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The terrestrial Triassic and Jurassic Systems in the Sichuan Basin, China
Abstract
The Sichuan Basin is geographically located in southwestern China, and is one of the famous large inland basins of China, showing great significance on the geoscience studies in China. The Mesozoic strata are well developed and continuously cropped out in the Sichuan Basin, including marine and non-marine Triassic to Cretaceous sequences. It is a very rare place that contains both marine and non-marine deposits of Mesozoic, many stratotype sections have been established in the basin, representing significant standard for regional and global correlation. There are plenty of famous biota in the Mesozoic of Sichuan Basin, such as the Xujiahe flora in north Sichuan, the Zhenzhuchong flora in east Sichuan, dinosaur (such as Mamenchisaurus) and diverse invertebrate faunas and wood assemblages in the Middle and Late Jurassic. Due to its importance of the geoscience study, long research history and rich academic accumulations, the Sichuan Basin shows significant effects in on the Mesozoic stratigraphy, paleontology, sedimentology, tectonic evolution, petroleum resources exploration in China.
This book covers a variety of subjects and variations of the Sichuan Basin with complicated contents. It introduces the geological background, stratigraphic divisions, stratigraphic sections, fossil assemblages, important stratigraphic boundaries as well as palaeogeography and evolution of sedimentary environment of Mesozoic in Sichuan Basin. The propose of this book is to introduce the latest research progresses of the Triassic and Jurassic studies of the Sichuan Basin, especially to promote the regional and global correlation of marine and terrestrial Triassic and Jurassic systems.
... However, fewer studies dealing with the patterns of terrestrial floral change have been published (McElwain et al. 2007; Barbacka et al. 2017;Zhou et al. 2021). In the eastern Tethys region, Upper Triassic and Lower Jurassic sequences are well-developed in China, and incorporate typical continental (fluvio-paludal), thick coal-bearing deposits in the Sichuan Basin (Wang et al. 2010), whereas the sedimentary successions of this age in northwestern Tethys regions (i.e. the North Atlantic/Central European Subprovince of Kustatscher et al. 2018), including Germany, Poland, Sweden and Greenland, are characterised by thin coals and deltaic to shallow marine deposits, with lesser fluvial and lacustrine continental successions (Lindström and Erlström 2006;Dzik and Sulej 2007;McKie and Williams 2009;Götz and Uhl 2022). The Upper Triassic strata represented by the Xujiahe Formation are well-exposed along the eastern and northeastern margins of the Sichuan Basin in southern China, and consist of coal-bearing, clastic rocks with abundant plant fossils (Wang et al. 2010). ...
... In the eastern Tethys region, Upper Triassic and Lower Jurassic sequences are well-developed in China, and incorporate typical continental (fluvio-paludal), thick coal-bearing deposits in the Sichuan Basin (Wang et al. 2010), whereas the sedimentary successions of this age in northwestern Tethys regions (i.e. the North Atlantic/Central European Subprovince of Kustatscher et al. 2018), including Germany, Poland, Sweden and Greenland, are characterised by thin coals and deltaic to shallow marine deposits, with lesser fluvial and lacustrine continental successions (Lindström and Erlström 2006;Dzik and Sulej 2007;McKie and Williams 2009;Götz and Uhl 2022). The Upper Triassic strata represented by the Xujiahe Formation are well-exposed along the eastern and northeastern margins of the Sichuan Basin in southern China, and consist of coal-bearing, clastic rocks with abundant plant fossils (Wang et al. 2010). As floral variation and the distribution of ecological traits are crucial for understanding the regional responses of palaeovegetation to environmental oscillations (McElwain et al. 1999(McElwain et al. , 2007Bonis and Kürschner 2012;Lu et al. 2023), the well-exposed, continuous plant-rich successions of the Sichuan Basin provide key data for investigating palaeoclimates and terrestrial palaeoenvironments preceding the Triassic-Jurassic transition. ...
