The Datang Formation black rock series deposited in an inter-platform basin are considered to be one of the main source rocks in Southwest China. However, their depositional conditions and organic matter enrichment in such a setting are not well understood. In this study, geochemical characteristics of total organic carbon (TOC), major, trace and rare earth elements (REEs) of thirty black rock series samples from a newly-cut roadside outcrop (Zhenning section) in Southern Guizhou, Southwest China are systematically investigated to examine provenance, paleoredox conditions, paleoclimate, paleoproductivity and sedimentary rate, and further to explore their influence on organic matter enrichment. Results show that TOC contents of the investigated samples range from 0.90% to 2.83%, with an average of 1.45%, with TOC variations being in accord with the stratigraphic cyclicity. These data also indicate that the target black rock series were deposited in a combination of continental island arc and active continental margin tectonic setting that exhibited moderate weathering, oxic/dysoxic oxygen levels, hot and arid to semiarid climate, and a higher sedimentary rate. Multiple paleoredox indicators (e.g., Ni/Co, V/Cr, U/Th and V/(V + Ni) ratios), together with slightly negative Ce anomalies and EF_U-EF_Mo covariation, totally suggest an oxic/dysoxic water environment, which is usually considered unfavorable for organic matter preservation. Average (La/Yb)_N ratios (1.41) reflect a higher sedimentary rate, resulting in shortening the exposure time of organic matter in the degradation region of aerobic bacteria under oxic/dysoxic conditions. Of the three factors that could affect organic matter enrichment, including paleoproductivity, paleoredox conditions and sedimentary rate, the relatively high paleoproductivity indicated by the relatively high TOC contents appears to be the dominant factor. In contrast, the other two factors, i.e., paleoredox conditions and the rate of sedimentation play relatively less significant roles. Based on these factors, an enrichment model of organic matter for the black rock series in Southern Guizhou Depression is established. These findings also contribute to constraining the sedimentary environment in such a setting and further deepen our understanding of the potential shale gas resources of the Southern Guizhou Province.

In recent years, there has been significant progress in shale oil exploration in the first member of the Qingshankou Formation (K₂qn¹) in the Qijia‐Gulong Sag, Songliao Basin, Northeast China: It shows good prospects for shale oil. However, the recognized lack of the geochemical and hydrocarbon generation and expulsion characteristics of K₂qn¹ source rocks limits an accurate evaluation of shale oil resource. This study systematically investigated the geological and geochemical characteristics, hydrocarbon generation and expulsion, and shale oil potential of the K₂qn¹ source rocks. The results show that the K₂qn¹ mudstones were mainly deposited in the semideep and deep lacustrine facies under reducing and weak reducing conditions. Compared with the southern Gulong Sag, the northern Qijia Sag has a higher salinity, more abundant prosperous aquatic organisms, and a greater paleoproductivity. The K₂qn¹ source rocks are pervasive and continuous in the entire sag, with maximum thicknesses greater than 110 m. They have a higher organic matter (OM) abundance (2.40% of the average TOC), are dominated by type I and II₁ kerogen, and are mature (0.8%‐0.1.3% VR), which indicate that they are good to excellent source rocks and have significant hydrocarbon generation potential. The source rocks in the Qijia Sag have a higher OM abundance, a better OM type, and a lower OM maturity than those in the Gulong Sag. The threshold and peak hydrocarbon expulsion values for marlstone source rocks are 0.85% VR and 0.95% VR, respectively. The volumes of hydrocarbons generated and expulsed from the K₂qn¹ source rocks are 121.8 × 10⁸ t and 46.9 × 10⁸ t, respectively, with a retention efficiency of 61.5%. The in‐place and recoverable resources of shale oil are 74.9 × 10⁸ t and (12.0‐13.5) × 10⁸ t, respectively, indicating that the entire sag has a significant shale oil potential, especially the Qijia Sag.

The black shale in the upper Permian Dalong Formation is considered as an excellent source rock in the Lower Yangtze region. However, mechanisms of organic matter (OM) accumulation in such a setting are scarcely understood. Here, the characteristics of total organic carbon (TOC) and elemental geochemistry of 33 rock samples from GD1 well are systematically investigated to characterize the paleoenvironmental conditions and OM accumulation mechanisms. Results show that the lower and middle parts of Dalong Formation (section A) display high TOC contents ranging from 1.19 to 6.45% (average 3.19%), whereas the upper part (section B) exhibits medium TOC contents varying from 1.18 to 4.90% (average 2.09%). These data also elucidate that the target shales were deposited in a complex paleoenvironment with moderate to strong water-mass restriction that was characterized by warm and semiarid–semihumid paleoclimate, high biotic productivity, fluctuating plaeoredox conditions, and a relatively high sedimentary rate. Compared to the organic-rich shales from section A mainly developed under an anoxic condition, shales from section B formed in an oxic-to-dysoxic water environment exhibited a comparatively higher sedimentary rate. Moreover, among all these factors that might affect OM accumulation, the paleoredox conditions appear to be the dominant controlling factors for section A, whereas the biotic productivity, paleoredox conditions, and sedimentary rate are the main controlling factors for section B. Finally, two formation models for OM accumulation in Dalong Formation shale in the Lower Yangtze region are proposed. The “preservation model” for OM accumulation in section A emphasizes that the reducing deep-water environment, which was mainly caused by the regional sea level rise, is favorable for OM preservation. The “integrated model” for OM accumulation in section B stresses that greater biotic productivity intensifies respiratory oxygen consumption in a water column and a higher sedimentary rate can greatly shorten OM exposure time for respiration by oxygen, both of which cause OM accumulation under an oxidizing water environment. These findings also add to our knowledge that despite the oxygenated water environment during shale deposition, TOC contents are not necessarily lower.