87Sr/86Sr record of Permian seawater

A population of 169 Permian articulate brachiopod shells was analysed for their Sr-87/Sr-86 ratios. 51 of these, characterised as well preserved and stratigraphically well defined, are utilized for delineation of the Permian seawater strontium isotope trend. The Sr-87/Sr-86 curve shows values of about 0.7080 in the lowermost Permian (Asselian), followed by a gradual decline to 0.70685 in the Capitanian and a minor rise in the Dzhulfian and lower Dorashamian to values of 0.70715 just below the Permian-Triassic boundary. The Early Permian decrease in the strontium isotope curve that commences in the early Sakmarian is coincident with the advancing deglaciation of the Gondwana and with the increased aridity in large parts of the Pangaea. These factors may have led to a reduced continental weathering of Rb-rich silicate rocks, and thus to the decline in seawater Sr-87/Sr-86. Starting with the Artinskian, the opening of the Neotethys and the associated widespread basaltic volcanism supplied low radiogenic strontium to seawater from an enhanced hydrothermal flux. In the Capitanian, basaltic volcanism in the entire Palaeotethys ceased and this may have been the reason for a slightly more radiogenic, seawater isotopic composition during the Lopingian. Higher input of riverine Sr due to expansion of humid areas may have been a contributory factor. (c) 2006 Elsevier B.V. All rights reserved.