Dinoflagellate Cyst Analysis Research Articles

A middle pleistocene shallow marine interglacial sequence, inner silver pit, southern north sea: pollen and dinoflagellate cyst stratigraphy and sea-level history

The Sand Hole Formation is a Pleistocene seismic–stratigraphic unit of restricted distribution in the Inner Silver Pit, southern North Sea. Pollen and dinoflagellate cyst analyses of this formation, penetrated by British Geological Survey borehole 81/52A and three juxtaposed vibrocores, enables division of the formation into two sequences of contrasting palaeoclimatic affinity. The lower sequence contains poorly-preserved pollen assemblages of low concentration dominated by residual reworked elements, and is coincident with cold, shallow marine dinoflagellate cyst and foraminiferal assemblages. This sequence overlies till and glacimarine sediments of the Anglian/Elsterian Swarte Bank Formation, and is also interpreted as late Anglian/Elsterian in age. The upper sequence contains well-preserved, high concentration, pollen spectra recording the latter half of an interglacial stage with Hoxnian affinities. The strong terrigenous signal preserved in this sequence suggests a subtidal depositional setting within a region of freshwater influence; correlation of the vibrocores with the longer record preserved in borehole 81/52A indicates that interglacial sedimentation rates increase southwards towards a suggested terrigenous source in the Wash area. The first half of the interglacial cycle is missing, indicating that a hiatus is present between the two sequences preserved within the Sand Hole Formation, but the termination of the interglacial is clearly preserved. The spatial and temporal distribution of the sediments and bounding unconformities in the region are consistent in recording the transgressive ravinement surface, highstand systems tract and subsequent regression within an interglacial eustatic cycle. The character, age and elevation of the preserved facies is typical of a glacio-isostatically controlled emergence cycle and lends support to the notion that this temperate stage (oxygen isotope stage 9) immediately followed extensive glaciation during the late Anglian/Elsterian.

Toxic dinoflagellate “blooms” in the Kattegat, North Sea, during the Holocene

Data are presented on the temporal distribution of the toxic dinoflagellate Gymnodinium catenatum in the Kattegat region of the North Sea. Based on dinoflagellate cyst and pollen analyses and a high resolution chronology, a relationship between climatic and oceanographic variations and the blooming of G. catenatum and other dinoflagellates is demonstrated. Gymnodinium catenatum first migrated into the Kattegat about 6200 yr B.P. and had its first occurrence of high numbers at about 4300–4500 yr B.P. At about 4000 yr B.P., in connection with an oceanographic change and climatic deterioration, the species decreased abruptly and subsequently disappeared. It became re-established again at about 2000 yr B.P. and occurred in massive “blooms” during the so-called mediaeval warm epoch round about 700–800 yr B.P. (1200–1400 A.D.). At the time of the so-called Little Ice Age, approximately 300 yr B.P. (1500–1600 A.D.), G. catenatum again became extinct in the Kattegat area. This study clearly demonstrates that massive “blooms” of toxic dinoflagellates occur in the historical record before any anthropogenic impact on the environment.

A Holocene dinoflagellate cyst record from offshore north-east England

SUMMARY Dinoflagellate cyst analysis of a British Geological Survey vibrocore from offshore north-eastern England has revealed a detailed record of Holocene marine conditions for the western North Sea area. Constrained by radiocarbon dating, the almost complete record reveals an initial warming trend followed by changing environmental conditions that can be best explained in terms of the various influences of Scottish or English Coastal Waters as previously defined. The increasing influence of North Atlantic water is present, as is some lowering of seawater salinity at the site during the interpreted Subatlantic with the possible increased run-off from the rivers Tyne, Wear and Tees. This study shows that dinoflagellate cyst analysis is proving to be a useful tool in the high resolution environmental elucidation of offshore marine Holocene sequences.

