Marine Geology and Geophysics

From the analysis of the satellite derived high resolution free air gravity data it is inferred that the evolutionary history of the Western Continental Margin of India to north and south of Goa appears to be totally different . The shelf edge is continuous and not disturbed in the northern part whereas to the south (south of 16°N) it has been affected by the onshore tectonics. It is hotly debated if the Laccadive Ridge (northern part of the Chagos-Laccadive Ridge) is continental or oceanic in nature or just of volcanic origin. From the filtered maps of the free air gravity anomalies, sources at different depths can be deciphered that help build an evolutionary model of the much debated Laccadive Ridge. The low pass filtered maps depicting deeper features, show a persistence of NW-SE to NS Dharwarian trends and it appears that the Laccadive Ridge to the north of around 8.5°N is of continental origin being bounded to the south and north by the offshore extension of the Bhavani Shear and Chapporo lineament respectively. It may have separated from India along with Madagascar during Cretaceous. At the Cretaceous Tertiary boundary as Laccadive-India passed over the Reunion hotspot, the pre-existing faults on the Laccadive Ridge were re-activated and the hotspot trace was left behind in the intermediate/shallow wavelength of the anomalies, as intrusives in the Laccadive Ridge. These are reflected in the High Pass filtered maps, depicting shallow to intermediate wavelength anomalies, which show NE-SW structures. The crustal structure derived from the 2D model of the satellite derived free air gravity data and a representative gravity-magnetic profile from ship borne data also depict continental nature of the Laccadive Ridge with emplacement of volcanic intrusives as it passed over the Reunion hotspot.

From the analysis of the satellite derived high resolution free air gravity data it is inferred that the evolutionary history of the Western Continental Margin of India to north and south of Goa appears to be totally different. The shelf edge is continuous and not disturbed in the northern part whereas to the south (south of 16°N) it has been affected by the onshore tectonics. It is hotly debated if the Laccadive Ridge (northern part of the Chagos-Laccadive Ridge) is continental or oceanic in nature or just of volcanic origin. From the filtered maps of the free air gravity anomalies, sources at different depths can be deciphered that help build an evolutionary model of the much debated Laccadive Ridge. The low pass filtered maps depicting deeper features, show a persistence of NW-SE to NS Dharwarian trends and it appears that the Laccadive Ridge to the north of around 8.5°N is of continental origin being bounded to the south and north by the offshore extension of the Bhavani Shear and Chapporo lineament respectively. It may have separated from India along with Madagascar during Cretaceous. At the Cretaceous Tertiary boundary as Laccadive-India passed over the Reunion hotspot, the pre-existing faults on the Laccadive Ridge were reactivated and the hotspot trace was left behind in the intermediate/shallow wavelength of the anomalies, as intrusives in the Laccadive Ridge. These are reflected in the High Pass filtered maps, depicting shallow to intermediate wavelength anomalies, which show NE-SW structures. The crustal structure derived from the 2D model of the satellite derived free air gravity data and a representative gravity-magnetic profile from ship borne data also depict continental nature of the Laccadive Ridge with emplacement of volcanic intrusives as it passed over the Reunion hotspot.

Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records.

Bengal-Nicobar Fan submarine fan Himalayan tectonics Asian monsoon Indian Ocean A holistic view of the Bengal-Nicobar Fan system requires sampling the full sedimentary section of the Nicobar Fan, which was achieved for the first time by International Ocean Discovery Program (IODP) Expedition 362 west of North Sumatra. We identified a distinct rise in sediment accumulation rate (SAR) beginning ∼9.5 Ma and reaching 250-350 m/Myr in the 9.5-2 Ma interval, which equal or far exceed rates on the Bengal Fan at similar latitudes. This marked rise in SAR and a constant Himalayan-derived provenance necessitates a major restructuring of sediment routing in the Bengal-Nicobar submarine fan. This coincides with the inversion of the Eastern Himalayan Shillong Plateau and encroachment of the west-propagating Indo-Burmese wedge, which reduced continental accommodation space and increased sediment supply directly to the fan. Our results challenge a commonly held view that changes in sediment flux seen in the Bengal-Nicobar submarine fan were caused by discrete tectonic or climatic events acting on the Himalayan-Tibetan Plateau. Instead, an interplay of tectonic and climatic processes caused the fan system to develop by punctuated changes rather than gradual progradation.

The western continental margin of India (WCMI) is among some of the most spectacular passive margins with numerous pronounced morpho-tectonic features. While it preserves early imprints of the final Gondwana dispersal, deep post-rift sedimentary archives on this margin are crucial for deciphering the India-Eurasia collisional tectonics and its long term climatic response. With a varying degree of magmatism along its ~2500 km long N-S stretch, the WCMI has a gently dipping wide shelf in the north as compared to the steep and narrower shelf in the south. Due to its vital link in understanding the formation and evolution of passive continental margins, the past few years have witnessed significant growth in the geoscientific studies especially led by the Indian geoscientific community. Here we collate some of the recent Indian contributions (2015-2018) aimed at augmenting our knowledge about the origin and subsequent evolution of this complex passive margin. Scientific contributions discussed in this review primarily focuses on various tectonic fragments/ domains along WCMI namely-submarine fan, shelf, seamounts, aseismic ridges, and abyssal basins.These recent studies using new seismic, bathymetric, potential field and magnetic data have targeted both aspects of the WCMI fairly well in terms of unraveling its early as well as late structural and tectonic evolution. We also make a particular mention of the firstever deep-sea drilling through the International Ocean Discovery Program (IODP) expedition 355 in the eastern Arabian Sea and the initial scientific findings emanating from it.

