1: Basic Geology / HDAR It all started here ➢ Siccar Point - a rocky promontory in the county of Berwickshire on the east coast of Scotland. 1788 Source: https://www.pinte rest.ph/pin/48885 1734547761318/ Correlations 1: Basic Geology / HDAR Stratigraphy ➢ The branch of geology concerned with the order and relative position of strata and their relationship to the geological time scale. ➢ The study of distribution of rocks and sequence of events in space and time. We use facies to interpret depositional environments from the rocks. Correlations 1: Basic Geology / HDAR Principles of Stratigraphy ⮚Law of Original Horizontality – Beds were deposited nearly horizontal due to gravitational pull. Correlations 1: Basic Geology / HDAR https://www.geologyin.com/2014/03/principle-of-original-horizontality.html Principles of Stratigraphy ⮚Law Superposition – The younger strata lies at the top of older strata. Correlations 1: Basic Geology / HDAR https://www.kisscc0.com/clipart/law-of-superposition-geology-superposition-princip-k59g1a/ Principles of Stratigraphy ⮚Law of Lateral Continuity – Strata is deposited laterally until the sediment supply last or encounter any geologic barrier Correlations 1: Basic Geology / HDAR http://www.intheplaygroundofgiants.com/the-art-of-doing-geology-and-unraveling-geologic-time/ Principles of Stratigraphy ⮚Unconformity - A break in time in a continuous rock sequence. - wavy and irregular erosional surfaces - Types: a. Angular Unconformity b. Disconformity c. Nonconformity Correlations 1: Basic Geology / HDAR https://www.quora.com/What-is-an-unconformity-in-geology Principles of Stratigraphy ⮚Law of Cross-cutting Relationships – a rock body, structure, or unconformity is older than what is cutting it. Correlations 1: Basic Geology / HDAR https://www.pinterest.ph/pin/1688918584772260/ Principles of Stratigraphy ⮚Law of Inclusion – fragments of one rock body that are contained within another must be older than the body that contains them. Correlations 1: Basic Geology / HDAR https://www.slideshare.net/mohammedalmusawi666666/ch09-geologic-timefall2007-1 Principles of Stratigraphy ⮚Law of Faunal Succession – fossils are found in consistent and predictable succession everywhere on Earth. Correlations 1: Basic Geology / HDAR https://www.pinterest.ph/pin/224898575117892296/ Stratigraphy ➢ William Smith ❑ Father of stratigraphy ❑ English engineer and geologist (17691839). ❑ In 1815 Smith produced the first modern geologic map, showing rock strata in England and Wales. Source: https://en.wikipedia.org/wiki/William_Smith_(geologist) Correlations 1: Basic Geology / HDAR Facies ➢ The character of a rock expressed by its formation, composition, and fossil content. ➢ Walther's Law states that any vertical progression of facies is the result of a succession of depositional environments that are laterally juxtaposed to each other. ❑ Transgression ❑ Regression Source: https://www.youtube.c om/watch?v=Bs7z_208 1T4 Correlations 1: Basic Geology / HDAR Facies Source: https://www.slideshare.net/MOHITRKSIN GH/walthers-law-of-correlation-of-facies Correlations 1: Basic Geology / HDAR Facies Source: https://www.slideshare.net/MOHITRKSIN GH/walthers-law-of-correlation-of-facies Correlations 1: Basic Geology / HDAR Facies ▪ Geologists agree that these causes the MT and MR: 1. Uplift and Subsidence 2. The amount of Water frozen in Glaciers 3. Rates of seafloor spreading Source: http://earthscience.xyz/SeaFloorSpreading Source: http://www.geologyinmotio n.com/2013/07/linksbetween-earthquakes-andother.html Correlations 1: Basic Geology / HDAR Source: https://unsplash.com/search/photos/thawing The Philippine Stratigraphic Guide ➢ Committee on Stratigraphic Nomenclature under Geological Society of the Philippines ➢ Published in 2001 ➢ For formal classification of rocks Correlations 1: Basic Geology / HDAR The Philippine Stratigraphic Guide ➢ Rock bodies are usually classified as: ➢Lithostratigraphic Units - based on lithologic properties of the rock bodies ➢Biostratigraphic Units - based on fossil content of the rock bodies ➢Chronostratigraphic Units - based on time of formation of the rock bodies Correlations 1: Basic Geology / HDAR The Philippine Stratigraphic Guide ➢ Stratigraphy - Traditionally defined as the descriptive science of rock strata but now includes