Depositional history and sequence stratigraphy of the Precambrian-Cambrian boundary stratotype section, Chapel Island Formation, southeast Newfoundland

Abstract

Facies relationshps in the Vendian to Lower Cambrian Chapel Island Formation of southeast Newfoundland are used to establish a sequence stratigraphic framework for this important boundary stratotype section. The formation consists of five members of sandstone, mudstone and minor limestone deposited in a variety of shoreline to shelf environments. Peritidal sandstone and shale units in member 1 are overlain by sandstone and silstone deltaic and shelf deposits of member 2. These make up a transgressive system tract in which small-scale changes in relative sea level are superimposed on autocyclic deltaic processes. The thickness (> 400 m) of nearshore and inner shelf sediments resulted from high sediment accumulation rates which for member 2 nearly kept pace with subsidence. Upper member 3 and member 4 consist of inner shelf mudstone and peritidal limestone that were deposited in a low-energy oxygen-stratified basin. These deposits are arranged in three large-scale shoaling cycles representing three foresteping parasequences of one highstand systems tract. An extensive limestone bed at the tope of member 4 contains a sequence boundary. Associated with, or shortly postdating, development of this surface is a significant epeirogenic event that resulted in basin reorganization, increased subsidence, and progradation of a thick clastic sequence represented by member 5. The deposits of this upper member consist of an upward-coarsening storm-dominated shelf to shoreface succession of sandstone and silstone. Deposits of nearly identical character are also found in New Brunswick, and suggest that these sediments and the underlying sequence boundary could be significant for interregional correlation. Global correlation of the paleobathymetric curve developed for the Chapel Island Formation is considered unfeasible, given the long history of epeirogenic movements during the Vendian and Early Cambrian in this region.