Abstract: During the Cambrian,the North China platform was a typical epeiric platform. A variety of carbonate facies developed in the North China platform of Miaolingian-Furongian epochs. This database contains 825 photomicrographs of 104 thin sections. The photomicrographs were systematically described using the Dunham (1962) classification scheme modified by Embry and Klovan (1971). The dataset consists of two subsets storing columnar sections and photomicrographs, at a total data volume of 390 MB. The two subsets are interlinked, providing a fundamental framework to better understand the Cambrian carbonate depositional sequences and processes along the North China platform. The dataset can be utilized for basic geological education and research, and may be useful for petroleum exploration, artificial intelligence, science popularization, outreach, and other related works.
Keywords: North China platform; Cambrian; carbonate microfacies; facies analysis
|Title||Photomicrograph dataset of Cambrian Miaolingian–Furongian carbonates at the Jiulongshan section in western Shandong|
|Data corresponding author||Chen Jitao (email@example.com)|
|Data author(s)||Xin Hao, Chen Jitao|
|Time range||We collected the rock samples, characterized the stratigraphic columns, and took images of lithofacies and outcrops for this study during 2006–2011. Photomicrographs were taken in 2020.|
|Geographical scope||Jiulongshan section (36°4'58.46" N, 117°44'42.20" E), Ji’nan, Shandong Province|
|Polarized microscope resolution||1388 × 1040 pixels|
|Data volume||380 MB|
|Data format||*.jpg, *.xls|
|Data service system||<https://dx.doi.org/10.11922/sciencedb.j00001.00095>|
|Source(s) of funding||National Natural Science Foundation of China (Grant No. 41302077); Strategic Priority Research Program of the Chinese Academy of Sciences(B) (Grant No. XDB26000000).|
|Dataset/Database composition||The dataset includes three data files, which are: “stratigraphic columns,” “photomicrographs,” and “information table”. (1) “Stratigraphic columns” include 26 pictures, with a data volume of 43.9 MB; (2) “Photomicrographs” contain 825 polarized photomicrographs (*.jpg) of 104 thin sections, with a data volume of 346 MB; (3) “Information table” of database (*.xls) contains data sheets for rock thin section identification, with a data volume of 15.9 KB.|
The North China platform formed during a second-order transgression, mainly consisting of a shallow marine facies from an epeiric sea[1-2]. Several geological events occurred across the Cambrian Miaolingian–Furongian boundary, including a positive excursion of carbon and sulfur isotopes, global sea-level fall, faunal turnover, diversification of new organisms, and microbe-metazoan transitions.
Based on the description and analysis of carbonate rocks of the Cambrian Miaolingian–Furongian sections in western Shandong, this paper provides systematic sedimentological data for understanding the sedimentary sequences and processes of carbonate rocks in the North China platform.
The western Shandong area lies in the east of the North China platform, characterized by widely developed and well-preserved Cambrian successions. The Jiulongshan section is located in Gangcheng District of Laiwu (now Jinan city, Fig. 1), where continuous Cambrian strata outcrops (Fig. 2). Since the 1980s, many studies have been conducted on lithostratigraphy, sequence stratigraphy, and biostratigraphy[5-9].
However, basic research material, photomicrographs, and data in this area are inadequate. Also, the degree of information sharing has been relatively low, resulting in unnecessarily repetitive work. Considering these problems, this paper summarizes the field and thin section data of the Jiulongshan section, while establishing the carbonate photomicrograph dataset, in order to provide a basis for subsequent scientific research, teaching, science popularization, outreach, and other relevant works.
The Jiulongshan section was selected as the focus of research conducted through literature review and fieldwork. The actual thickness and sedimentary characteristics of the strata were recorded in detail on the scale of 1:50. Photographs and samples were taken in consideration of the lithological variation, and thin sections were for the representative facies for the purposes of microscopic observation and analysis.
Observations of the thin sections were completed in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, using the Zeiss microscope and imaging system. The collection of photomicrograph information and the designation of thin sections were based on standards determined by standards provided in this special issue.
