Mineralogy of sediments from the Exmouth Plateau and Argo Basin

Correlation of mineral associations from sediment recovered on the northwestern Australian continental margin document the juvenile-to-mature evolution of a segment of the Indian Ocean. Lower Cretaceous sediments contain sandy-to-silty radiolarian claystone that consists of highly smectitic mixed-layered illite/smectite (I/S) in addition to minor amounts of diagenetic pyrite, barite, and rhodochrosite. These immature, poorly sorted sediments were derived from nearby continental margin sources. Discrete bentonite layers and abundant smectite are the alteration products of volcanic material deposited during early basin formation. Abundant quartz-replaced radiolarian tests suggest high surface-water productivity, and calcareous fossils indicate water depths were above the calcite compensation depth (CCD) in the juvenile Indian Ocean. The increase in pelagic carbonate from the mid- to Late Cretaceous signals the transition to mature, open-ocean conditions. Similar to other slowly deposited contemporaneous deep-sea sediments, mid- to Upper Cretaceous sediments of the northwestern margin of Australia contain palygorskite. This palygorskite is associated with calcareous sediment across the ooze-to-chalk transition, detrital mixed-layered I/S, and zeolite minerals in places. This palygorskite occurs above the transformation from opal-A to opal-CT. The underlying opal-CT sediment contains abundant smectite and zeolite minerals. Calcareous sediment dominates the Cenozoic, except at abyssal sites that were not inundated by calcareous turbidites. Paleocene and Eocene sediments contain abundant smectite and zeolite minerals derived from the alteration of volcanic material. Palygorskite was found to be associated with sepiolite and dolomite in Miocene sediments from Site 765 in the Argo Basin. Pliocene and Quaternary sediments contain detrital kaolinite and mixed-layered I/S, abundant opal-A radiolarian tests, and minor amounts of pyrite

Carbonate content in lower Cretaceous sediments of ODP Hole 123-765C

Sediments recovered during Ocean Drilling Program (ODP) Leg 123 from the Argo Abyssal Plain (AAP) consist largely of turbidites derived from the adjacent Australian continental margin. The oldest abundant turbidites are Valanginian-Aptian in age and have a mixed (smarl) composition; they contain subequal amounts of calcareous and siliceous biogenic components, as well as clay and lesser quartz. Most are thin-bedded, fine sand- to mud-sized, and best described by Stow and Piper's model (1984) for fine-grained biogenic turbidites. Thicker (to 3 m), coarser-grained (medium-to-coarse sand-sized) turbidites fit Bouma's model (1962) for sandy turbidites; these generally are base-cut-out (BCDE, BDE) sequences, with B-division parallel lamination as the dominant structure. Parallel laminae most commonly concentrate quartz and/or calcispheres vs. lithic clasts or clay, but distinctive millimeter- to centimeter-thick, radiolarian-rich laminae occur in both fine- and coarse-grained Valanginian-Hauterivian turbidites. AAP turbidites were derived from relatively deep parts of the continental margin (outer shelf, slope, or rise) that lay below the photic zone, but above the calcite compensation depth (CCD). Biogenic components are largely pelagic (calcispheres, foraminifers, radiolarians, nannofossils); lesser benthic foraminifers are characteristic of deep-water (abyssal to bathyal) environments. Abundant nonbiogenic components are mostly clay and clay clasts; smectite is the dominant clay species, and indicates a volcanogenic provenance, most likely the Triassic-Jurassic volcanic suite exposed along the northern Exmouth Plateau. Lower Cretaceous smarl turbidites were generated during eustatic lowstands and may have reached the abyssal plain via Swan Canyon, a submarine canyon thought to have formed during the Late Jurassic. In contrast to younger AAP turbidites, however, Lower Cretaceous turbidites are relatively fine-grained and do not contain notably older reworked fossils. Early in its history, the northwest Australian margin provided mainly contemporaneous slope sediment to the AAP; marginal basins adjacent to the continent trapped most terrigenous detritus, and pronounced canyon incisement did not occur until Late Cretaceous and, especially, Cenozoic time.

