Geoscience Reference
In-Depth Information
on sedimentology (e.g. Section 6.6). Table 6.5 provides a list of
some of the clues to look for when trying to decipher the
depositional environment. The most robust interpretation comes
from a wide range of evidence and no one set of observations
should be taken in isolation. In addition, for coastal
environments Appendix A6, Figure A6.14 shows the
dominance of different processes and resulting variation in
morphology.
6
Table 6.5
Summary of some of the processes/features and the sedimentary environments that they might
represent. In all cases it is the combination of different lines of evidence that will help to determine the
depositional environment.
Processes/ features
Possible environments
Water currents (current-formed
ripples, cross-stratifi cation, etc.)
Fluvial, lacustrine or marine
Waves (ripples, HCS, SCS, etc.)
Large standing body of water, i.e. large lake or the sea. Consider:
lacustrine or marine environments (high water mark to wave base)
Large-scale cross-stratifi cation
Aeolian, alluvial or movement of sand on the continental shelf or within
an inlet by tides
Tidal features (e.g. mud-draped
ripples, tidal bundles)
Marine environments near the coastline
Low diversity/brackish fauna
Restricted lagoon or estuary or coastal embayment
High diversity marine fauna
Shallow marine (or possible deep-marine condensed succession).
Consider strandplain or delta or barrier island
Mainly or totally pelagic fauna
Deep marine (unless there is another factor to exclude benthic
organisms such as evidence for anoxic conditions)
Abundance of fossilized plant remains
Delta or fl uvial or possibly lacustrine
Numerous coals
Delta or aggrading fl uvial system
Extensive evaporite deposits
Carbonate platform or lacustrine or aeolian
Fine-grained, laterally continuous
beds over 100s km
Deep marine; pelagic/hemipelagic or large-scale lacustrine
Mass gravity features
Alluvial fan or submarine fan but also consider synsedimentary faulting
and/or steep slopes such as at the edge of a carbonate platform
Wind features (frosted grains,
large-scale high-angle cross-
stratifi cation, impact ripples)
Aeolian (but if the evidence is not laterally extensive consider
backshore)
Cyclic successions
Any environment, but less likely to be regular in fl uvial and aeolian
Turbidites
Anywhere in water where there is a slope of more than a few degrees.
If they are extensive and associated with other deep-marine features
and mass fl ow deposits, possible submarine fan. Carbonate turbidites
will form off the edge of the carbonate platform due to the vertical
build-up of reefs, etc.
