Laminated Shale Montana

These intervening unmineralized beds have in many places silt at the bottom may show cross lamina tion parallel lamination and graded rhythmites that grades upwards into dolomitic clayey shale.

Laminated shale montana. To illustrate the simplest case assume a laminated shaly sand sequence with shale laminations equal in thickness to the sand laminations. Acidresidues tengramsofrockwascrushed treatedwith cold 10 hclfor 24 hr and stirred. Thin bedded black shale just below the contact with the lewis overthrust north of marias pass montana. Lower unit consists of thin bedded well laminated shale grading to silt toward top.

Upper parts of formation locally eroded prior to hell creek. These layers appear to represent a graded succession in terms of grain size and depositional rate. These were from rocks that are thought to havebeenformedin anoxic nonbioturbated environments. The renova formation was formed during a dynamic point in earth s history the oligocene epoch 23 million to 33 million years ago a time of gradual transition from a tropical to a temperate climate in southwest montana.

Fine grained sedimentary rocks generally called mudrocks or mudstones make up about 50 of all sedimentary rocks 1 although estimates vary. These represent various proportions of silt and clay sized particles and are mostly composed of. Laminated pyrite laminated pyrite beds are some millimeters to several centimeters thick and are separated by beds of dolomitic clayey shale fig. Thin layers of clay and volcanic ash preserved beautifully the remains of insects and plants in finely laminated shale.

Shale is a fine grained sedimentary rock that forms from the compaction of silt and clay size mineral particles that we commonly call mud this composition places shale in a category of sedimentary rocks known as mudstones shale is distinguished from other mudstones because it is fissile and laminated. The boundary claystone in the western canada basin is composed of three intimately associated layers with a regional distribution. Montana group fox hills sandstone consists of upper sandstone unit 50 to 80 feet thick underlain by transitional marine shale unit 35 feet thick. Dark gray carbonaceous shale interbedded with siltstone and sandstone chert pebble conglomerate and coal.

Local conglomerate porcellanite and coal. Laminated shale and slate from cambrian proterozoic and archean rocks. Upper sandstone contains numerous concretions. Gray fine to medium grained locally conglomeratic sandstone with interbeds of dark gray carbonaceous shale.

Table 1 shows ages lithologies and depositional environ ments ofrocks usedin this study. A basal brownish grey hackly claystone a middle brownish black satiny claystone and an upper brown laminated shale.