Search

Improvements in our capability to reconstruct ancient surface-ocean conditions based on organic-walled dinoflagellate cyst (dinocyst) assemblages from the Southern Ocean provide an opportunity to better establish past position, strength and oceanography of the subtropical front (STF). Here, we aim to reconstruct the late Eocene to early Miocene (37–20 Ma) depositional and palaeoceanographic history of the STF in the context of the evolving Tasmanian Gateway as well as the potential influence of Antarctic circumpolar flow and intense waxing and waning of ice. We approach this by combining information from seismic lines (revisiting existing data and generating new marine palynological data from Ocean Drilling Program (ODP) Hole 1168A) in the western Tasmanian continental slope. We apply improved taxonomic insights and palaeoecological models to reconstruct the sea surface palaeoenvironmental evolution. Late Eocene–early Oligocene (37–30.5 Ma) assemblages show a progressive transition from dominant terrestrial palynomorphs and inner-neritic dinocyst taxa as well as cysts produced by heterotrophic dinoflagellates to predominantly outer-neritic/oceanic autotrophic taxa. This transition reflects the progressive deepening of the western Tasmanian continental margin, an interpretation supported by our new seismic investigations. The dominance of autotrophic species like Spiniferites spp. and Operculodinium spp. reflects relatively oligotrophic conditions, like those of regions north of the modern-day STF. The increased abundance in the earliest Miocene of Nematosphaeropsis labyrinthus, typical for modern subantarctic zone (frontal) conditions, indicates a cooling and/or closer proximity of the STF to the site . The absence of major shifts in dinocyst assemblages contrasts with other records in the region and suggests that small changes in surface oceanographic conditions occurred during the Oligocene. Despite the relatively southerly (63–55∘ S) location of Site 1168, the rather stable oceanographic conditions reflect the continued influence of the proto-Leeuwin Current along the southern Australian coast as Australia continued to drift northward. The relatively “warm” dinocyst assemblages at ODP Site 1168, compared with the cold assemblages at Antarctic Integrated Ocean Drilling Program (IODP) Site U1356, testify to the establishment of a pronounced latitudinal temperature gradient in the Oligocene Southern Ocean.

New data from a continuously cored succession, the Mossy Grove core, near Jackson, central Mississippi, recovered ∼137 m of marine clays (Yazoo Formation), spanning ∼5 Ma and including the critical Eocene–Oligocene transition (EOT) event. These clay-rich sediments yield well-preserved calcareous microfossil and palynomorph assemblages. Here, we present a new organic-walled dinoflagellate cyst (dinocyst) biostratigraphic framework, including the recognition of 23 dinocyst bioevents. These are integrated with new age constraints based on calcareous nannofossil biostratigraphy and a reassessment of the existing radiometric dates and planktonic foraminiferal biostratigraphy, permitting the establishment of a robust and significantly refined age model for the core. According to this new age model, a major increase in sedimentation rate – from ∼2.1 to ∼4.7 cm kyr−1 – is observed at a core depth of ∼89.1 m (∼34.4 Ma). In the new age model the section is significantly older than previously thought, by up to 1 Ma, with the Eocene-Oligocene boundary (∼33.89 Ma) placed ∼34 m below the level previously identified. With these more accurate age estimates, future isotopic and palaeoecological work on this core can be more precisely integrated with other, globally distributed records of the EOT.

