The interaction of tectonics,climate and eustasy in controlling dolomitization: A case study of Cenomanian–Turonian,shallow marine carbonates of the Iberian Basin

During the Cretaceous, high global sea-level and low latitudinal temperature variations led to the growth of epeiric carbonate platforms. Platform-scale dolomitization of these platforms is not common, reflecting the low Mg/Ca ratio of seawater and a humid climate. This study describes the processes governing pervasive dolomitization of a land-attached carbonate platform within the Iberian Basin. Dolomite is planar to sub-planar with a geochemical signature consistent with dolomitization from penesaline seawater. Dolomitization was most pervasive during a 1 Myr period in the middle Cenomanian, by repeated reflux of seawater from brine pools formed on the top of a southward-prograding carbonate platform. Tilting and structural reorganization in the Upper Cenomanian led to a reversal in polarity of the platform, and dolomitization was restarted by the northward reflux of seawater. Rising relative sea-level and oceanic acidification led to back-stepping of the platform such that the supply of dolomitizing fluids was cut off. In the Lower Turonian, pervasively dolomitized rudist rudstone facies in the south of the study area indicate that dolomitization restarted, either penecontemporaneously or later, from highly evaporated Campanian–Maastrichtian seawater. A systematic increase in dolomite crystal size up-section ties broadly, but not entirely, to stratigraphy. It is possible that these textural differences reflect changes in fluid chemistry, limestone permeability or precursor rock texture. However, the lack of stratigraphic conformance, and the preservation of the earliest-formed dolomite only in the oldest sediments, could indicate a progressive recrystallization of early-formed dolomite through repeated reflux of brines. As such, the succession appears to preserve a fossilized record of dolomite recrystallization through time during the Cenomanian–Turonian. The results of this study therefore provide a record of the progressive dolomitization of a carbonate platform and demonstrate the important interplay of climate and basin-scale tectonics on dolomite distribution and crystallinity.     

Radioastronomical observations of comets IRAS-Araki-Alcock (1983d) and Sugano-Saigusa-Fujikawa (1983e)

Detections and upper limits to the continuum emission (1 ≤ λ ≤6 cm) and spectral line emission (OH, CO, CS, HCN, HCO⁺, CN, CH₃CN, CH₃C₂H, NH₃, H₂O, HC₃N, CH₃CH₂CN) are reported from radio observations of Comets 1983d and 1983e. Comparison is made with observations of CN at optical wavelengths. These results may be useful in planning future cometary observations.     

Palynofacies,organic geochemistry and depositional environment of the Tartan Formation (Late Paleocene), a potential source rock in the Great South Basin,New Zealand

Detailed palynofacies analysis of sidewall core samples taken from below, within and above the Tartan Formation (Thanetian, Late Paleocene, 58.7–55.8 Ma), a potential source rock in the epeiric Great South Basin, shows that the formation is characterised by very high percentages of degraded brown phytoclasts, rare marine algae and amorphous organic matter and thereby represents a mix of terrestrial and marine kerogen. The results indicate that the formation was deposited in a marginally marine (hyposaline), proximal environment under bottom conditions that varied from anoxic to oxic along a nearshore–offshore transect. Samples from the upper part of the underlying Wickliffe Formation indicate deposition in a marginal to normal marine, proximal environment under anoxic to oxic bottom environments. The lower part of the overlying Laing Formation was deposited in an open marine, relatively distal setting under anoxic to oxic bottom environments.     

The Atlantic ITCZ bias in CMIP5 models

Climate Dynamics - Precipitation over the tropical Atlantic in 24 atmospheric models is analyzed using an object-based approach, which clusters rainy areas in the models as precipitation objects...     

Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro‐geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO₂ and CH₄) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ²H and δ¹⁸O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface active layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ²H vs δ¹⁸O). Freeze‐out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze‐out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. This research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process‐based fine‐scale and intermediate‐scale hydrologic models. Copyright © 2016 John Wiley & Sons, Ltd.     

