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Ichnology and Paleoenvironmental Interpretations of the Cretaceous—Paleocene Rift Succession of Northeast Baffin Island Region, Nunavut, Canada

Abstract

Clastic strata cropping out along northeast Baffin Island, Canada, preserve an onshore stratigraphic record of rifting that formed the adjacent Baffin Bay region, beginning in the Early Cretaceous with seafloor spreading ceasing near the end of the Eocene. Cretaceous through Paleocene strata of this succession are preserved in the area around Pond Inlet, in Eclipse Trough along southwest Bylot Island, and in North Bylot Trough on north Bylot Island. Analysis of the ichnology and sedimentology of 35 stratigraphic sections of these strata was undertaken, in conjunction with palynological study, to better understand their evolving depositional environments and to provide an analogue for the associated offshore section in Baffin Bay. Lower Cretaceous syn-rift strata of Eclipse Trough include primarily fluvial facies. However, a unique interval containing wave ripples and mud-crack casts, as well as surface trails, trackways, resting traces, shallow dwellings, and microbial-induced sedimentary structures reflecting the Scoyenia Ichnofacies, is interpreted as lake-margin in origin. In another syn-rift section, Ophiomorpha characterize middle shoreface strata, and wave-rippled to hummocky cross-stratified beds contain a diverse, but opportunistic, archetypal Cruziana Ichnofacies within storm-dominated lower shoreface deposits. Overlying Upper Cretaceous transgressive mudstones reflect more distal marine deposition and are dominated by Phycosiphon. Shallower, proximal outer-shelf settings with distal Cruziana Ichnofacies assemblages are also seen in the mudstones where they transition to sandstones. These sandstones consist of progradational, storm-dominated, inner shelf through foreshore deposits, with alternating stratified and bioturbated beds containing either archetypal Cruziana Ichnofacies or Macaronichnus-dominated suites. Overlying Paleocene sandstones generally show evidence of high sedimentation rates suggesting deltaic deposition. Paleocene mudstones are rarely bioturbated, primarily by diminutive, marine, grazing traces. Palynological analysis indicates a lack of dinocysts in these rocks, supporting a brackish estuarine or prodeltaic setting. Seafloor sampling from Baffin Bay reveals similar facies to those seen onshore, demonstrating that the onshore record provides a vital analogue for understanding the adjacent offshore succession. These analyses help to document depositional complexities within an evolving rift system.