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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The early to middle Eocene Lookingglass Formation is exposed over a wide area in southwestern Oregon. The formation contains a thick sequence of turbidite deposits consisting dominantly of very coarse to fine-grained lithic wackes, with minor amounts of pebbly sandstone, siltstone, mudstone, or shale. Sediments, mainly from the Klamath region on the south, and partly from a volcanic arc on the east, were deposited in a north-trending fore-arc basin approximately 125 by 155 mi (200 by 250 km) in size.
Within the lower part of the sequence, the lithic wackes are mainly thick-bedded, normally graded, pebbly sandstones and very coarse to coarse sandstones that contain a shallow-water marine fauna. Channel-fill conglomerate lenses occur within some of the thick beds of sandstone. This part of the sequence is interpreted as a proximal submarine-fan deposit. The lithic wackes of the upper part of the sequence, however, generally form sheets of thinner bedded, medium to fine-grained sandstone with more matrix. They contain deeper water marine fauna and are devoid of channel-fill conglomerate lenses. This part of the sequence is interpreted as a distal submarine-fan deposit. Sedimentation took place at a high rate and was accompanied by rapid subsidence of the basin.
The lithic wackes have undergone fairly intense diagenetic alteration, which includes cementation by calcite, silica, chlorite, and clay minerals; the replacement of feldspar grains, lithic fragments, and matrix materials by calcite and chert; and the recrystallization of chlorite. Cementation and compaction have considerably reduced the porosity of these sandstones.
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