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Keys to Sedimentary Environments I Sediment Composition and Texture II Sedimentary Structures

Keys to Sedimentary Environments I Sediment Composition and Texture II Sedimentary Structures - Inorganic - Organic (Trace Fossils) III Geometry of Rock Body & Lateral Extent IV Facies Relationships V Stratigraphic Sequence VI Fossils - Distribution

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Keys to Sedimentary Environments I Sediment Composition and Texture II Sedimentary Structures

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  1. Keys to Sedimentary Environments I Sediment Composition and Texture II Sedimentary Structures - Inorganic - Organic (Trace Fossils) III Geometry of Rock Body & Lateral Extent IV Facies Relationships V Stratigraphic Sequence VI Fossils - Distribution - Preservation

  2. General Characteristics of Environments Note that there will be exceptions! • I Open Marine Settings • Subaqueous • Typically low energy • Typically area of deposition • Clastic or carbonate • Wide extent • Normal salinities • Diverse marine fauna

  3. General Characteristics of Environments (cont.) • II Transitional/Marginal Marine Settings • Subaqueous or subaerial • Typically high energy • Area of deposition (delta) or erosion (beach) • Clastic or carbonate • Limited lateral extent • May have abnormal salinities (high salinity in • arid environments, low salinity in humid) • Limited marine fauna, perhaps terrestrial or • freshwater elements as well

  4. General Characteristics of Environments (cont.) • III Nonmarine/Continental/Terrestrial Settings • Typically subaerial • Typically area of erosion • Clastic dominated • Limited lateral extent (eolian an exception) • Typically fresh water, but could be highly • saline (playas) • Limited nonmarine fauna

  5. I Shallow Sublittoral (Subtidal) - above wave base • Inner Continental Shelf • - Clastic Shelf • - Carbonate Shelf (Platform, Ramp) • Usually at low latitude and lack clastics • Epeiric/Epicontinental Seas • Intracontinental Basins

  6. Continental Shelves • General • - Gentle, < 1o (1:500) slope • - 30m -1300km wide (passive vs active margins) • - Shelf break at ~ 130m depth • - 9% of total ocean area (6% Earth’s surface) • - 2.5 km sediment thickness • - 15% of marine sediment volume • Note that there is an abundance of sand on • the continental shelfs today - why?

  7. Continental Shelves (cont.) Clastic Inner Shelf(P&S p. 187-188) - Wave dominated (High energy) - Tide dominated (Lower energy) • Sediments - quartz sand grading into muds • Sed struc - wave ripples, trough cross- • stratification, hummocky cross-stratification • Geometry - tabular sheets (wave dom), • lenses or ridges (tide dom) • Assoc envir - Down dip - deeper marine muds • - Up dip - deltas and beaches/barriers • Fossils - abundant (often abraded), vertical burrows

  8. Carbonate “Shelf” (P&S p. 250) • General • - Largely restricted to tropics and areas of clear water • (low clastic and low nutrient input) • - Variable energy levels • Sediment - typically few clastics present,occasional shales, • In situ limestones (carbonate mudstone to grainstone) • dominate • Sed struc - intraclasts, ooids and oncoids, hummocky • cross-stratification • Geometry - widespread, tabular sheets • Assoc envir • - Up dip peritidal or sabkah • - Down dip deeper marine fine-grained carbonates • - Reefs common • Fossils - abundant, marine, diverse, preservation variable

  9. Carbonate “Shelf” (cont.) • Carbonate Shelf • - Abrupt seaward termination • - Sedimentation exceeded sea-level rise • - Rimmed or nonrimmed (bypass) • - e.g. Florida • Carbonate Platform • - Abrupt termination • - Rimmed or nonrimmed • - More extensive than shelf • - e.g. Bahamas • Carbonate Ramp • - Gentle slope • - Sedimentation did not exceed sea-level rise • - e.g. Yucatan Peninsula, Persian Gulf

  10. Peritidal (P&S p. 242) • Sediments - carbonate muds, evaporites • Sed struc - mud cracks, tidal channels, birdseye • Geometry - thin, laterally continuous along strike • Assoc envir - carbonate shelf, reefs, continental • Fossils - low diversity, algal stromatolites

  11. Epeiric (Epicontinental) Sea • Located on top of continents, not at margins • More common in past than today • Hudson’s Bay a modern example? • Thin sequences relative to basins & passive margins • (little accommodation space) • Shallow-water • - High productivity • - Influenced by storms • (Hummocky cross-stratification common)

