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Oceanographic Controls on Sedimentology and Geomorphology of High-Energy Ramps: Integrated Field and Modeling Analysis of Holocene Shallow Marine Carbonates, Northeastern Yucatan, Mexico

Abstract

Many ancient carbonates deposited in ramps form prolific hydrocarbon reservoirs. Although the sequence stratigraphy of such successions is well-documented, the complex processes controlling sedimentologic variability and facies patterns are less well understood. This project tests the hypothesis that hydrodynamics and bathymetry directly influence sediment characteristics (size, sorting and type) and geomorphology of carbonate ramps. To develop more rigorous predictive conceptual models for the sedimentation and dynamics of carbonate ramps, this study describes field and lab observations of surface sediments with oceanographic models of the northeast coast of the Yucatan Peninsula, Mexico. This distally steepened Holocene carbonate shelf includes a long (30 km) and narrow barrier island, bordered on the north by the broad, gently dipping homoclinal Yucatan ramp with a large protected muddy lagoon (300 km2) to the south. Nine transects (5 to 10 km) with over 200 sediment samples show systematic shore-parallel spatial patterns of bottom and sediment type. Although the study area is within the tropics and lacks siliciclastic influx, heterozoan association sediment (bivalves, gastropods, echinoderms) dominates the shoreface with minimal photozoan association sediment (no ooids, scattered corals and green algae). The westward flowing Yucatan current brings in colder and more nutrient-rich waters along the coastline and likely is responsible for the dominance of heterozoan association sediment. To study the oceanographic controls (tides, wind, waves, and currents), two Acoustic Doppler Current Profiler meters measured in-situ wave, tide and current data from mid-February to mid-March 2014. This information, along with NOAA ocean model data and a recent bathymetric survey, provide the data to construct numerical hydrodynamic models analyzing the impact of a range of oceanographic processes on sediment transport pathways. Results show this high-energy ramp system is directly impacted by waves and swell from periodic large offshore storm events (> 2.5 m significant wave height); tides are micro-tidal and play a subordinate role in sediment transport. Wave and wave-driven currents likely are the primary oceanographic control on sedimentological spatial variability for this system. Overall, these results provide insights into fundamental sedimentological processes and can be useful analogs for ancient carbonate ramps.