Basin subsidence and Miocene/Pliocene sedimentary change in the Browse Basin, NW Australia

<p>The upper Miocene to Pliocene interval of the Browse Basin on the Australian North West Shelf (NWS) records a significant paleo-environmental change in its sedimentary record concerning the decay of middle to late Miocene tropical reefs. Seismic observations towards the Pliocene show a clear landward migration of carbonate build-ups in the eastern part of the basin, and very high subsidence rates seem to have outpaced most reef growth in distal shelf-edge positions. Nevertheless, the Scott Reef and the Seringapatam Reef were able to withstand shelf-edge drowning, which indicates a significant contribution of inversion-related uplift for reef survival. The contribution of basin subsidence as a driving factor for this reef decay and survival is still discussed and has not been studied in detail. This study provides an estimate for the laterally and through time changing late Miocene/Pliocene subsidence pattern. A 3D paleo-environmental reconstruction was generated by 3D quantitative backstripping, integrating 3D paleo-waterdepth information derived from seismic-based depositional system interpretation. The base of this analysis is a giant 2D and 3D seismic-reflection data set (>130.000 km&#178;) integrated with borehole data (logs, cores, cuttings), new Sr-isotope dating, X-ray diffractometry (XRD) and microfacies analyses, supporting paleo-bathymetric correction and ties to global sea-level data. The seismic-reflection data is covering a study area extending over 130.000 km&#178; and is supported by industry borehole data (logs, cores, and cuttings), SR-Isotope dating, X-Ray diffractometry (XRD) and microfacies analysis.</p>

Download Full-text

Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

Solid Earth ◽

10.5194/se-11-579-2020 ◽

2020 ◽

Vol 11 (2) ◽

pp. 579-606 ◽

Cited By ~ 1

Author(s):

Craig Magee ◽

Christopher Aiden-Lee Jackson

Keyword(s):

Seismic Reflection ◽

Surface Deformation ◽

3D Structure ◽

Dyke Swarm ◽

Normal Faults ◽

Borehole Data ◽

Seismic Reflection Data ◽

Reflection Data ◽

Dyke Swarms ◽

Nw Australia

Abstract. Dyke swarms are common on Earth and other planetary bodies, comprising arrays of dykes that can extend laterally for tens to thousands of kilometres. The vast extent of such dyke swarms, and their presumed rapid emplacement, means they can significantly influence a variety of planetary processes, including continental break-up, crustal extension, resource accumulation, and volcanism. Determining the mechanisms driving dyke swarm emplacement is thus critical to a range of Earth Science disciplines. However, unravelling dyke swarm emplacement mechanics relies on constraining their 3D structure, which is difficult given we typically cannot access their subsurface geometry at a sufficiently high enough resolution. Here we use high-quality seismic reflection data to identify and examine the 3D geometry of the newly discovered Exmouth Dyke Swarm, and associated structures (i.e. dyke-induced normal faults and pit craters). Dykes are expressed in our seismic reflection data as ∼335–68 m wide, vertical zones of disruption (VZD), in which stratal reflections are dimmed and/or deflected from sub-horizontal. Borehole data reveal one ∼130 m wide VZD corresponds to an ∼18 m thick, mafic dyke, highlighting that the true geometry of the inferred dykes may not be fully captured by their seismic expression. The Late Jurassic dyke swarm is located on the Gascoyne Margin, offshore NW Australia, and contains numerous dykes that extend laterally for > 170 km, potentially up to > 500 km, with spacings typically < 10 km. Although limitations in data quality and resolution restrict mapping of the dykes at depth, our data show that they likely have heights of at least 3.5 km. The mapped dykes are distributed radially across a ∼39∘ wide arc centred on the Cuvier Margin; we infer that this focal area marks the source of the dyke swarm. We demonstrate that seismic reflection data provide unique opportunities to map and quantify dyke swarms in 3D. Because of this, we can now (i) recognise dyke swarms across continental margins worldwide and incorporate them into models of basin evolution and fluid flow, (ii) test previous models and hypotheses concerning the 3D structure of dyke swarms, (iii) reveal how dyke-induced normal faults and pit craters relate to dyking, and (iv) unravel how dyking translates into surface deformation.

