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Papers by Mark Pilkington

Meteoritics & Planetary Science, 1997

Due to the effects of erosion, tectonism and burial, impact structures are often obscured or dest... more Due to the effects of erosion, tectonism and burial, impact structures are often obscured or destroyed. Geophysical methods are increasingly being used in detecting the signatures of impact structures. While gravity lows associated with impact structures are well understood, associated magnetic anomaly lows are not. In this study, drill cores from three Canadian impact structures were analyzed for rock magnetic

Meteoritics & Planetary Science, 2004

available online at http://meteoritics.org 1145 Abstract-The 65 Ma Chicxulub impact crater formed... more available online at http://meteoritics.org 1145 Abstract-The 65 Ma Chicxulub impact crater formed in the shallow coastal marine shelf of the Yucatán Platform in Mexico. Impacts into water-rich environments provide heat and geological structures that generate and focus sub-seafloor convective hydrothermal systems. Core from the Yaxcopoil-1 (Yax-1) hole, drilled by the Chicxulub Scientific Drilling Project (CSDP), allowed testing for the presence of an impact-induced hydrothermal system by: a) characterizing the secondary alteration of the 100 m-thick impactite sequence; and b) testing for a chemical input into the lower Tertiary sediments that would reflect aquagene hydrothermal plume deposition. Interaction of the Yax-1 impactites with seawater is evident through redeposition of the suevites (unit 1), secondary alteration mineral assemblages, and the subaqueous depositional environment for the lower Tertiary carbonates immediately overlying the impactites.

GEOPHYSICS, 2006

Separating the fields produced by sources at different depths is a common requirement in the inte... more Separating the fields produced by sources at different depths is a common requirement in the interpretation of potential field data. Approaches to this problem are generally data- or model-based. Data-based methods rely on breaks in the slope of the logarithmic power spectrum of the observed field to design filters that can effect the separation. When the power spectrum shows no identifiable spectral slope breaks, other approaches are necessary. We outline a model-based method that does not depend on power spectral information but requires estimates of the average depths of the source distributions. An ensemble of models is computed based on these known values and a set of filter parameters are determined that produce the closest fit (in a least-squares sense) to the theoretical fields generated by each source distribution. This approach is used to separate basement effects from intrasedimentary sources in magnetic data collected over the Colville Hills, Northwest Territories, Canada.

GEOPHYSICS, 2013

We have developed an approach for the interpretation of magnetic field data that can be used when... more We have developed an approach for the interpretation of magnetic field data that can be used when measured anomalies are affected by significant remanent magnetization components. The method deals with remanent effects by using the normalized source strength (NSS), a quantity calculated from the eigenvectors of the magnetic gradient tensor. The NSS is minimally affected by the direction of remanent magnetization present and compares well with other transformations of the magnetic field that are used for the same purpose. It therefore offers a way of inverting magnetic data containing the effects of remanent magnetizations, particularly when these are unknown and are possibly varying within a given data set. We use a standard 3D inversion algorithm to invert NSS data from an area where varying remanence directions are apparent, resulting in a more reliable image of the subsurface magnetization distribution than possible using the observed magnetic field data directly.

Geophysical Prospecting, 1990

ABDOH, A., COWAN, D. and PILUNGTON, M. 1990. 3D gravity inversion of the Cheshire Basin. Geophysi... more ABDOH, A., COWAN, D. and PILUNGTON, M. 1990. 3D gravity inversion of the Cheshire Basin. Geophysical Prospecting 38,999-101 1.

Abstract The Chicxulub impact in Mexico has been linked to the mass extinction of species at the ... more Abstract The Chicxulub impact in Mexico has been linked to the mass extinction of species at the end of the Cretaceous period. From seismic data collected across the offshore portion of the impact crater, the diameter of the transient cavity is determined to be about 100 km. ...

Lunar and Planetary Science Conference, 2003

Accurate transient and disruption cavity dimensions are critical for estimating the energy releas... more Accurate transient and disruption cavity dimensions are critical for estimating the energy release associated with impact. Transient and disruption cavity size can, in principle, be inferred from morphometric relationships based on crater diameter. However, locating the crater rim can be difficult for eroded terrestrial craters, and existing morphometric relationships are mostly based on observations of extraterrestrial craters where morphologic features at best provide imprecise constraints on the collapsed disruption cavity margin. Fortunately, magnetic survey data collected over terrestrial impact structures demonstrate that collapsed disruption cavity size can be estimated directly from changes in the magnetic anomaly character. A lower bound on this parameter can be defined by the outer limit of short-wavelength, intense magnetic anomalies produced by impact melt and/or suevite deposits. An upper bound is given by the inner limit of magnetic anomaly trends associated with the pre-impact target rock configuration. Using published values of crater diameters (D) and values of collapsed disruption cavity diameters (DCDC) derived from magnetic data for 19 complex terrestrial impact structures, we derive the relationship DCDC = 0.49D. These data and the possibility of geometrical similarity in crater collapse suggest that this relationship is independent of complex crater size over more than a decade of size variation.

Catastrophic Events and Mass Extinctions Impacts and Beyond, May 1, 2001

SEG Technical Program Expanded Abstracts 1992, 1992

International Workshop on Gravity, Electrical & Magnetic Methods and Their Applications, Beijing, China, October 10–13, 2011, 2011

Tectonophysics, 2009

ABSTRACT We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenz... more ABSTRACT We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300 m, 3.5 km and 400 km. The MRA is the largest amplitude (13 nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8–12 km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5 km) aeromagnetic data produces an average magnetization of 2.5 A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt.

$Research paper thumbnail of If geology is fractal, what do we do next?$

SEG Technical Program Expanded Abstracts 2002, 2002