Benthic foraminifers from the Japan Sea

Five holes were drilled at two sites in the Sea of Japan during Ocean Drilling Program (ODP) Leg 128. Site 798 is located on Oki Ridge at a depth of about 900 m. Sediment age at Site 798 ranges from Pliocene to Holocene. Site 799 is located in the Kita-Yamato Trough at depth of 2000 m and below the present calcite compensation depth (CCD); the sediment ranges from Miocene to Holocene in age. Samples from all holes contain benthic foraminifers. Faunal evidence of downslope displacement is frequent in Holes 799A and 799B. The vertical frequency distribution of some dominant species shows that significant faunal changes occur in Holes 798A-C on Oki Ridge. Based on the faunal change and the thickness of sediments, it appears that the Oki Ridge was uplifted more than 1,000 m during last 4 m.y. Benthic foraminifers also demonstrate that the water depth of Site 799 rapidly changed from upper bathyal to lower bathyal during middle Miocene time. The appearance of benthic foraminifer species common to anaerobic environments suggests that the dysaerobic to anaerobic bottom conditions existed during the evolution of the Sea of Japan. Faunal distributions also suggest that the 'Tertiary-type' species recognized in the Neogene strata of the Japan Sea coastal regions disappeared sequentially from the Sea of Japan during Pliocene to late Pleistocene.

Calcareous nannofossils in sediments of the Japan Sea

Preliminary results of the biostratigraphic analysis of calcareous nannofossils recovered from Ocean Drilling Program Leg 128, Sites 798 and 799, provide clues to the Quaternary oceanography of the Japan Sea. The distribution of calcareous nannofossils from the Quaternary sediments at Site 798 (903 m water depth) may record the position of an Oceanographic frontal boundary between warm water derived from a branch of the Kuroshio Current as it entered the Japan Sea through the Tsushima Straits to the south, and colder water introduced into the western portion of the Japan Sea derived from the winter chilling of northern Japan Sea surface waters. This Oceanographic front probably oscillated north-south over Site 798 in response to glacial/interglacial cycles, or perhaps to some other climatic event or combination of events unique to the Japan Sea. During the last 1.5 m.y., six major intervals are recognized when the Oceanographic front may have been north of Site 798 separated by five major intervals when the frontal boundary may have been south of the site. These migrations were centered around approximately 0.125, 0.29, 0.56, 0.62, 0.85, 0.91, 0.98, 1.0, 1.11, and 1.5 Ma, which correspond to the boundaries separating nannofossil-rich sediments from barren or nearly barren, low-carbonate intervals. Nannofossil-rich intervals may represent times when the frontal boundary was north of Site 798, and the site was above the CCD. Barren or nearly barren intervals represent times when the frontal boundary may have been south of Site 798 and the CCD was probably higher. The distribution of calcareous nannofossils at Site 799 (2073 m water depth) appears to be controlled more by the depth of the CCD than by any climatic effects. The FOD (first occurrence datum) of Emiliania huxleyi, the LOD (last occurrence datum) of Psuedoemiliania lacunosa, Helicosphaera sellii, Calcidiscus macintyrei (10 ?m), and the FOD and LOD of Reticulofenestra asanoi are recognized from Site 798 cores. The LOD of P. lacunosa is observed in sediments from Site 799. Only in the sediments younger than 1.5 Ma are the nannofossils from Sites 798 and 799 preserved well enough and sufficiently numerous for age dating and paleoceanographic conjecture. In-situ dissolution in older sediments at both sites precludes any dating or paleoenvironmental interpretations.

Geochemistry of black shales from Breitbach Creek

Lower Cretaceous sediments are frequently characterized by a well expressed cyclicity. While the processes influencing environments above the carbonate compensation depth (CCD) are reasonably well understood, almost nothing is known about the deep ocean. Cretaceous sub-CCD sediments from the Tethys and Atlantic Oceans typically show rhythmic black/green shale successions. To gain insight into the nature of these black/green shale cycles, we performed detailed geochemical analyses (X-ray fluorescence, Rock-Eval and reactive iron analysis) on a 3 m long section of latest Aptian age. The major-element distribution of the analyzed shale sequence indicates a periodic change from a high-productivity and well-oxygenated green shale mode to a low-productivity oxygen-deficient black shale mode. It is proposed here that the preservation of organic matter was dependent on the strength of salinity-driven deepwater generation. Furthermore, the data show that the Corg content covaries with changes in the detrital composition. Therefore we hypothesize that Tethyan deepwater circulation was sensitive to changes in the monsoonal system. Time series analysis suggests that these changes are periodic in nature, although we are currently unable to prove that the dominant periodicity is related to the precession component of the Milankovitch frequencies.

