Palynology and Dinocyst Stratigraphy of the Eocene and Oligocene in ODP Leg 105, Hole 647A, Labrador Sea

Abstract

Dinoflagellate cysts were recovered throughout the Paleogene succession of Hole 647A, which contains an almost complete deep-water record of early Eocene through early late Oligocene sedimentation in the Labrador Sea. Dinofla gellate cyst biostratigraphy is in general accord with that provided by other microfossil groups and is consistent with a lower Eocene age, as determined by nannofossils, for basal sediments in Hole 647A. These sediments overlie oceanic crust of Chron 24 age.Dinocyst assemblages indicate outer neritic to oceanic conditions throughout, although the persistent occurrence of Wetzeliellaceae specimens in the lower Eocene suggests a greater influence from shelf environments during this time. Lower Eocene dinocyst assemblages are similar to coeval assemblages from the Rockall Plateau, but those from the middle to upper Eocene have mixed affinities and may be related to the intensification of the proto-Gulf Stream from middle Eocene time. Oligocene dinocyst assemblages suggest the influence of both arctic and North Atlantic water masses at this site. The presence of protoperidineacean species in the upper Eocene and Oligocene may indicate in creased availability of nutrients, perhaps related to increased upwelling or the effects of water-mass mixing.Productive samples are dominated by dinocysts and acritarchs, while sporomorphs are represented mainly by bisaccate pollen. Preservational differences within samples may reflect mixing of penecontemporaneous dinocyst popula tions during the Eocene, and all samples examined may have a considerable allochthonous component. Variability in relative abundance of many species during the Eocene may be related to fluctuating water-mass properties.A total 175 dinocyst and acritarch taxa were recorded from 53 productive samples from the Paleogene. Only one Pa leogene sample was barren of palynomorphs. Of three Miocene samples processed, all were barren.

Upper Middle Eocene to Oligocene Dinoflagellate Biostratigraphy and Assemblage Variations in Hole 913B, Greenland Sea

“…This is consistent with its reported range in the Labrador Sea (Head and Norris, 1989). In Hole 913B, this species occurs sporadically down to Sample 913B-34R-2, 103-105 cm, which suggests that upper Eocene sediments may occur down to this level.…”

“…Just above this, in Sample 913B-35R-2, 103-105 cm, are the lowest occurrences of Corrudinium incompositum and Heteraulacacysta porosa. The lowest reported occurrences of C. incompositum are in the middle Eocene (see Head and Norris, 1989, for detailed discussion), whereas the lowest occurrence of H. porosa is in the upper middle Eocene (Bartonian; Bujak et al, 1980, Williams andBujak, 1985). Thus, the base of the studied interval (Sample 913B…”

“…Sample 913B-20R-2, 98-102 cm, contains Reticulatosphaera actinocoronata and Chiropteridium lobospinosum. These two species are generally considered not to range below the Oligocene (Powell, 1992;Williams et al, 1993;Williams and Bujak, 1985;Haq et al, 1987), although Head and Norris (1989) record R. actinocoronata in the uppermost Eocene at Site 647, and Brinkhuis and Biffi (1993) report it in the uppermost Eocene of central Italy. The presence of C. lobospinosum, however, indicates that this sample is no older than Oligocene.…”

“…Although specimens comparable to the type material of Bujak (in Bujak et al, 1980) occur in Hole 913B, I have also included within my concept forms with some variation in the degree of reticulation, that show morphologies closer to Corrudinium incompositum (see Head and Norris, 1989, for discussion on variations in reticulation and granulation of C. incompositum). Because of my broader taxonomic concept, the range of C. bartonensis may be artificially extended above that of the forms recorded by Bujak.…”

Methods

“…In addition, comparisons were made to relevant northern high-latitude studies, including those of Head and Norris (1989), , Williams and Manum (1999), and Eldrett et al (2004).…”