Mid-Cretaceous planktonic foraminifera off central Morocco

Sites 545 and 547 collectively penetrated 629 m of mid-Cretaceous strata (upper Aptian to upper Cenomanian) off central Morocco during Leg 79 of the Deep Sea Drilling Project. Site 545, at the base of the steep Mazagan Escarpment, records a virtually complete succession of hemipelagic sediments of early late Aptian to middle Cenomanian age. Minor faunal recycling occurred throughout much of the upper Aptian to middle Albian part of the sequence (Cores 55 through 41), reflecting bottom currents along the Mazagan Escarpment. This may be related to the strong upwelling regime and high surface water productivity over Site 545 during the latest Aptian through middle Albian. The upwelling system ceased rather abruptly in this area in late middle Albian time. Recycling of older strata by bottom currents also ceased in the late middle Albian and resulted in a slower average accumulation rate in the upper Albian to middle Cenomanian section of Site 545 (Cores 40 through 28). However, intervals of pebbly claystone conglomerates in Cores 40 and 34 record sporadic instability in the slope adjacent to Site 545. Site 547, located only about 15 km seaward, is situated in a small sub-basin adjacent to the basement block drilled by Site 544. It contains an expanded upper Albian to upper Cenomanian sequence as a result of the numerous conglomeratic intervals throughout much of the section. In contrast to Site 545, the conglomerates were not derived from older strata cropping out on the Mazagan Escarpment; rather, they originated penecontemporaneously from a local unstable slope. A detailed biostratigraphic framework based on planktonic foraminifers is established for the mid-Cretaceous sections of Sites 545 and 547 and a new composite zonal scheme is proposed for the early late Aptian through early late Cenomanian interval. Fifty-five species are recognized and illustrated

Dead Sea lake level for the last 260 ka

The rain regime of the Levant during the late Quaternary was controlled primarily by Mediterranean cyclonic systems associated with North Atlantic climate shifts. Lake levels in the Dead Sea basin have been robust recorders of the regional hydrology and generally indicate highstand (wet) conditions throughout glacial intervals and lowstands (dry) during interglacials. However, sporadic deposition of travertines and speleothems occurred in the Negev Desert and Arava Valley during past interglacials, suggesting intrusions of humidity from southern sources probably in association with enhanced activity of mid-latitude Red Sea synoptic troughs and/or low-latitude tropical plumes. The southerly incursions of wetness were superimposed on the long-term interglacial Levantine arid conditions, as reflected by the current prevailing hyperaridity, and could have had an important impact on human migra- tion through the Red Sea-Dead Sea corridor.

Calcareous nannofossil abundance in ODP Site 185-1149 sediments

Basal carbonate sediments recovered at Ocean Drilling Program (ODP) Site 1149 lie directly on magnetic Anomaly M12. They contain abundant and moderately well preserved calcareous nannofossils. Two nannofossil zones are recognized: the lower Calcicalathina oblongata Zone and the upper Lithraphidites bollii Zone, indicating a late Valanginian-late Hauterivian age. The close occurrence of two significant bioevents, the first occurrence (FO) of L. bollii and the FO of Rucinolithus terebrodentarius in Core 185-1149B-20R, together with dip data recorded during in situ geophysical logging, suggest the presence of an unconformity that corresponds to the lower Hauterivian sedimentary section. The continuous occurrence of L. bollii is reported for the first time in sediments from the Pacific Ocean. Other marker species regarded as cosmopolitan (e.g., C. oblongata) have a sporadic occurrence. Nannoconids, very useful zonal markers for Tethyan areas, are virtually absent. The presence of an unusually high abundance of Diazomatolithus lehmanii is also recorded and correlates with the Valanginian 13C positive excursion.

