Cenozoic geology of the continental slope and rise off western Nova Scotia

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution October 1985The outer continental margin of Nova Scotia is divided by a diapir province, 40-110 km wide and ~1000km long, that trends subparallel to the shelf edge along the upper continental rise and slope. The growth pattern for a small region of this margin (61°-64°W) during the Late Cretaceous and Cenozoic was studied using seismic stratigraphy and well data. Structure maps show that a steep continental slope existed landward of the diapir province (~2200-3800 m water depth) from Early Cretaceous until Miocene time when onlapping upper rise sediments reduced the gradient. Shelf edge canyons were cut during the late Maestrichtian-early Paleocene, Eocene-Oligocene, and Pleistocene. Extensions of Tertiary canyons onto the slope are poorly defined, but small Paleocene fans of interbedded chalk and mudstone on the upper rise indicate that slope canyons existed at that time. Abyssal currents eroded the upper rise and smoothed relief on the continental slope in the Oligocene and middle(?) Miocene. In the Miocene, turbidites may have ponded on the upper rise landward of seafloor highs uplifted by salt ridges or pillows. Pliocene-Pleistocene sediments drape over pre-existing topography. At the beginning and end of the Pleistocene, turbidity currents, caused by delivery of large sediment loads to the shelf edge by glaciers, eroded the present canyon morphology. The late Cenozoic section of the lower continental rise thins seaward from ~2 km near the diapir province and rests on Horizon Au, a prominent unconformity eroded during the Oligocene by abyssal currents. The morphology of the lower rise is largely due to construction by down-slope deposits shed in the Miocene-Pliocene from uplift of the diapir province. Abyssal currents episodically eroded sediment, but current controlled deposition formed only a thin (<300 m) deposit in the Pliocene(?). Uplift in the diapir province accelerated during the Pleistocene and olistostromes up to 300 m thick were shed onto the lower rise. In the latest Pleistocene, sediments transported down-slope by near-bottom processes accumulated west of a sharp boundary running near 62°30'W from 500 m seaward to the abyssal plain. To the east, hemipelagic sediments accumulated above 4300 m, while turbidity currents, originating in deep canyons to the east, and abyssal currents reworked sediments below 4300 m. A glacial sediment source and relict shelf morphology controlled sedimentation processes and, thus, the location of depocenters on the slope and rise

Modeling seafloor geoacoustic interaction with a numerical scattering chamber

Author Posting. © Acoustical Society of America, 1994. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 96 (1994): 973-990, doi:10.1121/1.410271.A numerical scattering chamber (NSC) has been developed to compute backscatter functions for geologically realistic seafloor models. In the NSC, solutions are computed to the elastic (or anelastic) wave equation by the finite-difference method. This has the following advantages: (a) It includes all rigidity effects in the bottom including body and interface waves. (b) It can be applied to pulse beams at low grazing angles. (c) Both forward scatter and backscatter are included. (d) Multiple interactions between scatterers are included. (e) Arbitrary, range-dependent topography and volume heterogeneity can be treated simultaneously. (f) Problems are scaled to wavelengths and periods so that the results are applicable to a wide range of frequencies. (g) The method considers scattering from structures with length scales on the order of acoustic wavelengths. The process is discussed for two examples: a single facet on a flat, homogeneous seafloor and a canonically rough, homogeneous seafloor. Representing the backscattered field by a single, angle-dependent coefficient is an oversimplification. In a strong scattering environment, time spread of the field is a significant issue and an angle-dependent separation of the wave field may not be valid.This work was carried out under support from the Office of Naval Research Acoustic Reverberation Special Research (Grant Number N00014-90-J-149

Finite difference modeling of geoacoustic interaction at anelastic seafloors

Author Posting. © Acoustical Society of America, 1994. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 95 (1994): 60-70, doi:10.1121/1.408298.A major problem in understanding seismic wave propagation in the seafloor is to distinguish between the loss of energy due to intrinsic attenuation and the loss of energy due to scattering from fine scale heterogeneities and bottom roughness. Energy lost to intrinsic attenuation (heat) disappears entirely from the system. Energy lost to scattering is conserved in the system and can appear in observations as incoherent noise (reverberation, time spread, angle spread) and/or mode converted waves. It has been shown by a number of investigators that the seafloor scattering problem can be addressed by finite difference solutions to the elastic wave equation in the time domain. However previous studies have not considered the role of intrinsic attenuation in the scattering process. In this paper, a formulation is presented which includes the effects of intrinsic attenuation in a two-dimensional finite difference formulation of the elastodynamic equations. The code is stable and yields valid attenuation results.This work was carried out under Office of Naval Research Grant no. N00014-89-J-1012

