Site C0018

During Integrated Ocean Drilling Program (IODP) Expedition 338, a slope basin seaward of the megasplay fault was logged with logging while drilling (LWD)/measurement while drilling (MWD) at Site C0018. The slope basin, characterized in 3-D seismic data by stacked mass transport deposits (MTDs) (Strasser et al., 2011) was drilled and sampled during IODP Expedition 333 in Hole C0018A (Fig. F1) (Expedition 333 Scientists, 2012a). The primary goals of operations at Site C0018 were to establish the stratigraphy of Quaternary mass-movement events and to sample the distal part of an exceptionally thick MTD for analyzing its rheological behavior to constrain sliding dynamics and tsunamigenic potential. Site C0018 (proposed Site NTS-1A; water depth = 3084.35 m) is located ~5 km southwest of IODP Sites C0004 and C0008, which were drilled and cored during IODP Expedition 316 (Screaton et al., 2009) (Figs. F1, F2). Site C0018 is located within a lower slope basin that (1) represents the depocenter for downslope mass transport, (2) is characterized by stacked MTDs that were seismically identified as acoustically transparent to chaotic bodies with ponded geometries (Fig. F2), and (3) includes a large (as thick as 182 m) MTD (Strasser et al., 2011). Hole C0018A was drilled at a location where the MTD bodies wedge out and basal erosion is thought to be minimal. Coring to ~314.15 meters below seafloor (mbsf) allowed sampling of the MTDs across this stratigraphic succession. Sediment cored in Hole C0018A are divided into two lithologic subunits. Lithologic Subunit IA (0–190.65 mbsf) is primarily composed of hemipelagic mud (i.e., silty clay) with interbedded volcanic ash layers and is affected by MTDs, whereas lithologic Subunit IB (190.65–313.65 mbsf) is a sandy turbidite sequence (Expedition 333 Scientists, 2012a; Strasser et al., 2012). Six MTDs (numbered 1–6 from top to bottom) ranging in thickness from 50 cm to 61 m are identified within Subunit IA (Expedition 333 Scientists, 2012a; Strasser et al., 2012) (Fig. F3). These MTDs are composed of chaotic and convolute bedding with intervals of coherent bedding and commonly have bases defined by shear zones. A mass-movement event related to deposition of the lowermost and most prominent MTD 6 is younger than 1.05 Ma (because an ash layer immediately below the thick MTD 6 is identified as the one dated on land as 1.05 Ma) but older than 0.85 Ma, as constrained by another marker ash layer overlying MTD 6 (Expedition 333 Scientists, 2012a; Strasser et al., 2012). Another mass-movement event related to the uppermost MTD 1 occurred later than 0.291 Ma, which is the age indicated by nannofossils ~10 m below this MTD (Expedition 333 Scientists, 2012a; Strasser et al., 2012). The ages of other MTDs are not well constrained. During Expedition 338, LWD in Hole C0018B was conducted as a contingency operation. It provided a high-resolution data set of natural gamma radiation (NGR) and resistivity as well as resistivity images to 350 mbsf, enabled us to correlate and integrate these data with core and seismic data of the MTDs, and hence enabled us to understand the comprehensive nature of MTDs and their bearing on sliding dynamics and tsunamigenic potential

Expedition 362 Preliminary Report: Sumatra Subduction Zone

Drilling the input materials of the north Sumatran subduction zone, part of the 5000 km long Sunda subduction zone system and the origin of the Mw ~9.2 earthquake and tsunami that devastated coastal communities around the Indian Ocean in 2004, was designed to groundtruth the material properties causing unexpectedly shallow seismogenic slip and a distinctive forearc prism structure. The intriguing seismogenic behavior and forearc structure are not well explained by existing models or by relationships observed at margins where seismogenic slip typically occurs farther landward. The input materials of the north Sumatran subduction zone are a distinctively thick (as thick as 4–5 km) succession of primarily Bengal-Nicobar Fan–related sediments. The correspondence between the 2004 rupture location and the overlying prism plateau, as well as evidence for a strengthened input section, suggest the input materials are key to driving the distinctive slip behavior and long-term forearc structure. During Expedition 362, two sites on the Indian oceanic plate ~250 km southwest of the subduction zone, Sites U1480 and U1481, were drilled, cored, and logged to a maximum depth of 1500 meters below seafloor. The succession of sediment/rocks that will develop into the plate boundary detachment and will drive growth of the forearc were sampled, and their progressive mechanical, frictional, and hydrogeological property evolution will be analyzed through postcruise experimental and modeling studies. Large penetration depths with good core recovery and successful wireline logging in the challenging submarine fan materials will enable evaluation of the role of thick sedimentary subduction zone input sections in driving shallow slip and amplifying earthquake and tsunami magnitudes, at the Sunda subduction zone and globally at other subduction zones where submarine fan–influenced sections are being subducted