Geochemistry, clay mineralogy and grain size distribution in various sediment cores drilled during ODP Leg 119 on the Antarctic continental shelf off Prydz Bay

Drilling was undertaken at five sites (739-743) on ODP Leg 119 on a transect across the continental shelf of Prydz Bay, East Antarctica, to elucidate the long-term glacial history of the area and to examine the importance of the area with respect to the development of the East Antarctic ice sheet as a whole. In addition to providing a record of glaciation spanning 36 m.y. or more, Leg 119 has provided information concerning the development of a continental margin under the prolonged influence of a major ice sheet. This has allowed the development of a sedimentary model that may be applicable not only to other parts of the Antarctic continental margin, but also to northern high-latitude continental shelves. The cored glacial sedimentary record in Prydz Bay consists of three major sequences, dominated by diamictite: 1. An upper flat-lying sequence that ranges in thickness from a few meters in inner and western Prydz Bay to nearly 250 m in the outer or eastern parts of the bay. The uppermost few meters consist of Holocene diatom ooze and diatomaceous mud with a minor ice-rafted component overlying diamicton and diamictite of late Miocene to Quaternary age. The diamictite is mainly massive, but stratified varieties and minor mudstone and diatomite also occur. 2. An upper prograding sequence cored at Sites 739 and 743, unconformly below the flat-lying sequence. This consists of a relatively steep (4° inclination) prograding wedge with a number of discrete sedimentary packages. At Sites 739 and 743 the sequence is dominated by massive and stratified diamictite, some of which shows evidence of slumping and minor debris flowage. 3. A lower, more gently inclined, prograding sequence lies unconformably below the flat-lying sequence at Site 742 and the upper prograding sequence at Site 739. This extends to the base of both sites, to 316 and 487 mbsf, respectively. It is dominated by massive, relatively clast-poor diamictite which is kaolinite-rich, light in color, and contains sporadic carbonate-cemented layers. The lower part of Site 742 includes well-stratified diamictites and very poorly sorted mudstones. The base of this site has indications of large-scale soft-sediment deformation and probably represents proximity to the base of the glacial sequence. Facies analysis of the Prydz Bay glacial sequence indicates a range of depositional environments. Massive diamictite is interpreted largely as waterlain till, deposited close to the grounding line of a floating glacier margin, although basal till and debris flow facies are also present. Weakly stratified diamictite is interpreted as having formed close to or under the floating ice margin and influenced by the input of marine diatomaceous sediment (proximal glaciomarine setting). Well-stratified diamictite has a stronger marine input, being more diatom-rich, and probably represents a proximal-distal glaciomarine sediment with the glaciogenic component being supplied by icebergs. Other facies include a variety of mudstones and diatom-rich sediments of marine origin, in which an ice-rafted component is still significant. None of the recovered sediments are devoid of a glacial influence. The overall depositional setting of the prograding sequence is one in which the grounded ice margin is situated close to the shelf edge. Progradation was achieved primarily by deposition of waterlain till. The flat-lying sequence illustrates a complex sequence of advances and retreats across the outer part of the shelf, with intermittent phases of ice loading and erosion. The glacial chronology is based largely on diatom stratigraphy, which has limited resolution. It appears that ice reached the paleoshelf break by earliest Oligocene, suggesting full-scale development of the East Antarctic ice sheet by that time. The ice sheet probably dominated the continental margin for much of Oligocene to middle Miocene time. Retreat, but not total withdrawal of the ice sheet, took place in late Miocene to mid-Pliocene time. The late Pliocene to Pleistocene was characterized by further advances across, and progradation of, the continental shelf. Holocene time has been characterized by reduced glacial conditions and a limited influence of glacial processes on sedimentation.

Benthic and planktonic foraminifera in the Japan Sea

Biostratigraphy and paleoenvironmental history of deep and surficial waters of the Japan Sea are addressed using sequences recovered from the floor of the backarc basin. The study is divided into two parts: (1) foraminifer biostratigraphy and paleoenvironmental assessment of sedimentary sequences recovered from above igneous basement at the four sites and (2) detailed planktonic foraminifer paleoenvironmental analysis of Quaternary and Pliocene sequences from Sites 794 and 797 in the Yamato Basin. A total of 253 samples were examined for the foraminifer biostratigraphy and 325 samples for the detailed paleoenvironmental study of Quaternary and Pliocene sequences. Low abundance and sporadic occurrence of foraminifers limited interpretation of results. Foraminifer-bearing intervals were correlated where possible to diatom and calcareous nannofossil zonations, and the sequences were successfully assigned to the foraminifer zonation of Matsunaga. Unfortunately, extensive barren intervals and sporadic occurrences of planktonic foraminifers prevented zonation of Quaternary and Pliocene intervals, although some interesting conclusions about paleoenvironment were possible and are listed below. A sequence of Neogene (sensu lato) paleoenvironmental events were identified: (1) deepening of the Yamato basins to middle bathyal depths by the early to middle Miocene, an event contemporaneous with the age of some deep basins known from uplifted sections adjacent to the Japan Basin; (2) cooling of the Japan Sea in the early middle Miocene; (3) oxygenation of deep waters in the late Miocene; (4) further cooling of surficial water masses between the Olduvai Subchron and the Brunhes/Matuyama Boundary; and (5) extermination of lower middle bathyal faunas and replacement by upper middle bathyal faunas near the base of the Quaternary.

