Refining the formation and early evolution of the Eastern North American Margin : new insights from multiscale magnetic anomaly analyses

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 122 (2017): 8724–8748, doi:10.1002/2017JB014308.To investigate the oceanic lithosphere formation and early seafloor spreading history of the North Atlantic Ocean, we examine multiscale magnetic anomaly data from the Jurassic/Early Cretaceous age Eastern North American Margin (ENAM) between 31 and 40°N. We integrate newly acquired sea surface magnetic anomaly and seismic reflection data with publicly available aeromagnetic and composite magnetic anomaly grids, satellite-derived gravity anomaly, and satellite-derived and shipboard bathymetry data. We evaluate these data sets to (1) refine magnetic anomaly correlations throughout the ENAM and assign updated ages and chron numbers to M0–M25 and eight pre-M25 anomalies; (2) identify five correlatable magnetic anomalies between the East Coast Magnetic Anomaly (ECMA) and Blake Spur Magnetic Anomaly (BSMA), which may document the earliest Atlantic seafloor spreading or synrift magmatism; (3) suggest preexisting margin structure and rifting segmentation may have influenced the seafloor spreading regimes in the Atlantic Jurassic Quiet Zone (JQZ); (4) suggest that, if the BSMA source is oceanic crust, the BSMA may be M series magnetic anomaly M42 (~168.5 Ma); (5) examine the along and across margin variation in seafloor spreading rates and spreading center orientations from the BSMA to M25, suggesting asymmetric crustal accretion accommodated the straightening of the ridge from the bend in the ECMA to the more linear M25; and (6) observe anomalously high-amplitude magnetic anomalies near the Hudson Fan, which may be related to a short-lived propagating rift segment that could have helped accommodate the crustal alignment during the early Atlantic opening.J. A. G. and M. T. thank the Department of Geology and Geophysics at Texas A&M University for their support of J. A. G.’s PhD program. M. T. and M. R. K. thank the Department of Earth and Environmental Sciences at Michigan State University for their support during M. R. K.’s MS thesis project, included in this study.2018-05-1

The role of premagmatic rifting in shaping a volcanic continental margin: An example from the Eastern North American Margin

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(11),(2020): e2020JB019576, doi:10.1029/2020JB019576.Both magmatic and tectonic processes contribute to the formation of volcanic continental margins. Such margins are thought to undergo extension across a narrow zone of lithospheric thinning (~100 km). New observations based on existing and reprocessed data from the Eastern North American Margin contradict this hypothesis. With ~64,000 km of 2‐D seismic data tied to 40 wells combined with published refraction, deep reflection, receiver function, and onshore drilling efforts, we quantified along‐strike variations in the distribution of rift structures, magmatism, crustal thickness, and early post‐rift sedimentation under the shelf of Baltimore Canyon Trough (BCT), Long Island Platform, and Georges Bank Basin (GBB). Results indicate that BCT is narrow (80–120 km) with a sharp basement hinge and few rift basins. The seaward dipping reflectors (SDR) there extend ~50 km seaward of the hinge line. In contrast, the GBB is wide (~200 km), has many syn‐rift structures, and the SDR there extend ~200 km seaward of the hinge line. Early post‐rift depocenters at the GBB coincide with thinner crust suggesting “uniform” thinning of the entire lithosphere. Models for the formation of volcanic margins do not explain the wide structure of the GBB. We argue that crustal thinning of the BCT was closely associated with late syn‐rift magmatism, whereas the broad thinning of the GBB segment predated magmatism. Correlation of these variations to crustal terranes of different compositions suggests that the inherited rheology determined the premagmatic response of the lithosphere to extension.Financial support was provided by the U.S. Department of Energy Award DE‐FE‐0026087 to Battelle Memorial Institute under the “Mid‐Atlantic U.S. Offshore Carbon Storage Resource Assessment” Project.2021-04-1

The PROCESS study: a protocol to evaluate the implementation, mechanisms of effect and context of an intervention to enhance public health centres in Tororo, Uganda.

