Sharp-based, mixed carbonate–siliciclastic shallow-marine deposits (upper Miocene, Betic Cordillera, Spain): The record of ancient transgressive shelf ridges?

Isolated sharp-based sedimentary bodies in shelf settings can develop via the reworking of regressive deposits during transgressions. An example of these are shelf ridges, formed under a wide range of processes, and widely studied due to their high reservoir potential. However, there is still a lack of examples in mixed (carbonate–siliciclastic) successions. This study presents an outcrop example from the Upper Miocene of the Betic Cordillera (Spain), with the aim to propose a model for the development of transgressive sharp-based mixed carbonate–siliciclastic deposits, and to provide criteria to differentiate these from their regressive counterparts. The studied succession is ca. 300 m-thick, and shows a cyclic alternation of coarse and fine-grained mixed deposits. Depositional cycles start with siliciclastic-dominated offshore to offshore transition deposits, progressively replaced by lower shoreface deposits. These are abruptly truncated by sharp erosive contacts bioturbated by passively-infilled large burrows; their ichnological features allow assignation to the Glossifungites ichnofacies. These contacts are interpreted as ravinement surfaces. They are overlain by mixed carbonate–siliciclastic barforms, rich in skeletal fragments and extraclasts, and displaying large-scale cross bedding. These form several m-thick and hundreds of m-long depositional elements interpreted as mixed shelf ridges. These ridges formed in a fine-grained, shallow-water shelf, which occasionally received coarse siliciclastic sediment supply via gravity flows, but had a coeval offshore carbonate factory, which provided the skeletal fragments. The sharp-based, coarser-grained nature and lithological break at the base of these mixed carbonate–clastic deposits could lead to their misinterpretation as forced-regressive wedges. However, the nature of their lower contact, combined with the reworked offshore skeletal fragments, and their stacking pattern are consistent with these mixed units forming during transgression. Other studies in relatively time-equivalent deposits have demonstrated the existence of coeval regressive, coarser siliciclastic-dominated shoreline systems in relatively close localities. These evidence a complex basin configuration in the area during the upper Miocene, with the development of local depocentres and relatively narrow corridors or seaways in the Mediterranean–Atlantic connection, which could have favoured shelf reworking processes, but also promoted the development of diverse stacking patterns, reflecting the differential interaction between active tectonics and sedimentation across the region.FEDER AndalucíaSecretaría de Estado de I+D+IAker BPUniversitetet i OsloUniversidad de Granada PID2019-104625RB-100, PID2020-114381GB-100European Regional Development Fund CGL2017-89618-RJunta de Andalucía B-RNM-072-UGR18, P18-RT-4074Agencia Estatal de Investigació

Rapid and sustained environmental responses to global warming: the Paleocene–Eocene Thermal Maximum in the eastern North Sea

The Paleocene–Eocene Thermal Maximum (PETM; ∼ 55.9 Ma) was a period of rapid and sustained global warming associated with significant carbon emissions. It coincided with the North Atlantic opening and emplacement of the North Atlantic Igneous Province (NAIP), suggesting a possible causal relationship. Only a very limited number of PETM studies exist from the North Sea, despite its ideal position for tracking the impact of both changing climate and NAIP activity. Here we present sedimentological, mineralogical, and geochemical proxy data from Denmark in the eastern North Sea, exploring the environmental response to the PETM. An increase in the chemical index of alteration and a kaolinite content up to 50 % of the clay fraction indicate an influx of terrestrial input shortly after the PETM onset and during the recovery, likely due to an intensified hydrological cycle. The volcanically derived zeolite and smectite minerals comprise up to 36 % and 90 % of the bulk and clay mineralogy respectively, highlighting the NAIP's importance as a sediment source for the North Sea and in increasing the rate of silicate weathering during the PETM. X-Ray fluorescence element core scans also reveal possible hitherto unknown NAIP ash deposition both prior to and during the PETM. Geochemical proxies show that an anoxic to sulfidic environment persisted during the PETM, particularly in the upper half of the PETM body with high concentrations of molybdenum (MoEF > 30), uranium (UEF up to 5), sulfur (∼ 4 wt %), and pyrite (∼ 7 % of bulk). At the same time, export productivity and organic-matter burial reached its maximum intensity. These new records reveal that negative feedback mechanisms including silicate weathering and organic carbon sequestration rapidly began to counteract the carbon cycle perturbations and temperature increase and remained active throughout the PETM. This study highlights the importance of shelf sections in tracking the environmental response to the PETM climatic changes and as carbon sinks driving the PETM recovery.publishedVersio

