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International Ocean Discovery Program (IODP) Expedition 359 is designed to address sea level, currents, and monsoon evolution in the Indian Ocean. Seven proposed drill sites are located in the Maldives and one site is located in the Kerala-Konkan Basin on the western Indian continental margin. The Maldives carbonate edifice bears a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. It has great potential to serve as a key area for better understanding the effects of this global evolution in the Indo-Pacific realm. Based mainly on seismic stratigraphic data, a model for the evolution of this carbonate bank has been developed, showing how changing sea level and ocean current patterns shaped the bank geometries. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system is thought to be directly linked to the evolving Indian monsoon. Fluctuations in relative sea level control the stacking pattern of depositional sequences during the lower to middle Miocene. This phase was followed by a two-fold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and the deposition of giant sediment drifts. The shapes of drowned banks attest to the occurrence of these strong currents. The drift sediments, characterized by off-lapping geometries, formed large-scale prograding complexes, filling the Maldives Inner Sea basin. Because the strong current swept most of the sediment around the atolls away, relict banks did not prograde, and steady subsidence was balanced by aggradation of the atolls, which are still active today. One important outcome of Expedition 359 is ground-truthing the hypothesis that the dramatic, pronounced change in the style of the sedimentary carbonate sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. Answering this question will directly improve our knowledge on processes shaping carbonate platforms and their stratigraphic records. Our findings would be clearly applicable to other Tertiary carbonate platforms in the Indo-Pacific region and to numerous others throughout the geological record. In addition, the targeted successions will allow calibration of the Neogene oceanic δ13C record with data from a carbonate platform to platform-margin series. This is becoming important, as such records are the only type that exist in deep time. Drilling will provide the cores required for reconstructing changing current systems through time that are directly related to the evolution of the Indian monsoon. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives. These data will be valuable for a comparison with proposed Site KK-03B in the Kerala-Konkan Basin (see Geological setting of the Kerala-Konkan Basin, below) and other monsoon-dedicated IODP expeditions. The proposed site in the Kerala-Konkan Basin provides the opportunity to recover colocated oceanic and terrestrial records for monsoon and premonsoon Cenozoic climate in the eastern Arabian Sea and India, respectively. The site is located on a bathymetric high immediately north of the Chagos-Laccadive Ridge and is therefore not affected by strong tectonic, glacial, and nonmonsoon climatic processes that affect fan sites fed by Himalayan rivers. The cores are expected to consist of a continuous sequence of foraminifer-rich pelagic sediments with subordinate cyclical siliciclastic inputs of fluvial origin from the Indian Peninsula for the Neogene and a continuous paleoclimate record at orbital timescales into the Eocene and possibly the Paleocene. 

International Ocean Discovery Program (IODP) Site U1446 is located in the Mahanadi offshore basin on the eastern margin of India (Figure F1). This sedimentary basin extends both onshore and offshore and was formed during the Late Jurassic rifting of Gondwana (Sastri et al., 1981; Subrahmanyam et al., 2008). Today, the Mahanadi River basin (19°21′ to 23°35′N, 80°30′ to 86°50′E; ~1.42 × 105 km2) drains a catchment composed of late Archaean and early Proterozoic granite batholiths and gneisses from the Eastern Ghats (~56%); Gondwana-age limestones, shales, and sandstones (~39%); and recent alluvium (~5%) (Mazumdar et al., 2015; Rickers et al., 2001), including one of the richest mineral belts on the Indian subcontinent. This mineralization results in higher concentrations of trace metals such as Fe, Cu, Zn, and Pb in suspended river sediments compared to other rivers in peninsular India (Chakrapani and Subramanian, 1990b). Kaolinite, chlorite, quartz, dolomite, and minor montmorillonite and illite are characteristic components of suspended sediments discharged by the Mahanadi River into the Bay of Bengal (Subramanian, 1980; Chakrapani and Subramanian, 1990b). 

The Andaman Sea is situated between the Andaman Islands and the Malay Peninsula (Figure F1). The Andaman-Sumatra island arc system results from the oblique subduction of the Indo-Australian plate beneath the Eurasian plate (Singh et al., 2013). Stretching and rifting of the overriding plate during the early Miocene (~25 Ma) resulted in two distinct plates (Sunda and Burma) separated by an active spreading center (Curray, 1991, 2005) located in the deepest portion of the Andaman Sea. An accretionary wedge complex scraped off the subducting slab lies west of the spreading center, forming a series of shallower basins associated with backthrust faulting within the accreted sediments (Figure F2). The Andaman Sea drilling sites are within the Nicobar-Andaman Basin, bounded on either side by the Diligent and Eastern margin faults. 

The main scientific objective of International Ocean Discovery Program (IODP) Expedition 353 was to analyze the variability of precipitation and runoff in the Bay of Bengal on suborbital to orbital timescales. To achieve this objective, site locations were selected according to their proximity to the main sources of freshwater feeding the northern Bay of Bengal, including the Mahanadi River and the Ganges-Brahmaputra river complex, and the Andaman Sea, including the Irrawaddy and Salween river systems. 

The Andaman Sea is situated between the Andaman Islands and the Malay Peninsula (Figure F1). The Andaman-Sumatra island arc system results from the oblique subduction of the Indo-Australian plate beneath the Eurasian plate (Singh et al., 2013). Stretching and rifting of the overriding plate during the early Miocene (~25 Ma) resulted in two distinct plates (Sunda and Burma) separated by an active spreading center (Curray, 1991, 2005) located in the deepest portion of the Andaman Sea. An accretionary wedge complex scraped off the subducting slab lies west of the spreading center, forming a series of shallower basins associated with back-thrust faulting within the accreted sediments (Figure F2). The Andaman Sea drilling sites are within the Nicobar-Andaman Basin, bounded on either side by the Diligent and Eastern margin faults. 

Structure and paleogeographic history of the northern Ninetyeast Ridge International Ocean Discovery Program (IODP) Site U1443 is located ~100 m southeast of Ocean Drilling Program (ODP) Leg 121 Site 758 on the crest of the Ninetyeast Ridge and is a redrill of Site 758 (Figure F1). The Ninetyeast Ridge represents the trace of the Kerguelen/Ninetyeast hotspot prior to middle Eocene rifting (Shipboard Scientific Party, 1989a). As a result of northward movement, Site U1443 moved from temperate southern latitudes during the Campanian, to ~5°S near the Oligocene/Miocene boundary, and to its present location of 5°N in the southernmost Bay of Bengal. The site has been within 10° of the Equator for the past 35 My (Shipboard Scientific Party, 1989a). The ridge-top location has prevented the deposition of sedimentary sequences typically associated with fan transport processes.