Glacial sedimentation in ODP Leg 119 samples

Although scientific evidence prior to that from ODP Leg 119 indicates the presence of an ice sheet on East Antarctica by at least the earliest Oligocene, the question as to the size and stability of that initial ice sheet is still contested. Current hypotheses include (1) the presence of a small ice sheet in the earliest Oligocene with stepwise growth during the Neogene, (2) the presence of a continental-sized ice sheet in the late middle Eocene with no major evidence of subsequent deglaciation, and (3) the presence of glacial ice in the earliest Oligocene with a major ice sheet during the mid-Oligocene, followed by growth and decay of several ice sheets with characteristics similar to the temperate ice sheets of the Pleistocene of North America but with changes over a longer time scale (millions of years vs. 100,000 yr). Principal results from Leg 119 suggest the presence of significant late middle and late Eocene glaciation in East Antarctica and the presence of a continental-size ice sheet in East Antarctica during the earliest Oligocene. Although the Leg 119 results provide only glimpses of the Neogene glacial history of East Antarctica, they do provide evidence of fluctuations in the extent of the ice sheet and the waxing and waning of glaciers across the Prydz Bay shelf during the later part of the late Miocene and Pliocene.

A seqüência mafra superior \ Rio Do Sul inferior (Grupo itararé, permocarbonífero) em sondagens testemunhadas da região de mafra (SC), Margem Leste da Bacia do Paraná

The Permo-Carboniferous Harare Group crops out in the Matra area, represented by Campo do Tenente, Mafra and Rio do Sul formations; they correspond in subsurface to Lagoa Azul, Campo Mourão and Tacïba formations. A composite sampling of the Group was performed through drilling of six wells, which average 60 m in depth; three of them cored the depositional sequence here designated as Upper Mafra\Lower Rio do Sul. The Upper Mafra Formation were sampled by TC-4 and BR-5 wells, and it consists of three units: the lower two are sandy, glacial-deltaic and fluvial-deltaic in origin, corresponding to a lowstand tract. The last unit is composed of two dirtying-upward successions of sandstone, diamictite and rhythmite, interpreted as deglaciation/transgressive events, and well represented in BR-5 drilling. The Lower-Rio do Sul Formation (Lontras Shale) is formed by two marine units: the lower one is represented by shale and bioturbated siltstone which culminate the previous deglaciation, transgressive succession, while the upper one, sampled by SL-2 well, is formed by shale and thin, turbidite sandstone, attributed to a highstand tract.

ICE-KEEL SCOUR MARKS IN THE GEOLOGICAL RECORD: EVIDENCE FROM CARBONIFEROUS SOFT-SEDIMENT STRIATED SURFACES IN THE PARANA BASIN, SOUTHERN BRAZIL

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Environmental change within the Balkan region during the past ca. 50 ka recorded in the sediments from lakes Prespa and Ohrid

Abstract. Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth.

Sedimentology of cores from the continental rise west of the Antarctic Peninsula

The continental rise west of the Antarctic Peninsula includes a number of large sediment mounds interpreted as contourite drifts. Cores from six sediment drifts spanning some 650 km of the margin and 48 of latitude have been dated using chemical and isotopic tracers of palaeoproductivity and diatom biostratigraphy. Interglacial sedimentation rates range from 1.1 to 4.3 cm/ka. Glacial sedimentation rates range from 1.8 to 13.5 cm/ka, and decrease from proximal to distal sites on each drift. Late Quaternary sedimentation was cyclic, with brown, biogenic, burrowed mud containing ice-rafted debris (IRD) in interglacials and grey, barren, laminated mud in glacials. Foraminiferal intervals occur in interglacial stages 5 and 7 but not in the Holocene. Processes of terrigenous sediment supply during glacial stages differed; meltwater plumes were more important in stages 2-4, turbidity currents and ice-rafting in stage 6. The terrigenous component shows compositional changes along the margin, more marked in glacials. The major oxides Al2O3 and K2O are higher in the southwest, and CaO and TiO2 higher in the northeast. There is more smectite among the clay minerals in the northeast. Magnetic susceptibility varies along and between drifts. These changes reflect source variations along the margin. Interglacial sediments show less clear trends, and their IRD was derived from a wider area. Downslope processes were dominant in glacials, but alongslope processes may have attained equal importance in interglacials. The area contrasts with the East Antarctic continental slope in the SE Weddell Sea, where ice-rafting is the dominant process and where interglacial sedimentation rates are much higher than glacial. The differences in glacial setting and margin physiography can account for these contrasts.