Grand Challenges (and Great Opportunities) in Sedimentology, Stratigraphy, and Diagenesis Research

No abstract available

Volcanism and carbon cycle perturbations in the High Arctic during the Late Jurassic – Early Cretaceous

This is the final version. Available on open access from Elsevier via the DOI in this recordLarge perturbations in the global carbon cycle recorded as carbon-isotope (δ13C) excursions (CIEs) in both organic carbon and carbonate records have been linked to volcanism during the emplacement of Large Igneous Provinces (LIPs). This link is based primarily on the purported temporal coincidence between CIEs and LIP emplacement. Mercury (Hg) concentration in sedimentary rocks has been used as a regional to global tracer of large-scale volcanic activity, yet few studies have been undertaken on Upper Jurassic – Lower Cretaceous sediments from Boreal localities compared to those for Tethyan (northern mid-latitude) successions. This has limited our understanding of the regional-to-global spatial impact of volcanic activity during this period. This study examines the Hg record as a proxy for volcanism, and the δ13C records from organic matter (δ13Corg) of CIEs from the uppermost Jurassic to Lower Cretaceous (Callovian – Aptian) successions from Axel Heiberg and Spitsbergen in the Canadian Arctic and Svalbard archipelagos, respectively. This interval includes three regional- to global CIEs. These sections show no significant variation in the ratio of Hg to total organic carbon (TOC) across the Boreal-wide Volgian negative CIE (Volgian Isotopic Carbon Excursion, “VOICE”), which has not been associated with LIP volcanism. The examined successions spanning this interval all show some influence from changing environmental or post-burial parameters, however, which could have (partially) overprinted a volcanic signal. Despite some problems in stratigraphically constraining the Weissert Event, increased Hg/TOC ratios are observed across this interval, which may be partially driven by volcanism associated with the emplacement of the Paraná-Etendeka Traps. A spike in Hg/TOC is observed immediately prior to the negative peak of the Aptian Oceanic Anoxic Event (OAE1a) CIE, supporting recent evidence of a pulse of High Arctic Large Igneous Province (HALIP) volcanic activity preceding this oceanic anoxic event

Tidal amplification and along-strike process variability in a mixed-energy paralic system prograding onto a low accommodation shelf, Edgeøya, Svalbard

The study describes the depositional development and sediment partitioning in a prograding paralic Triassic succession. The deposits are associated with the advance of large prism-scale clinoforms across a shallower platform area. Approaching the platform, the limited accommodation and associated relative higher rates of deposition generated straighter clinoforms with lower foreset angles. The vertical restriction across the platform is interpreted to have amplified the tidal signature. Sediment was redistributed from the coast into increasingly sandy delta-front deposits, compared to offshore equivalents. The deposits comprise extensive compound dune fields of amalgamated and increasingly clean sandbodies up-section. Rapid deposition of significant amounts of sand led to differential subsidence and growth-faulting in the delta front, with downthrown fault blocks further amplifying the tidal energy through funnelling. A mixed-energy environment created along-strike variability along the delta front with sedimentation governing process-regime. Areas of lower sedimentation were reworked by wave and storm-action, whereas high sedimentation rates preserved fluvially dominated mouth bars. A major transgression, however, favoured tidally dominated deposits also in these areas, attributed to increasing rugosity of the coastline. Formation of an extensive subaqueous platform between the coast and delta front dampened incoming wave energy, and tidally dominated deposits dominate the near-shore successions. Meanwhile formation of wave-built sand-bars atop the platform attest to continued wave influence. The strong tidal regime led to the development of a heterolithic near-shore tidally dominated channel system, and sandier fluvial channels up-river. The highly meandering tidal channels incising the subaqueous platform form kilometre wide successions of inclined heterolithic stratification. The fluvially dominated channels which govern deposition on the delta plain are narrower and slightly less deep, straighter, generally symmetric and filled with cleaner sands. This study provides important insight into tidal amplification and sand redistribution during shallowing on a wide shelf, along with along-strike process-regime variability resulting from variations in sediment influx