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Keys to Sedimentary Environments

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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 ) - 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.)
- 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 ) General - 2-6o slope - 140m to m 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 ) General ,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 ) 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 Variable Chemistry 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 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

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

46 Stream Landforms - Point bars 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

51 VII Mountain General - High energy - High relief - Rarely preserved
- Igneous and metamorphic cores Sediments - synorogenic conglomerates, immature sediments (arkoses) Sed struc - clastic wedges, unconformities Geometry - elongate features Assoc envir - glacial, alluvial fan, foreland basin Fossils - very few

52 VIII Foreland Basin General - stable continental area marginal to
an orogenic belt, “moat” generated by regional isostatic response to load of orogenic belt Sediments - synorogenic clastic wedges - Thick - Coarse - Poorly sorted - Immature mineralogies Geometry - elongate, parallel to mountain belts Assoc envir - uplifting mountain belts Fossils - rare

53 IX Glacial (P&S p. 157-158) General - abundance varies over time
Sediments - very poorly sorted deposits (tills), immature outwash, Sed struc - Glacial polish and striations, dropstones in lake and marine settings, varves in associated lakes Geometry - narrow, valley-fill (mountain glaciers) to extensive sheets (continental glaciers) Assoc envir - alpine, glaciofluvial (braided stream), loess plains, lakes Fossils - broken and abraded in tills, well preserved in lakes

54 Ice Facts 10% Earth’s land surface covered by ice today
20% Earth’s land surface consists of permafrost Ice caps up to 3,000 m thick Influences sea level (~100 m 12 Ka) Affects Earth’s albedo (reflectivity) and, therefore, climate Several intervals in Earth history had more extensive ice - Pleistocene (2 Ma - 10 Ka) - Pennsylvanian (300 Ma) - Proterozoic (650 Ma)

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