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Origin, Nature, and Distribution of Cryogenic Brine in the McMurdo Sound Region, Antarctica: Insights from Analyses of Diagenetic Carbonates
Abstract
Motivated by discoveries of cryogenic brine and associated 18O-depleted carbonate cements in a Neogene sediment core recovered in southern McMurdo Sound, Antarctica, this research investigates carbonate phases in nearby cored successions acquired by past drilling projects, namely Cape Roberts Project (CRP), Cenozoic Investigation in the Western Ross Sea Project (CIROS), Dry Valley Drilling Project (DVDP), and Antarctic Drilling Program (ANDRILL), to constrain the origin, nature, and distribution of cryogenic brine in this region. Carbonate cement phases and their paragenesis in over 200 sandstone samples collected from the cores were characterized by petrographic and geochemical methods. Results show that cements have low δ18O values. With temperatures constrained by clumped isotopes (Δ47) or inferred from local geothermal gradients, the cements are interpreted to have precipitated from 18O-depleted brine formed by cryogenic concentration of surface fluids with seawater affinities. Distinctive brine chemistry related to cryogenic processes also resulted in characteristic carbonate cementation patterns in subsurface sediments. The brine formed during at least two periods of climate cooling, associated with the middle Miocene Climatic Transition (c. 13 to 10 Ma) and Quaternary glaciation (c. 1.5 Ma to recent), respectively. The Miocene brine formed in fjord-like enclaves along the coast and flowed toward McMurdo Sound, becoming a volumetrically significant and regionally widespread pore fluid that due to its high density is still in place today. The brine led to a spatial trend in cement mineralogy characterized by prominent blocky aragonite at sites proximal to the brine source and dominantly calcite and subordinate dolomite cements at more distal sites. The Quaternary brine formed in coastal ice-dammed lake and offshore flexural trough settings. The younger Quaternary brine has only infiltrated and caused aragonite cementation in relatively shallow subsurface. This work demonstrates that cryogenic brine is spatiotemporally extensive and exerted a profound impact on diagenesis in subsurface sediments in the McMurdo Sound region. The findings may be extended to glaciomarine successions, both modern and ancient, in similar settings where brine is prone to form.
Subject Area
Geology|Geochemistry
Recommended Citation
Yang, Mingyu, "Origin, Nature, and Distribution of Cryogenic Brine in the McMurdo Sound Region, Antarctica: Insights from Analyses of Diagenetic Carbonates" (2019). ETD collection for University of Nebraska-Lincoln. AAI22588323.
https://digitalcommons.unl.edu/dissertations/AAI22588323