scholarly journals Triassic Low Temperature Hydrothermal Activities(LTHA) From the Ordos Basin of Northern China

2021 ◽  
Author(s):  
Jiyuan You ◽  
Yiqun Liu ◽  
Dingwu Zhou ◽  
Yiyao Yang
Keyword(s):  
Hydrothermal Vents ◽  
Sedimentary Environment ◽  
Ordos Basin ◽  
Sedimentary Rocks ◽  
Northern China ◽  
Source Rocks ◽  
Three Samples ◽  
The Ordos Basin ◽  
Hydrothermal Activities

Abstract Because few well-preserved hydrothermal channels have been found in terrestrial sedimentary rocks, research on LTHA in geological history is relatively sparse. In this study, we present our original discovery of “hydrothermal channels” from the Chang 7 source rocks of the Triassic Yanchang Formation in the Ordos Basin, China, and provide the best evidence for deciphering LTHA preserved in the geological record (i.e., sedimentary rocks). Three possible LTHA samples (i.e., samples 1551.6, 1551.6-2 and 1574.4) were collected for this study; they were interbedded with mudstones and oil shales, indicative of a deep-lake sedimentary environment. All three samples consist mainly of anhydrite, pyrite, and dolomite with the formation of mineral zoning across the walls of these structures, suggesting a sulfate-dominated stage and a carbonate-sulfide replacement stage. Moreover, their in situ geochemistry is characterized by high Eu, U, Th, Sr, Mn and U/Th ratios, which are typical indicators of hydrothermal vents. In addition, their S isotopes range from 7.89% to 10.88%, the magmatic sulfur accounted for approximately 94.3%, implying a possible magmatic trigger for these hydrothermal channels. All this evidence shows that the Triassic sedimentary rocks of the Ordos Basin probably contain LTHA. Comparing ancient LTHA to modern hydrothermal chimneys, we should note the important implications of LTHA; their formation mechanism may have been related to oil production, and they are possible indicators for future oil investigations. Further, they have great significance for studying the hydrothermal properties of primary dolomite.

scholarly journals Triassic hydrothermal chimneys from the Ordos Basin of Northern China

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jiyuan You ◽  
Yiqun Liu ◽  
Dingwu Zhou ◽  
Yiyao Yang
Keyword(s):  
Hydrothermal Vents ◽  
Sedimentary Environment ◽  
Ordos Basin ◽  
Sedimentary Rocks ◽  
Northern China ◽  
Hydrothermal Activity ◽  
Source Rocks ◽  
Three Samples ◽  
The Ordos Basin

AbstractBecause few well-preserved hydrothermal chimneys have been found in terrestrial sedimentary rocks, research on paleo-thermal vents in geological history is relatively sparse. In this study, we present our original discovery of “hydrothermal chimneys” from the Chang 7 source rocks of the Triassic Yanchang Formation in the Ordos Basin, China, and provide the best evidence for deciphering hydrothermal activity preserved in the geological record (i.e., sedimentary rocks). Three possible chimney samples (i.e., samples 1551.6, 1551.6–2 and 1574.4) were collected for this study; they were interbedded with mudstones and oil shales, indicative of a deep-lake sedimentary environment. All three samples consist mainly of anhydrite, pyrite, and dolomite with the formation of mineral zoning across the walls of these structures, suggesting a sulfate-dominated stage and a carbonate-sulfide replacement stage. Moreover, their in situ geochemistry is characterized by high Eu, U, Th, Sr, Mn and U/Th ratios, which are typical indicators of hydrothermal vents. In addition, their S isotopes range from 7.89% to 10.88%, near the values of magma sulfur, implying a possible magmatic trigger for these hydrothermal vents. All this evidence shows that the Triassic sedimentary rocks of the Ordos Basin probably contain hydrothermal chimneys. Comparing ancient hydrothermal chimneys to modern hydrothermal chimneys, we should note the important implications of ancient chimneys; their formation mechanism may have been related to oil production, and they are possible indicators for future oil investigations. Further, they have great significance for studying the hydrothermal properties of primary dolomite.