nonlayered rock bodies due to the geochronometric information that they may contain. Stratum - a layer or rocks characterized by certain lithologic properties or attributes that distinguish it from adjacent strata. Correlations 1: Basic Geology / HDAR The Philippine Stratigraphic Guide ➢ Stratigraphic Unit - A body of rock recognized as a distinct entity in the classification of the earth’s rocks based on any of the many properties or attributes that rocks may possess. Correlations 1: Basic Geology / HDAR The Philippine Stratigraphic Guide ➢ Lithostratigraphic Units Rock bodies characterized on the basis of their observable lithologic properties. ➢ Hierarchy of Lithostratigraphic Units a. b. c. d. e. f. Correlations 1: Basic Geology / HDAR Supergroup – formal assemblage of related groups and/or formations. Group Formation – fundamental unit of lithostratigraphic classification. Member – named entity within a formation w/ distinguishing characteristics from adjacent parts of the formation. Bed - smallest formal lithostratigraphic unit of sedimentary rocks. Flow - smallest formal lithostratigraphic unit of volcanic flow rocks. The Philippine Stratigraphic Guide ➢ Formation - Basic lithostratigraphic unit used in describing and interpreting the geology of a region. - It should possess a certain degree of internal lithologic homogeneity (e.g., chem composition, structures, etc.) or distinctive lithologic features (e.g., volcanic flows, etc.). - It should be mappable at the scale of 1:25,000 - Can vary from 1 meter to thousands of meters in terms of thickness. Correlations 1: Basic Geology / HDAR The Philippine Stratigraphic Guide ➢ Biostratigraphic Units - Rock bodies characterized on the basis of their fossil content. Correlations 1: Basic Geology / HDAR https://slideplayer.com/slide/4475807/ The Philippine Stratigraphic Guide ➢ Chronostratigraphic Units - Rock bodies formed and/or deposited within a corresponding geochronologic (or geologic) time interval. - Not measured by thickness, but with time. Correlations 1: Basic Geology / HDAR Chronostratigraphic Geochronologic Eonothem Eon Erathem Era System Period Series Epoch Stage Age The Philippine Stratigraphic Guide ➢ “Early and Late” vs. “Upper and Lower” - Early and Late are applied to geochronologic units (e.g., Early Miocene) - Lower and Upper designate relative position of rock units (e.g., Upper Cretaceous Sandstone) Correlations 1: Basic Geology / HDAR Sedimentary Structures ➢ features found within or on the surface of a sedimentary bed that formed during or following deposition and provide information pertaining to depositional environment or burial history. ➢ Uses: ❑Paleoenvironment indicators ❑Useful field parameter in determining the right side up of stratigraphic sequences. ❑Determine paleo-flow directions. ❑Process responsible for transportation and deposition of sediment Correlations 1: Basic Geology / HDAR Sedimentary Structures ➢ Sedimentary structures develop through physical and/or chemical processes. ✓Types of sedimentary structures 1. 2. 3. 4. 5. Depositional Structures Erosional Structures Penecontemporaneous Structures Biogenic Structures Diagenetic Structures Correlations 1: Basic Geology / HDAR Depositional Structures ➢ It include all kinds of features formed at the time of deposition. ❑Suspension – settling and current and wave formed structures ❑Wind formed structures ❑Chemically and Biochemically precipitated structures Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Beddings and Laminations ❑Bedding – stratification with thickness greater than 1cm ❑Lamination – thinner than 1cm ❑Change or break in deposition (change in grain size, color or mineralogy) produces a marked bedding plane: 1. Massive 2. Crossbeds 3. Graded Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Beddings and Laminations ❑Bedding – stratification with thickness greater than 1cm ❑Lamination – thinner than 1cm ❑Change or break in deposition (change in grain size, color or mineralogy) produces a marked bedding plane: 1. Massive 2. Crossbeds 3. Graded Correlations 1: Basic Geology / HDAR Source: https://en.wikipedia.org/wiki/Bed_(geology) Depositional Structures ➢ Beddings and Laminations ❑Massive Beds ✓Have no apparent internal structure ✓Formed through rapid sedimentation where there was insufficient time for