Late Early and Middle Jurassic Sequence Stratigraphy and Depositional History, Sverdrup Basin, Arctic Canada

Ashton Embry
GSC, Calgary, AB, Canada.

Late Early and Middle Jurassic (Pliensbachian -Callovian) strata of Sverdrup Basin comprise two, 2nd order sequences which share a major, 1st order boundary of latest Aalenian age. The Pliensbachian-Aalenian, 2nd order sequence contains three, 3rd order sequences and the strata consist of shallow to deep shelf siliciclastics. The shield areas to the east and south were the main source areas and sediment supply was moderate to low. The most extensive sandstone unit occurs in the upper portion of the Aalenian, 3rd order sequence and it prograded northwards. Crockerland, a source area which lay to the north, also contributed sediment and a Crockerland-derived, Aalenian sandstone occurs along the northwest margin of the basin.

Significant uplift occurred along the basin flanks in latest Aalenian and was associated with the final progradation of the Aalenian sandstone unit. In the far southwest portion of the basin, extensional faults which parallel the current Amerasia Ocean Basin developed for the first time. The oldest strata overlying the unconformity are earliest Bajocian.

The Bajocian-Callovian, 2nd order sequence consists of three 3rd order sequences which approximate the Bajocian, Bathonian and Callovian stages. Sediment supply to the basin was greatly reduced following the latest Aalenian, 1st order boundary. One input centre during the Bajocian-Callovian interval occurred in the southwestern corner of the basin and thick marine sandstone units derived from the south were deposited, with thicknesses partly controlled by north-south extensional faults. A small input centre occurred on northern Ellef Ringnes Island and Bajocian and Bathonian sandstones prograded southwards from the rift shoulder of the newly formed, Amerasia rift system. Over most of the basin, Bajocian and Bathonian strata are thin, often condensed sediments. There is no evidence of sediments of this age having been derived from the south or east over most of the basin.

A unit of Callovian shale, derived mainly from the south, occurs over much of the basin and equivalent shallow marine sandstone units are rarely preserved. The Callovian strata are separated from the overlying Upper Jurassic, Oxfordian strata by a 2nd order sequence boundary. Following this brief tectonic episode, sediment supply greatly increased from the south and east and no northerly-derived Oxfordian sediments have been identified.

The latest Aalenian sequence boundary is interpreted to coincide with the onset of rifting in the adjacent Amerasia Basin. The Aalenian strata appear to be the final sedimentary wedge derived from Crockerland which was subsequently broken up and buried as the Amerasia Basin evolved from Bajocian through Albian. The Middle Jurassic is a time of greatly reduced sediment supply for the western Arctic from the Barents Shelf to the Alaskan North Slope.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.