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Foraminiferal evidence for a Lower Miocene age of glaciomarine and related strata, Moby Dick Group, King George Island ( South Shetland Islands, Antarctica).
Abstract
Predominantly glaciomarine sediments of the Moby Dick Group yielded benthic foraminiferal assemblages of Early Miocene age. The index foraminifera for these deposits are: Cyclammina incisa, C. japonica, Haplophragmoides carinatus and Uvigerinella californica gracilis. Out of 49 foraminiferal species determined, more than half are Recent species. Basing on distribution of calcareous (I) versus arenaceous (II) and mixed (III) foraminiferal assemblages in lithostratigraphic columns of the Moby Dick Group, depth-ranges of the sedimentary basin suggest that the basal part of the Cape Melville Formation is characterized by deep-water arenaceous microfauna which is followed by mixed and calcareous assemblages indicating shallowing up of the basin to depths corresponding to shallow shelf. Higher up in the column, mixed assemblages are followed again by arenaceous ones indicating gradual deepening of the basin to depths comparable with bathyal zone. Two foraminiferal assemblage-zones have been distinguished corresponding to Early Miocene. The foraminifera-bearing sediments pre-date an intrusive event of andesite dyke swarm K/Ar dated at approx 20Ma.-from Authors Inst of Geol Sci, Polish Acad of Sci, ul Senacka 3, 31-002 Krakow, Poland.
... Although overall scarce and patchy, the foraminiferal fossil record of Antarctica still provides enough information to give us a glimpse of its Cenozoic fauna. For West Antarctica, the reported assemblages represent mainly communities of shallow, inner-shelf settings that are Eocene to Pleistocene in age (e.g., Birkenmajer and Łuczkowska, 1987;Gaździcki and Webb, 1996;Gaździcki and Majewski, 2012;Caramés and Concheyro, 2013;Majewski and Gaździcki, 2014), whereas those from deeper paleoenvironments are represented by some Miocene assemblages (Birkenmajer and Łuczkowska, 1987) and a couple of Paleocene ones (Huber, 1988; see paleoenvironmental revisions by Olivero et al., 2007 andMarenssi et al., 2012). For East Antarctica, it is the opposite, for very few occurrences from shallow, marine settings are known (see Quilty et al., 2010;Majewski et al., 2012Majewski et al., , 2017 and some outer-shelf to abyssal assemblages have been recovered from offshore deposits (see Thomas, 1989;Majewski et al., 2018). ...
... Although overall scarce and patchy, the foraminiferal fossil record of Antarctica still provides enough information to give us a glimpse of its Cenozoic fauna. For West Antarctica, the reported assemblages represent mainly communities of shallow, inner-shelf settings that are Eocene to Pleistocene in age (e.g., Birkenmajer and Łuczkowska, 1987;Gaździcki and Webb, 1996;Gaździcki and Majewski, 2012;Caramés and Concheyro, 2013;Majewski and Gaździcki, 2014), whereas those from deeper paleoenvironments are represented by some Miocene assemblages (Birkenmajer and Łuczkowska, 1987) and a couple of Paleocene ones (Huber, 1988; see paleoenvironmental revisions by Olivero et al., 2007 andMarenssi et al., 2012). For East Antarctica, it is the opposite, for very few occurrences from shallow, marine settings are known (see Quilty et al., 2010;Majewski et al., 2012Majewski et al., , 2017 and some outer-shelf to abyssal assemblages have been recovered from offshore deposits (see Thomas, 1989;Majewski et al., 2018). ...
... It is difficult to interpret the possibly diachronic presence of these cyclamminids. Both Cyclammina cancellata and Cyclammina placenta are absent in the underlying deposits, and only Cyclammina cancellata occurs in another pre-Quaternary deposit of West Antarctica, this being the early Miocene Cape Melville Formation on King George Island (Birkenmajer and Łuczkowska, 1987). Because these cyclamminids are also filled with sediment and display postfill fragmentation, like the other large agglutinated taxa, they certainly experienced similar, if not the same, diagenetic process; because this process spared the associated pristine, small foraminifers that are considered to be contemporaneous with Miocene and Plio-Pleistocene deposition (Badaró and Petri, 2019), the cyclamminids must be considered as older elements, possibly pre-Miocene. ...
