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
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
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
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
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 on
the 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 crossstratification, 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
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
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
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
What are the geologic characteristics of a reef?
•Massive
•Thick deposits
•Steep flanks
•Abrupt facies changes
•Few clastics
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 abyssal
sediments only occasionally exposed at convergent margins
Transitional/Marginal Marine Settings
•Subaqueous or subaerial
•Typically high energy
•Area of deposition (delta)
or erosion (beach)
I Sheltered Shallow Marine
•Clastic or carbonate
II Beach/Barriers/Spits
•Limited lateral extent
III Rocky Shore
•May have abnormal salinities
(high salinity in arid
environments, low salinity
in humid)
IV Tidal Flats/Sabkahs
•Limited marine fauna, perhaps
terrestrial or freshwater
elements as well
V Deltas/Fan Deltas
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
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
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
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
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
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
I Lakes (Lacustrine Systems)
P&S p. 149
•Origins
•Size
•Chemistry
•Life span
•Characteristic
features
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 50Ma
Green 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 crossstratification
•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
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
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)