The lower Oligocene (Rupelian) successions are climate record archives of the early icehouse world in the Cenozoic. Even though the number of studies focussing on the generally cold Oligocene is increasing, little is known about climatic variations in the mid-latitudes to high latitudes of the Northern Hemisphere. One of the major obstacles is the lack of stratigraphically complete uppermost Eocene to Oligocene successions in these regions. This study focusses on dinoflagellate cysts (dinocysts) from a thick nearly complete Rupelian succession in the Syracuse Oils Norge A/S well 11/10-1 drilled in 1969 in the Norwegian part of the North Sea basin. The well provides a record of mid-latitude dinocyst assemblages, which yield key biostratigraphical and palaeoenvironmental information. All the analyses were undertaken on ditch cutting samples. The dinocyst assemblages confirm that the well penetrates about 600 m of Rupelian sediments and (as supported by correlation with the Nini-1 well) that the lowermost Rupelian (below the top or the last occurrence of Areosphaeridium diktyoplokum) is expanded. These assemblages also indicate the presence of two hiatuses: the first extends from the Lutetian to the Priabonian (equivalent to the D9nb–D12nb zones), and the second spans the Rupelian–Chattian boundary (equivalent to the D14nb subzone or the NSO-5 zone). Despite the risk of caving, the dinocyst assemblages support the existing sequence stratigraphic framework. The assemblages reflect a clear transition from distal to proximal deposition in the vicinity of the site (across the regional seismic sequences OSS-1 – OSS meaning Oligocene seismic sequence – to OSS-2). The proximal deltaic deposits of the OSS-2 regressive system tract (RST) are characterised by pulses of high sea-surface productivity and pronounced shifts in the dinocyst assemblages, reflecting a highly dynamic environment in a restricted marine to marginal marine setting. The Rupelian succession penetrated by well 11/10-1 yields one new species, Areoligera? barskii sp. nov., which is described here in detail. The cold-water-tolerant dinocyst Svalbardella cooksoniae is present in two intervals in the studied succession. These intervals are related to the early Oligocene cooling maxima (the Oi-1a and the Oi-2 events). Furthermore, these two intervals correlate with two local sequence boundaries, suggesting that they are most probably of glacioeustatic origin. From these observations, I postulate that the early icehouse climate played an important role in the depositional development of the Oligocene succession in the North Sea basin. Even though the Eocene–Oligocene transition interval is not complete (i.e. Lutetian to Priabonian is either missing or condensed), well 11/10-1 merits high-resolution studies of the early icehouse climate for the North Sea region. Although any detailed studies should ideally be undertaken on conventional cores instead of ditch cuttings, no such samples spanning the Eocene–Oligocene transition exist in this area.

Detailed, stratigraphically well-constrained environmental reconstructions are available for Paleocene and Eocene strata at a range of sites in the southwest Pacific Ocean (New Zealand and East Tasman Plateau; ETP) and Integrated Ocean Discovery Program (IODP) Site U1356 in the south of the Australo-Antarctic Gulf (AAG). These reconstructions have revealed a large discrepancy between temperature proxy data and climate models in this region, suggesting a crucial error in model, proxy data or both. To resolve the origin of this discrepancy, detailed reconstructions are needed from both sides of the Tasmanian Gateway. Paleocene–Eocene sedimentary archives from the west of the Tasmanian Gateway have unfortunately remained scarce (only IODP Site U1356), and no well-dated successions are available for the northern sector of the AAG. Here we present new stratigraphic data for upper Paleocene and lower Eocene strata from the Otway Basin, southeast Australia, on the (north)west side of the Tasmanian Gateway. We analyzed sediments recovered from exploration drilling (Latrobe-1 drill core) and outcrop sampling (Point Margaret) and performed high-resolution carbon isotope geochemistry of bulk organic matter and dinoflagellate cyst (dinocyst) and pollen biostratigraphy on sediments from the regional lithostratigraphic units, including the Pebble Point Formation, Pember Mudstone and Dilwyn Formation. Pollen and dinocyst assemblages are assigned to previously established Australian pollen and dinocyst zonations and tied to available zonations for the SW Pacific. Based on our dinocyst stratigraphy and previously published planktic foraminifer biostratigraphy, the Pebble Point Formation at Point Margaret is dated to the latest Paleocene. The globally synchronous negative carbon isotope excursion that marks the Paleocene–Eocene boundary is identified within the top part of the Pember Mudstone in the Latrobe-1 borehole and at Point Margaret. However, the high abundances of the dinocyst Apectodinium prior to this negative carbon isotope excursion prohibit a direct correlation of this regional bio-event with the quasi-global Apectodinium acme at the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma). Therefore, the first occurrence of the pollen species Spinizonocolpites prominatus and the dinocyst species Florentinia reichartii are here designated as regional markers for the PETM. In the Latrobe-1 drill core, dinocyst biostratigraphy further indicates that the early Eocene (∼ 56–51 Ma) sediments are truncated by a ∼ 10 Myr long hiatus overlain by middle Eocene (∼ 40 Ma) strata. These sedimentary archives from southeast Australia may prove key in resolving the model–data discrepancy in this region, and the new stratigraphic data presented here allow for detailed comparisons between paleoclimate records on both sides of the Tasmanian Gateway.

