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Examples of Sedimentary Basins
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Turpan basin is a sedimentary basin located in North West China.It is
part of the Northern Xinjiang - Beishan mountains region.This region
includes other large sedimentary basins such as the Junggar,Turpan and
Yining basins.These large basins consist mostly of sands,shales and
sandy conglomerates.The sandstones mostly consist of Feldspathic
litharenite and litharenite.The Turpan basin is a large sedimentary
basin that was formed in the late permian.There are two types of
subsidence that lead to the formation of the Turpan basin.The first was
thermal susidence that took place during the late Permian and through
the early triassic.The second is flexural subsidence that took place
throughout the Middle triassic to Early Tertiary which produced periods
of extremely high subsidence rates.Very high susidence rates are also
common in the Late Triassic,Early Jurassic and Early cretaceous. The composition of the sandstones vary in time especially with its quarts content.In the permian the quartz content was only 11%.In the Triassic the quartz content increased to 27%,In the lower Jurassic it was 35%,In the upper Jurassic it was 36% and even reaching 47% in the Cretaceous and Tertiary. |
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| Fig
5.1.1. Map of the Turpan Basin. |
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5.1.2. Subsidence curve of the Turpan Basin. |
| The are two main subsidence
sources .These include thermal subsidence and flexural
subsidence.Thermal subsidence occurs as magma is made at the mid ocean
ridge it cools and builds a sedimentary basin.This is done through
thermal reequillibriation.As thermal susidence occurs the curve is
strongly concave down and and then smoother in a downward direction.This
indicates that at the beggining of the subsidence the subsidence
rate is very high as the sedimentary basin is rapidly subsiding.After
the magma cools that was produced at the mid ocean ridge the subsidence
rate is alot slower and is mostly due to the weight of overlying
sediment and water load.The highest rates of subsidence occur in the
Late Permian and early Triassic.High rates of subsidence occur
where there are large amounts of coarse clastic deposition.This reflects
that high rates of subsidence are linked to the rapid erosion of nerby
source regions.The greatest amounts of subsidence occur about 50 million
years after the onset of extension.This period coincides with the onset
of thermal subsidence and the evolution of the basin. There are four main periods of subsidence.The rapidly subsiding period occurs in the upper Permian and the Early Triassic.The actively subsiding period occurs during the middle triassic to the Jurassic.The reducing subsiding period occurs in the cretaceous and the increased subsiding period occurs in the early tertiary. |
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