Phosphorite organic-rich sediments from Weng’an Doushantuo Formation preserve earliest animals and multicellular life, though it has been investigated by many researchers but in terms of biomarker analysis still need to be known. Here we have applied various specific aliphatic and aromatic biomarkers (Molecular fossils) parameters with stable carbon isotope data. The biomarker investigation of sixteen phosphoritic rocks from Weng’an Doushantuo Formation, Guizhou, South China, was carried out to identify the paleo-depositional environment, source of its organic matter and thermal maturity by using gas chromatography-mass spectrometry/ mass spectrometry (GC-MS). Particular care was taken while doing geochemical analysis in order to get rid of possible contaminations. Geochemical results indicate the source rock extracts from Weng’an Doushantuo Formation have similarity in molecular composition. All the studied samples have a lower amount of TOC, ranging from 0.07% to 0.58%. Molecular fossils revealed that the source input of organic matter was mainly from eukaryotic algae including dinoflagellates (or their ancestors) and demosponges as confirmed by steranes and terpanes. Pristane and phytane are derivative of Chlorophyll-a suggesting the availability of photosynthesis process in early ocean. Maturity based parameters suggest that the Weng’an phosphorite are highly mature, which is consistent with the thermal history of Doushantuo sediments. Isotopic compositions of δ¹³C_saturated and δ¹³C_aromatic hydrocarbon fractions show the marine environment. Biomarker investigation revealed that the phosphorite rocks from Weng’an Doushantuo Formation are highly mature, experienced strongly anoxic, clay rich conditions with major contribution of eukaryotic micro-organisms.

This study presents a new interpretation of the seismic stratigraphic unit equivalent to the Late Cretaceous to Pliocene formations in the Salin basin. Many researchers investigated the outcrops of the stratigraphic succession of the Salin basin but there is a lack of comprehensive analysis by seismic interpretation. This study provides a comprehensive description of the structural development within the Salin basin, enhancing our comprehension of the regional stratigraphic evolution of the examined region. Seismic sequences were delineated using a combination of horizon mapping, internal reflection configuration, termination patterns, and thickness analysis. We identified two distinct mechanisms for lateral fault seals: (1) primary juxtaposition seals and (2) secondary fault rock seals (also known as membrane seals). Once the hydrocarbons are matured within the source formations (Late Cretaceous to Early Oligocene shales units): Kabaw (KB); Laungshe (LA); Tabyin (TA); Pondaung (PO); Yaw (YA); and Shwezettaw (SZT), they are migrated towards the reservoir formations (Pondaung (PO), Shwezettaw (SZT), Padaung (PA), Okhmintaung (OHK), and Kyaukkok (KK)) through these predicted paths. Generally, the primary migration takes place along the fault or fractured planes or pores within rock units. In the southwestern limb of the Yenangyaung anticline, the disharmonic folding and upward bending of the KK, PY, OHK, and PA formations resulted in the deformation of ductile strata within the PA Formation, forcing them towards the peripheral synclines. The main deep fore-thrust in the southwestern limb of the Chauk anticline rooted within the PA Formation flattened up while approaching the OHK and PY formations. Chauk anticlinal axis above the PY and OHK detachment level are more migrated toward the northeast. As a result, above the crest of the deep anticline, the shallow low-angle fore-thrust pushed up into the growth strata, leading to the uplift of the YA and SZT formations within the Letpando anticline. YA Formation crops out locally along the axis of the structure and is the major seal, with sandstones in the underlying Eocene PO Formation being the main reservoir.