Our knowledge of the foraminiferal fossil record of Antarctica is notoriously patchy but still offers us an overview of its Cenozoic faunas. Few occurrences have been reported for the continent, with deep-sea assemblages described mainly for its eastern portion. Here we describe 21 taxa of large agglutinated foraminifers from the Miocene Hobbs Glacier Formation and the Plio-Pleistocene Weddell Sea Formation on Seymour Island, West Antarctica, including the gigantic Ammodiscus vastus new species. Most of them consist of genera or species typical of deep-sea agglutinated assemblages. All specimens are completely filled and partially covered by lithified micrite. This, along with the postfill fragmentation of some tests, indicates their re-elaboration from older deposits. Because all of these foraminifers share the same taphonomic features and most of them represent taxa associated with deep-sea settings, they probably represent a flysch-type assemblage from an unknown deposit that was eroded and had its microfossils scattered through post-Paleogene sediments. A Paleocene age for this putative assemblage is indicated by the presence of Reticulophragmiun garcilassoi (Frizzell, 1943), a Paleocene index fossil, and by its association with the Cretaceous–Paleocene Ammodiscus pennyi Cushman and Jarvis, 1928. If taken as a coherent foraminiferal assemblage, it represents one of the few deep-sea assemblages known for West Antarctica, and the first flysch-type assemblage recognized for the Antarctic Cenozoic. In addition, it would show that the Paleocene foraminiferal communities of the West Antarctica's deep-sea floor were more like their Pacific counterparts than their Atlantic equivalents.
UUID: http://zoobank.org/0d281489-c0c6-47b4-9884-f820806485b7
... The notorious patchiness of the foraminiferal fossil record of West Antarctica prevents a comprehensive view of its Cenozoic faunas, but a few assemblages are known from the following deposits: Cretaceous-Palaeocene López de Bertodano Formation and Palaeocene Sobral Formation on James Ross Island, Seymour Island and Vega Island (Huber 1986(Huber , 1988; Eocene La Meseta Formation on Seymour Island (Gaździcki & Majewski 2012; see also Bitner 1996 for brachiopod-incrusting foraminifers and Badaró 2019 for rare agglutinated specimens); Oligocene Polonez Cove Formation on King George Island (Gaździcki 1989, Majewski & Gaździcki 2014; Early Miocene Cape Melville Formation, also on King George Island (Birkenmajer & Łuczkowska 1987), Middle Miocene deposits off Weddell Sea and Miocene Hobbs Glacier Formation (HGF) on James Ross Island (Jonkers et al. 2002, Concheyro et al. 2007; Pliocene Cockburn Island Formation on the homonymous island (Hennig 1910, Holland 1910, Gaździcka & Gaździcki 1994, Gaździcki & Webb 1996; and Pleistocene deposits on Vega Island (Caramés & Concheyro 2013, Concheyro et al. 2014. ...
... In addition, G. cf. subglobosa occur in the La Meseta Formation (Gaździcki & Majewski 2012), in the Oligocene Polonez Cove Formation (Majewski & Gaździcki 2014), in the Early Miocene Cape Melville Formation (Birkenmajer & Łuczkowska 1987) and in the Cockburn Island Formation (Gaździcki & Webb 1996). As for P. fusca, this species occurs in the Cretaceous-Palaeocene López de Bertodano Formation (Huber 1988) and in the Cape Melville Formation (Birkenmajer & Łuczkowska 1987), as well as in the Recent slope and abyssal plain of the Weddell Sea (Cornelius & Gooday 2004) and in inlets of King George Island, where it is found at depths of 20-250 m (Majewski 2005(Majewski , 2010. ...
... subglobosa occur in the La Meseta Formation (Gaździcki & Majewski 2012), in the Oligocene Polonez Cove Formation (Majewski & Gaździcki 2014), in the Early Miocene Cape Melville Formation (Birkenmajer & Łuczkowska 1987) and in the Cockburn Island Formation (Gaździcki & Webb 1996). As for P. fusca, this species occurs in the Cretaceous-Palaeocene López de Bertodano Formation (Huber 1988) and in the Cape Melville Formation (Birkenmajer & Łuczkowska 1987), as well as in the Recent slope and abyssal plain of the Weddell Sea (Cornelius & Gooday 2004) and in inlets of King George Island, where it is found at depths of 20-250 m (Majewski 2005(Majewski , 2010. Favulina hexagona was also reported (as Oolina hexagona) for the Cape Melville Formation (Birkenmajer & Łuczkowska 1987), but there is no other record of this species for the Cenozoic deposits of the Antarctic Peninsula, although other Favulina sp. are known, such as Favulina epibathra (reported as Conolagena epibathra) from the Pleistocene deposits of Vega Island (Caramés & Concheyro 2013) and a Favulina sp. ...
