Identifying depositional environments of chert using chemical techniques: An overview of general principles and a synthesis of 45 published results
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5591374
- Univ. of Rhode Island, Narragansett, RI (United States). Graduate School of Oceanography
Chemical approaches have their own limitations, reflecting analytical and interpretational constraints (due to the extremely high Si concentrations), as well as the potential for diagenetic resetting of the environmental signature. The effect of diagenesis is non-recoverable; for example, chemical fractionation during chert formation strictly precludes use of Si, Ca, Mg, P, Mn, Sr, and Ba, due to their affiliations with unstable biogenic phases. Thus, in many cases there are discouragingly few elements from which to choose an appropriate set of chemical criteria. The author has synthesized published results of major, trace, and rare earth element (REE) data from 45 chert sequences from Early Paleozoic to Neogene continental margin, pelagic, and ridge-proximal environments. The author presents a set of depositional criteria that allow for the analytical and diagenetic limitations inherent to the chemistry of chert, and which should be applicable to cherts regardless of their age, local diagenetic history, or tectonic region. Major element ratios, capitalizing on the affiliations of Al and Ti to terrigenous matter and of Fe to metalliferous input, yield reasonable criteria for distinguishing continental margin from ridge-proximal sedimentation, but cannot delineate pelagic deposition. Trace element data indicate that Zr and Cr in continental margin cherts are significantly lower than would be expected from their affiliation with detrital heavy minerals, and seem on average similar to values from pelagic and ridge-proximal cherts. Intra-REE ratios (e.g., the Ce anomaly) resolve all three depositional regimes and are independent of diagenetic modification.
- OSTI ID:
- 5591374
- Report Number(s):
- CONF-921058--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
- Country of Publication:
- United States
- Language:
- English
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