Sedimentary Environments: places and conditions under which sediment can accumulate.
Often leave particular signatures, including:
Particular sedimentary structures
Particular physical relationships between lithologies
In particular, we are concerned about the combinations of facies in a package of sediment. From the Latin for
"face" or "appearance", facies (singular is also "facies") are the sets of characteristics (lithologies, sedimentary
structures, suites of fossils, etc.) that represent a particular depositional environment. When we
talk about "depositional environments", though, we often mean broad regions; in the case of facies, these
can be micro-environments of very small spaces (for example, the channel of a small stream; the banks of a lake; etc.)
Soils generated in many regions, but are self-destroying.
So, paleosols are rare
Lacustrine - Lakes
Opposite of soils: smaller area of Earth surface, but by definition are areas of
deposition, so well represented in rock record.
Tend to have limited extent (although Lake Baikal/Great Lake-sized paleo-lakes can
leave huge deposits)
Sediments become finer towards topological center.
Low energy, poor oxygenation: bottom sediment generally poorly disturbed, so
laminae (very fine layers) common: preserved as shales
Fine grain size and limited disturbance allows excellent preservation of fossils.
Lake shales may be interrupted by bursts of bigger grain size (tempestites or "storm deposits")
Edges of lake deposits will have bigger grain size (silts & sands), bi-directional
ripple marks, mud cracks, trackways, etc.
Paludal - Swamp
HIGH amount of biological activity, so rocks of high organic content
Mixed muds & coal/peat/lignite, with some fluvial sediments cutting through
Often associated with other environments (deltaic, fluvial, coastlines, etc.)
Glacial - Glaciers
Vary in frequency throughout Earth history: very rare some periods, very common others
(i.e., ice ages).
MASSIVE erosive capability, MASSIVE transport ability.
Produces till (mixture of all particle sizes, from rock flour to boulders).
Till may be organized into moraines or spread out as outwash. If tills
become lithified, become a conglomerate called tillite.