(Table 1) Pollen analysis of clay-gyttja layers obtained in 1966 near Hitzhusen, north Germany

Bereits im Jahre 1956 wurde bei Baugrund-Aufschlußbohrungen für das zweite Kurmittelhaus in Bad Bramstedt bei einer Serie von 11 Bohrungen - ausgeführt durch die Firma Fritz Eising K. G. in Hamburg - in drei benachbart gelegenen Bohrpunkten an der südlichen Ecke des Gebäudes in einer Teufe von ca. 10 m u. T. eine offensichtlich organogene Schicht von ca. 2 m Mächtigkeit erbohrt. Eines dieser Bohrprofile hat folgenden Aufbau: -5,8 m Fein-Mittelsand, -7,7 m Mittelsand, Fein-Mittelkies, -10,0 m Mittelsand, wenig Kies, -12,0 m Gyttja, -15,0 m Mittelsand, Grobsand. Die bereits wiedergegebene Teufenangabe ist insofern recht interessant, als im Jahre 1966 bei der Brücke über die Bramau bei Hitzhusen, demnach in der Talaue der Bramau in einer Teufe von 8,55 m ebenfalls eine Gyttja erbohrt wurde. Die Tiefenlagen beider Vorkommen scheinen sich demnach relativ zu entsprechen. Das gesamte Profil bei Hitzhusen ist in einigen Punkten abweichend ausgebildet und enthält vor allem noch ein zweites Gyttja-Band in 11,25 m Teufe. Im Einzelnen wurde hier durch die Bohrfirma Paul Hammers A. G., Hamburg, diese Schichtfolge angetroffen: -1.55 m Fein-Mittelsand, Humus, -3,10 m Mittel-Grobsand, Kies, Steine, etwas Lehm, -4,50 m Mittel-Grobsand, -7,20 m Mittel-Grobsand, Kies, -8,00 m Grobsand, -8,55 m Grobsand, Kies, -8,65 m Schluff-Gyttja, -9,70 m Fein-Grobsand, -10,25 m Mittel-Grobsand, Kies, -10,75 m Mittel-Grobsand, -11,25 m Mittel-Grobsand, Schluffstreifen, -11,40 m Schluff-Gyttja, -12,10 m Mittelsand, -12,30 m Mittel-Grobsand, Kies, -17,85 m Geschiebemergel. Die gewonnenen Proben der Schluff-Gyttjen wurden näher untersucht. Da es sich in beiden Fällen um geringmächtige Lagen handelt (0,1 m resp. 0,15 m), und das Material durchaus als stark feinsandig bis schluffig zu bezeichnen ist (das spricht für eine wesentlich schnellere Sedimentation, als die einer reinen biogenen Gyttja), ist der Effekt einer 'Mischprobe' weitgehend ausgeschlossen. Außerdem lagen die Proben - obgleich wahrscheinlich mit einem Ventilbohrer gefördert - als relativ ungestörte Brocken mit erhaltengebliebener Feinschichtung vor. Auf den Schichtflächen waren gröbere Pflanzenreste erkennbar (in der Tabelle angegeben). Der sehr hohe mineralische Anteil läßt zunächst den Verdacht auf sekundären Pollen aufkommen. Keines der beiden pollenanalytisch ermittelten Vegetationsbilder liefert dagegen irgendeine Bestätigung hierfür.

Feldspar size measurements of tephra layers from ODP Leg 165 sites

Crystal size measurements have been carried out on tephra fall layers of Miocene to recent age from Sites 998, 999, and 1000 in the western Caribbean Sea. Maximum crystal size is used as a proxy for the grain size characteristics of the layers and an index of atmospheric dispersal from source eruptions. Crystal sizes range from 50 to 650 µm with the majority falling between 200 and 300 µm. All three sites exhibit a coarsening in the grain size of tephra layers with increasing age to the early Miocene that broadly correlates with an increase in the frequency of layers. Analysis of the present lower and upper level atmospheric circulation in the western Caribbean suggests that the layers were derived from source eruptions to the west of the sites somewhere in the Central American region. Minimum distances to these sources are of the order of 700 km. Crystal sizes in tephra layers at these distances are consistent with their derivation from energetic pyroclastic flow-forming eruptions that injected tephra to stratospheric levels by large-scale co-ignimbrite and plinian-style plumes. Coarsening of the layers during the Miocene peak of explosive volcanism cannot be attributed to any major change in paleowind intensity and is taken to represent the occurrence of more energetic eruptions that were able to disperse tephra over larger areas.

