Carbon isotope (δ13Ccarb) heterogeneity in deep-water Cambro-Ordovician carbonates, western Newfoundland

Carbonates of western Newfoundland span the Cambro-Ordovician interval and preserve a record of slope-basinal deposition in the Cow Head Group near Cow Head. This unit consists of conglomerates and ribbon and laminated limestone interbedded with shale that is well exposed in sea cliffs at Cow Head Peninsula. These conglomerates, although prevalent throughout the section, vary in thickness and abundance stratigraphically and record both local disruption and large-scale episodic sedimentation events. Microfacies drilled for carbon isotope (delta C-13(carb)) analysis of conglomerates reveal isotopic heterogeneity within individual samples, in some cases more than 1 parts per thousand While this might be an expected outcome of drilling multiple areas of a heterogeneous conglomerate hand sample, permil-level variability was observed both between individual clasts in a sample, between different parts of the same matrix, and between a clast and its surrounding matrix. No associated variation in delta O-18(carb) or trace element distributions exists to suggest that this delta C-13(carb) variability is the result of later-stage meteoric diagenesis. The delta C-13(carb) variability suggests multiple sources of dissolved inorganic carbon (DIC) associated with carbonate precipitation for phases within these individual samples. These data indicate that processes such as local organic matter remineralization and early authigenic carbonate precipitation during lithification at the sediment-water interface (SWI) are either contributing to or controlling delta C-13(carb) values in Cambrian carbonates, perhaps more so than at other intervals in Earth history. (C) 2015 Elsevier B.V. All rights reserved.