Return of `The Fan That Never Was': Westphalian turbidite systems in the Variscan Culm Basin: Bude Formation (south‐west England)

Thirty-®ve years ago, Harold Reading stated (1963; p. 69): `The precise depositional environment of the Bude Sandstones is not easy to establish'. Appropriately, two of his former students are still arguing whether the environment was a storm-affected shelf (Higgs, 1986a, 1987, 1991) or a deep-water fan (Burne, 1969, 1995). The paper by Burne (1995) questions my shelf interpretation, prompting this Discussion. Burne and I agree that deposition took place offshore, in a large Westphalian lake with occasional marine connections, based on faunal aspects and on the lack of evidence for emergence (Goldring & Seilacher, 1971; `Lake Bude' of Higgs 1986b, 1994). We also agree that the majority of the sandstone beds are turbidites, but whereas I argued for river-fed turbidites on a shelf, with storms accounting for both catastrophic rainfall (hence sandy under ows) and accompanying waves, Burne (1995) invokes slump-generated(?) turbidites on a deep-water fan below storm wavebase. The tectonic setting was the northern, passive margin of a foreland basin (Higgs, 1991; Burne, 1995). Burne (1995) argues that all of the sedimentary structures interpreted by Higgs (1991) as indicating shallow-water deposition (above storm wavebase) can also occur in deep-water turbidite settings. These structures are: quasi-symmetrical ripples; irregular cross-lamination; hummocky cross-strati®cation; multidirectional tool marks; and mud-draped scours. Rare symmetrical `wave' ripples occur in the Bude Formation, although Burne (1995; p. 130) points out that: `no convincing illustration of them has been published to date' (his italics). In the following Discussion, I shall sequentially address these and other contentious issues raised by Burne (1995). My intentions are threefold: (1) to question the basis of Burne's fan model; (2) to reiterate evidence for my lake-shelf model; and (3) to explain that the shelf origin has been `masked' for decades by certain unusual facies characteristics, including `slurried' and `slumped' beds formed in situ as seismites, but widely misinterpreted as debris ows and slumps. The shelf-vs.-fan debate is not only interesting academically, but also important economically, because the easily accessible cliffs of Bude are a magni®cent natural laboratory in which to gather data for petroleum-reservoir models.