Baarli (this issue, pp. 253-255) provides general support for our model of an easterly supply of sediment into the Oslo Region during the latest Ordovician and Rhuddanian. Our block model for the basin is necessarily schematic but, importantly, shows a series of half-grabens with their basement surfaces tilted eastwards. The interplay between fault movement and rate of sediment supply was thus able to produce sea floor topographies which differed from half-graben to half-graben and could show local eastward deepening, but with the overall transport of siliciclastic material into the basin from the east. However, Baarli also provides new and convincing evidence for the derivation of sediment of a new provenance, from the west, during the Aeronian. Our basin model can accommodate this with the continuation of an eastern source and westward dipping palaeoslope in the Hadeland segment of the basin.

C. J. R. Braithwaite & A. W. Owen, Department of Geology and Applied Geology, The University of Glasgow, Lilybank Gardens, Glasgow G12 8QQ, Scotland;
R. A. Heath, 4 Lammerton Terrace, Dundee DD4 7BW, Scotland.