Download Full-text

Application of 3D seismic techniques to evaluate ore resources in the West Wits Line goldfield and portions of the West Rand goldfield, South Africa

Geophysics ◽

10.1190/geo2012-0133.1 ◽

2012 ◽

Vol 77 (5) ◽

pp. WC163-WC171 ◽

Cited By ~ 24

Author(s):

Musa S. D. Manzi ◽

Mark A. S. Gibson ◽

Kim A. A. Hein ◽

Nick King ◽

Raymond J. Durrheim

Keyword(s):

Seismic Reflection ◽

Signal To Noise Ratio ◽

Mine Planning ◽

3D Seismic ◽

Borehole Data ◽

The West ◽

Seismic Reflection Data ◽

Witwatersrand Basin ◽

Reflection Data ◽

Time Migration

As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imaging of certain ore horizons in some of the Witwatersrand basin gold mines. The merged historical 3D seismic reflection data acquired for Kloof and South Deep mines forms an integral part of their Ventersdorp Contact Reef mine planning and development programme. The recent advances in 3D seismic technology have motivated the reprocessing and reinterpretation of the old data sets using the latest algorithms, therefore significantly increasing the signal-to-noise ratio of the data. In particular, the prestack time migration technique has provided better stratigraphic and structural imaging in complex faulted areas, such as the Witwatersrand basin, relative to older poststack migration methods. Interpretation tools such as seismic attributes have been used to identify a number of subtle geologic structures that have direct impact on ore resource evaluation. Other improvements include more accurate mapping of the depths, dip, and strike of the key seismic horizons and auriferous reefs, yielding a better understanding of the interrelationship between fault activity and reef distribution, and the relative chronology of tectonic events. The 3D seismic data, when integrated with underground mapping and borehole data, provide better imaging and modeling of critical major fault systems and zones of reef loss. Many faults resolve as multifault segments that bound unmined blocks leading to the discovery and delineation of resources in faulted areas of the mines.

Download Full-text

Predicting Missing Seismic Velocity Values Using Self-Organizing Maps to Aid the Interpretation of Seismic Reflection Data from the Kevitsa Ni-Cu-PGE Deposit in Northern Finland

Minerals ◽

10.3390/min9090529 ◽

2019 ◽

Vol 9 (9) ◽

pp. 529 ◽

Cited By ~ 2

Author(s):

Niina Junno ◽

Emilia Koivisto ◽

Ilmo Kukkonen ◽

Alireza Malehmir ◽

Markku Montonen

Keyword(s):

Seismic Reflection ◽

Seismic Velocity ◽

Seismic Velocities ◽

Self Organizing Map ◽

Borehole Data ◽

Self Organizing Maps ◽

Seismic Reflection Data ◽

Reflection Data ◽

Olivine Pyroxenite ◽

Self Organizing

We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. The site has been the target of extensive seismic reflection surveys, which have revealed a series of reflections beneath the Kevitsa resource area. The interpretation of these reflections has been complicated by disparate borehole data, particularly because of the scarce amount of available sonic borehole logs and the varying practices in logging of borehole lithologies. SOM is an unsupervised data mining method based on vector quantization. In this study, SOM is used to predict missing seismic velocities from other geophysical, geochemical, geological, and geotechnical data. For test boreholes, for which measured seismic velocity logs are also available, the correlation between actual measured and predicted velocities is strong to moderate, depending on the parameters included in the SOM analysis. Predicted reflectivity logs, based on measured densities and predicted velocities, show that some contacts between olivine pyroxenite/olivine websterite-dominant host rocks of the Kevitsa disseminated sulfide mineralization—and metaperidotite—earlier extensively used “lithology” label that essentially describes various degrees of alteration of different olivine pyroxenite variants—are reflective, and thus, alteration can potentially cause reflectivity within the Kevitsa intrusion.

