Abstract: Late Cretaceous to Early Paleogene shallow marine carbonates in Tibetan Himalaya have been determined to document the Neo-Tethys Ocean’s final stages. In this study, we use a polarized microscope and collected polarized microphotographs of carbonate and mixed carbonate–siliciclastic rocks from the Late Cretaceous Bolinxiala Formation, Jiubao Formation, Zhepure Shanpo Formation, and Early Paleogene Zongpu Formation in Tibetan Himalaya. The photomicrograph dataset includes 465 carbonate and mixed carbonate–siliciclastic samples from 5 stratigraphic sections. The dataset consists of information on sampling location and describes the stratigraphic age, lithology, and petrology of the samples, providing crucial geological information for reconstructing the sedimentary environments before and after the initial India–Asia continental collision and the closure of the Tethys Ocean.
Keywords: carbonate; Early Paleogene; Late Cretaceous; photomicrograph; Tibetan Himalaya
|Title||A photomicrograph dataset of Late Cretaceous to Early Paleogene carbonate rocks in Tibetan Himalaya|
|Data corresponding author||Hu Xiumian (firstname.lastname@example.org)|
|Data authors||Li Juan, Hu Xiumian|
|Time range||The samples were collected in 2006, 2012, and 2013, with a stratigraphic age from Late Cretaceous to Early Paleogene (i.e., 100 to 54 Ma). Polarized photomicrographs were taken in 2020.|
|Geographical scope||The sampling sections are located in the Tingri, Gamba, and Zanda counties in southern Tibet, bounded by the Lhasa terrane of the Indus–Yarlung–Zangbo suture to the north and neighboring the High Himalayan Crystalline sequences of the South Tibet Detachment System (STDS) to the south, with a longitude and latitude scope from 79°29′9″E to 88°31′39.1″E and 31°16′52.7″N to 28°16′41.2″N, respectively.|
|Polarized microscope resolution||4908*3264 pixels|
|Data volume||9.35 GB|
|Data format||*.png, *.jpg, *.xlsx|
|Data service system||<http://dx.doi.org/10.11922/sciencedb.j00001.00081>|
|Source of funding||The National Science Fund for Distinguished Young Scholars (Grant No. 41525007); National Key Research and Development Program of China (Grant No. 2018YFE0204201).|
|Dataset composition||The dataset includes four data files: (1) “Field photos.jpg” includes two full-view photos of the measured sections, with a data volume of 19.80 MB; (2) “Stratigraphic columns.jpg” includes two pictures showing the lithology, stratigraphic thickness, age, and sampling locations of the five measured sections, with a data volume of 704.31 KB; (3) “Photomicrographs” (*.jpg and *.png) comprises 930 polarized photomicrographs of the thin sections, with a data volume of 9.33 GB; (4) “Thin-section identification.xlsx” shows the microscopic characteristics of the rock samples, with a data volume of 127.36 KB.|
The Tethys Himalaya sedimentary zone is identified as one of the major tectonic domains within the Himalayan orogenic belt, stretching for about 1500 km from Zanskar (NW India) to southern Tibet (SW China). It is bounded to the Lhasa terrane by the Indus–Yarlung–Zangbo (IYS) suture to the north and neighbors the High Himalayan Crystalline sequences of the South Tibet Detachment System (STDS) to the south  (Fig. 1). The Tethys Himalaya sedimentary sequence represents the northern continental margin of the Indian subcontinent and preserves a continuous stratigraphic record from Ordovician to Early Eocene. It records the sedimentation and subsidence history of the northern passive continental margin of India [2–3] until its final collision with the Transhimalayan active margin of Eurasia at the end of the Paleocene (59 ± 1 Ma) .
Late Cretaceous to Early Paleogene shallow marine carbonates in Tibetan Himalaya have documented the sedimentation and subsidence history of northern Indian passive margin and recorded the closure of the Tethys Ocean. Detailed stratigraphical, sedimentological, and paleontological analyses allow the reconstruction of the sedimentary environments before and after the India–Asia collision and constrain the timing and process of the Tethys Ocean’s final closure. We sorted out microscopic images of 465 carbonate or mixed carbonate and siliciclastic rocks from 5 typical geological sections in the Tethys Himalaya (Fig. 1). These stratigraphic units are the Bolinxiala Formation, Jiubao Formation, Zhepure Shanpo Formation in the Late Cretaceous, and Zongpu Formation in the Early Paleogene (Fig. 2). The sample locations, stratigraphic ages, lithological identifications, and descriptions provide basic data to reconstruct the sedimentary environments before and after the India–Asia collision, and to constrain the final closure of the Tethys Ocean.
On the basis of the published literatures and field investigations, 5 representative stratigraphic sections were chosen for sample collection, observation, and description: the Zongpu I (S1), Zongpu II (S2), and Zengbudong sections (S3) in the Gamba area, the Gelamu section in the Tingri area (S4), and the Xiala section (S5) in the Zanda area. Samples were collected with an average spacing of 0.5–1 m. The description, identification, and classification of the thin sections are based on Hu et al. (2020)  and Flügel (2010) . Stratigraphic section-related data (including field images, sample locations, and strata thickness) and sample-related data (including sampling interval and lithology) are obtained in the field. Thin-section photomicrographs, stratigraphic columns, and thin-section identification reports are obtained through laboratory analysis.