Understanding Himalayan erosion and the significance of the Nicobar Fan

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

338 Summary

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a multidisciplinary scientific project designed to investigate fault mechanics and seismogenesis along subduction megathrusts through reflection and refraction seismic imaging, direct sampling, in situ measurements, and long-term monitoring in conjunction with laboratory and numerical modeling studies. The fundamental scientific objectives of NanTroSEIZE include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout an active plate boundary system. As part of the NanTroSEIZE program, operations during Integrated Ocean Drilling Program (IODP) Expedition 338 were planned to extend and case riser Hole C0002F, begun during IODP Expedition 326 in 2010, from 856 to 3600 meters below seafloor (mbsf). Riser operations extended the hole to 2005.5 mbsf, collecting a full suite of logging-while-drilling (LWD) and measurement-while-drilling, mud gas, and cuttings data. However, because of damage to the riser during unfavorable wind and strong current conditions, riser operations were cancelled. Hole C0002F was suspended at 2005.5 mbsf and left for reentry during future riser drilling operations, which will deepen the hole to penetrate the megasplay fault at ~5000 mbsf. Contingency riserless operations included coring at Site C0002 (200–505, 902–940, and 1100.5–1120 mbsf), LWD at IODP Sites C0012 (0–710 mbsf) and C0018 (0–350 mbsf), and LWD and coring at IODP Sites C0021 (0–294 mbsf) and C0022 (0–420 mbsf). These sites and drilling intervals represent key targets not sampled during previous NanTroSEIZE expeditions but relevant to comprehensively characterize the alteration stage of the oceanic basement input to the subduction zone, the early stage of Kumano Basin evolution, gas hydrates in the forearc basin, recent activity of the shallow megasplay fault zone system, and submarine landslides

Site COO21

During Integrated Ocean Drilling Program (IODP) Expedition 338, a slope basin seaward of the megasplay was logged and cored at Site C0021. The slope basin, characterized in 3-D seismic data by stacked mass transport deposits (MTDs) (Strasser et al., 2011), was drilled and sampled in IODP Hole C0018A during IODP Expedition 333 and logged during Expedition 338 (Figs. F1, F2, F3) (Expedition 333 Scientists, 2012a) to establish the stratigraphy of a Quaternary mass-movement event and to sample the distal part of a thick MTD for analyzing its rheological behavior to constrain sliding dynamics and tsunamigenic potential. Site C0018 was drilled at a location where the MTD bodies wedge out and basal erosion is minimal. During Expedition 338, logging while drilling (LWD) and coring to 294 and 194.5 meters below seafloor (mbsf), respectively, were conducted at Site C0021 (proposed Site NTS-1C) as contingency operations. This site is located ~2 km northwest of Site C0018 at a more proximal site for the MTDs analyzed at Site C0018 (Figs. F2, F3, F4). Therefore, LWD and coring at Site C0021 provided additional information on the nature, provenance, and kinematics of MTDs. By combining data from drilling and postexpedition laboratory experiments on samples from Sites C0021 and C0018 (see the “Site C0018” chapter [Strasser et al., 2014c]), we will improve our understanding of dynamics of submarine landslides as it relates to their tsunamigenic potential. Hole C0021B core processing and measurements were divided into two phases: shipboard and shore based. The lack of ship time to completely process Hole C0021B cores on board during Expedition 338 dictated that only whole-round examinations could be performed; all remaining sampling tasks and analyses were deferred to a shore-based sampling party at the Kochi Core Center (KCC). Selected personnel from the science party, with some shore-based researchers, met at KCC in Kochi, Japan, from 25 to 30 April 2013 to participate in the sampling party and complete the site chapter reports

