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|Title:||Relative Sea Level Control of Incised Shoreface Sediments in the Burnstick Member, Cardium Formaiton, Upper Cretaceous Alberta|
|Abstract:||<p>The Burnstick Member of the Cardium Formation (Turonian, Upper Cretaceous) occurs in the subsurface of southern Alberta and is underlain by the Hornbeck Member and overlain by the Raven River Member. These sediments were deposited into the Alberta Foreland Basin along the eastern margin of the Canadian Cordillera. The Burnstick Member sediments appear to be tens of kilometers east of the closest known paleoshoreline (Kakwa Member, Cardium Formation) which presents a major problem with respect to sediment transport in an offshore environment. Two possibilities exist for the deposition of the Burnstick Member sediments including, direct emplacement into an offshore environment by storm related currents ("offshore bars") or deposition in a shoreface environment during a rapid lowering of sea level (incised shoreface deposits). Approximately 200 cores and 800 geophysical well logs were used to determine the sedimentology and sand body geometry of the oil and gas fields at Caroline, Crossfield, Garrington and Lochend. Well log cross sections, core cross sections and isopach maps show that the Burnstick Member rests on a major erosional surface (E4) that outlines a "one-sided scour" or "bevel" which is open towards the northeast. The scours are between 2 - 6 m deep and are interpreted to have developed in shoreface environments. In between the fields the E4 surface merges with the T4 surface (Burnstick - Raven River Member contact) and forms the E4/T4 surface. The E4/T4 surface is flat relative to a horizontal lower marker and combined with the incised E4 surface underneath the four fields defines a step-like topography across the study area. Ten facies are combined into two vertical facies sequences; a coarsening upwards Burnstick Member sequence and a fining upwards lower Raven River Member sequence. Both facies sequences are best developed in the on-field positions, where they reach a maximum thickness of 7 meters. In contrast, the off-field development of the two facies sequences is poor and rarely exceeds 0.25 meters. The Burnstick Member sediments are concentrated in three long, linear and narrow belts in the study area and rest within the incised, one-sided scours of the E4 surface. The belts are approximately 15 km apart, oriented NW-SE and are traceable throughout the study area. The problem of transporting and focussing sediments in an offshore environment does net apply to the Burnstick Member sediments as they are interpreted to be incised shoreface deposits that were localized on the Cretaceous shelf during sea level fluctuations. Four sea level changes are hypothesized including one large lowering to move the shoreface from west of the study area to a position at Garrington, and three small rises to move the shoreface from Garrington to Caroline/Crossfield, from Caroline/Crossfield to Lochend, and from Lochend to west of the study area. Indirect evidence suggests that fluvial channels cut across the exposed shelf and supplied sediments to the incised shorefaces.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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