The climate paleogeography, especially the climate classifications, helps to interpret the global and regional climate changes and intuitively compare the climate conditions in different regions. However, the application of climate classification in deep time (i.e., climate paleogeography) is prohibited due to the usually qualitatively constrained paleoclimate and the inconsistent descriptions and semantic heterogeneity of the climate types. In this study, a climate paleogeography knowledge graph is established under the framework of the Deep-Time Digital Earth program (DDE). The hierarchical knowledge graph consists of five paleoclimate classifications based on various strategies. The classifications are described and their strengths and weaknesses are fully evaluated in four aspects: "simplicity, applicability, quantifiability, and comparability". We also reconstruct the global climate distributions in the Late Cretaceous according to these classifications. The results are compared and the relationships among these climate types in different classifications are evaluated. Our study unifies scientific concepts from different paleoclimate classifications, which provides an important theoretical basis for the application of paleoclimate classifications in deep time.
Abstract Direct dating of vertebrate fossils is difficult due to complex postburial diagenetic processes and the often low and heterogeneous concentration of radioisotopes (e.g., U) in fossilized bone material. Here, we demonstrate a novel approach to dating vertebrate fossils via laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of early diagenetic calcite cements precipitated within bone cavities of a Jurassic sauropod from the Sichuan Basin, South China. Early diagenetic calcite yielded a U-Pb age of 165.3 ± 3.6/5.6 Ma, in agreement with a maximum depositional age of 165.8 ± 1.0 Ma from detrital zircon ages of the surrounding rocks, suggesting that diagenesis occurred shortly after the death of the sauropod. This new age demonstrates that the best-known Jurassic large sauropod faunas in South China are much older than those in North America and Africa, suggesting the geographical isolation of South China. Authigenic apatite U-Pb dating on the fibrolamellar bones from the same sauropod gave a distinctly younger age, indicating more complex U-Pb system behavior, possibly due to U uptake by residual organic matter and recrystallization of apatite after early diagenesis. Our findings demonstrate that U-Pb dating of calcite cements within bone cavities has significant potential for constraining the burial age of vertebrate fossils, which could aid in constructing a more robust temporal framework for the radiation and evolution of vertebrates.
Abstract Geochemical and petrological diversity within transcrustal magmatic systems usually reflects the magma properties and magmatic processes and thus is critical to understanding the origin of magmatic complexes and the evolution of continental crust. Herein, we present an integrated study on the petrology, mineralogy, geochronology, geochemistry, and Sr-Nd-Hf isotopes of Triassic mafic-felsic dikes in the East Kunlun orogenic belt, northern Tibetan Plateau, to elucidate the nature and evolution of the transcrustal magmatic system. The studied dikes intruding into the granodiorite pluton (ca. 235–233 Ma) comprise coeval ca. 220–218 Ma gabbroic diorite porphyry, diorite porphyry, granodiorite porphyry, and alkali-feldspar granite, resembling composite dike swarms. The macrocrysts in these dikes show various zoning patterns, indicating episodic magma recharge and crystal resorption. The compositional gap between the intermediate-mafic dikes (SiO2 = 52.9–67.8 wt%) and the granitic dikes (SiO2 > 75 wt%), as well as their homogeneous whole-rock Sr-Nd isotopes, with (87Sr/86Sr)i = 0.708387–0.710995 and εNd(t) = −5.83 to −4.34, but variable zircon Lu-Hf isotopes, i.e., εHf(t) = −7.67 to −0.36, demonstrates that magma mixing rather than cogenetic fractional crystallization accounts for their origin. In combination with thermobarometric insights, these results suggest that the mafic and felsic parental magmas originating from an enriched lithospheric mantle and ancient continental crust, respectively, were ultimately emplaced and stagnated at varying crustal depths (~22–30 km and 8–17 km). Subsequently, the felsic magma mush was replenished and rejuvenated by the underplated mafic magma, leading to varying degrees of crystal-melt and/or melt-melt mixing. This mush-facilitated crust-mantle magma mixing is an important mechanism accounting for the compositional diversity of the transcrustal magmatic system.
The sedimentary record is important for the understanding of basinal geomorphology and evolution. Although the Pennsylvanian (late Carboniferous) Benxi Formation of the Ordos Basin is a highly explored sequence with thousands of boreholes, controversies persist about whether or not the depositional system had a southern provenance and how the sequence was developed. In this paper, the provenance, depositional environment and stratigraphic development of the Benxi Formation are investigated according to sedimentary structure analysis, paleo-tidal range calculation, sediment dispersal patterns, and trace and rare earth element geochemical data. The provenance analysis results show that most of the sediments were derived the north, from the relatively stable North China Cratonic Margin Orogenic Belt. In contrast, those that were derived from the south were sourced from the complex Qinling Orogenic Belt of arc-continent collision. The tidal-related sedimentary structures, co-existing with delta-related sedimentary structures, demonstrate that Benxi Formation was influenced by tides which were of mesotidal or to macrotidal range. These results, combined with sediment dispersal patterns described in detail by mapping large amounts of statistical drilling lithostratigraphic data, argue that the sandy sediment flux and macrotidal shelf induced the formation of a tidal-delta complex. Two carbonate interlayers were formed during pauses in input of exotic detritus. Benxi Formation source-to-sink paleogeography was reconstructed via multi sedimentary records. The results show that the differential source-to-sink systems and intensity of tidal reworking between the northern and southern regions constrained the sediment dispersal pattern of the late Carboniferous Benxi Formation and consequently influenced the quality of sandstone.
