Complex Patterns of Carbonate Sediment Deposition and Accretion Controlled by Suborbital Sea-Level Oscillations
Jackson, Kelly L.; Eberli, Gregor; Reid, Samuel B.; Harris, Paul (Mitch); Maier, Katherine L.; McNeill, Donald F.
Suborbital sea-level oscillations during highstands produce complex facies juxtapositions and patterns of lateral accretion in coastal carbonate systems. Because these oscillations occur on timescales of just a few thousand years they enable the lateral accretion of shoal systems that a single sea-level rise could not achieve. Antecedent topography from older sea-level oscillations and the repetition of sea-level oscillations during each subsequent highstand produces antecedent topography that further complicates the stratigraphic architecture.
Sea level oscillated up to 15 m during last interglacial highstand (MIS 5e) 115-125 ka ago and is the driving force of deposition and accretion of carbonate sediments in locations like Great Bahama Bank where the modern water depth is 8 m or less. The Exuma Cays and New Providence, Bahamas, feature stacked successions of carbonate grainstones that display complex patterns carbonate sediment deposition and accretion. While the backbone of these islands formed during MIS 9-11, the majority of accretion occurred during MIS 5e when sea level was + 7 m above present during early substage 5e, oscillated up to 15 m, and rose again to form the late substage 5e. Further island accretion took place in the Holocene 4-6 ka ago in the Exuma Cays with the development of windward margin dune and beach facies forming one carbonate cycle. Sea level has since transgressed and is now forming a second cycle with the deposition of modern sediments.
Field mapping and ground-truthing of satellite imagery of the Exuma Cays documents the patterns of Pleistocene and Holocene sediment deposition and accretion. Fourteen cores to a maximum depth of -23 m drilled in the Exuma Cays spanning ~100 km northwest to southeast document the vertical architecture featuring overstepping wedges prograding eastward towards Exuma Sound. Recognition of suborbital sea-level oscillations during highstands explains complex facies patterns observed on New Providence and the Exuma Cays and might explain laterally extensive shoal complexes in the ancient.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013