Rex Harland

A record of late Cenozoic stratigraphy, sedimentation and climate change from the Hebrides Slope, NE Atlantic Ocean

A punctuated 103.3 m thick succession of upper Palaeogene to Quaternary sediments has been recovered in a borehole from the upper Hebrides Slope, west of Britain. The borehole proved 11.2m of upper Oligocene, carbonate-rich muds at the base, unconformably overlain by 2.85 m of middle to upper Miocene, glauconitic sands. This is in turn unconformably overlain by 89.25 m of predominantly Plio-Pleistocene sands and muds, with a Holocene sea-bed veneer. The post-Miocene succession is subdivided into two units: the sand-dominated, Pliocene to lower middle Pleistocene, Lower MacLeod sequence between 89.25 and 67.82 m, and the mud-dominated, middle Pleistocene to Holocene, Upper MacLeod sequence above 67.82 m. Regional mapping indicates that these sequences are commonly associated with large-scale shelf-margin progradation and slope-front fan construction. The borehole core provides an excellent record of the transition from pre-glacial to glacial conditions in the mid-latitude NE Atlantic Ocean. Climatic conditions warmer than present prevailed in the late Oligocene, mid- to late Miocene and Pliocene, although the influx of ice-rafted detritus in the late Pliocene marks the onset of climatic deterioration. This deterioration continued, in a fluctuating manner, until the early mid-Pleistocene (0.44 Ma) when fully glacial conditions were established on the Hebridean Margin.

Glacially influenced basin plain sedimentation in the southern Faeroe-Shetland Channel, northwest United Kingdom continental margin

Abstract Quaternary sediments at the southwest end of the Faeroe-Shetland Channel are preserved as a basin plain succession of variable fill geometry and lithology. In high-resolution seismic profiles the basin plain succession is characterised by laterally discontinuous and transparent, mounded lensoid bodies interbedded with acoustically well-layered sediments which display drape and onlapping reflection configurations. The lensoid bodies comprise an up to 50 m thick amalgamated package of mass-flow deposits consisting primarily of debris-flow diamictons. They represent resedimented glacigenic deposits derived from the West Shetland Shelf. Accumulation of these packages was episodic and related to specific rapid phases of downslope resedimentation, most probably concomitant with ice-marginal deposition on the West Shetland Slope. The acoustically well-layered sediments include glaciomarine hemipelagites and contourites. These indicate phases of reduced sediment supply from the adjacent shelf and slope areas, and probably represent the more pervasive “background” sedimentation in the basin. Although weak bottom-current activity may have prevailed throughout the glacial episodes, the onset of vigorous bottom-current circulation occurred at the changeover from a glacial to an interglacial regime. The debris flow packages form about 50% of the basin-plain sediments in this part of the Faeroe-Shetland Channel, thereby forming a significant component of the deep-water succession.

Late Quaternary palaeontology, sedimentology and geochemistry of a vibrocore from the Witch Ground Basin, central North Sea

Abstract Results are detailed from analytical procedures carried out on a single closely sampled 5.7 m long vibrocore from the Witch Ground Basin, central North Sea. Information about the environmental conditions during the deposition of the Witch Ground Formation, of late Weichselian to Holocene age, was obtained by combining the various palaeontological, sedimentological and geochemical results. This has suggested that a complete glaciomarine to marine sequence from before 13,000 to after 10,000 B.P. is present in the central North Sea. An ash layer equated with the Vedde Ash of western Norway has been identified for the first time in the UK sector.

A dinoflagellate cyst record for the last 0.7 Ma from the Rockall Plateau, northeast Atlantic Ocean

Organic-walled dinoflagellate cyst analysis of samples previously used to establish a high resolution oxygen and carbon isotope stratigraphy for the last 0.7 Ma in the northeastern Atlantic is detailed. Data from Hole 552A, Leg 81 of the Deep Sea Drilling Project, drilled on the western flank of the Rockall Plateau reveal peaks of dinoflagellate cyst recovery relatable with isotope stages 1, 11, 13 and 17. Cysts most prersistently present include the oceanic Impagidinium species, Nematosphaeropsb labyrinthea (Ostenfeld) Reid and the ubiquitous Operculodinium centrocarpum (Deflandre & Cookson) Wall. The results offer a correlation between the oceanic oxygen isotope stratigraphy and the dinoflagellate cyst record. The potential for further correlation with the extensive Quaternary marine sequences of the continental shelf around the British Isles is explored. The dinoflagellate cyst signal is an important factor in understanding oceanographic changes both at the surface and at depth.

Quaternary organic‐walled dinoflagellate cysts from the South China sea and their paleoclimatic significance

Abstract Dinoflagellate cyst assemblages from Quaternary sediments recovered in eight cores from the South China Sea add to our understanding of the climate signal recorded at low latitude sites. Changes in the cyst assemblages may relate to fluctuations in sea level and the accompanying alterations in nutrient supply rather than as a direct result of temperature change. In this respect, the cysts of the heterotrophic dinoflagellate genus Protoperidinium allow the recognition of times during which the nutrient supply may have been enhanced.

Late quaternary dinoflagellate cyst biostratigraphy for sediments of the Porcupine basin, offshore western Ireland

Dinoflagellate cyst analysis reveals that two cores from the Porcupine Basin, offshore western Ireland, contain different Quaternary successions. Core 76 consists of Late Devensian sediments (> 13,000 B.P.), overlain uncomformably by Holocene deposits (< 10,000 B.P.), whereas Core 18, sited on a carbonate mound, contains possible early Bolling-Allerod deposits (13,000-11,000 B.P.), overlain also by Holocene sediments. The cyst assemblages within each core indicate marked climatically-induced changes in the palaeoenvironments.

Dinoflagellate cyst biostratigraphy of the last 2.3 Ma from the Rockall Plateau, northeast Atlantic Ocean

The organic-walled dinoflagellate cyst record for Hole 552A of Leg 81 of the Deep Sea Drilling Project is extended to 2.3 Ma. Peaks of dinoflagellate cyst recovery are noted for isotope stages 19, 23, 25 and two unnumbered stages in Cores 7 and 8. Impagidinium cysts are persistently present throughout and especially prominent in the older sediments of Cores 7 and 8 where they are the characteristic component of the oxygen-light units. Younger dinoflagellate cyst assemblages from isotope stages 19, 23 and 25 characteristically contain Nematosphaeropsis labyrinthus (Ostenfeld) Reid, Operculodinium centrocarpum (Deflandre & Cookson) Wall and Spiniferites spp., and are comparable to those recovered from sediments deposited over the last 0.7 Ma. This correlation of dinoflagellate cysts with the oxygen isotope stratigraphy over the last 2.3 Ma may provide a reference section for the eastern North Atlantic Ocean on the western flank of the Rockall Plateau.