Lower Pleistocene deltaic and marine sediments in boreholes from the central North Sea

Abstract

Lower Pleistocene sediments recovered in boreholes from the Aberdeen Ground Formation in the central North Sea indicate that the unit was deposited in a delta front to prodeltaishallow, open shelf marine setting. Possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin. The delta front sediments consist of interbedded, structureless to laminated sands and muds with organic debris, ferruginous nodules and common soft sediment deformation structures. Sporadic rippled and graded beds, basal scours to beds and starved ripples suggest periodic wavGcurrent reworking. Prodeltalshelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands. One exceptionally thick sand bed may represent a tidal sand body or submarine channel-fill although this remains uncertain. The estuarineklastic nearshore marine sediments include coarse channel-lag deposits and rippled and laminated subtidal sands. A rich microfossil assemblage recovered from the prodeitalshelf marine sequence indicates that deposition occurred under fluctuating climatic conditions.

Early Quaternary sedimentary processes and palaeoenvironments in the central North Sea

“…The Aberdeen Ground Formation is described as marine in nature, and associated lithological descriptions and gamma‐ray logs from the wells indicate background sedimentation is fine silts and clays (Fig. ), in agreement with descriptions from the shallower portions of the Aberdeen Ground Formation (Stoker and Bent, , ; Cameron et al , ; Knudsen and Sejrup, ). Well 30/6‐3 shows a coarsening‐upwards sequence with input of silty sandstones towards the top of the section (Fig.…”

“…Preliminary work on the lower Quaternary succession was undertaken during comprehensive mapping of the North Sea stratigraphy during the 1980s and 1990s, and relied on relatively widely spaced 2D seismic lines, which were calibrated shallow boreholes up to 250 m deep, and numerous short seabed cores up to 6 m long (Caston, ; Holmes, ; Stoker et al , ; Stoker and Bent, , ; Cameron et al , ; Sejrup et al , , , ; Knudsen and Sejrup, ). In the southern North Sea, Middle and Upper Pleistocene glaciogenic deposits are relatively thin; the boreholes and shallow cores were able to penetrate deep into the Lower Pleistocene deltaic and marine sequences, identifying a wide depositional plain from Britain to Denmark that was flooded at the onset of the Quaternary (Cameron et al , , 1989, 1993; Funnell, ; McMillan et al , ; Rose, ), but became subaerially exposed following a marine regression before the Middle Pleistocene (Cameron et al , , , ; Funnell, ).…”

Pockmarks in the Witch Ground Basin, Central North Sea

“…The Witch Ground Basin was again a deposition center during the Quaternary (~600 m of sediment). The shallow sediments and especially the Early Pleistocene sediments of the Aberdeen Ground Formation show evidence for subglacial, glaciomarine, and marine conditions (Buckley, 2012(Buckley, , 2016Rea et al, 2018;Reinardy et al, 2017;Rose et al, 2016;Sejrup et al, 1987;Stoker & Bent, 1987). On seismic reflection sections, the Aberdeen Ground Formation is characterized by laterally continuous, high amplitude reflections (Ottesen et al, 2014).…”

Mid‐Pleistocene thin‐skinned glaciotectonic thrusting of the Aberdeen Ground Formation, Central Graben region, central North Sea

“…), which includes pebbly and sandy sediments containing cold‐water foraminifera (Gatliff et al ., ). The Aberdeen Ground Formation has previously been interpreted as having been deposited in subglacial to proglacial environments of a grounded, tidewater glacier (Stoker and Bent, , ; Sejrup et al ., ), and as such represents the earliest evidence for glacial conditions within the central North Sea (Stoker and Bent, ).…”