Site synthesis report of DSPP sites 417 and 418

This document summarizes information relevent to planning, execution, and interpretation of results from a study of the interaction of sound in the 2-30Hz band with deep ocean seafloor using sea-surface sources, seafloor receivers, and borehole seismometers emplaced by wireline re-entry at Deep Sea Drilling Project sites 417 and 418 in the western North Atlantic. We summarize published scientific results from borehole sampling of water, sediment, and rock, from wire line logging, and from borehole seismic experiments. We present new results from analysis of total power recorded by receivers clamped in basement during the borehole seismic experiment on DSDP Leg 102. We document non-drilling investigations of the site and the nature and location of re-entry cones and transponders. We describe the physical oceanography of the region and the speed of sound in water. We provide an extensive bibliography on published results from scientific investigations at 417/418. This document was completed prior to 1989 surveys of sites 417 and 418.Funding was provided by the Johns Hopkins University, Applied Physics Laboratory under contract Number 602809-0

Lateral continuity of basement seismic reflections in 15 Ma ultrafast-spreading crust at ODP Site 1256

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Marine Geophysical Research 32 (2011): 429-439, doi:10.1007/s11001-011-9122-4.The Ocean Drilling Program (ODP) initiated drilling at Site 1256D in the Guatemala Basin, about 1000km off the East Pacific Rise to penetrate plutonic rocks, anticipated to be relatively shallow in this region, formed at an ultra-fast spreading rate. IODP Expedition E312 successfully drilled into gabbros at ~ 1150m in basement. Multi-channel seismic traces show weak laterally coherent sub-basement reflections at borehole depths. Synthetic reflectivity seismograms were computed using a Ricker wavelet and impedance profiles from borehole sonic logs. These seismograms show significant sub-basement amplitude peaks. A zero-offset vertical seismic profile, shot on E312, was processed to investigate the authenticity of these reflections and their relationship to borehole geology. A dual scheme of the median filtering and F-K dip filtering was used. Tests with synthetic seismograms indicate the approach is effective at reasonable SNR levels. Downgoing energy is clearly identified but negligible upgoing energy is visible over random noise. These results indicate that lava flows and igneous contacts in upper ocean crust have significant topography on lateral scales less than the Fresnel Zone (~ 300m) due to igneous and tectonic processes

Bathymetry and sediment thickness survey of the Hawaii-2 cable : cruise report for Kiwi expedition leg 2 on the R/V Roger Revelle

The primary purpose of this cruise was to identify at least two potential observatory sites along the Hawaii-2 cable that would be suitable for drilling a hole to basement. There is a funded program, the Hawaii-2 Observatory (H20), to install a junction box on the cable about mid-way between California and Hawaii (Figures 1 and 2). We want to identify sites in advance so that drilling will be possible near the observatory. This will permit a large range of borehole experiments to be cared out continuously and in real time. Based on available data we chose a section of cable between 140° and 143°W. This cable lies on a ribbon of 'normal' oceanic crust with well defined magnetic anomalies and relatively smooth bathymetry. The goals were to acquire SEABEAM bathymetry data and single channel seismic reflection data along this section of cable, to identify at least two potential sites along the cable and to car out SCS surveys within about 10km radius of the sites. Since the H20 cable has been given to the scientific community it is a valuable resource for research. While transiting to and from the site we felt that it would be wortwhile to acquire SEABEAM data along as much of the cable track as possible. This 'spec' data, Seabeam and magnetometer data between 130°W and 155°W may be useful to other investigators in the future.This work was carried out under the JOI Prime Contract OCE-93020477, JOI Budget Code 44505-J130l0

Late Cenozoic geology of the Central Persian (Arabian) Gulf from industry well data and seismic profiles

