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‘Controls on the Lower Cretaceous Punt Sandstone Member, a massive deep-water clastic deposystem, Inner Moray Firth, UK North Sea’ by J. D. Argent, S. A. Stewart and J. R. Underhill

Petroleum Geoscience, 6, 2000, 275–285

Reservoir Management Ltd, 7 Bon Accord Square, Aberdeen, Scotland AB32 6XH, UK (e-mail:s.cains@rml.co.uk)

J. D. ARGENT and S. A. STEWART

Amerada Hess Limited, 33 Grosvenor Place, London SW1X 7HY, UK (e-mail:john.argent@heass.com;simon.stewart@hess.com)

J. R. UNDERHILL

Department of Geology and Geophysics, University of Edinburgh, Grant Institute, King’s Buildings, West Mains Road, Edinburgh EH9 3JW, UK (e-mail:jru@ginger.ed.ac.uk)

The first 20% of the full text of this article appears below.

S. Cains writes: In this paper the authors correctly surmise that the distribution of the Punt sandstones was controlled by subtle pre-existing basin topography, i.e. the sandstones were deposited in subtle lows. However, it is striking that in the majority of their figures the sandstones are now on structural time highs (e.g. figs 4, 6 and 9b). This author has seen many similar examples in the Eocene and Paleocene of the Central and Northern North Sea. In these situations, interpreters are often keen to believe the sandstones are really located on topographic lows, so the underlying time high is explained as pull-up in time caused by the higher velocity sandstones. However, in this example the sonic logs indicate there is insuffcient velocity contrast to cause the required pull-up. Also, fig. 4 shows that the underlying time structure does not reduce in amplitude and broaden with depth, as would occur under a local velocity anomaly. Above the sandstone in fig. 4 there is some initial drape and differential compaction, but above this there is a parallel-bedded sequence from around 800 to 500 ms twt, with a structural high over the sandstones. These observations suggest that a single late deformation has produced the underlying and overlying structure as seen on fig. 4 at the location of the sandstones. Could the authors comment on whether this relationship of sandstone and structure is seen commonly in their study area? If so, it is unlikely that the later uplift followed exactly an early topographic low just by coincidence. It is more probable that this is some kind of inverted structure.

The most likely mechanism would be a flower structure along a wrench . . . [Full Text of this Article]