REE and istotopic composition of ODP Site 127-797 clays

X-ray diffraction analyses have been carried out on 128 samples of Miocene to Quaternary sediments from ODP Sites 794, 795 and 797. Some clay fractions of samples from Site 797 have also been studied for rare earth elements and by Nd isotopic analyses. These three sites display similar lithological and clay assemblages (with dominant chlorite, illite and smectite) showing that the sedimentation was homogeneous throughout the whole Japan Sea Basin. Three mineralogical zones are recognized. The first zone (Lower Miocene sandy clay of Sites 794 and 797) is mainly composed of chlorite resulting from hydrothermal transformation of arc-derived smectite, due to sill injections during the initial oceanic spreading stage. The second zone (Lower Miocene to Lower Pliocene siliceous claystone and diatomaceous silty clay) is dominated by arc-derived smectite; the abundance of this mineral decreases upwards while illite and chlorite increase. This trend reflects a change of detrital source, from an eastern arc-derived source (epsilon -Nd**t>-3.3); variable LREE enrichment) to a western continental crust source (epsilon-Nd**t<-9.4; shale-like REE patterns); climatic modifications in the current dynamics are proposed as a cause for this change. The third zone (Upper Pliocene to Recent silty clay with minor diatom oozes) is characterized at Site 797 by increasing amounts of illite and chlorite. This reflects a more and more important western supply which is assumed to be related to tectonic rejuvenations of the Asian margin or climatic modifications affecting the alteration conditions or the current dynamics. At Sites 794 and 795, the more or less sharp supply of chlorite seems to be driven by the incipient subduction zone on the eastern margin of the Japan Sea.

Chiasmolithus species in middle Eocene and Oligocene sediments of ODP Holes 105-647A and 120-748B

In this preliminary biometric study of the calcareous nannofossil species Chiasmolithus expansus, Chiasmolithus oamaruensis, and Chiasmolithus altus from the upper middle Eocene to lower Oligocene of Sites 647 and 748, we document a complete gradation of forms among all three species. Chiasmolithus oamaruensis has significantly higher morphologic variance than the other species. The Chiasmolithus population at each site changes from C. expansus to C. oamaruensis and then to C. altus. This may not reflect a true evolutionary sequence because a major reversal in shape change of the central cross-bar structure accompanies this sequence, and because C. altus is morphologically closer to C. expansus than it is to C. oamaruensis. The change in the width of the cross-bar structure is primarily a result of changes in the alignment of the central connecting bar, rather than of changes in the cross-bar angle. At Site 748, two fluctuations in morphology produce sample populations intermediate between all three species. In addition, reported stratigraphic and paleogeographic occurrences of C. oamaruensis and C. altus show different latitudinal distributions. These morphological and distributional patterns may be explained by a continuous morphologic gradient between C. oamaruensis and C. altus, with C. oamaruensis occurring more commonly in cool-water paleoenvironments, and C. altus occurring more commonly in cold-water paleoenvironments. Thus, paleoenvironmental fluctuations at Site 748 may be the cause of the morphologic fluctuations in Chiasmolithus. This hypothesis can be tested against previously proposed evolutionary models by more detailed sampling of sections along a latitudinal transect.

Calcareous dinoflagellates in Cretaceous to Recent sediments of DSDP Hole 39-356

Calcareous dinoflagellates often dominate the dinoflagellate cyst assemblage in Cretaceous to Recent oceanic sediments. However, their distribution in Paleogene sediments has scarcely been studied. The investigation of samples from DSDP Site 356 for their calcareous dinoflagellate content revealed 35 mainly long-ranging taxa. The associations and characteristic wall types (pithonelloid, oblique, radial, tangential) fluctuate quantitatively and qualitatively in distinct stratigraphic patterns. Significant shifts, primarily at the K/T boundary and the Paleocene/Eocene boundary, reflect changes in environmental conditions. Certain dinoflagellates forming calcareous cysts, such as Operculodinella operculata, were well adapted to the relatively rapid change of environmental conditions at the K/T boundary, thus blooming to dominate the carbonate flux to the ocean floor. In contrast to the stable Paleocene associations, Eocene calcareous dinoflagellates show fluctuations in relative abundances. These fluctuations can possibly be attributed to redeposition related to increased seaward transport of specimens, due to strengthened western boundary currents. The flora includes two new genera, one new species, and two new forms: Retesphaera diadema Hildebrand-Habel, Willems et Versteegh, gen. et. sp. nov., Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Sphaerodinella? tuberosa forma elongata Hildebrand-Habel, Willems et Versteegh, comb. et forma nov., Sphaerodinella? tuberosa forma variospinosa Hildebrand-Habel, Willems et Versteegh, comb. et forma nov. Three new combinations are proposed: Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Operculodinella operculata (Bramlette et Martini, 1964) Hildebrand-Habel, Willems et Versteegh, comb. nov., and Sphaerodinella? tuberosa (Kamptner, 1963) Hildebrand-Habel, Willems et Versteegh, comb. nov. The genus Operculodinella Kienel, 1994 is emended.

