Triassic-Jurassic (T-J) boundary successions record a paucity of carbonate in association with the mass extinction. Here we demonstrate that three globally disparate T-J sections contain volumetrically important early diagenetic carbonate, i.e., carbonate formed soon after deposition of the sediment but commonly ignored as secondary, that contains information about the extinction and may constitute a previously unrecognized pathway in the carbon cycle. Petrographic analyses of unusual carbonate fans from three sites reveal that they grew just below the sediment-water interface, nearly concomitant with primary sediment deposition. Thus, the shallow subseafloor can be a carbonate sink of unknown size, and may be a predictable consequence of ocean acidification where carbonate precipitation first returns within the sediment before recovering in the water column.
Greene S. E., Bottjer D. J., Corsetti F. A., Berelson W. M. & Zonneveld J.-P., in press. A subseafloor carbonate factory across the Triassic-Jurassic transition. Geology. doi: 10.1130/G33205.1. Article (subscription required).
