Paper No. 76-32
Presentation Time: 9:00 AM-5:30 PM
DETECTION OF ANOXIA AT THE DEVONIAN-CARBONIFEROUS BOUNDARY IN THE NAMUR-DINANTBASIN, BELGIUM
The Late Devonian was a time of significant climate change and extinction, associated with intervals of severe oceanic anoxia. Although Late Devonian anoxia is often associated with basinal black shales, these shales are not present in all locations in which anoxia can be demonstrated by other means. In recent years, anoxia has been recognized in shallow water environments in both continental shelf and oceanic island arc settings. The extent of anoxia in shallow water settings is a topic of ongoing investigation. Samples across the Devonian-Carboniferous boundary at the Royseaux section in southeastern Belgium (which does not have a black shale unit) were analyzed using X-ray diffraction (XRD), whole rock geochemistry, and scanning electron microscopy (SEM) to detect the presence or absence of anoxia in association with the Hangenberg Event. Whole rock geochemistry supports previous sedimentological and paleogeographic interpretations of a passive margin origin for clastic sediments in the basin. Field observations and analysis of bulk mineralogy via XRD show no evidence of an unconformity in this section at the D-C boundary. Initial SEM analysis has revealed the presence of uniformly disseminated framboidal pyrite ranging from 5-50 µm in diameter, indicating suboxic/dysoxic (rather than euxinic) conditions within the shallow waters of the basin. The preliminary evidence of significantly reduced oxygen levels in shallow oceanic waters in this section supports a link between oceanic anoxia and extinction that preferentially targeted pelagic ecosystems during the Hangenberg Event.