High resolution stratigraphy and paleoenvironmental reconstruction of the Upper Devonian Kettle Point Formation, southwestern Ontario, Canada

The Upper Devonian Kettle Point Formation of southwestern Ontario consists of interbedded organic-rich black shales and organic-poor greyish green mudstones and red beds, the distribution of which were controlled by water depth, primary productivity, paleoclimate, and tectonism associated with the concurrent Acadian orogeny. Black shales were deposited under anoxic conditions and represent the background deposition. Less abundant organic-poor lithologies were formed under dysoxic to oxic conditions caused by a drop in relative sea level (either eustatic or related to subsidence or uplift). Sulphur isotope data shows a largely consistent background value for the black shales around -20‰ δ34S, punctuated by a positive excursion of ~ 33‰ (up to +12.87) coincident with a significant interval of greyish green mudstone and red bed deposition. The correspondence of negative values to organic-rich sedimentation, and less negative-to-positive values associated with organic-poor lithologies, confirms their deposition in anoxic and dysoxic environments respectively. Four stratal packages (Units 1 to 4) can be identified in the Kettle Point Formation forming a lower (Units 1 and 2) and an upper (Units 3 and 4) cycle. Cross sections datumed using the base of the Foerstia Zone reveal that deposition prior to the Foerstia Zone (Cycle 1) took place over a platform feature that dipped towards a paleo-low in the southwest. Uplift occurred in the south-westernmost section of the study area near the end of the Foerstia Zone and deposition post-Foerstia Zone (Cycle 2) is characterized by intervals of thick organic-poor sediment in the southwest, which gradually thins outwards, away from the most southwestern well. Units 1 and 3 are composed of interbedded organic-rich and organic-poor sediment and were deposited above storm wave base as a result of minor fluctuations in relative sea level and biological activity. A rise in relative sea level resulted in the deposition of non-interlaminated black shales (Units 2 and 4) below storm wave base and the inundation of surrounding terrestrial environments. The Kettle Point Formation, along with other syndepositional black shales in eastern North America, demonstrate the complex nature of these deposits and the ease with which they form provided anoxia is present