Here we describe new microfossil assemblages for the Miocene Hobbs Glacier Formation and the first possibly indigenous assemblages for the Plio-Pleistocene Weddell Sea Formation on Seymour Island, West Antarctica. The assemblages are composed mainly of foraminifers, but radiolarians, calcitarchs and poriferan sclerites are also present. For the Hobbs Glacier Formation, we report the foraminifers Bolivina sp., Oolina globosa and Rosalina cf. globularis ; and for the Weddell Sea Formation, we report Favulina hexagona , Globigerinita uvula , Globocassidulina cf. subglobosa and Psammosphaera fusca . The low abundance and diversity of microfossils, allied with the complex taphonomical processes that prevailed in Antarctic glacial–marine palaeoenvironments, make it impossible to define whether the assemblages are composed of a mixture of indigenous and re-elaborated specimens or exclusively of re-elaborated remains. Nevertheless, the indigenous nature of some specimens is suggested by their inherent fragility, excellent preservation and/or taxonomic association with indigenous assemblages from correlated strata. The taxonomic compositions are not directly comparable with other Antarctic assemblages, although most of the species were previously reported from pre-Quaternary or modern deposits of both West and East Antarctica. This lack of correspondence is probably due to preservation biases, but any further significance is hidden by the complex taphonomy of the deposits.
... A comparatively deep-water, outer shelf environment for the unit was later suggested based on the composition of the macrobenthic assemblage (Förster et al. 1987;Feldmann and Crame 1998;Hara and Crame 2004). This was supported by evidence from microfaunal and microfloral data (Dudziak 1984;Birkenmajer and Łuczkowska 1987;Troedson and Riding 2002;Hara and Crame 2004). The presence of infaunal bivalves in life position, horizontal crab burrows and the vertical growth position of corals led Roniewicz and Morycowa (1987) to suggest deposition in low energy water interspersed with chaotic burial. ...
... Previous studies on the CMF focussed on taxonomic descriptions of the different marine invertebrate groups (Roniewicz and Morycowa 1985;Förster 1985; al. Förster et al. (1985Förster et al. ( , 1987, Jesionek-Szymańska (1987), Karczewski (1987), Roniewicz and Morycowa (1987), Szaniawski and Wrona (1987), Feldmann and Crame (1998), Bitner and Crame (2002), Jonkers (2003), Hara and Crame (2004), Anelli et al. (2006), Whittle et al. (2011Whittle et al. ( , 2012 and Beu and Taviani (2013) 1987; Jesionek-Szymańska 1987;Karczewski 1987;Szaniawski and Wrona 1987;Feldmann and Crame 1998;Bitner and Crame 2002;Jonkers 2003;Hara and Crame 2004;Anelli et al. 2006;Whittle et al. 2011Whittle et al. , 2012Beu and Taviani 2013), or intra-taxon assemblage characterisation (Whittle et al. 2012). Microfossils identified from the CMF included Polychaeta in the form of jaw elements, Foraminifera, Radiolaria, Ophiuroidea elements and Ostracoda (Birkenmajer and Łuczkowska 1987;Szaniawski and Wrona 1987). Fossils have been found from 14 different sites along the Cape Melville Peninsula (Fig. 1). ...
... Brachiopods were identified from the family Terebratulidae, genus Liothyrella and the family Laqueidae, Fig. 2 Reconstruction of the Cape Melville Formation fossil assemblage based on fossil data from this paper, all specimens were collected from approximately the uppermost 75 m of Unit D of Troedson and Riding (2002) and can be regarded as one time-averaged assemblage for the purposes of this study genus Paraldingia (Bitner and Crame 2002). Bryozoan fragments were noted by Birkenmajer and Łuczkowska (1987) in their microfossil collections. Echinoderms from Polish collections were identified to 3 genera in the families Cidaridae, Echinidae and Schizasteridae (?Notocidaris, ?Sterechinus and ?Schizaster). ...