BACKGROUND: Despite significant investments into health improvement programmes in Uganda, health indicators and access to healthcare remain poor across the country. The PRIME trial aims to evaluate the impact of a complex intervention delivered in public health centres on health outcomes of children and management of malaria in rural Uganda. The intervention consists of four components: Health Centre Management; Fever Case Management; Patient- Centered Services; and support for supplies of malaria diagnostics and antimalarial drugs. METHODS: The PROCESS study will use mixed methods to evaluate the processes, mechanisms of change, and context of the PRIME intervention by addressing five objectives. First, to develop a comprehensive logic model of the intervention, articulating the project's hypothesised pathways to trial outcomes. Second, to evaluate the implementation of the intervention, including health worker training, health centre management tools, and the supply of artemether-lumefantrine (AL) and rapid diagnostic tests (RDTs) for malaria. Third, to understand mechanisms of change of the intervention components, including testing hypotheses and interpreting realities of the intervention, including resistance, in context. Fourth, to develop a contextual record over time of factors that may have affected implementation of the intervention, mechanisms of change, and trial outcomes, including factors at population, health centre and district levels. Fifth, to capture broader expected and unexpected impacts of the intervention and trial activities among community members, health centre workers, and private providers. Methods will include intervention logic mapping, questionnaires, recorded consultations, in-depth interviews, focus group discussions, and contextual data documentation. DISCUSSION: The findings of this PROCESS study will be interpreted alongside the PRIME trial results. This will enable a greater ability to generalise the findings of the main trial. The investigators will attempt to assess which methods are most informative in such evaluations of complex interventions in low-resource settings. TRIAL REGISTRATION: Clinicaltrials.gov, NCT01024426

Heat flow in the Western Arctic Ocean (Amerasian Basin)

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(8), (2019): 7562-7587, doi: 10.1029/2019JB017587.From 1963 to 1973 the U.S. Geological Survey measured heat flow at 356 sites in the Amerasian Basin (Western Arctic Ocean) from a drifting ice island (T‐3). The resulting measurements, which are unevenly distributed on Alpha‐Mendeleev Ridge and in Canada and Nautilus Basins, greatly expand available heat flow data for the Arctic Ocean. Average T‐3 heat flow is ~54.7 ± 11.3 mW/m2, and Nautilus Basin is the only well‐surveyed area (~13% of data) with significantly higher average heat flow (63.8 mW/m2). Heat flow and bathymetry are not correlated at a large scale, and turbiditic surficial sediments (Canada and Nautilus Basins) have higher heat flow than the sediments that blanket the Alpha‐Mendeleev Ridge. Thermal gradients are mostly near‐linear, implying that conductive heat transport dominates and that near‐seafloor sediments are in thermal equilibrium with overlying bottom waters. Combining the heat flow data with modern seismic imagery suggests that some of the observed heat flow variability may be explained by local changes in lithology or the presence of basement faults that channel circulating seawater. A numerical model that incorporates thermal conductivity variations along a profile from Canada Basin (thick sediment on mostly oceanic crust) to Alpha Ridge (thin sediment over thick magmatic units associated with the High Arctic Large Igneous Province) predicts heat flow slightly lower than that observed on Alpha Ridge. This, along with other observations, implies that circulating fluids modulate conductive heat flow and contribute to high variability in the T‐3 data set.B.V. Marshall of the U.S. Geological Survey (USGS) was critical to the T‐3 heat flow studies and would have been included as a coauthor on this work if he were not deceased. The original T‐3 heat flow data acquisition program was supported by the USGS and by the Naval Arctic Research Laboratory of the Office of Naval Research. Over the decade of USGS research on T‐3 Ice Island, numerous researchers and technical staff, including B.V. Marshall, P. Twichell, D. Scoboria, J. Tailleur, B. Tailleur, and others, spent months on the island and endured difficult and sometimes dangerous conditions to acquire this data set alongside colleagues from other institutions. Outstanding support from the USGS Menlo Park office, transportation and logistics assistance from other U.S. federal government agencies, Arctic expertise supplied by native Alaskan communities, and collaboration with Lamont researchers made this research program possible. B. Lachenbruch and L. Lawver revived interest in this data set in 2016, and they, along with D. Darby and J. K. Hall, provided ancillary information on T‐3 studies. B. Clarke and M. Arsenault assisted with initial data digitization. We thank M. Jakobsson, R. Saltus, and G. Oakey for providing critical shapefiles and other data and R. Jackson and S. Mukasa for clarification on unpublished information. Reviews by J. Hopper, P. Hart, and W. Jokat improved the manuscript, and V. Atnipp Cross and A. Babb were instrumental in completion of data releases. The USGS's Coastal/Marine Hazards and Resources Program supported C.R. and D.H. between 2016 and 2019, and C.R. used office space provided by the Earth Resources Laboratory at the Massachusetts Institute of Technology during completion of this work. Data in Figure 11 were provided by the U.S. Extended Continental Shelf (ECS) Project. The opinions, findings, and conclusions stated herein are those of the authors and the U.S. Geological Survey, but do not necessarily reflect those of the U.S. ECS Project. Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital data, metadata, and supporting plots for T‐3 heat flow, navigation, and radiogenic heat content, along with Lamont gravity and magnetics data, are available from Ruppel et al. (2019), and the original T‐3 expedition report with explanatory metadata can be downloaded from Lachenbruch et al. (2019)

Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean : evidence for accelerated porosity reduction?

