Marine barite: A recorder of oceanic chemistry and productivity

Adina Paytan, Ph.D.
Scripps Institution of Oceanography

Friday, June 5, 1998
12:00 noon—Pacific Forum

Geochemical and isotopic data from authigenic marine minerals provide information about seawater composition, hence Earth's tectonics, sea level changes, hydrothermal activity, climate, oceanic circulation, and marine productivity. To be a reliable monitor, a mineral must reflect the chemical and isotopic composition of seawater, at the time of its deposition, and remain inert to chemical exchange after burial. Calcite, the phase most commonly used for paleoceanographic studies, has been shown to re-crystallize during burial and often change its chemical and/or isotopic composition. Therefore an alternative phase is needed.

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Separated Late Miocene barite (9.6Ma)

Barite is a ubiquitous minor phase in oceanic particulate matter, and pelagic sediments, particularly underlying regions of high biological productivity. Barite formation appears to be mediated by biological activity in the upper water column. There are indications that barite precipitates directly from seawater, in micro-environments containing decaying organic matter and siliceous remains. Barite is relatively insoluble and thus is less prone to burial diagenetic exchange than calcite. Barite contains a rather large spectrum of geochemically important minor and trace components at measurable concentrations. For these reasons barite has the potential of being a monitor of specific chemical and isotopic characteristics of seawater through time, such as Sr, S, Pb and Nd isotopic ratios, and sea water Sr/Ca ratio. Data indicating that marine barite is indeed a reliable monitor of oceanic chemistry and biological productivity will be presented.

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