bedforms to develop Source: https://www.sandatlas.org/limestone/ Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Graded Beds - results when a sediment-laden current (such as a turbidity current) begins to slow down. ➢ The grain size within a normal graded bed ranges from coarser at the bottom to finer at the top and if vice versa, reverse graded bed. ➢ Hence, graded beds may be used as "up indicators“. Correlations 1: Basic Geology / HDAR Source: https://en.wikipedia.org/wiki/Graded_bedding Depositional Structures ➢ Cross-bedding and Crosslamination ❑ Layers within the bed are inclined at the time of deposition ❑ Forms primarily by migration of ripples and dunes. Ripple and dune migration leads to formation of dipping foreset laminae owing to avalanching or suspension settling in the zone of separation on the lee sides of these bedforms Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Cross-bedding and Crosslamination ❑ Layers within the bed are inclined at the time of deposition ❑ Forms primarily by migration of ripples and dunes. Ripple and dune migration leads to formation of dipping foreset laminae owing to avalanching or suspension settling in the zone of separation on the lee sides of these bedforms Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Cross-bedding and Cross-lamination terminology Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Flaser Bedding ❑A type of ripple bedding in which thin streaks of mud occur between sets of cross-laminated sandy or silty sediment. Mud is concentrated mainly in the ripple troughs but may also partly cover the crests ❑Environment favors sand deposits (relatively strong currents most often) more sand than mud Correlations 1: Basic Geology / HDAR Source: http://www4.uwm.edu/course/geosci697/tidal/tidal-deposits.html Depositional Structures ➢ Lenticular Bedding ❑A structure formed by interbedded mud and ripple cross laminated sand in which the ripples or sand lenses are discontinuous and isolated both a vertical and a horizontal direction ❑Environment favors mud deposits (calm periods with a few short strong currents) ❑More mud than sand Correlations 1: Basic Geology / HDAR Source: http://www4.uwm.edu/course/geosci697/tidal/tidal-deposits.html Depositional Structures ➢ Wavy Bedding ❑ Fluctuating flows (start/stop currents) ❑ Alternating layers of sand ripples and mud ❑ Mud fills ripple troughs and thinly covers the crest ❑ Environment does not favor sand or mud deposits (currents alternate between a relatively strong current followed by a calm period) ❑ About equal amounts of sand and mud Correlations 1: Basic Geology / HDAR Source: http://www4.uwm.edu/course/geosci697/tidal/tidal-deposits.html Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Hummocky Cross Stratification Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks are undulations of the sediment surface produced as wind or water moves across sand Source: http://sain.scaa.sk.ca/items/close-up-of-ripple-marks-in-sand-of-dry-river-bedindicating-stream-flow-direction-from-left-to-right Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks ❑Wave-formed Ripples (Symmetrical Ripple or Oscillatory Ripple) - formed by the action of waves on non-cohesive sediment, typically symmetrical in shape. ❑NOTE: asymmetrical when one direction of wave motion is stronger than the other Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks ❑Current-formed Ripples (Asymmetrical Ripple or Unidirectional Ripple) - are small bed forms formed layer by the effects of boundary separation on a bed of sand (Baas 1999) ❑Produced by unidirectional currents (such as in streams or rivers) so they are asymmetric with a steep leeside and gentle stoss-side Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks ❑Wind Ripple ✓Asymmetric ✓Typically have long, straight, parallel crests with bifurcations like waveformed ripples ✓Ripple index is high; typically 10-70 Source: https://sites.google.com/a/maine207.org/2012-z8b9/sedimentary Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple marks ❑Ripple Index Correlations 1: Basic Geology / HDAR Depositional Structures ➢ Ripple cross lamination (Climbing Ripples) ❑Forms when deposition takes place very rapidly during migration of current or waves ripples. The ripples climb one another such as that the crests of vertically succeeding laminae are out of phase and appear to be advancing upslope Correlations 1: Basic Geology / HDAR Source: http://bp0.blogger.com/_c yXaHWpmJXI/RnKxAX07w YI/AAAAAAAAAu0/mQcAB 3OZtyU/s1600h/Image57.jpe Erosional Structures ➢ Erosion ➢Process in which soil and rock particles are worn away and moved elsewhere by gravity, or by a moving transport agent – wind, water or ice. ➢ Erosional Structures ➢Structures formed during the initially high shear stress before deposition of the bed ➢Erosional structures are in 2 forms: 1. Diastems that represent short-term pauses between depositional events. 