Depositional Environments and Conodont-Based Correlation of the Long Point Formation (Middle Ordovician), Western Newfoundland

Abstract

The depositional history of the neoautochthonous mid-Caradocian Long Point Formation, which overlies the lower clastic slices of the Humber Arm Klippe, is characterized by two major periods of sedimentation. Out of a total thickness of some 600 m, slightly less than 60 m make up a lower sequence of limestone, minor shales, and a basal sandstone unit, which appears to have been deposited in an environment (or series of environments) characterized by beachsands, mudflats, lagoons, (?) carbonate bank, and a fringing reef. The remainder of the Long Point deposits exhibit several criteria that are suggestive of the general environment of a prograding fluviomarine delta. It appears possible that uppermost Long Point strata are fluviatile in origin.In terms of graptolite and conodont zonations, the Long Point Formation belongs within the Diplograptus multidens and Amorphognathus tvaerensis Zones, respectively. The base of the Long Point Formation probably coincides with the base of the Climacograptus peltifer Zone of the British standard graptolite zonation and with that of the Prioniodus gerdae conodont subzone.