MARINE SEPIOLITE IN MIDDLE PERMIAN CARBONATES OF SOUTH CHINA: IMPLICATIONS FOR SECULAR VARIATION OF PHANEROZOIC SEAWATER CHEMISTRY
Contributor(s)The Pennsylvania State University CiteSeerX Archives
Full recordShow full item record
AbstractABSTRACT: It is now widely accepted that the composition of seawater varied significantly during the Phanerozoic, and that the Mg/Ca ratio of seawater is a major factor in synchronized secular oscillations in the mineralogical composition of marine evaporites and nonskeletal as well as biogenic carbonates. However, the nature of the Mg sink is still subject to debate. We describe early diagenetic sepiolite from the Chih-sia Formation (middle Permian) of South China. The Mg incorporated in sepiolite likely was furnished by stabilization of high-Mg calcite, and silica was derived from siliceous fossils. Two factors facilitated the ac-cumulation of sepiolite in the Chihsia Formation. The first is a Chih-sian depositional environment of an intra-oceanic carbonate platform that lacked detrital terrestrial input, which enhanced the availability of biogenic silica for sepiolite formation. The second is the chemical composition of Permian seawater, as the precipitation of high-Mg cal-cite was aided by a high Mg/Ca ratio associated with an aragonite sea.