C21B-0515
Sedimentary Facies And Sequence Stratigraphy Across The Middle Miocene Transition, AND-2A, Antarctica
In 2007, ANDRILL drilled a 1138.54 m-deep hole (AND-2A) in southern McMurdo Sound into early Miocene to Pleistocene strata, including an expanded middle Miocene section. Here we present a facies model and an analysis of the sequence stratigraphy of AND-2A and discuss its implications for the interpretation of eustasy and ice volume proxies across the middle Miocene transition. Sixty sequences were identified, each bounded by sharp-based conglomerates or diamictites. Although there is significant variability in the character and vertical arrangement of facies, two stacking patterns or motifs can be recognized. Motif 1 is diamictite- dominated and represents glacially dominated environments, including subglacial environments, with only brief intervals of ice-free coasts. Motif 2 includes a wider variety of facies and is more consistent with a dynamic ice-sheet with facies characteristic of open marine to iceberg-influenced environments. Based on the distribution of these facies motifs in the core it can be concluded that the middle Miocene Antarctic ice sheets were dynamic and accompanied by major base level changes. In the AND-2A core, the middle Miocene climatic optimum (15-17 Ma) as recognized in proxy records, is characterized by facies indicating ice sheet and sea ice minima with a larger biogenic component. A transition to glacially dominated facies associations indicates that ice expansion took place at ca. 15.5 Ma under strongly fluctuating sea surface temperatures until large ice sheets with massive ice shelves periodically became grounded on the shelf by ca. 13 Ma. These results suggest that ice sheet-ocean feedbacks may have played a role in the origin of the middle Miocene transition.
C21B-0516
Effect of the Drake Passage on the Cenozoic Glaciation of Antarctica
The Cenozoic glaciation of Antarctica marks the onset of a phase of the Earth's history characterized by the
existence of large continental ice sheets. The context of this climate shift took place by an acceleration of the
long term trend of decreasing atmospheric CO2 on the one hand, and by tectonic activity leading to the
opening and deepening of the Drake Passage (DP) on the other, which enabled the formation of the
Antarctic Circumpolar Current and the subsequent thermal isolation of the continent. Here we adopt an
original and novel approach based on a fully coupled climate-cryosphere model to investigate the role of
both forcing factors on Antarctica glaciation and on global climate. We performed a series of experiments with
shut and open DP at different pCO2 and we show that the ice sheet build up is strongly sensitive to the DP
configuration for CO2 concentration set to three times the pre-industrial atmospheric level (PAL). Because
isotopic reconstructions depict an atmospheric CO2 around 3 PAL at the Eocene-Oligocene boundary, our
results suggest that the DP played an important role in triggering the inception of the Antarctic ice sheet.
Moreover, non-linear interaction between major forcing factors explains the occurrence of large glaciation
already at 3 PAL, as recorded in delta18O data. The simulated Antarctic ice sheet build up may be compared
to real data that would provide some better constraints for our future modelling studies.
http://www.lsce.ipsl.fr/
C21B-0517
Mineralogy of Pleistocene Sediments Under the McMurdo Ice-Shelf (ANDRILL-MIS Project)
The criosphere in the McMurdo Sound region has undergone significant modifications during the last 1 Ma. Consequently, the sedimentary sequences under the McMurdo ice-shelf provide geological data to reconstruct variations in transport and depositional mechanisms of terrigenous material due to variations in ice sheet extension, grounding line position, main ice-stream flows and sea-ice coverage during glacial and interglacial periods. Our study aims to characterize the Pleistocene glacimarine sediments recovered during the ANDRILL-McMurdo Ice Shelf Project in Windless Bight (South of Ross Island) from a mineralogical point of view. Clay an heavy mineral from the clay and sand fractions, respectively, have been semiquantitatively determined using X-ray diffraction and SEM-EDS techniques. Illite, chlorite, and smectite comprise the clay mineral assemblage, being illite and smectite the principal components; olivine, titanoaugite and glass dominate the heavy mineral assemblage; diopside, orthopyroxene, amphibole, garnet and apatite are present in minor amount. The sets of analyses show that the sediments are a mix of local McMurdo Volcanic Group (MVG) rocks and Transantarctic Mountains (TAM) source rocks from the south and west. The down core variations of the two sets of data are not correlated. Clay mineral assemblage present a strong variation between 30 and 50 mbsf. Differently, variations in heavy mineral assemblage are linked to variation in sedimentological facies, as revealed by canonical discriminant function analyses.
C21B-0518
Sub-Sea Ice Sands Offshore of Dry Valleys: Potential Links between Onshore and Offshore Cenozoic Records
Onshore and offshore records of late Cenozoic history of Southern Victoria Land (SVL), Antarctica, depict strikingly different scenarios; onshore (Dry Valleys), the geomorphic record indicates long term (Ma) stability of polar deserts whereas offshore (e.g., ANDRILL 1B), the stratigraphic record reveals repeated ice sheet fluctuations and major cooling and establishment of modern conditions in the Late Pliocene. Recognition of facies deposited beneath near permanent sea ice offshore of the Dry Valleys provides an often overlooked but direct method of connecting the disparate records. As part of an initial effort to document facies characteristics, shallow marine cores >30 cm long were collected from a depth of ~20 m in Explorers Cove at the mouth of the Taylor Dry Valley. Shell material characteristics, bioturbation, grain size distribution, and surface textures of quartz grains were analyzed to elucidate taphonomic processes and sediment transport mechanisms, and to constrain the rate of sedimentation. Little shell material was found in the cores, but foraminifera were widespread and sponge spicules were locally abundant. Some bioturbation is apparent in the top 5 cm, and sediment, primarily medium to coarse sand, is poorly sorted and unlaminated with a coarser zone at 8-21 cm depth. Eolian features are abundant on quartz grain surfaces whereas features indicative of fluvial and glacial transport are less common. Eolian transport probably is the dominant transport process, with sediment blown onto the sea ice and eventually deposited on the sea floor via ice cracks. Small summer streams could also deliver sediment to coastal moats, transporting material beneath the sea ice to deeper nearshore water. Results from this study can be applied to analogous present-day habitats in Antarctica and to the interpretation of Cenozoic stratigraphic sequences in cores.
C21B-0519
Paleomagnetism of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica
Paleomagnetic data from Site AND-2A (77°45.488'S, 165°16.605'E, ~383.57 m water depth)
provide a rare view of geomagnetic field behavior at high latitude and are the basis for a
magnetostratigraphic study, which aims to date climatic change in the Ross Sea since the early Miocene. A
total of 813 mini-core samples were collected that span from the top of the section down to the base at
1138.54 mbsf. In addition, 11 U-channel samples were collected from a fine-grained, laminated interval at
1016-1040 mbsf to examine short-term geomagnetic field variability over a period of 100-200 k.y. in the early
Miocene. AF demagnetization was generally able to resolve a characteristic remanent magnetization (ChRM)
as well or better than thermal demagnetization. Above Lithostratigraphic Unit (LSU) 8 (436.18 mbsf), where
lithologies are generally more coarse grained than lower in the section, resolving a ChRM is difficult and
recent overprints or a drilling overprint are a concern. Within LSU 8 and below, most samples have a ChRM
that can be resolved. The ChRM is most likely an original depositional magnetization throughout most of this
lower section. Based on 40Ar/39Ar dates and diatom datums, the magnetozones identified from the base of
the hole up to ~266 mbsf are consistent with spanning from either Chron C6n (18.748-19.772 Ma) or
C6An.1n (20.040-20.213 Ma) up through Chron C5Br (15.160-15.974 Ma). The spacing of polarity reversals
below 266 mbsf and their correlation with the GPTS indicates that this part of the stratigraphic section was
deposited between 15 and 20 Ma at a mean sedimentation rate of about 18 cm/k.y. Analysis of the
inclinations from the mini-cores and U-channels allow us to assess the fidelity of the geomagnetic record and
to estimate geomagnetic field properties over the tangent cylinder (the cylinder coaxial with Earth's rotation
axis and tangent to the inner core/outer), where paleomagnetic data are rare and geomagnetic field
variability may provide clues about the nature of fluid flow in the outer core.
http://www.andrill.org
C21B-0520
ANDRILL educational activities in Italy: progettosmilla.it, a case-study of an interactive project
In January 2006, the Italian ANDRILL (Antartic Geological Drilling) team selected the project progettosmilla.it
and its instructor Matteo Cattadori, a high school teacher and collaborator of Museo Tridentino di Scienze
Naturali (TN - Italy) to represent Italy in the ANDRILL-ARISE team. The ARISE (Andrill Research Immersion for
Science Educators) comprised a group of teachers from 4 nations (US, New Zealand, Germany and Italy)
and is part of the initiative Public and Educational Outreach component of the ANDRILL project. The selected
teachers are sent to Antarctica and are actively involved in all stages of the scientific investigation, with the
main aim of establishing a bridge between research and the schools in the participating countries.
