| dc.description.abstract | A 2-dimensional coastal exposure of the Miocene-age Rellana carbonate platform (Cabo de Gata Region, Southeast Spain) provides an opportunity to study the facies and stratigraphy, determine the processes controlling deposition, and reflect on how those processes are expressed in associated basinal deposits. The platform developed on Neogene volcanic substrate that features a drainage divide separating a steep-dipping (~20°) south slope from a shallow-dipping (~5 °) north slope. The north slope steepens distally to 25° (1.3 km N of the drainage divide) before flattening as it eventually reaches the basin floor, defining the margin of the Agua Amarga basin. The Rellana platform formed a rim above the Agua Amarga basin for approximately 8 km and was a major source for carbonate accumulations. The steep southern slope is down dip and laterally equivalent to similar deposits on Ricardillo Peak across the San Pedro Embayment. Seven depositional sequences (DS1-7) comprising 13 facies are identified on the platform. Earliest carbonate deposition (late Tortonian) is restricted to the lowest elevations on the southern end of the platform (DS1a and b). These topography-filling and volcanic-basement- onlapping deposits contain predominantly heterozoan skeletal facies, suggesting a temperate climate during early platform development. Overlying carbonate strata (DS2) demonstrate continued ramp-dominated deposition on both sides of the drainage divide. These deposits feature an upward-increasing abundance of photozoan skeletal components, culminating in the preservation of detrital Tarbellastraea framestone. The third depositional sequence (DS3) contains abundant photozoan reef deposits that suggest a shift to sub-tropical/tropical climate. Reef development during this sequence is pronounced, and the shallow dip of the northern slope facilitated reef progradation during periods of stillstand and relative sea-level fall. While the steeply dipping southern slope DS3 deposits consist predominantly of fore-reef slope deposits punctuated by periods of reef growth. The uppermost carbonate deposits (DS4-7) consist of oolitic, microbial and local Porites reefs that were deposited in normal-to-restricted marine conditions associated with four high-frequency relative fluctuations in sea level. These deposits are interpreted to represent the terminal carbonate complex (TCC) that is well documented throughout the region. Comparison of the Rellana Platform area stratigraphy with that of Ricardillo Peak, San Pedro Embayment, and La Molata platform within the Rodalquilar Caldera to the southeast, provides a more regional view of the potential controls on carbonate development in the Cabo de Gata area. Results show that the paleoclimatic, paleotopographic and sea level history controls identified in the Rellana Platform area are consistent throughout the Cabo de Gata region, however, paleogeographic effects were also very influential on carbonate development, and responsible for observed variability between the study areas. Finally, in the third chapter, the Rellana Platform and Agua Amarga Basin are examined with the intention of testing predictive hypothesis regarding platform and basin sedimentary processes. Basinal deposits consist of grainy heterozoan-dominated shallow-water deposits, hemipelagic and pelagic deep-water deposits, carbonate/volcanic sedimentary breccias, as well as high- and low-density turbidites. Analysis of the distribution of the basinal breccias within the Agua Amarga basin demonstrates that the evolution of the Rellana platform had an effect on sediment dispersal into the Agua Amarga basin. During the platform reef phase, the initial reef margin was near the steep basin margin, and sourced coarse breccias into the basin. During a subsequent sea-level rise, the reef margin stepped backward resulting in backstepping of basinal breccias and an increase in fine-grained basin deposits. Highstand reef progradation towards the basin margin resulted in an increase of coarse-grained, mostly sediment gravity flow deposits in the basin. As sea level fell, reefs continued to prograde and downstep toward the basin, resulting in increasing amounts of coarse-grained basinal deposits, including breccias, that progressively stepped toward the basin center. Our results show that proximity of the reef margin to the basin margin increases the volume of coarse material deposited in the basin. Typical depositional models for resedimented deepwater carbonates fail to reflect the impact of platform topography on sediment redistribution. Our results challenge the highstand shedding model for this setting, suggest an alternative model that reflects observed platform and basinal characteristics, and identify platform paleotopographic controls that influence basinal deposition of coarse debrites in distally steepened ramp systems. | |
