Ghost Rocks sedimentary rocks

Unit symbol: TKgrs
Age range Tertiary, Paleocene, and Upper Cretaceous (72.1 to 61.6 Ma)
Lithology: Sedimentary
Group name: Ghost Rocks Formation and similar rocks
Consists of thick sections of argillite and local massive sandstone and chert-rich pebble conglomerate; locally contains tuff beds in Kodiak Island region. Limestone containing pelagic foraminifers occurs locally at depositional contacts with pillow basalt, both of which typically occur southeast of sandstone-rich unit and yield Late Cretaceous and early Tertiary ages. Sandstone beds show Bouma sequences indicative of deposition by turbidity currents. Locally, channelized conglomerate units as much as 100 m thick contain clasts up to 30 cm in diameter that are chert, sandstone, limestone, or greenstone. Interbedded andesite is locally present. Moore and others (1983) described the Ghost Rocks as complexly deformed sandstone and shale interbedded volcanic rocks and local hypabyssal intrusive rocks metamorphosed to prehnite-pumpellyite facies. Byrne (1981) mapped a distinctive subunit of the Ghost Rocks that consists of “* * * medium-bedded (10–40 cm thick beds) sandstone interbedded with similar thicknesses of shale. The sandstones and shales are rhythmically bedded and sole markings and graded beds indicate turbidite deposition.” Byrne (1981) interpreted these rocks as “slope basin sequences” and indicated that the subunit is distinctive in the Ghost Rocks because of its lack of metamorphism and presence of only rare thick-bedded (>1 m) sandstone. In addition, Byrne (1981) noted the absence of conglomerate and pebbly mudstone, igneous rocks, and the relative lack of deformation; these rocks may be lithologically similar to the basin-plain facies association of Nilsen and Moore (1979) that we describe as part of the Kodiak Formation (unit Kaf)

Source map information

Source map Moore, J.C., Byrne, Tim, Plumley, P.W., Reid, Mary, Gibbons, Helen, and Coe, R.S., 1983, Paleogene evolution of the Kodiak Islands, Alaska: Consequences of ridge-trench interaction in a more southerly latitude: Tectonics, v. 2, no. 3, p. 265-293.
Symbol Tga
Unit name Ghost Rocks Formation, argillite-rich unit, undivided
Description Massive sandstone beds and lesser amounts of argillite and medium- to thin-bedded sandstone. Sandstone beds show Bouma sequences indicative of deposition be turbidity currents. Locally, channelized conglomerate units up to 100-m-thick occur on the Aliulik Peninsula. Clasts in the conglomerate are up to 30 cm in size and consist of chert, sandstone, limestone, and greenstone. Andesite are also interbedded on the Aiulik Peninsula.
Lithology Sedimentary

Correlated geologic units

Label TKgha
Description Ghost Rocks Formation, argillite-rich unit, undivided
Geologic age Maastrichtian to Danian
Geologic setting Sedimentary, slope-and-deep-water
Lithology Form Importance
Argillite < Metaclastic < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Major
Metasiltstone < Metaclastic < Metasedimentary < Metamorphic Zeolitic (prehnite-pumpellyite) Minor