Progettosmilla.it was selected to take part in the first edition of ANDRILL-ARISE held at the American
Antarctic base of Mc Murdo during the 2006-2007 austral summer.The project makes use of different tools,
techniques and forms of communication-education to stimulate the interest and motivation of students,
teachers and organizers/trainers in ANDRILL research and polar sciences in general. Activities are organized
and scheduled according to a fixed timetable that cover 2/3 of an academic year and are centered on the
site www.progettosmilla.it. This site feature daily reports, as well as online activities and various services for
users in Italian schools. Among the online materials, more conventional ones are: - summaries of the
ANDRILL research and the Antarctic environment; including multimedia (1200 photos, 10 video and audio);
resource folders for teachers on 10 different subjects of study; course work for the participating school
students. - ITC-oriented materials such as: videoconferencing and chat sessions with Antarctica or between
classes, blogs, web-quest, animations and interactive teaching. -Many services are implemented in
collaboration with other teachers and allow the ARISE team to perform distant collaborative work between
classes of different nations. The project also envisages at least one follow meeting at each participating
school with Mr Cattadori and available ANDRILL researchers, in addition to daily support via e-mail to
students and teachers to facilitate knowledge transfer or organise teaching activities, such as visits to
research centers/museums, contact with other ANDRILL participants/researchers etc. Progettosmilla.it
involved 66 registered schools across 18 Italian provinces with a total of 2100 students, 70 meetings at
schools and 6000 visits per month to the website.
http://www.progettosmilla.it/
C21B-0521
Mineralogy of Neogene Mudrocks From ANDRILL AND-1B: Provenance Signal Dominates Sediment Composition Beneath the McMurdo Ice Shelf
The goal of the ANDRILL McMurdo Ice Shelf (MIS) Project is to define the Late Neogene tectonic, volcanic, paleoclimatic, and paleoenvironmental histories of the northwestern sector of the Ross Ice Shelf. To achieve this goal, a 1284.87 m-long drillcore (AND-1B) was recovered from beneath the present-day MIS during Oct- Dec 2006. The core contains a range of lithologies, including diamictites, sandstones and mudstones (some clast-bearing), diatomites, volcanic ash/tuff, and one lava flow. Because the mineralogy of fine-grained terrigenous sediments can provide valuable data about both sediment provenance and terrestrial weathering conditions, samples from fine-grained terrigenous intervals of AND-1B are being analyzed by x-ray diffractometry (XRD) of pressed powders. Data presently are available for 26 samples, and define large-scale compositional patterns through AND-1B. In scans of unglycolated pressed powders, the most abundant phases generally are quartz and feldspar. The quartz/feldspar ratio, estimated from the relative intensities of their largest XRD peaks, is low in Lithostratigraphic Unit 1 (LSU 1), intermediate in LSUs 2, 3, 4, and 8, and high but variable in LSU 6. These ratios are consistent with the relative importance of older mafic volcanic vs. more silicic "basement" sources identified for each LSU from sandstone and clast analyses. Analcime dominates the one sample from LSU 5, reflecting alteration of its contemporaneously erupted volcanic component. Calcite or dolomite is present in six samples in varying abundance, reflecting the heterogeneity of carbonate cementation observed during visual core description. In scans of glycolated pressed powders, the relative abundance of illite generally follows the pattern of the quartz/feldspar ratio, whereas the relative abundance of expandable clays ("smectites") follows the abundance of the "contemporaneous" volcanic component identified in smear slides. These compositional patterns are controlled by sediment provenance: older volcanics vs. "basement" vs. contemporaneous volcanics. The complete data set ultimately will provide significant compositional detail within each LSU, and may reveal variations linked to changes in terrestrial weathering conditions.
C21B-0522
Over-Sea-Ice Multi-Component VSP at the AND-2A Drill Hole: ANDRILL Southern McMurdo Sound Project
During the austral summer, 2007, the ANtarctic geological DRILLing Program (ANDRILL) drilled, cored and logged the AND-2A drill hole as part of the Southern McMurdo Sound (SMS) Project in the western Ross Sea, Antarctica. As part of the logging program, a single near-offset over-sea-ice Vertical Seismic Profile (VSP) was collected in the AND-2A drill hole. The VSP was collected using a Generator-Injector (GI) air-gun source that was suspended by a cable through a hole in the sea-ice. The GI air gun was selected to minimize the bubble-pulse effects common to explosive sources placed in the water column and because of the poor coupling of sea-ice surface seismic sources. Inconsistent injection-bubble timing caused source wavelet stretching and bubble oscillation. Two-pass deconvolution with short and long prediction lags helped shorten the wavelets and minimize oscillation. A single three-component geophone provided high-quality downgoing P- and S-wave data from which subsurface velocities were determined. The VSP P-wave time-depth curve closely agrees with the time-depth curve derived from whole-core velocity measurements. Downgoing P- wave events were recorded with strong water-bottom multiples occurring throughout the section. A P-wave corridor stack is in good agreement with the surface seismic data at the SMS site. Major seismic reflectors in the corridor stack correspond to important stratigraphic boundaries that are observed in the core. Downgoing and upgoing mode-converted PS-waves were also recorded on both radial and transverse components. Mode-conversion and S-wave birefringence indicate significant anisotropy beginning in the near sea floor (approximately 20 mbsf) and continuing to depth in the drill hole. The S-wave radial component travels as the slow shear wave and the transverse as the fast shear wave. This is in agreement with the overall fracture orientation expected from the regional stress regime. Two component rotation analysis generated an average fracture azimuth of N 45o W (+/- 10o). A 2C coarse-layer stripping method could better constrain fracture orientation over select intervals within the section.
C21B-0523
New Style Geologic Map of Mostly Later Holocene and Recent Features of the Greater South Pole Basin
Topographic contour maps of the East Antarctic Plateau show a prominent but apparently unrecognized
basin of ~700,000 km2 that lies ~200 m below surrounding surfaces. The
basin's defining hallmark is a remarkably straight, 900 km-long headwall or headslope,
passing almost under the pole and linking upper reaches of the Recovery and Foundation ice streams, the
two separated by a central platform (CP).
Throughout the basin a distinctive regional snow and firn unit, identifiable on satellite images by ~2km
wavelength, zebra-striped megadunes, forms the basal horizon for a new type of geologic map for the
Plateau. This unit underlies all other features, probably as an inactive paleo-climatic relic of diachronous
Holocene age. Most deposits covering it consist of several generations of successively overprinted
longitudinal dunes commonly intermingling with wind eroded channels, ice deformational features, and
regionally curving snow streamers. Above this complex, a widespread but discontinuous, smooth surfaced
deposit covers megadunes, local basins, major divides and floors of linear sags or extension zones. The
young unit is irregularly disrupted and sheared over active ice streams. Over all these features are
widespread, near-modern to modern fields or patches of active, longitudinal dunes with 100-300 m
wavelengths.
A prominent, graben-like, linear sag zone occurs along the headwall's brow line but
unlike those of traditional grabens, its edges show no visible fault offset at present resolutions. At the foot of
the headslope, a large bergshrund-like area is localized above the sub-glacial Recovery Lakes. Thick fill in
this area covers the megadune unit only to be disrupted by still younger sag zones. On the CP floor, a
number of sharp-edged, shear-bounded 100-300 km wide sub-provinces are defined by differences in
thickness and types of megadune cover and by amounts of extension or crevassing. At the heads of some
zones, shear lines encroach upslope into young cover while other zones show complex histories of
deformational abandonment and/or reactivation. Apparently, the overall ice sheet has a complex history of
zonal behavior involving unsteady or evolving local flow patterns.
Bedrock topography exerts significant control on these flow patterns as indicated by major ice streams or
basins localized above sub-glacial drainage channels and bedrock basins of the Recovery Lake and other
systems. Several other shear-bounded sub-provinces overlie bedrock basins or lie immediately upstream of
gaps in the Transantarctic Mountains. Just beyond the basin's edge,
'islands,' bounded by several generations of shear zones and
differing in depositional and deformational history, are localized above bedrock highs. The most significant
bedrock control is a probable fault line scarp, 900 km long and ~200 m high underlying the headslope.
