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

From glacial erosion to basin overfill: a 240 m-thick overdeepening–fill sequence in Bern, Switzerland

We drilled a 210 m-thick succession of Quaternary sediments and extended it 30 m upsection with information that we collected from an adjacent outcrop. In the 240 m-thick succession we identified 12 different lithofacies, grouped them into five facies assemblages, and distinguished two major sedimentary sequences. A sharp contact at 103 m depth cuts off cross-beds in sequence A and separates them from the overlying horizontal beds in sequence B. Although the lowermost facies assemblage of each sequence includes a till deposited during a period of ice cover, the two tills differ from each other. In particular, the till at the base of sequence A is dominated by large clasts derived from the underlying Molasse bedrock, whereas the till at the base of sequence B has no such Molasse components. Furthermore, the till in sequence A bears evidence of glaciotectonic deformation. Both tills are overlain by thick assemblages of subaqueous, most likely glaciolacustrine and lacustrine facies elements. The cross-bedded and steeply inclined sand, gravel, and diamictic beds of sequence A are interpreted as deposits of density currents in a subaqueous ice-contact fan system within a proglacial lake. In contrast, the lacustrine sediments in sequence B are considered to record a less energetic environment where the material was most likely deposited in a prodelta setting that gradually developed into a delta plain. Towards the top, sequence B evolves into a fluvial system recorded in sequence C, when large sediment fluxes of a possibly advancing glacier resulted in a widespread cover of the region by a thick gravel unit. Feldspar luminescence dating on two samples from a sand layer at the top of sequence B provided uncorrected ages of 250.3 ± 80.2 and 251.3 ± 59.8 ka. The combination of these ages with lithostratigraphic correlations of sedimentary sequences encountered in neighboring scientific drillings suggests that sequence B was deposited between Marine Isotope Stage 8 (MIS 8; 300–243 ka) and MIS 7 (243–191 ka). This depositional age marks the end of one stage of overdeepening–fill in the perialpine Aare Valley near Bern

PALEOMAGNETIC INVESTIGATION OF IGNEOUS ROCKS DEFORMED BY THE KEWEENAW FAULT IN THE NORTHWESTERN KEWEENAW PENINSULA.

One of the most prominent structural features associated with the ~1.1 Ga Midcontinent Rift (MCR) system is the \u3e350 km long Keweenaw Fault that bisects the Keweenaw Peninsula, separating the MCR-related Portage Lake Volcanics (PLV) and the younger Jacobsville Sandstone (JS). The fault trend is NE-NNE over most of its length, but changes to an easterly direction along the shore of Bête Grise Bay near the end of the peninsula. Conventionally, the Keweenaw Fault has been considered to be a continuous reverse (dip-slip) fault formed by inversion of an original rift-bounding normal fault during the Grenville Orogeny. However, recent mapping shows that the fault in this area is not a single continuous feature but instead is a fault system consisting of ENE and ESE-trending segments with substantial strike-slip movement. This segmented fault geometry could have resulted in local folding of PLV and JS strata adjacent to the fault segments. To test this hypothesis, a paleomagnetic investigation was conducted on samples of PLV basaltic flows from eight sites in the Lake Medora and Fort Wilkins map quadrangles. The sites represent the opposite flanks of a proposed anticline with an ESE-trending axis. All eight sites yielded reliable and consistent site-mean directions of characteristic remanent magnetization (ChRM). A paleomagnetic fold test conducted on these sites showed that after unfolding the ChRM directions are similar to the paleomagnetic direction expected from unfolded PLV rocks. Data from two sites also suggest rotations around a vertical axis consistent with strike-slip movement. Paleomagnetic directions obtained from three additional sites with brecciated PLV basalt and JS sandstone as well as a clastic dike of JS cutting PLV, are randomized within each site. These randomized directions provide additional evidence that paleomagnetic data from the PLV basalts were not affected by a later remagnetization event. Overall, the paleomagnetic results support the hypothesis of fault-induced folding of PLV strata in the study area. In addition, this research demonstrates that paleomagnetism represents a useful tool to investigate local structural deformation within the MCR system

Spatial simulation of the W-Sn ore grades of São Pedro das Águias skarn mineral deposit (Tabuaço, northern Portugal)

