Rocks under the Microscope Zone II Versions ZH1 Vol 5 (3) 2020
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A carbonate microscopic image dataset of the Permo-Carboniferous Taiyuan Formation in southern North China
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: 2020 - 06 - 30
: 2020 - 08 - 24
: 2020 - 07 - 14
: 2020 - 09 - 18
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Abstract & Keywords
Abstract: In this study, classified limestone micrographs of three sections were collected from the Permo-Carboniferous Taiyuan Formation in western Henan Province, a multiphase zone including a lagoon, restricted platform, open platform, and slope. The limestone sections were observed and photographed using a Zeiss polarizing microscope equipped with a photomicrography system. This study’s dataset includes 380 microscopic images of 95 limestone samples. These microscopic images show the petrographic features of mudstones, wackstones, and packstones. Among these petrofacies, wackstones with relatively high bioclastic grains are dominant. The dataset established in this study serves as a possible standard and reference for limestone microfacies research and would be useful for future works on understanding the paleoclimate and paleoenvironment evolution in North China during the late Paleozoic ice age.
Keywords: southern North China; late Paleozoic ice age; bioclastic limestone; micrographs
Dataset Profile
TitleA carbonate microscopic image dataset of the Permo-Carboniferous Taiyuan Formation in southern North China
Data authorsMa Rui, Yang Jianghai and Liu Chao
Data corresponding authorYang Jianghai (yangjh@cug.edu.cn)
Time rangeLate Carboniferous to Early Permian. Samples were collected from 2017 to 2019. Micrographs were taken from 2019 to 2020.
Geographical scopeSections are located in the central-west and northwest Henan Province, with a latitude and longitude of 113°9’36’’E–113°06’31’’E and 34°9’15’’N–35°14’03’’N, respectively.
Polarized microscope resolution2048 × 2048 pixels
Data volume2.02 GB
Data format*.xlsm, *zip
Data service system<https://dx.doi.org/ 10.11922/sciencedb.j00001.00045>
Source of fundingNational Natural Science Foundation of China (Grant No. 41572078)
Dataset compositionThe dataset includes two data files: “Photomicrographs.zip” and “Statistical database.xls.” “Photomicrographs.zip” is a dataset of polarized photomicrographs (*.zip) of thin sections, which contains 380 microphotographs of 95 limestone samples from three sections, with a volume of 2.02 GB; “Statistical database.xls” stores detailed identification of the thin sections, with a volume of 478 KB.
1.   Introduction
The microstructure and structural characteristics of carbonate are critical for petrographic classification and nomenclature[1]. Considering the particularity of carbonate’s genesis and structure, grain types and structure may reveal important information about the sedimentary environment, sedimentary processes, and diagenesis. According to the microfacies characteristics of carbonate, Researchers have analyzed the physical and chemical conditions of the sedimentary environment and established a foundation for carbonate classification[2-5]. Subsequently, Embery broadened and modified Dumham’s classification system by considering both biological and diagenetic factors, proposing semi-quantitative statistics of grain size[6]. Wilson summarized different sedimentary models of carbonate and integrating factors, including topography, hydrodynamic, and climate, and eventually posited 24 standard microfacies and 9 corresponding standard facies[7]. Researchers have also presented a systematic summarization of the limestone microfacies and developed a sedimentary microfacies model of carbonates, which were used as important indications of the sedimentary environment and processes[8-9]. Although there are different views on the standard of carbonate microfacies, microscopic observation and analysis of carbonate is a fundamental method to reconstruct the paleoenvironment and analyze the type and intensity of diagenesis. Meanwhile, carbonate microfacie also provides sedimentary evidence for determining the effectiveness of geochemical indicators, such as elements and isotopes[10-12]. We have summarized the micrographic characteristics of limestones from the Permo-Carboniferous Taiyuan Formation in southern North China and established a related microscopic dataset to objectively and systematically describe the information on the microfacies of carbonate.
2.   Data collection and processing
Through literature research and field exploration, a series of late Paleozoic deposits was found in Henan Province, southern North China[13-14]. In this study, three sections were systemically sampled in the Jiaozuo and Yuzhou regions of Henan Province (Figure 1 and Table 1). These successions being studied include the Upper Carboniferous to Lower Permian Taiyuan Formation (Figure 2).


