Complexity of the Intra-MIS 5e Stratigraphic Record: Challenge to the One SL Pulse-One Cycle Model, West Caicos, Caicos Platform, BWI

Abstract

Detailed analysis of the Pleistocene-Holocene record on carbonate platforms highlights the distinctly non-uniform distribution of time of deposition as compared to time of exposure during high-amplitude, high-frequency cycles. New insights into the complexity of the stratigraphic record of Pleistocene icehouse carbonate cycles are now coming from detailed analysis of the intra-marine isotope stage (MIS) 5e record such as the exposures of the Caicos Platform, British West Indies. We focus on the spectacular exposures of West Caicos to illustrate the complexity of this apparently simple Last Interglacial (LIG) “parasequence” or “high-frequency cycle”. A combination of UAV-based decimeter-scale mapping of the 9 km long western coast of West Caicos, coupled with airborn lidar-guided interpretation of the total 20 sq km of the island has led to a high-resolution model of the evolution of the island beginning with MIS 9/11 carbonates (approx. 320 ka) and ending with late Holocene ooid ridge accretion. In particular, the MIS 5e deposits are resolved into an early (5e_1) reef-dominated record forming during an initial +3.5 m highstand, and a later (5e_2) section showing a maximum SL elevation of +5m. This MIS 5e_2 cycle is dominated by a combination of foreshore-shoreface grainstones on the west coast and shingled foreshore-dune-ridge strata on the east, northeast, and north coasts of the island. Remarkably, it is this second MIS 5e_2 pulse that we speculate took place during the 120-118 late MIS 5e rise that accounts for 40% of the total island record. This type of non-uniform time vs. preservation record is also observed on Providenciales as well as on other platforms such as San Salvador and New Providence. Such “bursts” of deposition challenge our understanding of the quantitative depositional record during an interglacial, further stressing the non-uniform time-space distribution of carbonates and calling into question models that use time-averaged accumulation rates.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017