Rocks under the Microscope Zone II Versions EN1 Vol 5 (3) 2020
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Photomicrograph dataset of Early–Middle Jurassic rocks in the Tibetan Tethys Himalaya
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: 2020 - 06 - 15
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Abstract & Keywords
Abstract: Jurassic, well exposed in the Tethys Himalaya in southern Tibet (China), are important for studying the evolution of the paleo-ocean, paleoenvironment, and paleogeography of the eastern Tethys. Additionally, it is important to understand the interactions between Gondwana continental rifting, mid-ocean ridge expansion, large igneous provinces, and Earth’s greenhouse climate. The Lower–Middle Jurassic in Tingri and Nyalam are dominated by carbonate, intercalated with siliciclastic, and mixed carbonate–siliciclastic rocks. The Lower–Middle Jurassic includes the Zhamure, Pupuga, and Niexiongla Formations from bottom to top. To date, the Jurassic in southern Tibet remains less understood. Owing to repeated and incomplete stratigraphic records, it is still difficult to identify the strata accurately by comparing lithostratigraphic units. This study was initiated to further contribute to future studies on, for example, accurate regional stratigraphic comparisons and avoid repetitive petrological studies. Photomicrographs of 494 rock thin sections were collected from the Wölong (Tingri) and Nianduo (Nyalam) sections using a polarized microscope under polarized and orthogonal light. The dataset includes information on the tectonic setting, palaeogeographic location, sampling sites, stratigraphic age, and rock name of these two sections. It can be used to support geological research and improve work efficiency. These photomicrograph dataset can be integrated by Deep-time Digital Earth (DDE) platformto resolve major scientific issues in a broader space and time scale. It can also be used for mining and oil exploration, construction, education, and general science promotion.
Keywords: thin sections; polarized photomicrograph; Tethys Himalaya; Jurassic; carbonate rocks
Dataset Profile
TitlePhotomicrograph dataset of Early–Middle Jurassic rocks in Tibetan Tethys Himalaya
Corresponding authorHu Xiumian (huxm@nju.edu.cn)
Data author(s)Han Zhong, Hu Xiumian
Time rangeThe rock samples are attributed to the Early–Middle Jurassic stratigraphic age (ca. 196–168 Ma) and were collected from 2013 to 2016. Using polarized light, rock thin sections were photographed in 2019.
Geographical scopeThe rock samples were sampled from Tingri and Nyalam counties in Xigaze, Xizang Autonomous Region, China, or geomorphologically, the Himalaya of southern Tibetan Plateau, with a latitude and longitude of 86°08′07″E–87°02′03″E and 28°29′02″N–28°40′52″N, respectively.
Spatial resolution4908 × 3264 pixels
Data volume8.64 GB
Data format*.zip, *.xls, *.pdf
Data service system<https://dx.doi.org/10.11922/sciencedb.j00001.00030>
Source(s) of fundingNational Natural Science Foundation of China (NSFC) for Distinguished Young Scholars (Grant No. 41525007).
Dataset compositionThe dataset includes three data files, namely, “micrographs of thin sections.zip,” “stratigraphic columns.pdf,” and “identification report of thin sections.xls.”
(1) “Thin section micrographs.zip“ is a dataset of polarized light micrographs (*.jpg) of rock thin sections, including 1026 micrographs, with a data volume of 8.64 GB;
(2) “Stratigraphic columns.pdf” stores information on the stratigraphic thickness, age, and sampling location of the Wölong and Nianduo sections, with a data volume of 552 KB;
(3) “Identification report.xls” is a data sheet for identifying a total of 494 rock thin sections, with a data volume of 147 KB.
1.   Introduction
During the Early–Middle Jurassic, the Pangaea supercontinent gradually rifted and drifted, accompanied by various phenomena, such as strong tectonic events, mid-ocean ridge spreading, and magmatism, which profoundly affected the Mesozoic paleogeography, paleocurrent, and paleoclimate. During this period, severe biological and environmental disturbances frequently occurred, especially around the Central Atlantic magmatic province (~201 Ma) and Karoo–Ferrar large igneous province (~183 Ma). These disturbances were accompanied by extreme carbon cycle disturbances and biological–environmental events, called the Triassic–Jurassic boundary event and Toarcian oceanic anoxic event (T-OAE)[1-4]. These important geological events are key avenues to understand the interactions between tectonics, climate, environment, and biota during the greenhouse period. However, previous works are mainly from the case studies of the western Tethys and Boreal realms. Therefore, the understanding of their occurrence and evolution is still quite limited. Tibetan Tethys Himalaya was located at the southern margin of the eastern Tethys Ocean during the Jurassic (Fig. 1). It was an important area connecting the western Tethys and Panthalassa and develops continuous Jurassic successions (Fig. 2), which are important for solving the above-mentioned scientific problems on a larger spatial scale.