Author Posting. © Crown Copyright, 2015. This article is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 204 (2016): 1-20, doi:10.1093/gji/ggv416.The Canada Basin and the southern Alpha-Mendeleev ridge complex underlie a significant proportion of the Arctic Ocean, but the geology of this undrilled and mostly ice-covered frontier is poorly known. New information is encoded in seismic wide-angle reflections and refractions recorded with expendable sonobuoys between 2007 and 2011. Velocity–depth samples within the sedimentary succession are extracted from published analyses for 142 of these records obtained at irregularly spaced stations across an area of 1.9E + 06 km2. The samples are modelled at regional, subregional and station-specific scales using an exponential function of inverse velocity versus depth with regionally representative parameters determined through numerical regression. With this approach, smooth, non-oscillatory velocity–depth profiles can be generated for any desired location in the study area, even where the measurement density is low. Practical application is demonstrated with a map of sedimentary thickness, derived from seismic reflection horizons interpreted in the time domain and depth converted using the velocity–depth profiles for each seismic trace. A thickness of 12–13 km is present beneath both the upper Mackenzie fan and the middle slope off of Alaska, but the sedimentary prism thins more gradually outboard of the latter region. Mapping of the observed-to-predicted velocities reveals coherent geospatial trends associated with five subregions: the Mackenzie fan; the continental slopes beyond the Mackenzie fan; the abyssal plain; the southwestern Canada Basin; and, the Alpha-Mendeleev magnetic domain. Comparison of the subregional velocity–depth models with published borehole data, and interpretation of the station-specific best-fitting model parameters, suggests that sandstone is not a predominant lithology in any of the five subregions. However, the bulk sand-to-shale ratio likely increases towards the Mackenzie fan, and the model for this subregion compares favourably with borehole data for Miocene turbidites in the eastern Gulf of Mexico. The station-specific results also indicate that Quaternary sediments coarsen towards the Beaufort-Mackenzie and Banks Island margins in a manner that is consistent with the variable history of Laurentide Ice Sheet advance documented for these margins. Lithological factors do not fully account for the elevated velocity–depth trends that are associated with the southwestern Canada Basin and the Alpha-Mendeleev magnetic domain. Accelerated porosity reduction due to elevated palaeo-heat flow is inferred for these regions, which may be related to the underlying crustal types or possibly volcanic intrusion of the sedimentary succession. Beyond exploring the variation of an important physical property in the Arctic Ocean basin, this study provides comparative reference for global studies of seismic velocity, burial history, sedimentary compaction, seismic inversion and overpressure prediction, particularly in mudrock-dominated successions

Results of 1992 seismic reflection experiment in Lake Baikal

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95684/1/eost9857.pd

Arctic deep water ferromanganese-oxide deposits reflect the unique characteristics of the Arctic Ocean

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 3771–3800, doi:10.1002/2017GC007186.Little is known about marine mineral deposits in the Arctic Ocean, an ocean dominated by continental shelf and basins semi-closed to deep-water circulation. Here, we present data for ferromanganese crusts and nodules collected from the Amerasia Arctic Ocean in 2008, 2009, and 2012 (HLY0805, HLY0905, and HLY1202). We determined mineral and chemical compositions of the crusts and nodules and the onset of their formation. Water column samples from the GEOTRACES program were analyzed for dissolved and particulate scandium concentrations, an element uniquely enriched in these deposits. The Arctic crusts and nodules are characterized by unique mineral and chemical compositions with atypically high growth rates, detrital contents, Fe/Mn ratios, and low Si/Al ratios, compared to deposits found elsewhere. High detritus reflects erosion of submarine outcrops and North America and Siberia cratons, transport by rivers and glaciers to the sea, and distribution by sea ice, brines, and currents. Uniquely high Fe/Mn ratios are attributed to expansive continental shelves, where diagenetic cycling releases Fe to bottom waters, and density flows transport shelf bottom water to the open Arctic Ocean. Low Mn contents reflect the lack of a mid-water oxygen minimum zone that would act as a reservoir for dissolved Mn. The potential host phases and sources for elements with uniquely high contents are discussed with an emphasis on scandium. Scandium sorption onto Fe oxyhydroxides and Sc-rich detritus account for atypically high scandium contents. The opening of Fram Strait in the Miocene and ventilation of the deep basins initiated Fe-Mn crust growth ∼15 Myr ago.National Science Foundation Grant Numbers: 1434493, 1713677; NSF-OCE Grant Number: 15358542018-05-0

