BGS Seabed Geology: Offshore East Anglia version 1.0

The BGS Seabed Geology: Offshore East Anglia digital map provides detailed and accurate characterisation of the seabed geology, based on seabed and shallow-subsurface data. This dataset incorporates three complementary map components (Substrate Geology, Structural Geology, and Geomorphology), provided as discrete layers for viewing within a Geographic Information System (GIS). The bedrock geology of the mapped area comprises Cretaceous age Chalk Group sedimentary rocks. These rocks crop out extensively at seabed across the southern and central parts of the dataset forming an extensive bedrock platform and Europe’s largest known offshore chalk reef. This reef has been designated the Cromer Shoal Chalk Beds Marine Conservation Zone (MCZ) owing to the range of unique floral and faunal habitats that it supports. The Chalk Group is covered across the central (partly) and southern parts of the dataset by natural superficial deposits that accreted during the Quaternary. These include preglacial delta bottom-set (Westkapelle Ground Formation) and delta top-set (Yarmouth Roads Formation); and glacial sediments and landforms that were deposited and formed during at least two separate phases of glaciation that inundated parts of the southern North Sea and adjacent East Anglia during the Middle Pleistocene (Anglian / Elsterian) and Late Pleistocene (Late Devensian / Late Weichselian). Collective geological evidence includes extensive areas of out-cropping subglacial till; the presence of largely concealed and infilled over-deepened (>100 m deep) subglacial tunnel valleys, ice-marginal moraines, and a glacially disrupted chalk surface that includes the development of incised meltwater channels, detached and transported glacitectonic bedrock rafts and megablocks. Post-glacial environments from the Late-Pleistocene – Holocene (prior to marine inundation) included fluvial and estuarine deposition, that together with variable infill of late-glacial valleys are included within the Botney Cut Formation. Holocene marine transgression flooded the region, with shallow marine sedimentation active through modern times resulting in the variable cover of unconsolidated marine sediments, as well as the distribution of extensive current-induced bedforms, e.g., sediment banks, sediment waves and fields of mega ripples which are recorded within the Seabed Geomorphology dataset. Each theme is provided as distinct layers for viewing within a Geographic Information System (GIS). The “Substrate Geology” layer shows the distribution of bedrock and unlithified superficial deposits present at the seabed (below a thin veneer of seabed sediments, ‘one-metre principle’ described below) as a series of polygons; The “Structural Geology” layer represents the structural features observed at rockhead as a polylines layer, and “Geomorphology” theme consists of points, polylines, and polygons layers to portray the main seabed morphological and geomorphological features.