At one end this fault passes nearly under the pole while the other end splays to form a terrace in the
headslope. Near the pole a second, opposite-facing scarp combines with the main scarp to form an uplifted
horst block, isolating an arm of the greater basin, hindering ice drainage and forming an accumulation base
for a ~50,000 km2 semi-triangular tableland.
Geologic maps of this type may be helpful in correlations among drill cores and sampling sites, in estimating
the amounts and patterns of younger accumulation, in refining details of complex ice flowage, and in piecing
together a more unified overview of younger events on the Plateau.
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C21B-0524
Rationale for Proposed ANDRILL Drilling Targets on the Coulman High, Ross Sea, Antarctica.
ANDRILL (ANtarctic geological DRILLing) has proposed to drill two sites on the Coulman High (CH) located
near the leading edge of the Ross Ice Shelf (RIS), using the fast-moving RIS as the drilling platform. High
resolution seismic surveys of the sea-floor at the proposed CH drill sites are characterized by basement and
syn-rift strata (Cretaceous(?)-Paleogene) faulted into N-S half grabens, overlain by undeformed sediments
(upper Oligocene and Miocene) above a widespread angular unconformity. CH drill sites will provide new
stratigraphic data eastward out of the well understood Victoria Land Basin (VLB) targeting a Cretaceous(?)-
Paleogene to middle Miocene section in order to address fundamental questions of global climate evolution
and regional tectonics. This will enable us to determine fundamental shifts as well as transient excursions in
the Antarctic cryosphere that impacted global ocean and climate reorganization. CH drilling will supply a high
resolution record of the glacial and tectonic evolution of West Antarctica providing critical geologic
constraints for climate and ice sheet models, as well as provide a key stratigraphic reference section for
further exploration under the RIS towards West Antarctica. Four of ANDRILL's programmatic themes will be
addressed by an integrated approach involving site surveys, core recovery and analysis, regional
interpretations and numerical modeling: (1) history of Antarctic climate and ice sheets; (2) Antarctica's role in
Earth's ocean-ice-climate system; (3) evolution of polar biota; and (4) Antarctic tectonics. Two boreholes are
proposed to be advanced 1200 m below the sea floor beneath the greater than 250 m thick Ross Ice Shelf,
and through a 500 m-thick sub-ice water column. CH project results will provide insight on: (1) development
of the Antarctic cryosphere with a focus on the influences from West Antarctica; (2) magnitude and frequency
of West Antarctic cryospheric changes on millennial timescales; (3) influence of West Antarctic ice sheets on
Paleogene to Miocene climate, thermohaline circulation and eustasy; and (4) timing of Antarctic tectonic
episodes and the development of sedimentary basins in West Antarctica.
http://www.andrill.org
C21B-0525
Foraminiferal Record From Drillcore AND-2A, Southern McMurdo Sound, Antarctica.
ANDRILL's Southern McMurdo Sound Project (SMS) recovered a 1138.54 meter cored interval in drill core AND-2A. A total of four hundred and fifty-nine samples from lithostratigraphic units (LSUs) 1-14 of AND-2A were collected for initial foraminiferal analyses, of which 219 yielded foraminifera. Preliminary analyses resulted in the recognition of 25 taxonomic groups including 4 genera of planktonic and 21 genera of benthic foraminifera. Planktonic foraminifera are rare, occurring in LSUs 1, 2, 5, 7 and 12. Benthic foraminifera were recovered from LSUs 2-9, 11, 12, and 14 with diversity ranging from 1 to 10 taxa. Preservation ranges from Good to Poor with the best preservation of Good to Fair in LSUs 1, 2 and 3. The remaining intervals are represented by Fair to Poor preservation. Broad benthic foraminiferal zonations are observed. Zone 1 includes LSU 1 through LSU 5 and contains benthic foraminifera common to the late Miocene and mid- Pliocene assemblages of DVDP 10 and 11 from Taylor Valley. Zone 2 is restricted to LSU 7 and includes foraminifera indicating a possible early to mid-Miocene age and change in depositional environment. Foraminiferal Zone 3 is comprised of LSU 8.1 through 14. With the exception of LSU 9, this zone has the lowest diversity, poorest preservation and recovery in AND-2A. The foraminiferal assemblages reported are consistent with the current age model of the core, having affinities to early Miocene through mid- Pliocene assemblages from the Victoria Land Basin and its margins. Further analyses will increase the resolution of the foraminiferal zonations and allow for better correlation to not only DVDP 10 and 11 but to the additional drill cores from the Victoria Land Basin and its margin.
C21B-0526
A South Atlantic Iceberg-Rafted Debris Record of Antarctic Ice Sheet History for the Interval From About 930 ka to About 1145 ka
Iceberg-rafted debris (IRD) is definitive evidence of the presence of a continental (marine-based margin) ice sheet in the source area. We here provide a record of IRD from a South Atlantic location (ODP Site 177- 1090, 43° S, 9° E), for the interval from ~930 ka to ~1145 ka. This interval is currently of much interest, as it is thought to include the period across which the dominant periodicity of the global climate system shifted from 41 ka to 100 ka cycles (Raymo et al., 2006). At this distal site, IRD is found at relatively low levels, but persistently, even during the strong warm interglacial of Marine Isotope Stage (MIS) 31. Significant levels of IRD are present during most glacials. MIS 32 appears to be a relatively warm glacial, with IRD at levels as low as during most interglacials, and so perhaps should be instead considered a stadial within a longer MIS 31. The presence of garnets throughout this studied interval indicates a likely East Antarctic provenance for the IRD.
C21B-0527
Modelling Antarctic Ice Sheets Under Greenhouse Earth Conditions: Did Ice Sheets Exist on Antarctica Even Under Cretaceous Climates?
The polar regions during the Cretaceous period have traditionally been reconstructed as being warm and ice-free. Recent investigation of eustatic sea-level change that occurred during this period, however, suggests a glacial origin. The most plausible cause being the growth and decay of moderate sized ice- sheets. This project aims to investigate this hypothesis, by exploring the form of possible Antarctic ice-sheets during the Maastrichtian stage (70.5 – 65.5 Ma) of the Late Cretaceous. We use a palaeoclimatic proxy database to provide both boundary conditions and evaluation data for a suite of HadCM3l GCM predicted climates that reflect changing atmospheric CO2 levels, orbital configuration, and vegetation treatment. These climates are then used to drive an ice-sheet model, using a sensitivity study to investigate identified uncertainties within the ice-sheet model boundary conditions and parameterisations. A standard-parameter 2×CO2 ice-sheet is then integrated back into the boundary conditions of the HadCM3l GCM for a series of asynchronously coupled runs to investigate the coupling between ice sheet and climate. We conclude by considering the compatibility of the predicted ice-sheets with the sea-level record and geological climate proxies.
C21B-0528
Paleoclimatic and Faunal Significance of (Pliocene) Zoophycos in ANDRILL 1B
Zoophycos is a complex 3-dimensional trace fossil that is widespread in Cenozoic deep-sea sediments. It is most common at great depths (>1000 m), and where sedimentation rates and TOC levels are low; the Zoophycos-producer, probably a worm-like animal, was (is) a slow colonizer. Previously never reported from the Antarctic continental margin, Zoophycos occurs in the ANDRILL 1B core from 351 to 353mbsf. It is represented by horizontally oriented laminae that in two cases extend from an axial structure; no lamellae are visible within the laminae. This occurrence of Zoophycos both (1) constrains the Pliocene depositional and climatic conditions and (2) provides direct evidence about the origin of the Antarctic fauna. Zoophycos- is found in a thin (17m) unit of interglacial sediments bounded below by a thin muddy diamictite and abruptly truncated above by a glacial surface of erosion. The heterolithic unit was deposited during the transition from the warm Early Pliocene characterized by productive open waters to the cooler Late Pliocene with fluctuating subpolar ice sheets. The Zoophycos interval reflects both rapid deposition (debris flow deposits) and slow settling from suspension (silts, clay) consistent with a proglacial setting adjacent to the icesheet. Presence of the slow-colonizing Zoophycos-producer in the debris-flow deposits implies that the rapid sedimentation events were rare. On a larger scale, it indicates that favorable conditions for the producer, including low TOC (not met during highly productive open water periods) and low IRD (not met proximal to the icesheet) were extant long enough during the period of climate change for the Zoophycos- producer to migrate from the deep sea onto the continental margin. The Zoophycos in AND 1B also demonstrates clearly that deep-sea organisms migrated onto the Antarctic shelf when conditions permitted, documenting the process of "emergence" in origin of the Antarctic benthic fauna.
