NEW 87SR/86SR DATA FROM THE MARINE CARBONATE DEPOSITS OF THE PUCARÁ GROUP, PERU DURING THE TRIASSIC-JURASSIC TRANSITION

The chert and carbonate deposits of the Pucará group preserve continuous deposition of metazoan-rich marine sediments that are coeval with the time before, during, and after the end-Triassic mass extinction (ETE). The formations of the Pucará allow for a detailed examination of the effects of the ETE on the ecology of marine life in a depositional carbonate and glass ramp environment along the western edge of Pangea from the Rhaetian through to the Sinemurian. However a clear understanding of the location of the Triassic-Jurassic boundary is crucial to such an examination.

Here we present 87Sr/86Sr data from three stratigraphic sections of the Pucará, Cerro Toldo, Cerro Gavilan, and Tarmatambo, that have been previously described (Maxeiner 2020, Ritterbush et al. 2015, Rosas & Fontboté 1994) alongside concentrations of a suite of elements: Na, Mg, Al, K, Ca, Mn, Fe, Rb & Sr. Samples for this research were screened using cathodoluminescence and microscopy as a first approximation of diagenetic overprinting before being powdered and digested to be examined using an Inductively Coupled Plasma Mass Spectrometer. These analyses include material from the underlying Chambará, the middle Aramachay, and overlying Condorsinga formations within the Pucará group, spanning a time we propose to bracket the ETE, which is supported by 206Pb/238U derived dates from two ash deposits, 198.83 Mya for Cerro Toldo and 199.22 for Cerro Gavilan (Rosas et al. 2016). These data should help constrain the location of the extinction horizon allowing for more new and exciting ecological questions about the ETE to be answered.