--> ABSTRACT: Molybdenum, Uranium, and Chloride Abundances in the Marcellus Shale — Significance to Basin Hydrography and Organic Matter Preservation, by Lash, Gary; Blood, Randy; #90142 (2012)

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Molybdenum, Uranium, and Chloride Abundances in the Marcellus Shale — Significance to Basin Hydrography and Organic Matter Preservation

Lash, Gary *1; Blood, Randy 2
(1) Geosciences, SUNY Fredonia, Fredonia, NY.
(2) Pure Earth Resources, New Brighton, NY.

Trace element and metals abundances have proven useful to elucidating the hydrography and water mass chemistry of shale basins. Our analysis of several Marcellus Shale cores by use of handheld XRF technology has yielded a robust dataset that sheds light on the nature and evolution of the water column of the Marcellus basin. Regional covariance trends of molybdenum and uranium and their respective enrichment factors define a uniform Mo/U molar ratio of ≈ 2 - 3 times that of seawater. Moreover, Mo is enriched relative to U by as much as 10:1 suggesting accelerated transport of Mo to the seafloor by a particulate transport mechanism that would have been enhanced by an intermittently sulfidic water column and a fluctuating chemocline. However, a data subset defined by Mo and U values typical of bottom water depleted in Mo (Mo/U = 0.1 - 0.3 x seawater) is suggestive of local water column stratification and consequent drawdown of Mo. Intermediate FeT/Al values, seemingly inconsistent with anoxic to sulfidic conditions, reflect, instead, the relatively high clastic flux of the Marcellus system. An especially intriguing aspect of the Marcellus inorganic geochemistry is local enrichment of chloride, generally within early transgressive systems tract deposits. Chloride well in excess of background levels as well as the documented presence of evaporite minerals appears to record the episodic introduction of dense saline water, likely sourced on the flooded subtropical shelf, into the Marcellus basin to the east. Injection of such saline water would have favored the establishment and maintenance of anoxic or even euxinic conditions thereby contributing to the preservation of organic matter in the Marcellus Shale, especially its lower organic-rich interval, the Union Springs Member.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California