Reconstruction of Local and Global Marine Redox Conditions During Deposition of Late Ordovician and Early Silurian Organic-Rich Mudrocks in the Siljan Ring District, Central Sweden

The Ordovician-Silurian transition witnessed the second largest mass extinction in the Phanerozoic Eon and the Hirnantian glaciation. We measured U (as δ238U relative to standard CRM145 = 0‰) and Mo (as δ98Mo relative to standard NIST SRM 3134 = +0.25‰) isotope compositions on 26 organic-rich mudrock (ORM) samples of the Late Ordovician (Katian) Fjäcka Shale and the Early Silurian (Rhuddanian-Telychian) Kallholn Formation to infer local and global ocean redox conditions across the Ordovician-Silurian transition. The magnitude of Re, Mo, and U enrichments, Re/Mo and U/Mo ratios, and sedimentary Fe speciation point to euxinic and oxygenated bottom water conditions during deposition of the Fjäcka Shale and upper Kallholn Formation equivalent gray shales, respectively. The same proxies suggest that the more organic-rich samples of the Kallholn Formation were deposited under transiently euxinic conditions with the chemocline situated near the sediment-water interface. The Mo and U isotope compositions of the most euxinic shales provide the most relevant estimates of the extent of global ocean oxygenation. As expected, the euxinic Fjäcka Shale yields relatively higher average δ98Mo (0.82‰) of the studied units. Elevated Mo/TOC ratios (average: 13.5 ppm/wt%) of the Fjäcka Shale suggest no more than moderate basin restriction from the open ocean as well as large amounts of Mo in the euxinic bottom waters, which can lead to Mo isotope fractionation between seawater and sediments like that observed in the Cariaco Basin. Hence, we infer that the heaviest Mo isotope composition preserved the euxinic Fjäcka Shale (1.28‰) may be fractionated from contemporaneous seawater. As such, the Mo isotope paleoredox proxy is not reliable on its own. This interpretation is further supported by the high average authigenic δ238U (–0.05‰ to 0.02‰; or an average of ~0‰) in the Fjäcka Shale, which is only slightly lower than the modeled value of 0.1‰ for modern euxinic sediments in moderately restricted basins (i.e., between the highly restricted Black Sea [0‰] and open ocean euxinic sediments [0.2‰]). Widespread ocean anoxia should lead to deposition of ORMs with lower δ238U. Hence, the relatively high δ238U coupled with high Mo, Re, and U enrichments, and high Mo/TOC ratios in the Fjäcka Shale suggest a more oxygenated ocean prior to the Hirnantian glaciation than previously thought, though the extent of oxygenation was less than today. Integration of our data with previous studies further supports the hypothesis that ocean oxygenation intensified from the late Katian to the early-middle Hirnantian in association with global cooling, thus challenging the hypothesis that pronounced ocean anoxia persisted throughout the late Ordovician

Pattern Formation in a Bacterial Colony Model

We investigate the spatiotemporal dynamics of a bacterial colony model. Based on the stability analysis, we derive the conditions for Hopf and Turing bifurcations. Furthermore, we present novel numerical evidence of time evolution of patterns controlled by parameters in the model and find that the model dynamics exhibit a diffusion controlled formation growth to spots, holes and stripes pattern replication, which show that the bacterial colony model is useful in revealing the spatial predation dynamics in the real world

DriveDreamer: Towards Real-world-driven World Models for Autonomous Driving

World models, especially in autonomous driving, are trending and drawing extensive attention due to their capacity for comprehending driving environments. The established world model holds immense potential for the generation of high-quality driving videos, and driving policies for safe maneuvering. However, a critical limitation in relevant research lies in its predominant focus on gaming environments or simulated settings, thereby lacking the representation of real-world driving scenarios. Therefore, we introduce DriveDreamer, a pioneering world model entirely derived from real-world driving scenarios. Regarding that modeling the world in intricate driving scenes entails an overwhelming search space, we propose harnessing the powerful diffusion model to construct a comprehensive representation of the complex environment. Furthermore, we introduce a two-stage training pipeline. In the initial phase, DriveDreamer acquires a deep understanding of structured traffic constraints, while the subsequent stage equips it with the ability to anticipate future states. The proposed DriveDreamer is the first world model established from real-world driving scenarios. We instantiate DriveDreamer on the challenging nuScenes benchmark, and extensive experiments verify that DriveDreamer empowers precise, controllable video generation that faithfully captures the structural constraints of real-world traffic scenarios. Additionally, DriveDreamer enables the generation of realistic and reasonable driving policies, opening avenues for interaction and practical applications.Comment: Project Page: https://drivedreamer.github.i

