Rocks under the Microscope Zone II Versions EN1 Vol 5 (3) 2020
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A micrograph dataset of Late Ordovician carbonates in Northwest Tarim and South China
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: 2020 - 07 - 09
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: 2020 - 09 - 28
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Abstract & Keywords
Abstract: The Late Ordovician is a crucial period in the long geological history, during which carbonates deposited record the changes of the earth’s environment, as well as provide a foundation for the study of extinction events at the end of the Ordovician. In this study, we collected thin-section images of the Late Ordovician carbonate and identified all fossil fragment contents via a biological polarizing microscope. We focused on Kalpin of Northwestern Tarim and Yichang of South China and covered the stratigraphic range from the Sandbian to Katian stage with sampling intervals of 0.5–2 m and 0.2–0.3 m, respectively. The dataset can be compared with those from other regions to provide more details for subsequent studies on the paleoceanography and paleoenvironments of the Ordovician, as well as establish the spatial variation model of carbonate rocks deposited during the Late Ordovician.
Keywords: Upper Ordovician; Northwest Tarim; Middle Yangtze region; carbonate; fossil fragment
Dataset Profile
TitleA micrograph dataset of the Late Ordovician carbonate rocks in Northwest Tarim and South China
Data authorsChang Xiaolin, Hou Mingcai, Liu Xinchun, and Fan Taiyuan
Data corresponding authorHou Mingcai (houmc@cdut.edu.cn)
Time rangeLate Ordovician (Sandbian–Katian, ~458.4–448 Ma); Polarized photomicrographs of thin section were obtained in 2017 and 2019, respectively.
Geographical scopeThe Dawangou section is situated about 75 km southwest of the city of Akesu, 40°43′14.93″N, 79°32′8.29″E. The Puxihe section is situated on the North Bank of Puxi River Bridge, Fenxiang, Yichang City, Hubei Province, China, 30°55′35″N, 111°25′45″E.
Data volume1.96 GB
Data format*.jpg, *.xls
Data service system<http://www.dx.doi.org/10.11922/sciencedb.j00001.00043>
Source of fundingNational Natural Science Foundation of China (41672102)
Dataset compositionThe dataset includes 3 data files, which are 1. photomicrographs.zip: 348 polarized photomicrographs (*.jpg) of rock thin sections, with a data volume of 741 MB; 2. field photos of the measured section.zip: it has the field images of the measured section and the characteristics of the outcrop, with a data volume of 1.24 GB; 3. information table of database.xls: it contains all picture data and corresponding identification name, and the excel document includes sample number, corresponding level, and time ownership, with a data volume of 29.6 KB.
1.   Introduction
The Ordovician (485.4–443.8 Ma) is a crucial period in the long geological history. During this period, a series of significant changes in the earth’s environment occurred. Among them, the great Ordovician biodiversification event (GOBE) and Late Ordovician mass extinctions (LOME) have become the research focus of the Ordovician. The GOBE is characterized by a rapid increase in the diversity of marine organisms, coupled with a rise in ecosystem complexity [3]; meanwhile, the LOME is the first mass extinction event in the Phanerozoic, and the effect of biological extinction is second only to the mass extinction at the end of the Permian. However, the mechanism of and environmental changes during these events are controversial [4–6]. Most studies have focused only on the last 1–2 million years of the Ordovician. Paleoenvironmental conditions during the Late Ordovician between the GOBE and LOME have remained poorly understood, despite several efforts [7]. Therefore, it is crucial to minutely examine redox variations across the entire Late Ordovician to elucidate the environmental changes that caused the LOME.
Besides, it is well known that carbonate rocks record the information about the paleo-ocean when deposited, wherein abundant bioclasts can reflect changes in the abundance and diversity of organisms in the paleo-ocean, thereby reflecting the changes of the paleo-ocean environment. In this study, we selected the Dawangou section (Kalpin, Northwest Tarim) and Puxihe section (Yichang, middle Yangtze region) as the research areas. The Dawangou section became an auxiliary global stratotype section and point (GSSP) for the base of the Upper Ordovician (Sandbian) in 2001, with a well-exposed Ordovician sedimentary, and has been intensively studied regarding stratigraphy and paleontology. The lower–middle Upper Ordovician is best exposed at the Puxihe section of the middle Yangtze Block, and it records a deep ramp setting between a carbonate platform and a shelf basin. The Upper Ordovician strata are characterized by a low sedimentation rate; therefore, the stratigraphic thicknesses are moderate compared with the Dawangou section. During the Late Ordovician, the Tarim Basin, a peri-Gondwanan palaeo-plate, was situated close to the eastern edge of the Proto–Tethys Ocean at low to middle latitudes in the Southern Hemisphere, whereas the Yangtze Block was located in the northwest of South China, as part of a rifted microcraton off the northeastern margin of Gondwana. Based on this, we used the polarizing microscope to analyze and identify the rock slices from the Dawangou and Puxihe sections. These microscopic images provide detailed evidence for exploring the evolution of paleo-ocean environment and response of organisms to environmental changes.