C21B-0529
Miocene Glacio-eustasy and Carbonate Sequences on the Marion Plateau, Northeastern Australia: Inferences from Distal Slope Records
Understanding the timing and magnitude of eustatic changes (global sea-level) is key to improving sequence stratigraphic and sedimentologic models, with wide implications for environmental changes and future exploration of fossil fuels. In the Oligo-Miocene, the magnitude of eustatic changes also provides a clue on Antarctic ice volume. The current best eustatic curve is largely based on records from the New Jersey margin, which needs to be checked against independent records to insure for accuracy of the results. One such independent record is the carbonate sequences of the Marion Plateau (drilled during ODP Leg 194), which have been critical in reconstructing the amplitude of the middle Miocene sea-level fall. However, core recovery during Leg 194 was generally poor, thus hindering a detailed stratigraphic correlation needed for the interpretation of orbital scale sea-level changes. In this paper, we identify 3rd order sea-level sequences in distal slope carbonates by integrating sedimentological observations, downhole logging data, and new biostratigraphic age models between two distal carbonate slope sites. The two sites integrated into a common splice give an almost continuous and well-dated record that yield a sequence stratigraphic framework for this system. Sequences are then compared to glacio-eustatic events seen in the oxygen isotope records. We identified sedimentary sequences linked to glacio-eustatic events Mi3, Mi4, Mi5 and potentially Mi6. From this work we can constrain the timing of platform exposure and of the eventual platform demise, with implications for the quantification of middle Miocene sea-level changes and Antarctic ice volume.
C21B-0530
Past Warmer Climate Periods at the Antarctic Margin Detected From Proxies and Measurements of Biogenic Opal in the AND-1B Core: The XRF Spectral Silver (Ag) Peak Used as a new Tool for Biogenic Opal Quantification.
Quantification of biogenic opal in marine sediments is a time consuming job, but the results could indicate periods of higher bioproductivity and warmer conditions than today at the Antarctic margin. Within the international Antarctic Geological Drilling Program (ANDRILL), core AND-1B was drilled and recovered a 1285 m sequence from a flexural moat basin filled with glacimarine, terrigenous, volcanic and biogenic sediments below the McMurdo Ice Shelf. Our main goal is to study the variability and the stability of the Ross Ice Shelf from Miocene to Recent. The melting and collapse of large Antarctic ice shelves may cause a significant sea level rise because of accelerated inland ice glacier surges into the ocean. Biogenic opal content in sediments can be deduced indirectly from grain density measurements on single samples, or faster and more continuous by gamma ray attenuation measurements on the core, with subsequent wet bulk and grain density calculations. Spectral colour reflectance (b* value) measurements on the split core surface can also be a fast tool for opal content quantification. Of course, they all have disadvantages in comparison to direct measurement on samples using X-ray diffraction or geochemical leaching methods. Some major and minor chemical elements were measured directly on split core surfaces with a non- destructive X-Ray Fluorescence Core Scanner method (XRF-CS, Avaatech) in the field. Quantitative geochemical analyses like determination of total inorganic and organic carbon (TOC), biogenic opal as well as major and minor elements were done on core samples. We found a strong positive correlation between the counts per second of the XRF-CS Ag peak area and the biogenic opal content of the samples (r=0.81) not only in the AND-1B core but in others as well from the Antarctic margin. In literature, it is noted that diatoms could accumulate Ag in sediments, so at first we were pleased to find this Ag enrichment with our tool. But further geochemical analyses revealed that measuring these low Ag concentrations and their variability (< 2ppm) is not possible or at least problematic with the XRF-CS. The detector of the XRF-CS has an Ag collimator, possibly acting as an amplifier on perhaps higher induced X-ray emissions in opal rich sediments within the Ag energy spectrum range, which might have nothing to do with Ag itself. However, we are still studying the physics behind this measurement phenomenon. Nevertheless, this Ag peak can be used as a proxy for biogenic opal concentrations. It is negatively correlated to Fe and Ti and variability downcore has a high signal to noise ratio. Combining the opal calculations from fast measurements of the Ag peak (opal-Ag), the grain density (opal-GD), and the b* value (opal-b*) we yielded a new multi-parameter proxy (opal-MP) for a high-resolution record of biogenic opal concentration in the upper 600m of the core (spacing: about 2cm or 300y). This opal-MP proxy correlates very well with measured opal leaching data (r=0.88, n=481). The biogenic opal concentrations in combination with other high-resolution data will be used as a cyclostratigraphic approach to understand paleoenvironmental and climate changes. Periods with much higher accumulation of biogenic opal than today were detected in the core that indicate a retreat and perhaps a total decay of the Ross Ice Shelf.
C21B-0531
Dolomite highlights glacial to interglacial transitions in Ross Sea deposits investigated in AND-1B core, Antarctica
The retreats of Antarctica's ice masses during the Plio-Pleistocene were characterized by large-scale environmental changes at the continental margin. Increased melt water got in contact with seawater and build up particular conditions for a huge variety of chemical reactions. The precipitates of these reactions, within the sediment deposits, are reliable tools to reconstruct specific paleoenvironmental changes. Discrete horizons with high dolomite and calcite content (up to ~20 and ~30 % respectively) were detected in the AND-1B core from the ANDRILL McMurdo Sound Project. We measured the split core in the field during the austral summer 2006/2007 with a non-destructive AVAATECH XRF-Core Scanner. On discrete samples chemical analysis were carried out and the mineral composition was examined by X-ray diffraction measurements. At the depth of 162.71, 182.10, 224.59 and 292.15 mbsf these high dolomite values were found within the glacial to interglacial transition zones. Our hypothesis states that calcite and dolomite formation in the transition zones is possible under cold glaciomarine conditions with an increased melt-water runoff and a high amount of dissolved HCO3- in contact with Mg+ and Ca+ rich seawater at the grounding line region or in the sub-ice hydrological system. We also detected horizons containing other carbonates like ankerite (i.e. 143.23, 449.26 mbsf) and low Mg calcite that support this hypothesis. Whether in this environment the dolomite was (I) precipitated in the water column, or (II) in the pore water system where sub-ice freshwater was replaced and overlaid by heavier seawater during glacial to interglacial transitions, is under investigation. Anyhow, most of the dolomite formations in the AND-1B core could be related to shelf ice retreats and (bio?)geochemical processes at or close to the sediment surface.
C21B-0532
Quantitative Biostratigraphic Age Control of Glacimarine Sediments, ANDRILL 1B Drillcore, McMurdo Ice Shelf
Interpretation of glacimarine sedimentary records from Antarctic shelf drillholes has been greatly hampered by the ambiguous age of strata where erosional unconformities and coarse diamictite deposits truncate or omit the mangetostratigraphic and biostratigraphic units used for correlation. However, new quantitative biostratigraphic techniques enable the correlation of sparse, incomplete, and reworking-prone Plio- Pleistocene records of Ross Sea fossil diatom flora with the more extensively documented but potentially diachronous offshore history of species' first and last appearances (FAs and LAs). The approach uses a comprehensive regional database of fossil records and computer-automated search algorithms to (a) find the multidimensional line of correlation (LOC) that best fits local observations, and (b) map out confidence intervals based on the full range of equally parsimonious composite FA/LA sequences and local range-end adjustments. An integrated, quantitative chronostratigraphic model for the AND-1B drillcore was constructed iteratively: the initial LOC was based solely on preliminary on-ice observations of fossil diatom highest and lowest occurrences (HOs and LOs) and their correlation with a database of other local event records from 24 DVDP, CIROS, and IODP drillcore sections. The model was subsequently updated as off-ice work yielded additional biostratigraphic marker events and revised event horizons, Ar/Ar ages for volcanic material, better- constrained magnetostratigraphic interpretations, and refinements to computational/analytical methodology. The current quantitative biostratigraphic age model for the AND-1B hole integrates the local ranges of 29 diatom taxa, 5 dated ashes, and independently constrained ages of 5 paleomagnetic reversals. Results corroborate almost all of the on-ice geomagnetic polarity reversal age interpretations, but identify a previously unrecognized major disconformity (~800kyr hiatus) near 440mbsf. It is significant to note that in spite of drastic augmentation and progressive refinement of, the original AND- 1B input dataset, successive iterations of the output LOC retain the same fundamental structure/shape with only relatively minor, fine-scale differences. The age model's remarkable stability indicates that quantitative biostratigraphic analysis is capable of constructing robust and reliable regional correlation schemes and local section chronologies, even where records are somewhat rough or unfinished and include some errors and low-quality content, or lack independent age control. Large discrepancies between observed and expected HO/LO horizons reveal significant diachronism in the timing of a few species' FAs and LAs on the shelf vs. offshore. In other cases, positions of HOs and LOs that were predicted by the quantitative analysis were subsequently validated by collection of additional microfossil count data that documented occurrences of the taxon near the stratigraphic limits predicted by regional correlations. Quantitative biostratigraphic analysis of this type could potentially be useful in guiding more intensive, supplementary off-ice or post-cruise sampling and investigation.