... The Late Triassic flora of the Xujiahe Formation in the Sichuan Basin has been investigated for more than a century since the early work of Schenk (1883Schenk ( , 1884. A series of investigations focusing primarily on the stratigraphy and fossil systematics in this region has provided a fairly comprehensive understanding of the gross Late Triassic flora in the Sichuan Basin (Li 1964;Yang 1978;Ye et al. 1986;Huang and Lu 1992;Huang 1992Huang , 1995Wu 1999;Wang et al. 2010;Zhou et al. 2021). However, regional variation in the flora and associations of plant groups linked to particular sedimentary facies are less well resolved. ...
Triassic and Jurassic strata are thick and widely distributed in the Sichuan Basin, South China. In particular, the continental Upper Triassic Xujiahe Formation is well-exposed in this region, yielding rich assemblages of fossil plants. Here, a new Rhaetian fossil assemblage is reported from Zilanba in the Guangyuan area, northern Sichuan Basin. In this locality, 29 species of fossil plants belonging to 17 genera have been newly collected and identified within Member III of the Xujiahe Formation. Based on the floral assemblages and previous magnetostratigraphic and palynostratigraphic studies, the host strata are considered Rhaetian in age. This flora in the Guangyuan area is dominated by Cycadales and Bennettitales but also contains abundant ferns and less common sphenopsids, conifers and other gymnosperms. The occurrence of some climate-diagnostic plants, such as Dipteridaceae, Anthrophyopsis and Ptilozamites, indicate that this area experienced a humid and warm tropical or subtropical climate during the Rhaetian.
... However, abundant fossil wood has been discovered from the Penglaizhen Formation in the last two decades. More than 10 localities yielding fossil wood remain from the Penglaizhen Formation have been reported in the cities and counties in the central Sichuan Basin, in particular in Shehong City (Wang et al. 2010). Most of the fossil wood remains in Shehong are preserved as trunks and logs. ...
... These trunks and logs have been transported over some distance and are usually oriented parallel to the strata, but also vertical orientation occurs. Preliminary systematic studies on the Penglaizhen wood fossils by Wang et al. (2010) interpret that this wood flora is comprised of Podocarpoxylon Gothan, Piceoxylon Gothan, Protosciadopityoxylon Zhang, Zheng et Ding and Araucarioxylon Kraus (currently treated as Agathoxylon Hartig). However, detailed systematic studies of this material have so far not been well reported. ...
... Located in the East of the Qinghai-Tibet Plateau, the Sichuan Basin forms the northwestern part of the Yangtze Plate, covering an area of 180,000 km 2 exhibiting a NE-oriented rhombic shape ( Figure 1). It is a super-imposed basin of considerable size and experienced a complex tectonic history from the marine Craton basin in the Palaeozoic to a foreland basin during the Mesozoic-Cenozoic (Wang et al. 2010). The Upper Triassic to Cretaceous deposits in the basin are of terrestrial origin and consist, to a rather great extent, of massive red sediments of 1,500-3,000 m thickness (Wang et al. 2010). ...
Although abundant and diverse foliage fossils are well recorded in the Upper Triassic and Lower–Middle Jurassic of the Sichuan Basin in southern China, the Upper Jurassic plant fossils are rarely documented due to extensively developed red beds in this basin. Decades ago, abundant fossil wood specimens were discovered from the Upper Jurassic Penglaizhen Formation in the Sichuan Basin. However, detailed investigations on the systematic paleobotany of these wood fossils are very limited, which hinders further understanding of the terrestrial ecosystem and biota. Here, we describe anatomically well-preserved fossil wood specimens from the Penglaizhen Formation at Wangjiagou Village of Shehong City in the central Sichuan Province. These wood fossils exhibit Agathoxylon anatomy with usually uniseriate contiguous radial tracheid pitting and araucarioid cross-field pitting, representing a new record of Agathoxylon in the Sichuan Basin, and contributes to further understanding of the vegetation composition of the southern phytoprovince in China during the Late Jurassic. Independent paleoclimatic evidence from leaf, pollen, and sediments, indicates that the Agathoxylon trees from Shehong, have grown under generally hot and semi-arid or arid environmental conditions, probably in habitats at the banks of rivers and lakes with locally abundant water supply, as indicated by the indistinct growth rings.
