Geol Rundsch (1996) 85:723-754
9 Springer-Verlag 1996
H . W i l l e m s 9 Z. Z h o u 9 B. Z h a n g 9 K . - U . Gr~ife
Stratigraphy of the Upper Cretaceous and Lower Tertiary strata in the Tethyan Himalayas of Tibet (Tingri area, China)
Received: 21 September 1995 / Accepted: 26 February 1996
The 1500-m-thick marine strata of the Tethys Himalaya of the Zhepure Mountain (Tingri, Tibet) comprise the Upper Albian to Eocene and represent the sedimentary development of the passive northern continental margin of the Indian plate. Investigations of foraminifera have led to a detailed biozonation which is compared with the west Tethyan record. Five stratigraphic units can be distinguished: The Gamba group (Upper Albian - Lower Santonian) represents the development from a basin and slope to an outer-shelf environment. In the following Zhepure Shanbei formation (Lower Santonian - Middle Maastrichtian), outershelf deposits continue. Pebbles in the top layers point to beginning redeposition on a continental slope. Intensified redeposition continues within the Zhepure Shanpo formation (Middle Maastrichtian - Lower Paleocene). The series is capped by sandstones of the Jidula formation (Danian) deposited from a seaward prograding delta plain. The overall succession of these units represents a sea-level high at the Cenomanian/Turonian boundary followed, from the Turonian to Danian, by an overall shallowing-upward megasequence. This is followed by a final transgression - regression cycle during the Paleocene and Eocene, documented in the Zhepure Shah formation (?Upper Danian - Lutetian) and by Upper Eocene continental deposits. The section represents the narrowing and closure of the Tethys as a result of the convergence between northward-drifting India and Eurasia. The plate collision started in the Lower Maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and Abstract
H. Willems (N~) 9 K.-U. Gr~ife Fachbereich 5, Geowissenschaften,UniversitfitBremen, Klagenfurter Strasse, D-28359, Germany Fax: + +49 421 2184451 E-mail:
[email protected] Z. Zhou - B. Zhang Nanjing Institute of Geology and Palaeontology,Academia Sinica, 39 East Beijing Road, RC-210008 Nanjing, China Fax: + + 86 25 3357026
uplift. Stronger subsidence and deposition took place from the Middle Maastrichtian to the Lower Paleocene. The final closure of remnant Tethys in the Tingri area took place in the Lutetian. Biostratigraphy 9 Lower Tertiary- Indian shelf. Upper Cretaceous 9 Foraminifers 9 Lithostratigraphy 9 Passive continental margin 9 Tethys Himalaya 9 Tibet Key words
Introduction According to Gansser (1964) the Tethyan Himalayas are a tectonic unit which is bordered by the Central Crystallines of the High Himalayas to the south and the Indus - Yarlung Tsangpo suture zone to the north. The suture delimits the Tibetan Himalayas from the Gangdise batholith of the Lhasa block which forms the Trans-Himalayas. The Mesozoic and Lower Tertiary sedimentary series of the Tibetan Himalayas represent the depositional history of the Indian passive continental margin (Tapponier et al. 1981). During the Jurassic, Cretaceous, and Lower Tertiary, this continental margin bordered the Neo-Tethys Ocean to the south (Fig. 1). According to Seng/3r et al. (1988) the formation of the Neo-Tethys started with the rift-stage in the Triassic. During the narrowing and closing stage of the Neo-Tethys, the Indian plate drifted rapidly northward in the direction of the Eurasian plate. Subduction of Tethyan oceanic crust along the Eurasian margin, which was formed by the Lhasa block, started during mid-Cretaceous times and led to the formation of the magmatic arc of the Gangdise batholith. The forearc basin extending to the south is represented in the Xigaze flysch belt. The collision between the two continents took place during the uppermost Cretaceous and the Lower Tertiary, which led to the creation of the Indus - Yarlung Tsangpo suture zone. The Tethyan Himalaya zone situated south of the Indus - Yarlung Tsangpo suture can be subdivided into
724 Fig. 1 Upper Maastrichtian plate tectonic reconstruction of the eastern Tethys domain with the location of the Tingri profile. After Camoin et al. (1993). The first collisional event between India and Eurasia proposed herein is not shown