Radiochemical analyses and contents of organic carbon and CaCO3 in equatorial Pacific Ocean sediments

Uranium series nuclide concentrations have been measured on sediments from five box cores from an equatorial Pacific transect. 230Thexcess activities show discontinuities at the Holocene-glacial boundary as dated by 14C. The glacial sedimentation rates determined by 230Th and 14C are 2.5-3.0 cm/kyr. The Holocene rates from 230Th are much lower than those dated by 14C (1.9-2.3 cm/kyr) because of carbonate dissolution. 230Th sedimentation fluxes exceed water column supply by factors of 1.2-1.8 in the Holocene and 1.8-3.0 in the glacial sections. A number of models have been applied to calculate carbonate dissolution rates. The results show that carbonate dissolution rates in the Holocene (in g/cm**2 kyr) equal 1.5 * 10**-3 exp (1.4D) where D is water depth in kilometers. A point-by- point estimation of sediment fluxes through time show that clay accumulation rates in the area have been near constant at 0.1-0.2 g/cm**2 kyr over the past 20 kyr whereas carbonate accumulation rates have decreased dramatically from 0.6-1.0 g/cm**2 kyr in the glacial sections of the cores to 0.2-0.6 g/cm**2 kyr in the Holocene. The errors caused by the uncertainties in the age of the termination of the last glacial period have been investigated and results show that a range of 11-14 kyr leads to an error upper limit of about 30% in the estimation of CaCO3 dissolution rates. The response time of CaCO3 and 230Thex concentrations in the mixed layer of sediments due to an impulse of change in CaCO3 dissolution rate has also been discussed, showing that the observed changes in carbonate dissolution may be explained in terms of a single or a continuous change, depending upon the thickness of the mixed layer.

Neogene magneto- and biostratigraphy of ODP Leg 104 holes

Silicoflagellate assemblages of ODP Leg 104 Neogene sequences are the basis of an interpretation of changes in the Neogene paleoenvironment of the Norwegian Sea. Fluctuations in the percentages of temperature and nutrient-sensitive taxonomic groups document major changes in sea-surface conditions. A brief, but distinct, cooling event occurred at 18.0-17.5 Ma which resulted in the disappearance of Naviculopsis. Following this early Miocene cooling a long period of increasing surface-water temperature occurred, leading up to a thermal high in the early middle Miocene (14.0 Ma). The early late Miocene (10.0-9.0 Ma) was distinctly cooler than the middle Miocene, but warmer than the remainder of the Neogene. Conditions between 13.0 and 10.0 Ma are unrecorded because of a regional hiatus, which is the earliest evidence for an end to the more temperate and stable conditions of the early to middle middle Miocene. A major plunge in temperatures occurred between 8.5 and 7.4 Ma and during the remainder of the late Miocene and Pliocene; from 7.4 to 2.65 Ma subpolar conditions prevailed. Silicoflagellates disappeared, except for sporadic occurrences, at 2.64 Ma with the beginning of dominant glacial sedimentation. Biogenic opal is absent in sediments younger than 0.76 Ma, indicating the dominance of glacial conditions with extensive sea ice.

Sedimentology and geochemistry on core Co1204

Lakes Prespa and Ohrid, in the Balkan region, are considered to be amongst the oldest lakes in Europe. Both lakes are hydraulically connected via karst aquifers. From Lake Ohrid, several sediment cores up to 15 m long have been studied over the last few years. Here, we document the first long sediment record from nearby Lake Prespa to clarify the influence of Lake Prespa on Lake Ohrid and the environmental history of the region. Radiocarbon dating and dated tephra layers provide robust age control and indicate that the 10.5 m long sediment record from Lake Prespa reaches back to 48 ka. Glacial sedimentation is characterized by low organic matter content and absence of carbonates in the sediments, which indicate oligotrophic conditions in both lakes. Holocene sedimentation is characterized by particularly high carbonate content in Lake Ohrid and by particularly high organic matter content in Lake Prespa, which indicates a shift towards more mesotrophic conditions in the latter. Long-term environmental change and short-term events, such as related to the Heinrich events during the Pleistocene or the 8.2 ka cooling event during the Holocene, are well recorded in both lakes, but are only evident in certain proxies. The comparison of the sediment cores from both lakes indicates that environmental change affects particularly the trophic state of Lake Prespa due to its lower volume and water depth.

