2023 Vol. 29, No. 4

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2023, 29(4)
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2023, 29(4)
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Cenozoic tectonic sedimentation and magmatism
Cenozoic tectonics and geomorphic evolution of the lower Jinsha River on the southeastern margin of the Tibetan Plateau
WANG An, WANG Guocan, WANG Tuanle, SHI Yan, WEI Jie, LI Haoruo, LYU Ganyu
2023, 29(4): 453-464. doi: 10.12090/j.issn.1006-6616.2023043
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The southeastern margin of the Tibetan Plateau is distinguished by a vast transition zone with hundreds of thousands of square kilometers of low-relief surfaces, which provides an ideal window for unraveling the timing, process, and mechanisms of the tectonic propagation and surface uplift. In order to reveal the Cenozoic tectonic response and geomorphic evolution of the southeastern margin of the Tibetan Plateau, a comprehensive study in the lower Jinsha River was conducted with a tectonic investigation, tectonic-landform and low-temperature thermochronological data analysis. The results show that the southeastern margin of the Tibetan Plateau remained in NW-shortening as early as the Eocene, forming widespread folds. However, we suggest that in the Paleogene, the lower Jinsha River of the southeastern margin of the Tibetan Plateau was marked by a low hilly topography with rather limited surface uplift. In the Late Oligocene–Early Miocene, the study area was characterized by a long-term stage with low denudation rates, which promoted the formation of widespread low-relief surfaces. Since the late Neogene, the southeastern margin of the Tibetan Plateau has undergone regional shortening deformation and significant surface uplift with a simultaneous incision along large rivers, forming the present landforms characterized by high-elevation low-relief surfaces and deep gorges. The late Neogene surface uplift across the southeastern margin of the Tibetan Plateau is suggested to be closely related to the shortening deformation and associated crustal thickening. In contrast, the mid-lower crustal thickening by channel flow might not be indispensable.

Stratigraphic sequence characteristics and geochronology research progress of the Cenozoic in the arcuate tectonic belt on the northeastern margin of the Tibet Plateau
DONG Xiaopeng, LI Zhenhong, JING Xianghui, CUI Jiawei, HUANG Ting, KOU Linlin
2023, 29(4): 465-484. doi: 10.12090/j.issn.1006-6616.2023048
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The Cenozoic tectonic deformation and sedimentary processes in the arcuate tectonic belt along the northeastern margin of the Tibetan Plateau have been influenced by the remote effect of the subduction of the Pacific Plate as well as controlled by the northeastward extension of the Tibetan Plateau. Determining the sedimentary age of the Cenozoic strata is an essential prerequisite for understanding these tectonic deformation and sedimentary processes. However, the sequence and depositional age of the Cenozoic strata in the arcuate tectonic belt is still controversial. This paper systematically studied the Paleoproterozoic to Neoproterozoic sedimentary sequences and stratigraphic ages in the arcuate tectonic belt. The results show that the sedimentary ages of the Sikouzi Formation, the Qingshuiying Formation, the Zhang'enbao Formation, and the Ganhegou Formation in the arcuate tectonic belt are the Middle to Late Oligocene, the Late Oligocene–Early Miocene, the Middle Miocene–Late Miocene, and the Late Miocene-Pliocene, respectively. We systematically analyzed the two unconformities of the Paleocene to Neoproterozoic and refined their formation age as well as geotectonic significance. The first unconformity developed between the Qingshuiying Formation and the Zhang'enbao Formation in the Early-Middle Miocene, which indicates the appearance of the remote effect caused by the northeastward extrusion of the Tibet Plateau at about Early Miocene. The second unconformity developed between the Zhang'enbao Formation and the Ganhegou Formation, which implies the summit of tectonic activities caused by the northeastward extrusion of the Tibet Plateau at about the Late Miocene. It is concluded that the Cenozoic basins have evolved through three stages based on the coupling relationship between the sedimentary process and the tectonic evolution. From the Middle Oligocene to the Early Miocene, the tectonic stress field of the arcuate tectonic belt was controlled by extension under the remote effect of the rollback of the subducted Pacific Plate. The tectonic stress field changed into compression under the effect of the northeastward extrusion of the Tibet Plateau from the Middle to Late Miocene; Significant and sustainable tectonic uplift developed in the arcuate tectonic belt from the Late Miocene to Pliocene, and the Cenozoic basins were divided by the strike-slip fault systems.

