Geology Reference
In-Depth Information
Kiessling, W. (2001): Paleoclimatic significance of Phanero-
zoic reefs. - Geology,
29
,751-754
Murray, J.W. (1995): Microfossil indicators of ocean water
masses, circulation and climate. - In: Bosence, D.W.,
Allison, P.A. (eds.): Marine paleoenvironmental analysis
from fossils. - Geological Society of London, Special
Publications,
83
, 245-264
Ribaud-Laurenti, A., Hamelin, B., Montaggioni, L., Cardi-
nal, D. (2001): Diagenesis and its impact on Sr/Ca ratio in
Holocene
Acropora
corals. - International Journal of Earth
Sciences,
90
, 438-451
Rosenberg, G.D. (1990): The 'vital effect' on skeletal trace
element content as exemplified by magnesium. - In: Carter,
J.G. (ed.): Skeletal biomineralization patterns, processes
and evolutionary trends. Volume I. - 567-577, New York
(Van Nostrand)
Strauch, F. (1972): Zur Klimabindung mariner Organismen
und ihre geologisch-paläontologische Bedeutuung. -
Neues Jahrbuch für Geologie und Paläontologie, Abhand-
lungen,
140
, 82-127
Sun, S.Q., Esteban, M. (1994): Paleoclimatic controls on sedi-
mentation, diagenesis and reservoir quality: lessons from
Miocene carbonates. - American Association of Petroleum
Geologists, Bulletin,
76
, 519-543
Wefer, G., Berger, W.H. (1991): Isotope paleontology: growth
and composition of extant calcareous species. - Marine
Geology,
100
, 207-248
Further reading:
K155, K156 (trace elements), K158, K159
(stable isotopes), K171 (paleotemperature evaluation).
ation of oxygen isotopes is temperature dependent. The
ratio of the two most common isotopes (
16
O and
18
O)
in calcareous fossils can, in principle, be used to re-
construct the temperatures of ancient oceans. Foramin-
ifera are commonly analyzed in order to determine sea-
surface, deep-water and bottom-water temperatures
(Berger 1979). Mollusk and brachiopod shells as well
as carbonate cements have also been successfully used.
Difficulties of the technique include problems related
to the isotopic composition of ancient oceans, the pos-
sibility of non-equilibrium fractionation in organically
precipitated calcites (specially in macrofossils), and the
diagenetic alteration of the δ
18
O values of carbonate
shells (Corfield 1995). Further information in Arthur
et al. (1983), Wefer and Berger (1991) and Hoefs (1997).
Trace elements
The concentration of trace elements in fossils de-
pends on the physical chemistry of the skeletal forma-
tion process, the physiology of the organisms, various
environmental parameters, and diagenetic processes.
Many studies of minor element concentration and el-
emental ratios in fossils and carbonate sediments deal
with magnesium and strontium. These elements are used
to estimate water temperature ranges as well as other
environmental constraints. Magnesium concentration
correlates positively with water temperature in many
invertebrates. The correlation is especially apparent in
groups characterized by skeletons made by High-Mg
calcite (e.g. corallinacean red algae) but also occurs in
many other invertebrates. The Sr concentration of in-
organic calcite and aragonite is positively correlated to
increasing temperature. The strontium concentration of
biogenic aragonite and calcite shows positive as well
as negative correlations with water temperature. The
Sr/Ca ratio in coral skeletons reflects sea-surface tem-
peratures (Beck et al. 1992).
Magnesium and strontium concentrations can not be
used universally as paleothermometers, because the
correlation between temperature and rare element con-
centration may fit a major group (e.g. all brachiopods)
or only genera or species of a group (e.g. of mollusks).
See Moore (1989) and Dickson (1990) for further in-
formation.
12.1.7 Salinity
Understanding salinity controls on biota and micro-
facies is important specifically for carbonates that have
been formed in marginal-marine and nonmarine envi-
ronments.
Salinity is a measure of dissolved salts in seawater.
It is defined as the weight in grams of dissolved salts in
1000 g of seawater and commonly expressed in terms
of per mille (‰) which is equivalent to parts per thou-
sand (ppm) of dissolved solids in the water. Common
cations are Na, Mg, Ca, K, and Sr.
Terminology:
Salinity conditions of ancient environ-
ments are often described in rather general terms those
as normal marine water, brackish water or freshwater.
Normal marine
conditions are characterized by a sa-
linity in the range of 33 to 38‰, average 35‰.
Brack-
ish water
is an indefinite term for waters with a salinity
between that of normal seawater and that of normal
freshwater (see Fig. 12.11).
Freshwater
contains only
small quantities of dissolved salts. Salinity decreases
in areas of mixing with fresh water and varies strongly
in estuaries and intertidal settings. Salinity is low in
semiclosed sea basins (e.g. Baltic Sea). Salinities that
are substantially greater than that of normal seawater
(>40‰) are called
hypersaline.
They
occur
in arid
Basics: Seawater Temperature
Beck, J.W., Edwards, R.L., Ito, E., Taylor, F.W., Recy, J.,
Rougiere, F., Joannot, P., Henin, S. (1992): Sea-surface
temperature from coral skeletal strontium/calcium ratios.
- Science,
257
, 644-647
Francis, J.E., Smith, M.P. (eds., 2002): Paleoclimate recon-
structions using fossils and lithological indicators. -
Palaeogeography, Palaeoclimatology, Palaeoecology,
182
,
1-143
