Geochemical changes across a marginal marine Permo-Triassic boundary section on the Adria carbonate platform at Brsnina, Slovenia

Abstract

The Brsnina Permian–Triassic nearshore marine sediments were deposited on the Adria carbonate platform in tropical latitudes at the western end of the Neotethys Ocean. Continuous channel samples across the boundary show no consistent change in element or element/Al ratios, except that most element/Al ratios increase in the top 0.5 m of the Permian strata. Though there are sporadic higher values of some element/element ratios, such as Ti/Zr, Th/Sc, Zr/Sc, Cr/Ni, Y/Ni, Co/Th, Cu/Zn, and Nb/Ta, La/Sc, the overall geochemistry indicates that the sediments were derived from dominantly silica-rich continental rather than silica-poor sources though with some more silica-poor inputs at times. Sporadic high Ti/Zr ratios indicate periods of increased aridity, but no overall increase across the boundary. Various geochemical redox proxies suggest mainly oxic depositional conditions, with episodes of anoxia, but with little systematic variation across the boundary. Geochemical proxies for productivity indicate little change up the section with values two orders of magnitude less than elsewhere. The lack of consistent element geochemical changes across the boundary accompanied by significant C, S, and other isotopic changes suggests that atmospheric and oceanic chemical variations drove the Permian–Triassic boundary environmental changes at least on the sabkha environments of the tropical Adria platform.