A Playa Lake Usually Contains Laminated Mudstone

From 1 8 billion year old metamorphic rocks exposed in the black mountains to recent playa sediments deposited in the valley basins death valley possesses a superb geologic record.

A playa lake usually contains laminated mudstone.

Laminated to thick bedded. Burrowed massive 11111ds1011e dominated by sediment filled tubes having constant diameters and commonly containing soft sediment deformation features deep narrow mud cracks and lacustrine fossils is interpreted as intermiuently exposed shallow lake or swampy flood plain deposits. Playa lakes are characterized by laminated muds evaporites and mudcracks rock description of an outwash plane environment an outwash plane is characterized by sands silts clays and braided stream deposits. The base of an ideal perennial lake parasequence consists of laminated black shale overlain by laminated or massive gray mudstone both interpreted as perennial lake facies.

In figure 2 the maximum expansion strain ɛ max is plotted against the strength reduction index i s which is defined as i s 1 s cw s cd 100 where s cd and s cw. Tuff beds selected for 40ar 39ar analysis occur within laminated mudstone are matrix supported and lack evidence of reworking. Mudstone and shale are highly susceptible to slaking and undergo considerable expansion on wetting. An aggregate of dolomite mineral crystals that are usually microcrystalline.

Chang 7 2 contains mainly mudstone and fine sandstone facies with less shale facies suggesting that the deep lake facies began to shrink and large deltas developed in the northeast and southwest parts and extended lakeward. Perennial lake parasequences are capped by red siltstones and paleosols representing dry playa environments similar to those in the playa parasequences. This sometimes initiates microcrack formation the widening of existing cracks or disintegration of the rock mass. The deposits of eocene lake gosiute that constitute the green river formation of wyoming contain numerous tuff beds that represent isochronous correlatable strati graphic markers.

Eocene lake gosiute filled a large part of the green river basin in sw wyoming fig 1 and in this lake the grf was deposited with its largely laminated kerogen rich micrites oil shales that grade laterally into massive lime stones or siliciclastic mudstones. Is interpreted as subaerial playa mud flat deposits. It form sin very salty lagoons and desert playa lakes detrital rocks mudstone sandstone breccia and conglomerate. Playa lake laminated mudstone siltstone evaporites rock salt rock gypsum and others glacial environments outwash much like braided streams horizon bedded conglom and cross bedded sandstone mudrocks not there.