Record of carbonate preservation and the Mid‐Brunhes climatic shift from a seamount top with low sedimentation rates in the Central Indian Basin

In the present investigation, an age model of carbonate‐rich cores from a seamount top in the Central Indian Basin (CIB) was constructed using both isotopic (²³⁰Th_excess, AMS ¹⁴C, oxygen isotopes) and biostratigraphic methods. The chronologies using the two methods are in good agreement, yielding a record of the late Middle Pleistocene to the Pleistocene–Holocene transition (550 to 11.5 ka). The first appearance datum (FAD) of the radiolarian Buccinosphaera invaginata (180 ka) and coccolith Emiliania huxleyi (268 ka) and the last appearance datum (LAD) of the radiolarian Stylatractus universus (425 ka) were used. A monsoon‐induced productivity increase was inferred from carbonate, organic carbon and δ¹³C records in response to the Mid‐Brunhes Climatic Shift (MBCS), consistent with an increased global productivity. While the coccolith diversity increased, a decrease in coccolith productivity was found during the MBCS. At nearly the same time period, earlier records from the equatorial Indian Ocean, western Indian Ocean and eastern Africa have shown an increased productivity in response to the influence of westerlies and increased monsoon. The influence of easterlies from Australia and the intensification of aridity are evidenced by increased kaolinite content and clay‐sized sediments in response to the MBCS. An increased abundance of Globorotalia menardii and other resistant species beginning from marine isotope stage (MIS) 11 and the proliferation of coccolith Gephyrocapsa spp. indicate increased dissolution, which is consistent with the widespread global carbonate dissolution during this period. The relatively high carbonate dissolution during the transition period of MIS 3/2 and glacial to interglacial periods (MIS 6, 7 and 8) may be due to the enhanced flow of corrosive Antarctic Bottom Water (AABW) into the CIB.     

Geochemistry and petrogenesis of radioactive Palaeoproterozoic granitoids of Kinwat crystalline inlier,Nanded and Yeotmal districts,Maharashtra

Kinwat crystalline inlier exposes Palaeoproterozoic granitoids belonging to the northern extensions of younger phase of Peninsular gneissic complex (PGC) within Deccan Trap country in Eastern Dharwar Craton (EDC) and bounded in south by a major NW-SE trending lineament (Kaddam fault). Geochemically, the Kinwat granitoids are similar to high-K, calc-alkaline to shoshonite magnesian granitoids and subdivided into two major groups, i.e. felsic group (pink and grey granites) and intermediate to felsic group (hybrid granitoids). The felsic group (∼67–74% SiO₂) shares many features with Neoarchaean to Palaeoproterozoic high potassic granites of PGC such as higher LILE and LREE content and marked depletion in Eu, P and HFSE, especially Nb, Ti, relative to LILE and LREE. The hybrid granitoids (∼58–67% SiO₂) have comparatively higher Ca, Mg and Na contents and slightly lower REE content than the granitoids of felsic group. Both, felsic and hybrid granitoids are metaluminous to weakly peraluminous and belong to highly fractionated I-type suite as evidenced by negative correlation of SiO₂ with MgO, FeO^t, CaO, Na₂O, Al₂O₃, whereas K₂O, Rb and Ba show sympathetic relationship with SiO₂. Moderate to strong fractionated REE patterns (Ce/Yb_N: ∼54–387) and strong negative Eu anomalies (Eu/Eu*: 0.13–0.41) are quite apparent in these granitoids. The geochemical characteristics together with mineralogical features such as presence of biotite±hornblende as the dominant ferromagnesian mineral phases point towards intracrustal magma source, i.e. derivation of magma by partial melting of probably tonalitic igneous protolith at moderate crustal levels for felsic granites, whereas hybrid granitoids appear to be products of juvenile mantle-crust interaction, in an active continental margin setting.     

Morphological Features of Co-Rich Manganese Deposits and Their Relation to Seabed Slopes

Abstract

The morphological features associated with Co-rich manganese deposits, the size variations of nodules, and the occurrence of different substrates have been analyzed, to evaluate the influence of various seabed slope angles on the distribution of these features. The coverage and size of the crusts depend on their surface morphology and seabed topography, resulting in cobble-type, lineated, or step-like outcrops. Small nodules (1–4 cm in diameter) dominate all seabed slopes, with a few locations having nodules ranging from 1 to 8 or 1 to 10 cm. Sediments invariably occur as substrates for nodules and as cover for crusts, their coverage being inversely proportional to that of the nodules and crust outcrops.

