EOSC221 SEDIMENTARY STRUCTURES

Transcription

1 EOSC221 SEDIMENTARY STRUCTURES 1

2 SEDIMENTARY STRUCTURES LECTURE OUTLINE Sedimentary Structures Deposi?onal Erosional Post Deposi?onal Biological Components Nodules and Concre?ons 2

3 Sedimentary Structures - Structures produced during or soon aeer deposi?on of sediment - Both physically and biologically produced - Provide vita paleoenvironmental / stra?graphic informa?on - The following is a list of SOME sedimentary structures. It is NOT and exhaus?ve lis?ng: for much detail see EOSC320 hqp://upload.wikimedia.org/wikipedia/commons/5/58/logan_forma?on_cross_bedding_scour.jpg 3

4 DEPOSITIONAL FEATURES - Bedding and lamina+on - Most basic feature usually reflect changes in composi?on and / or grain size - Bedding generally layering > 1cm - Finer = lamina?ons hqp://en.wikipedia.org/wiki/file:heavymineralsbeachsand.jpg hqp://en.wikipedia.org/wiki/file:bedding.jpg 4

5 - Ripple marks, lamina+ons and cross stra+fica+on - i. Current ripples - Unidirec?onal flow in water or wind ripple crest ripple trough flow FLOW DIRECTION Ripple Crest : lee slope Ripple Trough hqp://sepmstrata.org/index.html 5

6 - Successive passage of ripples produces cross bedding or stra3fica3on - Can consider dunes to be LARGE ripples hqp://en.wikipedia.org/wiki/file:dunas_de_maspalomas.jpg hqp://sepmstrata.org/index.html hqp://en.wikipedia.org/wiki/file:dryforkdome.jpg 6

7 - ii Wave Ripples - Ripples produced by waves: inter?dal environments / lakes hqp://en.wikipedia.org/wiki/file:waveripple.jpg - Tend to be less asymmetrical than current ripples - Wave ripples will form when sediment /water interface is ABOVE wave base waterpar?cle orbits hqp://sepmstrata.org/index.html hqp://upload.wikimedia.org/wikipedia/commons/2/22/sym_ripple.jpg 7

8 - Differen?a?ng between wave and current ripples - i. Ripple crest differences wave ripples commonly bifurcate - ii. Symmetric / asymmetric wave current hqp://sepmstrata.org/index.html 8 hqp://en.wikipedia.org/wiki/file:мелкая_рябь.jpg

9 - Graded Bedding - Evidence of a waning current - Course / heavy material seqles out first hqp://depthome.brooklyn.cuny.edu/geology/events/nysga2007/nysga2007.htm hqp://en.wikipedia.org/wiki/file:gradierte_schichtung_en.jpg hqp:// 9

10 - Turbidites as examples of a graded deposit - Avalanche of sediment down slope Fining upwards = decreasing flow velocity hqp://blogs.agu.org/mountainbeltway/2010/12/24/gosf6-graywacke-turbidites/ 1 Bouma Sequence: typical set of sedimentary features deposited by a waning flow hqp://sepmstrata.org/index.html hqp://csmres.jmu.edu/geollab/fichter/sedrx/depomodels.pdf 10

11 EROSIONAL FEATURES - Flute marks - Spatulate apppearance - point up stream - Good way-up indicators - Common on the base of turbidite deposits but can also be found on flood plains Flow Flow hqp://sepmstrata.org/index.html 11 hqp://en.wikipedia.org/wiki/file:flute_casts_mcr1.jpg

12 - Groove / tool marks - Caused by objects being dragged along by a current - Skip & prod marks objects bouncing hqp://sepmstrata.org/index.html 12 hqp://en.wikipedia.org/wiki/file:flute_casts_mcr1.jpg

13 - Channels - Cross cut bedding planes below - Generally concave up in sec?on - OEen filled with coarser sediment than those they are cuwng into - Develop in many environments 13

