A BAYESIAN AGE-DEPTH MODEL FOR THE SILURIAN ALTAJME CORE, GOTLAND, SWEDEN

Age-depth models play a pivotal role in the investigation of environmental changes throughout Earth history as a way to provide rates of change in stratigraphic data. There are two approaches in creating an age-depth model: “classical” (e.g., linear regression, splines) and Bayesian approaches. Classical models often result in constant or near constant sedimentation rates between dated levels. Furthermore, classical methods often erroneously assume extremely small age uncertainties between dated levels. Over the past decade, a Bayesian-Markov Chain Monte Carlo (Bayesian-MCMC) modeling approach has become prevalent. Taking a Bayesian-MCMC approach to age-depth modeling addresses these issues. Bayesian-MCMC models can help to capture the variations in sediment accumulation rates as well as provide more realistic uncertainty estimates in accumulation rates between dated levels in a given stratigraphic section.

Here, we apply these methods to the Silurian succession preserved in the recently drilled Altajme Core from Gotland, Sweden. This core contains strata spanning from the Hirnantian Stage (Upper Ordovician) to at least the Homerian Stage (Wenlock Series, Silurian System). The presence of more than 20 bentonites preserved in the core, including three of which have been previously dated using high-precision CA-ID-TIMS U-Pb from zircons from outcrops on Gotland, provide an ideal opportunity to develop a Bayesian-MCMC age-depth model for this core. Such a refined age-depth model will allow the first statistically supported demonstration of the duration of two major biogeochemical events that took place during the Wenlock Epoch, namely the Ireviken and Mulde extinctions and global carbon cycle perturbations.