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A continuous record of abundant microspherules, pyrite framboids, and bacterial fossils is obtained from the Upper Ordovician in the Dawangou section of northern Tarim Basin, Northwest China. Chemical and physical characteristics of these microspherules were determined using a scanning electron microscope and an energy dispersive spectrometer. Microspherules were formed as a single spherule, spherule aggregates, and drop‐like particles. Physical morphology of the spherules has no relation to its formational process. Energy dispersive spectrometry results indicate that microspherules are mainly composed of Ca, C, O, Si, Al, S, Fe, and Ti. Thus, these microspherules are further categorized into 5 major types: iron, titaniferous‐iron, siliceous, calcareous, and organic microspherules. The first 3 types of microspherules are likely of volcanic origin rather than extraterrestrial origins (i.e., impact event or cosmic dusts) or modern industrial pollutions due to their morphologies and chemical compositions. Both calcimicrospherules and organic microspherules are biogenic, and they are distributed in the lower part of the studied section (Beds 4–6), in which cephalopods, brachiopods, and bacterial fossils are also commonly present and pyrite framboids are absent. These features generally point to an oxic condition. In contrast, other microspherules are abundant in the upper part of the section (Beds 9–13), in which tiny pyrite framboids (mean diameters 4.6–7.3 μm) are rather abundant and typical of euxinic to dysoxic conditions. Both microspherule and pyrite framboid evidences indicate that the northern Tarim region became oxygen‐poor conditions, which were coupled with intensive volcanic eruptions during the Late Ordovician. [ABSTRACT FROM AUTHOR]

The Jurassic was mainly a "greenhouse" period characterized by global warming and by significant peat accumulations in some continental basins. However, studies of Jurassic climate and environments have mainly focused on marine records and only a few on terrestrial sediments. Yili Basin, a mid-latitude terrestrial basin in present Northwest China, included accumulation of the important recoverable coal seams. In this study, geological data, clay mineral analysis, and palynological assemblages were employed on fine-grained samples from the Su'asugou section in southern Yili Basin. The factors (paleoclimate, depositional conditions, and paleo-vegetation) impacting peat accumulation were investigated. The results suggest that the siliciclastics may have been derived from exposed Carboniferous rocks in a continental arc environment. A warm and humid paleoclimate in the Yili basin dominated during the early-Early Jurassic deposition of the Badaowan Formation and the Middle Jurassic deposition of the Xishanyao Formation. This climate contributed to high sedimentary rates and to a high productivity of peat-forming paleo-vegetation that was preserved under dysoxic conditions. In contrast, during the late-Early Jurassic between these two formations, the Sangonghe Formation was an interval of relatively aridity that included red beds preserved under more hypoxic sedimentary conditions, and with an interruption in peat formation and preservation. [ABSTRACT FROM AUTHOR]