The initial time of the Fen–Wei graben system: Constraints from geochronology of the Qifeng granite porphyry dikes in the Zhongtiaoshan Mountains
CUI Jiawei, LI Zhenhong, JING Xianghui, KOU Linlin
2023, 29(4): 485-496. doi: 10.12090/j.issn.1006-6616.2023039
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The Fen–Wei graben system is an essential Cenozoic extensional fault–depression belt in the central part of the North China craton. Previous research achievements mainly focused on its formation process and dynamic mechanism, but the initial time has been unresolved due to the lack of quantitative dating objects. This paper first reports the granite porphyry dikes in the andesite of the Majiahe formation in the Xionger group of the Zhongtiaoshan orogenic belt adjacent to the Fen–Wei graben system. The dating results of the granite porphyry dikes indicate that the age sequence concentrates mainly in two stages, 1769.8 ± 8.7 Ma and 69.14 ± 0.85 Ma. The former is consistent with the primary age of the volcanic rocks of the Xionger group, representing the characteristics of inherited zircons, and the latter represents the formation age of the granite porphyry dikes. The Ga/Al value ratios of granite porphyry dikes of the Qifeng samples are all greater than 2.6, characterized by enriched silicon, alkali, potassium, depleted calcium, and high magnesium. The rare earth elements are enriched in light and depleted in heavy rare earth elements. The Qifeng granite porphyrite dikes are I-type granites, indicating that the tectonic setting is extensional. The research provides new evidence for the initial time of the southern part of Fenwei graben in the Cenozoic.

Late Pleistocene stratigraphic sequence and geologic significance of the Kaolao Tableland in the Yuncheng Basin
NAN Debin, LI Zhenhong, DONG Xiaopeng, KOU Linlin, WEI Lijie
2023, 29(4): 497-511. doi: 10.12090/j.issn.1006-6616.2023042
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The ancient Fen River diversion was a crucial earth's surface transformation in the Yuncheng Basin during the Cenozoic. The time frame for the diversion of the ancient Fen River is still characterized by two views: the middle Pleistocene and the late Pleistocene, which has yet to be finalized. This study investigated the late Pleistocene sedimentary sequence of the Kaolao Tableland in the Yuncheng Basin, and the critical time frame of the sedimentary sequence transition was determined based on optically stimulated luminescence (OSL) dating results. The causes of the late Pleistocene sedimentary sequence of the Kaolao Tableland and the geological factors that controlled the sequence were analyzed using detrital zircon U–Pb isotope dating. It is concluded that the late Pleistocene sedimentary sequence of the Kaolao Tableland in the Yuncheng Basin is characterized by a two-layer structure, with fluvial sands in the lower part and eolian loess in the upper part. Based on the OSL dating results, the formation time of the boundary between these two parts is between ~76–63 ka B.P. Comparative analysis of detrital zircon age sequences indicates that the early Pleistocene fluvial sands in the Kaolao Tableland and sediments in the ancient Fen River have similar age sequence characteristics. Therefore, it can be deduced that the regional tectonic uplift of the northeastern Emei Terrace in the middle of the late Pleistocene resulted in the diversion and exit of the ancient Fen River from the Yuncheng Basin and the sedimentary facies began to change from fluvial to eolian. The tectonic uplift in the middle of the late Pleistocene extensively developed around the Ordos Basin, and that indicates a significant tectonic uplift of the Tibet Plateau during this time, whose remote effect might be the major cause for the exit of the ancient Fen River from the Yuncheng Basin. This research provides new sedimentary evidence for the time frame of the ancient Fen River diversion in the Yuncheng Basin.

