Bedrock dredging in water depths between 4,060 and 550 m along the continental slope in the eastern Gulf of Alaska has revealed the existence of a previously unknown Eocene sequence that locally includes potential source and reservoir rocks. Argillaceous rocks in the sequence are soft to moderately indurated dark-brown shales and commonly glauconitic, pyritic, and in part concretionary or laminated siltstones. They locally contain extremely abundant microfossils, large fish scales, and carbonized plant fragments. Associated with the argillaceous rocks are relatively clean quartzofeldspathic sandstones that are in part carbonaceous and calcareous, sandstone matrix cobble-boulder conglomerate, and palagonitized basaltic tuff. The rocks range in age from late early Eocene to late Eocene and were deposited in relatively warm water at depths ranging from shallow to bathyal.
Source-rock analyses indicate that argillaceous rocks from six of the dredge hauls located between Yakutat Seavalley and Alsek Canyon contained more than 1% and as much as 1.6% organic carbon; the rocks are thermally mature to slightly immature and one sample contained extractable saturated hydrocarbons. Sandstone porosities are generally moderate and permeabilities are very low. However, recovery of one friable sandstone with 23.8% porosity and 35.9 md permeability suggests the presence of possible reservoirs in the sequence.
Seismic reflection data indicate that the Eocene sequence with the most favorable source potential dips northward from the slope beneath the adjacent Yakutat shelf where it could be a possible petroleum source and exploratory target.