Interpreting the Upper Carboniferous of the Dutch Cleaver Bank High

Abstract

The Dutch Cleaver Bank High is an area that has undergone a uniform structural and sedimentological history since the Lower Carboniferous. It is characterized by an absence of Upper Triassic and Jurassic sediments, and covers an area of some 8000 km 2 .The basement in this part of the Southern North Sea owes its origin to closure of the Tornquist Sea during the Acadian (late Caledonian) orogeny. NW-SE compressive structures were formed which were subsequently reactivated as normal faults during rifting in the late Devonian-Dinantian. Visean carbonates developed over most of the Dutch Cleaver Bank High but towards the Elbow Spit High, Yoredale facies sediments were deposited. After rifting ceased in the early Namurian, a thermal sag basin evolved which was infilled by marine and deltaic sediments of the Millstone Grit sequence.The Coal Measures sequence of Westphalian to early Stephanian age unconformably or disconformably overlies the Millstone Grit. The Coal Measures sequence consists of fluviatile and associated sediments and is at least 1200 m thick. It contains several regionally correlatable lithological units of remarkably constant thickness. Sedimentation appears to have been uninterrupted during the entire Westphalian in this area. This implies that subsidence was sufficiently rapid to counterbalance the tendency for erosion on the continental plain during periods of sea-level fall. The high rate of subsidence is thought to be due to flexure in the foreland of the Variscan mountain belt. The axis of the basin lies to the south of the Dutch Cleaver Bank High. The source area for the sediment was to the north.From base to top of the Coal Measures sequence there is a change in lithology from lacustro-deltaic to poorly drained continental sediments to well-drained continental sediments, indicative of overall terrestrial progradation. However, within this overall trend, higher frequency fluctuations in base level have had significant impact on lithological variations on a scale of 25-375 m. During periods of rapid base-level rise, thick packages of fluviatile sediment were deposited due to a high rate of accommodation on the continental plain. These fluviatile packages are equivalent to transgressive systems tracts (TST).Mapping reservoir intervals within the Coal Measures sequence is made possible by the uniformity of the strata over the entire Dutch Cleaver Bank High. The most important correlative unit is a TST of Westphalian A/B age which consists of a constant 375 m of poorly drained alluvial plain sediment. It represents a fluvial complex with dimensions greater than the Dutch Cleaver Bank High. The unit is highly reflective on seismic due to constructive interference of the seismic wavelet within fining-upwards parasequences of approximately 25 m thickness.A major rifting event occurred at the end of the Stephanian leading to extension, uplift and igneous activity. In places on the Dutch Cleaver Bank High more than 1000 m of the Coal Measures sequence were removed by erosion. The Elbow Spit High was for...

Geological factors controlling Early Carboniferous carbonate platform development in the Netherlands

“…In the Netherlands, a general NW-SE fault pattern is assumed to be of pre-Variscan origin (Quirk 1993). This was based on the structural trends in the northern offshore Dutch sector.…”

Geological controls on the sulphur content of coal seams in the Northumberland Coalfield, Northeast England

“…As a result shallow-water fluvio-deltaic conditions were maintained throughout deposition (Quirk, 1993;O'Mara and Turner, 1999), interrupted periodically by short-lived marine transgressions from the south and southwest, leading to the deposition of thin marine bands. These marine flooding events were of variable magnitude: those which record the greatest Range bars terminated at 10% sulphur.…”

“…In this model, coals form mainly under increasing levels of accommodation space in the transgressive systems tract (TST), up to the maximum flooding surface at the base of the high-stand systems tract (HST), with deeply incised, laterally extensive palaeovalley-fills denoting a low stand sequence boundary unconformity. This model proved difficult to apply to British Coal Measures because unconformably based incised valley-fill sandbodies are absent due to: (1) the lowrelief ramp setting of the alluvial plain, whereby lowering of sea level does not normally lead to erosion (Schumm, 1993;Shanley and McCabe, 1993;Posamentier and Allen, 1993); (2) the lack of any significant basinward shift of facies and stacking patterns indicative of a low stand sequence boundary Holz, 1998;Holz et al, 2002); and (3) the relatively uninterrupted sedimentation during the Westphalian A and B, when subsidence always exceeded base level fall, hence the lack of significant unconformities, except those tectonically induced (Quirk, 1993;O'Mara and Turner, 1999).…”

Reconstruction of burial history, temperature, source rock maturity and hydrocarbon generation in the northwestern Dutch offshore

“…2. A detailed and extensive overview of the regional geology and petroleum geology of the Netherlands and the Cleaverbank Platform is presented by Quirk (1993), TNO-NITG (2004), Duin et al (2006) and Wong et al (2007) and references therein. This geological setting is based on these publications and on the results of the recently completed mapping project (Kombrink et al, this issue).…”

“…This phase of uplift is attributed to rifting in combination with a global fall in sea level and caused widespread erosion in the platform areas (Mid and Late Kimmerian; Ziegler, 1990;. Lower Jurassic and Upper Triassic strata were completely removed in places (Quirk, 1993).…”