Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
Kathleen C Benison
The depositional origin of the Neoproterozoic Browne Formation of Australia is unclear. The Browne Formation consists of red-siliciclastic mudstone and siltstone (red beds), bedded and displacive halite and gypsum, and dolomitized stromatolites. Environmental interpretations of the Browne Formation range from a marginal marine lagoon to a playa lake deposit (Grey and Blake, 1999; Hill et al., 2000; Haines et al., 2004; Spear, 2013).;Primary fluid inclusions in Browne Formation bedded halite are the oldest known surface water remnants (Spear et al., 2014). Prior major-ion ratio analysis of these inclusions indicates that the Browne Formation formed from waters with unusually low sulfate concentrations. These waters differed significantly from modern seawater (Spear et al., 2014).;This study tested the non-marine interpretation of the Browne Formation via geochemical analyses. A non-marine interpretation is supported by the sedimentological characteristics it shares with geochemically distinct evaporites and red beds from acid-saline-continental settings (pH < 1; Benison and Goldstein, 2002). This thesis is the first examination of primary fluid inclusions from bedded halite from the Neoproterozoic Browne Formation through detailed fluid inclusion petrography, freezing-melting microthermometry, and laser Raman spectroscopy.;This thesis found that the Browne Formation inclusions are geochemically distinct. Freezing-melting attempts to determine major-ion composition and salinity were unsuccessful, this rare outcome indicates high inclusion salinity, and possible low pH. Efforts to determine pH through laser Raman spectroscopy were unsuccessful and do not indicate low pH (<1). Furthermore, no spectra of solutes or solids indicative of pH were detected. However, Raman analysis did detect anhydrite, disordered graphite, iron oxides, and several unidentified solids. Inclusion solids include exceptionally well-preserved suspect microbial life, including prokaryotes, spherules similar to Dunaleilla algae, and possible algal mats.;This study found no conclusive data of marine or non-marine Browne Formation parent waters. There is no diagnostic evidence of acid parent waters in the Browne Formation. Due to its unique freezing-melting and laser Raman characteristics, the Browne Formation may be a geologically unique evaporite deposit.
Bernau, Jeremiah A., "Fluid inclusion analyses of Bedded Halite from the Neoproterozoic Browne Formation of Central Australia to Determine Parent Water Origin and pH" (2017). Graduate Theses, Dissertations, and Problem Reports. 5192.