POSSIBLE BASEMENT INFLUENCE ON CRETACEOUS CARDIUM SAND BODY ORIENTATIONS IN THE GARRINGTON AREA, ALBERTA BASIN

Abstract

<p>The Upper Cretaceous Cardium Formation contains extremely long, linear sandstone and conglomerate bodies. Four of the most linear are; Caroline, Garrington, Crossfield and Lochend; they trend northwest -southeast. The factors controll ing the linearity of these sandbodies, which are presently interpreted to be incised shorefaces, have been questioned. Jones (1980) proposed that the orientation of these sandbodies is dictated by vertical faults in the basement that have effectively controlled the position of the Cardium oil fie lds. Hart and Plint (1993) suggested that remobilized basement structures during Cardium times affected the orientation of these sandbodies. Fourteen continuous stratigraph intervals from the top of the Mannville to the base of the Belly River were studied in the Garrington area by correlation of 797 resistivity well logs. Regional and residual trends were observed in isopach, quadratic trend surface, and residual maps. Residual trends occur at oblique angles to regional trends, which would indicate differing factors affecting local and regional sedimentation. Regional thinning trends were observed from SW - NE in Layers 4-2, 6-4, 12-11, 13-12, and 15-14; SE - NW in Layers 7-6, and 9-8; W - E in Layers 8-7, 11 -10, and 14-13; NW - SE in Layer 10-9; and NE - SW in Layer 16-15. No trends were found to penetrate through the stratigraphic layers, suggesting that underlying basement control was not important. Basement movements would have to propagate through 2.2 to 3.5 km of Phanerozoic sediment in order to influence the orientation of the Cardium sandbodies in the study area. Thus, the present sedimentological interpretation of these sandbodies, namely incised shorefaces deposited during a lowstand and then abandoned on the shelf during the following transgression, appears adequate.</p>