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Abstract A geologically rapid Neoproterozoic oxygenation event is commonly linked to the appearance of marine animal groups in the fossil record. However, there is still debate about what evidence from the sedimentary geochemical record—if any—provides strong support for a persistent shift in surface oxygen immediately preceding the rise of animals. We present statistical learning analyses of a large dataset of geochemical data and associated geological context from the Neoproterozoic and Palaeozoic sedimentary record and then use Earth system modelling to link trends in redox-sensitive trace metal and organic carbon concentrations to the oxygenation of Earth’s oceans and atmosphere. We do not find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era. We do, however, reconstruct a moderate long-term increase in atmospheric oxygen and marine productivity. These changes to the Earth system would have increased dissolved oxygen and food supply in shallow-water habitats during the broad interval of geologic time in which the major animal groups first radiated. This approach provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation, while highlighting the importance of later Palaeozoic oxygenation in the evolution of the modern Earth system. 

Accurately reconstructing original Total Organic Carbon (TOC) in thermally mature rocks is essential for the correct application of geochemical proxies and understanding organic carbon burial through time. To reconstruct original TOC using empirical methods, it is vital to have an accurate estimate of the original Hydrogen Index (HI). The two most common methods are estimating original HI using kerogen type or using average HI values from immature rocks elsewhere in the basin. This study tests the ability to use inorganic geochemical data to reconstruct original HI using the Upper Cretaceous-Paleogene Moreno Formation from the San Joaquin Basin, California, USA as a case study. The study utilized cores from the Moreno Formation that are thermally immature, thus preserving original HI values, and that span a range in initial HI. First, inorganic geochemical data were produced (elemental abundances and iron speciation) for samples previously analyzed for organic geochemistry. These data suggest that bottom water conditions during deposition of the Moreno Formation were ferruginous (anoxic and non-sulfidic), without development of sustained euxinia (anoxic and sulfidic). Next, a random forest machine learning analysis was implemented to analyze which inorganic geochemical variables best predict HI in the Moreno Formation. The most important proxies were those for detrital input (Ti, Th), marine export productivity (Cu, Ni), and redox proxies for suboxic conditions (Se, Cr, iron speciation). Finally, the random forest framework was used to predict HI values for three main study cores based on their inorganic geochemistry. These predictions were compared stratigraphically and statistically against the measured values and the kerogen type and average HI methods for reconstructing HI and show this new method has better predictive power than approaches based on single values. This indicates strong promise for using inorganic geochemistry, which is relatively immune to thermal maturation, to reconstruct organic geochemical parameters that are modified during burial and diagenetic process. 

Geochemical data from ancient marine sediments are crucial for studying palaeo-environments, palaeo-climates, and elemental cycles. With increased accessibility to geochemical data, many databases have emerged. However, there remains a need for a more comprehensive database that focuses on deep-time marine sediment records. Here, we introduce the Deep-Time Marine Sedimentary Element Database (DM-SED). The DM-SED has been built upon the Sedimentary Geochemistry and Paleoenvironments Project (SGP) database with a new compilation of 34 874 data entries from 433 studies, totalling 63 627 entries. The DM-SED contains 2 522 255 discrete marine sedimentary data points, including major and trace elements and some stable isotopes. It includes 9207 entries from the Precambrian and 54 420 entries from the Phanerozoic, thus providing significant references for reconstructing deep-time Earth system evolution. The data files described in this paper are available at https://doi.org/10.5281/zenodo.14771859 (Lai et al., 2025). 

It is clear from modern analogue studies that O2-deficient conditions favor preservation of organic matter (OM) in fine-grained sedimentary rocks (black shales). It is also clear that appreciable productivity and OM flux to the sediment are required to establish and maintain these conditions. However, debates regarding redox controls on OM accumulation in black shales have mainly focused on oxic versus anoxic conditions, and the implications of different anoxic redox states remain unexplored. Here, we present detailed multi-proxy sedimentary geochemical studies of major Paleozoic and Mesozoic North American black shale units to elucidate their depositional redox conditions. This is the first broad-scale study to use a consistent geochemical methodology and to incorporate data from Fe-speciation – presently the only redox proxy able to clearly distinguish anoxic depositional conditions as ferruginous (H2S-limited) or euxinic (H2S-replete, Fe-limited). These data are coupled with total organic carbon (TOC), programmed pyrolysis, and redox-sensitive trace element proxies, with almost all measurements analyzed using the same geochemical methodology. Consistent with expectations based on previous geochemical and paleontological/ichnological studies, these analyses demonstrate that the study units were almost exclusively deposited under anoxic bottom waters. These analyses also demonstrate that there is wide variance in the prevalence of euxinic versus ferruginous conditions, with many North American black shale units deposited under predominantly ferruginous or oscillatory conditions. TOC is significantly higher under euxinic bottom waters in analyses of both preserved (present day) TOC and reconstructed initial TOC values, although sediments deposited under both redox states do have economically viable TOC content. While this correlation does not reveal the mechanism behind higher organic enrichment in euxinic environments, which may be different in different basins, it does open new research avenues regarding resource exploration and the biogeochemistry of ancient reducing environments. 

The evolution of oxygen cycles on Earth’s surface has been regulated by the balance between molecular oxygen production and consumption. The Neoproterozoic–Paleozoic transition likely marks the second rise in atmospheric and oceanic oxygen levels, widely attributed to enhanced burial of organic carbon. However, it remains disputed how marine organic carbon production and burial respond to global environmental changes and whether these feedbacks trigger global oxygenation during this interval. Here, we report a large lithium isotopic and elemental dataset from marine mudstones spanning the upper Neoproterozoic to middle Cambrian [~660 million years ago (Ma) to 500 Ma]. These data indicate a dramatic increase in continental clay formation after ~525 Ma, likely linked to secular changes in global climate and compositions of the continental crust. Using a global biogeochemical model, we suggest that intensified continental weathering and clay delivery to the oceans could have notably increased the burial efficiency of organic carbon and facilitated greater oxygen accumulation in the earliest Paleozoic oceans. 

Proterozoic strata in central Yukon are exposed in the Coal Creek, Hart River and Wernecke inliers. The Paleoproterozoic and Neoproterozoic strata are well correlated across the inliers; however, correlation of the Mesoproterozoic units remains ambiguous. We present two stratigraphic logs of Mesoproterozoic units PP1 and PP2 (previously termed PR1 and PR2, respectively) in the Coal Creek inlier. PP1 is dominantly siltstone and sandstone, whereas PP2 is mostly dolostone. In one section where the contact is well exposed, PP2 gradationally overlies PP1, suggesting that these units, at least locally, are conformable. Based on similarities in the stratigraphy and contact relationships with underlying and overlying units, we suggest that PP1 and PP2 are correlative with the Pinguicula Group formally defined in the Hart River and Wernecke inliers. Resolving how PP1 and PP2 correlate with Proterozoic strata exposed in other inliers provides insight into basin development along northwest Laurentia during the Meso–Neoproterozoic.