Publication Date

2018-07-20

Availability

Open access

Embargo Period

2018-07-20

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Marine Geology and Geophysics (Marine)

Date of Defense

2017-06-13

First Committee Member

James S. Klaus

Second Committee Member

Donald F. McNeill

Third Committee Member

Peter K. Swart

Fourth Committee Member

André W. Droxler

Abstract

The diverse settings in which carbonate and siliciclastic sediments mix provides a challenge in developing predictive models of lithofacies distribution and sedimentologic heterogeneity. The skeletal carbonate and siliciclastic mud deposits of the Cibao Basin, in the northern Dominican Republic, are examined to better understand the dynamics of shelf sedimentation within a mixed-system and its diagenesis. The study examines the sedimentary components within the Gurabo Formation deposited during the late Miocene to early Pliocene. Deposition occurred during the time of a eustatic transgression known as the Zanclean Flood. This outcrop study examines the variations in the sediment grain composition through three shelfal depositional sequences. The advantage to these outcrops is that the majority of the lithofacies can be disaggregated, providing unusual grain-specific information. There is a mixing of carbonate and siliciclastic content within each of these sequences. In general, the bulk sediment within the transgressive cycles contained a greater abundance of quartz grains (fine sand and mud), and that of the regressive cycles were predominately skeletal carbonate grains. It is noteworthy that in this mud-dominated mixed system there was prominent reef development. The diagenetic susceptibilities within each of the depositional cycles differ due to changing hydrodynamic conditions. These conditions are likely more turbulent in transgressions than regressions (Mount, 1984). This creates a lithofacies distribution along the shelf that is not simply position-related, but must also be hydrodynamically considered due changing to physiographic and bathymetric conditions imposed through hydrodynamic cyclicity. In general, the transgressive cycles contained a greater abundance of quartz grains, and the regressive cycles were predominately comprised of skeletal carbonate grains. Diagenesis within this mixed-system was dynamic in that there was microbiologically-mediated marine precipitation of calcite cements within the siliciclastic-rich intervals to produce composite cemented grains. The carbonate-rich intervals experienced typical (tropical) meteoric diagenesis with dissolution of aragonite, and precipitation of secondary calcite and dolomite cements. Hydrodynamics were a key influence for the lithofacies changes along the shelf as described through transgressive and regressive cycles within the restricted shelf setting. The results of the sedimentology and geochemistry study comprise the necessary framework to illustrate the mixing of the components through temporal changes along the compressed shelf (~6 km wide inner shelf to outer shelf) tropical depositional system. This research along the inner to middle shelf provides a case study for the sedimentological dynamics within restricted water-circulation settings for carbonate-siliciclastic mixing, depositional lithofacies characterization, and the subsequent diagenetic tendencies therein.

Keywords

sedimentology; mixed-system; carbonate; siliciclastic; diagenesis; Miocene-Pliocene

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