Fig. 1   (A) Simplified tectonic map of the Tibetan Plateau showing the major blocks and sutures, modified after Chung et al. (2005). The red rectangle represents the sampling area. MFT: Main Frontal Thrust; MBT: Main Boundary Thrust; MCT: Main Central Thrust; STDS: Southern Tibetan Detachment System; ATF: Alty Tagh Fault; KF: Karakorum Fault. (B) Geological map of the Himalayas, modified after Gansser (1964)


Fig. 2   Comprehensive stratigraphic framework of the Lower–Middle Jurassic in Tingri and Nyalam counties
Studies by domestic and foreign researchers on the Jurassic stratigraphy, paleontology, and sedimentology of the Tibetan Himalaya are mainly concentrated in the last century. The Jurassic lithostratigraphic, biostratigraphic, and chronostratigraphic frameworks are basically established in this area [7-14]. The Lower–Middle Jurassic of the Tibetan Tethys Himalaya is usually divided into three stratigraphic formations from bottom to top (Fig. 2): Zhamure, Pupuga (equivalent to the lower Kioto Group [11]), and Nieniexiongla (equivalent to the upper Kioto Group and Laptal Formation [11]). Recently, the accumulation of research results and data on biostratigraphy, lithostratigraphy, sedimentary environment, and geochemistry gradually reveals response processes and details of paleoclimatic and palaeoceanic events in the Early–Middle Jurassic, which provides an excellent opportunity to discuss these events on a global scale.
The high-precision foraminiferal biostratigraphy precisely constrains the ages of the Zhamure (Sinemurian), Pupuga (Pliensbahcian), and Nieniexiongla (Toarcian-Bajocian) Formations. Microfacies studies indicate that the Zhamure Formation in southern Tibet is characterized by mixed carbonate–siliciclastic deposits on a barrier island and lagoon. This interval records negative carbon- isotope excursions at the Sinemurian–Pliensbachian boundary. The Pupuga Formation gradually evolved into shallow-water carbonate platform deposits dominated by bioclastic-rich grainstones. This formation recorded two important carbon-isotope excursions in the Algovianum and Lavinianum ammonite zones in the late Pliensbachian, which is respectively equivalent to the Margaritatus zone and Margaritatus–Spinatum zone boundary events in the Boreal realm, respectively [4]. Subsequently, the Kioto carbonate platform drowned in the early Toarcian caused by a rapid relative sea-level rise. The Pupuga Formation was abruptly replaced by Nieniexiongla Formation developingmiddle-outer carbonate ramp deposits affected by storm activities, and recording the T-OAE [15-18]. To date, the geochemical data of the Early–Middle Jurassic in the Tethys Himalaya are extremely limited. However, the existing data show that the characteristic carbon-isotope perturbations in the Early Jurassic were well recorded in the Tethys Himalaya, which are comparable to those recorded in the western Tethys and Boreal realms. Only by crossing a larger spatial scale (the entire Tethys) can we more accurately explore and understand the triggering mechanisms and processes of occurrence, development, and evolution of these major events in the Jurassic.
Although considerable data have been collected on the biostratigraphy and lithostratigraphy of the Tethys Himalaya, repeated and incomplete stratigraphic records are common in many sections due to orogenic belts. When other researchers work on the basis of previous researches, they can find only a few typical thin section photomicrographs in the publications. Owing to uncertainty issues on stratigraphic correlation and age, new researchers have to repeat the biostratigraphic and lithostratigraphic studies to confirm stratigraphic age and sedimentary environment. To efficiently utilize such data, this dataset summarizes the Early–Middle Jurassic thin sections of the Wölong (Tingri) and Nianduo (Nyalam) sections (Fig. 3). Additionally, the dataset shows their detailed information on (paleo)geography, tectonic setting, and lithology, which are accessible on a data platform that can be referred to and used by peers.


Fig. 3   Field pictures of the Wölong (Tingri) and Nianduo (Nyalam) sections in the Tibetan Himalaya
2.   Data collection and processing
A comprehensive survey of relevant literature and field trips was conducted on the relevant strata based on the above-mentioned scientific issues. First, we selected, described, and measured well-exposed and representative sections. Then, rock samples were systematically collected. Different sampling intervals were adopted according to specific conditions, such as the lithological changes and single-layer thickness. For example, the Zhamure Formation in the Wölong section has several terrigenous clastic deposits that are thick and have a single lithology. Therefore, one sample was collected for each layer; however, one sample per meter was collected for carbonates.
