HOW DO SHALLOW BIOGENIC CARBONATES RECORD WATER DEPTH CHANGE?

Sea level change will be one of the most devastating consequences of current and future warming. In order to understand how sea level could change in the future, we need to know how sea level has changed in the past in response to different climate and tectonic perturbations. Most of our archives of ancient sea level come from shallow-water biogenic carbonates because ice melts, paleoshorelines erode, and deep ocean isotope records get metamorphosed or subducted at plate margins. However, interpretations of how the sign and amplitude of sea level change can be translated from the architecture of carbonate stratigraphy remain controversial. We present new maps of bathymetry and biogenic carbonate facies from 3000 km² around northwest Andros Island (the Bahamas). The maps are generated by integrating multispectral satellite imagery, acoustic echosounder depth measurements, and quantitative grain size, mineralogy, shell-type, and shell δ¹³C-δ¹⁸O based facies determinations. Using Walther’s law and a probabilistic approach based on quantifying lateral facies transitions, we demonstrate how the current geographic distribution of water depth and sedimentary facies can be used to predict which stratigraphic sequences likely represent sea level change, and which sequences are indistinguishable from random processes such as tidal channel migration. Finally, we show how this framework based on observations from the modern geographic distribution of biogenic carbonates can be used to assign quantitative uncertainties to interpretations of sea level change in ancient stratigraphy.