Early syn-rift to rift climax transition in the Labrador-Baffin Seaway: Ichnological, sedimentological, and sequence stratigraphic record of the Lower-Upper Cretaceous interval, Bylot Island, Canada

Active faulting during development of marine rift basins defines the syn-rift phase, which includes a tectonically significant transition between the early syn-rift and rift climax stages. This transition, however, lacks detailed study because early syn-rift strata are often thin and deeply buried in the subsurface or poorly exposed in outcrop, and thus sparsely sampled. Offshore northeastern Canada, the Labrador-Baffin Seaway rift system has limited subsurface sampling, but associated onshore Cretaceous successions in the Bylot Island area preserve an important record of the syn-rift succession. This includes the Albian–Cenomanian Hassel Formation sandstones, mudstones and coals, which are overlain by the Turonian–Santonian Bylot Island formation mudstones. We contribute to the broader understanding of the early syn-rift to rift climax transition in marine rift basins through facies and sequence stratigraphic analyses of these units. The Hassel Formation includes lake margin deposits characterized by the Scoyenia and Mermia ichnofacies, fluvial and marsh settings, and foreshore to lower shoreface deposits with ichnological suites of the Macaronichnus assemblage and Skolithos and Cruziana ichnofacies. Inner to outer shelf deposits characterized by the Cruziana and Zoophycos ichnofacies, respectively, define the Bylot Island formation. The overall succession forms two rift sequences, separated by a late Cenomanian transgression at the formation boundary and also marking the early syn-rift to rift-climax transition. Our study has new implications for understanding the history of the Labrador-Baffin Seaway, as well as more broadly documents notable early syn-rift lacustrine ichnological assemblages and the complementary nature of sequence stratigraphy and rift-basin evolution.