The collected samples were polished by Chengxin Geological Service Co., Ltd. in Langfang, Hebei Province, to obtain 0.03-mm optical rock thin sections. The methods of photographing and information collection of rock thin sections were uniformly implemented following the standards of “Rocks under the Microscope[19]. Rock’s microscopic images were systematically collected, and their information was obtained simultaneously. The description and nomenclature of thin sections are based on the criteria described in “Rocks under the Microscopic”[19].
Table 1   Detailed information on measured sections in the Tibetan Himalya
AgeFormationAbbr.SectionLatitudelongitudeAmount
Early–Middle JurassicZhamureWWölong (Tingri)28°29′02″N87°02′03″E56
PupugaWWölong (Tingri)28°29′02″N87°02′03″E95
NNianduo (Nyalam)28°40′52″N86°08′07″E29
NieniexionglaWWölong (Tingri)28°29′02″N87°02′03″E139
NWölong (Tingri)28°40′52″N86°08′07″E175
3.   Sample description
The dataset is mainly composed of three parts: a comprehensive stratigraphic column, a thin section dataset, and an identification report of the thin sections of the Wölong and Nianduo sections. The specific GPS coordinates, lithostratigraphic units, and the number of thin sections of each formation collected from these two sections are shown in Table 1. Their relevant geographic locations are shown in Fig. 1. The supplementary figures (stratigraphic column of the Wölong and Nianduo sections) show the stratigraphic thickness, name of lithostratigraphic units, lithology, age, sampling interval, and sample’s position.
The dataset consists of 494 thin-section photomicrographs containing cross-polarized and plane-polarized light micrographs under the same field of view. Some of them that include special bioclasts or sedimentary structures have additional photographs. The composition of the photomicrograph is the same as that described in the identification report. The photomicrograph has a resolution of 4908 × 3264 pixels and is saved in JPG format.
The identification report contains three identification tables of these two sections, named “Wölong section,” “Nianduo section,” and “Sandstone identification table.” They include thin section information about the lithology, classification, and nomenclature of carbonates, mixed siliciclastic–carbonates, and clastic rocks. The detailed criterion for classification and identification contents is described in “Rocks under the Microscopic.”
Fig. 4 shows the detailed classification and statistics of the 494 thin sections identified and photographed in this report. There are 404 thin sections of limestone with basic sedimentological information, such as grain type and content, bioclastic type and content, texture and structure, and groundmass type. For limestones, there are 219 thin sectionsthin-sections of mudstone, 73 of wackestone, 25 of packstone, 82 of grainstone, 4 of floatstone, and 1 of coral limestone. There are 17 thin sections of terrigenous clastic rocks, including 12 of quartz sandstone and 5 of lithic quartz sandstone, which were described in grain type and content, texture, structure, and groundmass types in detail (see the identification table of sandstones). In addition, there are 70 thin sections of mixed siliciclastic–carbonate rocks and 3 thin sections of dolomites. The carbonate rock fraction of mixed siliciclastic-carbonate rock can be described in detail according to the basic carbonate grain and groundmass, and the clastic rock fraction can be recorded in the supplementary information column. Hence, mixed siliciclastic-carbonate rocks all are placed in the identification table of carbonates. In this study, there is a small amount of dolomite whose depositional texture and structure can be described according to the header information of limestone, and the recrystallized fraction of carbonate is according to the recrystallized structure. Therefore, they are also listed in the carbonate identification table. There are 70 thin sections of mixed siliciclastic-carbonate rocks, including 31 of sandy grainstone, 4 of andy packstone, 7 of sandy wackestone, 1 of sandy bioclastic floatstone, 1 of sandy bioclastic rudstone, 2 of micritic sandstone, and 24 of allochemic sandstone.


Fig. 4   Classification and statistics of thin sections from the Wölong and Nianduo sections in the Tibetan Himalaya
4.   Quality control and assessment
In the field trips, high sampling density of the Wölong and Nianduo sections has been performed, and therefore the GPS coordinates pertaining to the positions of these sections, rather than those of each sample, were recorded. Simultaneously, this dataset provides field photos, sampling position in the stratigraphic column. As a result, we can combine these observations with obvious differences in lithostratigraphic units, thickness, and marker beds to find sampling position of each sample in the field.The thickness of thin sections meets the national and international standards. During the processes of photomicrograph shooting and thin section identification, the interference colors of quartz observed in the same batch were all of high quality, suggesting that the thickness of the thin section meets the national standard (0.03 mm).
