Abstract: Micrographs of thin sections, which are even more important now than ever as Big Data is becoming a new engine of scientific discovery, have been the basis for geological research. Micrograph data are a powerful form of geoscience data. We collected samples, segmented thin sections, performed identification under a microscope, and obtained micrographs for the Middle Jurassic clastic rocks in the northeastern Ordos Basin. The dataset comprises 208 plane- and cross-polarized micrographs of 78 samples under four or ten times magnification. Most samples are lithic sandstone, followed by fine-grained sandstone. The quartz comprises single-crystal quartz, while the feldspar is primarily microcline and plagioclase. Debris are mostly clay and siliceous debris, followed by metamorphic debris. In the study area, the micrographs can reflect the mineralogy and sedimentary formation of respective strata. The dataset can be used to show the correlation between various geological factors, and on the basis of that, to attribute the causes of varied geological formations.
Keywords: geological data; micrograph data; informatization; mineralogy; sedimentology
|Title||A dataset of Middle Jurassic clastic rocks in northeastern Ordos Basin|
|Data authors||Chao Hui, Hou Mingcai, Cao Haiyang and Liang Ziruo|
|Data corresponding author||Hou Mingcai (firstname.lastname@example.org)|
|Time range||The rock thin sections were collected in 2017 with a stratigraphic age attributable to Middle Jurassic (Yanan Formation-Zhiluo Formation; ~174–163 Ma). The photomicrographs were taken in 2018.|
|Geographical scope||Both Shenshangou (39°45′89″N, 110°11′03″E) and Gaotouyao (40°2′6.8″N, 109°38′3.7″E) sections are in northeastern Ordos Basin.|
|Polarized microscope resolution||1280*960 pixels|
|Data volume||5.01 GB|
|Data format||*.tif, *.xls, *.jpg|
|Data service system||<https://dx.doi.org/10.11922/sciencedb.j00001.00087>|
|Source of funding||National Key Basic Research Program of China (973 Program) (Grant No. 2015CB453001)|
|Dataset composition||The dataset includes three data files: (1) “Photomicrographs.zip,” which is a dataset of polarized photomicrographs of the rock thin sections in tif format, with a data volume of 4.91 Gb; (2) “Field photos of the measured sections.zip,” which contains the field photos of the measured sections and the characteristics of outcrops, with a data volume of 107 Mb; (3) “Information table.xls,” which contains profile and corresponding identification data of the rock thin sections, with a data volume of 33 kb.|
With the development of Internet, society has become more digitized and gradually networked. Moreover, people’s information requires to have changed from text to image. Thus, obtaining massive image information has become a priority. Big Data has been introduced into geology, which has transformed geology from an observation discipline to data science. The earliest geology research relied on outcrop observation. The microscope enabled geological science to turn from macroscopic to microscopic. The microscopic thin observation can completely and truly reflect the characteristics of a rock sample microstructure and mineral composition, which is one of the most basic tools for geological research. Thus, it is essential to develop a micrograph dataset for rock samples. The Ordos Basin, which is the most well-preserved inland petroliferous basin in the Mesozoic in central and western China, lies in the North China platform. . In Middle Jurassic, the northeastern part of the basin is located at the intersection of Yinshan structural and Taihangshan structural belts. It is an ideal place to study the closure of the Mongolia-Okhotsk Ocean Basin, subduction of the palaeo-Pacific plate, and intracontinental orogenic . The northeastern part of the basin is the primary coal and uranium enrichment area. Based on the above, it is essential to analyze the sedimentary characteristics of northeastern Ordos Basin strata in the Middle Jurassic, which has an important guiding significance for clarifying the source of clastic materials, tectonic evolution, and discussing the origin of coal formation and mineralization.
In this study, considering the micro-sedimentary characteristics of Middle Jurassic clastic rocks in northeastern Ordos Basin as a goal, as per a thin micrograph, we construct a corresponding microscopic image dataset. The dataset could provide image information for additional geological research in a related area, improve the spatial and non-spatial nature of geology research, and promote a new scientific paradigm of multidisciplinary integration.
We collected 78 clastic rock samples, 34 from the Gaotouyao section and 44 from the Shenshangou section. Samples were collected from fresh surfaces without veins, roots, or strongly weathered surfaces.
2.2 Micrograph data
Under a polarizing microscope, the thin observation describes the crystallization characteristics of minerals, determines optical properties, investigates its mineral composition and structure, analyzes the formation sequence of minerals and genetic characteristics, and finally names the sample. The image is obtained and saved as per different magnifications.
The dataset includes macrograph (Fig.1), macrograph (Fig.2), and micrograph information table. The macrograph shows the macroscopic lithology, formation boundary, and sedimentary structure of the Middle Jurassic strata in the study section. Among them, 11 and 7 for the Gaotouyao and Shenshangou sections, respectively. The image format is *jpg.
