Geology Reference
In-Depth Information
trols, the concentration of manganese in seawater, Eh
conditions, organic matter and microbial processes. The
behavior and the vertical distribution of solid-phase and
dissolved manganese and iron in modern marine sedi-
ments are well known for pelagic and hemipelagic deep-
sea sediments (e.g. Aller 1990) and for anoxic coastal
muds of temperate shelf environments (references in
Berner 1980 and Chester 1990). Geochemical data from
tropical shelf sediments, particularly reef-derived car-
bonates and shallow-marine carbonate muds are less
common (Alongi et al. 1992).
originally of aragonite are usually Sr-rich; those con-
sisting of calcite are poor in Sr.
• Recognizing the primary aragonite and calcite min-
eralogy of fossils (Veizer 1983; Dodd and Stanton
1990).
Diagenesis
• Tracing marine, meteoric and burial diagenesis (e.g.
Al-Hashimi 1982). Commonly used elements are stron-
tium, manganese and magnesium.
• Recognizing meteoric diagenesis, typically with en-
richment of Fe and Mn and depletion in Sr and Na (e.g.
Pingitore 1978; Brand and Veizer 1980; Al-Aasm and
Veizer 1982).
• Checking possible diagenetic alterations of shells
used for stable isotopic studies (Grossman et al. 1996).
13.2.3 Significance of Trace Elements in
Facies Studies of Carbonate Rocks
A basic assumption in the use of trace elements for
facies interpretation is that a relationship exists between
the trace element content of a carbonate and the con-
centration of this element in the water where precipita-
tion takes place. Trace elements are applied to a wide
range of topics but many applications need further re-
finement.
Sedimentation patterns
• Recognizing the shallowing of basins, reflected by
decreasing Sr contents (Lintnerova et al. 1988).
• Recognizing breaks in sedimentation, discontin-
uities, hardgrounds (Marshall and Ashton 1980).
• Distinguishing allochthonous input and autochtho-
nous sedimentation input. Indication of the input of al-
lochthonous sediment (versus autochthonous origin).
Detrital input is indicated by elements related to sili-
cate minerals (e.g. Si, Al, K, Fe).
• Understanding bedded limestone sequences. Geo-
chemical analysis of bedded limestones can be im-
proved by sampling bed per bed, also analyzing the
intercalated marls and evaluating trace elements against
the background of overall non-carbonate contents
(Bausch 1994). Two-component diagrams are useful
in distinguishing clastic, semiclastic and diagenetic el-
ements and correlating profiles.
Depositional conditions
• Differentiating depositional and post-depositional
physico-chemical conditions.
Paleoenvironmental factors
• Recognizing paleosalinity. In neritic and coastal
marine environments, the Sr and Mg contents of fossil
carbonates are correlated, allowing these elements to
be used as indicators for the influence of continental
and marine waters (Renard 1986). Sr has been used as
a salinity indicator in Triassic lagoonal-reef systems
(Kranz 1976). The value of Na as a paleosalinity indi-
cator (Masaryk et al. 1993) is somewhat problematic
(Hardie 1987; Buggisch et al. 1994) but sodium is a
possible index to the salinity of diagenetic solutions.
• Recognizing paleowater depths (Shanmugam and
Benedict 1983).
• Differentiating low and high energy sediments, e.g.
low values in micritic lagoonal carbonates; high val-
ues in grainstones (Strohmenger and Dozet 1991).
Reefs and carbonate platforms
• Differentiating carbonate sediments formed in dif-
ferent parts of ancient reef complexes (Chester 1965;
Davies 1972; Flügel and Flügel-Kahler 1963; Matheos
and Morsch 1990; Oesterreich 1992).
• Differentiating inner and outer platforms (e.g.
Orehek and Ogorelec 1981).
Stratigraphy
• Assessing stratigraphic boundaries (Jorgensen 1981).
• Establishing chemostratigraphical correlations for
Mesozoic and Cenozoic pelagic carbonates based on
regional (and global) trace-element stratigraphy using
Sr and Mg contents (Renard 1986).
Primary mineralogy
• Recognizing the original mineralogical composition
of micrites and microspar. Sr and Mg concentrations in
micrites mimic the concentrations in the precursor ara-
gonite or Mg-calcite (Wiggins 1986), because these el-
ements are incorporated into calcite at equal rates dur-
ing diagenesis. During aragonite dissolution and cal-
cite precipitation Sr is excluded from aragonite and
builds up in solution. Phanerozoic micrites consisting
Long- and short-term paleoceanographic fluctuations
• The Sr content of pelagic carbonates varies with
time (Renard 1986). Long-term variations are influ-
