UPPER JURASSIC-CRETACEOUS STRATIGRAPHY of the VLIELAND BASIN, and ADJACENT AREAS, the NETHERLANDS Extended Abstract

UPPER JURASSIC-CRETACEOUS STRATIGRAPHY OF THE VLIELAND BASIN, AND ADJACENT AREAS, THE NETHERLANDS Extended Abstract

G. F. W. Herngreen, R. Smit & Th .E. Wong Geological Survey of The Netherlands, P.O. Box 157, 2000 AD Haarlem, The Netherlands

near coastal, environment. They are as Introduction signed to the Delfland Formation. The up This contribution presents an extended ab per part of the formation is developed in a stract intended for the proceedings of the (?paralic) coal facies in the area between symposium: The Jurassic in the southern wells Vlieland Oost-1 and Harlingen-1. Vol Central Graben, H0rsholm, (Denmark) canic ashes as mentioned in previous publi June 15-16, 1989. The full text entitled cations, are not considered to be primary "Tectonostratigraphic development of the tuffs, but are thought to represent reworked Vlieland Basin. The Netherlands" will ap tuffaceous rocks, the pyroclastic compo pear in the Proceedings 1st Conference Eu nents of which were derived from the Zuid ropean Association of Petroleum Geoscien wal-1 Volcano. These strata are included in tists (Berlin: May 29th - June 2nd, 1989). the Wadden Volcanoclastic Member, of the The Vlieland Basin is located in the Delfland Formation (Central Graben northern Netherlands; it covers the NW'ern Group). part of the province of Friesland to the off The Delfland strata are concentrated in shore area of the Frisian Island of Vlieland. two depocentres: The prominent northern It is a NW-SE striking structure which is and southern subbasins which are separated bounded to the W, S and SE by the Texel by the Zuidwal-1 volcanic plug and dome. It IJsselmeer High, and flanked by the Vlie is apparent from a stripped basement pro land High, an extension of the Schill Grund file, constructed after decompaction and un High, in the north, and the North Nether loading that the northern subbasin subsided lands High in the east. more than the southern subbasin. In well In the Vlieland Basin the major Zuidwal Vlieland Oost-1 Delfland deposits of Port gasfield is located, which recently started landian-Ryazanian age are underlain by ma production from the Lower Cretaceous rine strata of the Kimmeridge Clay Forma Vlieland Sandstone. tion (Scruff Group), dated as late Early to Late Portlandian. It is concluded that the Zuidwal-1 volcano acted as a barrier between the two Vlieland Stratigraphic subbasins. It separates the marine realm (Scruff Group) of the SE extension of the Development Central North Sea Graben from the ter Jurassic-Cretaceous boundary strata of lat restrial environment (Delfland Formation) est Kimmeridgian to Ryazanian age, were of the southern Vlieland Subbasin. mainly deposited in a terrestrial, and partly In some wells (Vlieland Oost-1 and Har-

17 lingen-1) the upper part of the Delfland For markably thin (up to about 200 m) in the mation is of Early Ryazanian age: in several area of the Vlieland Basin. An unconform other wells indications for this dating are ity at the top of the Ommelanden Chalk found. This suggests that a hiatus, repre separates Tertiary from Lower Maastrich senting the pre-Albidum Late Ryazanian, tian strata; also other hiatuses could be may exist throughout the entire study area. demonstrated in the Upper Cretaceous se The Vlieland Formation extends to the quence. Outside the Vlieland Basin, a fairly east as far as Leeuwarden, and hence well thick Upper Cretaceous (500 m in Barra beyond the area of sedimentation of the deel-1) and Lower Cretaceous sequence oc Jurassic/Cretaceous boundary strata of the curs, resting on Triassic rocks. The differ Delfland Formation. In the Leeuwarden ar ences in thickness of the Upper Cretaceous ea the Lower Cretaceous rests unconform limestones reflect tectonic inversion. ably on Triassic or Zechstein strata. The Lower Cretaceous transgression started in latest Ryazanian time, equivalent to the Albidum ammonite-zone. Most likely Tectonic Development brackish deposits near the base, and near The structural evolution of the Vlieland Ba shore marine sandstones of Valanginian sin is not fully understood. It underwent a age, form the Vlieland Sandstone Member number of events related to Variscian, Kim of the Vlieland Formation. The Vlieland merian, and Alpine tectonism. It seems Sandstone is a major reservoir rock for gas likely that a sequence of interrelated factors in the northern Netherlands. contributed to the development of this small Around the Valanginian/Hauterivian basin: boundary a remarkably thin sedimentary se quence (e.g. Zuidwal-2) is found within the 1. NW-SE oriented strike-slip faults, initia Vlieland Shale Member. This may be ex ting the formation of a small pull-apart plained by small hiatuses and/or by a con basin, accompanied by volcanism (Zuid densed sequence. This level concides with a wal-1 volcano); marked hiatus extending from the Late Va 2. Loading effect of the Zuidwal volcano; langinian to the Early Hauterivian in the 3. Thermal relaxation; Leeuwarden area. The younger Hauterivian 4. Loading by sediments; and Barremian shales of the Vlieland Shale 5. Minor withdrawal, dissolution or subro Member, which were deposited in a more sion of Zechstein salt. open marine offshore shelf facies, show no major breaks in sedimentation. The Vlie It is assumed that there is an interrelation land shales form an effective seal for the ship between the Vlieland Basin and the Vlieland Sandstone reservoir rock. major geological structures surrounding it, The typical tripartite subdivision of the in particular the Central North Sea Graben Holland Formation (a mainly marly se (CNSG) and the Lower Saxony Basin quence of Aptian to Albian age) is well (LSB). The link is in the form of an as yet developed in the studied area. A major re ill-defined, partly speculative, transform gional hiatus - representing at least the fault zone passing north of the Texel-Ussel Lower Aptian - is present near the base of meer High (TYH). A stable "Northwest the Holland Formation. This unconformity German Block" rotated anti-clockwise with includes the entire Aptian in the Leeuwar respect to the TYH and areas west of the den area, where red rocks of Albian age rest CNSG and south of the LSB, causing right on Barremian sediments. lateral slip along a diffuse transform fault Finally, the Upper Cretaceous Texel and zone. Approximately NW-SE striking Car Ommelanden Chalk Formations are re- boniferous faults are thought to have been

18 reactivated in latest Middle or earliest Late 3. During the Portlandian the Zuidwal-1 Jurassic times. volcano acted as a barrier separating a marine facies, which is related to the Central North Sea Graben, from a ter restrial one in the southeastern part of Conclusions/Summary the basin. 1. The Vlieland Basin is considered to be a 4. There is no evidence for an Upper Juras pull-apart basin, tectonically related to sic Lower Saxony facies ( calcareous and the Central North Sea Graben and the evaporitic). Lower Saxony Basin. 5. The Wadden Volcanoclastic sediments, 2. The Vlieland Basin, with mainly Portlan previously considered to be of primary dian and Ryazanian infilling, is a rela volcanic origin, presumably represent re tively young basin as compared with the worked material from the Zuidwal-1 vol Central North Sea Graben, where sedi cano. mentation started in Callovian time.