Fig. 1 Clastic rock in outcrop section of Middle Jurassic in the northeastern Ordos Basin
A：Section macrograph；B：Boundary of Cretaceous and Middle Jurassic；C：Ginger grit sandstone；D：Miscellaneous conglomerate；E：Gray white grit sandstone；F：Khaki fine sandstone with mudstone；G：Flesh red grit sandstone；H：Dark gray mudstone with carbonaceous
Fig. 2 Micrographs of Clastic rock of Middle Jurassic in the northeastern Ordos Basin
A：Silt mudstone with biotite, Monopolarization, Zhiluo Fm; B：Medium fine-grained feldspar quartz sandstone with sericite, Orthogonal polarized, Yanan Fm; C：Medium coarse lithic sandstone, potassium feldspar with cad type double crystal, Orthogonal polarized, Yanan Fm; D：Medium fine-grained lithic quartz sandstone, plagioclase with polycrystalline double crystal, Monopolarization, Yanan Fm; E：Medium coarse quartz sandstone, single-crystal quartz contact in grain linear, Orthogonal polarized, Yanan Fm; F：Coarse lithic sandstone, polycrystalline quartz contact in suture，Orthogonal polarized, Zhiluo Fm
Note that 516 micrographs of 78 clastic rock from the Middle Jurassic (J2y and Zhiluo Formation J2z of Yan’an Formation) in the northeastern margin of Ordos Basin. Thirty-four samples of Gaotouyao section, comprising 27 sandstones, 1 siltstone, and 6 mudstone samples, with 222 images; 44 samples of Shenshangou section, comprising 33 sandstones, 7 siltstones, and 4 mudstones, with 294 images (Table 1). Micrograph named after “sample name” + “magnification und” + “(orthogonal/single-polarization symbol),” and the image format is *tif.
|Section||Age||Geographical scope||Photo amount||Thin amount|
|Gao Touyao||Yanan Fm. Middle Jurassic（GtJ2y）|
Zhiluo Fm. Middle Jurassic（GtJ2z）
|Shen Shangou||Yanan Fm. Middle Jurassic（ShJ2y）|
Zhiluo Fm. Middle Jurassic（ShJ2z）
The micrograph information table comprises geological setting, strata age, and mineral composition (such as particle type and relative content), interstitial characteristics (such as terrigenous heterogeneity and splendid calcite), structure, and diagenesis. The image format is *xls.
In this study, we collected samples from the outcrop section. We compared them with previous studies to ensure the authenticity and credibility of stratigraphic data. Thin observations under the microscope and photomicrographs were obtained in the microscopy laboratory of the Chengdu University of Technology by sedimentology major students. For each field of view, the corresponding single-polarized or cross-polarized micrographs were taken, enabling the images to be clear and reliable.
Geological phenomena are complex, and the microcosm is ever-changing. Compared with the two sections in the study area, this micrograph dataset focuses on the Middle Jurassic strata of Ordos Basin, which is accurate and credible. Moreover, the dataset can provide a certain quantitative reference value in the study of the Ordos Basin in the Middle Jurassic.
Most of the previous study focuses on quantitative research such as pore image retrieval [5-6], mineral identification [7-9], and particle size calculation [10-11]. However, to date, geology is still a descriptive science category. Most geological processes, such as tectonics, magmatism, sedimentation, metamorphism, mineralization, coal formation, and oil and gas accumulation. However, few geological processed can be used simply deterministic or random mathematical models to determine . In this study, the dataset is more qualitative than the above. For example, diagenesis is determined based on the contact relationship of mineral particles, the sedimentary environment is discussed through the cement, and the sediment source is analyzed by counting the heavy mineral components.
However, the basic theory of geology is the geological age. Moreover, the change in geological conditions and rock properties of different ages varies. For example, Jurassic strata in Tibet were carbonate marine but were terrestrial during the same period in north China. Thus, this micrograph dataset is more non-subject, which can be obtained and used by anyone. By combining multiple geologic data, additional hidden relationships between geological elements will be explored.
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CHAO H, HOU MC, CAO HY, et al. A micrograph dataset of Middle Jurassic clastic rocks in the northeastern Ordos Basin. Science Data Bank, 2020. (2020-08-17). DOI: 10.11922/sciencedb.j00001.00087.
How to cite this article
CHAO H, HOU MC, CAO HY, et al. A micrograph dataset of Middle Jurassic clastic rocks in the northeastern Ordos Basin. China Scientific Data, 2020, 5(3). (2020-09-26). DOI: 10.11922/csdata.2020.0062.zh.