The thickness of subduction plate boundary faults from the seafloor into the seismogenic zone

The thickness of an active plate boundary fault is an important parameter for understanding the strength and spatial heterogeneity of fault behavior. We have compiled direct measurements of the thickness of subduction thrust faults from active and ancient examples observed by ocean drilling and fi eld studies in accretionary wedges. We describe a general geometric model for subduction thrust décollements, which includes multiple simultaneously active, anastomosing fault strands tens of meters thick. The total thickness encompassing all simultaneously active strands increases to ~100–350 m at ~1–2 km below seafl oor, and this thickness is maintained down to a depth of ~15 km. Thin sharp faults representing earthquake slip surfaces or other discrete slip events are found within and along the edges of the tens-ofmeters- thick fault strands. Although fl attening, primary inherited chaotic fabrics, and fault migration through subducting sediments or the frontal prism may build mélange sections that are much thicker (to several kilometers), this thickness does not describe the active fault at any depth. These observations suggest that models should treat the subduction thrust plate boundary fault as <1–20 cm thick during earthquakes, with a concentration of postseismic and interseismic creep in single to several strands 5–35 m thick, with lesser distributed interseismic deformation in stratally disrupted rocks surrounding the fault strands

Ontong Java Plateau, Leg 130: Synopsis of major drilling results

Sixteen holes were drilled at five sites on the northeastern flank of Ontong Java Plateau during Leg 130 (Sites 803 through 807). All of these sites are near the equator, but are at different depths (803: 02°26.0\u27N, 3410 m; 804: 01°00.3\u27N, 3861 m; 805: 01°13.7\u27N, 3188 m; 806: 00°19.1\u27N, 2520 m; and 807: 03°36.4\u27N, 2805 m). One of our goals was to obtain a depth transect of Neogene carbonate deposition for reconstructing the history of ocean climate, chemistry, and productivity, and for understanding the origin of acoustic reflectors. Another goal was to achieve considerable penetration into basement for elucidating the origin of the plateau. All sites yielded multiple Neogene sequences, which were cored using the advanced hydraulic piston corer (APC) to the ooze-chalk transition (10-14 Ma) and with the extended core barrel (XCB) below that. Sites 803 and 807 were drilled to basement and yielded incomplete Paleogene and Cretaceous sections. Penetration into basement was 25 m at Site 803 and 149 m at Site 807; 98 m of basalt was recovered. In all, we cored 5889 m, taking 639 cores. Of the record 4822 m recovered, 55% was taken with the APC, 39% with the XCB, and 6% with the rotary core barrel (RCB). All sites except Site 804 were logged. Neogene sedimentation rates were found to vary by more than a factor of 2, with a striking maximum in the latest Miocene to early Pliocene and a strong minimum in the Pleistocene. Fluctuations in carbonate content on the millionyear scale are highly coherent among depths over the last 12 m.y., perhaps less so before that. Many acoustic reflectors appear synchronous with carbonate reduction events (CREs) and other paleoceanographic events. Other reflectors are tied to diagenesis (e.g., the ooze-chalk transformation, which is diachronous). Recovery of the Cretaceous/Tertiary (K/T) boundary at Sites 803 and 807 demonstrates the presence of a deep carbonate-compensation depth (CCD) across the transition: one sequence is calcareous, the other is not. Because the K/T sections occur below and above major hiatuses, we postulate that special conditions for preservation existed during the transition. In addition, there is evidence of volcanic activity at that time. The basalts cored at Sites 803 and 807 are predominantly olivine-bearing and were erupted during the mid-Cretaceous. At Site 807, pillow lavas buried sediments. One thick flow (at about 28 m) was penetrated here, apparently a flood basalt. Magnetic paleolatitudes suggest that the Ontong Java Plateau has moved coherently with the Pacific Plate since the Early Cretaceous

Cruise Report prepared by INFOMAR and the Marine Institute, Galway, Ireland to the Department of Agriculture, Food and the Marine, the European Maritime and Fisheries Fund and the National Parks and Wildlife Service.

