Articles of Note
These are the first measurements of inclusion gas in halite chevron cornet and cumulate crystals from the Neoproterozoic Browne Formation (815± 15 Ma) in the Officer Basin, southwest Australia. Compared to traditional and more recent models, they show oxygen values much higher than expected (>10; green rectangle). It places the onset of significant oxygenation of the Neoproterozoic atmosphere and Tonian and in agreement with time of diversification of eukaryotes. This occurs at a time well before widespread metazoans and the biological diversification that marks the end of the Neoproterozoic (Ediacaran) and the start of the Cambrian.
Based on a close association between abundant eurypterid remains and salt hoppers in the Salina and Bertie groups, Eurypterid-bearing deposits from the late Silurian Appalachian basin are often interpreted as indicating Eurypterid undes live in close proximity to hypersaline conditions and likely were halotolerant. Rather, the disruptive nature of the hoppers in the Ellicott Creek Breccia, suggests that they formed within the sediment, not at the air-water interface. This implies that organic remains of the Eurypterids mayhave acted as nucleation points for developing displacive halite crystals. Halite saturation was achieved in the shallow subsurface via reflux and cooling of salina and sabkha hypersaline brines, displacing normal-marine pore fluids at the level of the Eurypterids in the buried sediments.
In diapir flanks, unconformity-bounded carbonate packages are associated with gravity-driven deposits are controlled by the ratio between the rates of sediment accumulation and rate of diapir rise. The Bakio Breccia Formation (Basque Country, Spain) corresponds to redeposited carbonate deposits laid down in response to the Bakio diapir growth during the Middle Albian. The breccias, calcirudites, calcarenites and marls, were deposited along the flanks of the diapir. This is a new model for carbonate-dominated halokinetic sequences. Diapir crest-fed carbonate sequences differ from their siliciclastic counterparts (depopods) as the sediment accumulation rate is controlled by carbonate platform growth on the topographic relief on top of the diapir, while the withdrawal sinks are starved of shallow-water sediment.
The Lower Mississippian (Tournaisian) Ballagan Formation in SE Scotland yields tetrapod fossils that mark the critical period when these animals first moved onto land. They lived on a coastal floodplain and marginal marine succession with palaeosols with thin evaporite beds, indicating a seasonally arid setting, much like parts of coastal Ghana today. Estimates of mean annual rainfall from palaeosol compositions are 1000–1500 mm per year. The high mean annual rainfall and variable soil alkalinities contrast markedly with dry periods that developed deep penetrating cracks and thin evaporite deposits. It is concluded that during the early Carboniferous, this region experienced a sharply contrasting seasonal climate and that the floodplain hosted a mosaic of closely juxtaposed but distinct habitats in which the tetrapods lived. The seasonal drying of the coastal lakes in these favored survival of species capable of movement over exposed land intervals.
In the massive Messinian salt sequence, the transparent layers ME1, ME2, ME3 and ME4 are composed of pure and uniform halite, while the other two layers — MC1 and MC2 are composed of clastic materials, mainly claystones. The total cumulative thickness of the clastic layers inside the Messinian sequence is 25–40 m. Meanwhile, the top-ME1 reflector is a 4–7 m thick single clastic layer, MC1 and MC2 are bundles of clastic layers interbedded in the halite. MC1 contains 3–4 clastic sub-layers with an average thickness of ~2 m, and MC2 contains even more clastic sub-layers than MC1 with an average thickness of ~1.5 m. Inside the Messinian evaporite sequence, shallower units are more deformed than deeper units. NNE–SSW folds and NW–SE thrust faults appear at the same time on the shallower internal reflectors (top-MC2, base and top-MC1), while only NW–SE folds can be observed on the TS. On a regional scale, the TS is generally horizontal while the other reflectors dip toward the NW. Unit ME4 is the only intra-unit that has a wedge shape thickening to the NW, while the other intra-units generally have uniform thickness.
Recent studies in greenstone belts indicate that asteroids 20 km to 70+ km in diameter were still striking the Earth as late as 3.2 Ga at rates significantly greater than the values estimated from lunar studies. Impacts caused heating of Earth’s atmosphere, ocean-surface boiling, and evaporation of tens of meters to perhaps 100 m of seawater. Rapid ocean evaporation resulted in abrupt sea-level drops, erosion of the exposed sea floor, and precipitation of distinctive layers of laminated silica and spherule beds representing marine siliceous sinter with an evaporite association. Pseudohexagonal shapes below a spherule bed suggest that they may represent nahcolite. The Spherule bed (sinter) is capped by a 15-cm-thick layer of micaceous laminated silica chips. Severe impact events as young and 3.2 Ga with significant vaporisation and associated lowering of sea level would have severely affected microbial communities, especially in shallow-water with photosynthetic microbes. And so, large impact events must have profoundly affected Archean crustal development, shallow marine environments, and biological evolution until 3.2 Ga, or even later.