C21B-0533
Re-Evaluation and Update of Age Models for Deep Sea Drilling Project Sites 270, 272, and 273 and Implications for Regional Climate and Tectonic History.
The ability to understand and model past climatic conditions and tectonic events depends upon our capability to isolate the stratigraphic record of that past time through precise chronostratigraphy Recovery and integration of biostratigraphic, magnetostratigraphic, chemostratigraphic, and radiometric data from geologic sections obtained over the past 30 years from the continental margin of Antarctica and the Southern Ocean, has enabled an ever improving understanding of regional chronostratigraphy. We have incorporated and updated biostratigraphic data for marine diatoms from Deep Sea Drilling Project Sites 270, 272, and 273 in the Ross Sea. New diatom event age data based on recent quantitative work allow refinement of outdated age models for these key cores. Integration into a regional chronostratigraphic framework that incorporates drill cores from the Victoria Land Basin, including the recently recovered ANDRILL 1B and 2A cores, highlights several regional events (unconformities) that likely have global significance. Of particular significance is a regionally extensive break in the stratigraphic records that occurred approximately 14 Ma. This early middle Miocene hiatus likely correlates to climatic cooling at the end of the Miocene Climatic Optimum. The new age models provide key constraint for the network of seismic data in the Ross Sea and will help guide future drilling.
C21B-0534
Transient Establishment of a Seasonal Sea-Ice Regime in the Late Pliocene, McMurdo Embayment, Ross Sea, Antarctica
The marine sediment drillcores collected by the Antarctic Geological Drilling (ANDRILL) Program from sites beneath the McMurdo Ice Shelf (AND-1B) and in Southern McMurdo Sound (AND-2A) together represent the longest, most complete record to date of Neogene climatic evolution proximal to the Antarctic continent. Multiple extensive, well-preserved diatomite units distributed throughout the upper six hundred meters of the McMurdo Ice Shelf (MIS) core provide a unique perspective on the transition from the mid-Pliocene climatic optimum into modern cold-polar conditions. While the diatom assemblages preserved within these diatomites record a variety of paleoenvironmental conditions, the modern, fully-developed sea-ice community that characterizes the modern Ross Sea environment is absent from the record. Here, we focus on two discrete diatomite units deposited between ~3.3 and 3.0 million years ago. The base of the lower unit, at 292 mbsf, is marked by the radiation of a Fragilariopsis species complex that is previously undescribed from Antarctic sediments. This complex dominates the diatom assemblage throughout the late Pliocene, comprising up to 55 % of the community at 288 meters. By contrast, modern sea-ice marker species are poorly represented in most mid- to late Pliocene sediments at AND-1B. However a transient sea-ice event is recorded in the upper portion of the diatomite unit that spans 252-258 mbsf. The assemblage at the base of this diatomite is similar in character to the diatomite units above and below, however the proportion of F. curta, a taxon with well-established sea-ice affinity, increases gradually, reaching a transient but significant maximum at 253.11 mbsf. The mid-Pliocene climatic optimum is not recovered from the shallower Southern McMurdo Sound (SMS) site, which is comprised predominantly of diamictite and mudstone. However a diverse Pliocene assemblage between 44.5 and 48.3 mbsf in AND-2A appears equivalent to the AND-1B diatomite 164-180 mbsf. Preserved in five pulses incorporated into sandy, clast-poor diamictite, this assemblage includes numerous age diagnostic species but lacks a significant contribution from the sea-ice assemblage that dominates modern Ross Sea coastal environments. The 1138-meter AND-2B drillcore includes only two meters of true diatomite (from the Miocene), reflecting both the continental proximity and shallow paleodepth of the site. In this context, the episodic nature of Pliocene diatom preservation in AND-2B suggests that sedimentation in Southern McMurdo Sound was paced by an unusual oscillating environmental or depositional influence around 2.5 million years ago. The nearshore Southern McMurdo Sound section also provides an opportunity to place the dynamic McMurdo Ice Shelf record within a regional context.
C21B-0535
Miocenic subaqueous volcaniclastic deposits in ANDRILL-MIS core
During the first season of drilling from the McMurdo Ice Shelf (MIS), the ANDRILL program recovered a 1285
m-long core (MIS AND-1B drill core) that represents the longest and most complete geological record from
the Antarctic continental margin. The core is a succession of cyclic glacimarine sediment and interbedded
thick volcanic deposits. During the on-ice sedimentologic description and lithostratigraphic subdivision of the
AND-1B core eight main lithostratigraphic units (LSU) and 25 subunits, based on lithological abundances
were recognized. LSU 5 (between 588 and 759.30 mbsf) represents the thickest and continuous volcanic
sequence of the whole core. Detailed successive visual observations on high-definition core images, coupled
with textural and compositional (by means of SEM-EDS and EPMA) characterization of volcanic detritus allow
discriminating between primary volcanic and secondary sedimentary processes The sequence comprises
two main sub-sequences distinguishable for sediment composition, texture and alteration style. The first sub-
sequence (759.30-714.80 mbsf) is composed by an almost monothematic sequence of stacked volcanic-rich
turbidites whose emplacement was interpreted as mainly due to gravity-driven epiclastic processes. The
second sub-sequence (714.80-588 mbsf) is mainly constituted by cm- to m-thick lapilli tuff, tuff breccia beds
and volcaniclastic diamictites; a 3-m thick lava flow also occurs. Almost the whole second sub-sequence was
attributed to primary volcanic submarine processes originating from a nearby volcanic complex with a long
lasting ( C21B-0536 Provenance Investigations Using Magnetic Susceptibility of Pebble- to Cobble-Sized Clasts in the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica
Magnetic susceptibilities of pebble- to cobble-sized clasts recovered in the ANDRILL SMS core (site AND-2A:
77° 45.488'S, 165° 16.605'E) (McMurdo Sound, Ross Sea) were measured on ice with a Bartington
MS-2B susceptibility meter. Measurements were made on thin section billets or on clasts themselves when
they were of suitable size for the instrument. The variability of the magnetic susceptibility is related both to
variations in the primary magnetic mineral content of the source rocks as well as to secondary magnetic
mineral formation/dissolution prior to and during the diagenetic process. Volcanic clasts, the dominant clast
type thoughout the core, display the highest susceptibility values, but there is extreme heterogeneity of
values within the same compositional type (i.e. felsic, intermediate, mafic). Given this, the susceptibilities of
volcanic clasts in the AND-2A core are poorly suited for provenance studies. In contrast, the basement clasts
(consisting of a variety of metasedimentary and intrusive rocks) can play an important role in defining ice
provenance and dynamics. The textures and mineralogical compositions of intrusive and metamorphic rocks
indicate the region between the Ferrar Glacier and the Mulock Glacier as the most likely provenance region.
In order to better understand this result, we chose to undertake a magnetic petrology study on the most
magnetic (Low-Field mass susceptibility, χ > 90*10-8 m3/kg) basement clasts sampled on ice. A
comparison of the magnetic susceptibilities of our AND-2A clasts with samples collected from the outcrops of
Southern Victoria Land (SVL) indicate that there is a good correlation between the highly magnetic
metamorphic rocks of the region south of Ferrar Glacier and the most magnetic basement clasts in the core.
In particular, the petrographic and magnetic features of metasedimentary clasts closely match both
metasandstones from Baronick Glacier (Skelton Glacier area) and gneisses and schists from Hobbs Peak
(Blue Glacier area), corroborating the inferences of the petrography-based provenance studies. These
preliminary results point out the importance of mineral magnetic measurements in providing additional
constrains and a useful data set for on-going provenance investigations of Cenozoic sediments recovered by
recent ANDRILL drillholes in the McMurdo Sound area.
