Synchronizing terrestrial and marine records of environmental change across the Eocene–Oligocene transition

Records of terrestrial environmental change indicate that continental cooling and/or aridification may have predated the greenhouse–icehouse climate shift at the Eocene–Oligocene transition (EOT) by ca. 600 kyr. In North America, marine-terrestrial environmental change asynchronicity is inferred from a direct comparison between the astronomically tuned marine EOT record and published 40Ar/39Ar geochronology of volcanic tuffs from the White River Group (WRG) sampled at Flagstaff Rim (Wyoming) and Toadstool Geologic Park (Nebraska), which are type sections for the Chadronian and Orellan North American Land Mammal Ages. We present a new age-model for the WRG, underpinned by high-precision 206Pb/238U zircon dates from 15 volcanic tuffs, including six tuffs previously dated using the 40Ar/39Ar technique. Weighted mean zircon 206Pb/238U dates from this study are up to 1.0 Myr younger than published anorthoclase and biotite 40Ar/39Ar data (calibrated relative to Fish Canyon sanidine at 28.201 Ma). Giving consideration to the complexities, strengths, and limitations associated with both the 40Ar/39Ar and 206Pb/238U datasets, our interpretation is that the recalculated 40Ar/39Ar dates are anomalously old, and the 206Pb/238U (zircon) dates more accurately constrain deposition. 206Pb/238U calibrated age–depth models were developed in order to facilitate a robust intercomparison between marine and terrestrial archives of environmental change, and indicate that: (i) early Orellan (terrestrial) cooling recorded at Toadstool Geologic Park was synchronous with the onset of early Oligocene Antarctic glaciation and (ii) the last appearance datums of key Chadronian mammal taxa are diachronous by ca. 0.7 Myr between central Wyoming and NW Nebraska

Timescales of methane seepage on the Norwegian margin following collapse of the Scandinavian Ice Sheet

Gas hydrates stored on continental shelves are susceptible to dissociation triggered by environmental changes. Knowledge of the timescales of gas hydrate dissociation and subsequent methane release are critical in understanding the impact of marine gas hydrates on the ocean–atmosphere system. Here we report a methane efflux chronology from five sites, at depths of 220–400 m, in the southwest Barents and Norwegian seas where grounded ice sheets led to thickening of the gas hydrate stability zone during the last glaciation. The onset of methane release was coincident with deglaciation-induced pressure release and thinning of the hydrate stability zone. Methane efflux continued for 7–10 kyr, tracking hydrate stability changes controlled by relative sea-level rise, bottom water warming and fluid pathway evolution in response to changing stress fields. The protracted nature of seafloor methane emissions probably attenuated the impact of hydrate dissociation on the climate system

Going with the flow: sedimentary processes along karst conduits within Chalk aquifers, northern France

Sediment-filled caves, conduits and voids are common in many karst regions. These voids and the sediment they contain are important palaeoclimatic and palaeoenvironmental archives, but often have an adverse impact on engineering projects, mineral extraction and hydrogeology. Most studies into fluvial sedimentation in karst aquifers have focussed on more traditional karst areas. However, the nature and extent of fluvial sedimentation within caves and conduits in the important Upper Cretaceous Chalk Group aquifer (NW and Central Europe), and their impacts are less well known. This is principally due to a lack of accessible Chalk caves with exposed 3D sediment archives for study. Fortunately, the discovery of the World's longest Chalk cave system by underground quarrying at Caumont in the Seine valley near Rouen, northern France, has exposed numerous sediment sections along 2.4 km of passage. Detailed analysis of the stratigraphy, mineralogy, sedimentology, provenance and the chronology of the exposed sediments including the novel use of Gamma-ray spectrometry, reveals complex stratigraphy and lateral facies distribution along a karst conduit. The depositional model comprises five allostratigraphical units since the mid-Chibanian, separated by periods of erosion. The units are derived from hyper-concentrated and sediment-laden flows, and include thalweg, channel, slackwater, backswamp speleothem facies and debris flow deposits that are interbedded. Speleothems precipitated during MIS 7, 6, 5e and 1. During MIS 7–6, detrital sediments filled almost all Chalk conduits, similar to other caves in the European Atlantic Margin, coevally with the Penultima (Saalian) Glacial Cycle and a maximum of the Earth eccentricity. Detrital sediments are derived from the erosion of local Chalk bedrocks as well as metamorphic and igneous rocks of remote areas, such as Morvan massif and Massif Central. The depositional model is consistent with the conception of the Chalk as a karst aquifer. Significant sediment aggradation caused upwards dissolution (paragenesis), conduit occlusion and subsequent genesis of new conduits by flow diversion, potentially altering the functioning of the chalk aquifer and the interpretation of Chalk hydrogeology (e.g., dye-tracing tests)