Temporal record of osmium concentrations and 187Os/188Os in organic-rich mudrocks: Implications for the osmium geochemical cycle and the use of osmium as a paleoceanographic tracer

The final publication is available at Elsevier via https://doi.org/10.1016/j.gca.2017.06.046 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We present a compilation of 192Os concentrations (representing non-radiogenic Os) and initial 187Os/188Os isotope ratios from organic-rich mudrocks (ORM) to explore the evolution of the Os geochemical cycle during the past three billion years. The initial 187Os/188Os isotope ratio of a Re-Os isochron regression for ORM constrains the local paleo-seawater 187Os/188Os, which is governed by the relative magnitudes of radiogenic Os (old continental crust) and unradiogenic Os (mantle, extraterrestrial, and juvenile/mafic/ultramafic crust) fluxes to seawater. A first-order increase in seawater 187Os/188Os ratios occurs from the Archean to the Phanerozoic, and may reflect a combination of increasing atmosphere-ocean oxygenation and weathering of progressively more radiogenic continental crust due to in-growth of 187Os from radioactive decay of 187Re. Superimposed on this long-term trend are shorter-term fluctuations in seawater 187Os/188Os ratios as a result of climate change, emplacement of large igneous provinces, bolide impacts, tectonic events, changes in seafloor spreading rates, and lithological changes in crustal terranes proximal to sites of ORM deposition. Ediacaran-Phanerozoic ORM have mildly higher 192Os concentrations overall compared with pre-Ediacaran Proterozoic ORM based on the mean and 95% confidence interval of 10,000 median values derived using a bootstrap analysis for each time bin (insufficient Archean data exist for robust statistical comparisons). However, there are two groups with anomalously high 192Os concentrations that are distinguished by their initial 187Os/188Os isotope ratios. Ediacaran-Cambrian ORM from South China have radiogenic initial 187Os/188Os, suggesting their high 192Os concentrations reflect proximal Os-rich crustal source(s), ultraslow sedimentation rates, and/or other unusual depositional conditions. In contrast, the unradiogenic initial 187Os/188Os and high 192Os concentrations of some Mesozoic ORM can be tied to emplacement of large igneous provinces. Excluding these two anomalous groups and repeating the bootstrap analysis, we find that, overall, the 192Os concentrations for the Ediacaran-Phanerozoic and pre-Ediacaran Proterozoic time bins are not significantly different. An improved understanding of Os geochemical behavior in modern environments is required before our compilation can be fully used to constrain the temporal evolution of the seawater Os reservoir.NSERC Discovery Grant || (RGPIN-435930

Uranium isotope compositions of mid-Proterozoic black shales: Evidence for an episode of increased ocean oxygenation at 1.36Ga and evaluation of the effect of post-depositional hydrothermal fluid flow

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.precamres.2017.06.016 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We report U isotope data for marine black shales of the early Mesoproterozoic Velkerri Formation (Roper Group) and late Paleoproterozoic Wollogorang Formation (Tawallah Group) from the McArthur Basin, Northern Australia. An average authigenic δ238U of 0.13±0.04‰ (1SD; relative to standard CRM145) was obtained for six U- and Mo-rich shales from a ∼1m interval that was deposited at 1361±21Ma (based on previous Re-Os geochronology). After correcting for a local U isotope fractionation of ∼0.60–0.85‰ associated with U removal to anoxic sediments, we infer that global seawater at 1.36Ga had a δ238U of ∼−0.47‰ to −0.72‰, which is ∼0.1−0.3‰ lighter than modern seawater (−0.39±0.01‰). Uranium isotope mass-balance modelling suggests that <25% of the seafloor was anoxic at 1.36Ga. This interpretation is consistent with high U and Mo enrichments in these samples compared with other Velkerri Formation and mid-Proterozoic black shales, which suggests a sizable dissolved oceanic Mo and U inventory developed in response to an episode of increased ocean oxygenation. Hence, a significant expanse of O2-bearing deep ocean waters may have existed at 1.36Ga. The O2 concentrations of those waters were not necessarily high given that a large expanse of weakly oxygenated deep waters is also consistent with the mass-balance model. A lower average authigenic δ238U of −0.08±0.18‰ (1SD) was obtained for comparatively U- and Mo-poor black shales from a ∼1m interval in the lower Velkerri Formation, deposited at 1417±29Ma. In contrast to the upper Velkerri interval, the mass-balance model permits widespread ocean anoxia during deposition of the lower Velkerri interval. Black shales of the ca. 1.73Ga Wollogorang Formation previously yielded an erroneously young Re-Os date of 1359±150Ma, likely due to post-depositional hydrothermal alteration at ca. 1640Ma. Higher δ238U is observed in samples closer to the base of the black shale unit where the greatest extent of open-system Re-Os behavior was observed. Hence, post-depositional hydrothermal fluid flow may overprint the depositional δ238U of black shales and cause erroneous estimates of ancient global ocean anoxia.NSERC Discovery Grant (RGPIN-435930