Download Full-text

SALT WELDING DURING CANOPY ADVANCE AND SHORTENING IN THE GREEN CANYON AREA, NORTHERN GULF OF MEXICO

10.31223/x5qk8t ◽

2021 ◽

Author(s):

Christopher Jackson ◽

Sian Evans ◽

Turki Alshammasi

Keyword(s):

Gulf Of Mexico ◽

Seismic Reflection ◽

Analytical Models ◽

3D Seismic ◽

Borehole Data ◽

Seismic Reflection Data ◽

Northern Gulf Of Mexico ◽

Reflection Data ◽

Tectonic System ◽

Migration Pathways

Welds form due to the tectonically-induced thinning and/or dissolution of salt, with their composition and completeness thought to at least partly reflect their structural position within the salt-tectonic system. Despite their importance as seals or migration pathways for accumulations of hydrocarbons and CO2, we have relatively few examples of drilled subsurface welds; such examples would allow us to improve our understanding of the processes and products of welding, and to test analytical models of the underlying mechanics. In this study we integrate 3D seismic reflection and borehole data from the Green Canyon Area of the northern Gulf of Mexico, USA to characterize the geophysical and geological expression of a tertiary weld, as well as its broader salt-tectonic context. These data show although it appears complete on seismic reflection data, the weld contains 124 ft (c. 38 m) of pure halite. This thickness is consistent with the predictions of analytical models, and with observations from other natural examples of subsurface welds. Our observations also support a model whereby compositional fractionation of salt occurs as the salt-tectonic system evolves; in this model, less mobile and/or denser units are typically stranded within the deeper, autochthonous level, trapped in primary welds, or stranded near the basal root of diapirs, whereas less viscous and/or less dense units form the cores of these diapirs and, potentially, genetically related allochthonous sheets and canopies. We also show that shearing of the weld during downslope translation of the overlying minibasin did not lead to complete welding.

Download Full-text

Premine study of shallow coal seams using high‐resolution seismic reflection methods

Geophysics ◽

10.1190/1.1443171 ◽

1991 ◽

Vol 56 (9) ◽

pp. 1494-1503 ◽

Cited By ~ 17

Author(s):

Harvey Henson ◽

John L. Sexton

Keyword(s):

High Resolution ◽

Seismic Reflection ◽

Roof Rock ◽

Drill Hole ◽

Coal Seams ◽

Borehole Data ◽

Seismic Line ◽

Seismic Reflection Data ◽

Reflection Data ◽

Roof Rocks

Geological investigations in the Illinois Basin coalfields have shown that significant differences in safe and economical exploitation of coal depends directly on accurate mapping of the roof rock overlying the seam, as well as on geological structures in the coal measures. In roof rock transition zones above the Herrin (No. 6) coal where the nonmarine Energy shale changes to the Anna shale, a change often occurs from low to high sulfur coal and from low to high stability roof rocks. In many instances, use of borehole data alone is inadequate to locate these features in advance of mining. High‐resolution seismic reflection data collected near Harco, Illinois were used as part of premine planning to help predict roof instability, areas of low sulfur coal, and geologic disturbances. Several faults, channels, and facies changes affecting the Herrin (No. 6) and the Springfield (No. 5) coal seams at depths of 137 m and 167 m, respectively, were interpreted and modeled. One‐ and two‐dimensional synthetic seismograms calculated from geological data from drill holes along the seismic line were used to aid in the interpretion of the seismic reflection data. Results obtained from the high‐resolution reflection survey combined with drill hole information clearly show that use of borehole data alone is inadequate to locate geological features that might affect coal mine operations, even if the boreholes were spaced 25 m apart. Thus, high‐resolution reflection surveying should be employed whenever feasible for the safe and economical exploitation of coal deposits.

Download Full-text