Late Neogene biostratigraphy of ODP Leg 135 sites

Integration of biostratigraphic and magnetostratigraphic results from Leg 135 sites has given additional information as to the position and reliability of various bioevents compared with previously published results. Two sites (834: Gilbert to Brunhes; and 836: Brunhes) provided excellent magnetic and biostratigraphic data. From these it is suggested that some bioevents are older than previously recorded: the first appearances (FAs) of Emiliania huxleyi (within the Brunhes Chron, at the same level as the FA of Helicosphaera inversa) and Globorotalia (Truncorotalia) truncatulinoides (within the upper Gauss Chron), and the last appearance (LA) of Gr. (Tr.) tosaensis (upper Matuyama Chron). The FA of Gr. (Tr.) crassaformis hessi is variable, but the oldest occurrence is just below the Cobb Mountain Subchron. Other key bioevents, such as the LAs of Discoaster pentaradiatus (just above the Réunion Subchron), D. tamalis (within the lower reversed part of the Matuyama Chron), Sphenolithus (lower Gauss Chron), and Amaurolithus primus (topmost Gilbert Chron) appear higher than previously recorded. Some key biostratigraphic taxa, such as Globigerinoides quadrilobatus fistulosus, Pulleniatina finalis, P. primalis, and Sphaeroidinella dehiscens, are either rare or their distribution is sporadic to the extent that they are unsuitable for biostratigraphic use in the area studied. Because of the rarity of P. primalis, the FA of Globorotalia (Globorotalia) multicamerata has been used to mark the base of Zone N17B. Though levels are present at most sites in which populations of Pulleniatina are sinistrally coiled, it is difficult to equate these coiling changes with previous records.

Neogene Radiolarians in Neogene sediments of the Norwegian Sea

Radiolaria are present in frequencies ranging from rare to abundant and with generally moderate to good preservation quality in Leg 104 sediments younger than 22 Ma. Preservation degrades in progressively younger sediments, and upper Pliocene to mid-Pleistocene radiolaria were found only at Site 644, where sporadic assemblages of moderate to poorly preserved specimens persist to approximately 0.75 Ma. Radiolaria are essentially absent in Leg 104 recovery older than basal Miocene. The stratigraphic ranges of 55 taxa of radiolaria are documented in 451 samples from the biosiliceous recoveries of Holes 642B, 642C, 642D, 643A, and 644A. The stratigraphic ranges of 25 of these species are used as boundary criteria for a new system of 28 Neogene zones and subzones that are used to characterize approximately 72% of the past 22 m.y. of sedimentation on the Vriring Plateau. This new scheme is intended to supercede the NRS zones provisionally proposed in the Leg 104 Initial Reports. The applicability of this regional biozonation beyond the Wring and Iceland Plateaus is not presently known. The radiolaria biostratigraphy serves as a basis for inferring a sequence of hiatuses and faunal overturns that may be associated with sea-level low stands and consequent cold-water isolation of the Norwegian Sea. Twenty-one new taxa are described as follows: Actinomma henningsmoeni, Actinomma livae, Actinomma mirabile, Actinomma plasticum, Ceratocyrtis broeggeri, Ceratocyrtis manumi, Ceratocyrtis stoermeri, Clathrospyris vogti, Corythospyris hispida, Corythospyris jubata sverdrupi, Corythospyris reuschi, Crytocapsella ampullacea, Cyrocapsella kladaros, Gondwanaria japonica kiaeri, Hexalonche esmarki, Larcospira bulbosa, Phormospyris thespios, Pseudodicytophimus amundseni, Spongotrochus vitabilis, Spongurus cauleti, and Tessarastrum thiedei.