Marine redox conditions during deposition of Late Ordovician and Early Silurian organic-rich mudrocks in the Siljan ring district, central Sweden

The final publication is available at Elsevier via https://doi.org/10.1016/j.chemgeo.2017.03.015 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 licenseThe Late Ordovician Period witnessed the second largest mass extinction in the Phanerozoic Eon and the Hirnantian glaciation. To infer ocean redox conditions across the Ordovician-Silurian transition, we measured the U (as δ238U relative to standard CRM145 = 0‰) and Mo (as δ98Mo relative to standard NIST SRM 3134 = +0.25‰) isotope compositions of 26 organic-rich mudrock samples from the Late Ordovician (Katian) Fjäcka Shale and the Early Silurian (Aeronian-Telychian) Kallholn Formation (Siljan ring district, Sweden). The magnitude of Re,Mo, and U enrichments, ReEF/MoEF and UEF/MoEF ratios, and sedimentary Fe speciation point to locally euxinic bottom water conditions during deposition of the Fjäcka Shale. The same proxies suggest that black shales of the Kallholn Formation were deposited under transiently euxinic conditions with the chemocline situated near the sediment-water interface, whereas gray shales stratigraphically equivalent to the upper Kallholn Formation were deposited from oxygenated bottom waters. These observations are consistent with higher δ98Mo and δ238U in the Fjäcka Shale compared with the Kallholn Formation. Because the Fjäcka Shalewas deposited from persistently euxinic bottomwaters, theMo and U isotope compositions from these rocks can be used to estimate the extent of global ocean euxinia and ocean anoxia (euxinic plus ferruginous conditions), respectively. Elevated MoEF and Mo/TOC ratios in the euxinic Fjäcka Shale suggest no more than moderate basin restriction from the open ocean as well as non-quantitative removal ofMo from the euxinic bottom waters, thus pointing toMo isotope fractionation between seawater and the euxinic sediments. Hence, we infer that even the highest δ98Mo(+1.28‰) preserved in the Fjäcka Shale is only aminimum estimate for theMoisotope composition of coeval global seawater. Correcting for seawater-sediment Mo isotope fractionation, the δ98Mo of late Katian seawater may have been +1.4–2.1‰, which corresponds to ~10–70% Mo removal into the euxinic sink. The average authigenic δ238U of the Fjäcka Shale is −0.05‰ to +0.02‰ after correcting for a range of possible detrital δ238U values, thus yielding an overall average of ~0‰. Taking into account isotope fractionation during U removal to euxinic sediments, we infer that late Katian seawater δ238U was about−0.85‰to−0.60‰. A steady-state U isotope mass balance model reveals that 46–63% of riverine U input was removed in anoxic settings. Based on the Mo and U isotope data, we infer that euxinic and anoxic waters may have covered b1% and at least 5% (potentially tens of percent) of the total seafloor area during the late Katian, respectively, based on previously publishedmodels that relate themagnitude of Mo and U burial fluxes to the areal extent of euxinic and anoxic seafloor. By comparison, only 0.21–0.35% and b1% of the total seafloor area was covered by anoxic waters today and during the Cenozoic, respectively. The difference between the estimated extent of ocean anoxia (euxinic plus ferruginous) and ocean euxinia points to an appreciable extent of ferruginous water masses during the late Katian. Integration of our data with previous studies thus supports the hypothesis that ocean oxygenation intensified during the subsequent Hirnantian glaciation (when seawater δ98Motemporarily reached values similar to today). Hence, environmental stresses related to glaciation, not an expansion of ocean anoxia,may have triggered the first phase of the Hirnantianmass extinction.NSERC Discovery grant || (RGPIN-435930) Chinese 973 program || (grant No. 2013CB955704) NSFC || (grant No. 41172030

Early Paleozoic Ocean Redox Dynamics: Perspectives from Uranium Isotopes of Sedimentary Rocks