The purpose of this study is the W-Sn grades simulation of São Pedro das Águias skarn ore deposit (Tabuaço, northern Portugal). This skarn deposit hosts a mineralization of scheelite and cassiterite. The grades modelling constrained by lens-shaped skarns is challenging, because they are numerous, thin, constrained to the structure shape and orientation, and recognized only in the drill-holes without indication of interconnections. Despite of the complexity, the proposed methodology constructs a geological model of the lens-shaped skarns, and generates a conditional model of the grades. The geological model construction begins with the automatic simulation of scenarios of the interconnections between the lens-shaped intersected by the drill-holes, conditioned to the orientation of the structure. For the simulated geometry scenarios represented by polylines in several cross-sections thicknesses are added according to the drill-cores, and the skarn relative proportion of each block is evaluated. Finally, the grid blocks between the cross-sections are filled using direct the DSS algorithm with local means from the skarn proportion variable (continuous variable). So long as the skarn thicknesses are much smaller than the blocks size, the morphological model reports the skarn proportion variable. The W-Sn grades model encompasses the local histograms estimation conditional to the geological model, and uses the PFS algorithm to generate the final images. The local histograms estimation results of a grades mixture according to the calculated skarn proportion between each block, and of a simple W-Sn simulated images conditional to the skarn and no-skarn lithological groups. The simulated grades are finally compared with the equivalent resources obtained by ordinary kriging. The simulated images enable the evaluation of the local uncertainty, and may be used for mine planning and optimizations

Kinematic analysis of the stage 5 design of the Kevitsa open pit mine

Abstract. The development of a new pushback in the Kevitsa Open Pit Mine has raised concerns regarding the potential impact of minor and major geological discontinuities on the overall stability of the pit. Furthermore, the daily mining operations are continuously threatened by frequent rock falls that occasionally exceed the bench slope scale, posing hazards in terms of safety and economics. Despite these challenges, the structures or group of structures responsible for most of the rock falls have not been confidently identified. This study reviews the effect of the structural features within the Kevitsa area into the open pit excavation and the proposed slopes of the Stage 5 pit design. To achieve this, structural mapping of rock surfaces was performed using 3D photogrammetry. The collected data was integrated with geotechnical logging data and laser scan data to characterize the dominant joint orientations of the deposit. Kinematic analyses of rock blocks were carried out by stereographic projection techniques to identify potential instabilities in the bench, inter-ramp, and overall slopes of the Stage 5 pit design. Results establish that two areas in the current pit and Stage 5 have major slope instability, where bench and inter-ramp slope failures are attributed to specific joint sets. Moreover, potential planar and wedge failures of overall slope scale are identified. Based on the findings, recommendations for pit optimization and geotechnical investigations are made

Rapid detection of bedding boundaries based on borehole images

Abstract The bedding is an important sedimentary structure phenomenon. The rock bedding structure, the direction of sedimentary transportation and the ancient sedimentary environment analysis can be studied by extracting the bedding boundaries and dips. Electric imaging logging can provide rich information of a borehole wall and circumference, which reflects formation resistivity variations. The bedding boundaries are detected by using the electrical imaging logging data based on an image recognition method in this paper. On an oriented, unwrapped image of a cylindrical borehole, the trace of a planar-bedding boundary appears as a sine wave. The bedding boundaries are detected by the recognition of the sine curves in borehole image. The influence problems of bedding boundary detection caused by fractures and other geological events are solved by statistical analysis technology. Through the techniques of the slope fitting, the speed and accuracy problems of bedding boundary detection are solved, which has good anti-interference performance. The processed results of the theoretical models and the measured borehole images at the varied dip segment indicate that the detected bedding boundaries reflect the real situation, which are identical to those derived by the Autodip

Characterization of bedding-parallel fractures in shale : morphology, size distribution and spatial organization

Natural fracture systems are important for production in shale gas reservoirs as they may contribute to permeability of the reservoir, or they may reactivate during hydraulic fracture treatment. However, little is known about their size scaling and spatial distribution. Bed-parallel, calcite-filled fractures are common in shale. Knowing the aperture-size scaling and spatial organization of bed-parallel fractures may contribute to improved modeling of the combined fracture network (hydraulic and natural). Ten fracture data sets were collected from the Vaca Muerta (7), Marcellus (2) and Wolfcamp (1) shale formations. Bed-parallel fracture attributes such as strike, dip, aperture size, spacing, length and texture were collected from outcrops of the Vaca Muerta Formation in the Neuquén Basin, Argentina. Further fracture aperture-size and spacing data for the Vaca Muerta, and for the Marcellus and Wolfcamp, were collected through measurement direct from cores, and from photographic panels of slabbed core. A total of 1093 fractures were measured along 10 scanlines of total combined length of 629m. The aperture size of bed-parallel fractures ranges over 4 orders of magnitude, from 15 µm to 87 mm. Nine out of ten datasets follow a negative exponential distribution. Fracture attributes such as intensity and size range are different in the 3 studied shales. Even within the same shale formation, fracture intensity and size range can be variable. Aperture size ranges of bed-parallel and vertical fractures in these shales are comparable as are fracture intensities for the Marcellus examples. Bed-parallel fractures, however, have higher intensities than vertical fractures in the Vaca Muerta examples. Spatial organization of bed-parallel fractures is investigated using a normalized two-point correlation technique that allows distinction between clustering, regular spacing and a random distribution. The relationship between fracture spatial organization and stratigraphy and mechanical interfaces within the host rock is also investigated, with preliminary results suggesting that bed-parallel fractures are more intense in organic-rich layers in some cases, but not in others.Geological Science