... Terrestrial sequences spanning the Triassic-Jurassic transition are well developed in the northeastern Sichuan Basin, South China. These units (the Upper Triassic Xujiahe Formation and the Lower Jurassic Zhenzhuchong Formation) constitute one of the most continuous Triassic-Jurassic continental successions in the eastern Tethyan realm and have yielded diverse macro-and micro-floras (Ye et al., 1986;Wang et al., 2010;Li et al., 2020;Zhou et al., 2021;Lu et al., 2023), together with key fossil insects (Lin, 1978;Li et al., 2007;Fang et al., 2013). A magnetostratigraphic study dated the Xujiahe Formation as ranging from 207.2 Ma to 201.3 Ma in the Qilixia section at Xuanhan, northeastern Sichuan Basin, South China. ...
... The Sichuan foreland basin formed during the Late Triassic in response to the collision of the South China Block, North China Block and other Asian plates. Foreland basin filling resulted in the shift of depositional environments from marine to terrestrial, and the sedimentary succession records numerous important environmental oscillations prior to and after the end-Triassic mass extinction (Wang et al., 2010). ...
... Upper Triassic to Lower Jurassic terrestrial lacustrine-fluvial to coal-swamp deposits are well-developed along the eastern and northeastern margins of the basin (Wang et al., 2010). This study focuses on the uppermost Triassic Xujiahe Formation and the lowermost Jurassic Zhenzhuchong Formation in the Qilixia section, one of the best-exposures of Upper Triassic-Lower Jurassic successions in the northeastern Sichuan Basin ( Figures 1C, D). ...
Plants and insects are the most diverse and ecologically important organisms in the terrestrial biosphere. Their interactions are also among the richest biotic relationships, and offer significant insights into the evolution of terrestrial ecosystem complexity through the geological record. This investigation of the late Rhaetian Xujiahe and the earliest Jurassic Zhenzhuchong floral assemblages provides the first data on foliar herbivory generated by terrestrial arthropods across the Triassic–Jurassic transition in the eastern Tethys (East Asia) region. The damage types from two fossil assemblages are collectively attributed to seven functional feeding and egg-laying categories (i.e., hole feeding, margin feeding, surface feeding, skeletonization, piercing and sucking, oviposition, and galling). Most feeding strategies are spread across the major plant groups and persist through the Triassic–Jurassic boundary, with the exception of skeletonization (a category of external foliage feeding), which was restricted to the latest Triassic within dipteridacean ferns. The survey reveals that the respective frequency and diversity of interactions between plants and insects prior to and following the end-Triassic mass extinction event are almost the same, despite a substantial turnover of floral components. This suggest that insect herbivores were largely able to transfer to alternative (but commonly related) plant groups during the dramatic floristic turnover and environmental changes at the end of the Triassic. Sporadic occurrences of foliar modifications, such as marginal cusps on pinnules of Pterophyllum and prominent ridges on the rachises of some ferns and bennettites are interpreted as adaptations for defense against insect herbivores. A few differences in taxonomic composition and herbivory representation between the latest Triassic Xujiahe flora and the earliest Jurassic Zhenzhuchong flora are more likely to be related to collection and preservational biases rather than reflecting palaeoecological changes. We encourage further investigations exploring the distribution of insect damage in fossil floras from other palaeolatitudinal zones and spanning other major extinction events to develop a better understanding of terrestrial ecosystem responses to major crises in Earth’s history.
... It presents a NE-oriented rhombic shape, covering an area of 180,000 km 2 . The Sichuan Basin is a sizeable superimposed basin that experienced complex tectonic movements from a Paleozoic marine Craton basin to a Mesozoic-Cenozoic foreland basin (Wang et al., 2010). In this basin, the Upper Triassic to Cretaceous deposits are of typical terrestrial origin: lacustrine and fluvial facies (Wang et al., 2005(Wang et al., , 2010 and are extensively represented by massive red deposits, varying from 1500 to 3000 m in thickness. ...