Figure 1   (A) Schematic map of North China and (B and C) locations of the studied Permo-Carboniferous successions in Jiaozuo and Yuzhou regions
Table 1   The geographic location of the sampled section
Sampling sectionsThe coordinates of latitude and longitude
Wenwan section, Yuzhou, Henan (WW)34°9’58’’N, 113°10’41’’E
Mojie section, Yuzhou, Henan (MJ)34°9’15’’N, 113°9’36’’E
Baipohe section, Jiaozuo, Henan (BPH)35°14’03’’N, 113°06’31’’E


Figure 2   The stratigraphic columns of Mojie, Wenwan, and Baipo sections with sample positions (black spots)
2.1   Data collection
Fresh carbonate samples collected from the sections are made of optical rock thin sections with a thickness of 0.03 mm in the laboratory of China University of Geoscience (Wuhan) according to the standard. Following the standard of “the digital micrograph of the sedimentary rocks,”15 rock thin sections are observed and photographed using a Zeiss polarizing microscope equipped with a micrographic system to obtain the micrographs and relevant information of rock thin sections. The description of thin sections and the designation of limestone rocks are based on the standard of “the digital micrograph of the sedimentary rocks.” The number of thin sections is numbered according to the number of sections + M + the number of micrographs + the symbol of crossed polarized light + orthe symbol of plane-polarized light ˗. The image dataset contains 380 micrographs with a resolution of 2048 × 2048 pixels.
2.2   Methods for processing microscopic data
The microscopic observation was conducted using a polarized light microscope Zeiss AXIO Image A1m at the Key Laboratory of Biogeology and Environmental Geology and School of Earth Sciences, China University of Geology (Wuhan). The test was conducted at 25℃ and 50% humidity. The dataset comprises 95 limestone samples and 380 microscopic images.
Dumham’s classification of limestone (Figure 3) was adopted in this study2,15, which used the naming framework of genetic properties (on-site/off-site), grain size, and support type. According to the standard, we classified and described the micrographs of limestone and identified three types of limestone, namely, mudstones, wackstones, and packstones.


Figure 3   Classification of limestones
3.   Sample description
The dataset’s content is primarily the information about carbonate microscopic images. The following is a brief description of the microstructural characteristics of the three types of limestone with representative samples.
3.1   Types of rock
3.1.1   Mudstones
Mudstones are mainly collected in the lower part of the Wenwan and Mojie sections and the middle part of the Baipohe section. Some samples, such as BPH-7 and BPH-18, were recrystallized into crystalline limestone because of late diagenesis. The microscopic characteristics of mudstones are described using the well-preserved sample WW18T-14.
Sample WW18T-14 (Figure 4 A, B) was taken from the middle part of the second part of the lower Taiyuan Formation in the Wenwan section (~4.7 m). The grain content was less than 5%, with moderate separation. The limestone was supported by a matrix, which was made of muds. The particles mostly comprised a small number of bioclasts and lithic fragments, which could be caused by bioturbation. In addition, bioclasts included fusuline (fu), grain size = 0.3–0.8 mm, well preserved; bivalve (bi) shell length = ~ 0.8 mm (shell filled with sparry calcite); and lithic fragment (l), particle size = 0.4–0.6 mm, (long columnar or elliptic). Furthermore, the edges of the particles were dissolved because of late diagenesis. So, it was named mudstone.


Figure 4   Microscopic image of typical limestone from the Carboniferous-Permian Taiyuan2.1.3 Packstones
Formation in Southern margin of North China. (A and B) Taiyuan Formation mudstone,comprising fusuline (fu),bivalve (bi), and lithic fragment (l), Wenwan section; (C and D) Taiyuan Formation wackstone , comprising fu,bi,crinoidea (cr), calcareous algae (c), ostracoda (o), and peloids (p), Mojie sections; (E and F) Taiyuan Formation packstone, comprise cr, fu, o, and l, Mojie sections. (A, C, and E) are the single-polarized vision fields; (B, D, and F) are the orthogonally polarized view fields.
3.1.2   Wackstones
Wackstone is widely distributed in the Wenwan, Mojie, and Baipohe sections. The sample MJ19T-19 is described below.
The sample MJ19T-19 (Figure 4 C, D) was taken from the top of the second part of limestone at the lower part of the Taiyuan Formation in the Mojie section (~ 6.5 m). The content of grains was ~20%, with poor separation. The limestone was supported by a matrix, which was made of muds. The particles mainly comprised bioclasts and peloids. In addition, bioclasts include fu, grain size = 0.2–0.4 mm, well preserved; bi, shell length = 0.3–1.6 mm (the shell was filled with sparry calcite), with a grain structure; calcareous algae (c), diameter = 0.5 mm, long columnar (spores were filled with muds); crinoids stem (cr), particle size = 0.5–0.7 mm, single crystal structure; ostracoda (o), particle diameter = ~0.3–0.4 mm, filled with sparry calcite inside the shell and presented wave extinction under an orthogonal microscope. Peloid (p) size was ~0.1–0.35 mm. So, it was named bioclastic wackstone.