Palynological data from four surface sections in northern Tierra del Fuego, southern Argentina, provide a biostratigraphical and palaeoenvironmental framework for the lower member of the La Despedida Formation and the Cabo Peña Formation in their type areas. Selected dinoflagellate cyst (dinocyst) events indicate that the age of the lower member of the La Despedida Formation is Middle Eocene and that of the Cabo Peña Formation is Late Eocene–earliest Oligocene. The age assigned to the La Despedida Formation agrees with determinations based on calcareous microfossils, but there is a potential discrepancy regarding the Cabo Peña Formation. According to recent stratigraphic studies, the Cabo Domingo Group, which includes the Cabo Peña Formation, is Late Eocene–Miocene in age. The palynomorph assemblages from the lower member of the La Despedida Formation contain the endemic ‘Transantarctic Flora’, which reflects marginal marine conditions. The maximum abundance of Enneadocysta spp. reflects more open-sea conditions and a warming event during the late Middle Eocene. The lower part of the Cabo Peña Formation has a high ratio of dinocysts to sporomorphs and an abundance of Nematosphaeropsis lemniscata, Reticulatosphaera actinocoronata and Impagidinium spp., suggesting an oceanic to outer neritic environment. Abundant Gelatia inflata and protoperidiniacean cysts indicate cool surface waters rich in dissolved nutrients. These cold-water markers may reflect the development of the Antarctic Circumpolar Current, an important event in the transition from a greenhouse to an icehouse climate mode. Toward the top of the sections, the lower ratios of dinocysts to sporomorphs, as well as the composition of the dinocyst assemblages, reflect a neritic rather than an oceanic setting. This palynological change may be due to eustatic sea-level lowering caused by cooling during the latest Eocene–earliest Oligocene. A new species, Spiniferites scalenus, is described and the new combination Lingulodinium echinatum proposed; an emendation for the latter species is also proposed.

The organic-walled dinoflagellate cyst Craspeodinium [sic] “ turonicum ” was described in German by Prossl (1990, pp. 108–109) from the Lower to Upper Turonian of the Konrad 101 borehole (NW Germany), translated here as: Diagnosis: The cavate cyst consists of a thicker endophragm and a thinner ectophragm. A rough to fine-mesh reticulum on the inside of the ectophram is partially connected to the endophragm by round or elongate columns. The outer side of the ectophragm is smooth, but partially folded. Description: The ectophragm is to a large part separated from the inner body, particularly in the left lateral region. In the ventral and dorsal area, as well as at the antapex it is closely appressed to the endophragm, with the result that two antapical horns are often visible. The paracingulum is often marked by two narrow parallel sutures. The parasulcus appears mostly not reticulate. The reticulum itself consists of a ‘coarse-meshed’ part of first order; within the thickened parts, a fine-mesh part of second order is superimposed. Based on the absence of the apical operculum, the outline of 6 precingular plates becomes visible. The archaeopyle corresponds to the type tAtI following Helenes (1983). The dinocyst became validly published on specifying a holotype in a succeeding paper (Prossl, 1992). Craspedodinium was questionably placed in the Subfamily Ovoidinioideae (Order Peridiniales) by Fensome et al . (1993), who considered that the archaeopyle is comprised of apical and intercalary …

The dinoflagellate cyst distributions and stratigraphies of two representative Cenomanian/Turonian (C/T) boundary sections from the Maine and Normandy regions of northern France are described. Siliciclastic-rich sediments which characterize the Upper Cenomanian in Maine, contrast with the coeval nodular chalk and hardground lithofacies of Normandy. Both areas display a transition to marly chalks in the Lower Turonian. Dinocyst assemblages are characterized by low diversities (38 taxa) and low overall abundances, and relatively few stratigraphically significant species. The continued occurrence of Epelidosphaeridia spinosa (Cookson & Hughes) Davey in the Upper Cenomanian of Maine is noted. Results are compared and contrasted with those from coeval sections elsewhere in the Anglo-Paris Basin. A major decline in cyst abundance and diversity is typical of the C/T boundary interval, which is characterized by a dominance of tolerant cosmopolitan forms such as Circulodinium distinctum (Deflandre & Cookson) Jansonius, Hystrichosphaeridium bowerbankii Davey & Williams, Oligosphaeridium complex (White) Davey & Williams, Odontochitina costata Alberti; emend. Clarke & Verdier and O. operculata (O. Wetzel) Deflandre & Cookson.

