Elemental geochemistry and micropaleontology of an upper Pennsylvanian black shale: The Haskell-Cass cycle (Douglas group), southeastern Kansas

Major and trace element concentrations and microfaunal distributions were determined for a detailed section of the Haskell-Cass cycle (upper Vinland Shale, Haskell Limestone, and lower Robbins Shale) near Peru, Kansas. Total organic carbon (TOC), loss on ignition (LOI), detrital elements, carbonate elements, trace and minor metals, and rare earth elements were analyzed and compared to the abundances of conodont elements and holothurian sclerites.

The lower Robbins Shale is a low organic carbon (< 2.0 wt. percent) gray shale. This offshore shale is atypically thick due to moderate influx of fine terrigenous elastics. A geochemically anomalous interval occurs in the lower Robbins Shale. This interval has the highest TOC, limited siliceous detritus, and when normalized to aluminum, moderate peaks of vanadium, nickel, chromium, and copper. This geochemical pattern suggests that a brief period of high marine productivity ultimately caused reduced conditions. Vanadium is more concentrated higher in the section, unlike Ni, Cr, and Cu, and is a geochemical indicator of open marine conditions. Conodont abundance is unusually low and sclerites are absent in the anomalous interval, but conodonts return to the expected "core shale" levels higher in the section. Gondolella appears higher in the section where vanadium levels are greater.