Mineralogy and geochemistry of sulfide minerals and bulk rocks from ODP Hole 176-735B

Ocean Drilling Program (ODP) Leg 176 built upon the work of ODP Leg 118 wherein the 500-m section that was sampled represented the most complete recovery of an intact portion of lower oceanic crust ever described. During Leg 176, we deepened Hole 735B to >1500 m below seafloor in an environment where gabbroic rocks have been tectonically exposed at the Southwest Indian Ridge. This new expedition extended the remarkable recovery (>85%) that allowed unprecedented investigations into the nature of the lower oceanic crust as a result of Leg 118. Sulfide mineral and bulk rock compositions were determined from samples in the 1000-m section of oceanic gabbros recovered during Leg 176. The sulfide assemblage of pyrrhotite, chalcopyrite, pentlandite, and troilite is present throughout this section, as it is throughout the 500-m gabbroic section above that was sampled during Leg 118. Troilite is commonly present as lamellae, and the only interval where troilite was not observed is from the uppermost 150 m of the section sampled during Leg 118, which is intensely metamorphosed. The common presence of troilite indicates that much of the sulfide assemblage from Hole 735B precipitated from a magmatic system and subsequently underwent low-temperature reequilibration. Evaluation of geochemical trends in bulk rock and sulfides indicates that the combined effects of olivine accumulation in troctolites and high pentlandite to pyrrhotite ratios account for the sporadic bulk rock compositions high in Ni. Bulk rock and sulfide mineral geochemical indicators that are spatially coincident with structural and physical properties anomalies indicate a heretofore unrecognized lithologic unit boundary in this section. Platinum-group element (PGE) compositions were also determined for 36 samples from throughout the section that were recovered during Leg 176. Whereas most samples had low (<0.4 ppb) PGE concentrations, rare samples had elevated PGE values, but no unique common trend between these samples is evident.

Distribution of calcareous nannofossils in upper Cretaceous and Cenozoic sediments of the Kerguelen Plateau

ODP Leg 119 drilled 11 sites on the Kerguelen Plateau (southern Indian Ocean) and Prydz Bay (East Antarctica). Upper Pliocene through Quaternary sediments were recovered at Site 736 on the northern Kerguelen Plateau; calcareous nannofossils occurred in only a few samples. Over 700 m of middle Eocene through Quaternary sediments was cored at Site 737 on the northern Kerguelen Plateau, and calcareous nannofossils are abundant in the middle Eocene through the middle Miocene sediments. Nearly 500 m of sediments ranging from the lower Turanian to the Quaternary was recovered at Site 738 on the southern Kerguelen Plateau; calcareous nannofossils are abundant from the Miocene downward. Calcareous nannofossils are also abundant in the upper Eocene through Miocene section from Site 744 on the southern Kerguelen Plateau. Except for Core 119-746A-13H, the Neogene sequences drilled at deep-water Sites 745 and 746 off the southern Kerguelen Plateau are devoid of calcareous nannofossils. Occurrences of calcareous nannofossils were generally rare and sporadic at Sites 739 and 742 in Prydz Bay and suggest that the diamictite sequences recovered is as old as middle Eocene-early Oligocene age. Other sites drilled in Prydz Bay (Sites 740, 741, and 743) did not yield calcareous nannofossils. Species diversity of calcareous nannofossils was low (about a dozen) in the southern Indian Ocean in the Late Cretaceous. High-latitude nanno floral characteristics are apparent after the Cretaceous/Tertiary boundary extinctions. Cold climatic conditions limited Oligocene calcareous nannofossil assemblages to fewer than a dozen species, and extinctions of species generally were not compensated by originations of new species. Only a few species of calcareous nannofossils were found in the Miocene sequences, in which Coccolithuspelagicus and one or two species of Reticulofenestra exhibit extreme (0%-100%) fluctuations in assemblage dominance, and these fluctuations may reflect rapid fluctuations in the surface-water temperatures. Further deterioration of climate in the late Neogene essentially excluded calcareous nannoplankton from the Southern Ocean. Significantly warmer water conditions during part of the early-middle Pleistocene were inferred by a few lower-middle Pleistocene calcareous nannofossil species found on the Kerguelen Plateau. The calcareous nannofossil zonation of Roth (1978 doi:10.2973/dsdp.proc.44.134.1978) can be applied to the Upper Cretaceous section recovered at Site 738, and the zonation of Okada and Bukry (1980 doi:10.1016/0377-8398(80)90016-X) can be applied without much difficulty to the Paleocene to middle Eocene sequences from the Kerguelen Plateau. However, some conventional upper Paleogene markers are not useful for southern high latitudes, whereas a few nonconventional species events are useful for subdividing the upper Paleogene sequences. The latter species events include the first occurrence (FO) of Reticulofenestra reticulata, the FO and last occurrence (LO) of Reticulofenestra oamaruensis, the LO of Isthmolithus recurvus, and the LO of Chiasmolithus altus. As the Neogene sequences from the southern Indian Ocean contain only a few long-ranging, cold-water species, or are devoid of coccoliths, calcareous nannofossil zonations remain virtually unworkable for the Neogene in the high-latitude southern Indian Ocean as in other sectors of the Southern Ocean.