Interstitial-water geochemistry of Kerguelen Plateau sediments

This report synthesizes all of the interstitial-water chemistry studies associated with the Kerguelen Plateau phase of ODP Leg 119. Sediments were cored at six sites (49°24'S to 59°36'S) in water depths ranging from 564 to 4082 m. A total of 77 interstitial-water samples was recovered as part of the routine sampling protocol. In addition, a novel, highresolution pore-water sampling program was tested during Leg 119 that enabled us to pinpoint reaction zones and extend our data base to deeper, drier levels that were heretofore inaccessible. Data collected include interstitial-water sodium, potassium, calcium, magnesium, pH, alkalinity, sulfate, ammonia, phosphate, aqueous silica, salinity, chloride, oxidation-reduction potentials, and sediment chemistry. The northern sector (Sites 736 and 737) is characterized by the highest sedimentation rates (up to 140 m/m.y.) and thermal gradients (70°-98°C/km) encountered on the Kerguelen Plateau during Leg 119. Site 737 represents the most reactive sediment column cored on the Kerguelen Plateau. Major cation fluxes at Site 737 are the strongest measured during Leg 119. High dissolved calcium concentrations (141.5 mM) were encountered near the bottom of Hole 737B. Elevated temperatures promote silica diagenesis and the alteration of volcanic material below 300 mbsf, and a diagenetic front was discovered near 370 mbsf at Site 737. The southern portion of the Kerguelen Plateau (Sites 738 and 744) records the lowest sedimentation rates (less than 5 m/m.y.) and thermal gradients (43°C/km) of the three study areas. Major cation fluxes at the southern sites are the lowest that we measured on the Kerguelen Plateau. High-resolution sampling provided evidence for significant silica release to the pore waters during the weathering of basement basalt. The relatively low thermal gradient does not appear to be sufficient for the formation of the opal-CT and quartz chert beds and nodules that were encountered below 120 mbsf at Site 738. Sediment-accumulation rates on the Eastern Kerguelen Sediment Ridge (Sites 745 and 746) are intermediate to those of the northern and southern sites. Deposition below the regional CCD accounts for the nearly carbonate-free, siliceous sediments. Despite their low organic carbon contents (mean = 0.15%), sediments on the Eastern Kerguelen Sediment Ridge exhibit the highest pore-water alkalinity (6.77 mM), ammonium (0.50 mM), and phosphate (23 µM) concentrations measured on the Kerguelen Plateau. Major cation fluxes are intermediate to those calculated for the northern and southern sites. The Eastern Kerguelen Sediment Ridge interstitial waters are unusual, however, in that the downward flux of magnesium is greater than the upward flux of calcium.

Cretaceous planktonic foraminifera of DSDP Hole 71-511

Lower and Upper Cretaceous sediments of the Maurice Ewing Bank, Site 511 (black shales, mudstones, zeolitic clays, and nannofossil chalk and ooze, 361 m thick) are characterized by an assemblage of planktonic foraminifers of low systematic diversity, including over 50 species. Representatives of Hedbergella, Globigerinelloides, Archaeoglobigerina, Whiteinella, Rugoglobigerina, and Heterohelix are predominant; species of Ticinella, Praeglobotruncana, Globotruncana, Schackoina, and Planoglobulina associated with some interbeds occur in smaller numbers. Planktonic foraminifers enable us to subdivide the Cretaceous sediments into Barremian-Aptian, Albian, upper Cenomanian, Turonian, Coniacian-Santonian, Santonian, Campanian, and upper Campanian-Maestrichtian intervals. The Lower Cretaceous (Albian) and Upper Cretaceous (upper Cenomanian-Turonian) are separated by a distinct hiatus and unconformity. In the Upper Cretaceous section, a hiatus may be present at the top of the Campanian. The upper Cenomanian-Santonian sediments are reduced in thickness, whereas the Campanian-Maestrichtian interval is expanded. In the Barremian-Aptian black shales, planktonic foraminifers are very rare: they were deposited in shallow water under anoxic conditions. In the Albian, when sedimentation conditions became oxidizing and the depth increased to 200-400 meters, they became more common. By the end of the Upper Cretaceous, depths appear to increase to 2000 meters. In the interbeds of calcareous sediments, planktonic foraminifers are common; in interbeds of zeolitic clays they are rare or absent (dissolution facies). Alternation of these types of sediments is especially characteristic of the Coniacian-lower Campanian, testifying to abrupt CCD fluctuations. The planktonic foraminifers of the Falkland Plateau belong to the Austral Province of the Southern Hemisphere. In their systematic composition they are extremely similar to microfauna of the Boreal Province of the Northern Hemisphere.