338 Methods

This chapter documents the methods used for shipboard measurements and analyses during Integrated Ocean Drilling Program (IODP) Expedition 338. Riser drilling was conducted, including cuttings, mud gas, logging while drilling (LWD), and measurement while drilling (MWD) from 852.33 to 2005.5 meters below seafloor (mbsf) in IODP Hole C0002F, which had been suspended for 2 years since being drilled during IODP Expedition 326 by the D/V Chikyu in 2010 (Expedition 326 Scientists, 2011). Due to damage incurred to the intermediate flex joint of the upper riser assembly during an emergency disconnect sequence after the passing of a cold weather front with associated high winds and rapid changes in wind direction while in the high-current area, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC)/Center for Deep Earth Exploration (CDEX) decided to discontinue riser operations at Site C0002 on 23 November 2012 (see “Operations” in the “Site C0002” chapter [Strasser et al., 2014b]). In light of this decision, we completed riserless coring in IODP Holes C0002H (1100.5–1120 mbsf), C0002J (902–926.7 mbsf), C0002K (200–286.5 mbsf), C0002L (277–505 mbsf), C0021B (0–194.5 mbsf), and C0022B (0–419.5 mbsf). Riserless LWD operations were completed in IODP Holes C0012H (0–710 mbsf), C0018B (0–350 mbsf), C0021A (0–294 mbsf), and C0022A (0–420.5 mbsf) (Table T1 in the “Expedition 338 summary” chapter [Strasser et al., 2014a]). Previous IODP work at Site C0002 included logging and coring during Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stages 1 and 2. LWD operations provided data from 0 to 1401.5 mbsf (Hole C0002A; Expedition 314 Scientists, 2009a) and 0 to 980 mbsf (Hole C0002G; Expedition 332 Scientists, 2011). Coring at Site C0002 previously sampled 0–203.5 mbsf (Holes C0002C and C0002D) and 475–1057 mbsf (Hole C0002B) (Expedition 315 Scientists, 2009b). During riser operations, we expanded the data sets at Site C0002. Gas from drilling mud was analyzed in near real time in a mud-gas monitoring laboratory and was sampled for postcruise research. Continuous LWD/MWD data were collected in real time for quality control and for initial assessment of borehole environment and formation properties. Recorded-mode LWD data provided higher spatial sampling of downhole parameters and conditions. Cuttings were sampled for standard shipboard analyses and shore-based research. Riserless coring in Holes C0002H and C0002J–C0002L provided additional core samples (whole round and discrete) for standard shipboard and shore-based research. Riserless operations at Site C0012 provided an extensive LWD data set for characterization of the sediment and basement conditions and properties. These logging data, which extend from 0 to 710 mbsf, complemented previous coring work at Site C0012 (Expedition 322 Scientists, 2010c; Expedition 333 Scientists, 2012b) and provided additional data in intervals where core recovery was sparse, especially within the basement. Hole C0018B was the logging complement to coring in Hole C0018A. The LWD hole provided in situ characterization of mass transport deposits (MTDs) that were cored in Hole C0018A (Expedition 333 Scientists, 2012c) as part of the Nankai Trough Submarine Landslide History ancillary project letter. Hole C0018A sampled a stacked series of MTDs that are related to active tectonic processes. Logging data provide additional characterization of the features in the MTDs and the sediments that bound them, which allows additional constraints on the evolution of MTDs. Riserless coring and LWD operations at Site C0021 (proposed Site NTS-1C) targeted a more proximal site for MTDs observed at Site C0018. Combined with LWD and core data obtained at Site C0018, LWD and coring at Site C0021 provide additional information on the nature, provenance, and kinematics of MTDs, as well as constraints on sliding dynamics and the tsunamigenic potential of MTDs. Riserless coring and LWD operations at Site C0022 (proposed Site NT2-13A) were initiated to provide new constraints on the timing of activity along the splay fault. Site C0022 is located between IODP Sites C0004 and C0008 (Expedition 314 Scientists, 2009b; Expedition 316 Scientists, 2009b, 2009c). The objectives of the site were to obtain samples for precise age dating of sediment deformation at the tip of the splay fault to determine the age of activity. Core data provided samples for dating and deformation analysis. Logging data provided in situ conditions and resistivity images of deformation features