This paper complies with the nomenclature of carbonate rocks previously proposed by Embry and Klovan on the basis of Dunham (Fig. 3). The nomenclature is based on the sedimentary texture, original components, supporting fabric, and grain content. In the Jiulongshan section, multiple types of carbonate facies, such as lime mudstone, wackestone, packstone, grainstone, floatstone, and rudstone, are identified. In addition, various microbialites are present in this section, showing abundant calcified microbial fossils, which have been described separately.
3.1 Columnar sections
All images in the sedimentologic columns subset are in JPG format and the total thickness of the succession is about 260 m. The rock assemblage, structural characteristics, and stratigraphic thickness of the Jiulongshan section are presented in detail on a scale of 1:50 (Fig. 4).
A subset of the photomicrographic data consists of 825 polarizing micrographs of 104 thin sections in JPG format (Figure 5). The micrograph is named “thin section number” + “m” + “digital serial number of camera field” + “plane-polarizing symbol, -”. Different scales, such as 1, 5, and 10 times, are selected, and a white line scale is placed in the lower right corner, with the unit of μm (the scale of the 5-fold line segment could not be automatically added due to equipment constraints, and the scale is displayed separately in the data subset).
3.3 Information table
The thin section identification information table consists of one carbonate rock identification form, which contains the basic information about the thin sections of lime mudstone, wackestone, packstone, grainstone, floatstone, rudstone, and microbialite in the Jiulongshan section. The data description includes information about the thin section name, rock name, grain type, image number, geographic location, and stratum location.
A total of 104 thin sections were identified and photographed (Table 1, Figure 6). Among them, there are 20 lime mudstones, predominantly composed of carbonate mud, clay, and/or microcrystals; 13 wackestones with grains of mainly calcite crystals, peloids, and intraclasts; 8 packstones with grains of bioclasts, calcite crystals, and intraclasts; 19 grainstones with grains of mostly ooids, bioclasts, and calcite crystals; 22 rudstones and 8 floatstones, all of which contain intraclasts. There are also 14 microbialites that are mainly composed of calcified microbes and other carbonate components.
The samples were collected from the Jiulongshan section. Only the representative and well-preserved carbonate samples were selected for sample preparation. In compliance with national and international standards, thin section thickness is 0.03 mm.
The micrographs were taken in high quality and contain no color differences. During the process of microscopic photography, automatic exposure and white balance levels were used to make eye observations and system photo colors as consistent as possible. The resolution varies according to different grain sizes, so the quality and clarity of microphotographs are reliable. In order to ensure the quality and accuracy of the data, the authors repeatedly checked and verified the process of thin section identification and description and discussed the data with fellow scholars.
This dataset is based on the second author's research on the Jiulongshan section, including sedimentary logs (columnar sections), photomicrographs, and the identification information table of the thin sections. The dataset contains detailed descriptions and illustrations of the microscopic characteristics of the rock samples, such as the location of sample collection, field macroscopic characteristics and component structures, which all provide an important basis for the in-depth understanding of carbonate sedimentary sequences and processes at the North China platform. Meanwhile, this dataset can be used in the teaching and research of geology and can provide basic materials for oil and gas explorations, artificial intelligence, popularization of science, and other related works.
The dataset is simple in structure and the following points should be noted when using it:
(1) All thin sections in the dataset are preserved in the research group of Chen Jitao, Nanjing Institute of Geology and paleontology, Chinese Academy of Sciences. If the micrographs provided in the above datasets cannot meet the needs of further research, the authors of this paper can be contacted to request further use of these thin sections.
(2) If the set of images is used on its own, it can be downloaded directly from the database. However, if we need to solve further geoscience related scientific problems, we need to combine the geographic location provided in the data information table as well as the geological age and tectonic background of the rock formation.
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XIN H, CHEN JT. A photomicrograph dataset of Cambrian Miaolingian–Furongian carbonates at the Jiulongshan section in western Shandong. Science Data Bank, 2020. (2020-09-02). DOI: 10.11922/sciencedb.j00001.00095.
How to cite this article
XIN H, CHEN JT. A photomicrograph dataset of Cambrian Miaolingian–Furongian carbonates at the Jiulongshan section in western Shandong. China Scientific Data, 2020, 5(3). (2020-09-29). DOI: 10.11922/csdata.2020.0066.zh.