A requirement exists to quantify the abundance and distribution of offshore biogenic and geogenic reef habitats in Irish waters to fulfil Ireland’s legal mandate and to generate baseline data from which appropriate monitoring systems can be established. To address this an extensive offshore reef survey of Ireland’s Northwest Continental margin was commissioned by the National Parks and Wildlife Service (NPWS), funded by the European Maritime and Fisheries Fund (EMFF), and coordinated and led by INFOMAR (Integrated Mapping for the Sustainable Development of Ireland’s Marine Resources) and Ireland’s Marine Institute. The objectives of the survey were to implement the EMFF’s Marine Biodiversity Scheme - Natura Fisheries by mapping offshore reef habitats with a view to protecting them from deterioration due to fishing pressures. The reef project aligns with sub-article 6.2 of the Habitats Directive (EC 92/43/EEC) which requires member states to take measures to avoid deterioration of protected habitats. A survey, Sensitive Ecosystem Assessment and ROV Exploration of Reef (SeaRover), took place in July 2017 aboard the ILV Granuaile equipped with the Marine Institute’s remotely operated vehicle (ROV) Holland 1 and a multidisciplinary team of scientists to observe seabed features and biological associations along the northwest continental shelf. The Holland 1 employs high-definition (HD) camera, various composite video feeds and a robotic arm to facilitate sample collection. The primary scientific objective was to map the distribution and abundance of geogenic and biogenic reef habitat along the northwest shelf edge of Ireland’s continental slope with HD video. Secondary objectives included the collection of biological samples for genetic and population analysis and the collection of sediment cores for ground-truthing seabed mapping data and analysis of micro-plastics within deep-water sediment

Downhole Logging as a Paeoceanographic Tool on Ocean Drilling Program Leg 138: Interface Between High-Resolution Stratigraphy and Regional Syntheses

On Ocean Drilling Program (ODP) Leg 138, standard shipboard procedures were modified to allow for the real-time monitoring of several laboratory core-scanning systems that provide centimeter-scale measurements of saturated bulk density, magnetic susceptibility and digital color reflectance. These continuous, high-resolution data sets were used to ensure the proper offset of multiple holes and to splice together complete sedimentary sections. Typically, the spliced, continuous sediment sections were found to be about 10% longer than the section drilled, as measured by the length of the drill string. While the source of this elongation is not yet fully understood, it must be compensated for in order to property determine sediment fluxes and mass accumulation rates. Downhole logging, in conjunction with inverse correlation techniques provided a means to determine where the distortion occurred and to correct back to true in situ depths. Downhole logging also provides a means, through the generation of synthetic seismograms, of precisely relating the paleoceanographic events found in the core record to the high-resolution seismic record. Once correlated to the seismic record, the spatial and temporal extent of paleoceanographic events can be traced well beyond the borehole. Most seismic events in the equatorial Pacific are related to rapid changes in carbonate content that, in turn, are related to both productivity events (often expressed as monospecific laminated diatom oozes) and times of enhanced dissolution. While many of these events may have oceanwide extent, others, like the absence of carbonate in the late-Miocene to Recent in the Guatemala Basin have been shown to be regional and confined to only the deeper portions of the Guatemala Basin. As we identify and trace specific paleoceanographic events in the seismic record, we can begin to explore the response of the ocean through gradients of latitude, productivity, and depth

Downhole logging as a paeoceanographic tool on ocean drilling program leg 138: Interface between high-resolution stratigraphy and regional syntheses

On Ocean Drilling Program (ODP) Leg 138, standard shipboard procedures were modified to allow for the real-time monitoring of several laboratory core-scanning systems that provide centimeter-scale measurements of saturated bulk density, magnetic susceptibility and digital color reflectance. These continuous, high-resolution data sets were used to ensure the proper offset of multiple holes and to splice together complete sedimentary sections. Typically, the spliced, continuousediment sections were found to be about 10% longer than the section drilled, as measured by the length of the drill string. While the source of this elongation is not yet fully understood, it must be compensated for in order to property determine sediment fluxes and mass accumulation rates. Downhole logging, in conjunction with inverse correlation techniques provided a means to determine where the distortion occurred and to correct back to true in sire depths. Downhole logging also provides a means, through the generation of synthetic seismograms, of precisely relating the paleoceanographic events found in the core record to the high-resolution seismic record. Once correlated to the seismic record, the spatial and temporal extent of paleoceanographic events can be traced well beyond the borehole. Most seismic events in the equatorial Pacific are related to rapid changes in carbonate contenthat, in turn, are related to both productivity events (often expressed as monospecific laminated diatom oozes) and times of enhanced dissolution. While many of these events may have oceanwide extent, others, like the absence of carbonate in the late-Miocene to Recent in the Guatemala Basin have been shown to be regional and confined to only the deeper portions of the Guatemala Basin. As we identify and trace specific paleoceanographic events in the seismic record, we can begin to explore the response of the ocean through gradients of latitude, productivity, and depth