The fossil community from the Early Miocene Cape Melville Formation (King George Island, Antarctica) does not show the archaic retrograde nature of modern Antarctic marine communities, despite evidence, such as the presence of dropstones, diamictites and striated rocks, that it was deposited in a glacial environment. Unlike modern Antarctic settings, and the upper units of the Eocene La Meseta Formation on Seymour Island, Antarctica, which are 10 million years older, the Cape Melville Formation community is not dominated by sessile suspension feeding ophiuroids, crinoids or brachiopods. Instead, it is dominated by infaunal bivalves, with a significant component of decapods, similar to present day South American settings. It is possible that the archaic retrograde structure of the modern community did not fully evolve until relatively recently, maybe due to factors such as further cooling and isolation of the continent leading to glaciations, which resulted in a loss of shallow shelf habitats.
... Certain clast lithologies were described by Birkenmajer and Butkiewicz (1988). There have been a number of publications describing the biotas of the CMF, including works on calcareous nannoplankton (Dudziak 1984), crustaceans (Forster et al. 1987;Feldmann and Crame 1998), and foraminifera (Birkenmajer and Luczkowska 1987). Chronostratigraphic studies have included K-Ar dating of associated volcanic rocks and dikes (Birkenmajer et al. 1985), and Sr-isotope dating of skeletal carbonate from both formations (Dingle and Lavelle 1998), the results of which are described in more detail below. ...
... Intact crustacean (crab and lobster) fossils are common in mudstone of the upper CMF. Previous paleontological studies have indicated that the CMF contains an outer-continental-margin assemblage of benthic foraminifera (Birkenmajer and Luczkowska 1987). Minor planktonic foraminifera and intact diatoms occur in mudstones of the upper CMF, and blackened diatom fragments occur in some beds of the lower CMF. ...
... A thorough study of the varied fossil fauna may reveal likely variations in depositional water depths through the CMF. One such study has been attempted previously, in which water depth variations were estimated on the basis of variations in the dominance of calcareous and arenaceous benthic foraminifera through the formation (Birkenmajer and Luczkowska 1987). The reported trends were attributed to carbonate dissolution associated with changes in water depth, and interpreted to reflect up-section shallowing of the sequence from mid-slope to shallow shelf water depths, followed by deepening to mid-slope depths. ...
The Cape Melville Formation (CMF), exposed on southeastern King George Island, South Shetland Islands, provides rare evidence of extensive earliest Miocene glaciation in the Antarctic Peninsula region. The formation records the presence of regional marine-based grounded ice on the continental shelf. It overlies disconformably the upper Oligocene Destruction Bay Formation, which consists of sandstones recording nonglacial shallow marine conditions. Four units have been identified within the approximately 150 m thickness of the CMF. The basal unit (A) consists of coarse glacigenic debris-flow facies interbedded with glaciomarine mudstone and sandstone. The overlying unit (B) is mainly fine-grained. This succession may represent relatively ice-proximal deposition followed by glacial retreat and/or relative sea-level rise. The upper CMF (units C and D) was deposited in an ice-distal marine environment, with intermittent input of coarse glacigenic debris, mainly from ice rafting. Thin beds of pelagic carbonate ooze within unit C indicate periods of low terrigenous sediment input and high productivity. Lithologically diverse glacigenic gravel clasts (mainly ice-rafted debris) in the CMF had a wide regional source area, suggesting that ice cover was widespread regionally and included calving ice margins. For a small proportion of clasts; the nearest known source is the mountains fringing the southern Weddell Sea. Such clasts were presumably transported north in debris-laden icebergs by a strong, cold Weddell Sea surface current. A temperate glacial setting is tentatively inferred from the CMF. Palynological results confirm and enhance the paleoenvironmental interpretation from the sedimentology, and include the first early Miocene dinoflagellate cyst assemblages recorded on the Antarctic Peninsula. This reappraisal of the glacial record from the CMF provides valuable constraints on the Antarctic cryosphere and regional paleoenvironments in the mid-Cenozoic.
... We note that Cretaceous reworking has not only been observed from the palynological assemblages. Recycled Cretaceous belemnites (Birkenmajer & ºuczkowska 1987) and calcareous nannoplankton (Dudziak 1984) provide a substantial addition to the indigenous marine fossil spectrum in the Cape Melville Formation. The latter embraces various bivalves, gastropods , brachiopods, solitary corals, crabs, echinoids, bryozoans, and calcitic and arenaceous foraminifera (Birkenmajer & ºuczkowska 1987). ...
