The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

[1] Multiple lines of evidence exist for a range of sediment mass movement processes within the shallow megasplay fault zone (MSFZ) area and the adjacent slope basin in the outer fore arc of the Nankai subduction zone, Japan. Diagnostic features observed in three-dimensional reflection seismic data and in cores of the Integrated Ocean Drilling Program (IODP) document a multifarious mass movement history spanning ∼2.87 million years. Various modes and scales of sediment remobilization can be related to the different morphotectonic settings in which they occurred. From this evidence, we decipher the tectonic control on slumping and mass transport deposition in the Nankai fore arc. Three periods of intensified mass wasting coincided with pulses of enhanced activity on the splay fault: (1) an initial phase of juvenile out-of-sequence thrusting ∼1.95 to 1.7 Ma, (2) a reactivation phase between ∼1.55 and 1.24 Ma, and (3) at about 1 Ma, during a phase of uplift of the fore-arc high and motion along the MSFZ. We suggest that slope oversteepening, extensional stress regimes, and lateral transmission of fluid overpressures may have preconditioned the slope sediments to fail. Individual mass-wasting events may have been triggered by dynamic loading from earthquake waves and/or transient pulses of pore pressure along the splay fault. Overall, our results provide insights into the complicated interplay between tectonic and submarine mass movement processes. We demonstrate that detailed knowledge about the spatial and temporal distribution of submarine mass movements can be integrated into a holistic reconstruction of tectonostratigraphic evolution of accretionary margins.

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Based on high-resolution reflection seismic and core data from IODP Expedition 359 we present a new channel-related drift type attached to a carbonate platform slope, which we termed delta drift. Like a river delta, it is comprised of several stacked lobes and connected to 3 3 a point source. The delta drifts were deposited at the exit of two gateways that connect the Inner Sea of the Maldives carbonate platform with the open ocean. The channels served as conduits focusing and accelerating the water flow; Entrained material was deposited at their mouth where the flows relaxed. The lobe-shaped calcareous sediment drifts must have formed under persistent water through flow. Sediment supply was relatively high and continuous, resulting in an average sedimentation rate of 17 cm ka-1. The two delta drifts occupy 342 and 384 km 2 , respectively; with a depositional relief of approximately 500 m. They have a sigmoidal clinoform reflection pattern with a particular convex upward bending of the foresets. In the Maldives the drift onset marks the transition from a sea-level controlled to a progressively current dominated depositional regime. This major event occurred in the Serravallian about 13 Ma ago, leading to the partial drowning of the carbonate platform and the creation of shallow seaways. The initial bank-enclosed topography resembles an "empty bucket" geometry which is rapidly filled by the drift sediments that aggrade and prograde into the basin. Thereby the depositional environment of the delta drifts changes from deep water (>500) to shallow-water conditions at their topsets, indicated by the overall coarsening upward trend in grain size and the presence of shallow water large benthic foraminifers at their top.

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Eighteen constant-rate-of-strain consolidation tests were performed on whole-round core samples from Integrated Ocean Drilling Program Sites C0002, C0006, and C0007. These sites are located along the Kumano transect of the Nankai Trough offshore south-central Japan; Site C0002 is in the forearc basin and the other two are in the frontal thrust zone. Sample depths range from ~35 to 920 m core depth below seafloor. The objectives of the laboratory tests were to obtain the compression characteristics of the sediments, to estimate the maximum pretest consolidation stress (P′ c ), and to determine values of hydraulic conductivity (K), intrinsic permeability (k), and compression index (C c ). Values of C c at Site C0002 range from 0.391 to 0.780 (average = 0.584); comparable values are 0.236 to 0.418 (average = 0.302) in the trench-wedge facies at Sites C0006 and C0007. Values of in situ intrinsic permeability (k i ) at Site C0002 show no trend with depth, ranging from 2.67 × 10 -17 m 2 to 2.56 × 10 -18 m 2 . Estimates of k i at Sites C0006 and C0007 decrease with depth and range from 1.85 × 10 -16 m 2 to 6.08 × 10 -18 m 2. Test-derived values of P′ c are consistently greater than the estimates of in situ hydrostatic vertical effective stress at equivalent sample depths, which means the specimens are overconsolidated. Environmental scanning electron microscopy was used to assess the degree of preferred particle orientation of the microfabric. The index of orientation averages 0.33 at Sites C0006 and C0007 and 0.38 at Site C0002. Most vertical sections show indexes of orientation greater than those for horizontal sections; exceptions to this pattern include several samples from Sites C0006 and C0007 where bedding dips >40°. Samples from deeper intervals of the forearc basin (Site C0002) and from the accreted upper Shikoku Basin facies at Site C0007 yielded the highest values of orientation index (>0.40), indicating better alignment of platy grains. IntroductionConsolidation characteristics of marine sediments and sedimentary rock are used to evaluate diagenetic, hydrologic, and compaction processes during subduction and accretion (e.g., Lee et al., 1973; Trabant et al., 1975; Carson, 1977; Shepard and Bryant, 1977; Taylor and Bryant, 1985;Morgan and Ask, 2004;Spinelli et al., 2007 Kinoshita, M., Tobin, H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., and the Expedition 314/315/316 Scientists Proceedings of the Integrated Ocean Drilling Program, Volume 314/315/316 J. Guo et al. Data report: consolidation characteristics of sedimentProc. IODP | Volume 314/315/316 2 from tectonically induced (nonvertical) stress, deformation, cementation, and/or uplift and erosion of overburden, whereas underconsolidation (values less than expected) can be caused by excess pore water pressure (i.e., greater than hydrostatic) and the presence of gas and gas hydrates. Consolidation tests also provide estimates of in situ fluid pressure, permeability, and bulk sediment compressibility (Ka...

This report documents clay mineral assemblages outboard of the Nankai Trough at two sites in the Shikoku Basin. The sites make up part of the Kumano transect, offshore south-central Japan. Coring began during Integrated Ocean Drilling Program (IODP) Expedition 322, as part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). IODP Site C0011 is located on the northwest flank of Kashinosaki Knoll, and IODP Site C0012 is located on the summit of the seamount. A total of 292 samples of hemipelagic mud and mudstone were analyzed by X-ray diffraction, using oriented aggregates of the clay-size fraction (<2 µm). Smectite varies the most among the clay-size constituents, ranging in abundance from 35% to 100% (where smectite + illite + chlorite + kaolinite + quartz = 100%). Specimens with smectite contents of 80% or more are classified as bentonites, and we identified 44 such samples. The estimated amount of smectite in bulk mudstone ranges from 24% to 87% (where total clay minerals + quartz + feldspar + calcite = 100%), and a substantial number of bulk samples contain >45% smectite. On average, the expandability of illite/smectite mixed-layer clay is equal to 77%, and the average proportion of illite in illite/smectite is 11%. There is no systematic progression of clay mineral diagenesis over the depths sampled. Most values of illite crystallinity index are consistent with a detrital source that contains sedimentary rocks that were exposed to anchizone conditions of incipient metamorphism. The smectite-rich clay mineral assemblage is typical of early to middle Miocene deposits within the lower part of the Shikoku Basin.

Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth's orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital timescale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ 18 O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition.