Date of Award

2018

Document Type

Open Access Thesis

Department

Marine Science

Sub-Department

College of Arts and Sciences

First Advisor

Howie Scher

Abstract

The Cascade Seamount is a wave-planated feature located on the microcontinent of the East Tasman Plateau (ETP). The minimum subsidence rate of the Seamount and the ETP can be estimated by dividing the present-day depth of the wave-cut surface (640 m) by the age of Cascade Seamount basalts as determined by potassium-argon (K-Ar) dating (33.4 and 36 Ma). This approach yields a subsidence rate of 18 m/Myr. However, a significantly more rapid subsidence rate of the ETP since the Eocene-Oligocene transition has been proposed based on sedimentological and biostratigraphic techniques. The late Eocene paleodepths determined by Stickley et al. (2004) using sedimentological and biostratigraphic techniques, indicate a subsidence rate of 85 m/Myr for the ETP. These two results present a paradox, which implies that the ETP subsided at a rate greater than the seamount itself over the same time interval. It also implies that the seamount formed above sea level. We posit that the subsidence ambiguity may be attributed to the presence of a turbidity current deposit in the sediment core, or uncertainty in the age of the wave-planated surface of the Cascade Seamount. Sr isotope stratigraphy (SIS) was used to measure the 87Sr/86Sr ratios in order to find the ages of the marine carbonate samples recovered from the Cascade Seamount during the August 2016 RV Investigator Voyage (IN2016_E01). The youngest geologically reliable age was reported to be 20.39 Ma, while the oldest age was 27.74 Ma. This gives the ETP a subsidence rate of 23.1 - 31.4 m/Myr. Results from statistical analyses of the published grain size measurements indicated the presence of a turbidity current deposit in ODP Site 1172. Therefore, the calculations put forth by Stickley et al. (2004) are misinterpretations of the events surrounding the Cascade Seamount.

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