Evolution of a high-latitude sediment drift inside a glacially-carved trough based on high-resolution seismic stratigraphy (Kveithola, NW Barents Sea)

Rebesco, Michele ... et al.-- Special Issue: PAST Gateways (Palaeo-Arctic Spatial and Temporal Gateways).-- 16 pages, 12 figures, 2 tables, supplementary data http://dx.doi.org/10.1016/j.quascirev.2016.02.007Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea, an epicontinental shelf sea of the Arctic Ocean located off northern Norway and Russia. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. In general, drift deposits are commonly characterized by high lateral continuity, restricted occurrence of hiatuses and relatively high accumulation rates, and thus represent excellent repositories of paleo-environmental information. We provide for the first time a detailed morphological and seismostratigraphic insight into this sediment drift, which is further supported by some preliminary lithological and sedimentological analyses. The complex morphology of the drift, imaged by combining all available multibeam data, includes a main and a minor drift body, two drift lenses in the outer part of the trough, more or less connected drift patches in the innermost part and small perched sediment patches in a structurally-controlled channel to the north. The seismic (PARASOUND) data show that the main and minor drift bodies are mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting the occurrence of more energetic sedimentary conditions. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics, along with the morphological and seismic information, suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Though both Atlantic and Arctic waters are known to enter the trough, from the west and the north respectively, brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind or floating ice shelves have persisted on the western Barents Shelf since that time. The units inferred to have been deposited under more energetic sedimentary conditions (tentatively dated to the Younger Dryas and to 8.9–8.2 cal ka BP) are suggestive of stronger BSW formation. In general, we infer that variations in the bottom current regime were mainly related to BSW formation due to atmospheric changes. They could also have been a response to successive episodes of grounded and sea ice retreat that allowed for a first limited, later open shelf current, which progressively established on the western Barents Sea shelfThe research cruise MSM30 CORIBAR and this study were partly funded through the MARUM DFG-Research Center/Cluster of Excellence “The Ocean in the Earth System” as part of MARUM project SD-2. This study contributes to the IPY initiative 367 NICESTREAM (Neogene Ice Streams and Sedimentary Processes on High- Latitude Continental Margins). The work was funded by the Italian projects OGS-EGLACOM, PNRA-CORIBAR-IT (PdR 2013/C2.01), ARCA (grant n. 25_11_2013_973) and PNRA-VALFLU, by the Council of Norway through its Centres of Excellence funding scheme (project number 223259), by the Spanish projects DEGLABAR (CTM2010-17386) and CORIBAR-ES (CTM2011-14807-E) funded by the “Ministerio de Economia y Competitividad”. The “Generalitat de Catalunya” is acknowledged for support through an excellence research group grant (2014SGR940). J.L. was funded by an FPI grant BES-2011-043614Peer Reviewe

The Transformation of Sediment Into Rock : Insights From IODP Site U1352, Canterbury Basin, New Zealand

ACKNOWLEDGMENTS We thank the crew of the RV JOIDES Resolution for professional seamanship, excellent drilling, and the scientific support on board. GHB and SCG thank the Australia–New Zealand IODP Consortium (ANZIC), and KMM thanks the Consortium for Ocean Leadership U.S. Science Support Program for partly funding this work. Thanks also to funding agencies of the respective authors, and Mark Lawrence (GNS Science) and Cam Nelson (University of Waikato) for their thoughtful comments on an earlier draft. Karsten Kroeger (GNS Science) helped by providing compaction data for New Zealand basins, and Michelle Kominz (Western Michigan University) provided data on which Figure 8 was developed. Further improvements were the result of thoughtful detailed reviews by Gemma Barrie, Bill Heins, Stan Paxton, Associate Editor Joe Macquaker, and Editor Leslie Melim.Peer reviewedPostprin