--> Abstract: Sequence Stratigraphic Model for the Oligocene-Miocene, Land-Attached Mixed Carbonate-Siliciclastic System of Guanica Harbor, Southwestern Puerto Rico, by Stephen E. Kaczmarek, Cyd Ruidiaz, Toni Simo, Hernan Santos, Shawn Fullmer, Wilson Ramirez, Franek Hasiuk, Gregor Baechle, and Sean Guidry; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Sequence Stratigraphic Model for the Oligocene-Miocene, Land-Attached Mixed Carbonate-Siliciclastic System of Guanica Harbor, Southwestern Puerto Rico

Stephen E. Kaczmarek1; Cyd Ruidiaz2; Toni Simo1; Hernan Santos2; Shawn Fullmer1; Wilson Ramirez2; Franek Hasiuk1; Gregor Baechle3; Sean Guidry4

(1) ExxonMobil Upstream Research Company, Houston, TX.

(2) Department of Geology, University of Puerto Rico, Mayaguez, Puerto Rico.

(3) ExxonMobil Production Company, Houston, TX.

(4) ExxonMobil Exploration Company, Houston, TX.

The Oligocene-Miocene outcrops of southwest Puerto Rico offer an opportunity to study the stratal architecture of a land-attached carbonate shelf and test models of mixed depositional systems. Measured stratigraphic sections were correlated on geo-referenced photopans. Rock samples were collected for petrographic analysis, 87Sr/86Sr, and biostratigraphy age dating. Porosity and permeability were measured on plugs to characterize rock properties. Gamma-ray and sonic data were collected in the field to capture petrophysical trends and differentiate lithologic units. The research program provides a 3-D (2 km x 4 km x 200 m) view of the stratigraphic complexity of the system. The outcrops are composed of two main depositional sequences of Oligocene (Chattian) and Mid-Miocene age that are separated by a tectonically enhanced unconformity displaying erosional truncation and onlap. The Oligocene succession has a maximum thickness of 140 meters and exhibits a transition from a low angle mixed carbonate-siliciclastic ramp with variable facies distribution to a steep margin with distinct back reef, margin, and slope facies. The lower strata within the Oligocene unit are characterized by alternating layers of fine-grained siliciclastic sediments and coral-rich carbonates. Internal architecture in the upper part of the Oligocene unit is composed of three high-frequency sequences characterized by (1) progradation, (2) backstepping and (3) further progradation. The Oligocene section is marked by distinct intervals exhibiting high gamma-ray values due to an abundance of volcanic rock fragments. The Miocene carbonate succession shows a progressive onlap of the Oligocene succession and consists of stacked higher-frequency sequences with near-shore environments grading into platform interior facies. The Miocene section has a maximum thickness of about 50 meters and contains no volcaniclastics. Our observations suggest that in addition to variations in eustatic sea level, tectonics and paleo-topography strongly influence the architecture and composition of the depositional system. The depositional model provides new insights about the interactions within a mixed system, and illustrates the effects of accommodation on stratigraphic architecture. Furthermore, this study highlights an industry/academic collaboration in which field-based data are used to provide a multidimensional view of seismic-scale outcrops in terms of depositional and reservoir quality-related parameters.