The Cambrian Period is the first period of the Phanerozoic Eon and witnessed the explosive appearance of the metazoans, representing the beginning of the modern earth-life system characterized by ...animals in contrary to the Precambrian earth-life system dominated by microbial life. However, understanding Cambrian earth-life system evolution is hampered by regional and global stratigraphic correlations due to an incomplete chronostratigraphy and consequent absence of a highresolution timescale. Here we briefly review the historical narrative of the present international chronostratigraphic framework of the Cambrian System and summarize recent advances and problems of the undefined Cambrian stage GSSPs, in particular we challenge the global correlation of the GSSP for the Cambrian base, in addition to Cambrian chemostratigraphy and geochronology. Based on the recent advances of the international Cambrian chronostratigraphy, revisions to the Cambrian chronostratigraphy of China, which are largely based on the stratigraphic record of South China, are suggested, and the Xiaotanian Stage is newly proposed for the Cambrian Stage 2 of China. We further summarize the integrative stratigraphy of South China, North China and Tarim platforms respectively with an emphasis on the facies variations of the Precambrian-Cambrian boundary successions and problems for identification of the Cambrian base in the different facies and areas of China. Moreover, we discuss stratigraphic complications that are introduced by poorly fossiliferous dolomite successions in the upper Cambrian System which are widespread in South China, North China and Tarim platforms.
► The Doushantuo Formation of South China is one of the key sedimentary units in the world for understanding Ediacaran geobiological processes. ► Sequence and high-resolution carbon isotope ...stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the Doushantuo Formation on the Yangtze platform. ► The results indicate that there are four δ13Ccarb excursions which can serves as a global reference chemostratigraphic profile for evaluating the Ediacaran seawater and life evolution.
The Doushantuo Formation of South China, consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies, is one of the key sedimentary units in the world for understanding Ediacaran geobiological processes. However, stratigraphic correlation and sedimentary facies evolution of the Doushantuo Formation remain controversial. Sedimentary facies analysis of the well-known sections of the Yangtze Gorges area and new sections in northern Yichang, western Hubei indicate that the Doushantuo succession in the Yangtze Gorges area was deposited in an offshore intra-shelf basin within the Yangtze platform. In contrast, the Doushantuo Formation in the northern Yichang area which is characterized by one or a few phosphate-rich horizons represents deposition on the subtidal or intertidal shelf, and so is similar to the succession in the Weng’an area (central Guizhou Province). The carbon isotope profiles of the different sections exhibit significant variation, which is interpreted to result from facies differences. Sequence and high-resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the Doushantuo Formation on the Yangtze platform. The results confirm that a prominent negative δ13Ccarb excursion (BAINCE, nadir down to −5‰) in the middle portion of the second sequence of the Doushantuo Formation is a widely traceable event. BAINCE together with three other δ13Ccarb excursions, namely CANCE at the base, WANCE near the first sequence boundary near the middle, and DOUNCE at the top of the Doushantuo Formation, constitute a complete carbon isotope profile for the Doushantuo Formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the Ediacaran Period.
U-Pb zircon dates from volcanic ash beds within the Doushantuo Formation (China) indicate that its deposition occurred between 635 and 551 million years ago. The base records termination of the ...global-scale Marinoan glaciation and is coeval with similar dated rocks from Namibia, indicating synchronous deglaciation. Carbon isotopic and sequence-stratigraphic data imply that the spectacular animal fossils of the Doushantuo Formation are for the most part younger than 580 million years old. The uppermost Doushantuo Formation contains a pronounced negative carbonate carbon isotopic excursion, which we interpret as a global event at circa 551 million years ago.
