Carbon and oxygen isotope curves for the Oxfordian of Central Poland

Abstract

Delta-13-carbon and delta-18-oxygen values are recorded in brachiopod shell material covering the almost complete succession of the epicontinental Oxfordian in Central Poland. A positive intercorrelation of the carbon and oxygen isotope curves is recognized. The high carbon isotopic ratio suggests the Oxfordian was a time of overfed ocean conditions in the study area, when put in terms of the overfed-to-hungry ocean fluctuation model. In the Upper Oxfordian, precisely in the Bimammatum and the lower Planula Zones, a distinct discrepancy in the magnitude of the carbon and oxygen isotopic shifts is correlated with two invasions of the Boreal fauna, and hence possible inflows of less saline waters from the hydrochemicalIy distinctive Boreal Realm.