Cenozoic planktonic foraminifera of the Falkland Plateau and Argentine Basin

Sites 511 and 512 (Falkland Plateau) and 513 (Argentine Basin) penetrated calcareous-siliceous oozes of the middle and upper Eocene and lower Oligocene with rather numerous planktonic foraminifers. Upper Oligocene, Miocene, Pliocene, and Quaternary sections are composed mostly of siliceous sediments (Sites 511-514) where planktonic foraminifers are rare or absent. High-latitude planktonic foraminifers of the Austral Province are characterized by impoverished assemblages - only representatives of Globigerina, Globigerinita, Globorotaloides, and Globorotalia with a rounded peripheral margin are found. In the Paleogene, these species are supplemented, in lesser amounts, by representatives of Globigerapsis, Acarinina, Pseudogloboquadrina, Pseudohastigerina, and Chiloguembelina. Assemblages of planktonic foraminifers have low stratigraphic resolution, especially in the upper Oligocene-Quaternary. This reflects the generally deteriorating Cenozoic climate, which evinced a sharp change in the upper Oligocene that is connected with initiation of the circum-Antarctic current near the Paleogene/Neogene boundary. Comparison of Paleogene and Neogene planktonic foraminifers of the South Atlantic (Falkland Plateau, Argentine Basin, 46-51°S) and the North Atlantic (Rockall Plateau, 55-56°N) indicates that the South Atlantic climate was much colder than that of the same latitudes of the North Atlantic. Paleogene oozes of the Falkland Plateau rest unconf ormably on Maestrichtian sediments and in their turn are overlain unconformably by Neogene-Quaternary oozes. Cenozoic sections are stratigraphically discontinuous: periods of intensive biogenic sedimentation resulting in a thick succession of sediments alternated with periods of nondeposition and strong erosion that resulted in hiatuses and unconformities. In the Argentine Basin, Oligocene calcareous-siliceous oozes rest on basalts of the oceanic basement; they are replaced upward in the section by Neogene-Quaternary siliceous oozes with some hiatuses. Planktonic foraminifers here clearly demonstrate the processes of oceanic subsidence and CCD fluctuations as well as Polar Front migrations during Cenozoic time. Fifty species of planktonic foraminifers are discussed and illustrated.

Geochemistry and physics on sediment cores from the Peru Basin

We studied preservation/dissolution cycles and paleoproductivity in eight sediment cores from the Peru Basin south of the highly productive surface waters of the eastern equatorial Pacific. Stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy. Sediment cores which span the last 8 m.y., were retrieved during cruise 79 with RV SONNE close to the carbonate compensation depth (CCD). In general, sediments show Pacific-type carbonate cycles. We interpret a pronounced carbonate peak between 6 and 7 Ma as the result of a western and northern extension of the highly productive Peru Current. Decreased carbonate contents from the late Miocene to the late Pliocene might be associated with a slow contraction of the latitudinal extent of the high-productivity belt north of the study areas. During the Pliocene, carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets, which should have been associated with pulsations of the Antarctic ice cap. An abrupt collapse of the carbonate system occurred at 2.4 Ma. Higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation. During the Quaternary, carbonate fluxes are high during glacials and low during interglacials. Large amplitude variations with long broad minima and maxima, associated with small migrations of the lysocline and the CCD (< 200 m), are indicative of the preservation/dissolution history in the Peru Basin. During the early Pleistocene, climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record. During the last 800 kyr, variability in the carbonate record was dominated by the 100 kyr eccentricity cycle. Fluxes of biogenic material (calcium carbonate, organic carbon, opal, and barium) were greatest during glacials, which imply higher productivity and export production of the Peru Current during cold climatic periods. Dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate. After the Mid-Brunhes Event (400 ka), we observe a plateaulike shift to enhanced dissolution and to intensified productivity.

