ALBERT

Description: Large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the Bransfield Strait, Antarctic Peninsula, at a water depth of 1950 meters and sub-zero bottom water temperatures. The chemistry, mineralogy, and stable isotope composition of this hydrated calcium carbonate phase, its environment of formation, and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation.

Description: A geophysical and geological survey conducted over the landward slope of the Middle America Trench offshore Guatemala, together with published well information from the outer shelf and Leg 67 drilling results from the toe of the slope indicate that imbricate slices of oceanic crust were emplaced in the landward slope offshore Guatemala in the Paleocene or early Eocene. Since that time, sediment apparently has accumulated on the landward slope primarily as a sediment apron blanketing an older, tectonically deformed prism of sediments and crustal slices. There is little or no evidence for continued tectonic accretion seaward of the volcanic arc during the late Tertiary. Seismic reflection and refraction surveys have revealed landward-dipping reflections that are associated with high compressional wave velocities, large magnetic anomalies, and basic-ultrabasic rock. Multifold seismic reflection data reveal that the edge of the continental shelf is a structural high of Cretaceous and Paleocene rock against which Eocene and younger sediments of the shelf basin onlap and pinch out. The upper part of the continental slope is covered in most places by a 0.5- to 1.0-km-thick sediment apron with seismic velocities of 1.8 to 2.6 km/s. The base of the sediment apron commonly coincides with the base of a gas hydrate zone where water is 1500 to 2300 meters deep. Immediately beneath the sediment apron an irregular surface is the top of an interval with velocities greater than 4 km/s. Within this interval, landward-dipping reflections are traced to about 6 km below sea level. These reflections coincide with the top of seismic units having oceanic crust velocities and thicknesses. The sediment apron pinches out on the lower continental slope where refraction results indicate only a few hundred meters of 2.5-km/s material lying over about a kilometer of 3.0-km/s sediment. Between the 3.0-km/s sediment and a landward continuation of ocean crust, an interval of 4.1- to 4.7-km/s material occurs that thins seaward. Near the interface between the 4 +-km/s material and oceanic crust with velocities of 6.5 to 6.8 km/s, reflection records indicate a landward-dipping horizon that can be followed about 30 km landward from the Trench axis. Coring on the continental slope returned gravels of unweathered metamorphosed basalt, serpentine, and chert, unlike rock generally found onshore in Guatemalan drainage basins feeding the Pacific coast. These gravels, which were probably derived from local subsea outcrops, are similar to lithologies found on the Nicoya Peninsula farther south. A canyon cut in the outer continental shelf and upper continental slope may be associated with faulting, as indicated by an offset of linear magnetic anomalies at the shelf edge. In a general way our observations are consistent with previous suggestions that slices of rock, some of which may have oceanic crustal lithologies, are imbedded in the upper slope. However, the reflection data collected for the Deep Sea Drilling Project site survey do not show the many concave upward landward-dipping reflections that have been reported from other areas offshore Guatemala. The lower slope is probably a tectonically deformed and consolidated sediment wedge overlying oceanic crust, but it is not clear that it is organized into a series of landward thinning wedges. The structures within the landward slope may have originated during the late Paleocene to early Eocene tectonic event and may not be the result of an ongoing steady-state process of sediment accretion by sediment offscraping at the toe of the slope or by underplating of sediment at the base of the sediment wedge beneath the continental slope and shelf.