... The Sichuan Basin is a sizeable superimposed basin that experienced complex tectonic movements from a Paleozoic marine Craton basin to a Mesozoic-Cenozoic foreland basin (Wang et al., 2010). In this basin, the Upper Triassic to Cretaceous deposits are of typical terrestrial origin: lacustrine and fluvial facies (Wang et al., 2005(Wang et al., , 2010 and are extensively represented by massive red deposits, varying from 1500 to 3000 m in thickness. The Jurassic System of the Sichuan Basin consists of the following litho-stratigraphic units in ascending order, that is, the Lower Jurassic Zhengzhuchong Formation and Ziliujing Formation, the Middle Jurassic Xintiangou Formation, Lower Shaximiao Formation, and Upper Shaximiao Formation, and the Upper Jurassic Suining Formation and Penglaizhen Formation (BGMRS, 1991;Wang et al., 2010). ...
... In this basin, the Upper Triassic to Cretaceous deposits are of typical terrestrial origin: lacustrine and fluvial facies (Wang et al., 2005(Wang et al., , 2010 and are extensively represented by massive red deposits, varying from 1500 to 3000 m in thickness. The Jurassic System of the Sichuan Basin consists of the following litho-stratigraphic units in ascending order, that is, the Lower Jurassic Zhengzhuchong Formation and Ziliujing Formation, the Middle Jurassic Xintiangou Formation, Lower Shaximiao Formation, and Upper Shaximiao Formation, and the Upper Jurassic Suining Formation and Penglaizhen Formation (BGMRS, 1991;Wang et al., 2010). ...
Fossil wood is one of the most important proxies for terrestrial vegetation composition and continental paleogeographical reconstruction in Earth's history. The conifer wood Brachyoxylon is commonly found in Mesozoic deposits in Europe, Africa, South America, and Antarctica with more than one hundred known occurrences to date. However, only few occurrences (~ 5%) are so far documented in China of East Asia. Here, we describe a fossil wood from the Middle Jurassic Upper Shaximiao Formation at Yongxin of Chongqing City in southeastern Sichuan Basin, China, obtaining typical Brachyoxylon anatomy with mixed radial tracheid pitting and araucarioid cross-field pitting. According to the characters of radial tracheid pitting, cross-field pitting, and ray height, the wood is recognized as Brachyoxylon trautii (Barale) Philippe 1995. To better understand the paleobiogeography of the Mesozoic Brachyoxylon, a global survey of its occurrences is performed, which shows that Brachyoxylon was globally expanding over time with the widest geographic distribution in the Cretaceous.
... However, little is known about fossil wood from the Middle Jurassic deposits in the Sichuan Basin, southern China. On the other hand, the Middle Jurassic Shaximiao Formation in the Sichuan Basin has been known in China for a long time, yielding diverse fossil dinosaurs and plant leaf fossils; the later consisting of Dicksoniaceae ferns, Sphenophytes, cycads, and conifers (Sze and Chow, 1962;Yang, 1978;Wang et al., 2010). However, up to now, only a single occurrence of fossil wood was reported from Qijiang of Chongqing City, southeastern Sichuan Basin (Zhang et al., 2015), but a detailed systematic paleobotanical study is still missing. ...
... It presents a NE-oriented rhombic shape, covering an area of 180,000 km 2 . The Sichuan Basin is a sizeable super-imposed basin that experienced complex tectonic movements from a Paleozoic marine Craton basin to a Mesozoic-Cenozoic foreland basin (Wang et al., 2010). In the Sichuan Basin, the Upper Triassic to Cretaceous sequences are of typical terrestrial origin-lacustrine and fluvial facies (Wang et al., 2005(Wang et al., , 2010 and are extensively represented by massive red deposits, varying from 1500 to 3000 m in thickness. ...