14 POST DEPOSITIONAL FEATURES - Slumps / convolute bedding hqp://jsedres.sepmonline.org/content/78/2.cover-expansion 14

15 - Flame structures and load casts - A loading or shock feature FLame WAY UP Load Cast hqp://sepmstrata.org/index.html hqp://course1.winona.edu/csumma/images/sedstrux/flame3.jpg 15

16 - Desiccation / aridity features - i. Mudcracks - Polygonal paqern of cracks formed in very fine-grained sediment - In x-section can provide a way up indicator - Cracks v downwards hqp://en.wikipedia.org/wiki/file:mudcracks_mcr3.jpg hqp://en.wikipedia.org/wiki/file:dried_mud_creeks_on_the_shores_of_the_wash_-_geograph.org.uk_-_10669.jpg hqp://en.wikipedia.org/wiki/file:mudcracks_roundtop_hill_md.jpg 16

17 - ii Salt pseudomorphs - Precipita?on & growth of halite crystals as a water body evaporites - Crystals dissolved and impression filled with later sediment hqp://en.wikipedia.org/wiki/file:saltcrystalcasts.jpg 17

18 Biological Components Body Fossils - Body parts of organisms (plant & animal) preserved in rock - Hard parts and shells are most likely preserved think fossil bias - Original material may be replaced by other minerals commonly silica or calcite - i. Macrofossils: big stuff Ammonite hqp://en.wikipedia.org/wiki/file:ammonite_asteroceras.jpg hqp://en.wikipedia.org/wiki/file:asteroceras_bw.jpg 18

19 - i. Microfossils: small stuff hqp://simple.wikipedia.org/wiki/file:marine-microfossils-major_hg.jpg 19

20 Organo-sedimentary Structures: Trace Fossils - Body parts of organisms (plant & animal) preserved in rock - Preserved tracks or signs of behaviors of animals in or on the substrate are also fossils (NOT the actual organism) hqp:// 20

21 hqp://en.wikipedia.org/wiki/file:asteriacitesdevonianohio.jpg hqp://en.wikipedia.org/wiki/file:coprolite.jpg hqp://en.wikipedia.org/wiki/file:cheirotherium_prints_possibly_ticinosuchus.jpg Coprolite: fossil poop 21

22 hqp://en.wikipedia.org/wiki/file:stromatolites_in_sharkbay.jpg Stromatolites - laminated bulbous structures Formed aeer colonies of bluegreen algae (cyanobacteria) 3.5 Ga - the oldest known Indicators of paleobathymetry hqp://en.wikipedia.org/wiki/file:stromatolites_hoyt_mcr1.jpg Cyanobacteria 22

23 Nodules and ConcreFons ConcreFon: Area where pore space filled with mineral cement Usually form early in burial history before rest of sediment turned to rock: DIAGENSIS see later lectures Grow by mineral precipita?on around some kind of nucleus hqp://en.wikipedia.org/wiki/file:splitconcre?on_keqlepointontario.jpg 23

24 Concre?ons oeen spherical / ovoid. Can be very large. Minerals include silica (SiO 2 ), calcite (CaCO 3 ), siderite (FeCO 3 ) OEen harder than surrounding material weather out forming spherical boulders. hqp://en.wikipedia.org/wiki/file:concre?ons_bear_valley.jpg hqp://en.wikipedia.org/wiki/file:cannonballconcre?oneastgreenland.jpg 24

25 Nodules: A replacement feature or growing into cavi?es Can be spherical to irregular in shape Can be hollow with crystals growing inward: geodes Form during diagenesis (rock forming) of sediment hqp:// 25

26 OEen follow bedding Chert / flint (silica nodules) common in chalk Silica replaces CaCO 3. How chert forms s?ll debated. Silica possibly from diatoms / sponge spicules hqp://en.wikipedia.org/wiki/file:microscopicspiculesfrompachastrellidsponge.jpg 26

27 GLOSSARY All lecture material is potentially examinable. Is up to you to know unfamiliar terms / names / people. Use this space to create your own lecture glossary TERMS / NAMES DEFINITION 27

28 TERMS / NAMES DEFINITION 28