Geology of Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 51

TABLE 2.3
General Depositional Environments of Select Clastic Sedimentary Deposits

Depositional
Environment Location Sedimentary Process Type of Deposit

Continental Alluvial Fan Stream deposits from fast-flowing

water. Also includes debris flows
and rock slides from adjacent
mountain slopes

Conglomerate and coarse sands
that are poorly to moderately
sorted

Rivers (fluvial) Deposition from fast- and slow-

moving water current on channel
beds and bars. Low-velocity
deposition on floodplains during
overbank flow generally during
floods

Sand, moderately to well-sorted
and potentially cross-bedded in
higher energy type deposits, to
clay and silt in floodplain
deposits

Deserts (eolian
or aeolian)

Sediment transport by wind (eolian
or sometimes referred to as
aeolian). Leads to formation and
migration of dune deposits

Sand, very well-sorted and
rounded, quartz-rich

Glaciers Wide-range of deposits from

unsorted till in moraines to well
sorted, coarse- to fine-grained
deposits near unique glacial type
deposits termed kames and kettles

Fine-grained conglomerate-type
deposits; poorly sorted to
moderately well-sorted kame
deposits

Lakes
(lacustrine)

Deposition of fine-grained sediments
in deep water to coarse-grained in
beach deposits. Also evaporation of
lake water causing chemical
precipitation, especially in arid
environments

Finely bedded silt and clay
deposits indicating deeper water
formation to coarse-grained sand
indicating beach deposits

Wetland Mainly composed of decayed

vegetative material and very
fine-grained sediments

Buried peat; when buried and
exposed to heat and pressure
may develop into coal

Transitional Deltas Deposition of fast- to slow-moving

water at the mouth of a river or
stream entering a large body of
water. Re-working of sediments by
wave action. Deposition of organic
debris in swamps

Sand moderately- to well-sorted
to silt and clay. May be
fossiliferous and may also
contain layers of peat

Beach Reworking of sediment layers by

waves. May also include formation
of dunes

Sand fine- to coarse-grained,
moderately- to well-sorted,
quartz-rich

Tidal flats High- to low-velocity flow in

channels and may also have sheet
flow. Periodic wetting and drying

Sand to clay deposits, fine-grained
and well sorted, may be organic
and fossiliferous, mudcracks and
trace fossils

Marine Reefs and

Lagoons

High to low energy low through
submarine locations and deposition
of increasingly finer material with
waning flow. May exhibit
submarine disturbance indicative
of sliding and debris flows

Conglomerate, sand, to clay.
Moderately well-sorted, typically
exhibits graded bedding
(coarse- to fine-grained upward
sequence). Also unsorted sliding
or debris flow deposits

Deeper water Abyssal plain-type deposits that

typically exhibit very fine non-
descript dark muddy-type deposits

Very fine-grained clay