Steeper seafloor areas have large crust outcrops exposed with no or few nodules and sediments associated with them. The intermediate slopes have a combination of nodules, sediments, and crusts in various proportions, depending on topography and gradient. Large-scale nodule occurrences, followed by sediment fields and crust outcrops on seabed slopes of < 3°, 3–7°, and > 15°, respectively, represent typical morphological distribution zones of the Co-rich manganese deposits on a seamount in the central Pacific Ocean. A transition zone between nodule-dominated fields and large crust outcrops occurs for slopes from 7° to 15°. This detailed study on distribution of Co-rich deposits gives a better understanding for purposes of their exploitation.     

Parameter estimation and simulation of dependence of constant pressure batch dewatering on initial solids concentration

The problem of predicting dependence of constant pressure batch dewatering of particulate suspensions on feed solids concentration is considered. Scaling transformations which demonstrate that evolution in the cake consolidation stage of dewatering is governed by an underlying self-similar behavior are proposed. The self-similar master curve, which can be obtained using only one set of experimental dewatering data obtained with a feed suspension having solids concentration above the gel point, is employed for estimating dependence of key dewatering process parameters on feed solids concentration. Using the parameter estimates in a Darcy's law based dewatering model, it is shown that the complete evolution of dewatering for a desired feed solids concentration can be predicted with reasonable accuracy. The approach is simpler to implement in comparison to available pressure filtration models, which require several suspension characterization experiments.     

ANALYSIS OF THE GRAVITY EFFECT OF TWO-DIMENSIONAL TRAPEZOIDAL PRISMS USING FOURIER TRANSFORM*

The gravity effect of an infinite horizontal trapezoidal prism is derived and its Fourier spectrum is analyzed so as to yield information about four parameters of the causative structure, namely the depths to the upper and lower surfaces, width of the upper surface, and the inclination of the sides. In order to test the applicability of the method, synthetic data are constructed by digitizing the theoretical gravity effect. Subsequently, the corresponding Discrete Fourier Transform (DFT) is obtained. The parameters evaluated from the DFT are observed to be sufficiently close to the chosen values.     

Crustal trajectory of sapphirine-bearing granulites from Ganguvarpatti, South India: evidence for an isothermal decompression path

Abstract Ganguvarpatti is part of a Precambrian terrane characterized by granulite facies rocks, including charnockites, mafic granulites, sapphirine-bearing granulites, leptynites and gneisses. A sequence of reactions deduced from the multiphase reaction textures provide information on the metamorphic history of this area, as they formed in response to decompression during uplift. Geothermobarometry and constraints from reaction textures define a segment of a P–T path traversed by the granulites of Ganguvarpatti. Near-peak metamorphic conditions of c. 800°C and 8 kbar were succeeded by a symplectitic stage at a significantly lower pressure ( c. 700°C and 4.5 kbar), documenting a nearly isothermal decompression P–T path and rapid uplift ( c. 12 km) followed by cooling. The presence of many fluid inclusions of extremely low density in the charnockites is consistent with a nearly isothermal uplift path. Attainment of a maximum pressure of c. 8 kbar indicates c. 27 km depth of burial during metamorphism. This would imply a total crustal thickness of c. 65–70 km at 2.6–2.5 Ga. Such a profound crustal thickness and a clockwise decompressive P–T path is interpreted as a consequence of tectonic thickening of crust, accomplished by collision tectonics of the southern granulite terrane against the Dharwar craton along the Palghat–Cauvery shear zone via northward subduction.     

Concrete evidence & geographically weighted regression: A regional analysis of wealth and the land cover in Massachusetts

Several studies indicate that there is a positive relationship between green vegetation land cover and wealthy socio-economic conditions in urban areas. The purpose of this research is to test for and explore spatial variation in the relationship between socio-economic and green vegetation land cover across urban, suburban, and rural areas, using geographically weighted regression (GWR). The analysis was conducted at the census block group level for Massachusetts, using Census 2000 data and impervious surface data at 1-m resolution. To explore regional variations in the relationship, four scenarios were generated by regressing each of the following socio-economic variables – median household income, percentage of poverty, percentage of minority population, and median home value – against two environmental variables – percent of impervious surface and population density. GWR results show that there is a considerable spatial variation in the character and the strength of the relationship for each model. There are two main conclusions in this study. First, the impervious surface is generally a strong predictor of the level of wealth as measured by four variables included in the analysis, at the scale of census block group; however, the strength of the relationship varies geographically. Second, GWR, not ordinary least squares technique, should be used for regional scale spatial analysis because it is able to account for local effects and shows geographical variation in the strength of the relationship.