HYDRODYNAMIC INFLUENCES ON SEDIMENTOLOGY OF A HIGH-ENERGY HOLOCENE CARBONATE RAMP: NORTHEASTERN YUCATAN, MEXICO

Although the geological record includes numerous carbonate successions deposited in ramp-like settings, due to a paucity of modern analogs, controls on sedimentologic variability on ramps have remained enigmatic. To characterize carbonate ramp systems in general, and to better understand the sedimentary dynamics and accumulations of a Yucatan shelf Holocene ramp system in particular, this project tests two hypotheses: 1) sediment size, sorting and type varies with geomorphic position on the ramp; 2) hydrodynamics and bathymetry control directly influence sediment characteristics and accumulation. Understanding the variability in hydrodynamic and sedimentologic conditions of carbonate ramps is important for constructing actualistic depositional models of variability within these systems, many of which provide important hydrocarbon resources (e.g., Permian, West Texas; Jurassic, Middle East).

Analysis of nine transects (5 to 10 km) with over 200 total sediment samples captures the range of variability of sediment size, sorting, type and abundance within the upper shoreface, foreshore, and lagoon environments and show shore-parallel zones of sediment and bottom type. Although the study area is tropical and lacks silicilastic influx, heterozoan association sediment dominates with minor photozoan association sediment (no ooids, scattered corals and green algae).

Complex hydrodynamic forces (tides, waves, and currents) and the bathymetry influence the deposition of sediments. In-situ measurements from two Acoustic Doppler Current Profiler meters, 30 years of spectral hind-cast wind and wave data, and bathymetric data provide the foundation for constructing numerical hydrodynamic models to analyze the impact of a range of hydrodynamic processes on sediment transport pathways (processing ongoing). The oceanward flank of this shoreface is directly impacted by waves and swell from periodic large offshore storm events per year (> 2.5 m significant wave height); tides play a subordinate role in sediment transport. Ultimately, wave and wave-driven longshore currents likely are the primary hydrodynamic control on sedimentological spatial variability for this system, and may have analogs in ancient high-energy carbonate ramp systems.