40Ar/39Ar ages of Quaternary volcanic rocks from the midwest of the Leizhou Peninsula, and their geologic significance
LI Xiang, ZHANG Zongyan, LI Haiyong, ZHANG Jianyu, BAI Xiujuan
2023, 29(4): 512-521. doi: 10.12090/j.issn.1006-6616.2023098
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Quaternary volcanic rocks are widely distributed in the Leizhou Peninsula, but the age of volcanic formation remains controversial. This study used the high-precision laser stepwise heating 40Ar/39Ar method to date the age of volcanic samples from the midwest of the Leizhou Peninsula, and two volcanic cycles were determined by combining the contact relationship with the neighboring strata. Volcanic rocks of the first cycle (Ⅰ) occur as interlayers in the Zhanjiang Formation, only seen in Borehole ZKC12, and the lithology is olivine tholeiite; volcanic rocks of the second cycle (Ⅱ) are the most widely distributed in the study area, unconformably overlaying on the Zhanjiang Formation, with 40Ar/39Ar ages ranging from 2.02 to 0.88 Ma, indicating that they were erupted from the early stage of the early Pleistocene to the end of the early Pleistocene. On the combination of contact relationship with surrounding strata, the second cycle can be further divided into four eruption stages. The first eruption stage (Ⅱ1) has the largest scale and the most extensive area, forming two eruption centers with 40Ar/39Ar age of 2.02±0.03 Ma. The second eruption stage (Ⅱ2) centers in the areas of Guokailing and Beicha with 40Ar/39Ar ages of 1.77±0.03 Ma and 1.70±0.03 Ma, respectively. The eruptional center of the third eruption stage (Ⅱ3) lies at Huoju Farm, and the age of 40Ar/39Ar is 1.51±0.07 Ma. The lithology of the fourth eruption stage (Ⅱ4) is dominated by basaltic lava of overflow phase formed by fissure eruption, and the 40Ar/39Ar age is 0.88±0.14 Ma. The volcanic activity is obviously controlled by NE-trending and NW-trending basement faults. These results provide reliable age data to constrain Leizhou Peninsula’s forming age, eruption periods, and the law of volcanic activity.

Cenozoic climate and environment
Reconstruction of climatic and environmental evolution in the Yinchuan Basin from MIS6 to MIS5 based on spore–pollen evidence
XU Keke, BI Zhiwei, YANG Huifeng, YANG Zhenjing, NING Kai, DAI Huimin, LIU Kai, LIU Guodong
2023, 29(4): 522-542. doi: 10.12090/j.issn.1006-6616.2023091
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MIS6 to MIS5 is a typical transition period from glacial to interglacial periods. The climate elements of MIS5 are similar to that of the current warm period, and studying its evolution process can better understand the climate change process of the current warm period and the future climate change trend. Based on modern spore–pollen and meteorological data, as well as stratigraphic spore–pollen and particle size indicators from the Yinchuan Basin in the monsoon margin area, the locally weighted average partial least squares method (LWWA-PLS) reconstruction results are considered to be the most robust after the selection of the training set, screening of the master climate parameters, cross-validation of the five reconstruction models, regional comparison, significance testing, and ecological interpretation. The climatic evolution from MIS6 to MIS5 can be divided into six stages. 157 to 131 ka, the climate was cold and humid, where wet and cold-loving arborvitae vegetation developed, with the average annual precipitation (Pann) being 424.99 mm and the average temperature in July (TJuly) 22.58 ℃. 131 to 119 ka, the climate turned wet and warm, and warm-loving trees and herbs developed; the Pann was 410.95 mm, and the TJuly was 23.62 ℃. 119 to 111 ka, the Pann was 369.50 mm, and the TJuly was 22.53 ℃; cold-loving herbs and trees developed in a cold and dry climate. 111 to 98 ka, the Pann is 378.39 mm, and the TJuly is 22.86 ℃; warm-loving trees account for a higher proportion in the early stage, and the number of cold-loving trees increased in the late stage; the climate was overall dry and warm, and the temperature increased first and then decreased. 98 to 85 ka, the Pann was 278.24, and the TJuly was 22.01 ℃; the overall climate was the driest and coldest, and cold-loving trees developed well. 85 to 78 ka, the Pann was 364.21 mm, and TJuly was 23.45 ℃; the climate turned warm and humid, and trees and herbs developed in this period. The reconstructed climate parameters' ensemble empirical mode decomposition (EEMD) results respond well to the 23 ka precessional cycle. Comparison with the mid- and high-latitude geologic record of the Northern Hemisphere suggests that solar radiation-influenced climatic variability in the North Atlantic primarily drives changes in the East Asian monsoon through the westerly wind circulation as well as the oceanic transport zone, which in turn influences climatic change in the Yinchuan Basin.