The photomicrographs were high resolution with no chromatic aberration. In the microscope shooting process, auto-exposure and auto-white balance were used to ensure that the color observed with the naked eyes is consistent with the system photos. The microphotograph resolution was set to 4908 × 3264 pixels, which is the highest value for the camera. All photos were saved in JPG format, so the quality and sharpness of these photomicrographs are reliable.
5.   Value and significance
The Early-Middle Jurassic sedimentary rocks in the photomicrograph dataset reflect the gradual evolution of sedimentary environment from a barrier island-lagoon environment (Sinemurian) to a shallow-water carbonate platform (Pliensbachian), and then abruptly to a relatively deep carbonate ramp during the T-OAE, likely until the Aalenian [18-19]. Based on the current data of biostratigraphy and carbon-isotope stratigraphy, this photomicrograph dataset also contains several extreme carbon isotope perturbations in the Early Jurassic, such as the Sinemurian–Pliensbachian boundary event, late Pliensbachian Margaritatus ammonite zone, Margaritatus–Spinatum ammonite zone boundary event, and the T-OAE [18-20]. The changing and diverse depositional environments in the Early–Middle Jurassic are favorable for more accurate stratigraphic correlation in various Tethys Himalaya locations. At the same time, the carbonate platforms are important places for shallow-water creatures. This provides us with an excellent opportunity to study the coevolution of shallow-water creatures, climate, and environment and discuss the relationship between these changes and continental breakup, magmatic activity, mid-ocean ridge spreading, and plate drift on a long-term scale. The photomicrograph dataset of these samples contains considerable information from the Jurassic. There are also potential universal laws of the global climatic and environmental evolution that deserve a thorough investigation.
The photomicrograph dataset is not only used for basic geological studies but also has important production and economic significance. This photomicrograph dataset is dominated by carbonates. Carbonate rocks are important reservoirs for petroleum and gas. They are also associated with metal minerals such as lead and zinc, copper, manganese, iron and nonmetal minerals such as gypsum, rock salt, potash, and phosphate rocks. Additionally, carbonates are essential materials in the chemical, metallurgical, cement, and construction industries. Bioclasts, oolites, pisoids, and oncoids in carbonate rocks are attractive and acclaimed components that can be treated as artwork and decorations.
After professional treatment, these samples can also be used for professional education and science promotion. As mentioned in the introduction, this batch of high-resolution photomicrograph datasets can be integrated into the global Early-Middle Jurassic sections under a unified temporal and spatial framework in the future by the Deep-time Digital Earth (DDE) platform, including biostratigraphic and stratigraphic information. Moreover, this dataset can provide essential information for a thorough analysis of the evolution of life and Earth’s environment during this period.
6.   Usage notes
The dataset format of this study is straightforward. One should pay special attention to the following points:
(1) All thin sections present in the photomicrograph dataset are collectively stored by the research group of Professor Hu Xiumian of Nanjing University. If the photomicrographs provided in this dataset cannot meet the requirements of further research, readers are encouraged to contact the authors to apply for the use of these thin sections.
(2) A series of academic papers on sedimentology research and interpretation has been published based on the thin section identification results of this dataset[17-18, 20]. Readers are encouraged to refer to these papers for further details
(3) The photomicrograph dataset can be directly downloaded from the database. However, when it is necessary to further solve scientific problems related to geosciences, linking the geographic location, geological settings, and sample age provided in the data table is required.
Acknowledgments
The authors would like to acknowledge An Wei, Li Juan, Li Shiyi, and Zhou Bo for their contribution in field section survey and sample collection.
[1] Jenkyns H C. Geochemistry of oceanic anoxic events. Geochemistry Geophysics Geosystems, 2010, 11: 1-30.
[2] Blackburn T J, Olsen P E, Bowring S A, et al. Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province. Science, 2013, 340: 941-945.
[3] Burgess S D, Bowring S A, Fleming T H, et al. High-precision geochronology links the Ferrar large igneous province with early-Jurassic ocean anoxia and biotic crisis. Earth and Planetary Science Letters, 2015, 415: 90-99.
[4] Storm M S, Hesselbo S P, Jenkyns H C, et al. Orbital pacing and secular evolution of the Early Jurassic carbon cycle. Proceedings of the National Academy of Sciences of the United States of America, 2020, 117: 3974–3982.
