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Sodium carbonate evaporites can provide important paleoclimatic constraints and economic resources but are relatively rare; most known examples are limited to the Cenozoic. The first known late Paleozoic occurrence was recently reported from the Fengcheng Formation in the northwestern Junggar Basin, NW China. However, its mineralogy, age, and geologic setting have been sparsely documented. To help establish a broader understanding of the formation of these important deposits, this paper presents a comprehensive new data set that includes drill core, well logs, petrographic analyses, X-ray diffraction data, organic geochemistry (biomarkers), and U-Pb zircon age data. Evaporite deposition is estimated to have occurred between ca. 305 Ma and 296 Ma in a series of extensional grabens that hosted a stratified, hypersaline lake (or lakes). The lake deposits are closely associated with coeval volcanic rocks, suggesting that subsurface interaction of these with CO2-enriched hydrothermal fluids may have contributed to the excess alkalinity required to precipitate Na-carbonate. Trona (NaHCO3 · Na2CO3 · 2H2O) in the Fengcheng Formation was likely formed syndepositionally and then partly replaced by wegscheiderite (Na2CO3 · 3NaHCO3). Other evaporite minerals most likely formed during diagenesis. The Fengcheng Formation also contains nahcolite (NaHCO3), which requires pCO2 >680 ppm to form, although no textural evidence was found to demonstrate a primary origin. The presence of extensive lacustrine evaporites nonetheless reflects a relatively warm and arid climate at ~40-50°N that apparently coincided with the late Paleozoic icehouse. [ABSTRACT FROM AUTHOR]

Abstract: Because of the need to understand the links and feedbacks of the carbon cycle during times of global greenhouse conditions numerous studies have focused on the Cretaceous climate. Much of what we know about this warm period in Earth's history comes from the study of ocean sediments recovered from both ocean drill cores and marine sediments exposed at the Earth's surface. In contrast, there are few studies of Cretaceous terrestrial sediments. The Songliao basin located in northeast China offers a unique opportunity to understand Cretaceous paleoclimate of terrestrial settings because it contains a nearly complete record of lacustrine sediments deposited throughout the Cretaceous and there is an active drilling program to recover core from this paleolake. We present carbon, oxygen and strontium isotopic data from ostracods collected from two drill cores (SK-1 (N) and SK-1 (S)) that cover a time interval that extends from the Turonian through the Maastrichtian. These data record robust isotopic trends with numerous carbon and oxygen isotope shifts that are both rapid and long-term. We tentatively interpret this record to reflect changes in both global climate and regional basin evolution. In the Turonian and Coniacian Qingshankou Formation we observe several carbon isotope shifts that appear to be correlative to marine isotopic records based upon timing and magnitude of the isotopic changes. We suggest that the carbon isotope record in the Songliao basin reflect the decrease in carbon isotope ratios following the strong positive excursion at the Cenomanian/Turonian boundary, a positive isotope excursion in the late Turonian, and the negative isotope shift that occurs at the Turonian/Coniacian boundary. Upward in the section, however, the marine and Songliao isotopic records diverge as sediment sources shift from the southwest, east and north to more northerly. Strontium isotopes record the change in source region as they increase markedly between the Coniacian/Santonian Yaojia and Santonian/Campanian Nenjiang Formations. As this is the first isotopic record of the Songliao basin we are cautious about many of our interpretations of these isotopic data. Yet it is clear that with tighter age constraints and focused sampling centered on many of the isotope excursions presented here will allow for a deeper understanding of the terrestrial response to changing climate and the hydrologic response to basin evolution. [Copyright &y& Elsevier]

From the latest Cretaceous (late Campanian to Maastrichtian, ~75–66 Ma) to the earliest Paleogene, fluctuations in greenhouse climate, inferred primarily from marine sediments, have been linked to volcanism, the Chicxulub asteroid impact, and the Cretaceous-Paleogene (K-Pg) mass extinction. In this paper, we summarize terrestrial climate records in mid-latitude East Asia during the latest Cretaceous and across the K-Pg boundary, based on a multi-proxy approach from the geochronologically well-constrained Sifangtai and Mingshui formations (SMF), accessed by scientific drilling of the Songliao Basin in northeastern China. Evolution of sedimentary environments is characterized by five depositional units of fluvial-deltaic-lacustrine facies. Development of four types of paleosols, including Inceptisols, Aridisols, Vertisols and Alfisols, is interpreted to primarily reflect climatic changes. Correlations among sedimentary facies, paleosol features, illite chemistry index, chemical index of alteration, as well as stable and clumped isotopes of pedogenic carbonates and clay minerals of the SMF validate their reliability for paleoclimate reconstruction, and indicate significant fluctuations in terrestrial climate and sedimentary environment. During global warming intervals possibly triggered by volcanism (e.g. ~69.5–68.5 Ma), the Songliao Basin experienced a warmer and wetter climate with stronger terrestrial chemical weathering and more monsoon-derived moisture sourced from the Pacific. In contrast, during global cooling intervals (e.g. ~70.5–69.5 Ma and ~ 68.5–66.5 Ma), the SMF record a cooler and drier climate with less intensive chemical weathering and more westerlies-derived moisture. Across the K-Pg boundary, dramatic changes in land temperatures and hydroclimate correspond to the latest Maastrichtian warming episode (~66.4–66.1 Ma), the transient cooling preceding the K-Pg boundary (~66.1–66.0 Ma), and the earliest Paleogene warming interval (~66.0–65.7 Ma). Temporal correlation of weathering index changes with the Deccan Traps volcanism suggests that volcanism and subsequent intensified weathering played a major role for climatic changes across the K-Pg boundary. The integrated records of sedimentological and geochemical datasets from the Songliao Basin robustly demonstrate that the terrestrial climate of mid-latitude East Asia responded strongly to greenhouse climate changes and to the catastrophic geological events from the latest Cretaceous to the earliest Paleogene. [ABSTRACT FROM AUTHOR]

