Seasonal extreme rainfall variability over India and its association with surface air temperature

Theoretical and Applied Climatology - Spatial variability in catchment processes is crucial for hydrologic and water resources planning and management. The spatial density of ground-based rain...     

Effects of beta-naphthoflavone on hepatic biotransformation and glutathione biosynthesis in largemouth bass (Micropterus salmoides)

We are investigating the effects of in vivo exposure of prototypical enzyme inducing agents on hepatic biotransformation enzyme expression in largemouth bass (Micropterus salmoides), a predatory game fish found throughout the United States and Canada. The current study targeted those genes involved in biotransformation and oxidative stress that may be regulated by Ah-receptor-dependent pathways. Exposure of bass to beta-naphthoflavone (beta-NF, 66 mg/kg, i.p.) elicited a 7-9-fold increase in hepatic microsomal cytochrome P4501A-dependent ethoxyresorufin O-deethylase (EROD) activities, but did not affect cytosolic GST catalytic activities toward 1-chloro-2,4-dinitrobenzene (CDNB) or 5-androstene-3,17-dione (ADI). Glutathione S-transferase A (GST-A) mRNA expression exhibited a transient, but non-significant increase following exposure to beta-NF, and generally tracked the minimal changes observed in GST-CDNB activities. Expression of the mRNA encoding glutamate-cysteine ligase catalytic subunit (GCLC), the rate-limiting enzyme in glutathione (GSH) biosynthesis, was increased 1.7-fold by beta-NF. Changes in GCLC mRNA expression were paralleled by increases in intracellular GSH. In summary, largemouth bass hepatic CYP1A-dependent and GSH biosynthetic pathways, and to a lesser extent GST, are responsive to exposure to beta-NF.     

Mixed terrigenous—Carbonate sedimentation in the Hispaniola—Caicos turbidite basin

Sedimentation in the 9500 km², 4100 m deep Hispaniòla—Caicos Basin is dominated by turbidity currents. Carbonate turbidites originate from the Bahama Islands, Great Inagua and Caicos at the north end of the basin. Mixed carbonate—non-carbonate flows come from Hispaniola and perhaps Cuba. Most flows originate on insular slopes rather than in shallow water. The relatively low CaCO₃ content of hemipelagic sequences throughout the entire basin reveals that the influence of non-carbonate Hispaniola—Cuba sources is widespread.The basin was sampled with closely spaced piston cores. Sand-layer isopach and frequency maps reveal four or five major basin entry points for turbidity currents. Flow size is proportional to the size of source areas. Average volumes of flows originating from Hispaniola—Cuba, the largest source, are 10⁹ m³. This compares to an average flow volume of 10⁶ m³ for flows derived from the smallest source area, the Southeastern Caicos Bank. Measures of turbidity-current activity, such as thickness and frequency, change in a regular fashion away from each entry point. Average lutite thickness (combining hemipelagic and turbiditic lutite) are greatest near the basin entry points. On the abyssal plain occupying the south half of the basin, Bouma turbidite sedimentary structure sequences tend to be complete. However, on the Caicos Fan, the sedimentary structure sequences in turbidites are characterized by missing or repeated units. Six radiocarbon dates of two widespread presumed pelagic units in the basin yielded younger dates in stratigraphically older positions. The reversed dates are assumed to reflect storm erosion of older sediment on adjacent insular shelves.Consideration of a north—south reflection seismic profile over the basin indicates that the present sediment regimen has pertained through much of the Neogene. The coherence, convergence and termination of reflections in the seismic section are consistent with and tend to confirm conclusions based on the core study regarding the greater extent and volume of sediment deposits derived from the Hispaniola source area.     

Pediment response to drainage basin evolution in south-central Arizona

The Sonoran Desert portion of the Basin and Range physiographic province contains a number of streams that now flow across once-closed basins. We explore here the research questions of if and how granitic rock pediments respond to the transition from rimming endorheic basins to bordering through-flowing streams. Granitic rock pediments of the northern Usery and eastern McDowell Mountains once graded to the closed Miocene–Pliocene Pemberton basin that occupied the present-day location of the confluence of the Salt and Verde Rivers. The process of lake overflow, which integrated these rivers, first aggraded fill terraces that, in turn, caused aggradation of a mantle of transported grus on bedrock pediments. Subsequent episodic incision of the Salt and Verde rivers lowered the base level; this led to the development of erosional features such as rolling topography of a degrading pediment mantle; exposure of the former piedmont angle and its associated zones of enhanced bedrock decay and regolith carbonate; and exposure of spheroidally weathered bedrock and emerging tors, some of which experienced 20^th century erosion. The granitic pediments of the former Pemberton Basin, which now transport grus to the Salt and Verde rivers, have actively adjusted to aggradational and degradational events associated with drainage integration and do not appear to be inherited from an ancient wet climatic interval.     

