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• Distribution and evolution of middle-deep groundwater in marine strata were studied. • Qinling-Dabie and Jiangnan orogenic belt affected the erosion of the strata. • Transfer direction of tectonic stress affects hydrochemical types and flow paths. • Salinity comes from connate water and/or dissolved rock flushed by rainwater. Large marine sedimentary basins often contain concentrated geothermal mineral resources. Chongqing Municipality, located in the Sichuan marine sedimentary basin and the surrounding mountainous area of southwest China, is rich in thermal waters and brines. Chongqing belongs to the Middle-Upper Yangtze Tectonic Block. Previous studies have mostly been based on basin structure, but less on the whole plate structure to study the distribution and evolution of groundwater. In this paper, 78 middle-deep groundwater samples in the study area were collected to better understand the occurrence and hydrochemical evolution of middle-deep groundwater using ionic ratios, hydrogen and oxygen isotopes, and geothermometers. Tectonic stress has been transferred from SE to NW in the Jiangnan Orogenic Belt and from NE to SW in the Qinling-Dabie Orogenic Belt, making the extent of tectonic denudation and its related properties such as hydrochemical type, reservoir temperature, and maximum circulation depth trend along the same directions. Four of the water samples have Br × 103/Cl and Na/Cl molar ratios >1.5 and <0.87, respectively, indicating that they are marine metamorphic brines. The ratios of the rest of the samples are mostly distributed in a range suggesting precipitation-dissolved halite or somewhere in between. This suggests that the study area is in the denudation leaching period of the hydrogeological cycle, and the middle-deep groundwater system is still in the dynamic process of formation water (residual metamorphic paleo-seawater) of the previous hydrogeological cycle diluted in places by rainwater. A conceptual circulation model for regional middle-deep groundwater is proposed. Rainfall in the late Pleistocene infiltrated as groundwater recharge via fractures and karst valleys and circulated to deep strata driven by gravity, where it could mix with residual, paleo-evaporated seawater. Then the groundwater was heated by geothermal and chemical energy sources, mixing with shallow groundwater as it moved upward along faults toward the surface eventually to emerge from springs. [ABSTRACT FROM AUTHOR]

A new sauropod-dominanted dinosaur fauna, including several new species of sauropods and stegosaurs, was recently excavated from the Lower Shaximiao Formation in Yunyang, northeastern Chongqing, southwestern China. Although this dinosaur fauna could possibly provide significant clues for a better understanding of the basal sauropod's evolution and diversification of basal sauropods in the Jurassic, many aspects of this fauna are not well defined constrained in terms of detailed stratigraphy, geochronology, and comparison with similar faunas in other regions of the Sichuan Basin. This paper reports on the petrological features of this locality, using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS), with laser ablation-multi-collector-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb geochronology for a tuffaceous siltstone layer beneath the dinosaur fossil-bearing layers from the fossil site. The SEM and XRD results show a typical tuffaceous mineral composition of this layer. Zircon U-Pb data yielded a weighted average age of 166.0 ± 1.5 Ma, indicating a maximum burial age for this dinosaur fauna. This fauna is chronologically comparable with the Shunosaurus-Omeisaurus Fauna, which is primarily found in the central Sichuan Basin. • 166.0 ± 1.5 Ma as the maximum burial age for dinosaur fauna in Chongqing, SW China. • Precise age constraints on newly discovered dinosaur in Lower Shaximiao Formation. • Basal sauropods in Sichuan Basin are younger than biostratigraphic ages. • Providing age constraints on the radiation of basal sauropods in Jurassic. [ABSTRACT FROM AUTHOR]