Abstract

The Lower Cretaceous Viking Formation of the Joffre field is characterized by complex reservoir architecture. Deposits of three discrete sequences were delineated using high-resolution sequence stratigraphy. The coarse-grained deposits of sequence 3, lying between BD-2 and an overlying open marine flooding surface, comprise the main reservoir interval within the Viking Formation of the Joffre field. This succession has previously been interpreted as an incised conglomeratic shoreface, stranded in a basinal position during transgression; however, sequence 3 displays characteristics difficult to reconcile with a shoreface interpretation, including an abundance of brackish mudstone interbeds and rip-up clasts, dominance of trough cross-stratification in the coarse clastics, and large-scale interfingering of the coarse clastics with fine-grained marginal-marine deposits. Despite the incised basal contact and brackish-water characteristics of the deposits, the succession does not reflect an estuarine incised valley complex, as conventional sequence stratigraphic wisdom might suggest. The shore-parallel orientation of the deposit, the lack of a convincing valley margin to the northeast, and parasequence orientations lying parallel to the strike of the deposit are inconsistent with an incised valley interpretation. Instead, the succession is interpreted as a broad brackish-water embayment of the shoreline, into which coarse-clastic bayhead delta and distributary channel complexes were deposited during incremental transgression. Such lagoonal or brackish bay complexes are ubiquitous in modern transgressive shorelines, but previously have been recognized only rarely in the ancient record.

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