The spore-pollen assemblages of the Miocene Baode Formation from Borehole ZK301 in the Yuncheng Basin and its geological significance
FAN Ruyi, YANG Mengmeng, ZHOU Junpeng, ZHAO Jianxin
2023, 29(4): 543-554. doi: 10.12090/j.issn.1006-6616.2023053
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The deposition period of the Baode Formation in the Miocene was crucial when the uplift and expansion of the Tibetan Plateau in the NE direction affected the Cenozoic basins around the Ordos Plateau. Previous research has mainly focused on tectonic and sedimentary aspects, with relatively few results on climate and environmental responses. We conducted a systematic sporopollen study on the Borehole ZK301 from the late Miocene Baode Formation in the E’mei tableland, Yuncheng Basin, characterized the deposited and redeposited spore-pollen and discussed the paleoclimate and paleotectonic background of the Baode Formation during its deposition. From bottom to top, the Miocene Baode Formation in the Yuncheng Basin can be divided into two spore-pollen assemblages, which are Ephedraceae–Chenopodiaceae–Gramineae zone and Artemisia–Chenopodiaceae–Humulus zone, indicating that the desert steppe dominated by Chenopodiaceae, Gramineae, and Ephedraceae developed into the desert steppe dominated by Artemisia and Chenopodiaceae in the late Miocene. Accordingly, the climate transitioned from relatively cold and dry to cold and dry, which was related to the influence of the remote effect of the uplift and expansion of the Tibetan Plateau on the climate in the late Miocene. The redeposited spore-pollen assemblages are mainly concentrated in the lower part of the Baode Formation, with the highest content of Ephedraceae, followed by Pinus, Picea, Cupressaceae, Chenopodiaceae, Juglandaceae and Pteridophyte, and a small amount of Classopollis and Elaeagnaceae, reflecting a warm and humid climate. The redeposited spore-pollens were mainly from the Paleogene strata on the northern margin of the Zhongtiaoshan Mountains, which indicates that there was a rapid uplift and denudation of the Zhongtiaoshan Mountains in the early stage of the Baode Formation deposition. The Baode Formation underwent the Paleogene strata’s denudation, transportation, and redeposited process. The research results can provide evidence for the late Miocene paleoclimate in the Yuncheng Basin and new evidence for the uplift of the Zhongtiaoshan Mountains in this period.

Characteristics and geological significance of the palynological assemblages of the Qingshuiying Formation in the Beilianchi section, northeastern margin of the Tibetan Plateau
MA Jie, XIE Fei, SHI Baoyin, WANG Zhiwen, WANG Dan, DU Penglong, WANG Haibo, YUN Wenqiang, ZHANG Wenjian
2023, 29(4): 555-568. doi: 10.12090/j.issn.1006-6616.2023012
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The uplift of the Tibetan Plateau is one of the most important geological events in the Cenozoic era, which has had a far-reaching impact on climate change in neighboring regions and even the world. Scholars have already considered that the uplift of this period has a good coupling with the warm and cold climate changes. The Beilianchi section is west of Liupan Mountain, the back edge of the arcuate tectonic belt on the northeast margin of the Tibetan Plateau. The Paleocene Qingshuiying Formation is mainly a set of shallow lacustrine deposits dominated by purple-red mudstone with thin gypsum layers containing rich paleoenvironmental and paleoclimatic information. The article systematically studied the palynological assemblage of the Beilianchi section and identified 60 genera and 65 species of sporopollen types as well as several undetermined species. The assemblage is characterized by dominant angiosperm pollen grains and rare gymnosperm pollen and fern spores. Based on the existing research results of regional sporopollen, the geologic age of the Qingshuiying Formation is believed to be the middle-late Oligocene–early Miocene. The sporopollen flora is dominated by deciduous broad-leaved plants such as Betulaceae, Juglandaceae, and Ulmaceae, and pollens from a few but diverse tropical-subtropical plants also occur in the assemblage. In contrast, the pollen content of typical arid shrubs and herbaceous plants is small, generally reflecting the warm-temperate zone's milder and wetter paleoenvironmental and paleoclimatic background. The absence of pollen from cold-tolerant mountain conifers in the palynological assemblage indicates that the regional climatic environment had not yet changed from warm to cold during this period and that the uplift and expansion of the Tibetan Plateau to the northeast had not yet affected the Liupanshan area. The results of this study provide new evidence to constrain the depositional age of the Qingshuiying Formation on the northeastern margin of the Tibetan Plateau and the impact of the uplift process of the Tibetan Plateau on the paleoecology and paleoclimate of the region.

