Abstract
AbstractProducts of onshore passive continental margin erosion are best preserved in offshore sedimentary basins. Therefore, these basins potentially hold a recoverable record of the onshore erosion history. Here, we present apatite fission track (AFT) data for 13 samples from a borehole in the southern Walvis basin, offshore Namibia. All samples show AFT central ages older or similar to their respective stratigraphic ages, while many single grain ages are older, implying none of the samples has been totally annealed post‐deposition. Furthermore, large dispersion in single grain ages in some samples suggests multiple age components related to separate source regions. Using Bayesian mixture modelling we classify single grain ages from a given sample to particular age components to create ‘subsamples’ and then jointly invert the entire dataset to obtain a thermal history. For each sample, the post‐depositional thermal history is required to be the same for all age components, but each component (‘subsample’) has an independent pre‐depositional thermal history. With this approach we can resolve pre‐ and post‐depositional thermal events and identify changes in sediment provenance in response to the syn‐ and post‐rift tectonic evolution of Namibia and southern Africa. Apatite U‐Pb and compositional data obtained during the acquisition of LA‐ICP‐MS FT data are also presented to help track changes in provenance with time. We constrain multiple thermal events linked to the exhumation and burial history of the continental and offshore sectors of the margin over a longer timescale than has been possible using only onshore AFT thermochronological data.
Highlights
The relationship between onshore erosion and the deposition of the products in sedimentary basins (‘source-to-sink’) has been the subject of many studies over the last 20 years or so (see Helland-Hansen et al (2016) for an overview)
We have presented a suite of apatite fission track (AFT) data, acquired using both the EDM and LA-ICP-MS methods, on 13 samples from a borehole from offshore Namibia
We identified AFT age components in each sample, and assigned the AFT data to their most probable age component to produce subsamples
Summary
The relationship between onshore erosion and the deposition of the products in sedimentary basins (‘source-to-sink’) has been the subject of many studies over the last 20 years or so (see Helland-Hansen et al (2016) for an overview). The relationship between onshore erosion and the deposition of the products in sedimentary basins (‘source-to-sink’) has been the subject of many studies over the last 20 years or so (Lee et al, 1997, Cherniak and Watson, 2001) and zircon fission track (ZFT) analysis (closure temperature: 240 ± 50°C) (Hurford, 1986, Bernet, 2009) are typically employed to investigate crustal formation, thermal evolution and sediment routing from the mountain range to the basin. Tend to experience lower magnitudes of erosion, often with protracted or multi-phase erosional histories (Moore et al, 1986; Cogné et al, 2011; Ksienzyk et al, 2014; Wildman et al, 2016; Amidon et al, 2016), the details of which are not resolvable with the higher temperature systems. Resolving the landscape evolution of the Namibian margin and linking this to the development of offshore sedimentary basins remains challenging
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