Stratigraphic record of continental breakup, offshore NW Australia
Author(s)
Reeve, Matthew T
Magee, Craig
Jackson, Christopher A-L
Bell, Rebecca E
Bastow, Ian D
Type
Journal Article
Abstract
Continental breakup involves a transition from rapid, fault-controlled syn-rift subsidence to relatively slow, post-breakup subsidence induced by lithospheric cooling. Yet the stratigraphic record of many rifted margins contain syn-breakup unconformities, indicating that episodes of uplift and erosion interrupt this transition. This uplift has been linked to mantle upwelling, depth-dependent extension and/or isostatic rebound. Deciphering the breakup processes recorded by these unconformities and their related rock record is challenging because uplift-associated erosion commonly removes the strata that help constrain the onset and duration of uplift. We examine three major breakup-related unconformities and the intervening rock record in the Lower Cretaceous succession of the Gascoyne and Cuvier margins, offshore NW Australia, using seismic reflection and borehole data. These data show the breakup unconformities are disconformable (non-erosive) in places and angular (erosive) in others. Our recalibration of palynomorph ages from rocks underlying and overlying the unconformities shows: (i) the lowermost unconformity developed between 134.98–133.74 Ma (Intra-Valanginian), probably during the localisation of magma intrusion within continental crust and consequent formation of continent–ocean transition zones (COTZ); (ii) the middle unconformity formed between ca. 134 and 133 Ma (Top Valanginian), possibly coincident with breakup of continental crust and generation of new magmatic (but not oceanic) crust within the COTZs; and (iii) the uppermost unconformity likely developed between ca. 132.5 and 131 Ma (i.e. Intra-Hauterivian), coincident with full continental lithospheric breakup and the onset of seafloor spreading. During unconformity development, uplift was focussed along the continental rift flanks, likely reflecting flexural bending of the crust and landward flow of lower crust and/or lithospheric mantle from beneath areas of localised extension towards the continent (i.e. depth-dependent extension). Our work supports the growing consensus that the ‘breakup unconformity’ is not always a single stratigraphic surface marking the onset of seafloor spreading; multiple unconformities may form and reflect a complex history of uplift and subsidence during continent–ocean transition.
Date Issued
2022-06-01
Date Acceptance
2021-12-23
Citation
Basin Research, 2022, 34 (3), pp.1220-1243
ISSN
0950-091X
Publisher
Wiley
Start Page
1220
End Page
1243
Journal / Book Title
Basin Research
Volume
34
Issue
3
Copyright Statement
© 2022 The Authors. Basin Research published by International Association of Sedimentologists and European Association of Geoscientists and Engineers and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Subjects
basin
breakup
CARNARVON BASIN
CRUST FORMATION
Geology
Geosciences, Multidisciplinary
LITHOSPHERIC BREAKUP
MAGMA-POOR
NORTH-WEST SHELF
palynology
PASSIVE MARGINS
Physical Sciences
rift
RIVER MOUTH BASIN
Science & Technology
SEAWARD-DIPPING REFLECTORS
seismic reflection
SEISMIC-REFLECTION
unconformity
uplift
VOLCANIC MARGIN
Publication Status
Published
Date Publish Online
2022-01-11