Late Neogene planktonic foraminifera of the Cibao Valley (northern Dominican Republic): Biostratigraphy and paleoceanography

An assemblage of planktonic foraminifera is described from 125 samples taken from the Cercado, Gurabo, and Mao Formations in the Cibao Valley, northern Dominican Republic. The primary objectives of this study are to establish a biochronologic model for the late Neogene of the Dominican Republic and to examine sea surface conditions within the Cibao Basin during this interval. The Cercado Formation is loosely confined to Zones N17 and N18 (∼ 7.0–5.9 Ma). The Gurabo Formation spans Zones N18 and N19 (∼ 5.9–4.5 Ma). The Mao Formation is placed in Zone N19 (∼ 4.5–3.6 Ma). Changes in the relative abundances of indicator species are used to reconstruct sea surface conditions within the basin. Increasing relative abundances of Globigerinoides sacculifer and Globigerinoides ruber, in conjunction with a decreasing relative abundance of Globigerina bulloides, suggests the onset of increasing sea surface temperature and salinity in conjunction with diminishing primary productivity at ∼ 6.0 Ma. Abrupt increases in the relative abundances of G. sacculifer and G. ruber at ∼ 4.8 Ma suggest a major increase in sea surface temperature and salinity in the early Pliocene. The most likely mechanism for these changes is isolation of the Caribbean Ocean through progressive restriction of Pacific–Caribbean transfer via the Central American Seaway. Periods of high productivity associated with upwelling events are recorded in the upper Cercado Formation (∼ 6.1 Ma) and in the middle Mao Formation (∼ 4.2 Ma) by spikes in G. bulloides and Neogloboquadrina spp. respectively. The timing of major increases in sea surface salinity and temperature as well as decreasing productivity (∼ 4.8 Ma) and periods of upwelling (∼ 6.1and 4.2 Ma) in the Cibao Basin generally corroborate previously suggested Caribbean oceanographic changes related to the uplift of Panama. Changes in sea surface conditions depicted by paleobiogeographic distributions in the Cibao Basin suggest that shoaling along the Isthmus of Panama had implications in a shallow Caribbean basin as early as 6.0 Ma. Major paleobiologic changes between ∼ 4.8 and 4.2 Ma likely represent the period of final closure of the CAS and a nearly complete disconnection between Pacific and Caribbean water masses. This study illustrates the use of planktonic foraminifera in establishing some paleoceanographic conditions (salinity, temperature, productivity, and upwelling) within a shallow water basin, outlining the connection between regional and localized oceanographic changes

Palynology of the NBP03–01A transect in the Northern Basin, Western Ross Sea, Antarctica: A late Pliocene record

Fifty‐seven samples taken from ten piston cores collected along a transect off the continental margin of the Northern Basin, Ross Sea, Antarctica were analyzed for palynomorphs. Moderately diverse assemblages of marine microplankton and terrestrial palynomorphs were recovered. The palynomorph assemblages have been subdivided into two main groups: the in‐situ flora (including acritarchs, dinoflagellate cysts, leiospheres and prasinophyte algae mainly composed of cymatiosphaerids), and the reworked flora (including dinoflagellate cysts, pollen and spores). The leiospheres are the most abundant palynomorphs. This prominence in the relative abundance of leiospheres has been reported as typical of assemblages found today at the limit between seasonal and pack ice in the Arctic. In‐situ dinoflagellate cysts are sparse. They are mainly represented by Lejeunecysta, which, based on species similarities to those from Cape Roberts, are believed to be of Oligocene to Pliocene age. All other dinoflagellate cysts recovered are the result of reworking from Eocene to Oligocene sediments. Reworked spores and pollen comprise the second most abundant group. They are of moderate diversity and include an Eocene or older assemblage of Nothofagidites, Podocarpaceae and Proteaceae. Other taxa are representative of warmer rainforest vegetation, with Oligocene and Neogene taxa that include representatives of woodland to herbaceous/low shrubby tundra vegetation growing in colder subpolar climates. These assemblages indicate either different periods of deposition or reworking from diverse sources. Through seismic correlation and diatom analysis, the sediments are believed to be Late Pliocene in age. On this basis, it is postulated that the major glacial advance, RSU 2 of Brancolini et al. (1995) or Unconformity 10 (U10) of Bart et al. (2000), occurred before 2.3 Ma, which is the oldest age of in‐situ species recovered in units above U10. As both terrestrial and marine reworked taxa include assemblages of Eocene to Oligocene age, it is assumed that those reworked components were yielded from a single source; most probably Eocene to Oligocene shallow marine strata eroded and transported from the area of Ross Island to the shelf margin through ice streams located in the Drygalsky and Joides basins. © 2006 by AASP Foundation

Local controls on sediment accumulation and distribution in a fjord in the West Antarctic Peninsula: implications for palaeoenvironmental interpretations

We analyse surface sediment and its distribution in Flandres Bay, West Antarctic Peninsula, in order to understand modern day sediment dispersal patterns in a fjord with retreating, tidewater glaciers. The surface sediment descriptions of 41 cores are included in this study. The sediment facies described include muddy diatomaceous ooze, diatomaceous mud, pebbly mud, sandy mud and mud, with scattered pebbles present in most samples. In contrast to a traditional conceptual model of glacial sediment distribution in fjords, grain size in Flandres Bay generally coarsens from the inner to outer bay. The smallest grain size sediments were found in the bay head and are interpreted as fine-grained deposits resulting from meltwater plumes and sediment gravity flows occurring close to the glacier front. The middle of the bay is characterized by a high silt percentage, which correlates to diatom-rich sediments. Sediments in the outer bay have a high component of coarse material, which is interpreted as being the result of winnowing from currents moving from the Bellingshausen Sea into the Gerlache Strait. Palaeoenvironmental reconstructions of glacial environments often use grain size as an indicator of proximity to the ice margin. After a detailed analysis of a large number of cores collected in the study area, our findings highlight the variability in sedimentation patterns within a fjord and provide a valuable evidence of the complexity that may occur in the sedimentary record