Publication Date

2015-02-04

Availability

Open access

Embargo Period

2015-02-04

Degree Name

Master of Science (MS)

Department

Marine Geology and Geophysics (Marine)

Date of Defense

2015-01-12

First Committee Member

Peter K. Swart

Second Committee Member

Gregor P. Eberli

Third Committee Member

Bernard Riegl

Abstract

The δ18O of carbonates is most one of the most popular tools used in both marine and terrestrial environments to reconstruct past climate and understand diagenesis. The major problem with the use of the δ18O is that the value within a carbonate is dependent both upon temperature and the δ18O of the precipitating fluid. This dilemma is potentially solvable using clumped signatures reported as Δ47 which is a direct measure of the temperature of formation only. This thesis consists of three projects all of which have applied the clumped isotope method. The common thread of all of these projects is to understand the distribution of the Δ47 in modern sediments and those which have been influenced by early diagenesis. The first of these project examines the Δ47 in a suite of mainly non-biogenic carbonates from Great Bahama Bank including mudstones, wackestones, packstones, grainstones and rudstone (ooids, pellets, peloids, and grapestone). Such data will serve as a reference for future diagenetic and paleoenvironmental studies involving non-biogenic sediments. In this study a facies control has been observed as the clumped signals increase and temperature values decrease from muddy facies to grainy facies. Temperatures of formation of the platform carbonates calculated using carbonate clumped isotope paleo-thermometry agree with expected sea surface temperatures on the platform. Oxygen isotopic values of the waters calculated from the δ18O of the carbonates and the clumped isotope data agree with the values previously measured. The second study examines the clumped isotopic signature in corals from the island of Tobago. These corals are seasonally bathed by waters originating from the Orinoco and the Amazon rivers and hence the δ18O of a coral skeleton is influenced by the magnitude of this fluviatile input as well as variations in temperature. Clumped isotope analysis makes it possible to distinguish the temperature induced δ18O signal from that exerted by the freshwater and consequently calculate the annual variation in the Orinoco discharge. The last study examines the Δ47 of young calcrete complexes. They are frequently used for the reconstruction of paleoclimate and paleoenvironmental conditions and record the δ18O values of rainfall, but the interpretation is frequently complicated by uncertainty as regards the formation temperature. The clumped isotope method allows to measure formation temperature of the calcrete samples and reveals knowledge of δ18O of the precipitating water. In the sub-arid conditions of Hog Cay the formation temperatures of calcretes are higher than the mean annual summer temperature, while formation temperature values are consistent with mean annual temperature in New Providence.

Keywords

clumped isotopes; coral; non-skeletal carbonates; calcrete; clumped isotope thermometry; Great Bahama Bank

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