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Bedrock geologic map of the 15' Sleetmute A-2 quadrangle, southwestern Alaska

November 6, 2020

Twelve unnamed, bedrock stratigraphic units are recognized within the Sleetmute A-2 1:63,360-scale quadrangle of southwestern Alaska. These units range in age from late(?) Proterozoic through Devonian and can be divided into two distinct facies belts: (1) a southern facies of dominantly shallow-water platform carbonate and minor siliciclastic rocks (including Early Ordovician–Early Devonian platform edge algal buildups) with subordinate transgressive tongues of deeper-water platy carbonates; and (2) a northern facies belt of approximately age equivalent deep-water carbonate and siliciclastic rocks deposited in slope and basinal environments. Both facies belts belong to the Farewell terrane of Decker and others (1994). Two structural provinces are also recognized, which correspond directly with these belts. The Farewell terrane is interpreted as a continental margin sequence that rifted from Siberia. Many of the bedrock units recognized in the Sleetmute A-2 quadrangle are equivalent to units previously recognized to the east and northeast in the Lime Hills, McGrath, and Medfra quadrangles. Shallow-water carbonate platform rocks make up the majority of the southern facies and occur primarily along the crest and north side (and to a lesser degree along the south side) of a prominent crescentic-shaped, east-west trending anticlinal axis exposed in the southern part of the Sleetmute A-2 quadrangle. Because of the relatively low thermal alteration indices of the rocks of this area and the presence of highly porous dolostone intervals of good reservoir quality in the platform facies, this region elicited interest for petroleum exploration in the 1980s. However, low total organic carbon (TOC) content of potential source rocks within the Ordovician–Silurian basinal facies belt indicates low petroleum resource potential for this area.

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