Snežna jama (Slovenia): Interdisciplinary dating of cave sediments and implication for landscape evolution

AbstractCaves are important markers of surface evolution, since they are, as a general rule, linked with ancient valley bottoms by their springs. However, caves can only be dated indirectly by means of the sediments they contain. If the sediment is older than common dating methods, one has to use multiple dating approaches in order to get meaningful results. U/Th dating, palaeomagnetic analysis of flowstone and sediment profiles, cosmogenic dating of quartz pebbles, and mammalian dating allowed a robust estimate of speleogenesis, sediment deposition, climatic change at the surface, and uplift history on the Periadriatic fault line during the Plio-Pleistocene. Our dates indicate that Snežna jama was formed in the (Upper) Miocene, received its sedimentary deposits during the Pliocene in a rather low-lying, hilly landscape, and became inactive due to uplift along the Periadriatic and Sava faults and climatic changes at the beginning of the Quaternary. Although it is only a single cave, the information contained within it makes it an important site of the Southern Alps

Corrigendum to “Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps” [Earth Planet. Sci. Lett. 449 (2016) 332–344]

This paper is not subject to U.S. copyright. The definitive version was published in Earth and Planetary Science Letters 475 (2017): 268, doi:10.1016/j.epsl.2017.07.037

Humid phases on the southwestern Arabian Peninsula are consistent with the last two interglacials

Past environmental and climatic conditions within the Arabian Peninsula are key to understanding the setting for hominin dispersal across the Saharo-Arabian dryland belt. The tufa deposits within the volcanic harrats on the southwest coast of Saudi Arabia fill a significant spatial gap in the distribution of palaeoenvironmental records on the west coast of the Arabian Peninsula adjacent to the Red Sea. In the catchment of Wadi Dabsa in the Harrat Al Birk, there are widespread fossil palustrine to shallow-lacustrine tufa deposits with fluvial elements. Several phases of tufa accumulation, separated by fluvial downcutting, are observable within these powerful palaeoenvironmental proxies. U–Th dating of targeted dense, banded tufa facies, yield ages that are stratigraphically consistent at the landscape scale, and indicate that tufa accumulation occurred during distinct humid phases broadly coeval with the last two warm interglacial Marine Isotope Stages (MIS 7 and MIS 5). For the first time this shows humid intervals in southwest Arabia coincident with the southern coast. There is a simlar pattern emerging further north in the Arabian Peninsula, The Sinai and Levant and further on into continental Europe. Furthermore, tufa δ18O ranges from −14.6 to −1.9‰, covering a range similar to those reported for tufa from north African oasis sites and speleothems elsewhere on the Arabian Peninsula and The Levant. The lowest δ18O values are derived from MIS 5e samples, a pattern in agreement with speleothems in Yemen and Oman, and consistent with an isotopic-enabled climate model simulation for this time slice. The δ13C and Sr isotopic compositions of dated tufa samples indicate deposition from shallow-circulating meteoric water, with no geothermal influence. This, along with the δ18O values, suggest a freshwater supply that was a potable water source in this landscape. The δ13C signatures at Wadi Dabsa are more negative than for parts of north Africa, suggesting Wadi Dabsa may have experienced comparatively higher biomass, thicker soils and wetter conditions with lower evaporative losses. This new record of tufa deposition during the middle and late Pleistocene, suggests for the first time that the west coast of Arabia experienced a similar history of humid phases over the past 250 ka as southern Arabia and the Nefud in the northern interior. These regional changes in hydroclimatic regime occur at timescales coincident with hominin dispersals

Reconstructing fluvial incision rates based upon palaeo‐water tables in Chalk karst networks along the Seine valley (Normandy, France)

Quantifying rates of river incision and continental uplift over Quaternary timescales offer the potential for modelling landscape change due to tectonic and climatic forcing. In many areas, river terraces form datable archives that help constrain the timing and rate of valley incision. However, old river terraces, with high‐level deposits, are prone to weathering and often lack datable material. Where valleys are incised through karst areas, caves and sediments can be used to reconstruct the landscape evolution because they can record the elevation of palaeo‐water tables and contain preserved datable material. In Normandy (N. France), the Seine River is entrenched into an extensive karstic chalk plateau. Previous estimates of valley incision were hampered by the lack of preserved datable fluvial terraces. A stack of abandoned phreatic cave passages preserved in the sides of the Seine valley can be used to reconstruct the landscape evolution of the region. Combining geomorphological observations, palaeomagnetic and U/Th dating of speleothem and sediments in eight caves along the Lower Seine valley, we have constructed a new age model for cave development and valley incision. Six identified cave levels up to ∼100 m a.s.l. were formed during the last ~1 Ma, coeval with the incision of the Seine River. Passage morphologies indicate that the caves formed in a shallow phreatic/epiphreatic setting, modified by sediment influxes. The valley's maximum age is constrained by the occurrence of late Pliocene marine sand. Palaeomagnetic dating of cave infills indicates that the highest‐level caves were being infilled prior to 1.1 Ma. The evidence from the studied caves, complemented by fluvial terrace sequences, indicates that rapid river incision occurred during marine isotope stage (MIS) 28 to 20 (0.8–1 Ma), with maximal rates of ~0.30 m ka−1, dropping to ~0.08 m ka−1 between MIS 20–11 (0.8–0.4 Ma) and 0.05 m ka−1 from MIS 5 to the present time