Generation of an optimal target list for the exoplanet characterisation observatory (EChO)

The Exoplanet Characterisation Observatory (EChO) has been studied as a space mission concept by the European Space Agency in the context of the M3 selection process. Through direct measurement of the atmospheric chemical composition of hundreds of exoplanets, EChO would address fundamental questions such as: What are exoplanets made of? How do planets form and evolve? What is the origin of exoplanet diversity? More specifically, EChO is a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planetary sample within its four to six year mission lifetime. In this paper we use the end-to-end instrument simulator EChOSim to model the currently discovered targets, to gauge which targets are observable and assess the EChO performances obtainable for each observing tier and time. We show that EChO would be capable of observing over 170 relativity diverse planets if it were launched today, and the wealth of optimal targets for EChO expected to be discovered in the next 10 years by space and ground-based facilities is simply overwhelming. In addition, we build on previous molecular detectability studies to show what molecules and abundances will be detectable by EChO for a selection of real targets with various molecular compositions and abundances. EChO’s unique contribution to exoplanetary science will be in identifying the main constituents of hundreds of exoplanets in various mass/temperature regimes, meaning that we will be looking no longer at individual cases but at populations. Such a universal view is critical if we truly want to understand the processes of planet formation and evolution in various environments. In this paper we present a selection of key results. The full results are available in Online Resource 1.     

The regional significance of Cretaceous magmatism and metamorphism in Fiordland, New Zealand, from U–Pb zircon geochronology

The western Fiordland Orthogneiss (WFO) is an extensive composite metagabbroic to dioritic arc batholith that was emplaced at c. 20–25 km crustal depth into Palaeozoic and Mesozoic gneiss during collision and accretion of the arc with the Mesozoic Pacific Gondwana margin. Sensitive high‐resolution ion microprobe U–Pb zircon data from central and northern Fiordland indicate that WFO plutons were emplaced throughout the early Cretaceous (123.6 ± 3.0, 121.8 ± 1.7, 120.0 ± 2.6 and 115.6 ± 2.4 Ma). Emplacement of the WFO synchronous with regional deformation and collisional‐style orogenesis is illustrated by (i) coeval ages of a post‐D1 dyke (123.6 ± 3.0 Ma) and its host pluton (121.8 ± 1.7 Ma) at Mt Daniel and (ii) coeval ages of pluton emplacement and metamorphism/deformation of proximal paragneiss in George and Doubtful Sounds. The coincidence emplacement and metamorphic ages indicate that the WFO was regionally significant as a heat source for amphibolite to granulite facies metamorphism. The age spectra of detrital zircon populations were characterized for four paragneiss samples. A paragneiss from Doubtful Sound shows a similar age spectrum to other central Fiordland and Westland paragneiss and SE Australian Ordovician sedimentary rocks, with age peaks at 600–500 and 1100–900 Ma, a smaller peak at c. 1400 Ma, and a minor Archean component. Similarly, one sample of the George Sound paragneiss has a significant Palaeozoic to Archean age spectrum, however zircon populations from the George Sound paragneiss are dominated by Permo‐Triassic components and thus are markedly different from any of those previously studied in Fiordland.     

Geochronology and geochemistry of high‐pressure granulites of the Arthur River Complex,Fiordland, New Zealand: Cretaceous magmatism and metamorphism on the palaeo‐Pacific Margin

The Arthur River Complex is a suite of gabbroic to dioritic orthogneisses in northern Fiordland, New Zealand. The Arthur River Complex separates rocks of the Median Tectonic Zone, a Mesozoic island arc complex, from Palaeozoic rocks of the palaeo‐Pacific Gondwana margin, and is itself intruded by the Western Fiordland Orthogneiss. New SHRIMP U/Pb single zircon data are presented for magmatic, metamorphic and deformation events in the Arthur River Complex and adjacent rocks from northern Fiordland. The Arthur River Complex orthogneisses and dykes are dominated by magmatic zircon dated at 136–129 Ma. A dioritic orthogneiss that occurs along the eastern margin of the Complex is dated at 154.4 ± 3.6 Ma and predates adjacent plutons of the Median Tectonic Zone. Rims on zircon cores from this sample record a thermal event at c. 120 Ma, attributed to the emplacement of the Western Fiordland Orthogneiss. Migmatitic Palaeozoic orthogneiss from the Arthur River Complex (346 ± 6 Ma) is interpreted as deformed wall rock. Very fine rims (5–20 µm) also indicate a metamorphic age of c. 120–110 Ma. A post‐tectonic pegmatite (81.8 ± 1.8 Ma) may be related to phases of crustal extension associated with the opening of the Tasman Sea. The Arthur River Complex is interpreted as a batholith, emplaced at mid‐crustal levels and then buried to deep crustal levels due to convergence of the Median Tectonic Zone arc and the continental margin.