摘要:
准噶尔盆地西北缘石炭纪地层主要由碎屑岩组成,沉积厚度达5000—7000米,前人认为属浅海沉积环境,然而,笔者在这套地层中首次发现了大量包括浊流在内的重力流沉积和其它一些深水沉积标志。它们集中出现于下石炭统(不包括底部)和中石炭统,该深水沉积标志除重力流沉积外,尚发现了平流岩、产于泥岩和硅岩中的硅质放射虫、多种深水遗迹化石以及与深水环境有关的沉积构造序列等。
Abstract:
The sedimentary environment of Carboniferous in the northwest border of Junggar Basin is regarded as a shallow-sea by preceding scientists. However, many deep-water in indicators including gravity flow have been found recently by the authors in the Carboniferous stratum of this area, thus an objection to the preceding conclusion is raised. According to incompletely-emerged profiles, the total thickness of Carboniferous sediments in the study area is about 5000-7000 meters and they are mainly a set of clastic sediments. In the early period of Early Carboniferous, transgression happened on the basis of the Devonian terrestrial sedimentation in the north-border region of the Aerjiatishan Mountain and the sedimentary sequence of shallow-sea tempestite was formed with the increase of sea level. In the middle-late period of Early Carboniferous, a set of thick clastic flysch facics generated by turbidity current, 1631-4574 meters in thickness, was taking shape in the Zhayier Mountain region, The proximal turbidite and contourite with the developed A and B sections of the Bouma sequence as well as the debris flow deposit were found in this flysch facies, and various deep-water indicators, including deep-water trace fossils and deep-water siliceous radiolaria, were also discovered, for example, Taphrhelminthopsis sp. in the subface of turbidite sandstones and Scolecocoprus sp, attached on the bedding surface of black mudstones. Middle Carboniferous sediments, 2300 meters in thichness, outcrop completely in the Halaalate Mountain region and shallow-layer turbidites are well developed upwards and downwards, especially in the lower section. They are composed o the B-E or C-E sections of the Bouma sequence. The siltstones In the C section are rich in trace fossil, Zoophycos, while in the mudstones of the E section are abundant siliceous radiolaria. In addition, on the bedding surface, such associations of deep-sea trace fossils have been found, such as Cosmorhaphe sp. Scolarituba sp. hetminthoida Labyrinthica, Scolecocoprus sp, etc. However, in the middle part of this series, grain sizebecomes-sharply coarse and this bed is composed of gravel-bearing coarse sandstones and coarse-grain graywackes. It is apparently charactized by the proximal turbidite and fluxoturbidite and forms a complete prograding sequence of turbidite fan with the thin-layer turbidite in the lower section. The regession of Upper Carboniferous appeared in a shallow-sea environment.