Zał ącznik 6. Sprawozdanie z XXXII Wyprawy Antarktycznej PAN dr Marek Gola Wydział geologii UW, oraz dr Szymon Ostrowski Prince Charles Mountains, E Antarctica . Russian Polish joint geologic and geomorphologic expedition. Prince Charles Mountains, Mac Robertson Land, East Antarctica. December 2007 - March 2008 53 RAE Autors Szymon Ostrowski, geologist, Polish Academy of Science Marek Gola, geologist, Polish Academy of Science 1. The aim of expedition Prince Charles Mountains are unique, and only East Antarctica area, where sedimentary rocks of Late Paleozoic to Early Mesozoic (Amery Group - Mond 1972) are outcropping. Moreover, Cenozoic deposits (Pagodroma Group - Hambrey and McKelvey 2000) are well developed and preserved in this area. Record of Cenozoic deglaciation, as well as rocks of post-glacial Perm and Triassic sedimentary basin can be clearly recognized (fig. 1). Fig. 1. Area of operation Although many expeditions, Russian and Australian, were held in the area of Prince Charles Mountains, sedimentary rocks of Amery Group and Pagodroma Group, were of marginal interests. Detailed sedimentological studies on Amery Group rocks, combined with geochemical researches of coal deposits, allow to reconstruct changes of sedimentary regimes, climatic impact and regional tectonic regimes in, supposedly post-glacial, sedimentary basin of Lambert Graben, - the prominent structural feature of southern Gondwana (Federov et al. , 1982). Sratigraphy of the Amery Group is based mainly on lithostratigraphic division so far, thus the attempt to establish biostratigraphic time scale will be made, on the basis of samples collected. Systematic studies of different subdivisions of Cenozoic Pagodroma Group will contribute to recognize glacial history of Antarctica during Cenozoic. Most sediments of Pagodroma Group are of glacimarine origin (Bardin 1982; Hambrey and McKelvey 2000), and their thicknesses are substantial. Main aim of the study is to establish chronology of Pagodroma Group, which might be subsequently correlated with chronology of glacial history already recognized on Antarctic Peninsula. Fragments of fauna detritus will be used for biostratigraphic and possibly geochronologic dating. Sedimentologic observations were held to recognize minute changes of glaciomarine environments. Preliminary researches held on Larsemann Hills were concentrated on thin, contemporary sedimentary cover and diminutive geomorphologic processes. Researches of this cover were neglected as far, and scientific questions aroused, might be the basis of further investigations. In addition, samples of stomach oil, from snow petrel ( Pagodroma nivea ) abandoned nests were collected in all visited sites. Geochemical dating of the layered, relatively thick beds of stomach oil, may allow to estimate the time of settling nests, which corresponds to deglaciation of the area. 2. Area of operation Fisher Massif Fisher Massif is isolated, uplifted mountain block in the central Prince Charles Mountains (Mac. Robertson Land). It extends from north-east to south-west, is 30 km long and 13 km wide. The massif is composed of Proterozoic metamorphic rocks with substantial Cenozoic cover (Laiba and Pushina, 1997). Amery Oasis The Amery Oasis is an ice-free area in northernmost part of the Prince Charles Mountains. Amery Oasis is located on the western side of Lambert Glacier and is composed of numerous massifs. The basement of Amery Oasis is composed of Proterozoic metamorphic rocks, which are covered by Permian and Triassic and Neogene sediments. Larsemann Hills Larsemann Hills are the cluster of ice free peninsulas and islands on the Ingrid Christensen Coast in Prydz Bay. Larsemann Hills basement is composed of Precambrian metamorphic rocks - metasedimentary gneisses and Paleozoic intrusive rocks - granite (Stüwe et al. , 1989). Quaternary deposit cover is thin and patchy. 3. Methods In all sites visited, detailed sections of sedimentary rocks were made. Sedimentary and lithologic observations were completed. Parallel sections of the same interval of deposits allowed to recognize lateral facies changes. All sections were sampled for further petrographic and geochemical analysis. Paleonthologic samples were collected for possible biostratigraphic dating. 4. Sections 4.1 Cenozoic sections Cenozoic deposits from Prince Charles Mountains are referred as Pagodroma Group (Hambrey and McKelvey 2000). It is believed that deposits are of glaciomarine origin (Laiba and Pushina 1997; Hambrey and McKelvey 2000, McKelvey et .al . 