Shelf-edge delta and slope deposition in the Upper Callovian – Middle Oxfordian Olympen Formation, East Greenland

The Upper Bajocian – Upper Volgian succession of the Jameson Land Basin in East Greenland forms an overall transgressive–regressive cycle. The Upper Callovian – Middle Oxfordian Olympen Formation represents the first regressive deposits after maximum flooding in the Middle to early Late Callovian. The formation was deposited during two southwards progradational phases separated by a major drowning event in the Early Oxfordian. The first phase was marked by incoming of massive slope and base-of-slope sand (Athene Member), but the delta front and top did not reach the area of present-day exposure. The second phase was initiated by deposition of a thick mud succession (Hades Member) indicating that the delta had shifted far to the north during the drowning event. Southwards progradation of the delta was heralded by gully erosion and the deposition of lenticular bodies of massive slope sand; on this occasion, medium- and largescale cross-bedded sand of the delta front and top (Zeus Member) reached the area. The boundary between Middle–Upper Callovian mudstones in the upper part of the underlying Fossilbjerget Formation and the Upper Callovian Athene Member sandstones formed at the turn-around point between sea-level rise and fall. The Athene Member sandstones are interpreted as an undifferentiated falling stage – lowstand systems tract and span a sequence boundary. The top of the Athene Member is the basinal correlative of the transgressive surface. The basal few metres of the overlying Hades Member mudstones represent the transgressive systems tract and a level with organic-rich mudstones is interpreted to represent the maximum flooding zone. The remainder of the Hades Member and the slope sandstones are assigned to the highstand systems tract. The succeeding cross-bedded delta front sandstones of the Zeus Member are placed in the falling stage systems tract and their sharp base is interpreted as a marine regressive surface of erosion. Comparison of this history with published sea-level curves suggests that the short term changes may be eustatic in origin including the Middle Callovian maximum flooding (K. jason – lower P. athleta Chronozones), Late Callovian regression (P. athleta – Q. lamberti Chronozones), latest Callovian – Early Oxfordian flooding (Q. mariae – C. cordatum Chronozones) and late Early – Middle Oxfordian regression (C. densiplicatum Chronozone).

Biostratigraphy of the Upper Jurassic-Lower Cretaceous bivalves Buchia and Aucellina of eastern Heilongjiang, northeast China

The biostratigraphic significance of the bivalves Buchia and Aucellina in northeast China is assessed. Buchia is abundant in four assemblages of the Dong'anzhen Formation, spanning the Jurassic-Cretaceous boundary: B. russiensis-B. fischeriana (Middle Volgian), B. fischeriana-B. unschensis (Upper Volgian), B. volgensis-B. cf. subokensis-B. cf. okensis-B. unschensis (Berriasian), and B. pacifica (Lower Valanginian). Aucellina is common in two Middle Barremian-Aptian assemblages: A. caucasica-A. aptiensis-A. jeletzkii in the lower part of the Upper Yunshan Formation, Longzhaogou Group, and in the lower part of the Chengzihe Formation, Jixi Group; A. cf. caucasica-A. cf. aptiensis in the upper part of the Upper Yunshan Formation. These assemblages can be correlated on a global scale and are particularly significant in dating the Early Cretaceous coalbearing measures of eastern Heilongjiang.

Stratigraphy, tectonics and palaeogeography of the Jurassic sediments of the areas north of Kong Oscars Fjord, East Greenland

The lithostratigraphic scheme currently in use for the Jurassic rocks of the Jameson Land area in East Greenland is extended northwards to cover the areas to the north, from Kong Oscars Fjord (72o N) to Store Koldewey (77o N). Most emphasis is laid on the Wollaston Forland area, whereas Traill Ø and Geographical Society Ø are only briefly reviewed. Jurassic sediments are all included in the Jameson Land Group except the latest Jurassic (Middle-Upper Volgian) rocks which are grouped into the Wollaston Forland Group together with Lower Cretaceous rocks of Ryazanian-Valanginian age. Only sediments belonging to the Jameson Land Group are treated here. The group is in the Wollaston Forland area divided into two formations: the Vardekløft Formation below and the Bernbjerg Formation above. The Vardekløft Formation is divided into three members: Pelion Member composed of estuarine sandstones of Bathonian-Late Oxfordian age; Jakobsstigen Member (new) composed of shallow shelf sandstones and mudstones of Early-Late Oxfordian age; and the Muslingebjerg Member (new) composed of barrier-lagoon sandstones and coals of presumed Late Oxfordian age. The overlying Bernbjerg Formation (new) is composed of dark often sandy mudstones of Late Oxfordian-Kimmeridgian (Early Volgian) age. The whole succession is at maximum 1 km thick and reflects deposition in progressively deeper water in a shelf area structurally built of slightly westwards tilted roughly N-S orientated fault blocks. Four regional transgressions controlled by basement faulting can be dated to Bathonian, Early Oxfordian, Late Oxfordian, and Early Kimmeridgian. Each transgression was followed by steady subsidence and prograding sedimentation.