C21B-0537 Developing a High-Resolution Sequence Stratigraphic Framework for Upper Lower Miocene Strata (18-16 Ma) From the ANDRILL AND-2A Drillcore, Southern McMurdo Sound Project, Antarctica
A high resolution sequence stratigraphic framework was developed for the upper lower Miocene (18-16 Ma)
in Southern McMurdo Sound. Southern McMurdo Sound Project (SMS) of the ANDRILL Program completed
the AND-2A drillcore (77° 45.488 S; 165° 16.613 E) from a floating sea-ice platform over
approximately 380 meters of water, reaching a total depth of 1138.54 mbsf, during the 2007 austral
spring/summer. One objective of the SMS Project was to recover a history of ice-proximal paleoenvironmental
variation during the early to middle Miocene, which includes the Early Miocene Climatic Optimum (EMCO,
17.8-16.1 Ma), the Middle Miocene Climatic Optimum (16.0-14.2 Ma), and the climatic cooling that followed.
The AND-2A drillcore recovered several distinct stratigraphic intervals including a thick middle Miocene
section (400 to 223 mbsf) and an expanded upper lower Miocene section (700-400 mbsf) that includes the
Early Miocene Climatic Optimum, with the latter being the focus of this study. Three motifs of stratigraphic
stacking patterns were recognized in the AND-2A borehole of which two are observed between 700-400
mbsf. Motif 2, which dominates above 523 mbsf, is characterized by a sharp-based conglomerate and
sandstone overlain by stratified, clast-poor diamictite. This is overlain by bioturbated clayey siltstone with
interlaminated sandstone and siltstone above it. This is overlain by diamictite. Motif 3 is only recognized
below 523 mbsf and is characterized by a sharp-based conglomerate and clast-rich sandstone overlain by
stratified diamictite which grades upward into interlaminated siltstone and very fine sandstone with diamictite
interbeds. This is overlain by fossiliferous diamictite. Each motif of stratigraphic stacking is capped with a
sharp-based conglomerate. A minimum of 15 cycles of stratigraphic stacking, occurring at roughly 20-meter
intervals between 700 and 400 mbsf, are recognized in core photographs and observations made on-ice
during core description. Cycle bases are expressed in the grain size data by abrupt increases in weight
percent of the coarse fraction indicative of the sharp-based conglomerates. At this preliminary stage in the
data analysis, there is a strong correspondence of cycle base identification with observation methods. Sub-
cycle patterns of stratigraphic stacking within individual sequences are observed at various depth intervals
within the core. Age data from the AND-2A Initial Report for the core are based on magnetostratigraphy,
biostratigraphy, and Ar/Ar dating of volcanic material, and provide excellent date constraints for the core,
especially within the early to middle Miocene section. The rhythmic cyclicity observed and expressed in the
grain size data reflects environmental changes which are a result of the combined effect of tectonic
subsidence, glacial proximity, glacio-isostasy and eustasy. The apparent regular distribution in this section of
the bases of the sequence cycles suggests a periodicity of 100 ± 12 kyr, which suggests eccentricity-
driven orbital forcing. Further work is continuing to increase the resolution of the grain size data to further
resolve dominant and sub-cycle stratigraphic stacking patterns. Spectral analysis will be performed to
precisely determine the periodicity of sequence stacking over time.
C21B-0538 A New Technique for Estimating Erosion Through Comparison of Tectonic Subsidence and Eustasy: Example From the ANDRILL-1B core
We present a novel technique for estimating maximum erosion in the mixed diamict and shelfal environment
of the Ross Sea in Antarctica over the past 5 million years. This technique is applied to the ANDRILL-1B MIS
core obtained during the austral summer 2006-2007. This technique utilizes backstripping to model the
tectonic subsidence observed within the ANDRILL-1B core. We assign the lower frequency signals to tectonic
processes, and remove that signal from the tectonic subsidence results. The remaining signals are higher
frequency glacial/interglacial changes, and are combined with the δ18O record of sea level change
from Lisecki and Raymo (2005), as correlated by Naish et al. (2008) for the ANDRILL-1B core. Specifically,
the amplitude of the modeled change in sea level is compared to the expected amplitude change of sea level
as predicted from the δ18O records. Using this comparison we estimate the maximum possible
amount of erosion, by determining the amount of erosion that would cause the observed sea level change
amplitudes to match the expected sea level amplitude from δ18O. Some of the assumptions made in
this technique include the degree to which the core captured the entire range sea level change and, the
degree that accommodation space was filled by sediment.
C21B-0539 Depositional Facies Recovered in Cores from the Northwestern Weddell Sea, Antarctica, from the Pre-Glacial Eocene through the Glacial Pliocene
During the 2006 field season, the SHALDRIL scientific drilling program recovered cores of Tertiary material at
four different locations in the northwestern Weddell Sea. The recovered cores are not continuous, yet
nonetheless provide a record of a changing climate with samples from the late Eocene, late Oligocene,
middle Miocene, and early Pliocene. Sedimentologic analysis of these cores includes basic lithologic
description, multi-sensor core logger records, laser particle size analysis grain size measurements, xray
analysis for pebble count and fabric, as well as onboard biostratigraphy for age constraints. Pre-glacial late
Eocene sediments sampled in the James Ross Basin are typically characterized by very dark greenish gray
muddy fine sand with some preserved burrowing, and are interpreted to represent a shallow water
continental shelf setting. Rare dropstones, primarily of better-cemented sandstones, represent limited
mountain glaciers and ice-rafted material, but overall the late Eocene material does not record any major
glaciation. The remaining three cores of Tertiary material were collected on the Joinville Plateau to the north,
at the tip of the Antarctic Peninsula. The late Oligocene sediments consist of dark gray sandy mud with
some clay lenses and many burrows, likely representing a distal delta or lower shoreface setting. This core
contains only one real dropstone, representing its location farther from the continent with no proximal
glaciers. The middle Miocene, also from the Joinville Plateau, represents a dramatic change in environment
and contains a pebbly gray diamicton, representing proximal glacial marine sediments. The lower Pliocene
facies also contains many ice-rafted pebbles but is dominated by sand units rather than diamicton and is
interpreted to represent a current-winnowed deposit, similar to the modern day sediment on the Joinville
Plateau.
C21B-0540 40Ar/39Ar chronology of volcanic events in the AND-1B drillcore - implications for age models and glacial history of the Ross Embayment
40Ar/39Ar dating of a suite of volcanic clasts and tephras, collected from throughout the AND-1B
drillcore, significantly aids the development of an age-depth model. High precision dates determined for a
variety of volcanic materials, provide the necessary pinning points useful in constraining the geochronology
of the drillcore. The ages for five stratigraphic intervals are 1) 85.53-85.85 mbsf felsic tephra
(1.014±0.004 Ma), 2) ~112-145 mbsf sequence of basaltic tephras (1.65±0.05 to
1.67±0.05 Ma), 3) 481.80 mbsf pumice-rich mudstone (480.00±0.076 Ma), 4) 646.30-649.34 mbsf
basaltic lava flow (6.48±0.13 Ma), and 5) ~1280 mbsf, three volcanic clasts (maximum depositional
age 13.57±0.13 Ma). Dating of volcanic clasts from the interval below ~650 mbsf, provide the best
means for constraining the depositional ages for this interval. Electron microprobe characterization of
numerous volcanic intervals indicates that preservation of volcanic tephra is highly dependent on
depositional depth. Tephras from 0 to ~650 mbsf, are generally fresh and well preserved, whereas
material from greater than ~650 mbsf exhibits high degrees of alteration. Volcanic clasts, unlike tephras
below 600 mbsf, display only minor alteration, and many are good candidates for 40Ar/39Ar
analysis. Both groundmass concentrates and feldspar mineral separates from volcanic clasts have yielded
high precision dates. We are currently working on a suite of 100 volcanic clasts in an attempt to provide
maximum depositional ages for the ~650-1285 mbsf interval.
C21B-0541 Contrasting Glaciomarine, Sub-ice Shelf and Subglacial Facies at the Ross Ice Shelf Edge
Data from cores collected at sites that were (prior to B-15 and C-19 calving events in 2000 and 2002) located
in front of and under the Ross Ice Shelf indicate that until recently, minimal deposition occurred beneath the
ice shelf. Facies successions indicate that advection and mixing by currents is a significant process in the
sub ice shelf region.
