HOUSTON, WILLIAM S., Colorado State University, Fort Collins, CO

ABSTRACT: Sandstone Petrography and Diagenesis of Lower Tertiary Sedimentary Rocks Along the Eastern Shore of Katmai National Park, Southwest Alaska

Seacliffs in Katmai National Park have been mapped by prior workers as the Eocene(?) West Foreland Formation and the Oligocene(?) Hemlock Conglomerate and/or equivalents. The outcrops comprise a thick sequence of non-marine lithic arenites, conglomerates, siltstones, shales and coals that were deposited in low to high sinuosity fluvial channels and associatedfloodplain environments. The sediments were deposited in a fore-arc basin developed during the evolution of the Mesozoic-Cenozoic arc-trench system of the northeast Pacific.

Lithic arenites, the dominant sandstone type, have major framework constituents of quartz, volcanic and metamorphic rock fragments, and plagioclase. Minor constituents include microcline, muscovite, chlorite, hornblend, and sparse heavy minerals.

Diagenetic cements include calcite, phyllosilicates, iron oxides, and silica. Calcite and phyllosilicates are pore-filling, but only phyllosilicates are pore-lining. The most abundant phyllosilicate is chlorite, which occurs as grain coats, and in radiating and microcrystalline pore-fill phases. Compaction and/or cementation has almost completely occluded pore space.

A progressive sequence of diagenetic features observed in these sandstones resembles paragenetic sequences developed for formations in other arc-related basins. This suggests a main-line diagenetic sequence for volcanic-rich sediments deposited in fore-arc basins. This sequence appears to be independent of whether the depositional setting is marine or non-marine, and comprises: (1) compaction and development of clay coats; (2)calcite cementation; (3) cementation by chlorite and/or otherphyllosilicates; (4) silica cementation; and (5) complex replacement and alteration.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.