Due to tidal dissipation, the Earth’s rotation has been slowing down, but the past rates of this process remain subject of debate. Here we conducted a comprehensive cyclostratigraphic analysis of eight geological datasets to further constrain the Earth's rotation history from the Neoproterozoic to Mesozoic. Our results allow us to further test theoretical physical tidal models, and support a suggested stair-shaped Earth’s rotation deceleration pattern during 650-280 Ma, thereby increasing the Earth-Moon distance about 20,000 km and the length of solar day approximately 2.2 hours. Specifically, the high rate of Earth’s rotation deceleration from 650 Ma to 500 Ma can be attributed to the enhanced tidal resonance. In contrast, the unusually low tidal dissipation during 500-350 Ma has led to a flatter trend of Earth’s rotation deceleration, closely followed by another high rate of Earth’s rotation deceleration during 350-280 Ma. These changes in Earth’s rotation are closely linked to alterations in Earth's tectonic contexts and ocean tidal resonance. Hence, we speculate that there might be a relationship between the Earth's rotation and geological processes.
The Laizhou Bay Sag, one of the oil-bearing sags with large exploration potential in the South Bohai Sea of China, contains two sets of high-quality hydrocarbon source rocks, i.e. Member 3 and Member 4 of Shahejie Fm (E 2 s 3 and E 2 s 4 ). As an important hydrocarbon accumulation zone in the sag, the KL16-1 low bulge is found to have oil reservoirs in the Neogene Guantao Fm (N 1 g), the Paleogene Dongying Fm (E 3 d), the Paleogene Shahejie Fm (E 2 s), and the Mesozoic buried hill formation. It is characterized by distinct features of composite reservoirs. Nonetheless, its hydrocarbon accumulation process and mechanism are unknown yet. In this paper, the hydrocarbon generation modelling of source rocks, combined with the characteristics of oil-source rock biomarker compounds and fluid inclusions, is used to restore the hydrocarbon accumulation process in the KL16-1 low bulge. Crude oil in all three KL16-1 plays is characterized by low Pr/Ph, low gammacerane, high 4-methyl sterane and high dinosterane. In other words, it is oil of low maturity to maturity. As the biomarker index of the oil is very similar to that of the E 2 s 3 source rocks, it is thought that E 2 s 3 is the primary source rock layer, while E 2 s 4 is the secondary source rock layer. In addition, episodic oil and gas charging happened in two phases under high pressure in the late period (from 5.0 Ma till now).
New zircon LA-ICP-MS U–Pb age, zircon Hf isotope, and whole-rock major and trace elemental data of the Late Cretaceous Ageledaban complex in the Karakorum Terrane (KKT), northwest Tibet, provide new constraints on the tectonic processes of the collision and thickening of the terrane between the Lhasa and Qiangtang terranes. The granitoids from the Ageledaban complex have a variable SiO2 content, from 62.83 to 73.35 wt.% and A/CNK<1.1 (except for YM61-2). They have rare earth element and trace element patterns that are enriched in light rare earth elements, Rb, Pb, Th, and U, and are depleted in Ba, P, Sr, Ti, and Nb, indicative of weakly peraluminous-metaluminous I-type affinity. Zircon U–Pb dating reveals that the Ageledaban complex was emplaced at ca. 80 Ma. Zircons from the monzogranite and monzonite samples with concordant 206Pb/238U ages about 80 Ma have a zircon εHf(t) of −6.6 to −1.1, corresponding to the Mesoproterozoic Hf crustal model ages (TDMC = 1.2–1.6 Ga); the remaining inherited zircons from the monzonite with concordant 206Pb/238U ages of about 108.1 Ma have εHf(t) values that range from −8.3 to −5.0, corresponding to the Mesoproterozoic Hf crustal model ages with an average of 1.6 Ga. These signatures indicate that the Ageledaban granitoids may have been derived from the partial melting of a mixed mantle-crust source. Together with the age and geochemical data in the literature, we propose that the collisional event in the KKT in northwestern Tibet would postdate the northern Lhasa–southern Qiangtang collision, which occurred first in the Amdo in the east and later in the Shiquanhe in central Tibet. Our results support the previous view that the collision of the Bangong–Nujiang suture zone (BNSZ) may be diachronous.
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