Environmental stressors and an ichnological model for an Early Cretaceous delta complex near the shelf edge of a passive margin, offshore Nova Scotia, Canada

ABSTRACT

Deltaic clastic wedges at the shelf edge and outer shelf form under environmental conditions that generally impart extreme to high ecological stresses on the benthos. The impoverished ichnological suites, ichnofabric, and ichnofacies expressions of these subenvironments, therefore, bear sets of evidence of their ambient stress factors and enable accurate reconstruction of a depositional model after integrating the sedimentological and ichnological datasets. The Lower Cretaceous (Barremian) upper Missisauga Formation (UM) in the Sable Subbasin, offshore Nova Scotia, exemplifies a deltaic clastic wedge near the paleo–shelf-edge passive margin. The ichnological study of conventional cores from the UM in the Glenelg and the Alma fields is based on an existing and revised sedimentological framework. In the northeastern Glenelg field, the UM records at least two parasequences reworked by tidal currents and sustained turbidity currents, featuring archetypal Rosselia, Phycosiphon, and Teichichnus ichnofacies suites indicative of inner- to medial-shelf clastic wedges. In contrast, the southwestern part shows a deeper-marine Phycosiphon Ichnofacies, indicating closer proximity to the paleo–shelf break. Cored intervals from Alma Field show Zoophycos Ichnofacies climax populations alternating with opportunistic Rosselia and Phycosiphon ichnofacies in episodic deposits, plus sporadically preserved archetypal Rosselia–Phycosiphon ichnofacies across UM stratigraphic levels. Ichnologic–sedimentologic integration in the Alma region points to deposition as wave-influenced marginal- to shallow-marine clastic wedges near the shelf–slope break, followed by autogenic abandonment. In both fields, substrate-controlled ichnofacies are also preserved along the discontinuity surfaces, with overlying bioclastic lag deposits indicating flooding surfaces that separate the parasequences.