Conference Agenda

In this paper, results of an integrated stratigraphic analysis and seismic mapping project (TNO-EBN DeVli Project) are presented. The area of interest comprises the Broad Fourteens and the West Netherlands basins that occupy a large part of the southern Dutch on- and offshore. The stratigraphic interval of interest is the predominantly non-marine Upper Jurassic Schieland Group and the marine Lower Cretaceous Rijnland Group. The Mesozoic basins were affected by the late Cimmerian rift, resulting in complex stratal relationships within rapidly changing paleo-depositional environments and a plethora of lithostratigraphic units that required a sequence stratigraphic perspective. The integrated seismic and stratigraphic approach made it possible to fit the pieces of the lithostratigraphic puzzle into a tectonostratigraphic framework. Seismic sections, time structure maps and time-thickness maps were compiled to better understand the complex evolution of these two basins. One of the most interesting findings is the presence of massive sandstone units, that were previously assigned to different stratigraphic units but are in fact time equivalent and belong to the same tectonostratigraphic mega-sequence. This basin wide event occurs at the transition from the Ryazanian to the Valanginian and reflects erosion of the rift shoulders and redeposition in the rift. In the West Netherlands Basin, this event is embodied in the Delft Sandstone Member, which is the most important targets for geothermal energy in the region. The high level of detail in both the seismic and stratigraphic analysis allowed to propose an alternative depositional model for the unit, in contrast with existing models.

The sedimentary record of the Sverdrup Basin in the Canadian Arctic encompasses all stages of the Cretaceous. Owing to a brief history of research (from 1952) and a limited number of publications (<100) it is manageable to database the entire Cretaceous fossil record of the basin. We completed this task for macrofossils, and have made major progress regarding microfossils and palynomorphs. At present, the database contains more than 3700 entries of two types: 1) approximately 1900 entries pertain to specimens collected by CASP, with each specimen receiving its own entry; 2) approximately 1800 entries document literature data, with each entry corresponding to one species at one locality. All entries are georeferenced and dated to stage level, and can be displayed and interrogated in GIS. Sample coverage of Cretaceous outcrop area is governed by accessibility, both with regard to exposure and logistics, but is reasonably dense, given the often challenging fieldwork conditions. The relevance of the dataset extends beyond the Sverdrup Basin limits given that marine connections via Baffin Bay, North Greenland and the Western Interior existed at times during the Cretaceous, and many species are common to other parts of the Boreal realm. Notable macrofossil records of regional significance include the Berriasian and Valanginian ammonite and bivalve faunas of the Deer Bay Formation, sporadic Albian to Santonian ammonite occurrences, and a Sphenoceramus community from the Santonian–Coniacian boundary interval. Microfossils and palynomorphs are recorded from all stages, and were mostly employed for biostratigraphy, but also hold great palaeoecological potential.

The Mesozoic in Greenland is an almost exclusively siliciclastic sedimentary succession. The Cretaceous is dominated by dark-grey, silty mudstones low in organic carbon and fossils – and has thus been considered boring and of little interest.

We present three Early Cretaceous exceptions with “carbonate” deposition.

1) Vividly-coloured, fauna- and flora-rich Ryazanian–Valanginian mudstone deposits on structural highs. They were considered ‘the first representative of limestone deposition’ since the Late Permian in Greenland, when first described by the early mapping geologist in the 1930-40’ies. However, the amount of carbonate, originating from calcareous nannofossils (CN), only qualify the unit as calcareous mudstones. Calcareous nanofossils as well as various ammonites, belemnites and brachiopods are partly of Tethyan origin and reflect major palaeoceanographic changes.

2) The re-discovery of the mid-1930’ies fauna-rich Hühnerbjerg locality represent pure carbonates that largely originate from inoceramid prisms. The setting was an isolated basement horst submerged in earliest Cretaceous (Valanginian–Hauterivian) and constituted a seamount, protected from siliciclastic input and hosted a rich fauna: brachiopods, in particular, ammonites, nautiloids, belemnites, bivalves, gastropods, crinoids, echinoids, serpulids, corals and crustaceans – and barren of calcareous nannofossils. The mount top carbonates were swept of the sides of the mount and transported in debris flows down the flanks and deposited as packstones and grainstones.

