Rock salt mass in the Paleoproterozoic sequence of the Onega trough in Karelia (from the Onega parametric well data)

A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb—Pb method.     

The Karoo Basin of South Africa: type basin for the coal-bearing deposits of southern Africa

The coal-bearing sediments and coal seams of the Karoo Basin, Southern Africa are described and discussed. The Karoo Basin is bounded on its southern margin by the Cape Fold Belt, onlaps onto the Kaapvaal Craton in the north and is classified as a foreland basin. Coal seams are present within the Early Permian Vryheid Formation and the Triassic Molteno Formation.The peats of the Vryheid Formation accumulated within swamps in a cool temperate climatic regime. Lower and upper delta plain, back-barrier and fluvial environments were associated with peat formation. Thick, laterally extensive coal seams have preferentially accumulated in fluvial environments. The coals are in general inertinite-rich and high in ash. However, increasing vitrinite and decreasing ash contents within seams occur from west to east across the coalfields. The Triassic Molteno coal seams accumulated with aerially restricted swamps in fluvial environments. These Molteno coals are thin, laterally impersistent, vitrinite-rich and shaly, and formed under a warm temperate climatic regime.Palaeoclimate, depositional systems, differential subsidence and basin tectonics influence to varying degrees, the maceral content, thickness and lateral extent of coal seams. However, the geographic position of peat-forming swamps within a foreland basin, coupled with basin tectonics and differential subsidence are envisaged as the primary controls on coal parameters. The Permian coals are situated in proximal positions on the passive margin of the foreland basin. Here, subsidence was limited which enhanced oxidation of organic matter and hence the formation of inertinitic coals. The coals in this tectonic setting are thick and laterally extensive. The Triassci coals are situated within the tectonically active foreland basin margin. Rapid subsidence and sedimentation rates occurred during peat formation which resulted in the preservation of thin, laterally impersistent, high ash, vitrinite-rich, shaly coals.     

Fluid-pressure variations and fault creep in central California

Observations of the change of water level in wells near the San Andreas fault in centra California indicate that there are pore-pressure changes associated with the process of fault creep. The sense of water-level and pore-pressure changes may indicate the direction of creep propagation.     

Wollastonite at Nuliyam,Kerala, southern India: a reassessment of CO2-infiltration and charnockite formation at a classic locality

The occurrence of a charnockitised felsic gneiss adjacent to a marble/calc-silicate horizon at Nuliyam, southern India, has been cited in recent literature as a classic example of the dehydration of crustal rocks resulting from the advective infiltration of CO₂-rich fluids generated from a local carbonate source. Petrographic study of the Nuliyam calc-silicate, however, reveals it to consist of abundant wollastonite and scapolite and contain locally discordant veins rich in wollastonite. At the pressure—temperature conditions proposed for charnockite formation in recent studies, 5 kbar and 725°C, this wollastonite-bearing mineral assemblage was stable in the presence of a fluid phase only if X _CO2 was near 0.25 and could not have coexisted with the fluid causing biotite breakdown and charnockite development in adjacent rocks (X _CO2>0.85). The stable coexistence of wollastonite and scapolite prohibits the calc-silicate from being a source for fluid driving charnockitisation at the required P-T conditions. Textural observations such as the limited replacement of wollastonite by calcite+quartz symplectites and mosaics, are consistent with late fluid infiltration into the calc-silicate. The extensive isotopic, chemical and mineral abundance data of Jackson and Santosh (1992) are re-interpreted and integrated with these observations to develop a model involving the infiltration of an externally derived CO₂-rich fluid during high-temperature decompression. Increased charnockite development next to the calc-silicate has arisen because the calc-silicate acted as a relatively unreactive and impermeable barrier to fluid transport and caused fluid ponding beneath antiformal closures. The Nuliyam charnockite/calc-silicate locality is an example of a structural trap in a metamorphic setting rather than a site where charnockite formation can be attributed to local fluid sources.     

Rock warming and drying under simulated intertidal conditions,part II: weathering and biological influences on evaporative cooling and near‐surface micro‐climatic conditions as an example of biogeomorphic ecosystem engineering

The way in which rocks and engineering materials heat‐up and dry‐out in the intertidal zone is of relevance to both weathering and ecology. These behaviours can be measured in the laboratory under controlled conditions designed to replicate those occurring in the field. Previous studies have demonstrated differences in thermal behaviours between rock types and through time as a result of soiling in terrestrial environments, but the influence of weathering and colonization on rock behaviours in the intertidal zone has not been previously assessed. We measured the warming and drying of blocks of rock (limestone and granite) and marine concrete during ‘low‐tide’ events simulated in the laboratory, before and after a period of exposure (eight months) on rock platforms in Cornwall, UK. As well as differences between the material types, temperatures of control (unexposed) and field‐exposed blocks differed in the order of 1 to 2 °C. Drying behaviours were also different after field exposure. Differences during the first few hours of exposure to air and heat were attributed to discolouration and albedo effects. Over longer periods of time, changes in the availability of near‐surface pore water as a result of micro‐scale bioerosion of limestone and the development of bio‐chemical crusts on marine concrete [observed using scanning electron microscopy (SEM)] are suggested as mechanisms enhancing and reducing, respectively, the efficiency of evaporative cooling. The retention of moisture by epilithic biofilms may also influence thermal and drying behaviours of granite. These observations represent one of the first examples of cross‐scalar biogeomorphic linkages in the intertidal zone. The significance of the results for the subsequent efficiency of weathering, and near‐surface micro‐climatic conditions experienced by colonizing organisms is discussed. The involvement of microorganisms in the creation of more (or less) ecologically stressful conditions through the alteration of substratum geomorphic properties and behaviours is suggested as an example of ‘biogeomorphic ecosystem engineering’. Copyright © 2011 John Wiley & Sons, Ltd.