The Ediacaran Period was a critical time in the history of life and Earth. Understanding the complex interactions between geological and biological events during this interval requires ...high-resolution chronostratigraphy. Thanks to its uniquely favorable palaeogeographic setting, South China is an ideal region for constructing a framework for global chronostratigraphic correlation of Ediacaran strata. Here, continuous Ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles. As part of the present study, 62 reference sections distributed throughout the Yangtze Platform were investigated. Analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies. Three major sequence boundaries occur respectively in the middle and upper parts of the Doushantuo Formation and in the middle part of the Dengying Formation. Subdivision and correlation of the Ediacaran successions of the Yangtze Platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections (1075 samples). The sequence boundary (SB2) in the middle part of the Doushantuo Formation is suggested here as the Lower (Xiadongian)/Upper (Yangtzean) series boundary of the Ediacaran which coincides with several globally recognizable events, namely 1) the end of the Neoproterozoic glaciations, 2) the first appearance of animals, 3) the sudden increase in the diversity of acanthomorphic acritarchs, and 4) a negative
δ
13C excursion. The Ediacaran System of South China may be subdivided into five stages. Furthermore, the criteria for defining these stages may be applicable throughout the world. Also, the composite carbon isotope profile of the Ediacaran of South China can be used as a global reference for chronostratigraphic subdivision and correlation. In addition to the globally recognizable, negative
δ
13C excursion in the cap carbonate at the base of the Ediacaran, the negative
δ
13C excursion in the uppermost Doushantuo/Wonoka/Shuram interval represents another, globally correlatable major excursion. The positive
δ
13C excursion immediately following the uppermost Doushantuo excursion and ending at 548 Ma is also useful for global correlation.
Current Ediacaran chronostratigraphy and global correlations indicate that the upper Doushantuo/Wonoka/Shuram negative
δ
13C excursion ranges from ca. 560 Ma to 551 Ma, and therefore coincides with the evolutionary renovation of life. Feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative
δ
13C excursion in earth history. Our chronostratigraphic correlations also imply that the earliest known metazoan biotas, namely the Weng'an and characteristic Ediacaran biotas, do not constitute two temporally separate evolutionary lineages, as proposed previously, but represent two parallel evolutionary pathways preceding the Cambrian explosion of animal life.
The early Paleozoic sediments document two major biological events: the Great Ordovician Biodiversification Event (GOBE) and Late Ordovician mass extinction (LOME). Many investigations have focused ...on taxonomic richness patterns during these major diversification and extinction events, providing insights into their timings and potential causes. However, the coarse temporal resolutions used in previous investigations hampered their ability to document fine-scale patterns. To address these issues, we employed CONOP analysis to data collected from a large suite of southern Chinese stratigraphic successions to construct a high-resolution (temporal resolution of ~21.0 Kyr) regional chronostratigraphy and document species richness dynamics during the middle–late Cambrian to early Silurian interval. Our results showed that the GOBE began in the early Tremadocian and ended at the Dapingian–Darriwilian boundary and consisted of two major radiation phases. The main pulse of GOBE, which lasted from the late Floian to the earliest Darriwilian, exhibited a species richness increase with elevated origination and extinction rates. Major marine groups showed no significant diachroneity during the GOBE, with most presenting richness peaks in this event's main pulse of the GOBE. Plankton demonstrated a significant diversification from the late Cambrian to the GOBE climax and subsequently dominated the marine realm in South China. Marine life experienced two extinction events in the Late Ordovician, the Katian extinction and Hirnantian extinction, which resulted in a regional species loss of ~67%.
•38,122 local records of 2986 species to construct the early Paleozoic biodiversity history•The biodiversity curve achieves a resolution of ~21.0 Kyr by using CONOP and supercomputer.•GOBE showed a two-phased exponential richness increase of ~9.9 times in ~16.6 Myr.•Two extinctions in the Late Ordovician eliminated ~67% marine species.
