Polonez Cove Formation Research Articles

U–Pb isotopic ages and provenance of some far-travelled exotic pebbles from glaciogenic sediments of the Polonez Cove Formation (Oligocene, King George Island)

Zircon grains from nine erratic pebbles of granite, granodiorite–tonalite and quartzite from the Polonez Cove Formation (southern King George Island) were studied for their U–Pb isotope ages and provenance. The calculated concordia ages of the studied pebbles are 108.79 ± 0.89, 119.7 ± 2.2, 178.6 ± 2.8, 180.7 ± 1.9, 207.4 ± 3.1, 231.1 ± 1.9, 1087.5 ± 4 and 1833 ± 4 Ma. The source area of individual pebbles was analysed and defined. Pebbles of crystalline rocks were derived from the Antarctic Peninsula, as well as from the Antarctic mainland. The erratic made of quartzite was eroded from the southernmost part of the Ellsworth Mountains (Linder Peak Member of Howard Nunatak Formation). Our isotope data analytically support the earlier thesis that the Oligocene ice-sheet covered a substantial part of Antarctica and its nucleus was located in its central part. Supplementary material: The U–Pb isotope data (Table S1) are available at https://doi.org/10.6084/m9.figshare.c.5233335

A new sediment-dwelling pholadid bivalve from Oligocene glaciomarine sediments of King George Island, West Antarctica

We present a re-description of the pholadid bivalve from the Oligocene Polonez Cove Formation, King George Island, West Antarctica, previously identified as Penitella sp. The study is based on a collection of 210 specimens, preserved exclusively in life position in flask-shaped Gastrochaenolites type borings which have been subsequently buried by glaciomarine diamictite. The systematic study showed that this pholadid is a new species belonging to the genus Pholadidea rather than to Penitella and we name it Pholadidea gradzinskii sp. nov. The species is one of very few Late Cretaceous—Paleogene pholadids that we could safely identify as Pholadidea. All of them are known exclusively from the southern Pacific and adjacent areas (New Zealand, Antarctica, and Patagonia). We demonstrate that the genus attained its Recent broad distribution before the middle Miocene, when the first species of Pholadidea appeared in the Northern Hemisphere. The mass occurrence of P. gradzinskii in the Oligocene of West Antarctica...

Echinoids from the Chlamys Ledge Member (Polonez Cove Formation, Oligocene) of King George Island, West Antarctica

Abstract New echinoid material from the Oligocene Chlamys Ledge Member (uppermost part of the Polonez Cove Formation) on King George Island, West Antarctica, includes the “regular” echinoid Caenopedina aleksandrabitnerae sp. n. and poorly preserved spatan-goids, here tentatively identified as members of the genus Abatus. Caenopedina aleksan-drabitnerae sp. n. is characterized by fully tuberculate genital plates, which sets it apart from most other species in the genus, by the uneven periproctal margin which indicates that periproctal plates were incorporated into the apical disc, and by moderately wide inter-ambulacral plates with a height/width ratio of 1:3. Among the modern Caenopedina species it is closest to the Australian and New Zealand representatives, which is in contrast to previ-ous reviews of Cenozoic Antarctic echinoid faunas that suggested limited relationship to the Australasian region. This is the first record of Caenopedina from Antarctica; it considerably extends its historical distribution to the south.

Shallow water benthic foraminifera from the Polonez Cove Formation (lower Oligocene) of King George Island, West Antarctica

We present the first description of benthic foraminifera from the lower Oligocene of the Antarctic Peninsula sector (South Shetlands) of West Antarctica. The single assemblage was collected at several sites and has no modern Antarctic analogue. It is dominated by robust calcareous species and represents a fan-delta front system. The assemblage includes a group of the most morphologically conservative Antarctic foraminifera known from other Cenozoic neritic sites around Antarctica, indicating their presence since at least the Eocene. Despite including some characteristic taxa, e.g., Ammoelphidiella sp., it is difficult to correlate this assemblage with any particular interval of the Ross Sea record, mainly because of a strong taxonomic imprint of a shallow water environment.

Shell beds from the Low Head Member (Polonez Cove Formation, early Oligocene) at King George Island, west Antarctica: new insights on facies analysis, taphonomy and environmental significance

AbstractShell bed levels in the Low Head Member of the early Oligocene Polonez Cove Formation at King George Island, West Antarctica, are re-interpreted based on sedimentological and taphonomic data. The highly fossiliferous Polonez Cove Formation is characterized by basal coastal marine sandstones, overlain by conglomerates and breccias deposited in fan-delta systems. The shell beds are mainly composed of pectinid bivalve shells of Leoclunipecten gazdzickii and occur in the basal portion of the Low Head Member. Three main episodes of bioclastic deposition are recorded. Although these shell beds were previously interpreted as shelly tempestites, we present an alternative explanation: the low fragmentation rates and low size sorting of the bioclasts resulted from winnowing due to tidal currents (background or diurnal condition) in the original bivalve habitat. The final deposition (episodic condition) was associated with subaqueous gravity driven flows. This new interpretation fits with the scenario of a prograding fan-delta front, which transported shell accumulations for short distances near the depositional site, possibly between fair-weather and storm wave bases. This work raises the notion that not every shell bed with similar sedimentological and taphonomic features (such as geometry, basal contact, degree of packing and shell orientation in the matrix) is made in the same way.