Geochemistry of reduction haloes in ODP Holes 135-834A and 135-837A

The sediment column overlying basement in the Lau Basin consists of a sequence of volcaniclastic turbidites interbedded with hemipelagic clayey nannofossil mixed sediments, overlain in turn by a sequence of hemipelagic clayey nannofossil oozes containing sporadic calcareous turbidites. The clayey nannofossil oozes and mixed sediments are pervasively stained by hydrothermally derived iron and manganese oxyhydroxides. Sharply defined, lighter colored bands occur in the hemipelagic sediments, immediately beneath some (but by no means all) volcaniclastic and calcareous turbidites. These are identified as reduction haloes, of a type previously identified in quite different turbidite/pelagic sequences. The haloes are attributed to the burial of labile surficial Corg by turbidites, followed by the remineralization of this Corg with Mn and Fe oxyhydroxides as electron acceptors. The resultant characteristic Mn and Fe concentration/depth profiles are described, and a model is proposed for their development. The color alteration of the halo is ascribed to the removal of Mn oxyhydroxides, because, although the Fe content fluctuates through the haloes, this does not appear to affect their color. Other elements (Co, Cu, and Ni) are also at low concentration levels in the haloes like Mn, consistent with remobilization and migration out of the halo section, although the profile shapes are not identical with those of Mn. The behavior of V is distinctive in that it appears to have migrated into the haloes to be enriched there. Haloes are unlikely to form if turbidite emplacement is erosive and removes the near-surface layer, which generally is the most fluid part of the sediment and contains the highest levels of reactive Corg to drive the reduction process. Conversely, the presence of a halo implies that emplacement of the overlying turbidite did not significantly erode the pre-existing sediment/water interface.

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.

Miocene radiolarians of the Sulu Sea

Radiolarians are sporadic in sediments collected in the Sulu Sea during ODP Leg 124. Due to the generally poor preservation and low abundance of radiolarians in Sulu Sea sediments, no biostratigraphic datums are well defined, although three radiolarian zones are identified. Most samples containing radiolarians are pelagic or hemipelagic clays with varying proportions of volcanic ash. Detailed analysis of Sulu Sea radiolarians was limited to Miocene successions. Pliocene and Quaternary occurrences of radiolarians were noted but have not been zoned. The late middle Miocene of Sites 769 and 771 is represented by an assemblage of radiolarians (Diartus petterssoni Zone) that is entirely replaced by massive pyrite. This type of preservation develops only under anoxic conditions. The development of widespread anoxia in Sulu Sea waters in the late middle Miocene was probably the result of hydrologic isolation of basin waters, and may be associated with eustatic sea level fall over the silled basin. Upper lower Miocene pelagic and hemipelagic sediments that overlie pyroclastics and basalt flows in the Sulu Sea sites contain moderately to very poorly preserved radiolarians of the Calocycletta costata Zone. A thin unit of marine claystone was recovered from between the thick pyroclastics and basement rocks at Site 768. Radiolarians present in these claystones are rare and very poorly preserved. This radiolarian assemblage probably represents the C. costata Zone, although very poor preservation and low abundance make this interpretation equivocal. The radiolarian zones identified constrain the age of basin formation to late early Miocene or earlier.

Distribution of tripylean radiolarians from ODP Leg 114 (Table 2)

The occurrence of tripylean radiolarians is reported for the first time from subsurface sediments of the subantarctic Atlantic Ocean. Although their occurrence is rare as well as sporadic, seven species belonging to four genera are recognized from Upper Cenozoic sediments drilled at Sites 699, 700, and 701 of ODP Leg 114 in 1987.