Sedimentology on cores from the Peru Basin

We investigated surficial sediments for physico-chemical composition from numerous sites of seven study areas in the manganese nodule field of the northern Peru Basin as part of a deep-sea environmental study. Major results from this study are strong variability with respect to water depth, productivity in surface waters, locality, bottom water flow, and seafloor topography. Sediment sites are located mostly in 3900 to 4300 m water depth between the lysocline and the carbonate compensation depth (CCD). Large fluctuations in carbonate content (0% to 80%) determine sediment density and compressional-wave velocity, and, by dilution, contents of opal and non-biogenic material. Mass accumulation rates of biogenic components as well as geochemical proxies (barium and phosphorus) distinguish areas of higher productivity in the northwest near equatorial upwelling and in the northeast close to coastal upwelling, from areas of lower productivity in the west and south. Comparisons between the central Peru Basin area (Discol) and western Peru Basin area (Sediperu) reveals, for the Sediperu area, a shallower CCD, more carbonate but less opal, organic carbon, and non-biogenic material in sediments at the same water depth as well as larger down-core fluctuations of organic carbon and MnO2. Bottom water flow in the abyssal hill topography causes winnowing of material from summits of seamounts and ridges, where organic carbon preservation is poor, to basins where organic carbon preservation is better. Down-core measurements in box cores indicate a three-fold division in the upper 50 cm of the sediment column. An uppermost semi-liquid top layer is dark brown, 5-15 cm thick and contains most of the ferro-manganese nodules. A 5-15 cm thick transition zone of light sediment color has increasing shear strength, lowest opal contents and compressional-wave velocities, but highest carbonate contents and sediment densities. The lowermost layer contains stiffer light gray sediments.

Sedimentological and geochemical characteristics of upper Cretaceous and lower Tertiary sediments of ODP Hole 108-661A

Based on sedimentological and geochemical data, the Upper Cretaceous and Tertiary sequence at Ocean Drilling Program Site 661 was subdivided into four intervals: Interval I (Campanian age) is characterized by sediments deposited below the calcite compensation depth (CCD) inside a high-productivity area and well-oxygenated bottom waters, indicated by the absence of carbonate, the major occurrence of zeolites and opal-CT, and intense bioturbation. Very fine-grained siliciclastic sediments and the lack of any erosional features suggest a low-energy environment. The terrigenous fraction was probably supplied by winds from the nontropical areas in South Africa. Interval II (Maestrichtian age) is characterized by high-amplitude variations in the carbonate content indicative of a deposition above the CCD, superimposed by (climate-controlled) short-term fluctuations of the CCD. The absence of both zeolites and opal-CT imply a position of Site 661 outside high-productivity areas. The first occurrence of higher amounts of kaolinite (especially during the middle Maestrichtian) suggests the onset of a terrigenous sediment supply from tropical areas. Interval III (between uppermost Cretaceous to early Tertiary) is characterized by the absence of carbonate and zeolites, interpreted as deposition below the CCD and outside an oceanic high-productivity belt. The kaolinite-over-illite dominance suggests a terrigenous sediment supply from tropical areas. Interval IV (between early Tertiary and Miocene age) is characterized by the occurrence of black manganeserich layers, major nodules/pebbles, and erosional surfaces, indicating phases of extremely reduced sediment accumulation and bottom-current activities. In the lower part of this interval (?Eocene age), higher amounts of zeolites occur, which suggest a higher oceanic productivity caused by equatorial upwelling. The source area of the terrigenous sediment fraction at Site 661 was the tropical region of northwest Africa, as suggested by the kaolinite-over-illite dominance.