Following the Cambrian Explosion, a significant extinction event occurred during the Cambrian Stage 4, with the extinction rate second only to that experienced in the end-Permian. To figure out the ...variation of N supply and elucidate the combined effect of O2 and N availability on the extinction event, this study presents the first set of high-resolution N isotope data from two shallow-water Cambrian Stage 4 drilling sections on the eastern Yangtze Platform. The results indicate that the sections are characterized by highly negative δ15N signatures during the lowermost and uppermost Cambrian Stage 4, which are indicative of strong NH4+ assimilation in an anoxic shallow ocean. During the rest of the Cambrian Stage 4, both of the study sections show stable δ15N values close to 0. This phenomenon can be best explained by enhanced N2 fixation in an oxic shallow ocean characterized by strong N limitation, resembling the low-latitude oligotrophic regions in the modern ocean. The oligotrophic environment was likely caused by enhanced denitrification/anammox as well as elevated P input associated with eustatic changes, and may have been widespread in the global shallow ocean during the Cambrian Stage 4. Our results lend new support to the traditional view that anoxia contributed to the mass extinction event. More importantly, it is emphasized that the oligotrophic environment may have played an important role in the prolonged decline of metazoan diversity during this stage.
The existing target tracking algorithm of the tennis dynamic image serving path cannot correct the serving path in time according to the physical characteristics of the target, resulting in poor ...correction accuracy and stability. To this end, this paper proposes correction algorithm of tennis dynamic image serving path based on symmetric algorithm. Dynamic images are obtained using the visual acquisition model. On this basis, the contour of the moving target is obtained by the symmetric algorithm, and the complete moving target is obtained by the background difference method. The physical properties of moving objects are analyzed through a tennis serve visual model. The path correction model based on physical features is used to construct the relevant model so as to realize the path correction of the moving target. The experimental results show that the highest accuracy of the algorithm for tennis net and bottom line is 92.88% and 93.10%, respectively, and the average image correction accuracy is 95%. The tracking accuracy of service paths in complex backgrounds is 95%. These data show that the proposed algorithm has high correction accuracy and stability.
The paleogeographic landscape is an important clue to clarify the controversy on the paleoposition of South China within the supercontinental cycles. We therefore conducted a study of directional ...structures (34 datasets) and detrital zircons (707 analyses of five samples) from the southeastern margin of the Yangtze Block (SMYB). The principal results are as follows. (1) The sedimentary transport directions indicated by cross-beddings and ripple marks are 295°-354°; the orientation of the relatively deep-water facies indicated by the lateral boundaries of different lithofacies is 332°; and the slump directions of sedimentary layers are 324°-359° and 280°-N-31° (or 100°-S-211°), based on the syndepositional faults and most of the syndepositional folds, respectively. (2) Detrital zircons have U-Pb ages of 3340–487 Ma, and the U-Pb spectrum of each sample has the same age-peak interval of 900–680 Ma. For the late Cryogenian-Ediacaran samples and Cambrian-Ordovician samples, the major age peaks, εHf(t) and Hf-TDM2 are characterized by ~740 Ma, negative values and clustering at 2.6–1.9 Ga, and by ~810 Ma, positive values and clustering at 1.5–0.9 Ga, respectively. These new data indicate that, during the Ediacaran to middle Ordovician, the landscape of eastern South China, from north to south, consisted of the following five paleogeographic domains: (i) the Yangtze Sea covering the Yangtze Platform; (ii) the Zhe-Gan-Wan Sea covering the SMYB basin with opposite dips on the north and south sides, and the northeast margin basin of the Cathaysia Block; (iii) the Zhe-Min Land located in the northeastern Cathaysia Block and derived from the Cryogenian land; (iv) the Gan-Min-Zhe Sea covering the northwest and south of the eastern Cathaysia Block; and (v) an unknown land, that was located to the south of the eastern Cathaysia Block and underwent the Grenvillian and Pan-African orogenies. According to the landscape configuration, South China may have been a peripheral component of East Gondwana, and the Cathaysia Block may have been adjacent to India, West Australia, and/or East Antarctica.
•An ancient land called ‘Zhe-Min Land’ was located in the NE Cathaysia Block.•The SE Yangtze Block was a basin with opposite dips on the NW and SE flanks.•South China adjoined a Grenvillian orogen that underwent the Pan-African orogeny.
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