Gas and gas hydrate distribution around seafloor seeps in Mississippi Canyon, Northern Gulf of Mexico, using multi-resolution seismic imagery

This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 25 (2008): 952-959, doi:10.1016/j.marpetgeo.2008.01.015.To determine the impact of seeps and focused flow on the occurrence of shallow gas hydrates, several seafloor mounds in the Atwater Valley lease area of the Gulf of Mexico were surveyed with a wide range of seismic frequencies. Seismic data were acquired with a deep-towed, Helmholz resonator source (220–820 Hz); a high-resolution, Generator-Injector air-gun (30–300 Hz); and an industrial air-gun array (10–130 Hz). Each showed a significantly different response in this weakly reflective, highly faulted area. Seismic modeling and observations of reversed-polarity reflections and small scale diffractions are consistent with a model of methane transport dominated regionally by diffusion but punctuated by intense upward advection responsible for the bathymetric mounds, as well as likely advection along pervasive filamentous fractures away from the mounds.This work was funded through ONR program element 61153N, and U.S. Department of Energy Grant DE-A126-97FT3423

A photographic and acoustic transect across two deep-water seafloor mounds, Mississippi Canyon, northern Gulf of Mexico

This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 25 (2008): 969-976, doi:10.1016/j.marpetgeo.2008.01.020.In the northern Gulf of Mexico, a series of seafloor mounds lie along the floor of the Mississippi Canyon in Atwater Valley lease blocks 13 and 14. The mounds, one of which was drilled by the Chevron Joint Industry Project on Methane Hydrates in 2005, are interpreted to be vent-related features that may contain significant accumulations of gas hydrate adjacent to gas and fluid migration pathways. The mounds are located not, vert, similar150 km south of Louisiana at not, vert, similar1300 m water depth. New side-scan sonar data, multibeam bathymetry, and near-bottom photography along a 4 km northwest–southeast transect crossing two of the mounds (labeled D and F) reveal the mounds' detailed morphology and surficial characteristics. Mound D, not, vert, similar250 m in diameter and 7–10 m in height, has exposures of authigenic carbonates and appears to result from a seafloor vent of slow-to-moderate flux. Mound F, which is not, vert, similar400 m in diameter and 10–15 m high, is covered on its southwest flank by extruded mud flows, a characteristic associated with moderate-to-rapid flux. Chemosynthetic communities visible on the bottom photographs are restricted to bacterial mats on both mounds and mussels at Mound D. No indications of surficial gas hydrates are evident on the bottom photographPartial support for the research cruises that collected the data for this study was provided by the Department of Energy, National Energy Technology Lab

Significance of northeast-trending features in Canada Basin, Arctic Ocean

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 4156–4178, doi:10.1002/2017GC007099.Synthesis of seismic velocity, potential field, and geological data from Canada Basin and its surrounding continental margins suggests that a northeast-trending structural fabric has influenced the origin, evolution, and current tectonics of the basin. This structural fabric has a crustal origin, based on the persistence of these trends in upward continuation of total magnetic intensity data and vertical derivative analysis of free-air gravity data. Three subparallel northeast-trending features are described. Northwind Escarpment, bounding the east side of the Chukchi Borderland, extends ∼600 km and separates continental crust of Northwind Ridge from high-velocity transitional crust in Canada Basin. A second, shorter northeast-trending zone extends ∼300 km in northern Canada Basin and separates inferred continental crust of Sever Spur from magmatically intruded crust of the High Arctic Large Igneous Province. A third northeast-trending feature, here called the Alaska-Prince Patrick magnetic lineament (APPL) is inferred from magnetic data and its larger regional geologic setting. Analysis of these three features suggests strike slip or transtensional deformation played a role in the opening of Canada Basin. These features can be explained by initial Jurassic-Early Cretaceous strike slip deformation (phase 1) followed in the Early Cretaceous (∼134 to ∼124 Ma) by rotation of Arctic Alaska with seafloor spreading orthogonal to the fossil spreading axis preserved in the central Canada Basin (phase 2). In this model, the Chukchi Borderland is part of Arctic Alaska.Funding for this work was provided in part through the Geological Survey of Canada as part of Canada’s UNCLOS Project and through the U.S. Geological Survey as part of the U.S. Extended Continental Shelf project