The dataset comprises four parts: field photos of measured sections, stratigraphic columns, thin-section photomicrographs, and thin-section identification reports. The latitude and longitude, formations, units, and thin-section numbers are shown in Table 1, while the section locations are shown in Fig. 1.
|Age||Formation||Unit||Section No.||Section Name||Latitude||Longitude||Thin-section No.|
|Early Paleogene||Zongpu||1||S1||Zongpu I||31°18′14.42″N||88°10′54.37″E||129|
|Late Cretaceous||Zhepure Shanpo||S4||Gelamu||28°28′48.0″N||87°2′24.0″E||37|
3.1 Field photo dataset
3.2 Stratigraphic column dataset
3.3 Thin-section photomicrograph dataset
The thin-section photomicrograph dataset consists of 465 photomicrographs taken using a polarizing microscope from 5 measured sections. Each thin-section has a cross-polarized and a plane-polarized photomicrograph for the same location. The plane-polarized and the cross-polarized photomicrographs are numbered -01 and -02, respectively. The photomicrographs are saved in the JPG/PNG formats, with a resolution of 4908 × 3264 pixels (Fig. 5).
3.4 Thin-section identification report dataset
The thin-section identification report dataset consists of four identification tables, and shows the rock type, composition, classification, and sample information (Table 2).
The thin-section identification results indicate that the rock samples of the 5 measured sections were dominated by limestones (n = 453), with subordinate dolomites (n = 8), mixed carbonate and siliciclastic rocks (n = 3), and sandstone (n = 1) (Table 2). The limestone samples are characterized by packstones and wackestones, with subordinate mudstones and floatstones containing abundant bioclasts, typical of carbonate platform deposition. The size of the bioclasts is less than 2 mm. As shown in Fig. 6, the Zongpu Formation with abundant large benthic foraminifera is dominated by packstones (with subordinate wackestones, grainstones, mudstones, and floatstones), indicating that it is less affected by siliciclastic supply. The lagoon environment characterized by dolomites and the high-energy shoal environment marked by grainstone limestone are rare and only observed in member 1 of the Zongpu Formation. The Jiubao Formation is dominated by wackestones, with less abundant planktonic foraminifera. The Zhepure Shanpo Formation is dominated by carbonate rocks, with subordinate mixed carbonate and siliciclastic rocks and quartz sandstones, indicating that it is significantly affected by siliciclastic supply. The carbonate rocks are dominated by packstones with abundant planktonic foraminifera. The Bolinxiala Formation is dominated by packstones and wackestones without the influence of siliciclastic supply.
Rock samples are collected with an average spacing of 0.5–1 m to ensure representativeness. We also made sure to avoid weathering surfaces and veins in the field. The thin sections are made in Chengxin Geological Service Co., Ltd, Hebei Province, China. They are 0.03 mm thick and meets the international standards.
The microphotographs were taken using a Nikon Eclipse LV100 POL polarizing microscope under the automatic exposure and automatic white balance modes. The photomicrographs are saved in JPG/PNG formats, with a resolution of 4908 × 3264 pixels to ensure high definition and prevent color differences.
The grain content in thin-section identification was estimated according to the “visual comparison charts” of Flügel , with an error range of 0–5 %. We identified bioclasts to the class level and some to the genus level. All thin sections were identified and checked by Dr. Marcelle BouDagher-Fadel, a paleontologist from the University of London, UK, to ensure accuracy.
The carbonate rocks presented in the photomicrograph dataset are important historical witnesses of the evolution of the northern Indian continental margin and the Tethys Ocean’s closure. It can provide data for reconstructing the sedimentary environments before and after the Indian–Asian collision, constraining the timing of the closure of the Tethys Ocean, and evaluating reservoirs for oil and gas exploration. The sedimentary characteristics and biotic assemblages of the shallow-water carbonate platform shown in this photomicrograph dataset can be used in scientific research, teaching, and popular science activities.
The format of the photomicrograph dataset is simple, and the following points should be paid special attention:
(1) The rock samples and thin sections presented in this photomicrograph dataset are preserved in the lab of Xiumian Hu at Nanjing University. If the photomicrographs provided in this dataset are not enough to meet study needs, please contact the corresponding author for further information.
(2) Papers based on this photomicrograph dataset have been published [8–10] and are available for further reference.
We thank Jiangang Wang, Gaoyuan Sun, Wei An, Zhong Han, and Bo Zhou for their assistance in the field.
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LI J, HU XM. A photomicrograph dataset of Late Cretaceous to Early Paleogene carbonate rocks in Tibetan Himalaya. Science Data Bank, 2020. (2020-08-03). DOI: 10.11922/sciencedb.j00001.00081.
How to cite this article
LI J, HU XM. A photomicrograph dataset of Late Cretaceous to Early Paleogene carbonate rocks in Tibetan Himalaya. China Scientific Data, 2020, 5(3). (2020-09-26). DOI: 10.11922/csdata.2020.0072.zh.