2. Unconformities that represent long-term cessation of deposition. Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Sole Marks ❑ Are bedding plane structures preserved on the bottom surfaces of beds. ❑ They generally result from the filling in of impressions made into the surface of soft mud by the scouring action of the current, or by the impacts of objects carried by the current. ❑ If sand is deposited later over the mud, filling in these structures, they will be preserved in relief on the bottom of the sandstone bed. ❑ These structures are not usually seen on the surfaces of shale beds because they tend to weather away. Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Sole Marks ❑ Flute Cast - are produced by erosion or scouring of muddy sediment, forming "scoop-shaped“ depressions. ❑ They are commonly preserved as bulbous or mammillary natural casts on the bottoms of sandstone beds. Because of their geometry, flute marks (also called flute casts) can be used to determine paleocurrent directions. ❑ The nose of the flute points upstream, and the flare shallow end points downstream Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Sole Marks ❑Obstacle Scour – Horseshoe-shaped or crescent shaped grooves that are eroded by fluid flowing around an obstacle such as pebble or shell. Source: https://www.stephanielarmagnat.com/research Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Impressions formed by objects such as sticks, shells, bones, or pebbles, carried in the water flow. ❑Bounce, skip, roll, or drag along the sediment surface. They are commonly preserved on the lower surfaces of sandstone beds as thin ridges. Tool marks are generally aligned parallel to the direction of current movement. Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Grooves – narrow, nearly straight, sharply defined elongate marks created from infilling of erosional relief produced by dragging or rolling of a tool across the surface of cohesive sediment ❑Commonly have the same general orientation, although they may diverge at slight angles and even cross Correlations 1: Basic Geology / HDAR Source: http://www.seddepseq.co.uk/SEDIMENTOLOGY/Sedimentology_Features/ToolMarks/ToolMarks.h tm Erosional Structures ➢ Tool Marks ❑Prod Marks - The tool reaches the sediment surface at fairly high angle and it is then lifted up and away by a current. Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Skip Marks - The tool travels down current with a saltating movement, hitting the sediment surface at nearly regular intervals. Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Bounce Marks - The tool approaches the sediment surface at a low angle and immediately bounce back into the current. Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Roll Marks - The tool roll over the sediment surface, producing a continuous roll mark Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Chevron Marks - linear strip of stacked V-shaped or chevron-shaped marks formed by an object being dragged along the bottom, and the deformation of weak but cohesive mud ❑The V points in a downstream direction ❑Formed by tools moving just above the sediment surface but not touching the surface, causing rucking-up of the sides of the groove Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tool Marks ❑Rill Marks - small-scale dendritic channels formed by the erosion of non-cohesive sand ❑Typically found on the tops of beds of sand ❑Few centimeters to tens of centimeters wide, and they commonly form on beaches and riverbanks as water drains across a gently sloping surface Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Rain Imprints ❑Small craterlike pits with slightly raised rims commonly occur together with and