Bathymetry on a Carboniferous reef

Abstract

Broadhurst, F. M. & Simpson, I. M.: Bathymetry on a Carboniferous reef. In the Lower Carboniferous deposits of Castleton, Derbyshire, well bedded shelf limestones, apparently of shallow water origin, pass northwards into a marginal tract of poorly bedded apron‐reef limestones which dip at about 30° downwards and away from the ‘shelf’. Geopetal infillings of shell cavities in the apron‐reef indicate only minor movement since deposition, and the observed dip must be due to deposition on a sloping sea floor. At certain times this sea floor was colonised by stromatolitic algae and corals such as Lithostrotion at the apron‐reef crest where there was minimum water depth, followed to progressively increasing depths by (1) a fauna dominated by the coral Michelinia, (2) a fauna of small brachiopods, bryozoa, molluscs, trilobites, and other organisms and (3) a fauna dominated by Pseudamussium. At other times crinoidal debris was the dominant component of the apron‐reef, when an alignment of crinoid stems parallel to the dip of the slope occurred at low levels, but a random orientation at the apronreef crest. Other sediments on the apron‐reef are apparently devoid of macrofossils. Volcanic activity occurred during the development of the apron‐reef, and it is suggested that uplift of the shelf area preceded the subaerial flow of a lava tongue which reached and plunged down the apron‐reef slope and into the sea.

Dinantian sedimentation and the basement structure of the Derbyshire Dome

“…Bridges (1984) examined the nature of the southwest margin of the Derbyshire Dome during the Chadian and interpreted the transition to the Widmerpool Gulf as a westward-dipping carbonate ramp. Studies by Ludford et al (1973) and Aitkenhead et al (1985) show that during the Asbian the western margin of the Derbyshire Dome was marked by a distinct shelf margin of a similar type to that described from the Castleton area by Broadhurst and Simpson (1973). These studies support the ramp to rimmed shelf model of sedimentation at the western margin of the Derbyshire Dome proposed by Miller and Grayson (1982) and Grayson and Oldham (in press).…”

Quantitative approaches to palaeozonation and palaeobathymetry of corals and coralline algae in Cenozoic reefs

“…Sometimes, inshore-offshore trends may be directly identified from field data based on morphological and geometrical relationships between facies. This classical approach has been used for numerous studies (Broadhurst & Simpson 1973;Frost 1981;Frost et al 1983;Schafersman 1983;Bloy et al 1989;Copper & Fay 1989;Lehmann & Simo 1989;Stanley 1989;Bosellini & Russo 1992).…”

“…Determination of palaeo-depth is generally based on palaeoenvironmental facies interpretations using indicators derived from biological or sedimentological criteria. When this information is combined with stratigraphic and geometric data it can be used to establish models like onshore-offshore trends or proximality trends (Ziegler 1965;Allen 1967;Seilacher 1967;Broadhurst & Simpson 1973;Benedict & Walker 1978;Aigner & Reineck 1982;Baarli 1985Baarli , 1988Brett et al 1993). Palaeodepths derived from this approach can only be relative, however, because there are neither biological nor sedimentological criteria for precise and absolute water depth.…”

“…Biotic assemblages and community structure (i.e. a synecological approach) can also be informative in palaeobathymetric analysis, as these may be related to depth zones, especially if they are defined along onshoreoffshore trends (Ziegler 1965;Broadhurst & Simpson 1973;Fortey 1975;Fortey & Owens 1978;Benedict & Walker 1978;Petersen 1986;Brett et al 1993). Moreover, statistical techniques can be used to provide information on depth gradients.…”

Changes of palaeozonation patterns within Miocene coral reefs, Gebel Abu Shaar, Gulf of Suez, Egypt

“…This zonation has often been recognized within fossil reefs, although reef assemblages have rarely been studied in detail or quantitatively (Kissling & Lineback 1967;Randall et al 1984;Collins 1988;Budd et al 1989;Ko Ènigshof et al 1991;Stemann & Johnson 1992;Weidlich et al 1993;Bosellini & Perrin 1994;Perrin et al 1995). Fossil reef zonation is usually reconstructed from palaeoenvironmental interpretation of reef facies and sometimes from geometrical relationships between facies, providing identi®cation of inshore±offshore trends (Broadhurst & Simpson 1973;Frost 1981;Frost et al 1983;Schafersman 1983;Copper & Fay 1989;Lehmann & Simo 1989;Bosellini & Russo 1992). Relatively well-preserved reef facies outcropping continuously over some distance, however, allows reefs to be surveyed quantitatively or semi-quantitatively and the palaeozonation of their reef-building assemblages to be recorded more precisely.…”