Transgression–regression processes since the MIS 3 in the coastal zone of Quanzhou Bay, Fujian
ZHAO Hongmei, MAO Xin, LIU Chunlei, LI Yasong, LIU Linjing
2023, 29(4): 569-583. doi: 10.12090/j.issn.1006-6616.2023046
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The coastal zone is sensitive to sea–land interaction, making it an ideal place to study the transgression–regression process in Quaternary coastal areas. Based on the stratigraphic and lithologic characteristics of two Quaternary drill cores (DZ01 and DZ02) in the coastal zone of Quanzhou Bay, Fujian Province, a stratigraphic chronological framework was established by using AMS-14C and OSL dating methods. Combined with the statistical analysis results of geochemical element content of indicating facies in modern sediments in Quanzhou Bay, the geochemical element ratios, foraminifers, and ostracods' environmental indicators were used to identify transgressive strata since the Late Pleistocene. The transgression–regression processes since the MIS 3 in Quanzhou Bay were analyzed by comparing it with the regional borehole data. The results show that the Sr/Ba and Mn/Fe values vary significantly in the marine sediments at different water depths in Quanzhou Bay, making them suitable as indicator elements in the marine and sea–land transitional sediments in the Quanzhou Bay coast, with the limit values of Sr/Ba<0.16 and Mn/Fe<0.23, respectively; there have been two transgression–regression processes since the MIS 3 in Quanzhou Bay. The first transgression occurred in the MIS3, corresponding to the regional "Fuzhou transgression," which peaked at about 35 ka B.P. The second transgression occurred in the Holocene, corresponding to the regional "Changle transgression," which peaked at about 7–4 ka B.P. The research results are significant for reconstructing the history of sedimentary environment changes in coastal zones, understanding sea–land interaction, and predicting future environmental changes.

Neogene spore-pollen assemblages and paleovegetation succession of Borehole ZKA02 in Beihai, Guangxi
YANG Wenqiang, JIA Xiaohui, WANG Zhihong, LEI Yong
2023, 29(4): 584-598. doi: 10.12090/j.issn.1006-6616.2023047
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The history of vegetation and climate change during the Cenozoic has been reconstructed by systematically analyzing the sporopollen assemblage from Borehole ZKA02 in Beihai, Guangxi. Through the analysis of spore-pollen data, four sporopollen assemblages can be recognized. From the Early Miocene to the Middle Miocene, this area was covered mainly by deciduous broad-leaved mixed forest–wet meadow vegetation, with a mild and semi-humid climate. From the end of the Middle Miocene to the early Late Miocene, the study area was dominated by coniferous and broad-leaved mixed forest-wet meadow vegetation, with mild and semi-humid. The middle Late Miocene was a mixed deciduous broad-leaved forest–wet meadow vegetation, with increasing conifers and ferns, and the climate was warm and humid. In the late Late Miocene to Pliocene, it was deciduous broad-leaved mixed forest–wet meadow vegetation. The species of evergreen broad-leaved trees in tropical rain forests and subtropical low mountains increased obviously, and the fern molecules decreased obviously. The climate in the Late Pliocene was warm and semi-arid, drier than the previous three stages. Spore-pollen assemblages reflected the climate change characteristics during the Neogene, which have good comparability with the trend of global climate change.

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2023, 29(4): 1-2.
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