Paleogeographic Controls on Post-OAE 1a Carbonate Factory Recovery: A Texas-Sized Window into Patterns of Reestablishment in Shelf Settings

Ocean anoxic event (OAE) 1a had a profound effect on the productivity and health of carbonate factories at a global scale in the Early Aptian. Numerous studies have documented sedimentation changes within the OAE interval, but fewer have investigated the record of shelfal carbonate recovery following the event. This study provides a sedimentological perspective on the recovery of these systems on the Comanche Platform of Texas following OAE 1a, highlighting in particular the role of preexisting paleogeographic features in carbonate recovery. The James Limestone (Cow Creek Formation) preserves a record of the variable degrees of carbonate community reestablishment across the northern Gulf Coast. Recovery is illustrated by a slow increase in carbonate sedimentation rate driven by the initial establishment of a eutrophic community (e.g. oysters, echinoderms, and microbes), followed by faunal diversification. A review of multiple locales across Texas and the broader Gulf Coast reveals that recovery varied spatially and temporally. In most regions, “full” carbonate factory recovery (e.g., diverse fauna, photozoans, robust sedimentation rate) was not achieved, instead being limited to eutrophic faunas (oysters and algae) in the nearshore to mid-shelf realm. However, in some select regions a diverse productive photozoan fauna (e.g., coral and rudist reefs) was successfully established. These communities are observed in the mid-shelf realm on topographic highs (e.g. salt domes, arches, fault blocks), suggesting that oceanic conditions were optimal for carbonate reestablishment in the shallow-water realm of the mid-shelf, while the deeper seafloor of the mid-shelf extending up into nearshore inner shelf environments remained unsuitable.