3.1.3   Packstones
Packstone is widely distributed in the Wenwan, Mojie, and Baipo River sections. The sample MJ19T-11 is described below.
The sample MJ19T-11 (Figure 4 E, F) was taken from the bottom of the second part of limestone in the Mojie section of the Taiyuan Formation (~3.7 m). The content of grains was ~50%, with poor separation, and mainly constituted bioclasts and lithic fragments. The limestone was supported by particles, and the interstitial materials were muds. The bioclasts were mainly cr, which accounted for 90% of the total grain content, and the grain size was 0.2–1.2 mm, elliptic or columnar, with single crystal extinction. The pores in the middle part were filled with muds, and some grains showed serrated edges due to pressure solution. In addition, bioclasts include fu, whose size was 0.4–0.5 mm and was poorly preserved; o with particle size of 0.6–0.8 mm were filled with micrites in their cavity. The particle size of l was 0.5–1.2 mm with a micrite structure and irregular shape. In short, it was named bioclastic packstone.
The grain types and characteristics of carbonate are an important foundation of rock microscopic observation and classification of microfacies. Both endogenous and exogenous grains are found in the limestone thin sections of the Taiyuan Formation. The endogenous grains mainly consist of bioclasts and endoclasts, while exogenous grains mainly consist of terrestrial quartz grain.
3.2   Types and characteristics of grains
The grain types and characteristics of carbonate are an important foundation of rock microscopic observation and classification of microfacies. Both endogenous and exogenous grains are found in the limestone thin sections of the Taiyuan Formation. The endogenous grains mainly consist of bioclasts and endoclasts, while exogenous grains mainly consist of terrestrial quartz grain.
3.2.1   Bioclasts
As determined from the samples, bioclasts mainly consist of foraminifera, echinoderms, brachiopods, bivalves, calcareous algae, and ostracoda. Foraminifera fossils are common in the late Paleozoic. Samples WW18T-6 and WW8T-14 (Figure 5A, B) were taken as examples to describe their characteristics. For fusuline, the diameter is 1.2 mm, and chambers were filled with calcite. The spiral arms are thick and consist of dense and honeycomb layers. The wrinkle of dissepiment is a strong fold. For small foraminifera, with a particle diameter of 0.6 mm, a thick shell wall, and chambers were filled with sparry calcite.


Figure 5   Microscopic image of typical limestone grains from the Carboniferous - Permian Taiyuan Formation in Southern margin of North China
A and B are foraminifera fossils. A is fusuline fossil, and B is small foraminiferal fossils; C is Echinodermata fossil; D is brachiopods fossil; E is bivalve fossil; F is ostracoda fossil; G calcareous algae granules; H and I are lithic fragments; A–H is the single-polarized light field, and I is the orthogonal polarized light field.
The echinodermata fossils in the observation unit are stem fragments of crinoids, the original components of the fossils were high magnesium calcite, and all of them were converted to low magnesium calcite in the late diagenesis. The lamellae in the thin sections are mostly broken with different degrees of abrasion. Sample MJ19T-2 (Figure 5C) was taken as an example for description purposes. The grain size of the crinoid stem is 0.6 mm in the oblique section, with irregular long columnar with a single crystal structure. The edge is a serrated twisted structure due to pressure solution.
Brachiopod fossils are widely distributed in the observation unit, and the sample MJ19T-24 (Figure 5D) is taken as an example for description purposes. The primary mineral composition of the shell is low magnesium calcite. The shell length is 2.4 mm and has a parallel flake structure. Different shells show the diagenetic transformation.
Bivalve fossils in the observation unit are widely distributed, and the sample WW18T-54 (Figure 5E) was taken as an example for description purposes. The primary mineral composition of the bivalve shell is aragonite or high magnesium calcite, and the shell in the thin section has been transformed into low magnesium calcite with a secondary granular texture; however, the characteristic prismatic structure can be well distinguished. The shell length is 0.5 mm.
Ostracoda is mainly distributed in the Mojie and Wenwan sections. Sample WW18T-1 (Figure 5F) was taken as an example for description purposes. The shell is calcareous chitin, brown, and dark brown. The single layer shell length is 0.4 mm, with a glass fiber structure, and the cavity filled with sparry calcite.
Calcareous algae fossil was mainly distributed in wackstones at the lower part of the Mojie and Wenwan sections, and the sample MJ19T-19 (Figure 5G) was taken as an example for description purposes. The cross-section of calcareous alga is a long columnar. The alga is transformed into a grain structure by diagenesis, and its primary mineral is presumed to be aragonite or high magnesium calcite. The pore of the spore is filled with micrite.