... The Sichuan Basin is a sizeable super-imposed basin that experienced complex tectonic movements from a Paleozoic marine Craton basin to a Mesozoic-Cenozoic foreland basin (Wang et al., 2010). In the Sichuan Basin, the Upper Triassic to Cretaceous sequences are of typical terrestrial origin-lacustrine and fluvial facies (Wang et al., 2005(Wang et al., , 2010 and are extensively represented by massive red deposits, varying from 1500 to 3000 m in thickness. The Jurassic System of the Sichuan Basin includes the following lithostratigraphic units in ascending order: the Lower Jurassic Zhengzhuchong Formation and Ziliujing Formation, the Middle Jurassic Xintiangou Formation and Shaximiao Formation, and the Upper Jurassic Suining Formation and Penglaizhen Formation (BGMRS, 1991;Wang et al., 2010). ...
The Jurassic System in the Sichuan Basin of eastern Asia is represented by the extensive development of massive thick red beds, mainly composed of purplish-red sandstones and mudstones. Abundant invertebrate and vertebrate fossils have been recovered from these Jurassic red beds. However, fossil woods are much less documented. Here, we describe fossil woods from the Middle Jurassic Shaximiao Formation at Qijiang of Chongqing City in southeastern Sichuan Basin, China, obtaining typical Brachyoxylon anatomy with mixed radial tracheid pitting
and araucarioid cross-field pitting. Owing to a novel combination of radial tracheid pitting, cross-field pitting and ray height, a new species, Brachyoxylon qijiangense Xie, Wang et Tian sp. nov. is recognized here. Based on the tree mean sensitivity and leaf retention time analysis, along with the comparison with other invertebrate and leaf fossils in the Shaximiao Formation, the new fossil woods bearing true growth rings with abundant, well-formed earlywood and extremely narrow latewood indicates that B. qijiangense sp. nov. was an evergreen tree growing in a warm and humid climate with mild seasonality during the Middle Jurassic in Qijiang, probably in a flooding-disturbed, streamside condition.
... The Sichuan Basin is located in the central-southern part of the Asian continent (Li et al. 2016) and is one of the four largest basins in China (Wang et al. 2010). The Sichuan Basin is on the western edge of the South China block, which includes the Yangzi Platform in the northwest and the Cathaysis in the southeast . ...
... Under the influence of the Indosinian movement, the Sichuan Basin evolved into an inland lake basin in the Late Triassic. Over the Mesozoic, thick purple-red sandstones and shales, up to 3000-4000 m, were deposited in the basin (Wang et al. 2010). The Mesozoic red layer is widely developed in the Sichuan Basin (Wang et al. 2019). ...
... The Mesozoic red layer is widely developed in the Sichuan Basin (Wang et al. 2019). The Jurassic sedimentary stratigraphy is mainly a series of red clastic rock systems exhibited as fluvial and lacustrine deposits (Wang et al. 2008(Wang et al. , 2010. Based on lithologic and biostratigraphic features, from the bottom to the top, the Jurassic strata can be hierarchised into the Zhenzhuchong and Ziliujing formations (Lower Jurassic), the Xintiangou, Xiashaximiao (or Lower Shaximiao) formations (Middle Jurassic), the Shangshaximiao (or Upper Shaximiao), and the Suining and Penglaizhen formations (Upper Jurassic), with a thickness of 1000-2000 m (BGMRSP (Bureau of Geology and Mineral Resources of Sichuan Province) 1991; Wang et al. 2010;Tong et al. 2012a;Hu et al. 2020;Zhou et al. 2022). ...
A new Chengyuchelys latimarginalis (Xinjiangchelyidae) specimen is reported based on a well-preserved, nearly complete shell from the upper part of the Upper Jurassic Shangshaximiao Formation of Qijiang District, Chongqing Municipality, China. The Xinjiangchelyidae were widely distributed in Asia during the Jurassic and were the dominant turtle group in Asian freshwater ecosystems during the Late Jurassic. The Qijiang specimen adds a new element to the yet poorly known freshwater vertebrate fauna and extends the geographical distribution of C. latimarginalis. This paper discusses the intraspecific variation in C. latimarginalis for the first time. It provides a new insight for studying the evolution, habitat, and diversity of xinjiangchelyids.
