Facies analysis of three members of the Scarborough Formation (Middle Jurassic : Lower Bajocian) in the Cleveland Basin, northeast England : Blea Wyke, Byland Limestone and Crinoid grit members
The Scarborough Formation is the youngest marine horizon of formation status within the dominantly deltaic Aalenian - Bajocian Ravenscar Group, Cleveland Basin, northeast England. Sedimentary facies analysis has been performed on the three conformable lithostratigraphic units which make up the bulk of the Scarborough Formation outcrop: Blea Wyke, Byland Limestone and Crinoid Grit Members. This form of analysis was performed in an effort to determine the depositional environments of the members. The information derived from the study enables one to trace the palaeogeographic evolution of the Cleveland Basin throughout much of Scarborough Formation times.The clastic Blea Wyke Member [6 facies] is attributed to deposition in a shallow [<4m], essentially microtidal,delta-destructive marine embayment. This embayment formed through non-eustatic marine transgression initiated by the compactional subsidence of an abandoned [Gristhorpe Member] delta lobe. Open to the east, the embayment covered some 2000km2 of the Cleveland Basin when fully established. A range of sand bodies evolved on the silty embayment floor in response to spatial and temporal changes in the wind-forced wave and current regime. These sand bodies included subtidal shoals, laterally extensive storm-emplaced sand blankets, and a classic delta-destructive sheet sand formed through the landward translation of a low-profile barrier bar.Under sustained rate-of-subsidence controlled marine transgression, clastic input to the Blea Wyke Member embayment eventually waned. In response, the overlying Byland Limestone Member [6 facies] was deposited in the western part of the Cleveland Basin in the form of a carbonate-dominated lagoon-barrier-inner shelf complex. The barrier component of the complex evolved through transgressive upward-shoaling under the influence of wind-forced wave and current activity. Composed of pellet lime grainstones, it protected a lagoon within which the dominant deposits were pellet lime mudstones, wackestones and packstones. Lithological and faunal similarities between the lagoon and inner shelf suggest that much of the shelf region may have comprised former back-barrier lagoon-fills exhumed during transgression.Byland Limestone Member times were terminated by an acceleration in the rate of marine transgression followed by tectonic uplift and subsequent geomorphic decay of the major landmass to the north [Mid North Sea High]. Transgression generated an east-west orientated epeiric seaway connecting the Sole Pit Trough with an areally restricted Pennine Massif. Within this seaway, clastic sediment derived chiefly from the Mid North Sea High was deposited in the form of a progradational, regional-scale composite sheet sand body: the Crinoid Grit Member [8 facies]. Deposition occurred under the combined influence of tidal currents, wind-forced currents and wave activity. Three main facies belts are recognised: paralic tidal sandwave complex, storm-dominated inner shelf and sandy middle shelf. The presence of a tidal sandwave complex is particularly interesting; it indicates that the forging of a marine connection to the west of the Cleveland Basin was necessary before tidal cyclicity could become prominent within the basin.