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The AAPG/Datapages Combined Publications Database

Alaska Geological Society


Journal of the Alaska Geological Society, third volume. Proceedings of the 1982 Symposium: Western Alaska Geology and Resource Potential, 1983
Pages 25-31

Diagenesis of Sandstones in Lower Cook Inlet Basin, Alaska, and its Implications for Petroleum Plays

J. G. Bolm, Thane H. McCulloh, Richard J. Stewart


Chlorite, smectite, calcite, and laumontite and other zeolites are the principal diagenetic phases in the Paleogene and Mesozoic arkosic and lithic sandstones of the Lower Cook Inlet Basin. While crystallization of any diagenetic phase in pores of sandstones degrades reservoir quality, laumontite is an indicator of especially destructive changes that generally preclude commercial oil production.

The diagenetic surface or top of laumontitized rock in the basin is grossly discordant with structurally deformed stratigraphic surfaces. Laumontite is not generally present in rocks younger than Early Cretaceous but has been identified locally in rocks as young as Oligocene. Laumontite has not only filled pores but has also replaced plagioclase wherever temperature, fluid Previous HitpressureTop, and pore-fluid chemistry have been appropriate. Some sandstones rich in detrital or early diagenetic carbonate have escaped laumontitization. Although there may have been a period of regional laumontitization in Paleogene time, the surface defined by the shallowest stratigraphic occurrence of authigenic laumontite in the basin is probably not isochronous.

Exploration for potential reservoirs in the basin should target early-formed structures where hydrocarbons may have accumulated prior to laumontitization, calcareous facies where laumontitization may have been chemically inhibited, and those parts of the stratigraphic column that may locally be above the shallowest laumontitized rock.

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