--> The Impact of Paleotopography on Transport of Reef Carbonates to Basinal Settings: Lessons From the Upper Miocene of SE Spain

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

The Impact of Paleotopography on Transport of Reef Carbonates to Basinal Settings: Lessons From the Upper Miocene of SE Spain

Abstract

Depositional models for resedimentation of reefal carbonates to deep water typically do not consider the impact of substrate topography. The Cabo de Gata region in SE Spain is known for 3D exposures of Miocene reefal carbonates on substrate with mappable paleotopography. The Las Negras area was a Miocene archipelago setting during reef development. When steep-sided volcanic slopes (>15 degrees) were in shallow water, processes of bypass dominated. Initially, fringing reefs developed on the steep slopes, but steep slopes and relative sea-level falls promoted transport to deep water, without preservation of reefs in place. This resedimentation served to subdue paleotopography downslope and created some substrates with gentle slopes (<15 degrees). When shallow water intersected these areas, reef complexes with aggradational, progradational, and downstepping geometries were preserved, indicating preservation of much of the sea-level cycle. An area to the north of Las Negras shows an extensive platform (La Rellana) that developed on the southwest margin of the Agua Amarga basin. Most of this platform developed on a ~ 5 degree basinward dipping substrate slope that traces for 1.3 km towards the basin. The substrate slope then steepens to 25 degrees (basin margin) and flattens as traced into the basin (Sweeney, 2016). This substrate topography is similar to topography generated on a distally steepened ramp. During lowstand and initial transgression, when shallow water intersected the 25-degree basin-margin-slope and distal part of the 5-degree surface, reefal debris was bypassed into the basin. With continued sea-level rise, the reef margin stepped back 1.3 km from the basin margin. During highstand and falling stage, reef complexes were preserved in place and the coarsest resedimented material was trapped on the 5-degree surface; mostly fine-grained turbidites and hemipelagics were deposited in the adjacent basin. As the reef margin prograded and downstepped during the falling stage, coarse resedimented material was bypassed into the basin when the reefal margin reached a position of 0.4 km from the steep basin margin, and dropped below it. The greatest resedimentation of coarse material occurred during falling stages, lowstands, and early transgressions. These results contrast with the highstand shedding model, and may apply to carbonate systems characterized by substrates that show a transition from a low-angle basinward slope to distal steepening.