(Table 1) Strontium isotope ratios (87Sr/86Sr) of Neogloboquadrina pachyderma (sinistrally coiling) tests from ODP Hole 151-910A

The sediment sequence at Ocean Drilling Program (ODP) Site 910 (556 m water depth) on the Yermak Plateau in the Arctic Ocean features a remarkable "overconsolidated section" from ~19 to 70-95 m below sea floor (m bsf), marked by large increases in bulk density and sediment strength. The ODP Leg 151 Shipboard Scientific Party interpreted the overconsolidated section to be caused by (1) grounding of a marine-based ice sheet, derived from Svalbard and perhaps the Barents Sea ice sheet, and/or (2) coarser-grained glacial sedimentation, which allowed increased compaction. Here I present planktonic foraminiferal d18O data based on Neogloboquadrina pachyderma (sinistrally coiling) that date the termination of overconsolidation near the boundary between isotope stages 16 and 17 (ca. 660 ka). No evidence is found for coarser grained sedimentation, because lithic fragments >150 µm exhibit similar mean concentrations throughout the upper 24.5 m bsf. The overconsolidated section may reflect more extensive ice-sheet grounding prior to ca. 660 ka, suggesting a major change in state of the Svalbard ice sheets during the mid-Quaternary. Furthermore, continuous sedimentation since that time argues against a pervasive Arctic ice shelf impinged on the Yermak Plateau during the past 660 k.y. These findings suggest that Svalbard ice-sheet history was largely independent of circum-Arctic ice-sheet history during the middle to late Quaternary.

(Table 3) Pollen analytical and carpological record of the outcrop Hölle below Dwadieden Park, Rügen Island

Pollen analyses and 14C-datings were carried out on two late glacial profiles from Ruegen Island, Mecklenburg-Vorpommern at the southwestern Baltic coast. The palaeoclimatic and palaeoecologic interpretations were supported by carpological investigations. The organogenic deposits of the 'Hoelle' outcrop near Dwasieden Park were chosen because of their unique stratigraphic position, which according to PANZIG (1989), lay under a m3m-Glacial Till of the Mecklenburg Advance (W3). The results indicated that the initial phase of the late glacial sedimentation in a relatively small and asymmetrical lake basin (in comparison with the larger Nieder- and Credner lake to the southwest), probably had its origin in the older Alleroed (II a) after FIRBAS (1949). The basal clastic sediments were rapidly followed by peat deposits and later, due to a rising water table, by muds rich in organic matter. The area was covered with sparse Betula-(Pinus) forests having heliophilous late-glacial elements typical of the surrounding areas during the younger Alleroed (II b). With the climatic change to colder and drier conditions at the beginning of the Younger Dryas (III), the vegetation decreased and enhanced erosional processes led to the fill up of the depression with fine clastic sediments. The intense relief differences of the surroundings coupled with high water saturation in the sediments led to solifluction in the m3m-Glacial Till and its placement discordantly over the organogenic sequence.

Seafloor spreading magnetic anomaly isochron map compilation for the Weddell Sea and Scotia Sea

The deep sea sedimentary record is an archive of the pre-glacial to glacial development of Antarctica and changes in climate, tectonics and ocean circulation. Identification of the pre-glacial, transitional and full glacial components in the sedimentary record is necessary for ice sheet reconstruction and to build circum-Antarctic sediment thickness grids for past topography and bathymetry reconstructions, which constrain paleoclimate models. A ~3300 km long Weddell Sea to Scotia Sea transect consisting of multichannel seismic reflection data from various organisations, were used to interpret new horizons to define the initial basin-wide seismostratigraphy and to identify the pre-glacial to glacial components. We mapped seven main units of which three are in the inferred Cretaceous-Paleocene pre-glacial regime, one in the Eocene-Oligocene transitional regime and three units in the Miocene-Pleistocene full glacial climate regime. Sparse borehole data from ODP leg 113 and SHALDRIL constrain the ages of the upper three units. Compiled seafloor spreading magnetic anomalies constrain the basement ages and the hypothetical age model. In many cases, the new horizons and stratigraphy contradict the interpretations in local studies. Each seismic sedimentary unit and its associated base horizon are continuous and traceable for the entire transect length, but reflect a lateral change in age whilst representing the same deposition process. The up to 1240 m thick pre-glacial seismic units form a mound in the central Weddell Sea basin and, in conjunction with the eroded flank geometry, support the interpretation of a Cretaceous proto-Weddell Gyre. The base reflector of the transitional seismic unit, which marks the initial ice sheet advances to the outer shelf, has a lateral model age of 26.6-15.5 Ma from southeast to northwest. The Pliocene-Pleistocene glacial deposits reveals lower sedimentations rates, indicating a reduced sediment supply. Sedimentation rates for the pre-glacial, transitional and full glacial components are highest around the Antarctic Peninsula, indicating higher erosion and sediment supply of a younger basement. We interpret an Eocene East Antarctic Ice Sheet expansion, Oligocene grounding of the West Antarctic Ice Sheet and Early Miocene grounding of the Antarctic Peninsula Ice Sheet.