Hydrous olivine alteration on Mars and Earth

Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars.     

The first dinosaur tracksite from Xinjiang, NW China （Middle Jurassic Sanjianfang Formation, Turpan Basin） a preliminary report

A new dinosaur tracksite was discovered in a steeply inclined sandstone layer of the Middle Jurassic Sanjianfang Formation in the Shanshan area of the Turpan Basin. The site is the first record of dinosaur footprints from Xinjiang Province in northwestern China. More than 150 tridactyl theropod dinosaur footprints are preserved as positive hyporeliefs on the lower bedding plane of a fine-grained sandstone body. Most of the footprints are isolated and appear to be randomly distributed. Some show well defined phalangeal pads, heels and rarely indistinct impressions of the distal part of the metatarsus. Two distinct morphotypes are present: a larger type with relatively broad pads shows similarities to Changpeipus and Megalosauripus, and a slightly smaller, slender and gracile type which is similar to Grallator, Eubrontes and Anchisauripus. In both morphotypes, digit III is the longest with a length between 11.4 and 33.6 cm. A single imprint shows prominent scratches, probably formed during slipping of the track maker.     

Efficiency of different mesh sizes for isolating fossil chironomids for stable isotope and radiocarbon analyses

We examined the effects of sieving with different mesh sizes on the efficiency of processing fossil chironomids from lake sediments for isotope analyses. Results obtained for three different sediments indicate that each of the studied sieve fractions (100–150, 150–200, 200–250, 250–300, >300 μm) contain a similar proportion of the overall mass of chironomid fossils in a sample. However, the sorting time needed to separate chironomids from other sieve residue is disproportionately large for smaller mesh sizes. Employing sieves with a 200-μm rather than the 100-μm mesh commonly used for standard palaeoecological analyses of fossil chironomids decreased processing time for a given mass of fossils by 30–58% in our study. For optimizing the efficiency of chironomid sample processing for stable isotope and radiocarbon analysis we therefore recommend a 200-μm mesh size sieve, although the sorting of all >100-μm fractions may be necessary in sediments with low chironomid abundances. Excluding certain small taxa from isotope analysis, may structurally bias isotope values of samples. Therefore, further studies on taxon-specific isotope analysis are required to quantify these effects.     

The metamorphic geology of the Windmill Islands,Antarctica: A preliminary account

Rocks of the Windmill Islands, Antarctica (Lat. 66°S, Long. 110°E) consist of a layered sequence of schists, gneisses, and migmatites (the Windmill Metamorphics) intruded by a charnockite (the Ardery Charnockite) and a porphyritic granite (the Ford Granite), and cut by two swarms of easterly‐trending dolerite dykes.

The rocks have undergone four deformations. The first two produced tight isoclinal folds, the third developed broader less appressed concentric folds, and the last deformation produced gentle warps which plunge steeply southwards.

The metamorphic grade of the Windmill Metamorphics ranges from (i) upper amphibolite facies (sillimanite‐biotite‐orthoclase) in the north, through (ii) biotite‐cordierite‐almandine granulite to (iii) hornblende‐orthopyroxene‐granulite in the south. The boundary between (i) and (ii) above is marked by the incoming ortho‐pyroxene and also the outgoing of sphene, and that between (ii) and (iii) by the outgoing of cordierite. Other metamorphic variations, apparent in the field are (i), the southward colour change of biotite (sepia—>red‐brown) and hornblende (blue‐green—>brown‐green) and (ii) the greater abundance of migmatites and pegmatites in the north of the area.

Major‐element rock chemistry suggests that the pre‐metamorphic nature of the schists and gneisses probably consisted of acid and basic volcanics interbedded with sediments ranging from greywacke‐type sandstones to shales. Partial melting of these rocks is thought to have produced some of the more acidic gneisses of the area.

The abundances of the elements K, Rb, and Th are lower than those of terrains of similar grade elsewhere. This is regarded as reflecting original rock composition. The ratios K/Rb, Th/K, and K/(Rb/Sr), however, are comparable with those from similar terrains elsewhere where K, Rb, and Th enrichment by crustal fractionation has been suggested. This suggests that the Windmill Metamorphics were not derived by retrogression from upper granulite‐facies rocks.     

COCORP: new perspectives on the deep crust

Summary. Relict sutures from colliding continents, regions characterized by a "young" Mono, layering and faulting throughout the crust, mid-crustal magma traps, and seismic "bright spots" which suggest deep crustal fluids are among recent COCORP findings. In addition, new studies of signal penetration, noise mitigation, recording geometry, and coherency filtering have yielded better understanding of, and substantial improvements in, data quality. Amplitude anomalies, or "bright spots", in the Basin and Range may be due to magma at mid-crustal levels; in one case, a normal fault appears to link the deep magma with young surface volcanics. Another bright spot. 15 km deep in southeastern Georgia, has a flat geometry that suggests a gas/liquid interface, perhaps within fluids underthrust along an Appalachian suture. The Mono continues to appear relatively undisturbed in many regions of past deformation, suggesting that its formation post-dates these major tectonic episodes. The diversity of reflection patterns from the U.S. Cordillera casts further doubt on the generality of the common model of a reflective, layered lower crust underlying a transparent upper crust.     

Global change revealed by palaeolimnological records from remote lakes: a review

Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.     

Fault‐controlled fluid flow inferred from hydrothermal vents imaged in 3D seismic reflection data,offshore NW Australia

Fluid migration pathways in the subsurface are heavily influenced by pre‐existing faults. Although studies of active fluid‐escape structures can provide insights into the relationships between faults and fluid flow, they cannot fully constrain the geometry of and controls on the contemporaneous subsurface fluid flow pathways. We use 3D seismic reflection data from offshore NW Australia to map 121 ancient hydrothermal vents, likely related to magmatic activity, and a normal fault array considered to form fluid pathways. The buried vents consist of craters up to 264 m deep, which host a mound of disaggregated sedimentary material up to 518 m thick. There is a correlation between vent alignment and underlying fault traces. Seismic‐stratigraphic observations and fault kinematic analyses reveal that the vents were emplaced on an intra‐Tithonian seabed in response to the explosive release of fluids hosted within the fault array. We speculate that during the Late Jurassic the convex‐upwards morphology of the upper tip‐lines of individual faults acted to channelize ascending fluids and control where fluid expulsion and vent formation occurred. This contribution highlights the usefulness of 3D seismic reflection data to constraining normal fault‐controlled subsurface fluid flow.     

Geoelectrical inversion and evaluation of lithology based on optimized Adaptive Neuro Fuzzy Inference System (ANFIS)

Soft computing tools play a vital role in fixing certain non-linear problems related to the earth. More specifically, digging out the mysteries of subsurface of the earth, the nonlinearity can be converging to assemble an approximate solution which resembles the real characteristics of the earth. Adaptive Neuro Fuzzy Inference System (ANFIS) tool is one of the best soft computing tools to estimate the complex data analysis. ANFIS was applied to estimate the subsurface parameters of earth using the Vertical Electrical Sounding (VES) data. Classifying the lithology based on the resistivity values by ANFIS is employed here in this paper. As the resistivity of each formation varies in range of values, ANFIS tool thus approximates the subsurface features based on effective training. In this study, ANFIS performance was checked with training data, and successively it has been tested with the field data. Optimized ANFIS algorithm provides the necessary tool for predicting the non-linear subsurface features. The best training performance of this soft computing tool efficiently predicts the subsurface lithology. Also the interpreted results show the true resistivity and thickness of the subsurface layers of the earth. The proposed technique was represented in Graphical User Interface (GUI), and the lithological variables are predicted in texture format and linguistic variables.