The Sunda Trench where the Indo-Australian Plate subducts beneath the Sunda and Burma Plate, is an active seismogenic zone which generated the 2004 Mw 9.2 mega-earthquake and devastating tsunami offshore Northern Sumatra, characterized by a large shallow slip near the trench and an extremely thick (>4 km) incoming section at the deformation front. To investigate the nature and impact of the incoming section on seismogenic processes, the International Ocean Discovery Program (IODP) Expedition 362 drilled into the Indo-Australian Plate ~225 km distance from the trench at 2 primary sites offshore Northern Sumatra during August to October 2016. Here, we report preliminary results from shipboard structural observation on the recovered cores. The lithostratigraphic sequence of the oceanic plate acquired from Site 1480 consists of Unit I: subsurface calcareous and silty clay (~26.4 m), Unit II: silty clay and sand of the Nicobar Fan sequence (~26.4-1250 m), Unit III: pelagic gray-green to reddish-brown tuffaceous claystone and chalk (~1250-1327 m), Unit IV: basaltic lava flows and volcaniclastic/tuffaceous sandstone (~1327-1350 m), Unit V: chalk and calcareous claystone with magmatic intrusion/extrusion with abundant mineral veins (~1350-1420 m), and Unit VI: basaltic basement cut by veins (1420 m~). Units I and II exhibit little deformation as observed from the continuously near-horizontal bedding dips (<10°), except for several localized horizons of syn-sedimentary normal faults in Unit II and intervals of slumping and folds. The bottom of Unit II (~460 m interval) was particularly undeformed, possibly reflecting the most distal portion of the fan deposit. A distinct concentration of normal faults was observed in Unit III, characterized by primarily two sets of thin anastomosing normal faults which randomly cross-cut each other. Sand injections and lighter-colored diagenetic spots also occur in the sediments, and the normal faults generally cut through the sand injections but generally leave the diagenetic spots uncut. The flattened geometry of the diagenetic spots overprinting the normal faults and the high conjugate angle (>90°) and curvy geometry of the faults may imply that the normal faulting occurred before significant compaction.

Introduction 5 Sedimentology and petrology 13 Structural geology 23 Biostratigraphy 38 Paleomagnetism 43 Geochemistry 46 Physical properties 51 Downhole measurements 54 Core-log-seismic integration 55 References F2). The smaller bit can cut a semi-indurated core with less torque and fluid circulation than the main bit, potentially improving recovery. The XCB cutting shoe extends ~30.5 cm ahead of the main bit in soft sediments but is allowed to retract into the main bit when hard formations are encountered. XCB core barrels are 9.5 m long. The bottom-hole assembly (BHA) used for APC and XCB coring was composed of an 11 7 ⁄ 16 inch (~29.05 cm) drill bit, a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, five 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch transition drill pipe, and a crossover sub to the drill pipe that extended to the surface. The RCB system is a rotary system designed to recover firm to hard sediments and igneous basement. The BHA, including the bit and outer core barrel, is rotated with the drill string while bearings allow the inner core barrel to remain stationary (Figure F3). RCB core barrels are 9.5 m long. The RCB BHA included a 9⅞ inch drill bit, a bit sub, an outer core barrel, a modified top sub, a modified head sub, a variable number of 8¼ inch control length drill collars, a tapered drill collar, two stands of 5½ inch drill pipe, and a crossover sub to the drill pipe that extended to the surface. Nonmagnetic core barrels were used in APC, HLAPC, and RCB deployments. APC cores were oriented with the Icefield MI-5 and FlexIT core orientation tools when coring conditions allowed. Formation temperature measurements were taken with the advanced piston corer temperature tool (APCT-3), and one deployment was attempted with the temperature dual-pressure (T2P) tool (see Downhole measurements). Information on recovered cores, drilled intervals, tool deployments, and related information are provided in the Operations section of each site chapter. Figure F1. APC system used during Expedition 362. ID = inner diameter. Orientation alignable retrieving cup Shear pins Inner seals Outer seals Quick release Rod Vents Honed ID drill collar Clear plastic liner Piston head and seal Shoe 3.80 inch bit ID 9.5 m stroke Seafloor Core Before stroke to take core After stroke to take core Figure F2. XCB system used during Expedition 362.

This extensively revised, restructured, and updated edition continues to present an engaging and comprehensive introduction to the subject, exploring the world's landforms from a broad systems perspective. It covers the basics of Earth surface forms and processes, while reflecting on the latest developments in the field. Fundamentals of Geomorphology begins with a consideration of the nature of geomorphology, process and form, history, and geomorphic systems, and moves on to discuss: • Structure: structural landforms associated with plate tectonics and those associated with volcanoes, impact craters, and folds, faults, and joints. • Process and form: landforms resulting from, or influenced by, the exogenic agencies of weathering, running water, flowing ice and meltwater, ground ice and frost, the wind, and the sea; landforms developed on limestone; and landscape evolution, a discussion of ancient landforms, including palaeosurfaces, stagnant landscape features, and evolutionary aspects of landscape change. This third edition has been fully updated to include a clearer initial explanation of the nature of geomorphology, of land-surface process and form, and of land-surface change over different timescales. The text has been restructured to incorporate information on geomorphic materials and processes at suitable points in the book. Finally, historical geomorphology has been integrated throughout the text to reflect the importance of history in all aspects of geomorphology. Fundamentals of Geomorphology provides a stimulating and innovative perspective on the key topics and debates within the field of geomorphology. Written in an accessible and lively manner, it includes guides to further reading, chapter summaries, and an extensive glossary of key terms. The book is also illustrated throughout with over 200 informative diagrams and attractive photographs, all in colour. Richard John Huggett is a Reader in Physical Geography at the University of Manchester, UK.