Geology Reference
In-Depth Information
freshwater brackish marine
0.5‰ 5‰ 10‰ 18‰ 30‰ 40‰
limnic brackish marine brackish normal restricted
brackish restricted marine marine marine
oligohaline mesohaline brachyhaline euhaline hypersaline
Cyanobacteria .................................++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Dasyclad green algae ...................................................................................................................................+++++++
Udoteacean green algae ...............................................................................................................................+++++++
Charophycean algae .............................++++++++++++++++++++++++++++++++
Corallinacean red algae ...................................................................................................................+++++++++++
Agglutinated benthic foraminifera .......................................................+++++++++++++++++++++++++++++++++++++
Calcareous benthic foraminifera ...............................................................................++++++++++++++++++++++
Radiolaria .................................................................................................................................................+++++++
Coralline demosponges ................................................................................................................................+++++
Hexactinellid sponges ...............................................................................................................................+++++++
Corals .......................................................................................................................................................+++++++
Bryozoans .......................................................................................................................+++++++++++++++++++
Brachiopods .........................................................................................................................++++++++++++++++++
Serpulids ...........................................................................................+++++++++++++++++++++++++++++++++++
Gastropods .....................................+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Bivalves ..........................................+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Cephalopods ......................................................................................................................................++++++++++
Ostracods ........................................+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Balanid crustaceans ..................................................................................+++++++++++++++++++++++++++++
Echinoderms ......................................................................................................................................++++++++++
Fig. 12.11.
Approximate distribution of some recent organisms relative to salinity. The figure does not include rare excep-
tions (e.g. freshwater sponges). The subdivisions follows the Venice System (Oertli 1963).
evaporitic settings (e.g. parts of the Red Sea; Persian
Gulf), in salinas and restricted lagoons as well as in
semiclosed basins and bays. The term
schizohaline
de-
scribes strongly fluctuating salinity conditions which
may be caused by episodic flushing of hypersaline en-
vironments by freshwater (Folk and Siedlecka 1974;
Pl. 50/6).
Estimations of paleosalinity are based predominantly
on biotic, microfacies and geochemical data.
Organisms are stenohaline or euryhaline.
Stenoha-
line
organisms do not or are only able to tolerate a nar-
row range of salinity.
Euryhaline
organisms tolerate
wide fluctuations in salinity. The differentiation of eu-
ryhaline and stenohaline organisms on a higher taxo-
nomic level is a widely used approach in estimating
paleosalinities.
Stenohaline are planktonic foraminifera, radiolar-
ians, corals, most bryozoans, brachiopods, cephalopods,
and with a few exceptions echinoderms. Common eu-
ryhaline are cyanobacteria, sponges, many bivalves,
gastropods, and ostracods.
12.1.7.1 Biotic and Microfacies Proxies of
Paleosalinity
Important paleontological criteria that can be used
in estimating paleosalinities are
•
Salinity ranges.
Comparison of the salinity depen-
dence of modern and ancient organisms. Fig. 12.11
shows the salinity ranges of some groups. The distri-
bution of major taxonomic units within these groups
may be more specific than the range of the whole group
as demonstrated by the foraminifera. Textulariina are
abundant in brackish waters, Miliolina occur in waters
of normal to hypersaline salinity and Rotaliina are com-
mon in waters of normal salinity.
•
Faunal composition
. The lack or scarcity of steno-
haline invertebrates is characteristic of environments
with fluctuating salinity conditions.
• Extended
microbial mats and stromatolites
(e.g. Per-
sian Gulf; Shark Bay, Australia).
Paleontological data
are heavily used in reconstruct-
ing paleosalinities and discriminating normal marine,
brackish and freshwater environments, although salin-
ity is rarely the only parameter influencing faunal com-
position and diversity. But if salinity is the dominant
factor, salinity gradients can be determined using ben-
thic associations, particularly of mollusks (Fürsich and
Werner 1986).
Some difficulties arise in differentiating hypersaline
and brackish conditions using paleontological data
alone. The capability to regulate the osmotic pressure
may allow organisms to thrive both in hypersaline and
brackish waters and biota as well as microfacies types
may exhibit considerable similarities (e.g. Fürsich et
al. 1995).
