KOEPNICK, RICHARD B., and ROGER E. DENISON, Mobil Research and Development Corp., Dallas, TX

ABSTRACT: Variation in {87}Sr/{86}Sr of Permian Seawater: an Overview

The Phanerozoic seawater curve is marked by a dramatic decline and rise of {87}Sr/{86}Sr through the Permian and across the Permian-Triassic boundary. This abrupt decline and rise of {87}Sr/{86}Sr may record the last in a series of Paleozoic declines and rises that reflect a Paleozoic-style of plate interaction associated with the assembly of Pangea. Increased input of low-ratio Sr from mafic crustal sources contributed to the low Late Permian seawater values. Development of a new spreading center along the southern margin of the Tethyian embayment together with plate interactions and plate-margin volcanism increased both hydrothermal exchange of Sr between seawater and oceanic crust, and input of low-ratio Sr from mafic sources in plate-margin settings. Also, interior drainage and co tinental sedimentation on the Pangean supercontinent caused a decrease in the input of high-ratio Sr to the ocean. Rainfall, runoff, and chemical weathering appear localized along Pangean continental margins. Because these margins more likely contained sources of low-ratio Sr than Precambrian shield areas of the Pangean interior, preferential chemical weathering of continental margin terraines, lowered the {87}Sr/{86}Sr value of continental runoff. The subsequent increase in {87}Sr/{86}Sr of seawater from Late Permian to Early Triassic reflects return to a more normal supply of high-ratio Sr to the ocean from continental interiors. Ongoing erosion led to the "spillover" of sediment from interior basins, bringing high-ratio Sr to humid continental margins where chemical weathering release high-ratio Sr to the oceans.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.