Anomalous Carbonate Precipitates: Is the Precambrian the Key to the Permian?
View/ Open
Publisher's version--dark file (2.453Mb)
Access Status
Full text of the requested work is not available in DASH at this time ("restricted access"). For more information on restricted deposits, see our FAQ.Published Version
https://doi.org/10.2307/3515096Metadata
Show full item recordCitation
Grotzinger, John P., and Andrew H. Knoll. 1995. Anomalous carbonate precipitates: is the precambrian the key to the permian? Palalios 10(6): 578-596Abstract
Late Permian reefs of the Capitan complex, west Texas; the Magnesian Limestone, England; Chuenmuping reef, south China; and elsewhere contain anomalously large volumes of aragonite and calcite marine cements and seafloor crusts, as well as abundant microbial precipitates. These components strongly influenced reef growth and may have been responsible for the construction of rigid, open. reefal frames in which bryozoans and sponges became encrusted and structurally reinforced. In some cases, such as the upper biostrome of the Magnesian Limestone, precipitated microbialites and inorganic crusts were the primary constituents of the reef core. These microbial and inorganic reefs do not have modern marine counterparts; on the contrary, their textures and genesis are best understood through comparison with the older rock record, particularly that of the early Precambrian. Early Precambrian reefal facies are interpreted to have formed in a stratified ocean with anoxic deep waters enriched in carbonate alkalinity. Upwelling mixed deep and surface waters, resulting in. massive seafloor precipitation of aragonite and calcite. Luring Mesoproterozoic and early Neoproterozoic time, the ocean became more fully oxidized, and seafloor carbonate precipitation was significantly reduced. However, during the late Neoproterozoic, sizeable volumes of deep ocean water once again became anoxic for protracted intervals; the distinctive ''cap carbonates'' found above Neoproterozoic tillites attest to renewed upwelling of anoxic bottom water enriched in carbonate alkalinity and C-12. Anomalous late Permian seafloor precipitates are interpreted as the product, at beast in part, of similar processes. Massive carbonate precipitation was favored by: I) reduced shelf space for carbonate precipitation, 2) increased flux of Ca to the oceans during increased continental erosion, 3) deep basinal anoxia that generated upwelling waters with elevated alkalinities, and 4) further evolution of ocean water in the restricted Delaware, Zechstein, and other basins. Temporal coincidence of these processes resulted in surface seawater that was greatly supersaturated by Phanerozoic standards and whose only precedents occurred in Precambrian oceans.Citable link to this page
http://nrs.harvard.edu/urn-3:HUL.InstRepos:3190367
Collections
- FAS Scholarly Articles [18258]
Contact administrator regarding this item (to report mistakes or request changes)