... Recycled Cretaceous belemnites (Birkenmajer & ºuczkowska 1987) and calcareous nannoplankton (Dudziak 1984) provide a substantial addition to the indigenous marine fossil spectrum in the Cape Melville Formation. The latter embraces various bivalves, gastropods , brachiopods, solitary corals, crabs, echinoids, bryozoans, and calcitic and arenaceous foraminifera (Birkenmajer & ºuczkowska 1987). The exact location of the Cretaceous sediments that acted as a source for the recycled belemnites and nannofossils is also unknown. ...
Palynological analyses of 12 samples from the Cape Melville Formation, which crops out on easternmost King George Island, Antarctica, provide new information on the type of vegetation that covered the South Shetland Islands during the early Miocene Melville Glaciation, c. 23À21 Ma. The assemblage recovered was mostly characterised by in situ algae such as leiospheres along with acanthomorph acritarchs, both glacial indicators. The sparse in situ terrestrial palynomorph assemblage included tundra-indicative moss spores Coptospora sp., rare podocarp conifer and various angiosperm pollen. The latter includes pollen of several species of Nothofagidites, plus rare Asteraceae, Caryophyllaceae (Colobanthus-type) and Chenopodipollis. The majority of the palynomorphs recovered are interpreted as reworked, denoting glacial scouring and redeposition from various sites in the Antarctic Peninsula and the South Shetland Islands. These reworked palynomorphs are of Permian to Paleogene age. This reworked component provides insight into the potential sources of reworking, and is consistent with multiple cycles of glacial advances to the Melville Peninsula at the time of deposition. The penecontemporaneous palynomorphs recovered provide new data on the climatic regime and glacial intensification during the early Miocene on King George Island.
... A precise palaeontological age for the glacio-marine Cape Melville Formation, on easternmost King George Island, has proven elusive despite an abundance of in situ macrofossils, but benthic foraminifera suggest that the formation is Early Miocene (Birkenmajer & Luczkowska 1987). Bracketing by field relationships indicates a maximum age of < 25.3 ± 0.8 or < 23.6 ± 0.7 Ma (by 87 Sr/ 86 Sr and K-Ar dating, respectively) obtained on brachiopods and a basaltic tuff, respectively, in the underlying marine sedimentary Destruction Bay Formation , 1988b, Dingle & Lavelle 1998. ...
King George Island (South Shetland Islands, Antarctic Peninsula) is renowned for its terrestrial palaeoenvironmental record, which includes evidence for potentially up to four Cenozoic glacial periods. An advantage of the glacigenic outcrops on the island is that they are associated with volcanic formations that can be isotopically dated. As a result of a new mapping and chronological study, it can now be shown that the published stratigraphy and ages of many geological units on eastern King George Island require major revision. The Polonez Glaciation is dated as c. 26.64 ± 1.43 Ma (Late Oligocene (Chattian Stage)) and includes the outcrops previously considered as evidence for an Eocene glacial ('Krakow Glaciation'). It was succeeded by two important volcanic episodes (Boy Point and Cinder Spur formations) formed during a relatively brief interval (< 2 Ma), which also erupted within the Oligocene Chattian Stage. The Melville Glaciation is dated as c. 21–22 Ma (probably 21.8 Ma; Early Miocene (Aquitanian Stage)), and the Legru Glaciation is probably ≤ c. 10 Ma (Late Miocene or younger). As a result of this study, the Polonez and Melville glaciations can now be correlated with increased confidence with the Oi2b and Mi1a isotope zones, respectively, and thus represent major glacial episodes.
... In situ shallow-water calcareous foraminiferal assemblages are known from several other exposures around Antarctica, i.e. in Pliocene strata of the Sørsdal Formation in the Prydz Bay area (Quilty et al., 1990;Quilty, 2010) and in the Antarctic Peninsula sector in Lower Eocene (Gaździcki and Majewski, 2012), Lower Oligocene (Majewski and Gaździcki, 2014), Miocene-Pliocene (Jonkers et al., 2002), and Pliocene (Gaździcki and Webb, 1996). Deeper-water communities in the same areas were reported much less frequently (Birkenmajer and Łuczkowska, 1987;Carames and Concheyro, 2013), indicating that marine shallow-water environments were especially favorable for sustaining and preserving calcareous microfossils in much of Cenozoic Antarctica. It may also suggest that over long periods, conditions around deeper parts of the continental shelf of East Antarctic and around the Antarctic Peninsula were unfavorable for development and/ or preservation of calcareous benthic foraminiferal assemblages. ...
