Abstract The hydrological budget of the three major Asian rivers, namely the Indus, the Ganga and the Brahmaputra, is controlled by the Indian monsoon and Westerlies but their contribution in these basins are highly variable. Widely varying average annual precipitation has been reported within these basins. A poor network of in situ rain gauges, particularly in mountainous regions, inaccessible terrain, high variations in altitude and the significantly large size of basins forces adaption of satellite-based average annual precipitation. We investigate precipitation patterns for these three basins by using satellite-based Tropical Rainfall Measuring Mission (TRMM-3B42) data and compare and validate it with Asian Precipitation Highly Resolved Data Integration Towards Evaluation (APHRODITE) and India Meteorological Department (IMD) interpolated gridded precipitation data. The entire basins as well as basinal areas within the geographic limits of India have been considered. Our study shows that the precipitation broadly follows an east–west and north–south gradient control. The easternmost Brahmaputra Basin has the highest amount of precipitation followed by the Ganga Basin, and the westernmost Indus Basin has the least precipitation; precipitation is highest on the higher elevations than compared to lower elevations of the basins. A seasonal- and elevation-based approach is adapted to estimate snow precipitation and is discussed in terms of overall precipitation.

A petrographic and geochemical comparison of suevites from the LB-07A and LB-08A cores recovered during 2004 by the International Continental Scientific Drilling Program with suevites from outside of the crater rim of the Bosumtwi impact structure indicates contrasting mechanisms of formation for these respective impact breccias. The within-crater suevites form only a small part of the lithic impact breccia–dominated impactite crater fill, in contrast to the impactites from outside of the crater, which consist solely of suevite. The clasts of suevites from within the crater display relatively low levels of shock (for most material <45 GPa). The numbers of shocked quartz grains, as well as fragments of diaplectic glass of quartz and feldspar in suevites decrease with depth through the LB-07A core (maximum three sets of planar deformation features [PDFs]). In contrast, the out-of-crater suevites sampled north and south of the crater contain up to four PDF sets in quartz clasts, ballen cristobalite, and higher proportions of diaplectic glass than the within-crater suevites. In addition, the suevites from outside of the crater contain significantly more melt particles (18–37 vol%) than the within-crater suevites (<5 vol%). Melt fragment sizes in suevites from outside the crater are much larger than those from suevites within the crater (maximum 40 cm versus 1 cm). The currently known distribution of impactites outside of the crater would be consistent with a low-angle impact from the east. We propose that the within-crater suevites and polymict lithic breccias were emplaced either via slumping off the crater walls or lateral movement of some melted and much displaced target rock within the crater. Limited admixture of fallback material from the ejecta plume is evident in the uppermost impactite deposit encountered in core LB-05B. In contrast, the out-of-crater suevites formed by fallout from a laterally differentiated ejecta plume, which resulted in different clast populations to the north and south of the crater.

The study of α-quartz and α-cristobalite ballen in rocks from 16 impact structures (Bosumtwi, Chesapeake Bay, Chicxulub, Dellen, El'gygytgyn, Jänisjärvi, Lappajärvi, Logoisk, Mien, Popigai, Puchezh-Katunki, Ries, Rochechouart, Sääksjärvi, Ternovka, and Wanapitei) shows that ballen silica occurs mainly in impact melt rock and also in suevite, and more rarely in other types of impactites. Ballen α-cristobalite by itself was observed only in samples from the youngest craters studied here (at Bosumtwi and El'gygytgyn), but it occurs in association with α-quartz ballen in impactites from structures with intermediate ages (from ca. 35 to 120 Ma); thus, our observations suggest that α-cristobalite ballen are back-transformed to α-quartz with time. Transmission electron microscope observations show that α-cristobalite and α-quartz ballen have similar microtextures and are formed of several tiny angular crystals with sizes up to ~6 μm. The observation of toasted α-quartz ballen, notably at the Popigai impact structure, further supports the notion that toasting is due to vesicle formation after pressure release, at high post-shock temperatures, and, thus, represents the beginning of quartz breakdown due to heating. Our investigation increases the number of impact structures at which ballen silica has been found to 35.