A Playa Lake Usually Contains Laminated Mudstone

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.

A playa lake usually contains laminated mudstone.

Pink and red orthoquartzite. Tuff beds selected for 40ar 39ar analysis occur within laminated mudstone are matrix supported and lack evidence of reworking. 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. This sometimes initiates microcrack formation the widening of existing cracks or disintegration of the rock mass.

Laminated to thick bedded. 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. This resulted in the large scale deposition of sandy debris flow in the deep lake region. 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.

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. Is interpreted as subaerial playa mud flat deposits. At lake hill the lower unit contains the cephalopod armenoceras and several species of the. Mudstone and shale are highly susceptible to slaking and undergo considerable expansion on wetting.

Perennial lake parasequences are capped by red siltstones and paleosols representing dry playa environments similar to those in the playa parasequences. 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. 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. 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.