2.   Data acquisition and processing methods
The source of this dataset was rock samples. Data acquisition could be divided into two steps—rock sample collection and carbonate rock microscopic image acquisition.
2.1   Sample collection and processing
The collection of rock samples needs to follow these steps: literature review, previous research results summary, target horizon and profile locking, clarification of section stratigraphic units, field measurement, and sample collection. A total of 106 samples were collected from the Dawangou section with a sample interval of 0.5–2 m, including Sargan Formation, Kanling Formation, Qilang Formation, Yingan Formation, and Tierekeawati Formation; a total of 34 rock samples were collected from the Puxihe section with a sample interval of 0.2–0.3 m, including the Miaopo Formation and Pagoda Formation. The samples were collected away from the surface weathered rocks, and fresh samples were taken as far as possible. The samples were collected from fresh surfaces without veins, roots, or strongly weathered surfaces, which include microcrystalline limestones, micritic limestones, argillaceous limestones, shales, and siltstones.
After obtaining the rock samples, it is necessary to perform indoor processing to prepare thin slice samples.
2.2   Microscopic image collection
A total of 140 rock slices were imaged and analyzed using Nikon Ci-POL polarizing microscope. The observation and identification were performed simultaneously, focusing on the characteristic fossil fragments. Then, unidentified fossil fragments were searched and identified.
3.   Sample description
This dataset includes two sections—the Dawangou section in Kalpin of Northwest Tarim and the Puxihe section in Yichang of South China. The dataset is composed of three parts—the outcrop photos, thin-section photos, and information table of thin-section photos.
The field outcrop photos of the profile in the dataset mainly include lithology (Table 1), boundary contact relationship, fossil characteristics, and sedimentary structure. Among them, there are 72 photos from the Dawangou section and 16 photos from the Puxihe section.
Table 1   Summary of rock types and lithology information in northwestern Tarim and South China
LithologyNumberRock type and quantity
Shale61 carbonaceous shales, 2 clay shales, and 3 mudstones
Limestone10728 micrite, 46 muddy, 17 argillaceous, 13 nodular, and 3 bioclastic limestones
Sandstone11 litho-quartzose sandstone
The dataset contained 348 microscopic images (Fig. 1), including 93 and 255 images from the Dawangou and Puxihe sections, respectively. The abundance of bioclasts in carbonate rocks of the two sections was quite different, and the biological abundance and diversity of the Puxihe section were significantly higher than those of the Dawangou section. The information on the sections include initial of the section and number (the sample number of the Dawangou section was DWG- the order of sample; the sample number of the Puxihe section was PXH-layer number-intralayer number), photo number, photo content, two magnification factors, and plane-polarized light (−) or perpendicular-polarized light (+) (Table 2).
Fig. 1   Thin-section micrograph of Upper Ordovician carbonate rocks
PXH-5A-2 2 Foraminifera(+10)PXH-5A-2 4 Crinoids(+10)
PXH-11-1 1 Ostracod(+4)DWH54-2 The cavernous cavity was filled with a large amount of strawberry pyrite(+10)
Table 2   Profile information of Northwest Tarim and South China
TimeGroup/Group nameSection nameCoordinate latitudeCoordinate longitudeNumber of thin-section photos
KatianKanling Fm.Dawangou section, Kalpin, Northwestern Tarim40°43′14.93″N79°32′8.29″E42
KatianQilang Fm.Dawangou section, Kalpin, Northwestern Tarim40°43′14.93″N79°32′8.29″E51
SandbianMiaopo Fm.Puxihe section, Yichang, South China30°55′35″N111°25′45″E7
KatianPagoda Fm.Puxihe section, Yichang, South China30°55′35″N111°25′45″E248
The information table of the database was consistent with the microscopic images, including the sample number, photo number, photo content, magnification factor, optical characteristics, lithostratigraphic units, and the ages of the samples.
4.   Data quality control and evaluation
The accuracy of the research data mainly depended on the following three aspects— the accuracy of the stratigraphic boundary, sampling location, and thin-section identification.
First, the Dawangou section (Kalpin, Northwestern Tarim) became the auxiliary GSSP for the base of the Upper Ordovician (Sandbian) in 2001, and the Puxihe section in Yichang was also in the same area of GSSP in the Middle and Upper Ordovician (Huanghuachang and Wangjiawan sections). In addition, the predecessors have conducted extremely strict and meticulous stratigraphic work in these study areas [9,10]. On this basis, in this study, a high-resolution sampling could ensure the accuracy of chronostratigraphic and geological chronostratigraphic boundaries. Further, the process of profile measurement and sampling was extremely strict, and the measurement and calculation of bed thickness are performed according to the fieldwork standard to minimize errors. Finally, the identification of thin sections was completed by a paleontologist with the guidance of experts. The data were carefully contrasted with previous data, and the acritarchs were recorded to ensure the accuracy of identification.
