INTERVALS OF ZINC HYPER-ENRICHMENT IN THE MIDDLE DEVONIAN MARCELLUS SHALE: IMPLICATIONS OF A SPECIAL TYPE OF EUXINIA, PHOTIC ZONE EUXINIA, AND THE ACTIVITY OF PHOTO-TROPIC SULFUR OXIDIZING BACTERIA

In this study, we examine a zone of zinc hyper-enrichment (ZHE) in the Marcellus Shale, with zinc concentrations measured at 31,063 ppm. Zinc hyper-enrichment events of this magnitude have only been described in two other ancient deposits, the Bakken shale (maximum 38,000 ppm) and the Cretaceous age, Atlantic Ocean black shale (maximum 7,158 ppm), and in only one modern environment, Framvaren Fjord, Norway (maximum 5,400 ppm). High resolution micro XRF was run over a core segment covering the Marcellus ZHE event. The ZHE event measured about 1.2—1.8 mm in thickness. Decompaction of this interval using a range of possible depositional rates provides an estimate of between 1 and 249 years for deposition of the ZHE event. In the Bakken, ZHE has been connected to photo-tropic sulfur oxidizing bacteria (PSOB) through identification of biomarkers. In Framvaren, two ZHE events were tied to events of record fish kills, suggesting photic zone euxinia (PZE). The potential connection of ZHE with PZE and PSOB has important implications for paleoceanographic conditions during deposition of the Marcellus. The apparent brief duration of the Marcellus ZHE event as recorded in core has important implications for short-term fluctuations in ocean water chemistry. The thickness of the event in core measured by micro XRF highlights issues of spatial aliasing when elemental analyses are conducted at spacings of greater than 2 cm, which is typical in shale geochemical studies