... Geological description of the Destruction Bay Formation can be found in Biernat et al. (1985) and Birkenmajer and Łuczkowska (1987). ...
A new species of genus Panopea Menard de la Groye, named P. (P). andreae sp. n. is described in detail. It is the most common of bivalve species recorded in the Destruction Bay Formation (Early Miocene) of King George Island (South Shetland Islands, West Antarctica). The bivalve material collected includes in addition: P. (P) aff. worthingtoni Hutton, Eurhomalia cf. antarctica (Shermann and Newton) and E. cf. newtoni (Wilcknes). -Author
... The lower Miocene benthic foraminiferal assemblages from Cape Melville Fm. (Birkenmajer and Łuczkowska, 1987), which are geographically very close, have been dated at 22.6 Ma (Dingle and Lavelle, 1998) and are significantly younger. Moreover, they are rich in agglutinated species and represent a markedly deeper-water outershelf environment (Birkenmajer, 1995;Uchman and Gaździcki, 2010) than the assemblage presented in this study. ...
... Diverse foraminiferal assemblages from the Antarctic Peninsula have been documented from the Upper Cretaceous (MacFadyen 1966;Huber 1988;Gennari 1995;Concheyro et al. 1997;Hradecká et al. 2011;Florisbal et al. 2013), Paleocene (Huber 1988 and Eocene outcrops (Gaździcki andMajewski 2009, 2012). Less diverse foraminiferal assemblages have been recorded from Oligo− cene (Gaździcki 1989), Miocene (Birkenmajer and Łuczkowska 1987;Bertels− −Psotka et al. 2001;Jonkers et al. 2002;Lirio et al. 2003;Concheyro et al. 2007;Majewski et al. 2012;Nývlt et al. 2011), Miocene-Pliocene (Adamonis et al. 2010 and Pliocene to early Pleistocene exposures (Holland 1910;Gaździcki and Webb 1996;Jonkers et al. 2002;Lirio et al. 2003;Caramés and Concheyro 2013). ...
Micropaleontological and palynological samples from three Cenozoic diamictites at Cape Lamb, Vega Island, James Ross Basin were analysed. Fossiliferous samples yielded reworked and autochthonous assemblages of Mesozoic calcareous nannofossils, impoverished Cretaceous foraminifera together with Neogene species, as well as Late Cretaceous dinoflagellate cysts, pollen, spores and abundant Cenozoic microforaminiferal linings. The recovered nannoflora indicates Early Cretaceous (Hauterivian–Albian) and Late Cretaceous (Santonian–Early Campanian) ages, suggesting an intensive reworking of marine sediments. The presence of the Early Cretaceous species Nannoconus circularis Deres et Acheriteguy in the diamictite represents its first record for the James Ross Basin. The scarce foraminiferal fauna includes Pullenia jarvisi Cushman, which indicates reworking from lower Maastrichtian–lower Paleocene sediments, and also the Neogene autochthonous Trochammina sp. aff. T. intermedia. The inner−organic layer observed inside this specimen appears to be identical to microforaminiferal linings recovered from the same sample. Palynomorphs found in the studied samples suggest erosion from the underlying Snow Hill Island and the Lopez de Bertodano Formation beds (upper Campanian–upper Maastrichtian). These recovered assemblages indicate either different periods of deposition or reworking from diverse sources during Cenozoic glaciation, originating in James Ross Island and the Antarctic Peninsula with the influence of local sediment sources.
... These episodes are dated at the end of deposition of unit 3 and the onset of deposition of unit 6. They may correlate with the two postulated episodes of short-lasting shallowing of the shelf, based on changes in foraminiferal ecosystems (Birkenmajer & Luczkowska 1987). Most of the deposits in the CMF contain a varying admixture of vocanogenic material, which is consistent with glaciation in a young magmatic arc that had started to separate from Antarctic Peninsula. ...