The trajectory of global ocean oxygenation could have greatly influenced the metazoan evolutions because O2 could provide valuable energy to support biological activities. Remarkable metazoan diversifications occurred during the Late Neoproterozoic (i.e., Ediacaran; 635–539 Ma) and Early Paleozoic (i.e., Cambrian, Ordovician, and Silurian; ca. 538–419 Ma), such as the appearance of Ediacaran Biota and the “Cambrian Explosion”. However, an increasing number of studies suggest that a near-modern level of Earth’s surface oxygenation was not established during the Late Neoproterozoic (ca. 680 Ma), but rather during the Devonian (ca. 419–359 Ma). Therefore, it is of great importance to understand the co-evolution of global ocean redox conditions and metazoan diversifications during the Early Paleozoic (ca. 538–419 Ma). The uranium isotope compositions (δ238U) from sedimentary rocks (e.g., organic-rich mudrocks, carbonates) have been used as a global ocean redox proxy and provided insights on ocean redox dynamics. Understanding the local bottom water redox conditions is crucial to interpret δ238U values, as different δ238U offsets occur under various redox settings. Relatively larger δ238U offsets are observed in sediments from modern euxinic basins compared with the other redox settings, suggesting seawater δ238U values are sensitive to the extent of global euxinic seafloor area. Uranium isotope mass balance modelling could be further used to quantitatively estimate the areal extent of euxinic seafloor in the oceans. In this thesis, U isotopes from sedimentary rocks are used to investigate ocean redox conditions, with a focus during the Ordovician Period (ca. 487–443 Ma) when there is rapid evolutionary change. The coupled use of molybdenum and uranium isotope compositions from euxinic organic-rich mudrocks are investigated to better reconstruct ancient ocean redox conditions. Local depositional conditions of each formation were firstly examined by sedimentary Fe speciation, covariations between Mo and TOC, and between Mo and U enrichment factors. The Mo and U isotope compositions from individual formations were observed to exhibit negative, positive, and no correlations, suggesting different controlling mechanisms (e.g., bottom water H2S concentrations, basin restrictions, global ocean redox conditions). This study provides a general framework of using coupled Mo-U isotopes from the same euxinic organic-rich mudrocks to disentangle the effects of local depositional environment and global ocean redox states. Specifically for the Ordovician, a positive correlation of Mo-U isotope data from the late Katian Fjäcka Shale suggests an episodic ocean oxygenation event prior to the Hirnantian. The Late Ordovician mass extinction event (LOME; ca. 445–443 Ma) wiped out 85% of species. However, metazoan biodiversity started to decline during the Katian (ca. 453–445 Ma; prior to the LOME) and coeval global ocean redox conditions are not well understood. The Katian organic-rich sedimentary rocks in southern Ontario, namely the Collingwood Member (upper Lindsay Formation) and succeeding Rouge River Member (lower Blue Mountain Formation), were deposited during the Taconic Orogeny. Samples of both units were collected from several drillcores that cover southern Ontario. Paleosalinity (strontium/barium and sulfur/total organic carbon) and paleoredox (redox sensitive trace metals, Fe speciation, and Corg : P ratios) proxies were used to constrain the local depositional environment of both units. In addition, the δ238U of both units were used to deduce coeval ocean redox conditions. Lower estimated seawater δ238U during deposition of the Collingwood Member suggests an expansion of global ocean euxinia, whereas higher seawater δ238U during deposition of the Rouge River Member represents a contraction of ocean euxinia. A three-sink U isotope mass balance model suggests a global ocean euxinic seafloor area of 0.5–31.6% and 0.2–2.0% during deposition of the Collingwood Member and Rouge River Member, respectively. Combined with other studies, fluctuating ocean redox conditions occurred during a decline of biodiversity prior to the LOME. The base Stairsian mass extinction event (BSME; ca. 482 Ma), accompanied with a positive carbon isotope excursion (CIE), is one of the best studied mass extinction events in the Tremadocian, Early Ordovician (ca. 487–471 Ma). New trace metal concentrations and δ238U of carbonates from three sections (along a proximal-to-distal transect: Ibex area, Shingle Pass, Meiklejohn Peak, respectively) in the Great Basin (western USA) were analyzed to quantitatively constrain the role of global ocean euxinia on the mass extinction event. Carbonate δ238U data show different trends among the three sections. The proximal Ibex section shows a negative δ238U excursion during the CIE, whereas the distal Shingle Pass section only has one sample with unusually low δ238U and the Meiklejohn Peak section does not have any samples with unusually low δ238U. The lowest δ238U values from each of the Ibex and Shingle Pass sections are associated with the highest Mn/Sr ratios in those sections, suggesting diagenetic overprints. Carbonate δ238U data from the other two distal sections likely record the open ocean δ238U signals and limited variations in these sections suggest no significant change in global ocean euxinia during the BSME. A three-sink U isotope mass balance model suggests 0.2–15.8% global euxinic seafloor area during the studied interval. Although there was no expansion of euxinia, there is evidence of expanded ocean suboxia-anoxia based on concurrent positive carbon and sulfur isotope excursions during the BSME. Limited changes in global ocean euxinia are further proposed during the post-SPICE Cambrian and Early Ordovician because other carbon isotope perturbations during this time are smaller than that associated with the BSME. Combined with previous studies, fluctuating ocean redox conditions were possibly the key character during the Early Paleozoic (ca. 538–419 Ma), though limited non-traditional metal isotope data are available for the Early-Middle Ordovician (ca. 487–458 Ma) and Silurian (ca. 443–419 Ma). The notable “Cambrian Explosion” has been suggested to coincide with pulses of ocean oxygenation, however, several recent studies proposed that this metazoan radiation could be facilitated by overall dynamic Cambrian ocean redox conditions. Nonetheless, more studies are needed to better understand the Early Paleozoic ocean redox conditions and the co-evolution of metazoans. For example, there is a great potential to study marine redox conditions during the “Great Ordovician Biodiversification Event” as metal isotope data during this event have not been reported

