Palaeoenvironmental changes in slope carbonates across the Late Cambrian–Early Ordovician in western Newfoundland

Abstract

The Martin Point section (western Newfoundland, Canada) spans the uppermost Cambrian Broom Point and Martin Point members of the Green Point Formation (upper Furongian). The investigated interval (~90 m) consists of rhythmites of thinly-bedded marine carbonates (lime mudstones) alternating with green and black shale and thin conglomerate beds. Samples were extracted from the micritic carbonates, and their preservation was evaluated by multiple petrographic and geochemical examinations. The δ 13 C org profile exhibits a positive shift (~2‰) associated with the globally well-documented negative δ 13 C carb HERB (Hellnmaria-Red Tops boundary) excursion and correlated with similar distinct shifts in the Al, Si, and ∑REE components, thus suggesting contributions from detrital organic matter relatively depleted in 12 C induced likely by a eustatic sea-level drop and enhancement of terrigenous inputs. Similarly, the δ 15 N org variations are consistent with the proposed sea-level drop. This is also correlated with positive shifts on the Fe and Mn profiles reflecting the overprint of terrigenous inputs rather than redox conditions.