Publication Date

2011-12-09

Availability

Open access

Embargo Period

2011-12-09

Degree Name

Master of Science (MS)

Department

Marine Geology and Geophysics (Marine)

Date of Defense

2011-10-28

First Committee Member

Peter K. Swart

Second Committee Member

Gregor P. Eberli

Third Committee Member

James S. Klaus

Abstract

Four prograding reef terraces (6, 15, 30, and 50 m) have been repetitively exposed to marine and freshwater alteration during the Pliocene and Pleistocene periods. Prolonged freshwater alterations have resulted in many diagenetic overprints that obscure early diagenetic products. This study investigates the sequence of the diagenetic processes and products in the terrace deposits using five long cores and 14 short cores taken from these different reef terraces. The lithologic changes in the cores were documented for reconstruction of the original depositional frameworks prior to embarking on a diagenetic study. Both textural and geochemical changes were examined within all four different terraces in order to characterized the diagenetic history. The textural changes observed in the cores and thin sections, provided preliminary evidence of the diagenetic environment. Through the use of X-ray diffractometry, stable isotopes (C and O), and trace element data, the interpretation of the diagenetic environment can be constrained. The reef terraces were deposited as as shallowing upward units following a down-stepping carbonate sequence. The lithology of the cores is dominated by reefal facies, which consist of the back reef, reef crest, front, and fore reef facies. The exposure surfaces, observed at various depths, constrained the interpretation of early diagenetic environments (met. vadose and phreatic). Three major diagenetic environments can be characterized from the cores, these are meteoric vadose, meteoric phreatic, and dolomitizaton. These diagenetis environments produced different geochemical signatures, which can be quantified through analysis of the stable isotopes and trace elements incorporated into the cements. The different reef terraces represent different duration of exposure, with the higher terraces having been exposed longer than the lower ones. This study enables the documentation and comparison of the processes and products of the meteoric diagenesis that occurred within these different terraces. In addition, this study also constrain the early dolomitization observed in sigmoidal reef deposits. In order to further quantify the process of early dolomitization, mineralogy, isotopes C and O, trace elements, and the Sr-isotopes were examined as well.

Keywords

meteoric diagenesis; stable isotopes; trace elements; sr-isotope; dolomitization; plio-pleistocene reef terraces; southern dominican republic

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