[5] Chung S L, Chu M F, Zhang Y Q, et al. Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism. Earth-Science Reviews, 2005, 68: 173-196.
[6] Gansser A. The Geology of the Himalayas. New York, Wiley Interscience, 1964.
[7] Wang Y G, Zhang M L. Strata of mount Qomolangma region-Jurassic. Scientific Investigation Report on Mount Everest. Beijing: Geological Publishing House, 1974.
[8] Yu G M, Zhang Q H, Gou Z H, et al., Subdivision and correlation of Jurassic system in the Nyalam aera, Xizang(Tibet). Beijing: Geological Publishing House, 1983.
[9] Westermann G E G, Wang Y G. Middle Jurassic Ammonites of Tibet and the Age of the Lower Spiti Shales. Palaeontology, 1988, 31: 295-339.
[10] Shi X Y, Yin J R, Jia C P. Mesozoic to Cenozoic sequence stratigraphy and sea-level changes in the Northern Himalayas, Southern Tibet, China. Newsletters on Stratigraphy, 1995, 33: 15-61.
[11] Jadoul F, Berra F, Garzanti E. The Tethys Himalayan passive margin from Late Triassic to Early Cretaceous (South Tibet). Journal of Asian Earth Sciences, 1998, 16: 173–194.
[12] Liang D Y, Nie Z T, Dong W T, et al. Extension - unconformities within the upper Triassic - Jurassic sequence in the Nyalam area, Southern Tibet and stipulation of various foamations concerned. Geoscience, 2000, 14: 333-341 (in Chinese with English abstract).
[13] Wan X Q, Yin J R. Proceedings of the Third National Stratigraphical Conference of China. Beijing: Geological Publishing House, 2000, pp. 215-220 (in Chinese).
[14] Li X H, Wang C S. Reinterpretation of the Jurassic across the main Himalayan ridge north of Nyalam, southern Tibet, China. Geological Bulletin of China, 2005, 24: 1121-1126 (in Chinese with English abstract).
[15] Wignall P B, Hallam A, Newton R J, et al. An eastern Tethyan (Tibetan) record of the Early Jurassic (Toarcian) mass extinction event. Geobiology, 2006, 4: 179–190.
[16] Newton R J, Reeves E P, Kafousia N, et al. Low marine sulfate concentrations and the isolation of the European epicontinental sea during the Early Jurassic. Geology, 2011, 39: 7–10.
[17] Han Z, Hu X M, Li J, et al. Jurassic carbonate microfacies and relative sea-level changes in the Tethys Himalaya (southern Tibet). Palaeogeography Palaeoclimatology Palaeoecology, 2016, 456: 1–20.
[18] Han Z, Hu X M, Kemp D B, et al. Carbonate-platform response to the Toarcian Oceanic Anoxic Event in the southern hemisphere: Implications for climatic change and biotic platform demise. Earth and Planetary Science Letters, 2018, 489: 59–71.
[19] Hu X M, Lai W, Xu Y W, et al. Standards for taking and information collecting of digital photomicrograph of sedimentary rock. China Scientific Data, 2020. (2020-03-02). DOI: 10.11922/csdata.2020.0008.zh.
[20] Han Z, Hu X M, BouDagher-Fadel M, Jenkyns HC, Franceschi M, 2021. Early Jurassic carbon-isotope perturbations in a shallow water succession from the Tethys Himalaya, southern hemisphere. Newsletters on Stratigraphy. DOI: 10.1127/nos/2021/0650.
Data citation
HAN Z, HU XM. A photomicrograph dataset of Early–Middle Jurassic rocks in the Tibetan Tethys Himalaya. Science Data Bank, 2020. (2020-07-24). DOI: 10.11922/sciencedb.j00001.00030.
Article and author information
How to cite this article
HAN Z, HU XM. Photomicrograph dataset of Early–Middle Jurassic rocks in the Tibetan Tethys Himalaya. China Scientific data, 2020, 5(3). (2020-07-24). DOI: 10.11922/csdata.2020.0048.zh.
Han Zhong
Contribution: field survey, sample collection, thin section identification and photographing, data sorting, and paper writing.
Ph.D and associate researcher. Research area: palaeoceanography, palaeoenvironment, and palaeoclimatology.
Hu Xiumian
Contribution: subject and fieldwork design, dataset design, and paper writing.
huxm@nju.edu.cn
Ph.D and professor. Research area: sedimentology.
Publication records
Published: Sept. 21, 2020 ( VersionsEN1
Released: July 24, 2020 ( VersionsZH2
Published: Sept. 21, 2020 ( VersionsZH4
References
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