| dc.description.abstract | As one of the end-members of carbonate platform types, carbonate ramps have long been characterized and interpreted with regard to large-scale controls such as tectonics, sea level, climate, and biota. Yet, details on the impacts of oceanographic processes on facies patterns of ramps remains uncertain. To explore these understudied processes, this study examines carbonate ramp dynamics by integrating in situ field measurements, remote sensing data, and hydrodynamic modeling of the Holocene northeastern Yucatán Shelf, Mexico. The goal is to better understand the links between geomorphic and sedimentologic variability and the physical and chemical oceanographic forces of the nearshore areas of ramp systems. The results reveal how sediment production and accumulation are influenced by the complex interactions of the physical, chemical, and biological processes on the ramp. Upwelled, cooler nutrient-rich waters are transported westward across the ramp and concentrated along the shoreline by cold fronts, westerly regional currents, and longshore currents. This influx supports this transitional heterozoan and photozoan grain association. Persistent trade winds, periodic tropical storms and winter storms generate waves that propagate onto shoreface. This mixed energy, wave-dominated ramp system includes lagoon, barrier island, and upper shoreface geomorphic environments. Extensive shore-parallel sand bodies (beach ridges and subaqueous dune fields) of the high-energy upper shoreface and foreshore are composed of fine to coarse skeletal sand, lack mud, and includes highly abraded, broken and bored grains. The large shallow lagoon is also mixed energy, wave-dominated near the opening to the shoreface, transitioning to tide dominated in the more protected central and eastern regions. Lagoon sediment consists of Halimeda-rich muddy gravel and sand. Hydrodynamic forces are especially strong where bathymetry focuses water flow, as along the promontory and at the lagoon opening, and forming large subaqueous dunes. Explicit comparison with conceptual numerical models and other shoreface systems demonstrate the influences of hydrodynamics across a wider spectrum of settings. Results reveal that sediment transport patterns are determined by wave height and direction relative to the shoreface, and tidal forces locally control geomorphic and sedimentologic character. Similarly, the physical oceanographic processes that occur throughout the year (e.g. daily tides, episodic winter Nortes, and persistent easterly winds and waves) have more impact on ramp geomorphology and sedimentology than infrequent hurricanes. Overall, this study provides perspectives on how upwelling and nutrient levels, and hydrodynamic forces influence the varied geomorphic and sedimentologic character of the nearshore areas of this Holocene high-energy carbonate ramp system. These results also provide for more accurate and realistic conceptual models of the depositional variability for a spectrum of modern and ancient ramp systems. | |