are thought to be impressions made by the impact of rain ❑Commonly only a few millimeters deep and less than 1 centimeter in diameter, and they may occur as either widely scattered pits or very closely spaced impressions Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Tafoni (Honeycomb Structure” or “Swiss-cheese rock”) ❑Small cave-like features in granular rock with round entrance and smooth, concave walls. Often found in connected networks that have carved into cliffsides, hills and rocky areas. Source: https://www.tripadvisor.com.sg/LocationPhotoDirectLink-g32540-d156597-i47801783Salt_Point_State_Park-Jenner_Sonoma_County_California.html Correlations 1: Basic Geology / HDAR Erosional Structures ➢ Pot Holes ❑Circular depressions created by the abrasive action of particles swirling in fast-moving eddies Source: http://www.kruger-national-park.de/pages/english/image-gallery/blyde-rivercanyon/bourkes-luck-potholes.php Correlations 1: Basic Geology / HDAR Erosional Structures Source: http://www.geocoops.com/landforms.html Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Also known as Post-depositional Structures ❑ Is the general term for changes to the fabric and layering of beds of recently deposited sediment. ❑ Three principal processes of soft sediment deformation are: 1. Liquefaction - is a shorter-term process that happens when a mass of saturated sediment is affected by a shock, such as an earthquake, and becomes momentarily liquid, behaving like a viscous fluid. 2. Fluidization - is the process of whereby a granular material is converted from a static solid like state to a dynamic fluid like state 3. Over pressuring Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Also known as Post-depositional Structures ❑ Process of elutriation – is a process for separating particles based on their size, shape and density, using a stream of gas or liquid flowing in a direction usually opposite to the direction of sedimentation. Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures due to sediment instabilities ❑Slump structures typically form in mudstone and sandy mudstone beds that were rapidly deposited. Deformation results shortly after deposition, by the movement of unconsolidated (or semi-consolidated) sediments, primarily under the influence of gravity. Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures due to sediment instabilities ❑ Slumped beds - are deformed into layers that will typically show a fold structure with the noses of the anticlines oriented in the downslope direction. ❑ Slump scars - The surface left as the slumped material is removed and is preserved when later sedimentation subsequently fills in the scar. ✓ Spoon shaped surfaces Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures due to fluidization (Dewatering Structures) ❑Encompass a variety of features that form when fluids escape sometime following deposition. ❑They commonly develop in coarser sediment, usually sandstone, which is rapidly deposited. ❑Thus, they are commonly found in turbiditic successions. Some of these features are useful in determining depositional stratigraphic relationships. Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures due to fluidization (Dewatering Structures) ❑Dish and Pillar Structure ✓Dish structures - are concave disruptions to the layering in sediments a few centimeters to tens of centimeters across formed by the upward movement of fluids. ✓Pillar structures - also known as elutriation pipes, are vertical waterescape channels that can be simple tubes or have a vertical sheet-like form. Correlations 1: Basic Geology / HDAR Source: https://www.researchgate.net/figure/Occurrences-and-sketches-of-dish-and-pillarstructures-and-syndepositional-faults_fig5_252142368 Penecontemporaneous Structures ➢ Structures due to (Dewatering Structures) ❑Clastic Dikes fluidization ✓Fluidization of a large body of sediment in the subsurface and can result in elutriation of sediment and the formation of vertical clastic dykes centimeters to tens of centimeters across. Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures due to fluidization (Dewatering Structures) ❑Sand volcanoes – are formed from the extruded liquefied sediment brought to the surface in isolated pipes ❑Extruded sheet – sand brought up to the surface through clastic dykes that are spread out on the surface in thin sheet like structure. Correlations 1: Basic Geology / HDAR Source: https://oregonstate.edu/instruct/oer/earthquake/10%20chapter%208_color.html Penecontemporaneous Structures ➢ Structures related to Loading ❑Load Casts – form where the higher density sand has partially sunk into the underlying mud to form downwardfacing, bulbous structures. ❑Flame Structure (Tongue Structure) ✓ are wavy or flamed shaped tongues of mud that project upward into an overlying layer, which is commonly sandstone. The crests of some flames are bent over or overturned and tend to all point in the same direction ✓ deposition of sand layers on wet mud ✓ formed by injection of water saturated material upward into soft sediment above Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures related to Loading ❑Ball and Pillow Structure - are masses of clastic sediment that take the form of isolated pillows or protruding ball structures Source: http://www.columbia.edu/dlc/c up/ricci/ricci17pl126.html https://en.wikipedia.org/wiki/S oftsediment_deformation_structur es Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures related to Loading ❑Diapirs – form where the instability due to density differences between layers of unconsolidated sediment results in movements of material on a large scale ❑Two types 1. 2. Salt diapirism - salt tectonics Mud diapirism - occurs where a layer of sediment has a high porosity and its density is reduced due to the presence of a high proportion of water mixed with the sediment Correlations 1: Basic Geology / HDAR Penecontemporaneous Structures ➢ Structures related to Loading ❑Convolute Bedding - is a structure formed by complex folding or intricate crumpling of beds or laminations into irregular, generally small–scale anticlines and synclines Correlations 1: Basic Geology / HDAR Biogenic Structures ➢ Organic or biogenic sedimentary structures are those which are formed by living organisms interacting with the sediment. The organisms may be animals which walk on or burrow into the sediment, or they may be plants with roots which penetrate the sediment, or they may be bacterial colonies which trap and bind the sediment to produce layered structures. Correlations 1: Basic Geology / HDAR Biogenic Structures ➢ Trace fossils or ichnofossils ❑It includes tracks, trails, burrows, borings, and other marks made in the sediment by organisms. ❑They are bioturbation structures formed as the activities of organisms disrupt the sediment. ❑As organisms tunnel through sediment, they destroy primary sedimentary structures (such as laminations) and produce burrow marks. ❑Bioturbation continuing over a long period of time will thoroughly mix and homogenize the sediment. ❑Through this process, a laminated sediment can be altered to a massive, homogeneous sediment with no readily discernable layering or other sedimentary structures. Correlations 1: Basic Geology / HDAR Biogenic Structures ➢ Trace fossils or ichnofossils ❑Tracks or footprints impressions on the surface of a bed of sediment produced by the feet of animals. In some cases, tracks are found as sole marks on the bottoms of beds, where sediment has infilled the tracks, and preserved them as casts. Correlations 1: Basic Geology / HDAR Source: http://radaractive.blogspot.com/2013/03/dinosaur-tracks-intelligent-evidence.html Biogenic Structures ➢ Trace fossils or ichnofossils ❑Trails - are groove-like impressions on the surface of a bed of sediment produced by an organism which crawls or drags part of its body. Trails may be straight or curved. Source: https://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookPaleo1.html Correlations 1: Basic Geology / HDAR Biogenic Structures ➢ Trace fossils or ichnofossils ❑ Burrows ✓ Are excavations made by animals into soft sediment. ✓ Burrows may be used by organisms for dwellings, or may be produced as a subterranean organism moves through the soil or sediment in search of food. ✓ Burrows are commonly filled in by sediment of a different color or texture than the surrounding sediment, and in some cases, the burrows may have an internally laminated backfilling. ✓ Burrow fillings may become cemented and hard, weathering out of the rock in rope-like patterns. Correlations 1: Basic Geology / HDAR Biogenic Structures ➢ Trace fossils or