ORIGIN OF EARLY CARBONIFEROUS DIAMICTITES FROM WESTERN NEWFOUNDLAND

The Crouse Harbour Formation, exposed along the French Shore of the Great Northern Peninsula of western Newfoundland, is a localized succession, more than 275 m thick, of conglomerates, diamictites, shale, and thin limestone. The unit consists of massive conglomerates at its base but becomes a series of interstratified, massive, mud-supported to clast-supported polymictic diamictites upsection. Many of the individual diamictite intervals lower in the section consist of massive, mud-supported strata with lenses and tongues of stratified, clast-supported, cobble to boulder conglomerate. Stratified diamictites typically contain a sandy matrix and display isolated clasts or trains of cobbles and boulders. Some of the stratified diamictites are inversely graded and interfinger with black, laminated shale and dolomite. A small percentage of the diamictite clasts (≈ 5%) display striations. Interstratified within the diamictite layers are intervals of dark gray to black, laminated silty shale and siltstone and interbedded dolostone. These fine-grained intervals commonly contain scattered and isolated, rounded pebbles to cobbles.

The Crouse Harbour Formation is partially overlain by and coeval with the Cape Rouge Formation, a thick interval of thinly interbedded fine-grained sandstone, gray shale, and tan laminated limestone and dolostone. Both the Crouse Harbour and Cape Rouge formations preserve miospore floral components of the Spelaeotriletes pretiosus assemblage zone which confirms a late Tournaisian (Tn3) age.

We interpret the Crouse Harbour diamictites to represent a succession of debris flows that intergrade laterally into fine-grained subaqueous lake deposits of the Cape Rouge Formation. These debris flows are presumed to have formed at the toe of a lacustrine fan delta complex constructed along the southeastern edge of the Euramerican paleocontinent. The presence of striated clasts within the diamictites and occurrence of dropstone clasts within the black shaly intervals enigmatically suggest that the Crouse Harbour fan delta may have formed in a region that was undergoing active deglaciation. The Tn3 age for the unit is contemporaneous with high latitude glacial deposits of Gondwana.