December 7, 2013
Marine Fossils Discovered In Upper Part Of The Permian Linxi Formation, China
Science China Press
In a recent study, large numbers of bryozoan and other typical marine fossils were discovered for the first time in the thick limestone layers and lenses of the upper part of the Linxi Formation of the Guandi section, Linxi County, eastern Inner Mongolia. These marine fossils provide the first evidence for the Xingmeng area being in a marine or mainly marine environment at the end of the later part of the late Permian.
There has been a long history of debate over two major geological issues in the Xingmeng area. The first concerns the final amalgamation of the North China Plate, the Siberian Plate and several intermediate massifs in the area, and the other is about the folding and lifting of the Xingmeng Trough. Disagreements have arisen because of uncertainties about the tectonic-paleogeographical environment of the upper Permian deposits of the Linxi Formation. The Linxi Formation (upper Permian) is generally considered to be either (a) an exclusively continental deposit or (b) separated into earlier marine-terrigenous facies (the Lower to Middle Linxi Formation) and later continental deposits (the Upper Linxi Formation).
This study describes the discovery of large numbers of bryozoan and other typical marine fossils in the thick limestone layers and lenses of the upper part of the Linxi Formation in the Guandi section of Linxi County in eastern Inner Mongolia (Figure 1). At the same time, abundant bryozoan fossils were found in sedimentary tuff slices collected from the upper part of the Taohuayingzi Formation in the Taohuayingzi section in Ar Horqin Banner, and many crinoid stems were found in the dark shale of the Yangjiagou Formation in the Yangjiagou section, Jiutai County, Jilin Province.
From an ecological viewpoint, most modern bryozoans are marine, and they can survive in tropical, temperate, and polar oceans. Only a very small group (the Phylactolaemata) lives in fresh water, but these do not have a mineralized skeleton and thus do not preserve as fossils. Bryozoan adaptability is very strong. They are found distributed from coastal tidal flats to the deep sea at depths of 5500 m.
Sponges are generally considered to be the most primitive and the lowest marine multicellular animal. Sponge body walls are supported by needle-shaped elements, called spicules. Sponge spicules can be preserved as fossils in ancient strata. Crinoids are a type of echinoderm, first found in Carboniferous strata. Although they are animals, they live in the sea and resemble plants, hence the name sea lily. Thus the bryozoan remains, sponge spicules and crinoids fossils in the upper Permian strata of this region are typical marine fossils.
This study provides new constraints on the final closure of the Xingmeng marine basin. It will promote changes in the way that petroleum research is undertaken in the region, especially regarding the potential for new oil and gas, and shale gas (or oil) prospects, in addition to other mineral exploration in the Upper Permian rocks in the Xingmeng region of NE China.
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