Estimating ancient seawater isotope compositions and global ocean redox conditions by coupling the molybdenum and uranium isotope systems of euxinic organic-rich mudrocks

The final publication is available at Elsevier via https://doi.org/10.1016/j.gca.2020.08.032. © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The sedimentary Mo and U isotope systems have been commonly used as novel global ocean redox tracers due to their long oceanic residence times and redox-sensitive behavior. However, local sedimentary environments and global ocean redox conditions both influence the Mo and U isotope compositions of euxinic organic-rich mudrocks (ORM). Here, we further develop the coupled use of Mo and U isotope data from euxinic ORM to more robustly infer coeval global ocean redox conditions. We measured ẟ238U from eight late Neoproterozoic to middle Paleozoic ORM units that have previously reported Mo isotope and Fe speciation data. Integration of our new data with previously published Proterozoic and Phanerozoic Mo and U isotope data reveals that there is no overall correlation between the Mo and U isotope compositions of euxinic ORM. This observation confirms that the extent to which local versus global environments influenced the preserved Mo and U isotope compositions in ORM was variable. Individual ORM units can have negative, positive, or no correlation between ẟ98Mo and ẟ238U. A negative correlation between ẟ98Mo and ẟ238U in the Upper Devonian Kettle Point Formation is similar to the observations from modern euxinic basins, reflecting a major control on the Mo-U isotope systematics by changes in the local depositional environment, such as bottom-water sulfide concentrations. A positive correlation between ẟ98Mo and ẟ238U observed in the Upper Ordovician Fjacka Shale is best explained by changes in global ocean redox conditions that simultaneously shifted the Mo and U isotope compositions of the global seawater and the Fjacka Shale ORMs in the same direction. No correlations between ẟ98Mo and ẟ238U for euxinic ORM may be caused by specific local depositional changes, a lack of or a combination of local and global environmental changes, and/or is an artifact of limited data. For example, a vertical trend (variable ẟ98Mo but similar ẟ238U) is shown by most samples from Member IV of the Ediacaran Doushantuo Formation, implying a strong influence on the Mo isotope data by an Fe-Mn particulate shuttle. A horizontal trend (similar ẟ98Mo but variable ẟ238U) is observed from the Paleoproterozoic Zaonega Formation, implying that relatively constant bottom water sulfide concentrations caused similar magnitudes of Mo isotope fractionations whereas other factors (e.g., U reduction pathways, aqueous U species, productivity) were responsible for variable U isotope fractionations. Relatively constant elemental concentrations and isotope compositions from the Tanezzuft Formation are indicative of stable conditions at local and global scales. We further propose a method to estimate the coeval seawater Mo and U isotope compositions based on a coupled Mo-U isotope mass balance model and the observations from modern euxinic basins. The coupled Mo-U isotope data from euxinic ORMs provide more insights on the local and global environmental controls on the preservation of both isotope systems than previously realized. Our study highlights the importance of examining the local depositional environment and using large datasets of coupled Mo-U isotope compositions from euxinic ORM intervals to reconstruct paleocean redox conditions