Discovery and geological significance of the Magma-hydrothermal micro-jets at the bottom of a lake: A case from the Chang 7 section of the Yanchang Formation of the Triassic in the Ordos Basin, China

2020 ◽  
Author(s):  
Jiyuan You ◽  
Yiqun Liu ◽  
Dingwu Zhou
Keyword(s):  
Hydrothermal Vents ◽  
Ordos Basin ◽  
Hydrothermal Activity ◽  
Life Forms ◽  
Major Elements ◽  
Source Rocks ◽  
Geological History ◽  
Yanchang Formation ◽  
The Ordos Basin

<p>The "black chimney" type of hydrothermal vents in the modern deep sea have become a popular research topic in many disciplines. Due to the actual conditions, the research on palaeo-thermal vents in geological history is relatively low. Fortunately, the discovery of hydrothermal vents and bio-fossils from the Chang 7 source rocks of the Yanchang Formation of the Triassic in the Ordos Basin, China, provides the best evidence for deciphering hydrothermal activity during geological history. Here, we report a case study. Through ordinary sheet observation, scanning electron microscopy and electron probe observation, layered grained siliceous rocks, dolomites, and hydrothermal mineral combinations, such as pyrite + dolomite + gypsum and calcite + barite, are found. Their unique petrological characteristics, mineral composition, and structure confirm the existence of palaeo-thermal fluid vents. We further analysed the geochemical characteristics and in situ isotope characteristics. The study found that Cs, U, Th, Pb, Ba and other trace elements of the sample showed positive abnormalities, in which values of U/Th were high; in addition, the enrichment of major elements such as Sr, Mn, and the in situ sulphur isotopes of pyrite reached 7.89%-10.88%. This study of hydrothermal vents over geological history is expected to provide new insights on the life forms of various extreme microorganisms in hydrothermal environments and on their formation of high-quality source rocks.</p>

scholarly journals Analysis of the charging process of the lacustrine tight oil reservoir in the Triassic Chang 6 Member in the southwest Ordos Basin, China

2017 ◽  
Vol 54 (12) ◽  
pp. 1228-1247
Author(s):  
Zhengjian Xu ◽  
Luofu Liu ◽  
Tieguan Wang ◽  
Kangjun Wu ◽  
Wenchao Dou ◽  
...  
Keyword(s):  
Ordos Basin ◽  
Source Rocks ◽  
Driving Mechanism ◽  
Tight Oil ◽  
Geological Time ◽  
Tight Sandstone ◽  
Main Production ◽  
The Ordos Basin ◽  
Homogenization Temperatures ◽  
Quartz Grains

With the success of Bakken tight oil (tight sandstone oil and shale oil) and Eagle Ford tight oil in North America, tight oil has become a research focus in petroleum geology. In China, tight oil reservoirs are predominantly distributed in lacustrine basins. The Triassic Chang 6 Member is the main production layer of tight oil in the Ordos Basin, in which the episodes, timing, and drive of tight oil charging have been analyzed through the petrography, fluorescence microspectrometry, microthermometry, and trapping pressure simulations of fluid inclusions in the reservoir beds. Several conclusions have been reached in this paper. First, aqueous inclusions with five peaks of homogenization temperatures and oil inclusions with three peaks of homogenization temperatures occurred in the Chang 6 reservoir beds. The oil inclusions are mostly distributed in fractures that cut across and occur within the quartz grains, in the quartz overgrowth and calcite cements, and the fractures that occur within the feldspar grains, with blue–green, green, and yellow–green fluorescence colours. Second, the peak wavelength, Q650/500, and QF535 of the fluorescence microspectrometry indicate three charging episodes of tight oil with different oil maturities. The charging timings (141–136, 126–118, and 112–103 Ma) have been ascertained by projecting the homogenization temperatures of aqueous inclusions onto the geological time axis. Third, excess-pressure differences up to 10 MPa between the Chang 7 source rocks and the Chang 6 reservoir beds were the main driving mechanism supporting the process of nonbuoyancy migration.