Description: Slope deposits drilled during Leg 67 were later detailed in redisplayed seismic-reflection records. These deposits are of significantly lower seismic velocity and probably lower density than the underlying basement. This relationship indicates a contact between rocks of differing consolidation rather than a continuous sedimentary sequence. The slope deposits cover basement terranes of three different topographies. The shelf edge is an arch whose seaward flank forms a steep (up to 15°) upper slope. The midslope area has a rugged topography covered by thick slope deposits. The lower slope is relatively smooth except where broken locally by benches. The upper and middle slope areas are associated with strong magnetic anomalies and rare, landward-dipping reflections truncated by the rough surface. The rough midslope topography may reflect erosion succeeding the Paleocene uplift of this area and at least local subsidence in the early Miocene. Slope deposits covered the Trench landward slope, contemporaneous with the increased arc volcanism indicated by ash layers and with the present period of subduction. The subducting ocean crust and sediment of the Cocos Plate has a linear horst and graben topography of hundreds of meters relief that disappears beneath the landward slope of the Trench without disturbing its topography. This passive assimilation of oceanic material without significant accretion in the late Neogene argues for significant decoupling at the front of the subduction zone. A base of gas-hydrate reflection is evident in many of the redisplayed seismic records off Guatemala. These reflections are most common where slope deposits are thick; the reflections have not been identified in the underlying acoustic basement. This observation is consistent with the geochemical evidence that gas hydrate has its source in the organic- rich slope sediment. The hydrate depth and the temperature measurements in drill holes indicate a temperature gradient of 30°C/km.

Description: Deep-tow data across the Middle America Trench and the lower part of the landward Trench slope off Guatemala provide high-resolution information on the geological setting of four Leg 67 drill sites. Our 6-kHz profiler data resolve stratified sediments seaward of the Trench floor, which we interpret as deposits of Trench turbidites that flowed part way up the seaward slope of the Trench. Reflectors in the Trench fill are laterally continuous and relatively undisturbed. The Trench is segmented into diamond-shaped basins by ridges that intersect it at oblique angles. The acoustic stratigraphy in the Trench fill in these sub-basins is different on either side of an oblique ridge. A mound of variable height and width occurs at the base of the lower Trench slope; the mound could be either deformed Trench strata or an accumulation of debris that slumped from the Trench slope. The lower part of the landward Trench slope is steep and is linear along strike. There is no evidence on our 6-kHz or side-scan sonar data of large gravity slides in this area. Slope sediments are ponded on a bench along the landward Trench slope. They are acoustically stratified, but are not as continuous laterally as are the Trench strata. The structure parallel to the strike of the Trench slope is variable, with many small-scale folds and faults.

Description: Psephitic particles in the region of the Iceland-Faeroe-Ridge have been transported and deposited by means of a complex interplay of glacier movements and drifting icebergs. The composition of the particle association is controlled by the sedimentation of basaltic rock particles derived from the ridge itself and, in addition to that and in southern parts of the ridge, from the Faeroe Islands, the Faeroe-Bank and the Bill Baileys-Bank. Besides, there are crystalline and sedimentary dropstones showing a very varied petrography and a wide range of particle sizes. Their percentage becomes greater as the distance from the ridge increases. The association of dropstones is relatively homogeneous in the region of the ridge and only at greater distances from the ridge it becomes more differentiated. Owing to their composition and distribution, as well as on the basis of characteristic fossils and rock types, the dropstones are derived from Scandinavia and Great Britain. During periods of maximum glaciation, the Iceland-Faeroe-Ridge, the Faeroe-Bank and the Bill Baileys-Bank were under ice.

Description: The aragonite compensation depth was described by pteropods in surface sediments at the northeastern Atlantic continental margin between 12° and 48° N. It rises from 3100 m up to 400 m water depth in the high-productivity zones of fertile upwelling and river discharge.

