Geology of the Iniskin-Tuxedni region, Alaska

Abstract

The Iniskin-Tuxedni region, on the west side of Cook Inlet, Alaska, is an area of about 710 square miles between Iniskin Bay and Tuxedni Bay.

Bedrock geologic map of the northern Alaska Peninsula area, southwestern Alaska

“…In this area, moderately indurated, bedded rocks appear to underlie glacial deposits and overlie indurated rocks of unit KJkr; unfortunately, the data is not adequate to show the distribution of these rocks on the map. Detterman and Reed (1980) suggested a possible correlation of the rocks on Iliamna Lake with lithologically similar rocks in the Seldovia quadrangle (Detterman and Hartsock, 1966) on the west side of Cook Inlet that they assigned to the Kenai Formation (now Kenai Group). Work by Calderwood and Fackler (1972) and Kirschner and Lyon (1973) (Detterman and Hartsock, 1966).…”

“…Detterman and Reed (1980) suggested a possible correlation of the rocks on Iliamna Lake with lithologically similar rocks in the Seldovia quadrangle (Detterman and Hartsock, 1966) on the west side of Cook Inlet that they assigned to the Kenai Formation (now Kenai Group). Work by Calderwood and Fackler (1972) and Kirschner and Lyon (1973) (Detterman and Hartsock, 1966). Thin coal beds are interbedded with the siltstone and shale.…”

“…The Bruin Bay Fault is a high-angle-reverse fault and may have left-lateral offset (Detterman and Hartsock, 1966). It was a growth fault during deposition of the Jurassic sedimentary sequence and has approximately 3 km of stratigraphic throw (Detterman and Hartsock, 1966).…”

“…The volcanoes are emplaced through and on top of this backbone and the young volcanic rocks represent only a small fraction of the bedrock, even in the immediate vicinity of these volcanoes. Bedrock east of the batholith along the Cook Inlet coast consists of the Talkeetna Formation and overlying Jurassic sedimentary rocks of the Tuxedni Group and other sedimentary rock units as young as Tertiary (Detterman and Hartsock, 1966;Detterman and Reed, 1980;Nelson and others, 1983). The rocks of the southern Alaska Range and northern Aleutian Range at this latitude are characteristic of the Alaska Peninsula terrane (Wilson and others, 1985(Wilson and others, , 2015(Wilson and others, , 1999 where the batholith and roof pendants form the Iliamna subterrane and the sedimentary rocks are typical of the Chignik subterrane.…”

“…It is a region of transition from the classic magmatic arc geology of the Alaska Peninsula to the accretionary geology of south-central and southwest Alaska and to the poorly understood, tectonically complex sedimentary basins of southwestern Alaska. A wide range of sources were used to compile this map, including the published mapping of Robert Detterman and others in the Iliamna and Kenai quadrangles (Detterman and Hartsock, 1966;Reed, 1973, 1980;Magoon and others, 1976) and unpublished mapping of J.N. Platt and E.H. Muller in the Taylor Mountains quadrangle (J.N.…”