Two episodes of structural fractures: Numerical simulation of Yanchang Oilfield in the Ordos basin, northern China

2018 ◽  
Vol 97 ◽  
pp. 223-240 ◽  
Author(s):  
Yaohua Li ◽  
Yan Song ◽  
Zhenxue Jiang ◽  
Lishi Yin ◽  
Qun Luo ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Ordos Basin ◽  
Northern China ◽  
The Ordos Basin

The composition and distribution of nodular monazite in the Lower Palaeozoic rocks of Great Britain

1987 ◽  
Vol 51 (360) ◽  
pp. 271-280 ◽  
Author(s):  
D. Read ◽  
D. C. Cooper ◽  
J. M. McArthur
Keyword(s):  
Great Britain ◽  
Host Rock ◽  
Sedimentary Rock ◽  
Sedimentary Rocks ◽  
Source Rocks ◽  
Low Grade ◽  
South West ◽  
Lower Palaeozoic ◽  
South West England

AbstractMillimetric, ellipsoidal monazite nodules found within Lower Palaeozoic sedimentary rocks in Wales, south-west England and Brittany are characterised by a pronounced zonation of light and heavy REE, an inclusion fabric of low-grade metamorphic minerals indistinguishable from the host rock and a low Th content. They are interpreted as the product of in situ recrystallization of detrital monazites derived from pegmatitic or granitic source rocks and are potentially useful as indicators of Lower Palaeozoic sedimentary rock provenance.

GEOCHEMICAL CHARACTERISTICS AND SOURCE OF CHANG 8 CRUDE OIL IN THE EAST PART OF SHANBEI SLOPE, ORDOS BASIN, CHINA

2021 ◽  
pp. 1-31
Author(s):  
Zhenglu Xiao ◽  
Shijia Chen ◽  
Xiangdong Yin ◽  
Pan Wang ◽  
Jiang Zhu ◽  
...  
Keyword(s):  
Crude Oil ◽  
Source Rock ◽  
Higher Plants ◽  
Saturated Hydrocarbon ◽  
Vitrinite Reflectance ◽  
Sedimentary Environment ◽  
Ordos Basin ◽  
Aquatic Organisms ◽  
Source Rocks ◽  
East Part

There are three sets of potential source rocks in the Yanchang Formation in the east part of the Shanbei Slope in the Ordos Basin. Based on the experimental results of total organic carbon, vitrinite reflectance, rock organic matter extraction, and saturated hydrocarbon chromatography (GC-MS), we have analyzed the geochemical and biomarker characteristics of the Chang 7, Chang 8, and Chang 9 source rocks, and the Chang 8 reservoir extracts and find that the Chang 7, Chang 8, and Chang 9 source rocks were deposited in the sedimentary environment of weak oxidation and weak reduction. Higher plants contribute more in the parent materials of the Chang 7 and Chang 9 source rocks, whereas lower aquatic organisms contribute more to the Chang 8 source rock. However, the source of the Chang 8 crude oil in the east part of Shanbei Slope does not match the chemical fingerprint of the Chang 8 source rock. To address this problem, we examined samples taken from the Zhidan oilfield, where our results show that the Chang 7, Chang 8, and Chang 9 source rocks all have hydrocarbon-supplying capacity. The relative abundance of regular steranes (C27, C28, C29) and hopane (17α(H), 21β(H)-hopane, 17β(H)-rearranged hopane, 18α(H)-22,29,30-trinorhopane) provides a means to assign the crude oil components to a given. Further analysis of the biomarkers of the three source rocks and those of the Chang 8 crude oil indicate that crude oil in the Chang 8 reservoir was not generated in situ; rather, it was supplied by the underlying Chang 9 source rock.

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