Details
| Original language | English |
|---|---|
| Article number | e12243 |
| Journal | Island Arc |
| Volume | 27 |
| Issue number | 3 |
| Early online date | 27 Feb 2018 |
| Publication status | Published - May 2018 |
Abstract
Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer-scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro-laminae and calculated sedimentation rate, the micro-lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo-Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.
Keywords
- Cretaceous, humid climate, Jurassic, lake, Mongolia, oil shale, U–Pb age, varve
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
Sustainable Development Goals
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In: Island Arc, Vol. 27, No. 3, e12243, 05.2018.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia
AU - Hasegawa, Hitoshi
AU - Ando, Hisao
AU - Hasebe, Noriko
AU - Ichinnorov, Niiden
AU - Ohta, Tohru
AU - Hasegawa, Takashi
AU - Yamamoto, Masanobu
AU - Li, Gang
AU - Erdenetsogt, Bat Orshikh
AU - Heimhofer, Ulrich
AU - Murata, Takayuki
AU - Shinya, Hironori
AU - Enerel, G.
AU - Oyunjargal, G.
AU - Munkhtsetseg, O.
AU - Suzuki, Noriyuki
AU - Irino, Tomohisa
AU - Yamamoto, Koshi
N1 - Funding information: Grant-in-Aid for Scientific Research (B), Grant/ Award number: 21403008 and 25302011; Fujiwara Natural History Foundation; Grant for Environmental Research Projects from the Sumitomo Foundation, Grant/Award number: 143485; Young Scientific Research (B), Grant/ Award number: 25870309 We are grateful to B. Gantsolmon, S. Kito, S. Yogo, M. Nozaki and A. Matsumoto for their analytical and technical assistance. We are also grateful to Enkhtogs and Orgil of Cameco Mongolia LLC for donation of chronological samples. We also appreciate to Y. Kouchi for comments and corrections for the U–Pb age data. We are also grateful to R. Barsbold, K. Tsogtbaatar, Y. Khand, N. Katsuta and F. Hirsch for fruitful comments of the manuscript. We are also grateful to detail and constructive reviews by Y. I. Lee, H. Weissert, and AE S. Bajpai. This paper is a contribution to UNESCO-IUGS IGCP608 “Cretaceous ecosystems and their responses to paleoenvironmental changes in Asia and the Western Pacific”. This study was supported financially by Grant-in-Aid for Young Scientific Research (B) (No. 25870309), Grant for Environmental Research Projects from the Sumitomo Foundation (143485), and Fujiwara Natural History Foundation provided to H. Hasegawa, and Grant-in-Aid for Scientific Research (B) (No. 21403008 and 25302011) provided to H. Ando.
PY - 2018/5
Y1 - 2018/5
N2 - Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer-scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro-laminae and calculated sedimentation rate, the micro-lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo-Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.
AB - Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer-scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro-laminae and calculated sedimentation rate, the micro-lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo-Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.
KW - Cretaceous
KW - humid climate
KW - Jurassic
KW - lake
KW - Mongolia
KW - oil shale
KW - U–Pb age
KW - varve
UR - http://www.scopus.com/inward/record.url?scp=85042543180&partnerID=8YFLogxK
U2 - 10.1111/iar.12243
DO - 10.1111/iar.12243
M3 - Article
AN - SCOPUS:85042543180
VL - 27
JO - Island Arc
JF - Island Arc
SN - 1038-4871
IS - 3
M1 - e12243
ER -