(poster p.) G. Capponi1, L. Crispini1, G. Di Vincenzo2 & R. Palmeri3,
1Dipartimento per lo studio del Territorio e delle sue Risorse, Genova University, Italy;
<capponi@dipteris.unige.it>, <crispini@dipteris.unige.it>;
2Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy; <g.divincenzo@igg.cnr.it>;
3Museo Nazionale dell' Antartide, Siena University. Italy; <palmerir@unisi.it>.
In northern Victoria Land, the boundary between the Wilson and the Bowers terranes is a first rank tectonic lineament, running from the coast of the Ross Sea to the Pacific ocean. The boundary is well exposed in the Lanterman Range where it is known as Lanterman fault zone (BRADSHA w et al. 1982).
The Lanterman fault zone displays a poliphase structural evolution (CAPPONI et al. 2000): after a W over E thrusting under amphibolite facies metamorphism, it experienced shearing with a strike-slip movement. A microtextural and petrological study carried out on metabasic rocks sampled along the Lanterman fault zone, revealed a contrasting metamorphic evolution between samples from the boundary of the Wilson Terrane (WT) and those from the Bowers Terrane (BT). Samples from the WT display different degree of structural and metamorphic re-equilibration under the shear deforma-tion. They vary from slightly retrogressed amphibolite (mainly high AlIV Mg-hornblende + oligo-clase and rare actinolite) to mylonite schist where amphibole porphyroclasts are high AIIV parga-site/edenite and Mg-hornblende within a matrix composed of a new acicular Mg-hornblende with lower AIIV and K content. green biotite, chlorite, albite and rare oligoclase. Actinolite is rare and usually is present along porphyroclastic cleavages. Samples from the BT are fine-grained mylonite schists, mainly consisting of amphiboles of different size (from 6 up to 300 µm), which occur as large blades, equant subgrains or syn to post-kynematic needles. Amphiboles of every size are characterized by an actinolite core rimmed by high AIIV Mg-hornblende. Post-kynematic needles of a new actino-lite have also been found. Plagioclase is both albite and oligoclase.The results indicate that along the Lanterman fault zone shear deformation on metabasites from the WT begun to develop under amphibolite facies metamorphic conditions and later evolved to transitional amphibolite/ greenschist facies conditions. At the boundary of the Bowers Terrane, on the other hand, temperature increased during shear deformation from greenschist to transitional amphibolite/greenschist facies, then retro-gressed toward greenschist facies during the latest deformational stages.
Incremental laser heating 40 Ar-39 Ar analyses on amphibole se~arates of samples from both the Wilson and the Bowers terranes gave irregularly discordant age. Ar-39 Ar age-steps, including the low-temperature region dominated by amphibole intergrown with other K-rich mineral phases (phyllo-silicates), chiefly yielded ages >420440 Ma and up to 490 Ma for the amphibole domains. thus suggesting a negligible influence of the Devonian-Carboniferous Borchgrevink Orogeny.
Bradshaw, J.D .. laird, M.G. & Wodzicki, A (1982): In: C. Craddock (ed). Antarctic Gcosciences, 809-816.
Capponi. G .. Crispini. L & Meccheri. M. (2002): In: J.A. Gamble, D.N.B. SkiMer & S. Henrys (Eds). Antarctica at the Close of a Millennium, 105-112.
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46-The late Eocene, terrestrial, vertebrate fauna from Seymour Island:
Judd A. Case
The tails of the Eocene patagonian size distribution
(oral p.)
Department of Biology, St. Mary's College of California, Moraga, CA 94575; <jcase@stmarys-ca.edu>.
The late Eocene, Antarctic, terrestrial vertebrate fauna from Seymour Island (= Isla Marambio), Antarctic Peninsula, exhibits a wide range of body sizes from small insectivorous, omnivorous and granivorous mammals (e.g. derorhynchid, prepidolopid, microbiotheriid and polydolopid marsupials along with a sudamericid gondwanathere) to moderate to large-sized ungulates (e.g. litoptems and astrapotheres), plus a large-sized sloth and large cursorial birds (a ratite and a phororhacoid). The fauna lacks medium-sized, mammals in the size range represented by rabbit- to deer-sized animals.
Thus, the fauna has a bimodal distribution of body sizes in that it contains small mammals and large mammals and birds, but nothing in between.
