Abstract:

The Red Sea boasts a ~4000km long fringing reef system that lines the desert shores of Egypt, Israel, Jordan, Saudi Arabia, Yemen, Djibouti, Eritrea, and Sudan and represents Earth’s best example of mixed carbonate-siliciclastic sedimentation in an active rift basin. The upland side of the shoreline comprises ephemeral desert stream systems (wadis) that collectively drain >500,000 km² of mountainous drylands and deliver siliciclastic sediment to the coast in episodic flash floods. The near-total absence of land plants and clear water column makes the region ideal for combined land-marine remote sensing applications. This study uses topographic (JAXA, TanDEM-X), bathymetric (GEBCO, multibeam) and field (outcrop, submersible) datasets to assess feedbacks between desert hinterland surface processes, coastal carbonate ecology, and Quaternary climate/sea level cycles that facilitate sediment transfer, mixing/partitioning, and deposition in a steep arid rift setting.

Along the Egyptian and Saudi Arabian margins of the northern Red Sea the near-absence of a continental shelf forces the photozoan-dominated carbonate factory to hug the siliciclastic-dominated coast. The broadest areas of carbonate shelf sedimentation occur on the subaqueous portions of siliciclastic fan deltas adjacent to the largest wadi catchments and can be more than 3 orders of magnitude wider than the shelf average. These fan deltas build shallow shelf infrastructure needed for photozoan ecosystem proliferation. In response, reef growth influences siliciclastic sediment transfer to the basin by 1) increasing confinement and effective depth of submarine canyon heads by aggrading canyon walls to sea level or 2) by plugging submarine canyon heads associated with inactive wadi systems. In the latter case siliciclastic transfer to the basin is altered or barred due to obstructions created by immobile reefs that reroute siliciclastic sediment into littoral cells or trap it in backreef lagoons.

Continuous topographic-bathymetric profiles were created by combining elevation gradients of longest streams in wadi catchments with projected linear bathymetric profiles from GEBCO data or, where available, digitized thalwegs associated with submarine canyons identified in multibeam data. In regions characterized by a relatively broad continental shelf knickpoints develop at or near the -120m bathymetric contour consistent with location of the composite Pleistocene lowstand shoreline. These relatively broad shelf areas effectively choke siliciclastic sediment transfer in contrast to regions with a relatively narrow or absent continental shelf where knickpoints migrate upstream into active wadi channels and promote direct bypass of the shelf during flash floods.  In regions where wadis become distributary before reaching the coast they deposit amalgamated fan deltas that source a line-fed slope system in contrast to steep, erosion-dominated profiles that source a direct fed slope system characterized by canyons, ridges, and submarine fans. Depending on location multiple wadi channels combine to feed a single submarine canyon or a single wadi channel may alternate through time as a feeder for multiple discrete submarine canyons.

The apparent feedbacks between carbonate and siliciclastic deposition in the study area call into question long held paradigms regarding a universally suppressive impact of siliciclastic influx on carbonate deposition and instead suggests that, at the basin scale, influx of intermittent high siliciclastic loads may be critical for carbonate shelf expansion in rift basins or other steep and deep mixed settings. Likewise, this study highlights the overlooked influence carbonate frame builders can have on siliciclastic sediment routing and underscores the importance of tectonic and climatic setting for linking terrigenous and marine processes in mixed depositional settings.

Bio:

I am from the United States where I earned a B.S. in Geology from St. Lawrence University and an M.S in Geology from Idaho State University before spending 4 years in the Carbonate Stratigraphy and Reservoir Systems group at the ExxonMobil Upstream Research Company. While working in industry I was responsible for integrating sequence stratigraphic concepts from subsurface datasets and outcrop analogues with static petrophysical data and dynamic engineering data to improve subsurface models for supergiant carbonate oil and gas fields in the Middle East. In 2017 I left ExxonMobil to pursue a PhD at the University of Texas at Austin under Dr. Charlie Kerans where I focused on relative influences of tectonic and glacioeustatic processes on shaping Late Paleozoic and Pleistocene carbonate platforms. My recent and current work uses combined remote sensing and field data to investigate how interactions between Earth’s various subsystems are recorded in carbonate and mixed carbonate-siliciclastic settings with the goal of improving predictive concepts.