Site C0002

Integrated Ocean Drilling Program (IODP) Site C0002 (proposed Site NT3-01B; Fig. F1) is the centerpiece of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project (Tobin and Kinoshita, 2006). Planned scientific and technical targets for IODP Expedition 338 included collecting logging-while-drilling (LWD), cuttings, and core data in the lower Kumano forearc basin and in the inner wedge of the Nankai accretionary complex and extending riser Hole C0002F to 3600 meters below seafloor (mbsf). This would extend the hole beyond the 20 inch casing point (860 mbsf), which was cemented in place during IODP Expedition 326 in 2010 (Expedition 326 Scientists, 2011) (Fig. F2). Riser drilling with the D/V Chikyu during Expedition 338 was to sample the interior of the accretionary complex in the midslope region beneath the Kumano forearc basin with both cores and drilling cuttings and to collect an extensive suite of LWD and mud-gas data to characterize the formation. Through the installation of two casing strings (16 inch casing from 860 to 2300 mbsf and 13⅜ inch casing from 2300 to 3600 mbsf), Expedition 338 was to prepare Hole C0002F for deeper drilling expected to reach the megasplay target during the 2014 and 2015 International Ocean Discovery Program riser drilling seasons. Because of weather and current conditions that caused the suspension of riser drilling operations (see below), LWD data and cuttings were only obtained from 860 to 2005 mbsf (Figs. F2, F3), and additional riserless coring (200–500, 900–940, and 1100–1120 mbsf) (Fig. F3) was completed at Site C0002 as part of contingency operations. The uppermost 1400 m section at Site C0002 was characterized with a comprehensive LWD program during IODP Expedition 314 (Hole C0002A) (Fig. F4) (Expedition 314 Scientists, 2009). The intervals 0–204 and 475–1057 mbsf were cored during IODP Expedition 315 (Holes C0002D and C0002B) (Expedition 315 Scientists, 2009b). The Kumano forearc basin sedimentary package extends from the seafloor to ~940 mbsf and is underlain by the deformed inner wedge of the accretionary package. The seismic reflection character of the entire zone from ~940 mbsf to the megasplay reflection at ~5200 mbsf exhibits virtually no coherent reflections that would indicate intact stratal packages, which is in contrast to the outer accretionary wedge seaward of the megasplay fault system (Fig. F2; also see Moore et al., 2009). This seismic character is thought to indicate complex deformation within the inner wedge of the Nankai accretionary prism

Chasing the 400 kyr pacing of deep-marine sandy submarine fans: Middle Eocene Ainsa Basin, Spanish Pyrenees

In an attempt to understand the relative importance of climate and tectonics in modulating coarse-grained sediment flux to a tectonically active basin during what many researchers believe to be a greenhouse period, we have studied the Middle Eocene deep-marine Aínsa Basin, Spanish Pyrenees. We use orbital tuning of many spectral gamma-ray-logged fine-grained siliciclastic sections, already shown to contain Milankovitch frequencies, in conjunction with a new high-resolution palaeomagnetic study through the basin sediments, to identify polarity reversals in the basin as anchor points to allow the conversion of a depth-stratigraphy to a chronostratigraphy. We use these data, in conjunction with a new age model incorporating new biostratigraphic data, to pace the development of the deep-marine sandy submarine fans over c. 8 million years. Timing for the sandy submarine fans shows that, unlike for the fine-grained interfan sediments, coarse-grained delivery to the basin was more complex. Approximately 72% of the sandy fans are potentially coincident with the long-eccentricity (400 kyr) minima and, therefore, potentially recording changing climate. The stratigraphic position of some sandy fans is at variance with this, specifically those that likely coincide with a period of known increased tectonic activity within the Aínsa Basin, which we propose represents the time when the basin was converted into a thrust-top basin (Gavarnie thrust sheet), presumably associated with rapid uplift and redeposition of coarse clastics into deep-marine environments. We also identify sub-Milankovitch climate signals such as the c. 41.5 Ma Late Lutetian Thermal Maximum. This study demonstrates the complex nature of drivers on deep-marine sandy fans in a tectonically active basin over c. 8 Myr. Findings of this study suggest that, even during greenhouse periods, sandy submarine fans are more likely linked with times of eccentricity minima and climate change, broadly consistent with the concept of lowstand fans. However, hysteresis effects in orogenic processes of mountain uplift, erosion and delivery of coarse siliciclastics via fluvial systems to coastal (deltaic) and shallow-marine environments likely contributed to the complex signals that we recognize, including the 2–3 Myr time gap between the onset of deep-marine fine-grained sediments in the early development of the Aínsa Basin and the arrival of the first sandy fans