High resolution paleoceanography of the Guaymas Basin, Gulf of California, during the past 15000 yeras

Deep Sea Drilling Project Site 480 (27°54.10'N, 111°39.34'W; 655 m water depth) contains a high resolution record of paleoceanographic change of the past 15000 years for the Guaymas Basin, a region of very high diatom productivity within the central Gulf of California. Analyses of diatoms and silicoflagellates were completed on samples spaced every 40-50 yr, whereas ICP-AES geochemical analyses were completed on alternate samples (sample spacing 80-100 yr). The Bolling-Allerod interval (14.6-12.9 ka) (note, ka refers to 1000 calendar years BP throughout this report) is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals, suggesting conditions somewhat similar to those of today. The Younger Dryas event (12.9-11.6 ka) is marked by a major drop in biogenic silica and an increase in calcium carbonate. Increasing relative percentage contributions of Azpeitia nodulifera and Dictyocha perlaevis (a tropical diatom and silicoflagellate, respectively) and reduced numbers of the silicoflagellate Octactis pulchra are supportive of reduced upwelling of nutrient-rich waters. Between 10.6 and 10.0 ka, calcium carbonate and A. nodulifera abruptly decline at DSDP 480, while Roperia tesselata, a diatom indicative of winter upwelling in the modern-day Gulf, increases sharply in numbers. A nearly coincident increase in the silicoflagellate Dictyocha stapedia suggests that waters above DSDP 480 were more similar to the cooler and slightly more saline waters of the northern Gulf during much of the early and middle parts of the Holocene (~10 to 3.2 ka). At about 6.2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom A. nodulifera marks a major change in oceanographic conditions in the Gulf. A winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions (El Nino-driven?) of the North Equatorial Countercurrent during the summer. Beginning between 2.8 and 2.4 ka, the amplitude of biogenic silica and wt% Fe, Al, and Ti (proxies of terrigenous input) increase, possibly reflecting intensification of ENSO cycles and the establishment of modern oceanographic conditions in the Gulf. Increased numbers of O. pulchra after 2.8 ka suggest enhanced spring upwelling.

Sedimentological and palynological study of sediment cores from the northern Mekong River Delta

A sedimentological and palynological study of three sediment cores from the northern Mekong River Delta shows the regional sedimentary and environmental development since the mid-Holocene sea level highstand. A sub- to intertidal flat deposit of mid-Holocene age is recorded in the northernmost core. Shoreline deposits in all three cores show descending ages from N to S documenting 1) the early stages of the late Holocene regression and 2) the subsequent delta progradation. The delta plain successions vary from floodplain deposits with swamp-like elements to natural levee sediments. The uppermost sediments in all cores show human disturbance to varying degrees. The most intense alteration is recorded in the northernmost core where the palynological signal together with a charcoal peak indicates the profound change of the environment during the modern land reclamation. The sediments from at least one of the three presented cores do not show a "true" delta facies succession, but rather estuary-like features, as also observed in records from southern Cambodia. This absence is probably due to lack of accommodation space during the initial phase of rapid delta progradation which impeded the development of "true" delta successions as shown in cores from the southern Mekong River Delta.

Organic geochemistry of sediment samples from Prydz Bay

High molecular weight aliphatic hydrocarbons were extracted from sediments at two sites (741 and 742) drilled during Ocean Drilling Program Leg 119 in Prydz Bay, a major embayment on the continental shelf of East Antarctica. The distributions of n-alkanes and triterpenoid and steroid hydrocarbons suggest that the n-alkanes and steranes are mainly of terrestrial origin and that the hydrocarbons are immature to slightly mature in the Lower Cretaceous sediments and immature to mature in the Tertiary sediments. At Site 741, the Lower Cretaceous depositional sequence, which is generally characterized by immature hydrocarbons, is interrupted by sediment having more mature components, suggesting a change of source during part of Early Cretaceous time. At Site 742, the mature geochemical parameters of a Pliocene sample correlate with results reported elsewhere for Site 739. In all but one of the other Tertiary samples, the geochemical parameters indicate intermediate maturity. The Lower Cretaceous and Pliocene sediments average about 1.9% organic carbon, a value of interest from the point of view of potential sources of petroleum offshore from Antarctica.

Elevation Models of Antarctica and Greenland derived from CryoSat-2 in the period 2011 to 2013

This study focuses on the present-day surface elevation of the Greenland and Antarctic ice sheets. Based on 3 years of CryoSat-2 data acquisition we derived new elevation models (DEMs) as well as elevation change maps and volume change estimates for both ice sheets. Here we present the new DEMs and their corresponding error maps. The accuracy of the derived DEMs for Greenland and Antarctica is similar to those of previous DEMs obtained by satellite-based laser and radar altimeters. Comparisons with ICESat data show that 80% of the CryoSat-2 DEMs have an uncertainty of less than 3 m ± 15 m. The surface elevation change rates between January 2011 and January 2014 are presented for both ice sheets. We compared our results to elevation change rates obtained from ICESat data covering the time period from 2003 to 2009. The comparison reveals that in West Antarctica the volume loss has increased by a factor of 3. It also shows an anomalous thickening in Dronning Maud Land, East Antarctica which represents a known large-scale accumulation event. This anomaly partly compensates for the observed increased volume loss of the Antarctic Peninsula and West Antarctica. For Greenland we find a volume loss increased by a factor of 2.5 compared to the ICESat period with large negative elevation changes concentrated at the west and southeast coasts. The combined volume change of Greenland and Antarctica for the observation period is estimated to be -503 ± 107 km**3/yr. Greenland contributes nearly 75% to the total volume change with -375 ± 24 km**3/yr.