  12. Epeiric (Epicontinental) Sea (cont.) • Very low gradient (1m/50,000m) (continental shelf is 1:500) • - Greatly influenced by eustasy • - Broad facies belts • - Frictional Damping • Irwin & Shaw XYZ model • (Perhaps hypersaline) • (Perhaps stagnant) • Associated sedimentary rocks • - Typical shallow-water sediments • (Frequently low-energy - broad inner, Z zone) • - Widespread black shales - • Dev. Chatanooga Shale, Jur. Posidonia Schieffer • - Evaporites - Perm. Zechstein

  13. Intracratonic Basins • General • - High accommodation (downwarping) • - Not due to active tectonism/mountain building • (e.g. Foreland Basins), perhaps due to old rifts • - Particularly common in Paleozoic of North America • - e.g. Permian Oquirrh Basin of Utah • Sediments - thick accumulations of shallow-water sediment • Geometry - oval plan shape, saucer-shaped in cross • section • Assoc envir - domes (sediments thin across domes), • epeiric seas • Fossils - may be abundant

  14. II Carbonate Buildups (P&S p. 258-259) • Sediments - boundstone core, fore reef talus/breccia, back reef wackestones, core often dolomitized • Geometry - mound or bank like, variable size • Assoc envir - peritidal/sabkah, lagoon, basin muds • Fossils - framework builders have varied over time, include corals, stromatoporoids, rudistid bivalves, calcareous algae

  15. What are the geologic characteristics of a reef? • Massive • Thick deposits • Steep flanks • Abrupt facies changes • Few clastics

  16. III Deep Sublittoral • General • - Low energy • - Typically fine-grained sediments • - Low temperature • - May exhibit low oxygen levels (particularly • in stratified basins) • - Potential for high carbon preservation • Outer Continental Shelf • Continental Slope • Continental Rise • Abyssal Plain

  17. III Deep Sublittoral (cont.) Outer Continental Shelf • General • - Lower energy, may still experience storms • - Abundant present day sands are a relict from • the last ice age • - May be cut by submarine canyons • Sediments - clay or carbonate muds • Assoc envir - shallow shelf, continental slope • Fossils - preservation may be good (low energy), although • sedimentation rates are often low, Cruziana - • Zoophycos ichnofacies

  18. III Deep Sublittoral (cont.) • Continental Slope (Bathyal)(P&S p. 196-197) • General • - 2-6o slope • - 140m to 300-800m depth • - 6% of ocean area (4% Earth’s area) • - Cut by submarine canyons • - 9 km sediment thickness • - 41 % of marine sediment volume

  19. III Deep Sublittoral (cont.) • Continental Rise(P&S p. 196-197) • General • - 800 - 4,000 m depth • - 6% of ocean area (4% Earth’s area) • - Cut by submarine canyons • - 8 km sediment thickness • - 31 % of marine sediment volume • - Submarine fan systems may contain coarse • sediments • - Extremely important hydrocarbon • reserves

  20. III Deep Sublittoral (cont.) • Continental Slope and Rise (P&S p. 196-197) • Sediments - hemipelagic muds, channel sands (fans), • turbidites, slump and slide deposits • Geometry - thick wedge or lens shape • Assoc envir - deep marine, abyssal plain • Fossils - rare, some broken shells from continental • shelf, some forams

  21. III Deep Sublittoral (cont.) • Abyssal Plains (and some epicratonic basins)(P&S p. 209) • General (abyssal plains) • - < 1:1000 slope (very flat) • - 4-6 km depth • - 78% of ocean area (55% Earth’s surface) • - 0.6 km sediment thickness • - 13% of marine sediment volume • - potentially dysaerobic or anaerobic

  22. III Deep Sublittoral (cont.) • Abyssal Plains (and some epicratonic basins)(P&S p. 209) • Typically low sedimentation (1mm/ka) • Sediments - pelagic, thin bedded, finely laminated • calcareous and siliceous oozes and • red clays (from deserts) • Geometry - very widespread, thin sheets • Assoc envir - sandy turbidite deposits • Fossils - low macrofossil density, abundant • planktonic fossils, surface feeding burrows • Note that oldest seafloor is Jurassic (~150Ma), also abyssal • sediments only occasionally exposed at convergent margins