... The Xujiahe Formation represents a coal-bearing clastic sequence with yellowish-grey and light-grey sandstones, dark mudstones, coal and conglomerates, yielding abundant fossil plants as well as less diverse lamellibranchiates, gastropods, conchostracans and ostracods (Gu and Liu, 1997;Wang et al., 2010). It is divided into four to seven, with Members I, III, V and VII of the of Xujiahe Formation as fine members, with dark grey or grey mudstones inter-bedded with carbonaceous shale and coal. ...
Storm deposits or tempestites are event sequences formed by storms, requiring at least a water temperature of 26.5°C. While inland lakes are unlikely to form storm deposits because of their limited width and water temperature. The Upper Triassic Xujiahe Formation in the Sichuan Basin is a set of coal-bearing, clastic sequences with dominant sedimentary facies varying from braided river delta to lacustrine settings, with storm deposits widely reported. In the Zilanba of Guanyuan area, in situ tree trunks on a palaeosol surface in Member V of the Xujiahe Formation provide new evidence of a storm event. Six fallen-down directions of nine in situ tree trunks were predominant in the NW direction, contrary to the palaeocurrent direction of the underlying strata, suggesting that the southeasterlies prevailed during the end-Triassic in the northern Sichuan Basin. Massive mud clasts were frequently recorded in sandstones of the Xujiahe Formation, as well as in the Xindianzi section. These mud clasts showed a rip-up or a plastic deformation with upside-down V-shapes, were capped on an erosional surface, showed no transport traces and were therefore interpreted as a storm lag deposit. The megamonsoonal climate prevailed during the Late Triassic, although the megamonsoons themselves could not generate a storm deposition in the Xujiahe Formation due to its low maximum surface wind speed. The driving mechanism for generating storm deposits in the Xujiahe Formation is suggested to be tropical cyclones over the Tethys Ocean moving eastward, further landfalling on the western margin of the Sichuan Basin. Statistics of storm events in the circum-Tethys region show a widespread storm surge in low latitudes during the end-Triassic. The storm deposits at the top of the Xujiahe Formation represent a sedimentary response to the end-Triassic hyperthermal event.
The rare clam shrimp (spinicaudatan) genus Carapacestheria Shen, 1994 was originally described from the upper Lower–lower Middle Jurassic of Antarctica. Later, it was reported from the Middle Jurassic of Argentina and the lowest Cretaceous of the United Kingdom. Here, a new species, Carapacestheria cangshanensis sp. nov., is described from the Upper Jurassic Penglaizhen Formation in southwestern China. The subquadrate-shaped carapace of the new species has a distinct ornamentation pattern, which transitions from medium-sized reticulations to radial lirae. There are punctae within the polygonal cells and between the lirae. According to its geological range and geographical distribution, Carapacestheria first occurred in Antarctica, and later appeared in the northern hemisphere during the Late Jurassic.
A possible turtle swim track from the Third Member of the Late Triassic Xujiahe Formation (Norian-Rhaetian) represents the oldest ichnological evidence of the group from China, supplementing previous reports of more abundant tracks from the Middle Jurassic of the region. The specimen is younger than the known pantestudinate (‘stem-turtle’) body fossils from China but matches the stratigraphic distribution of testudinate skeletons in other regions, for example, in Thailand, Europe and North America. Caution should be used to distinguish turtle swim tracks from those of crocodylomorphs and theropod dinosaurs, especially where only small samples are available. Therefore, we do not completely exclude an affinity with these groups or other archosaurs, such as phytosaurs. Nevertheless, the morphology of the imprints is most similar to turtle tracks, and it is most likely that an early non-crown group representative was the responsible producer. Of interest is also the depositional environment of the track-bearing deposit, which can be considered a deltaic plain marsh.
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