Mineral inclusions in fibrous diamonds: constraints on cratonic mantle refertilization and diamond formation

We analyzed mineral microinclusions in fibrous diamonds from the Wawa metaconglomerate (Superior craton) and Diavik kimberlites (Slave craton) and compared them with published compositions of large mineral inclusions in non-fibrous diamonds from these localities. The comparison, together with similar datasets available for Ekati and Koffiefontein kimberlites, suggest a general pattern of metasomatic alteration imposed on the ambient mantle by formation of fibrous diamond. Calcium and Fe enrichment of peridotitic garnet and pyroxenes and Fe enrichment of olivine associated with fibrous diamond-forming fluids contributes to refertilization of the cratonic mantle. Saline—carbonatitic—silicic fluid trapped by fibrous diamonds may represent one of the elusive agents of mantle refertilization. Calcium enrichment of peridotitic garnet and pyroxenes is expected in local mantle segments during fibrous diamond production, as Ca in the carbonatitic fluids is deposited into the surrounding mantle when oxidized carbon is reduced to diamond. Harzburgitic garnet evolves towards Ca-rich compositions even when it interacts with Ca-poor saline fluids. An unusual trend of Mg enrichment to Fo_95–98 is observed in some olivine inclusions in Wawa fibrous diamonds. The trend may result from the carbonatitic composition of the fluid that promotes crystallization of magnesian olivine and preferentially oxidizes the fayalite component. We propose a generic model of fibrous and non-fibrous diamond formation from carbonatitic fluids that explains enrichment of the mantle in mafic magmaphile and incompatible elements and accounts for locally metasomatized compositions of diamond inclusions.     

The age of orogenesis in the Nambucca Slate Belt: A K‐Ar study of low‐grade regional metamorphic rocks

K‐Ar ages of biotite and hornblende from undeformed granodiorite plutons and of slaty and phyllitic rocks, ranging from prehnite‐pumpellyite metagreywacke to greenschist fades, have been determined in an attempt to define the age of orogenesis in the eastern part of the Nambucca Slate Belt. The plutons have K‐Ar ages of 226–227 m.y. (biotite) and 228–231 m.y. (hornblende) that provide a younger age limit for deformation. The lower grade metamorphic rocks yield a range of ages including some comparable with the depositional age of the rocks as indicated by fossils. Rocks of pumpellyite‐actinolite and greenschist facies give a more coherent group of ages which suggest orogenesis at about 250–255 m.y. Specimens of these latter rocks that have been affected by a later structural episode than that during which slaty cleavage formed, yield slightly older ages, which may result from the inclusion of minor amounts of environmental excess ⁴⁰Ar.

Support for the 250–255 m.y. age comes from previously determined radiometric ages from the western part of the Slate Belt, although the presence of granitic bodies perhaps as old as 289 m.y., some closely associated with high‐grade regional metamorphic rocks, may indicate the presence of additional earlier orogenic movements in this region.     

Post-peak,fluid-mediated modification of granulite facies zircon and monazite in the Trivandrum Block,southern India

The quarry at Kottavattom in the Trivandrum Block of southern India contains spectacular examples of fluid-assisted alteration of high-grade metamorphic rocks. Garnet-biotite gneiss has undergone a change in mineral assemblage to form submetre scale orthopyroxene-bearing patches, later retrogressed to form an amphibole-bearing lithology. These patches, often referred to as arrested or incipient charnockite, crosscut the original metamorphic foliation and are typically attributed to passage of a low aH₂O fluid through the rock. Whilst this conversion is recognised as a late stage process, little detailed chronological work exists to link it temporally to metamorphism in the region. Zircon and monazite analysed from Kottavattom not only record metamorphism in the Trivandrum Block but also show internal, lobate textures crosscutting the original zoning, consistent with fluid-aided coupled dissolution-reprecipitation during formation of the orthopyroxene-bearing patches. High-grade metamorphism at the quarry occurred between the formation of metamorphic monazite at ~585 Ma and the growth of metamorphic zircon at ~523 Ma. The fluid-assisted alteration of the garnet-biotite gneiss is poorly recorded by altered zircon with only minimal resetting of the U–Pb system, whereas monazite has in some cases undergone complete U–Pb resetting and records an age for fluid infiltration at ~495 Ma. The fluid event therefore places the formation of the altered patches at least 25 Myr after the zircon crystallisation in the garnet-biotite gneiss. The most likely fluid composition causing the modification and U–Pb resetting of zircon and monazite is locally derived hypersaline brine.