A 160,000-year-old history of tectonically controlled methane seepage in the Arctic

The geological factors controlling gas release from Arctic deep-water gas reservoirs through seabed methane seeps are poorly constrained. This is partly due to limited data on the precise chronology of past methane emission episodes. Here, we use uranium-thorium dating of seep carbonates sampled from the seabed and from cores drilled at the Vestnesa Ridge, off West Svalbard (79°N, ~1200 m water depth). The carbonate ages reveal three emission episodes during the Penultimate Glacial Maximum (~160,000 to 133,000 years ago), during an interstadial in the last glacial (~50,000 to 40,000 years ago), and in the aftermath of the Last Glacial Maximum (~20,000 to 5,000 years ago), respectively. This chronology suggests that glacial tectonics induced by ice sheet fluctuations on Svalbard mainly controlled methane release from Vestnesa Ridge. Data corroborate past methane release in response to Northern Hemisphere cryosphere variations and suggest that Arctic deep-water gas reservoirs are sensitive to temperature variations over Quaternary time scales

U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway

We investigated methane-derived authigenic carbonate (MDAC) crusts and nodules from a cold seep site on the northern Norwegian continental shelf in ca. 220 m water depth to determine the timing and mode of their formation. Gas bubbling observed during remotely operated vehicle (ROV)-assisted sampling of MDAC crusts revealed ongoing seep activity. Authigenic carbonates were present as crusts on the seafloor and as centimetre-size carbonate-cemented nodules at several intervals within an adjacent sediment core. Aragonite-dominated mineralogy of the MDAC crusts suggests formation close to the seafloor at higher rates of sulphate-dependent anaerobic oxidation of methane (AOM). In contrast, dolomite-cemented nodules are consistent with the formation at the sulphate-methane-transition zone deeper within the sediment at lower rates of AOM. The δ13C-carbonate values of bulk rock and of micro-drilled aragonite samples vary between − 22.2‰ and − 34.6‰ (VPDB). We interpret the carbon in aragonite to be mainly derived from the anaerobic oxidation of thermogenic methane, with a minor contribution from seawater dissolved inorganic carbon (DIC). AOM activity is supported by high concentrations of AOM-related biomarkers of archaea (archaeol and 2-sn-hydroxyarchaeol) and sulphate-reducing bacteria (iso and anteiso-C15:0 fatty acids) in the crusts. The dolomite nodules exhibit higher δ13C-carbonate values (− 12‰ VPDB) suggesting a smaller amount of methane-derived carbon, presumably due to the contribution of DIC migrating from depth, and lower AOM rates. The latter is supported by orders of magnitude lower concentrations of archaeol and sn-2-hydroxyarchaeol in the sediment interval containing the largest dolomite nodules. δ18O values of pure aragonite samples and dolomite nodules indicate the precipitation of carbonate close to isotopic equilibrium with seawater and no influence of gas hydrate-derived water. U-Th dating of two MDAC crusts shows that they formed between 1.61 ± 0.02 and 4.39 ± 1.63 ka BP and between 2.65 ± 0.02 and 4.32 ± 0.08 ka BP. We infer both a spatial and temporal change in methane flux and related MDAC formation at this seep site. These changes might be caused by regional seismic events that can affect pore pressure or re-activation of migration pathways thus facilitating fluid flow from deep sources towards the seabed

Discharge of meteoric water in the Eastern Norwegian Sea since the Last Glacial Period

Submarine groundwater discharge could impact the transport of critical solutes to the ocean. However, its driver(s), significance over geological time scales, and geographical coverage are poorly understood. We characterize a submarine groundwater seep from the continental slope off northern Norway where substantial amount of meteoric water was detected. We reconstruct the seepage history from textural relationships and U‐Th geochronology of authigenic minerals. We demonstrate how glacial‐interglacial dynamics have promoted submarine groundwater circulation more than 100 km offshore and result in high fluxes of critical solutes to the ocean. Such cryosphere‐hydrosphere coupling is likely common in the circum‐Arctic implying that future decay of glaciers and permafrost in a warming Arctic is expected to attenuate such a coupled process and thus decreases the export of critical solutes