Isotopic and mineralogical variations in the infill of Chondrites from organic-rich black shale (Posidonia Shale, Germany) for assessing the mode of colonization

Abstract

The compositional variations of the infill of Chondrites within the Toarcian (Lower Jurassic) organic-rich black shale of southern Germany were evaluated on the basis of organic carbon-isotope and XRD analyses of the infill, surrounding black shale, and overlying greenish-grey mudstone for assessing the mode of colonization by the trace-maker. Both carbon-isotope rations and the mineralogical compositions (i.e., quartz/calcite peak-height-ratio) of the infill show much larger variations than those of the overlying mudstone and ambient black shale. These limes of evidence strongly confirm the prolonged upward migration model, and the short-term opportunistic colonization model is not likely in this case. Although the obtained data cannot directly provide any evidence of the chemosymbiotic trace-maker model, this study also indicates that the isotopic and mineralogical variations recorded in the infill of Chondrites can be used as good indicators to assess the trace-maker’s colonization style, furthermore to distinguish opportunistic/climax trace fossil