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2/22/15
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Depositional Environments Geographic area in which sediment is deposited
Characterized by a combination of geological process & environmental conditions
Depositional Environments Geological processes:
Nature of currents Water, wind, ice
Plate tectonic setting Presence of volcanic activity
Generates abundant sediment Climate
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Depositional Environments Environmental conditions:
Kind & amounts of water Ocean, lake, river, ice
Topography Lowland, mountain, shallow ocean, deep ocean
Biological activity
Non-marine Depositional Environments
Alluvial Fans Braided and Meandering Fluvial
Systems Deserts Lacustrine Systems
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Desert
Depositional Environments Continental Environments ~ Desert
Desert - dunes and arid-region streams Transporting agent - wind Sediments - sand and dust (loess)
• Sand dunes are large features with steep faces Ripples, cross-bedding formed from sand dunes
• Well sorted, quartz-rich sands • May have internally draining lakes • Mudcracks in wet area between sand dunes • Oases are spring that show up in rock record
Climate - arid Organic processes - little organic activity, mainly
surface tracks and trails
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Eolian stratigraphy
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web.ncf.ca
Eolian Dune internal architecture Eolian dunes commonly are built by climbing wind ripples that produce climbing translatent strata. The angle of climb determines the angle of the layers. Visually the laminae have a “pinstripe” appearance and internally they commonly are inversely graded.
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Eolian dunes change as climate changes
eas.unl.edu
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Eolian Cross-bedding
drc.oberlin.edu
Eolian Cross-bedding
Geol.umd.edu
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Figure 2. Composite stratigraphic section of exposed Nepean Formation at study
location.
MacNaughton R B et al. Geology 2002;30:391-394
©2002 by Geological Society of America
Evolutionaryfairytale.com
Eas.unl.edu
Navajo Sandstone - Southwestern
U.S.
This well-known sandstone (it occurs in Grand Canyon, Zion National Park in south-western U.S.) records arid conditions that were common during the Jurassic!
Monsoonal circulation is recorded in these rocks!
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Navajo Sandstone has large-scale cross-bedding produced by the migration of large sand dunes, similar to those in
modern Sahara desert
The cross-bedding in the Navajo Sandstone indicates it formed during the yearly migration
of the monsoon circulation; large extent of deserts, as well as widespread storm deposits caused by hurricanes suggests “Megamonsoon”
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rationalskepticism.org
Criteria to identify Eolian Facies
1. 2. 3. 4. 5.
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Lakes are standing bodies of water formed on land and as such they can contain many of the same features that form along shorelines
(e.g., deltas, turbidites, slumps)
Lacustrine Delta Deltas form anywhere that running water enters a standing body of water
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Fluvial system entering a lake makes an elongate delta
Inclined cross-bedding was produced by Gilbert-type delta
prograding into a lake
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Green River Formation above Cretaceous strata in Utah preserves
lacustrine features
Leaf fossils can be common in some lacustrine facies
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The Solenhofen Limestone in Germany is an important unit for it preserves
Archeopteryx fossils - the first evidence of birds, feathers
Stromatolites can grow in lakes and carbonate can accumulate along
shorelines
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Fish fossils can be very common in lacustrine deposits
Rhythmically bedded lacustrine sediments (varves), colors relate to
grain size and oxygenation of the lake
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Triassic - Jurassic Rifting of Eastern N.A.
Triassic-Jurassic Rifting
Asymmetric basins were filled with non-marine and marine sedimentary rocks
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Triassic-Jurassic Rifting Evaporites
formed in some of the rift basins
Evaporites were
formed from evaporation of sea water
Triassic-Jurassic Rifting
Louann Salt!
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Triassic - Jurassic Rifting of Eastern N.A.
Basalt sills and dikes are common within the rift basins developed as North America and Africa separated!
Triassic-Jurassic Rifting
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Sedimentary Cycles
Criteria to identify lacustrine facies
1. 2. 3. 4. 5.