Integrated High-Resolution Cretaceous Stratigraphy & Basin Analysis

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Approximately one hundred million year old Cretaceous rocks beneath the Plains of western Canada are globally-significant because they provide one of the most complete records of Cretaceous climate and sea-level change. Abundant records from oil and gas boreholes allow us to map rock layers in great detail, reconstructing ancient shorelines, rivers, deltas and flood- plains. One of the most interesting results coming from our mapping is that sea-level oscillated up and down by perhaps 5-20 m on time-scales of about 20,000 to 400,000 yrs. Such changes are most logically attributed to the growth and melting of modest ice-caps on the Antarctic continent. This however is contrary to the popular conception of the Cretaceous climate as being a 'greenhouse', ice-free world with very high atmospheric CO2 levels. Our results from western Canada have led us to collaborate with scientists in Canada, the UK, US, Czech Republic and Poland to study paleoclimate, high-precision radiometric dating, biostratigraphic and sequence-stratigraphic correlation in an attempt to demonstrate that sea-level changes observed in Canada are of global extent, - proof of which would greatly strengthen the argument for waxing and waning Antarctic ice caps, and cause serious re-thinking of the nature of the 'Cretaceous greenhouse'. In addition to interpretation of sea-level changes, our subsurface and outcrop mapping of Cretaceous strata have allowed us to better understand how the Western Canada Basin subsided under the weight of the growing Rocky Mountains. Our results show that the advance of the deforming and uplifting Rocky Mountains took place in discrete segments, typically 200-300 km long. The adjacent basin was pushed down, forming a semi-circular moat-shaped depression, which rapidly filled with sediment. As stress was relieved in one sector of the mountains, another part, located several hundred km away, would start to deform. As a result, the crust subsided as a series of overlapping, lozenge-shaped sub-basins, rather than one simple basin. Few studies appear to have recognized this complexity.