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STUDY ON ANCIENT SHALLOW SEA CARBONATE STORM DEPOSITS(TEMPESTITE)IN NORTH CHINA AND DINGJIATAN MODEL OF FACIES SEQUENCES

Meng Xianghua Qiao Xiufu Ge Ming Yan Keming (Chinese Academy of Geological Sciences)  
A great deal of tempestites horizon have been recognized in strata from late-precambrian to palaeozoic in North China, among which the Late Cambrian sections particularly have a high frequence of occurences, where in many regions almost all the sections are made up of the frequent alternating successions caused by fair and storm weather. The types of ancient shallow sea carbonate tempestites in North China are given as follows: 1)DGravel of clastic(flat and tabular block)emerges radiating arrangement and the typ etop-bedding surface is coarse limestone with cloud-shaped of autochthonous and the coarse limestone of allochthous type(e. g. storm debris flows limestone ) in disorderly arrangement from non-gradation to gradation. The identification of their characters is shown in Table 1, 2 plate Ⅲ, 3、 4; 2 ) cm and mm grade type graded turbidity limestone ( plate Ⅲ, 5、 Ⅳ, l); 3 ) cutting structure type bioherm limestone (Fig. 2, Plate 1,1、2, (3),1); 4) Hummocky cross stratification type wackestone (Plate Ⅳ)-3 ) and 5 ) Resedimental type oolitic shoal limestone (Plate Ⅱ-2, 3). The sedimentary facies sequences of the Late Cambrian tempestites in Dingjiatan, near the West Mountain of Beijing, is made up of base cycle, lower cycle and upper cycle (Fig. 4), representing the gradual evolution of sedimentary environment from tidal flat-shoal, ramp to slope and basin. As the sedimentary facies sequences include various environments and all kinds of tempestite types, it is possible for an ideal and local model to be set up ( Fig. 5 ) . The author has carefully studied de-positional patterns of carbonate storm in different origin in early Paleozoic in North China: 1 ) turbidity current pattern of basin storm ( Fig. 6, A, B, C, ); 2 ) debris flows pattern of basin-slope storm ( Fig. 6, D ) ; 3 ) depositional pattern of basin slope of sedentary storm ( Fig. 7 ) ; 4)bioherm on the slope of platform fringe-storm flows pattern ( Fig. 8 ) . The patterns of tempestite facies of basin can be subdivided into distal and proximal types. The distal fine tempestites developed on the slope of shallow sea basin just near or below the storm wave base ( see Fig. 6, A, B ) . The D25-D27 and D30 horizons of Dingjiatan facies sequences in Fig. 5 are attributed to this facies pattern; however the proximal coarse tempestites developed on the slope above the storm wave base (see Fig. 6, C( Fig. 5, D29 horizon of Dingjiatan facies sequences ) . This kind of facies sequence is in concert with those storm turbidits which has been vast reported and researched, however, the small hummocky bedding of the Dingjiatan facies sequences often are intergrowth with muddy lbanded limestone of distal basin facies, or attached vertically with the adjacent sediments, which shows these positions of small hummocky cross-bedding are far closer to the storm wave base or near it than those large hummocky cross-bedding. The facies sequences of storm clastic flows of slope in basin mainly developed above the storm wave base on slope of basin in farther distantance. The deposite sequences are composed of the allochthonous storm coarse grainstone, storm fine grainstone and muddy banded limestone and fine quartzite siltstone ( see Fig. 6, D. ) . The typical facies sequences are 30-40cm thick, and some are half a metre. The D20-D22 horizons of Dinjiatan facies sequences in Fig. 5 are attributed to this kind of facies pattern. The facies pattern of the autochthonous storm deposits of the slope in basin shows coarse grainstone sequences of the massive autochthonous storm. These sequences consist of four units ( see Fig. 7, and Plate Ⅵ6). The muddy banded limestone which developed in the lower unit ( a ) is the sediments of fair weather. The interrupted and regular banded platy gravel bed which occure in lower unit ( b ) shows the primitive remake of the banded limestone caused by the early storm encircling flows and vortices . In the middle unit ( c ) , the tabular blocks of coarse grainstone show vertical fan arrangement; the top surface of vertical fan horizon sho
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