Late glacial sea level and ocean margin environmental changes interpreted from biostratigraphic and lithostratigraphic studies of isolation basins in northwest Scotland

Abstract Detailed biostratigraphic and lithostratigraphic analyses from isolation basins at Ardtoe, Rumach, Loch nan Eala and Fearnbeg, northwest Scotland, allow an interpretation of sea level movements and environmental changes within the Lateglacial Interstadial and Younger Dryas (13-10 ka BP ). Microfossil analyses illustrate the gradual transition of the isolation basins from marine basins to freshwater lakes within an area of isostatic uplift. These data provide evidence for a fall in relative sea level in northwest Scotland from the mid-Lateglacial Interstadial to the early Holocene. Pollen, diatom and dinoflagellate cyst (dinocyst) analyses link the oceanic record of major climate and oceanic circulation changes with the terrestrial biostratigraphic record. Movement of the oceanic Polar Front west and north during a period of relative climatic amelioration within the Lateglacial Interstadial and a corresponding change in the position of the North Atlantic Current may be inferred from the dinocyst record. This is followed by a relative cooling.

Regional implications of micropalaeontological and palaeo-environmental investigations of the early Eocene interval in BGS borehole 90/3, offshore NW Scotland

Synopsis In BGS borehole 90/3, drilled 110 km NNW of Cape Wrath, the lowermost interval (96.00–187.50 m below sea bed) consists mainly of claystone, with subordinate sandstone and silt-stone. Lignite is present in thin in situ bands and as derived clasts. Other organic debris is also common. The sandstone is predominantly volcaniclastic. Some local reworking is evident. Preliminary dinoflagellate cyst analysis suggested a Late Cretaceous age for this interval, but this was incompatible with the sediment characteristics and known palaeogeography. Low vitrinite reflectance values obtained from the organic matter (average 0.25) were also inconsistent with some of the dark spore colours observed. Further palynology has confirmed an early Eocene age (Balder Formation/Beauly Member equivalent). The older marine dinoflagellate cysts (of McIntyre Suite affinities) have been reworked into a younger deltaic environment which was receiving eroded Late Cretaceous material as well as locally and contemporaneously derived organic, plant and volcanic debris.

Dinoflagellate cysts and Holocene oceanography of the northeastern Atlantic Ocean

Dinoflagellate cyst analysis of two sediment cores, taken on the continental slope off the western coast of Scotland, has revealed new detail and complexity in the oceanography of the Holocene. Changes in the dinoflagellate cyst assemblages suggest at least three fluctuations in the strength or disposition of the North Atlantic Current over the last 10 Ka together with a consequent change in the oceanographic regime of the northeastern Atlantic. These changes, based on comparison to well- constrained data from the Arctic, include the first influx of the North Atlantic Current at about 10 Ka, together with some change in oceanography at between 8 and 6 Ka and between 4 and 2 Ka. These oceanographic changes are based upon fluctuations in the numbers of dinoflagellate cysts per gram of sediment and by their relative proportions. Dinoflagellate cysts have, therefore, a significant role to play in reconstructing the complex history of Holocene environmental change.

Paleohydrology and paleoclimatology off Northwest Africa during the last glacial-interglacial transition and the Holocene: Palynological evidences

Pollen and dinoflagellate cyst analyses of deep-sea core located off Morocco provide a continuous record of paleoclimatic and paleohydrological change off Northwestern Africa since the last glacial episode. The stratigraphy is given by isotopic analysis ( δ 18O) of planktonic foraminifera, which shows a two-step deglaciation. Xeric conditions on the adjacent land, marked by the increase of steppe taxa ( Artemisia, Chenopodiaceae/Amaranthaceae, Ephedra), and the development of the montane taxon, Cedrus atlantica are observed before Termination IA and during the Younger Dryas. These intervals are also marked by a high abundance of Pinus pollen grains, which indicates a strengthening of the northeastern (NE) trade winds. Variations of the surface water temperatures are shown by the fluctuations of dinoflagellate cyst assemblages which reflect a cooling of the surface waters during Termination IA and the Younger Dryas episode. Intensification of the upwelling system off Morocco resulting from enhanced trade winds occurred during these two key-periods. Quercus forests, which are an important part of the present-day vegetation of the Maghreb region, developed around 8500 yr B.P. Dinoflagellate cyst assemblages suggest that present-day oceanic conditions were established during this period.

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 Bølling-Alleröd 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.

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 &amp; 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.

Dinoflagellate cyst analysis of the basal London Clay of southern England

Dinoflagellate cyst analysis of the basal London Clay of southern England