EVIDENCE OF RECENT FLOOD DEPOSITSITION WITHIN A DISTAL SHELF DEPOCENTER AND THE IMPLICATIONS FOR TERRESTRIAL CARBON PRESERVATION IN NON-DELTAIC SHELF SETTINGS

Extreme episodic events have the capacity to transport large amounts of terrestrial material to the coastal ocean. While estuaries and deltas are typically thought to be the primary sink for this material, some of this material escapes these coastal features and is transported to distal depocenters along the continental shelf. These distal shelf depocenters can act as the ultimate sink for these event deposits, yet event sedimentation and the impact of terrestrial carbon burial within these shelf deposits remains understudied. Therefore, this study investigated event sedimentation within the Texas Mud Blanket (TMB) a distal shelf depocenter for the Brazos River located in the northwestern Gulf of Mexico. Using a core that was collected from the TMB during a months-long elevated discharge event in late 2015-early 2016 we applied a multi-proxy approach to delineate the event deposit. We utilized physical sediment properties (fabric, texture, and bulk density), radioisotopes (⁷Be and ²¹⁰Pb), and organic geochemical properties (𝛅13C and lignin-phenols) to identify at 10 cm thick event layer at the surface of the core. From this layer we interpret a depositional sequence where the base of the deposit is characterized by the initial event pulse overlain by remobilized flood sediment that was initially deposited proximal to mouth and re-worked over the subsequent months. Using the event layer characteristics, we identified three other potential event deposits in the core that we have attributed to events in 2010, 2007, and 2001. From these results, this study has demonstrated that the TMB can be an archive for Brazos River event sedimentation, that drought-flood sequences in succession improve event-layer preservation potential, and that distal depocenters are important sites of long-term carbon burial. Ultimately this study highlights the potential for distal shelf depocenters as potential organic carbon burial “hotspot,” and postulates that this role may increase in the future as climate change increases the intensity and frequency of extreme events.