Description: Seven sediment cores from the cruises of the "Meteor" and "Valdivia" were examined palynologically. The cores were retrieved from the lower continental slope in the area of between 33.5° N and 8° N, off the West African coast. Most of the cores contain sediments from the last Glacial and Interglacial period. In some cases, the Holocene sediments are missing. Some individual cores contain sediments also from earlier Glacial and Interglacial periods. The main reason for making this palynological study was to find out the differences between the vegetation of Glacial and Interglacial periods in those parts of West Africa which at present belong to the Mediterranean zone, the Sahara and the zones of the savannas and tropical forests. In today's Mediterranean vegetation zone at core 33.5° N, forests and deciduous forests in particular, are missing during Glacial conditions. Semi-deserts are found instead of these. In the early isotope stage 1, there is a very significant development of forests which contain evergreen oaks; this is the Mediterranean type of vegetation development. The Sahara type of vegetation development is shown in four cores from between 27° N and 19° N. The differences between Glacial and Interglacial periods are very small. It must be assumed therefore that in these latitudes, both Glacial and Interglacial conditions gave rise to deserts generally. The results are in favour of a slightly more arid climate during Glacial and a more humid one during Interglacial periods. The southern boundary of the Sahara and the adjacent savannas with grassland and tropical woods were situated more to the south during the Glacial periods than they were during the Interglacial ones. In front of today's savanna belt, it can be seen from the palynological results that there are considerable differences between the vegetation of Glacial and Interglacial periods. The woods are more important in Interglacial periods. During the Glacial periods these are replaced from north to south decreasingly by grassland (savanna and rainforest type of vegetation development). The southern limit of the Sahara during stage 2 was somewhere between 12° N and 8° N which is between 1.5 and 5 degrees in latitude further south than it is today. Not only do these differences in climate and vegetation apply to the maximum of the last Glacial and for the Holocene, but they apparently apply also to the older Glacial and Interglacial periods, where they have been found in the profiles. The North African desert belt can be said to have expanded during Glacial times both towards the north and towards the south. All the available evidence of this study indicates that the grassland or the semi-deserts of Southern Europe came into connection with those of N Africa; there could not have been any forest zone between them. The present study was also a good opportunity for investigating some of the basic marine palynological problems. The very well known overrepresentation of pollen grains of the genus Pinus in marine sediments can be traced as far as 21° N. The present southern limit for the genus Pinus is on the Canaries and on the African continent at approximately 31° N. Highest values of Ephedra pollen grains even occur south of the main area of the present distribution of that genus. There does not seem to be any satisfactory explanation for this. In general, it would appear that the transport of pollen grains from the north is more important than transport from the south. The results so far, indicate strongly that further palynological studies are necessary. These should concentrate particularly on cores from between 33° N and 27° N as well as between 17° N and 10° N. It would also be useful to have a more detailed examination of sediments from the last Interglacial period (substage 5 e). Absolute pollen counts and a more general examination of surface samples would be desirable. Surface samples should be taken from the shelf down to the bottom of the continental slope in different latitudes.

Description: 33 species of polychaetes were collected, 27 of them were determined to species level. The majority of the species are cosmopolitans. Pulliella armata FAUVEL was found the first time in the Atlantic Ocean off Northwest Africa.

Description: The new Harpacticoidea genus Thieliella nov. gen. of the family Ancorabolidae SARS sensu LANG, 1909 with two new species from 500 m depth of the Island-Faroer-Ridge is described and discussed: Thieliella nordatlantica nov. spec. and Th. reducta nov. spec.

Description: 80 species of polychaetes were collected, 76 of them were determined to species level. One species (Harmothoe [Austrolaenilla] meteorae n. sp.) was described as new species. The majority of the species including the species of the cruises 26 and 44 are cosmopolitans (18%); 16% are distributed in cool temperate to tropical zones, 12.5% have their distribution in the eastern Atlantic and the Mediterranean, and 11% are distributed in tropical-subtropical to warm temperate zones.

Description: Nine species of Flustridae were collected by the R.V. "Meteor" in one subantarctic and three antarctic stations. Two new genera (Austroflustra and Neoflustra) and three new species (Austroflustra gerlachi, A. australis and Neoflustra dimorphica) are described. The diagnosis of the family is emended to include species with adventitious avicularia. Nematoflustra bifoliata D'HONDT and Flustra thysanica MOYANO are placed in the genus Securiflustra SILEN, and Flustra vulgaris KLUGE is transfered to Austroflustra.

Description: The species Stenhelia (Delavalia) noodti n. sp., Stenhelia (Delavalia) islandica n. sp., Pseudomesochra scheibeli n. sp. and Ameira faroerensis n. sp. are described from 500 m depth on the Island-Faroer-Ridge. Of special interest is Stenhelia (Delavalia) noodti n. sp. showing a reduction of the Exp A2 to one segment, a character described for this genus for the first time.