(Table 1) Minerals of bulk sediment at DSDP Holes 64-480 and 64-481

This paper provides a brief, descriptive, sedimentological background for the chapters on hydraulic piston core Site 480 in this symposium, and supplements data given in the site chapter for Sites 479-480 (this volume, Pt. 1). Sediments are composed primarily of planktonic diatoms, with minor numbers of silicoflagellates, radiolarians, and varying amounts of both benthic and planktonic foraminifers, along with a large terrigenous component of olive brown, silty clay. The section contains meter-thick intervals of finely laminated facies alternating with nonlaminated zones. A few paleoenvironmental events are documented within the generally uniform sequence by sporadic occurrences of thin turbidites, phosphatic concretions, fish debris concentrations, an ash layer, and a thin layer of diagenetic dolomite. The distribution of nonlaminated and laminated zones is attributed to fluctuations of bottom-water oxygen content caused by variations in circulation, fertility, and productivity. Homogeneous sections are interpreted as coinciding with cooler climatic periods, whereas laminated sections seem to correspond to upwelling conditions during drier periods.

Sediment facies of the Indian-Pakistan continental margin, Indian Ocean Expedition

The studies described here base mainly on sedimentary material collected during the "Indian Ocean Expedition" of the German research vessel "Meteor" in the region of the Indian-Pakistan continental margin in February and March 1965. Moreover,samples from the mouth of the Indus-River were available, which were collected by the Pakistan fishing vessel "Machhera" in March 1965. Altogether, the following quantities of sedimentary material were collected: 59.73 m piston cores. 54.52 m gravity cores. 33 box grab samples. 68 bottom grab samples Component analyses of the coarse fraction were made of these samples and the sedimentary fabric was examined. Moreover, the CaCO3 and Corg contents were discussed. From these investigations the following history of sedimentation can be derived: Recent sedimentation on the shelf is mainly characterized by hydrodynamic processes and terrigenous supply of material. In the shallow water wave action and currents running parallel to the coast, imply a repeated reworking which induces a sorting of the grains and layering of the sediments as well as a lack of bioturbation. The sedimentation rate is very high here. From the coast-line down to appr. 50 m the sediment becomes progressively finer, the conditions of deposition become less turbulent. On the outer shelf the sediment is again considerably coarser. It contains many relicts of planktonic organisms and it shows traces of burrowing. Indications for redeposition are nearly missing, a considerable part of the fine fraction of the sediments is, however, whirled up and carried away. In wide areas of the outer shelf this stirring has gained such a degree that recent deposits are nearly completely missing. Here, coarse relict sands rich in ooids are exposed, which were formed in very shallow stirred water during the time when the sea reached its lowest level, i.e. at the turn of the Pleistocene to the Holocene. Below the relict sand white, very fine-grained aragonite mud was found at one location (core 228). This aragonite mud was obviously deposited in very calm water of some greater depth, possibly behind a reef barrier. Biochemic carbonate precipitation played an important part in the formation of relict sands and aragonite muds. In postglacial times the relict sands were exposed for long periods to violent wave action and to areal erosion. In the present days they are gradually covered by recent sediments proceeding from the sides. On the continental margin beyond the shelf edge the distribution of the sediments is to a considerable extent determined by the morphology of the sea bottom. The material originating from the continent and/or the shelf, is less transported by action of the water than by the force of gravity. Within the range of the uppermost part of the continental slope recent sedimentation reaches its maximum. Here the fine material is deposited which has been whirled up in the zone of the relict sands. A laminated fine-grained sediment is formed here due to the very high sedimentation rate as well as to the extremely low O2-content in the bottom water, which prevents life on the bottom of the sea and impedes thus also bioturbation. The lamination probaly reflects annual variation in deposition and can be attributed to the rhythm of the monsoon with its effects on the water and the weather conditions. In the lower part of the upper continental slope sediments are to be found which show in varying intensity, intercalations of fine material (silt) from the shelf, in large sections of the core. These fine intercalations of allochthonous material are closely related to the autochthonous normal sediment, so that a great number of small individual depositional processes can be inferred. In general the intercalations are missing in the uppermost part of the cores; in the lower part they can be met in different quantities, and they reach their maximum frequency in the upper part of the lower core section. The depositions described here were designated as turbid layer sediments, since they get their material from turbid layers, which transport components to the continental slope which have been whirled up from the shelf. Turbidites are missing in this zone. Since the