Revealing deep structural influences on the Upper Cretaceous Chalk of East Anglia (UK) through inter-regional geophysical log correlations

Abstract

New borehole geophysical log interpretations between Wiltshire and north Norfolk show detailed lateral changes in the spatial relationships of Chalk Group marker beds. They show how marker beds in the Turonian and Coniacian Chalk Group in East Anglia pass laterally into their correlatives further west, and reveal unusual lateral thickness changes affecting stratigraphical intervals in the East Anglian succession. Newly enhanced regional gravity and magnetic data indicate that these thickness changes are probably related to WNW to ESE trending structural lineaments in the Palaeozoic basement rocks of the buried Anglo-Brabant Massif.The later part of the Mid Turonian and early part of the Late Turonian succession across East Anglia is greatly thickened, and shows almost no lateral variability. These relatively soft, smooth-textured chalks equate with thinner, hard, nodular beds formed in both shallow marine and deeper basinal settings elsewhere in southern England. Since it seems unlikely that there was greater sediment accommodation space across East Anglia at this time compared to basinal areas, this thickening may reflect a localised coccoliths productivity pulse, or perhaps a sheltered palaeogeographical position that protected the area from sediment-winnowing marine currents.A residual gravity low across north Norfolk, previously interpreted as a granite pluton, may instead represent two elongated (?fault-bounded) sedimentary basins.

Plio‐Pleistocene fault reactivation within the Crag Basin, eastern UK: implications for structural controls of landscape development within an intraplate setting

“…The subparallel alignment of structures throughout the basin, coupled with the occurrence of similar‐trending Cenozoic structures across southern Britain, northern France and Belgium (e.g. Bevan 1985; Bristow 1985; Vandycke 2002; Woods & Chacksfield 2012; Aldiss 2013) imply that this regional structure is inherited from a pre‐existing tectonic structure (cf. Şengör et al .…”

“…Structures within the Crag Basin may also correspond to older ‘basement’ structures. Woods & Chacksfield (2012) and Woods (2015) draw attention to the inheritance of possible basement structures beneath the study region that influenced sedimentation patterns during the Late Cretaceous. One prominent basement high recognized by deep geophysics is the Sudbury‐Bildeston Ridge (Fig.…”

Under-representation of faults on geological maps of the London region: reasons, consequences and solutions

“…Mortimore (1993Mortimore ( , 2011 and Mortimore and Pomerol (1997) argue that tectonic control of Chalk sedimentology and stratigraphy is widespread, as also shown by Woods and Chacksfield (2012). It is likely, therefore, that the Chalk of East Kent, which includes the classic sections near Dover (Robinson, 1986;Gale, 1989Gale, , 1995Mortimore, 1997) differs somewhat from that found in other parts of southern England: it cannot be assumed to be representative of the Southern Chalk Province (Mortimore et al, 2001) as a whole.…”

“…115-116), which appears to be a surface expression of faults along the north-east margin of the Midlands Microcraton (Mortimore, 2011, fig. 74;Woods and Chacksfield, 2012, fig. 7).…”

Geophysical log characterization of the Flamborough Chalk Formation (Late Cretaceous, Santonian – Early Campanian), East Yorkshire, UK: implications for understanding the onshore and offshore occurrence of the Late Campanian Rowe Chalk Formation

“…A well-established relationship between Chalk stratigraphy and borehole geophysical logs across southern England can be traced northwards into parts of East Anglia (Murray 1986;Mortimore 1986;Mortimore & Pomerol 1987;Woods & Aldiss 2004;Woods 2006;Woods & Chacksfield 2012).…”