4 Sep (GEOL) Jonathan Husson, Stratigraphy and Biogeochemistry

Speaker: Jonathan Husson, University of Victoria, Canada 

Title: Constraints on the geologic CaCO₃ cycle across Earth history: a data synthesis approach 

Time: Thu, 4 Sep, 4:30pm EDT 

Location: Exploratory 1309 and via Zoom (for link, email lhinnov@gmu.edu) 

Host: Linda Hinnov 

ABSTRACT: On geological timescales, the total quantity of carbonate sediment deposited on Earth's surface is determined by chemical weathering fluxes and the input of alkalinity to the global ocean. Where this buried carbonate is sequestered, however, is sensitive to biologic, tectonic and climatic boundary conditions that have changed across Earth history. The locus of carbonate burial is important because (for example) carbonate on the deep sea floor helps to buffer the ocean during transient CO₂ pulses and ocean acidification, and also contributes to volcanic CO₂ fluxes when subducted. Direct evidence arguing for (or against) carbonate burial in deep ocean basins is not available for time periods older than ~200 million years ago, due to the lack of preserved oceanic crust. Here we use paleogeographic models, the Macrostrat database and geologic maps to describe the age and quantity of carbonate in continental sediments to address this question. Our results indicate that the locus of carbonate deposition has likely changed over time, from primarily oceanic crust over much of the Precambrian to primarily continental crust over much of the Paleozoic, returning in large part to the deep sea after the evolution of pelagic calcifying organisms in the early Mesozoic. Notably, we find evidence to suggest that most, if not all, of the global alkalinity flux could have been trapped on the continental crust during the Paleozoic, leaving the deep sea floor depleted in carbonate sediment. Progressive subduction of carbonate-laden Precambrian sea floor during the Paleozoic, and its replacement by carbonate-depleted sea floor, likely contributed to declining CO2 influx over this era and may have accentuated the effects of environmental perturbations at the end of the Paleozoic.