  23. Transitional/Marginal Marine Settings • Subaqueous or subaerial • Typically high energy • Area of deposition (delta) • or erosion (beach) • Clastic or carbonate • Limited lateral extent • May have abnormal salinities • (high salinity in arid • environments, low salinity • in humid) • Limited marine fauna, perhaps • terrestrial or freshwater • elements as well • I Sheltered Shallow Marine • II Beach/Barriers/Spits • III Rocky Shore • IV Tidal Flats/Sabkahs • V Deltas/Fan Deltas

  24. I Sheltered Shallow Marine • Environments • - Lagoons • - Bays • - Estuaries - mixing of fresh and salt water, • highly productive • - Salinas - restricted circulation • General • - Low energy • - May mimic deep-water settings • - Variable salinities

  25. I Sheltered Shallow Marine (cont.) • Sediments - fine-grained, clay or carbonate muds, • coals or carbonaceous (organic rich) sediments, • evaporites • Associated environments • - Up dip - beach, continental • - Down dip - shallow, open marine, reef, barrier • Fossils - may have a restricted fauna, • preservation usually good

  26. II Beaches/Barriers/Spits (P&S p. 175, 181-182) • General • - High energy, dynamic (barriers migrate) • - Subaerial dunes to swash to shoreface • Sediments - coarse, well-sorted sediments, mature quartz sands, heavy mineral lags • Sed struc - eolian dunes, planar bedding (swash zone) symmetrical (wave) and asymmetrical (current) ripples

  27. II Beaches/Barriers/Spits (cont.) • Geometry - tabular, seaward dipping shoreface, barriers may be elongate • Assoc envir • - Laterally deltas • - Up dip lagoon, peritidal, or continental • - Down dip - shallow, open marine • Fossils - marine, broken, poor preservation

  28. III Rocky Shore • General - high energy • Features • - Sea cliffs • - Wave terraces • - Wave cut notches • - Sea stacks • Sediments - coarse conglomerates • Associated environments • - Rocky intertidal zone • - Up dip continental • - Down dip shallow, • open marine • Fossils - poor preservation, • may have rock boring trace fossils

  29. IV Littoral (Tidal) (P&S p. 171) • General • - May be high energy • - Energy may vary on daily basis • Sediments - Cyclically alternating clastic sands and muds • Sed struc • - Flasers • - Interference ripples • - Herringbone cross-stratification • - Mud cracks • - Rip ups, mud balls • - Algal mats in supratidal • - Possible evaporites (arid Sabkah)

  30. IV Littoral (Tidal) - cont. • Geometry - tabular, channels lenticular • Associated settings • - Up dip continental settings or sabkah • - Down dip shallow, open marine • Fossils - harsh environment, fauna often limited to a few species, may be heavily • bioturbated • May show strong biotic zonation • - Subtidal • - Intertidal • - Supratidal

  31. V Deltas (P&S p. 164, 168) • General • - Variable energy • - High sedimentation rate • - Highly productive • - Important oil producing • area • Distinct subenvironments • - Delta plain • - Delta fringe • - Prodelta • Delta types • - River dominated - • birds foot • - Wave dominated • - Tide dominated

  32. V Deltas (cont.) • Sediments - muds (prodelta, interdistributary bays) to sands (distributary channels, channel mouth bars), coals • Sed struc • - Teepee structures • - Ball and pillow • - Mud diapirs • - Growth faults • - Distributary channels • - Steeply inclined delta foresets

  33. V Deltas (cont.) • Geometry - thick wedge, triangular, possible very large • Assoc envir - fluvial, continental, barrier, deeper marine • Fossils - mixture of continental and • fresh-water fossils (poorly preserved) and marine fossils (well preserved), heavy bioturbation

  34. Nonmarine/Continental/Terrestrial • I Lake/Lacustrine • II Playa • III Swamp/Paludal • IV Fluvial • V (A)eolian • VI Alluvial Fans • VII Mountain • VIII Foreland Basins • IX Glacial • Typically subaerial • Typically area of erosion • Clastic dominated • Limited lateral extent (eolian an exception) • Typically fresh water, but could be highly • saline (playas) • Limited nonmarine fauna

  35. I Lakes (Lacustrine Systems) P&S p. 149 • Origins • Size • Chemistry • Life span • Characteristic • features

  36. Variable origins • Faults – graben • Cenotes (sinkholes) • Calderas (volcanoes) • Abandoned channels - oxbow lakes • Landslide dams • Glacial - scour - bedrock basins • - deposition - kettle lakes