Chemical composition of volcanic ash layers from ODP Leg 134 sites

Volcanic ash layers (1-3 cm thick) are abundant in the North Aoba Basin drill sites but less common at forearc sites. Ash deposited on the forearc slopes is liable to be redistributed as turbidites. In addition, the westerly upper winds also minimize ash-fall on the western (forearc) side of the New Hebrides Island Arc. Crystalline components in the ashes are primarily plagioclase (An90-An44), clinopyroxene (Ca46Mg49Fe5-Ca43Mg33Fe24), olivine (Fo87-Fo62), and titanomagnetite. There are also small amounts of orthopyroxene, magnetite, apatite, and quartz. Glass shards occur in most of the ashes and range in composition from basalt to rhyolite. There is often a variety of glass compositions within a single ash layer. One explanation for this is that the rate of accumulation of ash from several different eruptions or eruptive phases exceeded the background sedimentation rate: there may also have been a certain amount of reworking. The high-K and low-K trends previously recognized in volcanic rocks from the New Hebrides Island Arc are clearly represented in the Leg 134 glasses. All of the ashes investigated here are thought to have originated from the Central Chain volcanoes. The source of the high-K group was probably the Central Basin volcanoes of Santa Maria, Aoba, and Ambrym. The lower-K series includes a distinctive group of dacites and is likely to have originated from the Epi-Tongoa-Tongariki sector of the arc where major pyroclastic eruptions, associated with caldera collapse, have occurred during the Holocene, perhaps as recently as 400 yr ago.

GIS layers of seafloor characteristics in the Azores region (North Atlantic), links to files in ArcGIS format

Inventory of some important datasets related to the physical characteristics of the seafloor surrounding the Azores Archipelago. The objective is to ensure that our compilation is readily available for any researchers interested in this type information but also to support institutions responsible for the management and conservation of local resources.

Quarternary tephra layers in sediment cores from the Bellingshausen Sea and Scotia Sea

The Southern Ocean is a region of the world's ocean which is fundamental to the generation of cold deep ocean water which drives the global therrno-haline circulation. Previous investigations of deep-sea sediments south of the Polar Front have been significantly constrained by the lack of a suitable correlation and dating technique. In this study, deep-sea sediment cores from the Bellingshausen, Scotia and Weddell seas have been investigated for the presence of tephra layers. The major oxide and trace element composition of glass shards have been used to correlate tephra isochrons over distances in excess of 600 km. The source volcanoes for individual tephra layers have been identified. Atmospheric transport distances greater than 1500 km for >32 pm shards are reported. One megascopic tephra is identified and correlated across 7 sediment drifts on the continental rise in the Bellingshausen Sea. Its occurrence in a sedimentary unit that has been biostratigraphically dated to delta 18O substage 5e identifies it as a key regional marker horizon for that stage. An unusual bimodal megascopic ash layer erupted from Deception Island, South Shetland Islands, has been correlated between 6 sediment cores which form a 600 km NE-SW transect from the central Scotia Sea to Jane Basin. This megascopic ash layer has been 14C dated at c. 10,670 years BP. It represents the last significant input of tephra into the Scotia Sea or Jane Basin from that volcano and forms an important early Holocene marker horizon for the region. Five disseminated tephras can be correlated to varying extents across the central Scotia Sea cores. Together with the megascopic tephra they form a tephrostratigraphic framework that will greatly aid palaeoclimatic, palaeoenvironrnental and palaeoceanographic investigations in the region.