2.5 Lake Sediments
2.5.9 Summary (Lake Sediments)
Lakes and their drainage areas represent relatively simple erosional-depositional systems.
Lakes are characterized by a low-diversity fauna
and flora, and their sediments are very sensitive
to c1imate change.
Sediments of open lakes are dominated by detrital c1astics and biogenic carbonates and/or silica.
Closed lakes precipitate various types of
evaporites, inc1uding evaporitic carbonates and
abiotic chert.
The types and successions of evaporite minerals
are largely controlled by the chemistry of the
inflowing water and c1imate-controlled lakelevel fluctuations.
The peaks of arid phases may be reflected in
c10sed systems by inland sabkhas, dryed mudflats, and paleosols (e.g. calcretes).
Organic production is high in most lakes even in
salt lakes. Black shales form in both open (±
tropical, stratified) and c10sed lakes (during
93
highstand). These shales, as weil as residual
brines containing rare elements, are often of
economic interest.
- The lifetime of many lakes is short due to high
sedimentation rates, unless these are balanced by
subsidence.
- Some of the most distinctive features of lake
sediments are:
* A limited number of faunal elements, sparce
bioturbation, absence of marine fauna.
* Black shale horizons containing !ittle pyrite.
* The occurrence of sodium carbonate minerals
which are absent in marine evaporites (cf. Sect.
6.4).
* Repeated intervals of desiccation and soil formation (c1osed basins).
* Successions with marked lithological variations and pronounced cyc1icity.
2.5.9 Summary (Lake Sediments)
Lakes and their drainage areas represent relatively simple erosional-depositional systems.
Lakes are characterized by a low-diversity fauna
and flora, and their sediments are very sensitive
to c1imate change.
Sediments of open lakes are dominated by detrital c1astics and biogenic carbonates and/or silica.
Closed lakes precipitate various types of
evaporites, inc1uding evaporitic carbonates and
abiotic chert.
The types and successions of evaporite minerals
are largely controlled by the chemistry of the
inflowing water and c1imate-controlled lakelevel fluctuations.
The peaks of arid phases may be reflected in
c10sed systems by inland sabkhas, dryed mudflats, and paleosols (e.g. calcretes).
Organic production is high in most lakes even in
salt lakes. Black shales form in both open (±
tropical, stratified) and c10sed lakes (during
93
highstand). These shales, as weil as residual
brines containing rare elements, are often of
economic interest.
- The lifetime of many lakes is short due to high
sedimentation rates, unless these are balanced by
subsidence.
- Some of the most distinctive features of lake
sediments are:
* A limited number of faunal elements, sparce
bioturbation, absence of marine fauna.
* Black shale horizons containing !ittle pyrite.
* The occurrence of sodium carbonate minerals
which are absent in marine evaporites (cf. Sect.
6.4).
* Repeated intervals of desiccation and soil formation (c1osed basins).
* Successions with marked lithological variations and pronounced cyc1icity.