Dinoflagellate cysts (dinocysts) are abundant in the Eocene of the North Sea and provide a high-resolution biostratigraphic zonation. Twelve species are erected to accommodate zonal markers that have not been previously described. These are Areosphaeridium ebdonii, Areosphaeridium michoudii, Cerebrocysta magna, Diphyes brevispinum, Diphyes pseudoficusoides, Hystrichosphaeropsis costae, Hystrichostrogylon clausenii, Membranilarnacia compressa, Phthanoperidinium clithridium, Phthanoperidinium distinctum, Phthanoperidinium powellii and Phthanoperidinium regalis.

Selected dinocyst taxa from the Brent Group equivalent (Bathonian-Aalenian) of the northern North Sea are described. The diagnosis of Dissiliodinium (Drugg 1978) is emended. Two new species: Dissiliodinium willei and Durotrigia aspera are introduced. In addition, several new taxa are informally described and illustrated.

INTRODUCTIONThick sequences of clastic deposits of Late Cretaceous age (1000–1500 m) are present offshore mid and north Norway. Dinoflagellate assemblages from these deposits have arctic affinities and are dominated by species of Chatangiella, Trithyrodinium and Isabelidinium. The First Appearance Datum (FAD) of Heterosphaeridium difficile is an important correlation point within this sequence and is equated with a Turonian age in most current zonal schemes. Our observations on the relative ranges of H. difficile, members of the Endoceratium dettmanniae–E. ludbrookiae plexus and other key index species in well materials offshore mid and north Norway are not consistent with ranges documented from European stratotypes and suggest a Cenomanian age for the correlation point. This note is intended as a basis for discussion pending a more detailed account of these deposits.OBSERVATIONSThree released offshore wells with good control from sidewall and core samples were selected for study. All of the well sections produced rich typical middle Cretaceous dinocyst assemblages with common H. difficile. At some levels typical forms of H. difficile with discrete processes intergrade with morphotypes having shorter, wider, coalescing processes, probably related to species in the Cyclonephelium membraniphorum complex. As recognized here, H. difficile is restricted to forms similar to the holotype, with discrete processes. Species of Endoceratium are present consistently in the lower part of the H. difficile range zone. There is gradation between forms close to E. dettmanniae and E. ludbrookiae to reticulate forms similar to E. lurneri.Well 35/3–5 is located about 190 km . . .

Durotrigia daveyi gen. et sp. nov. is described from the Inferior Oolite (Early Bajocian) of Dorset, England. It is the earliest distinctly tabulated gonyaulacacean dinocyst with a precingular archaeopyle. The archaeopyle is apparently variable, involving the loss of between 1 and 5 precingular plates. This variability poses some interesting taxonomic problems, particularly the implications to the value of the archaeopyle type as a high-level classification criterion. Some possible causes of archaeopyle variability are discussed.

Topotype material of all known species of the Jurassic dinocyst genera Energlynia and Wanaea has been examined, and forms the basis of a brief review of the genera. Observations and interpretations of specific morphological features are presented. A new species Wanaea thysanota is described and the diagnosis of Wanaea digitata emended.

Scanning electron microscope (S.E.M.) observation techniques have enabled paratabulation formulae to be elucidated (in both Kofoidian and Taylor-Evitt notation) for the partiform gonyaulacoid dinocyst genus Druggidium Habib. Archaeopyle variability within the species of this genus is highlighted, further emphasising the uncertainties concerning the taxonomic significance of archaeopyle type. The genus Druggidium is therefore emended, as is the species D. jubatum Duxbury. One new species, D. augustum, is described.