Brachiopods from the Chlamys Ledge Member (Polonez Cove Formation, Oligocene) of King George Island, West Antarctica

Brachiopods from the Chlamys Ledge Member (Polonez Cove Formation, Oligocene) of King George Island, West Antarctica

Invertebrates from the Low Head Member (Polonez Cove Formation, Oligocene) at Vauréal Peak, King George Island, West Antarctica

AbstractEight taxa of marine invertebrates, including two new bivalve species, are described from the Low Head Member of the Polonez Cove Formation (latest early Oligocene) cropping out in the Vauréal Peak area, King George Island, West Antarctica. The fossil assemblage includes representatives of Brachiopoda (generaNeothyrissp. andLiothyrellasp.), Bivalvia (Adamussium auristriatumsp. nov., ?Adamussiumcf.A. alanbeuiJonkers, andLimatula(Antarctolima)ferrazianasp. nov.), Bryozoa, Polychaeta (serpulid tubes) and Echinodermata. Specimens occur in debris flows deposits of the Low Head Member, as part of a fan delta setting in a high energy, shallow marine environment.Liothyrellasp.,Adamussium auristriatumsp. nov. andLimatula ferrazianasp. nov. are among the oldest records for these genera in King George Island. In spite of their restrict number and diversification, bivalves and brachiopods from this study display an overall dispersal pattern that roughly fits in the clockwise circulation of marine currents around Antarctica accomplished in two steps. The first followed the opening of the Tasmanian Gateway at the Eocene/Oligocene boundary, along the eastern margin of Antarctica, and the second took place in post-Palaeogene time, following the Drake Passage opening between Antarctic Peninsula and South America, along the western margin of Antarctica.

The Polonez Cove Formation of King George Island, Antarctica: stratigraphy, facies and implications for mid‐Cenozoic cryosphere development

The middle to late Oligocene Polonez Cove Formation, exposed on south‐eastern King George Island, South Shetland Islands, provides rare evidence of mid‐Cenozoic West Antarctic cryosphere evolution. A revised lithostratigraphy and facies analysis and a review of the palaeoenvironmental significance of the formation are presented here. The diamictite‐dominated basal member of the formation (Krakowiak Glacier Member) records the presence and retreat of marine‐based ice on a shallow continental shelf. Five overlying members are recognized. These consist of basaltic‐sourced sedimentary rocks and lavas and represent a variety of shoreface and shallow continental shelf environments in an active volcanic setting. These units contain diverse reworked and ice‐rafted exotic clasts that become sparse towards the top of the formation, suggesting a continuing but waning glacial influence. New 40Ar/39Ar dates from interbedded lava flows indicate a late Oligocene age (25·6–27·2 Ma) for the Polonez Cove Formation, but are slightly younger than skeletal carbonate Sr‐isotope ages obtained previously (28·5–29·8 Ma). There is evidence for wet‐based subice conditions at the base of the Polonez Cove Formation, but no sedimentary facies to suggest substantial meltwater. This may reflect a subpolar setting or may result from lack of preservation or a high‐energy depositional environment. A northern Antarctic Peninsula/South Shetland Islands provenance is probable for most non‐basaltic clasts, but certain lithologies with possible origins in the Transantarctic and Ellsworth Mountains also occur sparsely throughout the formation. There is evidence to suggest that the presence of such far‐travelled clasts within subglacially deposited facies at the base of the formation reflects the advance of a local ice cap across marine sediments containing the clasts as ice‐rafted material. The presence of these clasts suggests that extensive marine‐based ice drained into the southern Weddell Sea region and that a strong Weddell Sea surface current operated both before and during deposition of the Polonez Cove Formation.

Oligocene and Pliocene interglacial events in the Antarctic Peninsula dated using strontium isotope stratigraphy

Strontium isotope stratigraphy is used to date two interglacial-marine deposits in the Antarctic Peninsula region. On King George Island, interglacial pectinid-rich sediments in the Low Head Member of the Polonez Cove Formation give a strontium isotope stratigraphy age of 29.0 +0.7 −0.6 to 29.8 +0.8 −0.7 Ma (mid-Oligocene), which, in conjunction with previous K–Ar dating of volcanic rocks, indicates a glacial episode in the Antarctic Peninsula between middle Eocene (42.0 ±1.0 Ma) and mid-Oligocene time. In addition, an inter-glacial deposit (Pecten Conglomerate) from tectonically-elevated exposures on Cockburn Island is dated as Pliocene (3.5–5.3 Ma). Published data suggest these latter sediments were deposited under shallow marine conditions, which were warmer than those of present-day Antarctica.

TheChlamys coquinas in glacio-marine sediments (Pliocene) of King George Island, West Antarctica

The fossiliferous glacio-marine sequence of the “Pecten conglomerate” (=Low Head Member of the Polonez Cove Formation) of King George Island contains numerous pelecypod shells ofChlamys anderssoni (Hennig), which sometimes form lumachelles. These allochthonous coquinas, often with intraclasts, can be interpreted as storm deposits (tempestites). Their mode of distribution in the deposits of the Low Head Member suggests that sedimentation of this sequence was episodically interrupted by storm-generated energy events resulting in resedimentation of the biota assemblages.

Cretaceous and Tertiary fossils in glacio-marine strata at Cape Melville, Antarctica

Glacio-marine sediments of the Cape Melville Formation (King George Island, South Shetland Islands, West Antarctica) contain a rich and predominantly invertebrate fauna. The occurrence of nannoplankton and belemnites might be used as evidence for dating the glacio-marine Cape Melville Formation as Cretaceous. However, the co-occurrence of the coral genus Flabellum (Eocene–Recent) and the foraminiferal genus Uvigerina (Eocene–Recent) indicate that recycling of the nannoplankton and belemnites has occurred. The sediments of the Cape Melville Formation contain a variety of glacially striated ice-rafted dropstones (up to 2 m) of Antarctic continent provenance. These sediments lie between lavas of the Sherratt Bay Formation and Pliocene Polonez Cove Formation, and may correlate with a late Miocene glaciation of Antarctica.