Ross Sea sub-ice shelf deposits recovered from NBP03-01 and NBP03-06 survey areas are defined by two
units; 1) olive to olive grey mud with a high silt content, med-high sub-rounded to sub-angular pebble
component, and average total diatom abundances, 50% of which are modern species, and 2) a dark grey to
olive grey, laminated to homogeneous clayey silt unit with relatively few grains larger than 2mm, and low
diatom concentrations dominated by reworked species. Subglacial sediment can be distinguished in this
case by its high bulk density values, poorly sorted, clast rich character, as well as the dramatic decrease in
diatom abundance, and presence of almost entirely of reworked species. Differentiating between
Glaciomarine and sub-ice shelf sediments is more difficult as a result of the proximity of the NBP03-01 and
NBP03-06 cores to the calving edge, although in general, very high diatom abundances acted as the
distinguishing feature between the two facies. This research indicates that sub-ice shelf facies can not be
clearly defined by one type of sediment; dynamic locations close to the ice shelf edge where the position of
the shelf edge varies over short timescales, and where currents advect material under the ice shelf, cause
facies boundaries to blur and makes facies interpretations difficult.
In addition, facies in eastern Ross Sea cores and their corresponding ages may suggest cyclicity in the
movement of the grounding line prior to 10,130 (corrected) yrs B.P., characterized by multiple fining up
packages composed of fine-clayey silt (distal sub ice-shelf deposits) grading into coarse pebbly mud (sub
ice-shelf proximal to the grounding line). Evidence of the ice sheet grounding close to the core site is also
visible in Multibeam and CHIRP high-resolution 2-D SCS data from cruise NBP03-06.
C21B-0542 Dating Antarctic climatic and tectonic events of the Neogene – Age models from the ANDRILL 1B and 2A cores
A network of seismic surveys in McMurdo Sound provides an image of the tectonic, glacial, and sea-level
controls on accumulation of Cenozoic strata in the West Antarctic Rift. Integration with previously recovered
drill cores revealed a younger Neogene succession, which was the target of drilling from floating ice platforms
under the ANDRILL program in the austral summers of 2006 and 2007. Continuously recovered core from
the ANDRILL 1B and 2A drillholes provides key paleoenvironmental data regarding climatic variation and ice
volume fluctuation of the Antarctic Ice Sheets through the Neogene. Chronostratigraphic data available from
the drillcores includes diatom and nannofossil biostratigraphy, magnetic polarity stratigraphy, 40Ar/39Ar ages
on numerous ashes from the McMurdo Volcanic Complex, and strontium dates on carbonate material.
Integration and optimization of the currently available data provides a robust age model for the Plio-
Pleistocene (upper 600m) of the AND-1B drillcore and the middle and lower Miocene (224-1139m) interval of
the AND-2A drillcore. The Plio-Pleistocene record is punctuated by multiple hiatuses that correlate with
climate (ice sheet and sea level fluctuations) events and account for approximately half of the time spanned
by the record. Despite these hiatuses, the distribution of chronostratigraphic data still enable the
identification of orbital influence in remaining strata. The lower 600m of the AND-1B extends well down into
the Miocene as constrained by a 40Ar/39Ar age of approximately 13.8 Ma towards the base of the core. The
upper 300m interval of the AND-2A core contains punctuated middle Miocene to Pliocene succession with
hiatuses accounting for more than two thirds of the time spanned by the record. The ~800-m thick lower
Miocene interval of the AND-2B core is nearly continuous and enables new constraints on regional tectonic
and climatic events of the West Antarctic Rift sedimentary succession.
C21B-0543 Quantitative Stress Determination by Wire-line Hydraulic Fracturing Tests in the ANDRILL South McMurdo Sound Drillhole
In general, knowledge of the state of stress within the Antarctic lithosphere remains largely unconstrained
due in part to Antarctica's inaccessibility and because of the paucity of seismic focal
mechanism solutions. As such, an important component of the ANDRILL project was to acquire new
information on the stress directions and magnitudes within the upper crust. Extensive fracture mapping of
the core and oriented ultrasonic televiewer logging, as presented in a related contribution, provided strong
constraints on both stress orientations and the faulting regime. The first hydraulic fracturing stress
determinations in Antarctica were also carried out to provide complimentary stress magnitudes. These
measurements were accomplished using a wireline transported hydraulic fracturing system consisting,
essentially, of two synthetic polymer packers that were inflated to isolate the 1-m long pressurization interval.
The tests were conducted at the end of the drilling and logging in a ~130-m section specially drilled
below 1000 mbsf for hydraulic fractures. This zone was drilled primarily through competent, dense, and low
permeability diamicts. The core fracture and televiewer logging information was used to site twenty separate
measurements. Classic hydraulic fracturing pressurization records with unambiguous breakdown and
fracture closure pressures were obtained in about half of the measurements. The remaining tests provided
fracture propagation and closure pressures that are consistent with the classic breakdown curves, but they
did not include a clear breakdown pressure and are indicative of the reopening of either natural or drilling
induced fractures in the wellbore wall. Comparison of the televiewer images obtained before and after the
hydraulic fracturing tests highlighted the existence of at least one artificial hydraulic fracture; more could not
be obtained because blockage of the wellbore did not allow the lowest sections to be logged a second time.
The preliminary analysis of the results are in generally good agreement with the stress directions indicated
by the core fracture logging and the stress regime suggested by the character of the drilling induced core
fractures.
C21B-0544 Rock-magnetic characterization of the AND-1B Core, ANDRILL McMurdo Ice Shelf Project, Antarctica
We present new rock magnetic data from the upper 800-m (0-7 Ma) of the ANDRILL McMurdo Ice Shelf
Project core AND-1B. Discrete samples were collected every 1-4 m and analyzed for magnetic hysteresis
parameters, induced remanences, and temperature-dependent order-disorder transitions. The magnetic
mineral assemblage in diamictite, coarse clastic units, mudstone, and diatomite units is characterized by
pseudo-single-domain and multidomain particles and S-ratios near to 1. Volcaniclastic units are characterized
by finer pseudo-single-domain particles. SIRM/χ values are between 5-30 kA/m, indicating the
presence of iron sulfides throughout the core. Diamictite, clastic units, and mudstones display Curie
temperatures consistent with magnetite. Volcaniclastic units display multiple Curie temperatures in the range
of 360-380 C, 400-500 C, and 550-580 C indicative of iron sulfides, titanium-rich titanomagnetite, and
titanium-poor titanomagnetite, respectively. Work in progress includes disaggregating and sieving selected
samples at 45-500 μm and extracting the iron oxide grains for analysis via reflected light and electron
microscopy. Detailed characterization of the magnetic mineral assemblage can aid in tracing of sediment
provenance and past ice flow directions.
C21B-0545 ANDRILL's Southern McMurdo Sound Project (SMS): overview of outcomes, broader impacts and correlations, and future plans
During late 2007, the ANtarctic geological DRILLing Program (ANDRILL), an international collaboration
between Antarctic research programs of Germany, Italy, New Zealand and the United States, successfully
cored (with 98% recovery) a 1138 meter drill hole that documents an excellent history of high latitude
paleoenvironmental conditions and climate/glacial variation during Miocene climatic optimum periods. In
addition, fracture mapping, core orientation success, and borehole hydrofracture experiments reveal details
regarding the history and current stress regime in the western Ross Sea. We present initial correlations of
the AND-2A drillcore to global proxies of sea-level and deep-sea geochemical stratigraphy, guided by a
robust chronostratigraphic framework for the early and middle Miocene. Changes evident in stratigraphic
sequences, physical properties (borehole and core), and geochemical logs, record fine details of glacial,
climatic, tectonic and eustatic influence in the western Ross Sea, which will help establish, through correlation
to existing records how local changes evident in the drillcore relate to regional and global events. These
records combined with paleontological and geochemical evidence for terrestrial - marine paleotemperatures
provide important data input for climate and ice-sheet model reconstructions and testing. An abundance of
volcanic materials reveals evolution of the McMurdo Volcanic Group, including episodes of explosive
volcanism. Substantial subsidence occurred within the last 2 Ma associated with volcanic loading from Ross
Island, reversing the persistent littoral to shallow neritic depths evident through most of the cored sequence.
