GEOCHEMICAL ANALYSIS OF THE CAMBRO-ORDOVICIAN COW HEAD GROUP, WESTERN NEWFOUNDLAND

The Cambro-Ordovician marks a time period of extreme change in Earth’s life and environment. The Cambrian explosion saw rapid diversification of many complex forms of life, but the diversity and abundance of organisms remained low for ~40 million years after the early Cambrian extinction. Following this depauperate interval, the Ordovician biodiversification event was a time of adaptive radiation during which skeletal groups flourished and took over as dominant carbonate producers. The driving force behind this delayed diversification remains poorly understood. Carbonates of the Cambro-Ordovician Cow Head Group in western Newfoundland, Canada, span this interval of time and record the appearance of complex skeletal life present in deep water environments of the Ordovician. Here, we report new data from the later Cambrian through Middle Ordovician portion of the Cow Head Group, Cow Head Peninsula, northern Newfoundland. The Cow Head Group is ~225 m-thick at Cow Head and consists of conglomerates, shale and limestone. Carbon isotopes were measured from the matrix of conglomerates and fine-grained limestones. The ¹³C_carb profile revealed a significant positive isotope excursion (from -5‰ to +1‰) in a Furongian Cambrian to Lower Ordovician 18-m thick conglomerate and overlying 5-m fine-grained dolomitic carbonate. This excursion may be related to the large positive excursion reported at the Cambro-Ordovician boundary in other places, but future work will determine if this is a globally correlative excursion.