| 西藏措勤盆地下白垩统多巴组沉积环境分析 |
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| 引用本文： | 王冠民.西藏措勤盆地下白垩统多巴组沉积环境分析[J].沉积学报,2000,18(3):349-354. |
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| 作者姓名： | 王冠民 |
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| 作者单位： | 石油大学资源系 山东东营 257062 |
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| 摘 要： | 西藏措勤前陆盆地下白垩统多巴组是一套分布面积广大,比较特征的碳酸盐、陆源碎屑混合沉积的地层,本文通过对几条较完整的主干剖面的详细沉积相分析,揭示了多巴组的主要沉积环境包括潮坪、低能潮下带、近岸碳酸盐台地缓坡、台缘介壳滩及碳酸盐台地等几种主要类型,建立了多巴组的沉积相模式,并指出多巴组的沉积演化主要受控于盆地构造运动和全球海平面变化,这将有助于该地区的构造沉积演化研究。
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| 关 键 词： | 西藏 前陆盆地 多巴组 沉积环境 |
| 文章编号： | 1000-0550(2000)03-0349-06 |
| 收稿时间： | 1999-01-18 |
| 修稿时间： | 1999年1月18日 |
Sedimentary Environment of the Lower CretaceousDuoba Formation of the Cuoqin Foreland Basin in Tibet |
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| WANG Guan-min.Sedimentary Environment of the Lower CretaceousDuoba Formation of the Cuoqin Foreland Basin in Tibet[J].Acta Sedimentologica Sinica,2000,18(3):349-354. |
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| Authors: | WANG Guan-min |
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| Institution: | Petroleum University,Dongying Shandong 257062 |
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| Abstract: | Cuoqin foreland basin is located in the north of Tibet, bettwen Gangdisi Arc and Bangong lake - Nu river frac-ture belt. It zonaly extents along east and west from Geji,Nima to Bange. Thousands of meters marine strata of theMesozoic Tethys is developed in the basin. The Lower Cretaceous Duoba Formation is a set of mixed sediments ofcarbonates and terrigenous clastics. In this paper,according to a detailed study for several sedimentary sections,theauthor expounds sedimentary evolution of the Duoba Formation and its main controlling factors.
The lower part of Duoba Formation is made up of some non - isopach cycles which are composed of clasticrock, especially gray medium - thin layer feldspathic litharenite. Each cycle represents a depositional phase that de-trital material of tidal - flat facies rapidly progradate and then retrogradate. These cycles can include tidal - flatchannel,md-flat and mud-flat sediments. There are always some carbonaceous fragments on sandstone layers. Inthe middle part of Duoba Formation, diffrent kind of medium- thin layer carbonate facies and clastic facies com-pose a series of sedimentary cycles. Carbonate rock increases upward in these cycles. Each cycle is 80 - 130 meters,showing a transformation from the tip of tidal - flat deposition to carbonate platform deposition. The upper part ofDuoba Formation is composed of three sedimentary cycles which is about 130 - 200 meters. From bottom to top,each cycle includes mudstone of low-energy subtidal facies, sandstone of tidal- flat end facies, mudstone of subti-dal facies,carbonate rock of platform and its edge facies. Comparing with the middle part, carbonate rock distinctlyincrease and thicken, and thick layer rudist limestone or orbitolina limestone of shoal facies occurs too.
As a whole, progradation of tidal - flat facies is primary in the early of depositional phase of the Duoba Forma-tion, and retrogradation of tidal - flat facies and extention of Carbonate platform is prominent in the late. This depo-sitional character shows not only in the whole Duoba Formation, but also in each sedimentary cycle of the DuobaFormation.
Synthesizing depositional character of the Duoba Formation, a depositional model can be reached. It is a mixedsediments model near shore for carbonates and terrigenous clastics, with plentiful supply of clastic and a gentleslope. From land to sea, there are two parts in the model:one by land is tidal-flat, and the other is carbonate plat-form, bettwen them develops mixed sediments of low-energy subtidal facies.
From the south to the north, difference in depositional feature is obvious within narrow basset area of the Duo-ba Formation along east and west in Cuoqin basin. During deposition of the Duoba Formation, there are two car-bonate platforms about Guiya - Lunpola and Dongcuo, and Geji - Yanhu maybe is the third.
Palaeotectonic system clearly controls distribution and depositional feature of the Lower Cretaceous includingthe Duoba Formation in Cuoqin basin. Bouned by Jiangrna - Geang lake fracture, the south near the Gangdisi Arcdevelops pyroclastic sediments with 2000 meters thick near Cuoqin, and its sedimentary environment is wedge-topand foredeep of foreland basin. This set of stratum is called Zhenong Formation(K1zl). On the contrary, the northdevelops mixed sediments of carbonates and terrigenous clastic. Its sedimentary environment is foredeep and fore-lift. This sediments forms the Duoba Formation. Clastic material mainly come from Gangdisi Arc and wedge-top.Towards basin uplift near Bangong lake- Nu river fracture belt, carbonate rock in strata increases,and formationthickness reduces and gradully pinch - outs. These obviously show a sedimentary fracture of foreland which is con-troled by thrust belt. |
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| Keywords: | Tibet foreland the Duoba Formation depositional environment |
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