ThIntegrated analysis of high-quality three-dimensional (3D) seismic, seabed geochemistry, and satellite-based surface slick data from the deep-water Kwanza Basin documents the widespread occurrence of past and present fluid flow associated with dewatering processes and hydrocarbon migration. Seismic scale fluid flow phenomena are defined by seep-related seafloor features including pockmarks, mud or asphalt volcanoes, gas hydrate pingoes, as well as shallow subsurface features such as palaeo-pockmarks, direct hydrocarbon indicators (DHIs), pipes and bottom-simulating reflections (BSRs). BSR-derived shallow geothermal gradients show elevated temperatures attributed to fluid advection along inclined stratigraphic carrier beds around salt structures in addition to elevated shallow thermal anomalies above highly conductive salt bodies. Seabed evidences of migrated thermogenic hydrocarbons and surface slicks are used to differentiate thermogenic hydrocarbon migration from fluid flow processes such as dewatering and biogenic gas migration. The analysis constrains the fluid plumbing system defined by the three-dimensional distribution of stratigraphic carriers and seal bypass systems through time. Detailed integration and iterative interpretation have confirmed the presence of mature source rock and effective migration pathways with significant implications for petroleum prospectivity in the post-salt interval. Integration of seismic, seabed geochemistry and satellite data represents a robust method to document and interpret fluid flow phenomena along continental margins, and highlights the importance of integrated fluid flow studies with regard to petroleum exploration, submarine geohazards, marine ecosystems and climate change.e Azag minibasin is a lozenge-shaped depocenter completely enclosed by tectonic boundaries interpreted as welds after former salt anticlines or salt walls. The exposed ca. 3000 m-thick fill is asymmetric; layers are tilted to the W defining a rollover geometry. Areally-restricted sedimentary discontinuities and wedges of growth strata near the basin margins indicate sedimentation contemporaneous with diapiric rise of a Triassic ductile layer. Facies evolution through the basin reflects local accommodation by salt withdrawal and regional events in the High Atlas rift. The early basin infill in the Sinemurian and Pliensbachian shows thickness variations indicative of low-amplitude halokinetic movements, with reduced exposed thicknesses compared to surrounding areas. The exposed Toarcian and Aalenian deposits are also reduced in thickness compared to areas outside the basin. Subsidence increased dramatically in the Bajocian-early Bathonian (?), the main phase of downbuilding, when over 2600 m of carbonates and shales accumulated at a rate > 0.5 mm/a in the depocentral area of the minibasin governed by W-directed salt expulsion. The stratigraphic units distinguished often show maximum thicknesses and deeper facies in the depocentral area, and rapidly change to shallower facies at the basin margins. The Bajocian carbonate facies assemblage of the minibasin include: reservoir facies as microbialite-coral reefs in the basin margins (formed during periods of strong diapir inflation and bathymetric relief), basin-expansive oolite bars (formed during episodes of subdued relief), and organic-rich, dark lime mudstones and shales that show source-rock characteristics.
Integrated analysis of high-quality three-dimensional (3D) seismic, seabed geochemistry, and satellite-based surface slick data from the deep-water Kwanza Basin documents the widespread occurrence of past and present fluid flow associated with dewatering processes and hydrocarbon migration. Seismic scale fluid flow phenomena are defined by seep-related seafloor features including pockmarks, mud or asphalt volcanoes, gas hydrate pingoes, as well as shallow subsurface features such as palaeo-pockmarks, direct hydrocarbon indicators (DHIs), pipes and bottom-simulating reflections (BSRs). BSR-derived shallow geothermal gradients show elevated temperatures attributed to fluid advection along inclined stratigraphic carrier beds around salt structures in addition to elevated shallow thermal anomalies above highly conductive salt bodies. Seabed evidences of migrated thermogenic hydrocarbons and surface slicks are used to differentiate thermogenic hydrocarbon migration from fluid flow processes such as dewatering and biogenic gas migration. The analysis constrains the fluid plumbing system defined by the three-dimensional distribution of stratigraphic carriers and seal bypass systems through time. Detailed integration and iterative interpretation have confirmed the presence of mature source rock and effective migration pathways with significant implications for petroleum prospectivity in the post-salt interval. Integration of seismic, seabed geochemistry and satellite data represents a robust method to document and interpret fluid flow phenomena along continental margins, and highlights the importance of integrated fluid flow studies with regard to petroleum exploration, submarine geohazards, marine ecosystems and climate change.
Whirlwinds, dry convective helical vortices, move large gypsum crystals in the Andes Mountains of northern Chile. The crystals are entrained from a saline pan surface, where they grew in shallow surface brines. They are transported as much as 5 km and deposited in large dune-like mounds. The dune gravel is cemented relatively quickly by gypsum cement precipitating from near-surface saline groundwater, resulting in gypsum breccia. This marks the first occurrence of gravel-sized grains moved efficiently in air by suspension, provides a new possible interpretation for some ancient breccias and conglomerates, and improves understanding of limits of extremity of Earth surface environments.
Halite study shakes up traditional view of Neoproterozoic O2 levels
Eurypterids: halotolerants or buried and brined?
Halokinetic sequences in platform carbonates: Middle Albian Bakio Breccias, Spain
Early tetrapods improved their walking skills in seasonally arid hypersaline settings
Combination of seismic and wireline reveals the internal
character of Messinian in the Levant Basin, Eastern Mediterranean
Geologic record of partial ocean evaporation triggered by giant asteroid impacts, 3.29–3.23 billion years ago
Structural and facies architecture of a diapir-related carbonate minibasin (lower and middle Jurassic, High Atlas, Morocco)
Subsurface fluid flow in the deep-water Kwanza Basin, offshore Angola (importance of halokinetic salt in fluid focusing)
Gypsum gravel devils in Chile: Movement of largest natural grains by wind?
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