Date

2019

Department or Program

Geosciences

Primary Wellesley Thesis Advisor

Katrin Monecke

Additional Advisor(s)

Kristin D. Bergmann

Additional Advisor

Marjorie D. Cantine

Abstract

The Bråvika Member in Northeastern Svalbard is a Cryogenian-aged (630 to 720 Ma), northward-thickening and coarsening-upward wedge of sandstones and dolomites that sits at the boundary between two vastly different climate states: the overlying Wilsonbreen Formation, representing the Marinoan Snowball Earth glaciation, and the underlying Elbobreen Formation, representing a nonglacial interval between the Sturtian and Marinoan glaciations. Large-scale sedimentological and isotopic studies of the Bråvika Member and the surrounding stratigraphy have resulted in three endmember hypotheses for the facies that the Bråvika represents: 1) a fluvial proglacial (sandur) facies related to the Wilsonbreen Formation (Halverson et al., 2004); 2) a glacial or nonglacial aeolian facies (Halverson, 2011); and 3) a nonglacial fluvial facies related to the Elbobreen Formation (Hoffman et al., 2012). This study uses a combination of petrography, energy-dispersive spectroscopy (EDS), scanning electron microscope (SEM) microtextural analysis, and non-metric multi-dimensional scaling (NMDS) analysis to characterize and assess the facies represented in the mid-lower Bråvika Member in Buldrevågen, Svalbard at a microtextural scale, and is the first study to do so. This study is also the first microtextural study to consider the viability of SelFrag electric pulse disaggregation (EPD) as a method to prepare consolidated samples for microtextural analysis. Two samples of the mid-lower Bråvika Member from Buldrevågen and one modern periglacial aeolian sample from Lake Vanda, Antarctica were compared with 16 other samples from the literature using NMDS. The 16 literature samples represented five different facies: fluvial, glaciofluvial, nonglacial aeolian, periglacial aeolian, and till. The NMDS ordination showed that the two samples from the mid-lower Bråvika Member closely plotted with samples from periglacial aeolian facies. This evidence, taken in conjunction with new and existing field evidence for syndepositional ice (ice-cemented sandstone clasts, a clast of the Wilsonbreen diamictite in the Bråvika) and aeolian transport (large-scale cross-stratification, grain frosting), respectively, is consistent with the interpretation that the mid-lower Bråvika Member in Buldrevågen represents a periglacial aeolian facies, implying that this facies is more closely related to the Marinoan Wilsonbreen Formation.

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