Changes in the provenance of pebbly detritus in southern Britain and northern France associated with basin rifting

Abstract

Stratigraphical and geographical variations in the composition of pebble suites in Upper Jurassic and Lower Cretaceous rocks in southern Britain and northern France provide a means for studying both local and regional changes in tectonic conditions associated with basin development. Local variations in pebble suites provide evidence of major fault-associated uplift and erosion of intrabasinal and basin-margin highs during earliest Cretaceous times, and the subsequent post-faulting subsidence and marine onlap in mid-Cretaceous times.Regional provenance studies have demonstrated that the Upper Jurassic and Lower Cretaceous pebble suites of southern Britain and Normandy are separable into six assemblages.

The Lower Albian (Lower Cretaceous) Monk's Bay Sandstone Formation (formerly the Carstone) of the Isle of Wight: Its distribution, litho- and biostratigraphy

“…The base of the formation is marked by a 0.12 m thick pebble-rich unit (Bed 21), containing small, polished quartzite pebbles, up to 10 mm in size. Elsewhere on the island, Garden (1991, Fig. 7D) identified a clast assemblage of rounded quartz pebbles but with significant numbers of Carboniferous "shelf chert" and Jurassic-derived chert pebbles from three sites exposing this basal unit (Red Cliff, Rock and Compton Bay).…”

“…The sediment includes material (pebbles) reworked from Carboniferous and Jurassic strata, the weathered and oxidized pyritic mudstones of the latter contributing to the iron-rich character of the Monk"s Bay Sandstone (Garden, 1991;Ruffell & Garden, 1997). For example, a considerable proportion of limonite grains and small clasts is present in the Monk"s Bay Sandston at Compton and Red Cliff, indicating proximity to a structural high source area.…”

Influence of extensional faults and relay ramp on palaeo‐topography and lacustrine carbonate facies: Purbeck Limestone Group (Upper Jurassic – Lower Cretaceous), Wessex Basin, UK

“…The absence of Purbeck limestones north of the faults and on the footwall blocks is consistent with footwall uplift of this area and indicates either non‐deposition or deposition and subsequent erosion of this area. This is part of the Aptian‐Albian unconformity (Garden, 1991; Harvey & Stewart, 1998; Lake, 1985) prior the deposition of the Gault Formation.…”