A 23-km long, 2.5-km wide area with excellent exposures of the Jackfork Group occurs on and near the southern shore of DeGray Lake. This area, despite moderate to heavy vegetative cover, offers an opportunity to study the lateral extent of turbidite and associated submarine-fan lithofacies and to develop a model for estimating the extent of subsurface turbidite reservoirs using data from one or more wells. The extent of arenaceous lithofacies in the study area is also important to the local stone-quarrying industry.

Over 1,000 m of published and newly measured stratigraphic sections were studied to determine lithofacies present using the 1978 classification system of E. Mutti and F. Ricci-Lucchi. Lithofacies were then correlated along strike (which is generally within 20° of paleocurrent heading) using stratigraphic correlations, aerial photographs, field checking, and field tracing of nearly continuous outcrops.

Sandy sequences in which lithofacies B or C predominate, but which may contain lithofacies A, form ridges. These ridges are especially prominent where arenaceous intervals reach 10-30 m in thickness. Individual beds within these intervals are nearly all less than 1.2 m thick and are difficult to trace laterally. The arenaceous intervals, however, can be traced as units for up to 6 km and correlated for up to 8 km or more along strike. Shaly stratigraphic sequences of lithofacies G, D, E, and, rarely, F are poorly exposed, but can be correlated along strike for up to 6.5 km, with topographic expression and vertical lithofacies sequence being important guides.

End_of_Article - Last_Page 240------------