In contrast to Antarctic fauna is the contemporaneous Eocene mammalian fauna from Patagonia, which has a reasonably normal distribution of body sizes and is most heavily represented by medium-sized ungulate herbivores. The body size distribution is directly opposite to that of the Antarctic fauna. A comparison of the late Eocene Antarctic fauna to the Eocene Patagonian fauna is appropriate, due to the taxonomic affinities between the two faunas. If the Patagonian fauna is the source for the Antarctic fauna, then the 13 Antarctic taxa could be expected to be distributed equally among the eight size classes present in the Patagonian fauna (at 1.62 taxa/size class). A Chi Square based G-test between the observed Antarctic body size data to this possible equal size class representation or to the "normal" distribution of the Patagonian fauna, shows that the Antarctic fauna is statistical different from either size class distribution.
The bimodal body size distribution is not an unusual pattern for a high latitude, homeothermic, vertebrate fauna, as it can also be seen in the modem boreal (i.e. higher latitudes, >45 degrees) mammalian fauna of North America. The modem boreal fauna also displays a low frequency of taxa in the medium-sized animals, which range in body size from 3-20 kilograms (i.e rabbit- to deer-sized mammals).
The bimodality of body sizes in these Antarctic terrestrial vertebrate fauna is an apparent derivation of Bergmann's Rule, where homeotherms in colder(= higher latitudes) climates are larger than related taxa in warmer climates(= lower latitudes) in order to conserve heat by creating smaller surface area to volume ratios. The small sized marsupials, would adapt to the cool climatic conditions through physiological means (e.g. torpor) and occupying small insulated nest sites. The larger mammals and birds have adapted to the climatic conditions by conserving heat by means of their larger body size.
The absence of medium-sized mammals may be related to the fact that these animals could not utilize either physiological strategy of torpor or heat conservation exhibited by the tails of the body size distribution as they lack sufficient body size to conserve heat, nor are they small enough to occupy insulated nests or burrows and thus they would be at a selective disadvantage.
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-The Antarctic Seismic Data Library System for Cooperative Research (poster p.)
Jonathan R. Childs1, Nigel Wardell2, Alan K. Cooper3 & Giuliano Brancolini4 'U.S. Geological Survey, Menlo Park, CA, USA; <jchilds@usgs.gov>;
2Istituto Nazionale di Oceanografiae di Geofisica Sperimentale, Trieste, Italy;
3U.S. Geological Survey and Stanford University, Stanford, California; Istituto 4Nazionale di Oceanografiae di Geofisica Sperimentale, Trieste, Italy.
The Antarctic Seismic Data Library System for Cooperative Research (SOLS) was designed by mem-bers of the Antarctic geoscience community to facilitate open access to multichannel seismic reflec-tion data, and to promote collaborative research based on those data. The SOLS was formally adopted in 1991 under the auspices of the Scientific Committee on Antarctic Research (SCAR) and mandates of Antarctic Treaty Consultative Meeting Recommendation XVI-12. Since that time, library branches have been established in countries worldwide, and more than 100,000 km of digital seismic reflection profile data have been provided to the SOLS by data collectors in 10 countries.
The library system is a dynamic library where data resides for use by all members of the research community in collaboration with data collectors. Data are available at the SOLS during the period between four and eight years following data collection, after which the data are sent to a World Data Center. The SOLS system protects intellectual property rights of data collectors and provides open access to data, as required by the Antarctic Treaty, to facilitate timely and multinational geoscience research products.
We present an updated design for the SOLS that incorporates a variety of new features and capabili-ties utilizing modem technology and current standards for the organization and dissemination of geo-spatial data, while retaining the basic tenets and guidelines upon which the library system was adopted. This updated design will be discussed in detail at an SOLS workshop during the ISAES IX symposium to ensure that it will meet the current and future needs of the Antarctic scientific community.
The prototype for the updated SOLS:
• includes not only the binary seismic datasets (SEG-Y), but also images of the profiles in standard formats (e.g. tiff) suitable for viewing and printing without specialized seismic processing software;
• is principally Web-based, allowing on-line access to digital datasets. Security and access to data will be controlled according to the terms of the original SOLS agreement. On-line access to sensitive data files (detailed shotpoint maps, SEG-Y data files and high-resolution images for data less than eight years old) will be protected by either password control or off-line storage (e.g.
DVD) accessible only at the SOLS library locations;
• includes spatially referenced location figures at a standard projection and scale to enable the con-venient production of location maps. The use of consistent map parameters and layered map ele-ments facilitates the ease with which data from different datasets can be combined and interpreted;
• establishes a common set of descriptors about each dataset in order to provide more consistent and complete documentation about datasets in the library than now exists.
The updated SOLS, like its predecessor, will be a community research tool that relies on active data-input and use by data collectors and geoscientists to achieve ultimate success. Additional information about the SOLS is available at: http://walrus.wr.usgs.gov/sdls/
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