Industry seismic reflection profiles shot in the 60's and early 70's in the central Persian (Arabian) Gulf are used to map two late Tertiary unconformities, and velocity data from a centrally located well is used to convert travel time to depth to the unconformities. The deeper horizon correlates with a regional unconformity at the end of the Eocene in most wells and dips monotonically to the northeast, whereas the shallower horizon is flatter and correlates with the mid-upper Miocene section in one well. Isopach maps based on wells indicate that sedimentation was relatively uniform across the region until the middle to late Miocene. Sediments deposited since the late Miocene thicken from 100-200 m on the Arabian side of the Gulf to >1000 m near Iran reflecting deposition of sediments eroded from the rapidly uplifting Zagros fold-belt. As a result of the rapid deposition, the velocity gradient in the upper 1 km decreases from ~4 km/sec per km near Arabia to about 2 km/sec per km on the Iranian side of the Gulf.This research was jointly supported by the Office of Naval Research, though grants N00014-96-1-0548 and 96PR04120-00, and by the Naval Oceanographic Offic

Development of an evidence-based practice guideline for UK public health nurses (health visitors) to use with parents of infants at risk of obesity

Introduction: Evidence about effective interventions that reduce obesity risk during infancy is needed. This project aimed to systematically review published Randomised Controlled Trials (RCTs) of behavioural and non-behavioural interventions which address potential risk factors for obesity to inform a guideline for UK health visitors. Methods: A multiprofessional Guideline Development Group (GDG) was convened to undertake a systematic review, based on the National Institute for Health and Clinical Excellence (NICE) guidelines. Findings from the review were used to develop a guideline which was subsequently externally reviewed by national experts and practitioners. Results: We identified 28 RCTs reporting behavioural and non-behavioural interventions delivered during infancy with breastfeeding and/or weight outcomes measured during the first two years of life. A number of on-going studies were also identified. Inclusion criteria for intervention studies included parental breastfeeding intentions and first time parents. Good evidence exists for breastfeeding promotion and support interventions. Evidence exists for parental education around responsive feeding, aspects of infant diet and soothing/sleep expectations. These behavioural components informed the guideline. Despite good evidence that infants fed lower protein formula milk gained less weight compared to milk with higher protein levels, it was not possible to incorporate the evidence from the non-behavioural studies into the guideline. Conclusion: Further research is needed to establish clinically effective interventions for obesity prevention during infancy. Continuous dialogue between commissioners, policy makers, health visitors and parents is essential to ensure existing UK policies are not a barrier to implementing obesity prevention strategies in the first year of life

Guideline for UK midwives/health visitors to use with parents of infants at risk of developing childhood overweight/obesity

A guideline for members of the health visiting team to use with parents of infants at risk of overweight/obesity has been developed. The guideline contains recommendations about identification of infants at risk as well as a number of strategies that could be used for prevention of overweight/obesity. The guideline needs to be applied alongside health visitors’ professional judgement. It is not intended to replace normal UK clinical practice which is guided by the Healthy Child Programme and complements existing guidance such as the Framework for Action for tackling obesity

Signal and noise levels in numerical scattering chamber snapshots

A study was carried out to quantify the level of numerical noise in numerical scattering chamber (NSC) calculations and to compare these noise levels with signal levels of body waves, interface waves and ambient noise. The amplitudes of signal and noise in snapshots from the numerical scattering chamber were quantified at 50 and 65 periods for a few reference models. Models with homogeneous subseafloor structure were studied to determine the level of numerical noise; models with a wavenumber-correlation length product of one were examined to determine signal levels. Models were run with both Higdon and telegraph equation absorbing boundaries since the numerical noise within the grid depends on the boundary formulation. Amplitudes were measured along data traces obtained at a grid depth of 3.33 λw and at the seafloor. Forward traveling head waves had typical amplitudes of ±125 but may reached ±250 near the direct wave. Diffraction amplitudes were observed up to ±300. Stoneley wave amplitudes ranged from ±800 up to ±20,000. Numerical noise levels were less than ±25 in most areas of the water and less than ±350 along most of the seafloor. Regardless of the absorbing boundary type, however, there was a region of noise extending up to 15 λw behind the first seafloor reflection at 3.33 λw in which noise levels range from ±100 up to ±600. In this region it is difficult to resolve signal from systematic numerical noise.This work was carried out under ONR Grant #N00014-90-J-149