whole upper continental slope shows a low oxygen-content of the bottom water the structure of the turbid layer sediments is more or less preserved. The lenticular-phacoidal fine structure does, however, not reflect annual rhythms, but sporadic individual events, as e.g. tsunamis. At the lower part of the continental slope and on the continental rise the majority of turbidites was deposited, which, during glacial times and particularly at the beginning of the post-glacial period, transported material from the zone of relict sands. The Laccadive Ridge represented a natural obstacle for the transport of suspended sediments into the deep sea. Core SIC-181 from the Arabian Basin shows some intercalations of turbidites; their material, however, does not originate from the Indian Shelf, but from the Laccadive Ridge. Within the range of the Indus Cone it is surprising that distinct turbidites are nearly completely missing; on the other hand, turbid layer sediments are to be found. The bottom of the sea is showing still a slight slope here, so that the turbidites funneled through the Canyon of the Swatch probably rush down to greater water depths. Due to the particularly large supply of suspended material by theIndus River the turbid layer sediments show farther extension than in other regions. In general the terrigenous components are concentrated on the Indus Cone. It is within the range of the lower continental slope that the only discovery of a sliding mass (core 186) has been located. It can be assumed that this was set in motion during the Holocene. During the period of time discussed here the following development of kind and intensity of the deposition of allochthonous material can be observed on the Indian-Pakistan continental margin: At the time of the lowest sea level the shelf was only very narrow, and the zone in which bottom currents were able to stir up material by oscillating motion, was considerably confined. The rivers flowed into the sea near to the edge of the shelf. For this reason the percentage of terrigenous material, quartz and mica is higher in the lower part of many cores (e.g. cores 210 and 219) than in the upper part. The transition from glacial to postglacial times caused a series of environmental changes. Among them the rise of the sea level (in the area of investigation appr. 150 m) had the most important influence on the sedimentation process. In connection with this event many river valleys became canyons, which sucked sedimentary material away from the shelf and transported it in form of turbidites into the deep sea. During the rise of the sea level a situation can be expected with a maximum area of the comparatively plane shelf being exposed to wave action. During this time the process of stirring up of sediments and formation of turbid layers will reach a maximum. Accordingly, the formation of turbidites and turbid layer sediments are most frequent at the same time. This happened in general in the older polstglacial period. The present day high water level results in a reduced supply of sediments into the canyons. The stirring up of sediments from the shelf by wave action is restricted to the finest material. The missing of shelf material in the uppermost core sections can thus be explained. The laminated muds reflect these calm sedimentation conditions as well. In the southwestern part of the area of investigation fine volcanic glass was blown in during the Pleistocene, probably from the southeast. It has thus become possible to correlate the cores 181, 182, 202. Eolian dust from the Indian subcontinent represents probably an important component of the deep sea sediments. The chemism of the bottom as well as of the pore water has a considerable influence on the development of the sediments. Of particular importance in this connection is a layer with a minimum content of oxygen in the sea water (200-1500 m), which today touches the upper part of the continental slope. Above and beyond this oxygen minimum layer somewhat higher O2-values are to be observed at the sea bottom. During the Pleistocene the oxygen minimum layer has obviously been locatedin greater depth as is indicated by the facies of laminated mud occuring in the lower part of core 219. The type of bioturbation is mainly determined by the chemism. Moreover, the chemism is responsible for a considerable selective dissolution, either complete or partial, of the sedimentary components. Within the range of the oxygen minimum layer an alkaline milieu is developed at the bottom. This causes a complete or partial dissolution of the siliceous organisms. Here, bioturbation is in general completely missing; sometimes small pyrite-filled burrowing racks are found. In the areas rich in O2 high pH-values result in a partial dissolution of the calcareous shells. Large, non-pyritized burrowing tracks characterize the type of bioturbation in this environment. A study of the "lebensspuren" in the cores supports the assumption that, particularly within the region of the Laccadive Basin, the oxygen content in the bottom sediments was lower than during the Holocene. This may be attributed to a high sedimentation rate and to a lower O2-content of the bottom water. The composition of the allochthonous sedimentary components, detritus and/or volcanic glass may locally change the chemism to a considerable extent for a certain time; under such special circumstances the type of bioturbation and the state of preservation of the components may be different from those of the normal sediment.