THE BLACK SHALES OF THE MANUELS RIVER FORMATION, AVALON PENINSULA, NEWFOUNDLAND, CANADA: IMPLICATIONS OF GEOCHEMISTRY AND MICROFACIES FOR CAMBRIAN PALAEOCLIMATE AND PALAEOGEOGRAPHY

The sedimentary rocks at Manuels River, a classic locality on the south coast of Conception Bay, Newfoundland, Canada, comprise a concordant succession deposited on the former microcontinent Avalonia during the Cambrian. The succession rests on magmatic rocks of Neoproterozoic age and is conformably overlain by Ordovician sedimentary rocks.

The part of the succession examined comprises highly fossiliferous grey to black shales, with interbedded volcanic ash layers of the Drumian (middle Cambrian) Manuels River Formation. In contrast to previous studies at the Manuels River location, a detailed study of the microfacies allows the interpretation of a sedimentary environment with influence from sea-level changes, differing much from previous interpretations. The sediment contains differing amounts of organic carbon suggesting deposition under varying levels of oxygenation. This pattern also seems to be related to sea-level changes.

A detailed study of clay mineral composition shows that the diagenetic overprint is lower than previously assumed, and much lower than compared with other Paleozoic Avalonian sedimentary rocks. A Palaeozoic age of the subsidence can be assumed. The clay minerals are shown to be of both detrital and diagenetic origin. Despite the diagenetic influence, the results enable palaeoclimatic interpretations, which entail significant changes in previous reconstructions of Cambrian climate and the palaeogeographic position and movement of Avalonia.

Financial support by the Klaus Tschira Foundation (KTS 00.195.2011) is gratefully acknowledged.