two subzones of different lithological compositions (Yin 1988; Liu and Einsele 1994), which are separated by the E-W running Gyirong-Kangmar Intracrustal thrust (Liu 1992). The northern zone is characterized by slightly metamorphosed outer shelf, continental slope, and deeper-water deposits, and the southern zone by nonmetamorphic shallow-water deposits. Our study area is situated in the southern zone. This zone comprises a more than 13-km-thick series of Cambrian to Eocene strata. A brief description of these sedimentary successions of the Tibetan Himalayas, as well as an introduction to the history of geological research, can be obtained from Liu and Einsele (1994). The marine Cretaceous and Lower Tertiary strata of the southern Tethyan Himalaya zone, which we focus on in our paper, are best exposed in the mountain ranges east of Gamba (Gamba - Tatsang Range; Willems and Zhang 1993a) and west of Tingri (Zhepure Mountain; Willems and Zhang 1993b). The good exposure conditions made Sun and Zhang (1983) suggest that the two areas (Fig. 2) be established as local stratotypes for the Cretaceous and Lower Tertiary in South Tibet. The purpose of this study was to document the Upper Cretaceous and Lower Tertiary record of the Tethys Himalaya sequences in the region of the village of Tingri. In the past, more stratigraphic studies were carried out in the Gamba area than in the Tingri area (Zhang Binggao 1979, 1980; Wang Yigang et al. 1980; Wen Shixuan et al. 1980; Zhang Binggao and Geng Liangyu 1983; Wen Shixuan 1974, 1987a, b; Hao Yichun and Wan Xiaoqiao 1985; Wan Xiaoqiao 1991; Wan Xiaoqiao et al. 1993; Willems and Zhang 1993a). The papers of Liu (1992) and Liu and Einsele (1994) represent a
review of the paleogeographic development and basin evolution of the Neo-Tethys in the central Tibetan Himalayas from the Upper Permian to the Eocene on the basis of sequence stratigraphic reconstructions. As the database of this area is still limited, the detailed investigation of the Cretaceous and Paleogene stratigraphy in the area of Tingri is important for a biostratigraphic framework and for understanding the sedimentary history of the Neo-Tethyan Ocean before its closure. Furthermore, in comparison to Gamba, the Tingri area plays a special role with respect to the sedimentary evolution during the Maastrichtian and lowermost Paleocene, which resulted from the first collision between India and Eurasia. Therefore, the purpose of this paper is to give a more complete and precise lithofacial and microfacial evaluation and a precise biostratigraphic dating of the Upper Cretaceous and Lower Tertiary sedimentary units in Tingri. The lithofacies, sedimentary environment, and biostratigraphy of the Gamba profile have been partly described previously (Willems and Zhang 1993a). A brief description of the situation in Gamba is given in this study for comparison. Our stratigraphic terminology follows the recommendations of Code-Committee (1977) especially in the usage of chronostratigraphic terms. The chronostratigraphic framework presented in this study was elaborated in two steps. Firstly, we established a foraminiferal biozonal succession for our research area. Secondly, we compared this biozonation with the West European and West Tethys standard zonation and chronostratigraphy (e.g., Birkelund et al. 1984; Caron 1985). Thus, our chronostratigraphic scheme follows the recommendations of the Copenhagen Meeting (Birkelund et al.
725 Fig. 2 P r i n c i p a l g e o l o g i c a l map of the eastern part of the Tibetan Tethys Himalaya zone, showing the location of the investigated Tingri section
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Upper Cretaceous and Lower Tertiary lithostraUgraphy of the Tingri area
According to Yin (1988) and Liu and Einsele (1994), the Cretaceous and Lower Tertiary series of the southern Tethyan Himalaya subzone (Fig. 2) consists mainly of carbonatic and terrigenous shallow-water deposits, whereas the northern zone is characterized by siliciclastic and terrigenous sediments of outer shelf, continental slope, and deeper-water environments. The sedimentary series represented in this paper is an example from the southern lithofacies subzone. Extending from west to east, the Cretaceous and Lower Tertiary sediments of the southern lithofacies subzone in the area of Tingri are distributed to the south of Laguigangri Mountain (Fig. 2). This subzone can be followed eastwards to the regions of Gamba and Ttina. The studied area - the Zhepure Mountain Range - is located west of Old Tingri (Shekar). The mountain is formed by an E - W running synclinorium with the axis slightly dipping from west to east at the locality where the section is taken. The Cretaceous strata crop out on both flanks of the tectonic structure, and the Lower Tertiary massive limestones comprise the crest of the mountain range (Fig. 3). The measured section contains a 1500-m-thick series which starts at the northern foot of Zhepure Mountain, where the Upper Albian part of the Gamba Group is exposed. The section ends at the mountain crest which consists of the youngest massive Lutetian limestones. The strata are well exposed and dip gently between 30 and 50 ~ to the south. The uppermost Cenomanian to middle Turonian and the Campanian parts of the strata
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