--> --> Abstract: Characterization of Onlapping Reef Sequences: Dominican Republic Drilling Project, by James S. Klaus, Donald F. McNeill, Albertus Ditya, Yula Hernawati, Gregor P. Eberli, and Peter K. Swart; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Characterization of Onlapping Reef Sequences: Dominican Republic Drilling Project

James S. Klaus1; Donald F. McNeill2; Albertus Ditya2; Yula Hernawati2; Gregor P. Eberli2; Peter K. Swart2

(1) Geological Sciences, University of Miami, Coral Gables, FL.

(2) Marine Geology and Geophysics, University of Miami - RSMAS, Miami, FL.

Coral reefs present special challenges for geological and geophysical studies. Reefs are often comprised of disparate carbonate facies in unpredictable and complex three-dimensional arrangements. Furthermore, the petrophysical attributes of reefs can be highly variable at small spatial scales within facies. During high-frequency sea level cycles these challenges can become compounded by the formation of onlapping parasequences and iterative phases of diagenetic alteration. The Plio-Pleistocene reefs of the southern Dominican Republic (DR) provide a unique opportunity to study the complex three-dimensional architecture and resulting petrophysical attributes of reefs during a period of high frequency sea level oscillation and superimposed sequential diagenesis. A combination of core borings and outcrops are used to evaluate the coral-rich clinothems that form a series of onlapping parasequences. Nine new core borings, over forty outcrop cores, and numerous outcrop samples document the facies within five different depositional events ranging from the late Pliocene to Pleistocene. The uplifted southern coast of Hispaniola exposes several terraces that consist of low-angle (5-7° foreslope, ~1° topset) clinoform (sigmoidal) deposits composed of skeletal sand, coral debris, and in situ framework. Petrophysical measurements (Vp, Vs) of cylindrical miniplugs (2.5 cm in diameter) from characteristic lithologies of different depositional and diagenetic environments provide preliminary characterization of the inherent variability seen in the DR reef rocks. Vp measurements are typically above values predicted by Wyllie’s time average equation. This likely due to the pervasive micritic cementation, and increased grain-grain contacts observed in the samples analyzed to date.