ichnofossils ❑Borings ✓ Are holes made by animals into hard material, such as wood, shells, rock, or hard sediment. ✓ Borings are usually circular in crosssection. Some snails are predators and produce borings or "drill holes" into other mollusks, such as clams, to eat them. ✓ Another mollusk, known as the "shipworm", drills holes into wood. Sponges also produce borings, commonly riddling shells with numerous small holes. Correlations 1: Basic Geology / HDAR Sourcehttps://woostergeologists.scotblogs.wooster.edu/2016/05/13/woosters-fossil-of-the-week-arecent-sponge-boring-from-south-carolina/ Biogenic Structures ➢ Trace fossils or ichnofossils ❑Root marks ✓Are the traces left by the roots of plants in ancient soil zones (called paleosols). ✓Root marks typically branch downward in a pattern resembling an upside-down tree. ✓Root marks are sometimes gray or greenish, penetrating reddishbrown paleosols. This contrast in color can make them easy to see and identify. Correlations 1: Basic Geology / HDAR Sourceh :https://tracefossils.wordpress.com/2014/03/07/all-about-trace-fossils/ Biogenic Structures ➢ Trace fossils or ichnofossils ❑Stromatolites ✓ Are mound-like structures formed by colonies of sediment-trapping cyanobacteria (commonly called blue-green algae). ✓ These organisms inhabit some carbonate tidal flats, and produce dome-like laminations in lime mud (fine-grained limestone or micrite). ✓ Stromatolites are "organo-sedimentary “structures", and not fossils because they contain no recognizable anatomical features. ✓ Stromatolites form today in only a few places in the world, primarily in hypersaline environments (such as Shark Bay, Australia), and a few freshwater carbonate- precipitating lakes. ✓ In the geologic record, most stromatolites are found in Precambrian and lower Paleozoic limestones. The cyanobacteria which formed these stromatolites were photosynthetic, and they are therefore responsible for changing the character of the Earth's atmosphere from one dominated by carbon dioxide to one with significant quantities of free oxygen. Correlations 1: Basic Geology / HDAR Biogenic Structures ➢ Trace fossils or ichnofossils ❑Stromatolites Sourceh https://economictimes.indiatimes. com/news/science/oldestevidence-of-life-on-earth-foundinaustralia/articleshow/61658155.c ms?from=mdr Correlations 1: Basic Geology / HDAR Diagenetic Structures ➢ Nodules and Concretions ❑Nodules - is a mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition,. Forms as irregular cemented patches ▪ Large nodules are sometimes referred to as doggers Correlations 1: Basic Geology / HDAR Diagenetic Structures ➢ Nodules and Concretions ❑Concretions - form as minerals within a rock and begins to precipitate within cracks and cavities. It has a symmetrical, round or discoid features. Correlations 1: Basic Geology / HDAR Diagenetic Structures ➢ Nodules and Concretions ❑Septarian concretions - The interiors of some carbonate concretions in mudstones display an array of cracks that are often filled with sparry calcite. "turtle-back" appearance. Correlations 1: Basic Geology / HDAR Diagenetic Structures ➢ Chert ❑Primary chert - Chert form directly from siliceous ooze deposited on the sea floor. ❑Secondary chert - may also form in concretions or nodules as a result of the concentration of silica during diagenesis. ❑Flint is the specific name given to nodules of chert formed in the Cretaceous Chalk. Correlations 1: Basic Geology / HDAR Diagenetic Structures ➢ Carbonates ❑Neomorphism The diagenetic replacement of a mineral by a different crystal form of the same mineral. ❑Carbonate Cements ✓Isopachous cement (occurs in the phreatic zone) ✓Meniscus cement (occurs in the vadose zone) Correlations 1: Basic Geology / HDAR Some Selected References Nichols, G. (2009). Sedimentology and Stratigraphy Second Edition. 9600 Garsington Road, Oxford: Wiley Blackwell A John Wiley & Sons Ltd. Publication Lutgens, F., Tarbuck, E. and Tasa, D. (2012). Essentials of Geology Eleventh Edition. Upper Saddle River, New Jersey: Pearson Prentice Hall. Boggs, S. Jr. (2006). Principles of Sedimentology and Stratigraphy. Upper Saddle River, New Jersey: Pearson Prentice Hall https://www.encyclopedia.com/earth-and-environment/geology-andoceanography/geology-and-oceanography/stratigraphy Correlations 1: Basic Geology / HDAR