5.   Usage notes and recommendations
This dataset shows the abundance and diversity of organisms in the Late Ordovician for Northwest Tarim and South China, which can be combined and compared with the research data of other areas in the Late Ordovician. In addition, it can provide more detailed data supplement for subsequent paleo-ocean and paleoenvironment research on Ordovician. Further, it provides a spatial change model for paleo-ocean carbonate rock deposition of the Late Ordovician for data support. During usage, it is suggested to refer to the articles of the author's team. Based on request, more information can be obtained from the authors.
[1] SERVAIS T, OWEN A W. Early Palaeozoic palaeoenvironments and the ‘explosion’ of diversity of marine species, genera and families. Palaeogeography Palaeoclimatology Palaeoecology, 2010, 294(3): 95-98.
[2] Sheehan P M. The Late Ordovician mass extinction. Annual Review of Earth & Planetary Sciences, 2001, 29: 331-364.
[3] Zhan Renbin, Zhang Yuandong, Yuan Wenwei. A new concept in the life process of the earth -- the Ordovician biological large radiation. Progress in Natural Science, 2007, 17(8): 1006-1014.
[4] Brenchley P J. Extinction: Late Ordovician Mass Extinction. John Wiley & Sons, Ltd., 2002: 331-364. DOI: 10.1038/ npG.els.0001652.
[5] RONG J Y, HUANG B. Thirty years of mass extinction research . SCIENCE CHINA Earth Sciences, 2014, 44(03): 377-404. (in Chinese)
[6] Chen Xu, Fan Junxuan, Melchin M J, et al.Process and mechanism of graptolite extinction and survival at the end of Ordovician in South China. Rong Jiayu, Fang Zongjie. Mass Extinction and Recovery: Evidence from the Paleozoic and Triassic in South China. Hefei: University of Science and Technology of China Press, 2004:9-54.
[7] CHANG X L, HOU M C, LIU X C, et al. Abundant microspherules from the Upper Ordovician of northern Tarim Basin, Northwest China. Origin and palaeoenvironmental implications. Geological Journal, 2018, 53 (S1). DOI: 10.1002 / gj. 3128.
[8] Bergstrom S M, Finney S C, Chen X, et al. The Dawangou Section, Tarim Basin (Xinjiang Autonomous Region), China:Potential as global stratotype for the base of the Nemagraptus gracilis Biozone and the base of the global Upper Ordovician Series. Acta Univeritatis Carolinae -- Geologica Sinica, 1999, 43 (1/2): 69-71.
[9] ZHOU Zhiyi, CHEN Piji. Biostratigraphy and geological evolution of Tarim Basin. Beijing: Science Press, 1990:20-86.
[10] WANG Zhihao, LI Yue, WANG Jianpo, et al.Conodonts of the Upper Ordovician in the central uplift area of Tarim Basin. Acta Micropalaeontologica Sinica, 2009, 26(2): 97-116.
Data citation
CHANG XL, HOU MC, LIU XC, et al. A micrograph dataset of Late Ordovician carbonates in Northwest Tarim and South China. Science Data Bank, 2020. (2020-08-04). DOI: 10.11922/sciencedb.j00001.00043.
Article and author information
How to cite this article
CHANG XL, HOU MC, LIU XC, et al. A micrograph dataset of Late Ordovician carbonates in Northwest Tarim and South China. China Scientific Data, 2020, 5(3). (2020-09-18). DOI: 10.11922/csdata.2020.0059.zh.
Chang Xiaolin
Main responsibilities: data collection, data set production, data quality control, data paper writing.
born in Luoyang, Henan Province, Ph.D., lecturer, research direction is paleoceanography.
Hou Mingcai
Main responsibilities: overall scheme design, data quality control.
houmc@cdut.edu.cn
born in Nanchong City, Sichuan Province, doctor, professor, research direction is sedimentology.
Liu Xinchun
Main responsibilities: data collection, rock sample collection.
born in Xiangfan, Hubei Province, Ph. D., lecturer, research interest is geochemistry.
Fan Taiyuan
Main responsibilities: image quality maintenance, initial English translation.
born in yibin city, Sichuan province, bachelor degree, research direction is geology.
Publication records
Published: Sept. 28, 2020 ( VersionsEN1
Released: Aug. 4, 2020 ( VersionsZH3
Published: Sept. 28, 2020 ( VersionsZH4
References
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