3) Imbedded in dark Barremian mudstones are methane seep carbonates. The seep mounds attracted a rich and diverse fauna and provide a rare preservation window to the otherwise almost barren Barremian marine succession.

In northern Germany the Berriasian stage is represented by an overall brackish sedimentary sequence which was deposited in the landlocked, continuously subsiding Lower Saxony Basin (LSB). The brackish inland sea of the LSB extended for 400 km from west to east and ca. 100 km from south to north. It formed the southernmost extension of the North Sea Basin. The Berriasian deposits are lithologically attributed to the Purbeck and Wealden type facies, with the upper part of the Münder Formation dominated by carbonates and evaporites, and the overlying Bückeberg Group (= German Wealden) by siliciclastics.

This study improves our understanding of the parameters controlling the sedimentation patterns of the German Wealden, which accumulated up to 700 m of siliciclastics in the basin center. An integrated bio- and lithostratigraphic approach helps to reconstruct the spatial distribution and relationship between the different sandstone bodies in the Deister-Hils Embayment of the southeastern margin of the LSB. We provide new micropaleontological data from cores and outcrops, recalibrating the stratigraphic position of the sandstones. We further present an updated biostratigraphic range chart of the well established ostracod zonation. Several intercalated brackish–marine ingressions are documented from the central basin and the coarser grained siliciclastics of the margin, which allow a sequence stratigraphic interpretation. We propose a sequence stratigraphic model, which can also be applied to other parts of the LSB. This model will help to better understand the facies distribution for geothermal and hydrocarbon exploration as well as for potential CO2 storage.

The Lower Cretaceous Tuxen and Sola formations in the Danish Central Graben (North Sea) constitute one of the oldest chalk successions recorded globally. Forming a regionally extensive succession in the Central Graben with similar, age-equivalent units widespread across the southern Boreal Realm, it comprises a heterogeneous mixed carbonate–siliciclastic stratigraphy of predominantly bioturbated pelagic chalks and hemipelagic marlstones and mudstones, which straddle the global early Aptian Oceanic Anoxic Event 1a (OAE-1a). Despite testifying to a dynamic basin-filling history influenced by relative sea-level changes of both eustatic and intra-basinal tectonic origin, the Lower Cretaceous pelagic carbonates are relatively overlooked compared to their Upper Cretaceous – Danian counterparts of the Chalk Group characterized by more homogeneous, clean white chalk. Consequently, the timing, magnitude and depositional controls on these basin events remain to be fully understood.

We present herein an updated depositional and sequence stratigraphic model of the Tuxen and Sola formations in the Danish Central Graben, based on high-resolution sedimentological analysis combined with a new integrated stratigraphic framework from biostratigraphic and well-log data. The succession records c. 20 Myr of transgressive–regressive cycles, superimposed by numerous lower-order events controlled by local, global and (potentially) orbital forcings. The study thereby serves as a benchmark for deciphering sequence stratigraphic controls at multiple scales in pelagic successions, where this distinction is typically challenging.

Opoka is a carbonate-siliceous rock that forms thick Campanian-Maastrichtian successions in Poland, Ukraine, and Russia, and has also been documented in Western Europe (France, Germany, and the Nederlands). Its mineralogical composition has only recently been thoroughly examinated, and studies have revealed that the main component of the insoluble residue (remaining after calcium dissolution) is opal-CT. This silica polymorph forms a siliceous rock network composed of adjoining lepispheres. Opoka is usually characterized by a low content of terrigenous material and contains intercalated horizons of marls and cherts. The latter can be distinguished from flints by their different mineralogical composition—namely, the presence of primary opal-CT, which differs from the nano-α-quartz typical of flints. A common feature of opoka the presence of siliceous sponge fossils, often preserved only as voids resulting from spicule dissolution.

The recognition of opoka mineralogical composition and the origin of its components has helped constrain the Si cycle during pre-Eocene times. This also opens the discussion about the abiotic sources of Si in porewater, and the role of siliceous sponges in delivering Si into sediments, and subsequently contributing to chert formation. Proper mineralogical verification of rock types identified within the Late Cretaceous epicontinental European Basin also sheds new light on existing bathymetric models of chalk and opoka facies distribution.