Persistent sediment supply into western Victoria Land Basin during a steady phase of thermal subsidence
produced a thick stratigraphic sequence from which we are reconstructing the details of paleoclimatic,
eustatic and glacial variations on the shallow marine coast of the Transantarctic Mountains. Coincident with
the ongoing data generation and interpretation by the SMS Project Science Team, we begin to develop the
science plan and program for a seismic survey that would be required to identify a new drilling target to
repeat the middle Miocene to Recent stratigraphic section of the AND-2A core in a deeper water depositional
setting. The target sequence identified to the east of ATS-05-02 line, and within the PD-90-46 seismic profile
presents a more continuous and expanded interval across the middle Miocene transition. A new core located
~10 to 15 km eastward of the SMS drillsite will augment and expand the current SMS research effort by
providing a depth transect, upon which the fine details of glacio-eustatic variation can be interpreted and
correlated to similar global records (e.g. New Jersey margin, and that anticipated for the pending Canterbury
Plains IODP drilling.
C21B-0546 Paleocurrents in the Ross Sea: Magnetic Fabrics of Plio-Pleistocene Samples from the AND-1B Core, ANDRILL McMurdo Ice Shelf Project
The ANDRILL McMurdo Ice Shelf (MIS) Project successfully recovered 1,285 meters of core from below the
Ross Ice Shelf, an area known for significant bottom water formation, providing an opportunity to investigate
near-ice and open water Plio-Pleistocene paleocurrents that may have effected global circulation. Initial
characterization of the core established the presence of eleven recurring lithofacies, or characteristic
depositional environments (Krissek et al, 2007). Those lithofacies that represent depositional environments
in front of the grounding line of the ice shelf may provide information about paleocurrent energies present
beneath, or in absence of, the ice shelf at the MIS site. Previous studies have indicated the utility of magnetic
fabrics (i.e. P') to obtain information on the relative velocity of the depositional environment when
analyzing paramagnetic sediment samples; application to a sequence of varying and lithified lithologies is
more complicated but offers the potential to derive relative current information within an individual lithofacies
(rather than between lithofacies). Approximately 240 paleomagnetic samples were obtained from AND-1B
and analyzed on a KLY-4S KappaBridge, focusing on Lithofacies 1, 2, 3, and 6v. Analysis of Lithofacies 6v,
interpreted to be primarily turbidite deposits with a significant volcanic component, allows testing of the
methodology; strong grain alignments are expected with turbidity currents. As predicted, the P' values
extended higher than any of the other lithofacies sampled (~1.02-1.50), although the bulk magnetic
susceptibilities (MS) of these samples fell in the middle range (mostly between 5x10-4 and 5x10-3
SI). Further analysis may reveal whether this relates to the mineralogy or the grain orientation resulting from
a strong turbidity current (or both). The diatomites (Lithofacies 1), representing open water deposition, with
varying hemipelagic or fallen iceberg debris inputs, had very low MS (ranging from ~2x10-5 to
3x10-3 SI) and relatively low P' values (~1.01-1.11) that varied within the repeated analysis of a
single sample; continued work may indicate if the signal is reliable enough to be used for these samples.
Lithofacies 2 and 3 were characterized as mudstones likely derived from hemipelagic sedimentation possibly
proximal to or distal from grounded ice; these paramagnetic-rich samples (MS values ~2x10-4 to
9x10-3 SI and P' values ~1.01 to 1.16) likely afford the greatest opportunity to derive
paleocurrent information over time.
C21B-0547 The early-mid Pliocene Marine Environment from McMurdo Sound Antarctica as recorded in the ANDRILL AND-1B Core.
A productive open-marine environment is recorded within the early-mid Pliocene diatomites of the ANDRILL
AND-1B core. This is in stark contrast with the current sub-shelf environment present at the site with only
transported diatoms from the Ross Sea present in surface sediments. Biosiliceous sedimentation in the Ross
Sea today is dominated by species highly associated with the modern sea-ice environment; the species
observed in the AND-1B diatomites indicate open-water production with often low numbers of sea ice
associated species. One diatomite interval of particular interest is 80m in length with continuous deposition
preserved in the upper 60m. This whole diatomite unit is subdivided by several debris flows of mixed
sedimentological origin but with abundant volcanic clasts; several of which are thought to have significant
losses of time associated with them. Sedimentation rates change throughout this unit, indicated by the
presence of both bioturbation and laminations. Species indicative of a near-shore open-marine setting with
cooler waters and local sea-ice influence is observed at the base, while the diatomite above contains several
species in high abundance that today are only observed in such numbers far to the north of this site. The
lowest samples in the upper 60m interval have species indicating cool environmental conditions and the
presence of local sea ice. These are followed by several distinct intervals reflecting changes in the local
marine environment that persisted for extended periods of time represented in 10-20m of diatomite each.
The relative proportions of species known to be associated with sea ice, those associated with open water
near sea ice and those negatively correlated with sea ice fluctuate within this upper 60m and record a
dynamic and varying marine environment.
C21B-0548 Reconstructing the contribution of the Weddell Sea sector, Antarctica, to sea level rise since the last glacial maximum, using numerical modelling constrained by field evidence.
A numerical ice sheet model constrained by recent field evidence is employed to reconstruct the Last Glacial
Maximum (LGM) ice sheet in the Weddell Sea Embayment (WSE). Previous modelling attempts have
predicted an extensive grounding line advance (to the continental shelf break) in the WSE, leading to a large
equivalent sea level contribution for the sector. The sector has therefore been considered as a potential
source for a period of rapid sea level rise (MWP1a, 20 m rise in ~500 years). Recent field evidence suggests
that the elevation change in the Ellsworth mountains at the LGM is lower than previously thought (~400 m).
The numerical model applied in this paper suggests that a 400 m thicker ice sheet at the LGM does not
support such an extensive grounding line advance. A range of ice sheet surfaces, resulting from different
grounding line locations, lead to an equivalent sea level estimate of 1 - 3 m for this sector. It is therefore
unlikely that the sector made a significant contribution to sea level rise since the LGM, and in particular to
MWP1a. The reduced ice sheet size also has implications for the correction of GRACE data, from which
Antarctic mass balance calculations have been derived.
C21B-0549 ANDRILL Borehole AND-1B: Well Log Analysis of Lithofacies and Glacimarine Cycles.
During the 2006-2007 austral summer, the Antarctic geological drilling program ANDRILL recovered cores of
sedimentary rock from a 1285-m-deep borehole below the McMurdo Ice Shelf. Well logging instruments were
deployed to a depth of 1017 mbsf after core recovery. This study focuses on two intervals of the AND-1B
borehole: upper HQ (238-343 mbsf; Pliocene) and NQ (698-1017 mbsf; upper Miocene), which were logged
with natural gamma ray, induction resistivity and magnetic susceptibility tools. To understand how the well
logs fit into a more complete physical properties data set, we performed factor and cluster analyses on a
suite of well logs and core logs in the upper HQ and NQ intervals. In both intervals, factor analysis groups
resistivity and core P-velocity into a factor that we interpret as being inversely proportional to porosity. It also
groups natural gamma and potassium (from the XRF core scanner) into a factor that we interpret as a
particle-size or lithology index. An additional factor in the NQ interval, influenced by clast number and
magnetic susceptibility, distinguishes subglacial diamictites from other lithofacies. The factors in each
interval (2 in HQ, 3 in NQ) are used as input to cluster analysis. The results are log data objectively
organized into clusters, or electrofacies. We compare these electrofacies to the lithofacies, well logs and
unconformity-bounded glacimarine cycles of AND-1B.
Patterns in the glacimarine cycles are observed in the well logs and electrofacies. In the NQ glacimarine
sediments, an electrofacies pattern is produced between subglacial diamictites at the bottom of each
sequence and the glacial retreat facies above. Subglacial diamictites have higher values for the additional
NQ factor, corresponding to clast number and magnetic susceptibility, than the muds and sands that form the
retreat facies. Differences in the porosity factor are not observed in any electrofacies pattern in the NQ
interval, but subtle patterns in the resistivity well log are observed. Subglacial diamictites have greater
resistivities than most retreat facies. In the HQ interval, there is only one glacimarine cycle that resembles
those in the NQ interval, and most of the interval is subglacial or ice-proximal diamictite. There are only two
and a half cycles in the HQ interval, but they contain an incipient electrofacies pattern. In the lower two
cycles, the potassium/gamma factor is low at the bottom and high toward the top, and porosity, as indicated
by the porosity factor, is low at the bottom and high toward the top. Throughout most of the HQ interval,
potassium and natural gamma correlate with porosity. Two exceptions are the lower half of the top cycle, in
which resistivity increases toward the top, and the two diatomite beds at the top of the two lower cycles, in
which potassium/gamma is low and porosity is very high.
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