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Abstract

The Indian (southwest) summer monsoon is one of the most intense climatic phenomena on Earth. Its long-term development has been linked to the growth of high topography in South and Central Asia. The Indian continental margin, adjoining the Arabian Sea, offers a unique opportunity to investigate tectonic-climatic interactions and the net impact of these processes on weathering and erosion of the western Himalaya. During International Ocean Discovery Program Expedition 355, two sites (U1456 and U1457) were drilled in Laxmi Basin in the eastern Arabian Sea to document the coevolution of mountain building, weathering, erosion, and climate over a range of timescales. In addition, recovering basement from the eastern Arabian Sea provides constraints on the early rifting history of the western continental margin of India with special emphasis on continental breakup between India and the Seychelles and its relationship to the plume-related volcanism of the Deccan Plateau.Drilling and coring operations during Expedition 355 recovered sediment from Sites U1456 and U1457 in the Laxmi Basin, penetrating 1109.4 and 1108.6 m below seafloor (mbsf ), respectively. Drilling reached sediment dated to 13.5-17.7 Ma (late early to early middle Miocene) at Site U1456, although with a large hiatus between the lowermost sediment and overlying deposits dated to <10.9 Ma. At Site U1457, a much longer hiatus occurs near the base of the cored section, spanning from 10.9 to ~62 Ma. At both sites, hiatuses span ~8.2-9.2 and ~3.6-5.6 Ma, with a possible condensed section spanning ~2.0-2.6 Ma, although the total duration for each hiatus is slightly different between the two sites.A major submarine fan draining the western Himalaya and Karakoram must have been supplying sediment to the eastern Arabian Sea since at least ~17 Ma. Sand mineral assemblages indicate that the Greater Himalayan Crystalline Sequence was fully exposed to the surface by this time. Most of the recovered sediment appears to be derived from the Indus River and includes minerals that are unique to the Indus Suture Zone, in particular glaucophane and hypersthene, most likely originating from the structural base of the Kohistan arc. Pliocene sandy intervals at Site U1456 were deposited in lower fan "sheet lobe" settings, with intervals of basin plain turbidites separated by hemipelagic muddy sections deposited during the Miocene. Site U1457 is more distal in facies, reflecting its more marginal setting. No major active lobe appears to have affected the Laxmi Basin since the Middle Pleistocene (~1.2 Ma).We succeeded in recovering sections spanning the 8 Ma climatic transition, when monsoon intensity is believed to have changed strongly, although the nature of this change awaits postcruise analysis. We also recovered sediment from a large mass transport deposit measuring ~330 and ~190 m thick at Sites U1456 and U1457, respectively. This section includes an upper sequence of slump-folded muddy and silty rocks, as well as underlying calcarenites and limestone breccias, to...

Free gas accumulations in basal shear zones of mass-transport deposits (Pearl River Mouth Basin, South China Sea): An important geohazard on continental slope basins

“…There are no wells drilled through the MTDs investigated in this paper and, thus, the petrophysical properties of MTDs cannot be directly assessed. Yet, the MTDs in the study area are likely fine-grained as deduced from units drilled at ODP Site 1146, and are similar to strata documented in the Amazon Fan (Piper et al, 1997;Shipp et al, 2004), Nankai Accretionary Wedge (Strasser et al, 2011), Gulf of Mexico (Dugan, 2012), Ulleung Basin (Riedel et al, 2012) and Arabian Sea (Pandey et al, 2015). The MTDs in these locations were drilled by ODP/IODP and exploration wells.…”

“…Moreover, all MTDs documented in the these regions showed similar petrophysical characteristics (e.g. Piper et al, 1997;Dugan, 2012;Riedel et al, 2012;Alves et al, 2014;Pandey et al, 2015), suggesting that the petrophysical character of these same deposits is predictable and probably associated with a common lithology. Hence, the petrophysical data acquired by previous ODP/IODP expeditions can be used in this study.…”

Tectono‐morphological evolution of the Cauvery, Vaigai, and Thamirabarani River basins: Implications on timing, stratigraphic markers, relative roles of intrinsic and extrinsic factors, and transience of Southern Indian landscape

“…Previous geomorphological and seismic studies on the Western Ghats documented periodic uplift since Middle Mesozoic until Holocene along Archean and Proterozoic faults and shear zones (Radhakrishna, 1993;Valdiya & Rajagopalan, 2000;Valdiya, 2001aValdiya, , 2001bValdiya, , 2008 and significantly since the commencement of Himalayan Orogeny. It also led to the physiographical diversity and the youthful character of its mountain ranges (Sharma & Rajamani, 2000a, 2000bSingh & Rajamani, 2001;Sensarma et al, 2008 (Bonnet et al, 2014(Bonnet et al, , 2016 followed by four stages of kaolinite formation in Western Ghats, namely, 1, 3.5, 9, and 39 Ma ± 0.24-1.537 ago (Mathian et al 2019) Although the reversal of drainage flow directions was initiated by the evolution of WGE (Fainstein et al, 2012) Most recent studies, involving multiproxies (Singhvi & Krishnan, 2014) and deep-sea high-resolution data (Pandey et al, 2015), opined that this SW monsoon became intense since 10-8 Ma. It signifies the attainment of orographic barrier effect of WGE during 10-8 Ma, FIGURE 21 (a,b).…”

Regional Pliocene exhumation of the Lesser Himalaya in the Indus drainage

“…P. D. Clift et al: Regional Pliocene exhumation of the Lesser Himalaya 2 Marine erosion records Scientific drilling conducted in 2015 by International Ocean Discovery Program (IODP) Expedition 355 now provides the opportunity to examine how Himalayan erosion has changed since ∼ 10.8 Ma (Pandey et al, 2015). Although drilling in the Laxmi Basin offshore western India was able to reach the Cretaceous basement at Site U1457 (Fig.…”