2001) and are composed mainly of unconsolidated or unconsolidated diamictites and subordinary tillites. The Pagodroma Group is divided into four formations. Fisher Bench Formation and Mount Johnston Formation are outcropping on Fisher Massif, Bardin Bluffs Formation and Battye Glacier Formation, outcropping on the Amery Oasis. Stratigraphic range of Pagodroma Group is not precisely defined. Some microfossils found, are suggesting Miocene for Fisher Bench Formation (Laiba and Pushina 1997) and from Lower Miocene or Oligocene for Mt. Johnston Formation to Pliocene for Battye Formation (McKelvey et .al . 2001) 4.1.1 Fisher Bench Formation Fisher Bench Formation outcrops along the southeastern edge of Fisher Massif (fig. 2). Altitude of its base is slightly descending to northeast along the Massif. It is ranging from nearly 350 m asl on the south to less than 100 m asl on the central and north part of the Massif. Thickness of deposits is reaching up to 370 m. Fig. 2. Schematic map of Fisher Massif Five sections of Fisher Bench Formation were researched. Four of them in the south- eastern part of Fisher Massif (sections over Skaly Jugo-vastotshnyje ) and one on north-eastern part of the Massif (attachment 1). Sections can be hardly correlated with each other, even on short distances. Sediments composing Fisher Bench Formation are unsorted, poorly consolidated or unconsolidated diamictites, sandy and aleuritic (fig. 3). Subordinate layers of sand, aleurites and gravel can be found. In general, clasts derived from Fisher Massif (mostly dark metabazites) are poorly rounded, while clasts of rocks absent on the massif are moderately, or seldom well rounded. Layering of sediments is insignificant, or absent. Sedimentary structures are strongly obscured by slope processes. Only sedimentary structures noticed in diamictites, were horizons of flat, horizontally oriented cobbles (residual?) in finer grained diamictites (fig. 4), and horizons of well sorted, densely packed gravel with shell detritus. Fig. 3. Outcrops of Fisher Bench Formation Fig. 4. Horizon of flat, horizontally oriented cobbles in finer grained diamictites A set of sedimentary structures can be found in sand and aleurite horizons. Low angle cross lamination, channel cross lamination and subordinate ripplemark lamination are noticed in sand horizons in the basal parts of sections. Aleurite horizons are massif or horizontally laminated. Lamination is centimeter scale and is manifested by following dark and light-grey layers. Individual example of diminutive flow erosion structure (whirl erosion) was found in aleurite facies. Siderite concretions were found in one of the sections within aleuritic facies. Insignificant, 30-meter scale alternations of diamictites of sandy and aleuritic matrix were recognized in one of the sections. Interpretation of these alternations as fining upward cycles is tempting, however no distinctive boundaries of them can be found. Thus such interpretation can not be properly supported. Sections of Fisher Bench Formation are hardly corelatable, even on short distances. Neither diamictite sets, nor aleuritic parts of sections can be followed on distances bigger than 100-200 meters. Thus mentioned sets must be regarded as lenses. Boulder horizons continuing for over 0,5 km were noticed. Sand layers are located in the bottom of sections. Distribution of sand, its thickness is varying laterally The thickest sand horizon has been found in the section D, located in front of the mouth of small valley eroded in basement (Dolina Parallelnaja ). The thickness of the sand horizon is gradually decreasing southward. Sand content in diamictitesets reveal the same regularity. It might be suggested, that Paralelnaja valley was the source of sand material during the deposition of Fisher Bench Formation. The change of angularity of bigger grains was noticed along the outcrops. Mean angularity of clasts is decreasing on southern part of outcrop, where basement rocks forming step edge (paleorelief) close to the outcrop. 4.1.2. Mount Johnston ( Nadkarovaja ) Formation Mount Johnston Formation outcrops on the southern slope of Nadkarovaja Mt. on Fisher Massif. Outcrops are laterally distributed along the edge of Kar Bolshoy, about 2 km from east to west. The deposits are horizontal and their thickness do not exceed 100 m. Basis of the formation is on the altitude of 1360 m asl and erosional top is on 1450 m asl. One section researched, located to the east of Mt. Nadkarovaja top, covers whole formation depositional record (attachment 2). Sediments composing Mt Johnston Formation are unsorted, unconsolidated diamictites of sandy matrix. Clasts are moderately to well rounded, up to 30 cm in diameter, composed mainly of felsitic igneous rocks and gneisses. Clasts of locally derived, unrounded rocks are predominant only in the vicinity of the top of Nadkarovaja Mt (erosional relict of basement). Layering of the deposits is hardly visible. Finer grained diamictites are absent in the section. Only one horizon