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The stratigraphy of the mid Cretaceous (Albian) Upper Greensand Formation of the Wessex Basin and South West England, UK

Gallois R., Owen H.

Acta Geologica Polonica

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2018

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Vol. 68, no. 2

161--180

EN

The Upper Greensand Formation, mostly capped by the Chalk, crops out on the edges of a broad, dissected plateau in Devon, west Dorset and south Somerset and has an almost continuous outcrop that runs from the Isle of Purbeck to the Vale of Wardour in south Wiltshire. The Formation is well exposed in cliffs in east Devon and the Isle of Purbeck, but is poorly exposed inland. It comprises sandstones and calcarenites with laterally and stratigraphically variable amounts of carbonate cement, glauconite and chert. The sedimentology and palaeontology indicate deposition in marginal marine-shelf environments that were at times subject to strong tidal and wave-generated currents. The formation of the Upper Greensand successions in the region was influenced by penecontemporaneous movements on major fault zones, some of which are sited over E-W trending Variscan thrusts in the basement rocks and, locally, on minor faults. Comparison of the principal sedimentary breaks in the succession with the sequence boundaries derived from world-wide sea-level curves suggests that local tectonic events mask the effects of any eustatic changes in sea level. The preserved fauna is unevenly distributed, both laterally and stratigraphically. Bivalves, gastropods and echinoids are common at some horizons but are not age-diagnostic. Ammonites are common at a few stratigraphically narrowly defined horizons, but are rare or absent throughout most of the succession. As a result, the age of parts of the succession is still poorly known.

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The stratigraphy of the Upper Greensand Formation (Albian, Cretaceous) of the Isle of Purbeck, Dorset, UK

Gallois R., Owen H.

Acta Geologica Polonica

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2017

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Vol. 67, no. 3

405--424

EN

At its maximum development in the type area on the Devon coast, the Upper Greensand Formation comprises up to 55 m of sandstones and calcarenites with laterally and stratigraphically variable amounts of carbonate cement, glauconite and chert that were deposited in fully marine, shallow-water environments. The formation is divided into three members, in ascending order the Foxmould, Whitecliff Chert and Bindon Sandstone, each of which is bounded by a prominent erosion surface that can be recognised throughout the western part of the Wessex Basin. The full thickness of the formation, up to 60 m, was formerly well exposed in cliffs in the Isle of Purbeck in the steeply dipping limb of the Purbeck Monocline. The upper part of the succession is highly condensed in comparison with the Devon succession and exhibits lateral variations over distances of hundreds of metres that are probably related to penecontemporaneous fault movements. Much of the fauna is not age-diagnostic with the result that the ages of parts of the succession are still poorly known. However, the Isle of Purbeck sections contain diverse ammonite faunas at a few stratigraphically well-defined levels that enable the succession to be correlated with that of east Devon and west Dorset.

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Ammonites and associated macrofauna from the early Late Albian of the Zippelsforde 1/64 core, NE-Germany

Lehmann J., Troger K., Owen H.

Acta Geologica Polonica

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2008

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Vol. 58, no. 4

437-453

EN

The macrofaunal content of an exceptionally fossiliferous Late Albian core section is described from Zippelsforde in the Brandenburg district in eastern Germany. The main faunal horizon includes among others Euhoplites vulgaris, Mortoniceras (Deiradoceras) albense, Neohibolites minimus, Inoceramus cf. anglicus and Actinoceramus sulcatus. This assemblage indicates a Hysteroceras varicosum Zone, Hysteroceras orbignyi Subzone age. That interval is known from the Anglo-Paris as well as from the Lower Saxony Basin in western Germany, but not was previously recorded from the North East German Basin. Therefore, the record fills a palaeogeographical gap between the Albian in the Carpathians and that of Central Europe. The superjacent interval contains Aucellina gryphaeoides, dating it as latest Albian (Mortoniceras (M.) inflatum Zone, late C. auritus Subzone or younger), and thus indicating a significant condensation within the Late Albian.