3.2.2   Nonbioclasts
Nonbioclasts in the observation unit were mainly found in mudstone in the Mojie and Wenwan sections, which can be divided into two types according to grain source. The first type is endoclasts (Figure 5H), mainly consisting of lithoclastic fragments, with the size of grains ~0.5–1.2 mm, which is usually in oblong brecciated, elliptic, circular, or lenticular shape, with a visible reddish-brown oxide halo at the edge. The grains are well-sorted and aligned, cemented by grayish-brown calcium carbonate, and contain few bioclasts. The second type is extraclasts (Figure 5I), mainly composed of terrestrial quartz particles, with the size of particles ~0.01–0.5 mm, oval, brecciated, or poorly rounded.
3.3   Information table of carbonate micro-image dataset
The microscopic image dataset consists of 95 carbonate thin sections and 380 polarized photomicrographs. Each rock sample contains a single-polarized photomicrograph and an orthogonal photomicrograph of the same color as that observed by the naked eye under a polarized photomicrograph, and the composition in the micrograph is the same as that described in the identification report.
The thin section identification report is composed of one carbonate identification form that mainly covers the basic information of mudstone, wackstone, and packstone in the above three measured sections. The dataset description includes classifications, type of carbonate rock grain, structure, diagenesis, and so on. Table 2 is a summary table of carbonate types and lithologic information contained in the dataset.
Table 2   Type and quantity of limestone
lithologyType of limestoneAmount
limestonepackstone11
wackstone64
mudstone20
4.   Quality control and assessment
The carbonate samples in the dataset were collected from western Henan and Central Henan areas in the southern margin of North China. Based on detailed field section measurement, appropriate limestone samples were selected to create carbonate thin sections and ensure the reliability of sample sources. The carbonate slices were made following national and international standards. The thickness of the thin sections is ~0.03 mm, meeting the required standard of microscopic observation and photography.
Photomicrograph is high definition and chromatic aberration-free. In the process of microscope shooting, automatic exposure and automatic white balance are adopted to keep the color of visual observation and system photos as consistent as possible. The resolution varies according to different grain sizes, and the resolution range is 2048 × 2048 pixels. The images are uniformly saved in JPG format, ensuring the quality and clarity of micro-photos are reliable. At the same time, the authors participated in the observation and discussion of rock thin sections and micrographs, described and summarized the carbonate characteristics from different angles, and reduced the subjective deviation of carbonate classification and micrograph description.
5.   Value and significance
This dataset mainly comprises the micro-sedimentary characteristics of Permo-Carboniferous limestones of the Taiyuan Formation in southern North China. North China was situated in low latitudes during the late Paleozoic glaciation periods. This dataset can be used to link sedimentary records in low latitudes with high latitude glacial evolution. Based on the accurate field sampling and objective microscopic observation, this dataset could be combined with other related microscopic datasets to study sedimentary petrology. Moreover, it can be used as teaching material in geology, oil, and gas resources and to provide a reference for artificial intelligence identification of lithofacies.
Acknowledgments
Thank Professor Hu Xiumian and Professor Hou Mingcai, who served as special editors for the sedimentary rock micrographs. The authors thank Meng Qi for his assistance with photomicrography and thin section identification.
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Data citation
MA R, LIU C, YANG J H. A carbonate microscopic image dataset of the Permo-Carboniferous Taiyuan Formation in southern North China. Science Data Bank, 2020. (2020-07-14). DOI: 10.11922/sciencedb.j00001.00045.
Article and author information
How to cite this article
MA R, LIU C, YANG J H. A carbonate microscopic image dataset of the Permo-Carboniferous Taiyuan Formation in southern North China. Science Data Bank, 2020, 5(3). (2020-08-28). DOI: 10.11922/csdata.2020.0052.zh.
Ma rui
Main tasks: ground observation and sampling, thin sections authentication and pictures, data arrangement, and article writing.
Postgraduate student; Research direction is sedimentology.
Liu Chao
Main tasks: ground observation, guide thin sections authentication and pictures, and thesis modification.
liuchao661030@126.com
Associate professor; Research direction is Carbonate sedimentary geology.
Yang jianghai
Main tasks: Field planning design, dataset design, and thesis modification.
Associate professor; Research direction is sedimentology.
Wang yuan
Main tasks: ground observation and sampling and data arrangement.
Doctoral student; Research direction is sedimentology.
Liu jia
Main tasks: ground observation and sampling and data arrangement.
Postgraduate student, Research direction is sedimentology.
Publication records
Published: Sept. 18, 2020 ( VersionsZH1
Released: July 14, 2020 ( VersionsZH2
Published: Sept. 18, 2020 ( VersionsZH3
References
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