  37. Lakes -Variable size • Inland seas • - Caspian 144,000 km2 area • - Lake Baikal 1742 m deep • Small ponds • Variable Chemistry • Typically fresh • May be saline - centripetal drainage • (e.g. Great Salt Lake) • May have high carbonate content (hardness) • (e.g. East African Rift Lakes)

  38. Lakes - Geologically ephemeral • Most only 12-14 ka - since last ice age • Pleistocene pluvial lakes • - Bonneville – UT • - Lahontan – NV • - Channeled scablands - WA • Extensive lakes in western US at 50Ma • Green River and Fossil Lakes

  39. Lakes (P&S p. 149) • General - may mimic ocean settings, but usually fresh water • Sediments - fine grained clay muds (except for shoreline, deltaic), • often organic rich, limestones possible, evaporites (playa), • ash beds • Sed struc - varves, mud cracks • Geometry - limited area to widespread, circular or elongate • in map view, lenticular cross section, individual beds are • thin, tabular • Assoc envir - continental, fluvial, beach, deltaic, swamp, marsh • Fossils - well preserved, nonmarine, snails, clams, ostracods, • fish, possibly stromatolites

  40. II Playas • Indicates arid environment • Centripedal drainage • Evaporite minerals

  41. III Paludal (Swamp) • General • - Low energy • - High productivity • Sediments - coals common, • clay muds • Sed struc - root casts • Assoc envir - fluvial, • possibly shallow marine • systems • Fossils - well-preserved • plants common

  42. IV Fluvial Systems • Produced by precipitation, • powered by gravity. • Major shaper of the • Earth’s surface. • Parts of a stream • Profile • Stream types • Stream landforms • Characteristics

  43. Parts of a stream • Channel • Levees • Flood plain • Headwaters (origin) • Mouth (terminus)

  44. Stream Profile • Channel shape • Gradient • Tributaries • Discharge • Velocity • Load

  45. Stream Types • “Slope wash” • (large area) • Arroyos • Headwaters/ • Mountain (High • gradient) • Braided (Low gradient, • high sed load) • Meandering (Low • gradient)

  46. Stream Landforms • Erosion • - Channels • - Cut banks • Deposition • - Terraces • - Levees • - Flood plains • - Point bars • - Alluvial fans • - Deltas

  47. Braided Stream(P&S p. 136) • General - near source at change in gradient • Sediments - gravel near fans, sandy more distal, few fines • Sed struc - channel lag gravels, sandy trough cross- • stratification • Geometry - sheet sands, or elongate lenticular • Assoc envir - alluvial fan, alluvial plain • Fossils - few or no

  48. Meandering Stream(P&S p. 144) • General • - Low gradient • - Much more fine-grained material than braided stream • Sediments - channel lag gravels, sandy channels, • floodplain silts and muds • Sed struc - plane beds, trough cross-stratification, • ripples in pointbars; mudcracks, rain drop impressions, • climbing ripples on floodplain • Geometry - long, ribbon-like “shoestring” sands within • shales • Assoc envir - lakes, deltas, floodplains • Fossils - wood, bone, freshwater molluscs

  49. V (A)Eolian Deposits P&S p. 153-154 Named after Greek god of wind – Aeolus • General • - Most important in arid regions • (< 250mm or 10" per year ppt) • - Require wind, sediment supply, lack of plants • Sediments - deposits are well sorted, fine grained • (sand or silt), sands may be frosted • Sed struc - Pavements and ventifacts, • dunes with high angle cross-strata and • thick bed sets (cross-strata orientation often variable) • Geometry - Widespread, thick, tabular • Assoc envir - interdune facies may include playas • Fossils - rare footprints and root casts

  50. VI Alluvial Fan P&S p. 134 • General • - Associated with uplift • - Fluvial and mass wasting processes dominate • - Fan deltas empty directly into lakes or oceans • Sediments - Immature (poorly sorted and angular) sands, • coarse sieve deposits (orthoconglomerates), debris flows • Sed struc - cross-stratified sandstones, gravel channel lags, channel lenses, radiating paleocurrent indicators • Geometry - thick, wedge-shaped deposits, limited areal • extent • Assoc envir • - Up dip high relief areas • - Down dip alluvial plain (braided fluvial to meandering) • Fossils - rare terrestrial species, poor preservation

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