Pebbles and carbonate nodules Legs 56-57 Holes

At all DSDP Leg 56 drilling sites, exotic pebbles occur commonly, throughout the cores. Chips of carbonate nodules occur only at Site 434 on the lower inner trench wall. Both exotic pebbles and carbonate nodule chips sometimes tend to be concentrated at particular levels of cores. Exotic pebbles are generally well rounded and consist of various rock types, such as dacite, andesite, basalt, tuff, gabbro, granodiorite, metaquartzite, biotite hornfels, lithic wacke, mudstone, etc., of which dacite occurs commonly at all the sites. Almost all pebbles at Site 436 and most at Sites 434 and 435 may have been rafted by ice. Some at the latter sites may have been derived by down-slope slumping. Carbonate nodules consist of microcrystalline dolomite, manganoan calcite, and siderite; CaCO3 content ranges from 22 to 65 per cent. They are also generally characterized by a high content of P2O5. The nodules are commonly rich in diatom remains, some of which indicate that the nodules are autochthonous. Some nodules contain abundant glass shards, with a modal refractive index of 1.499, almost identical to shards in the surrounding mud and ooze. These facts suggest that the carbonate nodules may have been formed diagenetically, in situ. This may throw light on problems of the formation of carbonate nodules in ancient "geosynclinal" sediments. It is also very important to point out that these carbonate nodules were formed within sediment deposited well below the CCD.

Calcareous nannofossils of ODP Hole 123-765C and DSDP Hole 27-261

Sediments from the Argo Abyssal Plain (AAP), northwest of Australia, are the oldest known from the Indian Ocean and were recovered from ODP Site 765 and DSDP Site 261. New biostratigraphic and sedimentologic data from these sites, as well as reinterpretations of earlier findings, indicate that basal sediments at both localities are of Late Jurassic age and delineate a history of starved sedimentation punctuated by periodic influx of calcareous pelagic turbidites. Biostratigraphy and correlation of Upper Jurassic-Lower Cretaceous sediments is based largely on calcareous nannofossils. Both sites yielded variably preserved nannofossil successions ranging from Tithonian to Hauterivian at Site 765 and Kimmeridgian to Hauterivian at Site 261. The nannofloras are comparable to those present in the European and Atlantic Boreal and Tethyan areas, but display important differences that reflect biogeographic differentiation. The Argo region is thought to have occupied a position at the southern limit of the Tethyan nannofloral realm, thus yielding both Tethyan and Austral biogeographic features. Sedimentary successions at the two sites are grossly similar, and differences largely reflect Site 765's greater proximity to the continental margin. Jurassic sediments were deposited at rates of about 2 m/m.y. near the carbonate compensation depth (CCD) and contain winnowed concentrations of inoceramid prisms and nannofossils, redeposited layers rich in calcispheres and calcisphere debris, manganese nodules, and volcanic detritus. Lower Cretaceous and all younger sediments accumulated below the CCD at rates that were highest (about 20 m/m.y.) during mid-Cretaceous and Neogene time. Background sediment in this interval is noncalcareous claystone; turbidites dominate the sequence and are thicker and coarser grained at Site 765. AAP turbidites consist mostly of calcareous and siliceous biogenic components and volcanogenic smectite clay; they were derived from relatively deep parts of the continental margin that lay below the photic zone, but above the CCD. The Jurassic-Lower Cretaceous section is about the same thickness across the AAP; turbidites in this interval appear to have had multiple sources along the Australian margin. The Upper Cretaceous-Cenozoic section, however, is three times thicker at Site 765 than at Site 261; turbidites in this interval were derived predominantly from the south. Patterns of sedimentation across the AAP have been influenced by shifts in sea level, the CCD, and configuration of the continental margin. Major pulses of calcareous turbidite deposition occurred during Valanginian, Aptian, and Neogene time-all periods of eustatic lowstands and depressed CCD levels. Sediment redeposited on the AAP has come largely from the Australian outer shelf, continental slope, or rise, rather than the continent itself. Most terrigenous detritus was trapped in epicontinental basins that have flanked northwestern Australia since the early Mesozoic.

Foraminiferal species and dissolution index at DSDP Hole 78-541

The calcite compensation depth (CCD) fluctuates as a result of changes in the water-mass system, thereby producing a distinct dissolution pattern. Differential dissolution changes the composition of the foraminiferal assemblages, reflecting the depositional environment in respect to the fluctuating CCD. The dissolution pattern for the comparatively shallow Site 541 on the Barbados Ridge indicates a depositional environment mostly above the CCD, but below the foraminiferal lysocline during the late Miocene to early Pleistocene. In contrast, sediments of the deeper-water Site 543 indicate a depositional environment above the CCD during the late Pliocene to early Pleistocene only. Furthermore, similarities in the dissolution pattern of corresponding time intervals of Site 541 (represented by superimposed faulted intervals termed Tectonic Units A and B) are recognizable. Sediments deposited clearly above the foraminiferal lysocline are rare