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

I Open Marine Settings

•Subaqueous•Typically low energy •Typically area of deposition•Clastic or carbonate•Wide extent•Normal salinities•Diverse marine fauna

General Characteristics of Environments

Note that there will be exceptions!

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

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

General Characteristics of Environments (cont.)

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

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 onthe continental shelfs today - why?

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

•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

Carbonate “Shelf” (P&S p. 250)

•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

Carbonate “Shelf” (cont.)

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

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)

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

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

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

•Massive•Thick deposits•Steep flanks•Abrupt facies changes•Few clastics

What are the geologic characteristics of a reef?

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

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

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

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

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

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

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 abyssalsediments only occasionally exposed at convergent margins

I Sheltered Shallow Marine

II Beach/Barriers/Spits

III Rocky Shore

IV Tidal Flats/Sabkahs

V Deltas/Fan Deltas

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

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

I Sheltered Shallow Marine

•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

I Sheltered Shallow Marine (cont.)

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

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

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

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)

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

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

•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

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

V Deltas (cont.)

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

Nonmarine/Continental/Terrestrial

I Lakes (Lacustrine Systems)

•Origins

•Size

•Chemistry

•Life span

•Characteristic features

P&S p. 149

Variable origins

•Faults – graben

•Cenotes (sinkholes)

•Calderas (volcanoes)

•Abandoned channels - oxbow lakes

•Landslide dams

•Glacial - scour - bedrock basins

- deposition - kettle lakes

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)

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 50MaGreen River and Fossil Lakes

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

II Playas

•Indicates arid environment

•Centripedal drainage

•Evaporite minerals

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

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

Parts of a stream

•Channel •Levees•Flood plain•Headwaters (origin)•Mouth (terminus)

Stream Profile

•Channel shape•Gradient•Tributaries •Discharge•Velocity•Load

Stream Types

•“Slope wash” (large area)

•Arroyos

•Headwaters/ Mountain (High gradient)

•Braided (Low gradient, high sed load)

•Meandering (Low gradient)

Stream Landforms

•Erosion

- Channels - Cut banks

•Deposition

- Terraces - Levees - Flood plains

- Point bars - Alluvial fans - Deltas

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

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

V (A)Eolian Deposits

Named after Greek god of wind – Aeolus

P&S p. 153-154

•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

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

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

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

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

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 lower @ 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)