Geological records of Milankovitch cycles provide a temporal framework for reconstructing Earth climate evolution and mapping out the history of the ancient Solar System. Understanding the fundamental celestial mechanics driving astronomical rhythms during the Permian Period from stratigraphic record is challenging because of the inherent limitations of astronomical solutions, the chaotic nature of Solar System motion, and the paucity of cyclostratigraphic studies of geological records. The Junggar and adjacent basins of northwestern China constituted a large tectonic lake in the Middle Permian, which deposited one of the thickest and richest petroleum source rock intervals in the world. Constructing an accurate timescale for the Permian Junggar Basin is critical to understand the processes that controlled organic carbon burial as well as paleoclimatic and paleoenvironmental background conditions. In this study, detailed spectral analyses of natural gamma ray (NGR) data were performed on the lacustrine muddy-dominated Lucaogou Formation from five exploitation wells. The results reveal significant meter-scale sedimentary cycles of 37.8 m, 10.7–10 m, 3.85–3.2 m, and 2.0–1.58 m, reflecting oscillations in lithologies (variations in changing clay content within the mudstone, sandstone and dolomite). These cycle wavelength ratios match well with those of the Milankovitch cycles predicted for Middle Permian Period. The depositional duration of the Lucaogou Formation was estimated at ~3 Myr. Correlation of the ~1.2 Myr obliquity modulation cycles among the NGR logs, sedimentation rates, and lake levels of the Junggar Basin, as well as with the Middle Permian global sea level, suggests that long-term astronomical "grand cycles" tightly forced climatic and sedimentary processes throughout the Lucaogou Formation. According to two independent approaches, we reconstruct Middle Permian astronomical parameters (Earth precession constant: k and fundamental frequencies terms: g i ; i = 1, 2, 3, 4, 5) and calculate astronomical periods (eccentricity, obliquity and precession). These results document astronomical forcing of Paleozoic lake systems, constrain Earth-Moon orbital evolution, and refine the fundamental astronomical frequencies of the Solar System during the Middle Permian. • First report of Milankovitch cycles in Middle Permian terrestrial strata • The Lucaogou Formation, in Junggar Basin was deposited at ~270–267 Ma. • The "grand cycle" influenced climate and depositional processes in middle Permian. • Two approaches are used to estimate the Middle Permian astronomical parameters. • Cyclostratigraphic analyzing refined the Earth-Moon history in the Paleozoic. [ABSTRACT FROM AUTHOR]

• Reviews on tectonics and paleoenvironment of the Junggar Basin are present. • An updated chronostratigraphic framework is provided for Permian Junggar Basin. • Dry climate and evaporative environment prevailed during deposition of source rocks. • Stable salinity stratification and limited dilution promoted organic matter burial. • Organic carbon burial in lakes may act as a significant carbon sink in Permian. The Junggar Basin in northwestern China is a typical "walled" sedimentary basin that has a prolonged basin evolution history from the Paleozoic to Cenozoic and is rich in petroleum resources. Permian strata reach thousands of meters in thickness and have been intensively studied for their record of regional tectonics and paleoenvironments. They have also been exploited for oil and gas for the past several decades. In this paper, we summarize perspectives on tectonic evolution, stratigraphic framework, sedimentary environments, and the paleoclimate of the Permian Junggar Basin and the adjacent Turpan Basin. Further, we discuss the mechanism and consequences of massive organic carbon burial. Based on a compilation of published radiometric dating datasets, an updated chronostratigraphic framework was proposed for the Junggar Basin. This framework constrains the ages of two main petroleum source intervals, the Fengcheng Formation and the Lucaogou and equivalent formations, as Early Permian and Middle Permian, respectively. Although a global warming and drying trend was present throughout the Permian Period, the regional climate over the Junggar Basin was drier in Early Permian and more humid in the Middle-Late Permian with short-term climatic fluctuations. During the deposition of the two petroleum source intervals, dry and temperate climate prevailed and evaporative lacustrine environment dominated. Organic matter enrichment was promoted by stable salinity stratification and limited dilution by inorganic sediments, leading to one of the richest lacustrine source rock deposits in the world. The average organic carbon burial rates were 11.2 gC/m2/yr for the Lucaogou Formation and 3.5 gC/m2/yr for the Fengcheng Formation, lower than the average organic carbon burial rate in modern lakes. However, considering the large areas of global tectonic lakes in the Permian Period, organic carbon burial in lacustrine environments could act as a significant carbon sink and impact the global carbon cycle and climate evolution. [ABSTRACT FROM AUTHOR]