The Cape Melville Formation (CMF) on King George Island (South Shetland Islands) provides a unique geological record of the earliest Miocene (23-20 Ma) icesheet progradation in West Antarctica (Birkenmajer 2001; Troedson & Riding 2002). Elewhere in the Antarctic Peninula region coeval glacial deposits have not been recognized, which focused scientific effort on this particular formation since its discovery in 1982. New field investigation of the CMF during the 2008/2009 austral summer, followed by the ongoing petrographic and geochemical survey allows to provide detailed lithostratigraphic subdivision of the formation, and attempts to reconstruct its depositional history. The CMF (up to 150 m thick, top erosional) rests transgressively on the latest Oligocene non-glacial, tuffaceous clastic deposits of the Destruction Bay Formation (25-24 Ma). It is here subdivided into eleven units of a member rank that occur in stratigraphic order. They record three major stages of the icesheet progradation and retreat, coupled with sea-level changes in the shelf area: 1) the lower three units (1 to 3) consist of massive to bedded glacigenic diamictite interspaced with sandstone and mudstone, and represent icesheet progradation, with grounded ice resting in part on a shelf bottom; 2) the overlying three units (4 to 6) embrace a sequence of mudstone and sandstone with exotic clasts of various size that records a sea-level rise and ice shelf formation; 3) the upper part of the CMF (units 7 to 11) is the thickest and dominated by (calcareous) mudstone and siltstone with varying content of exotic clasts. This part records a retreat of icesheet and subsequent drowning to deep shelf muddy environment that collected iceberg-rafted material. The provenance of this material has shifted upwards from South Shetland Islands to Antarctic Peninsula and also Ellsworth Mountains. Overlapped on the icesheet history in the CMF were two episodes of tectonic activity that led to deformation of sea bottom by faults and flexures, development of synsedimentary slopes, and gravity mass transport deposits. These episodes are dated at the end of deposition of unit 3 and the onset of deposition of unit 6. They may correlate with the two postulated episodes of short-lasting shallowing of the shelf, based on changes in foraminiferal ecosystems (Birkenmajer & Luczkowska 1987). Most of the deposits in the CMF contain a varying admixture of vocanogenic material, which is consistent with glaciation in a young magmatic arc that had started to separate from Antarctic Peninsula. Ash-full tuff beds are common in the middle part of the sequence, in units 4 to 6 in particular. Increasing upwards content of marine organic matter in the upper part of CMF witnesses to enhanced biological productivity in the shelf area liberated from ice cover. Most of the organic matter is planktonic in origin, though the abundance of benthonic fossils suggests oxygentaed bottom waters. Common authigenic pyritization of organic matter suggests however dominating anoxic sulphidic environment in bottom sediments.
... Foraminiferal studies from pre-Quaternary sediments of West Antarctica are also fragmentary. Oligocene planktonic (Gaździcki 1989) and Miocene benthic foraminiferal assemblages (Birkenmajer & Łuczkowska 1987) were reported from King George Island, South Shetland Islands. Pliocene assemblages were found on Cockburn Island, Antarctic Peninsula (Gaździcki & Webb 1996). ...
Benthic foraminiferal assemblages are described for the first time from the early Eocene of West Antarctica. They come from the lower member (Telm1) of the La Meseta Formation of Isla Marambio (Seymour Island). Two distinctive assemblages, dominated by Nonionellina, Nonionella, Globocassidulina, and Eilohedra, as well as by Globocassidulina, Cribroelphidium, Guttulina, and Lobatula, indicate restricted, shallow marine, nearshore conditions. Their most characteristic species show distinct affinities with Eocene faunas of New Zealand and Patagonia, as well as with stratigraphically younger Antarctic foraminiferal communities.
... A fauna é composta por braquiópodes (Biernat et alii, 1985;Bitner & Crame, 2002), nanoplâncton calcário (Dudziak, 1984), crustáceos (Föster et alii, 1987), foraminíferos (Birkenmajer & Luczkowska, 1987), corais (Roniewicz & Morycowa, 1987) equinoides (Jesioneck-Szymanska, 1987), e moluscos cefalópodes (Birkenmajer et alii, 1987), gastrópodes (Karczewski, 1987) ...
... THE DIVERSE Cenozoic marine biota of the Cape Melville Formation, King George Island, West Antarctica ( Fig. 1) has been subject of numerous papers dealing with the brachiopods (Biernat et al. 1985, Bitner & Crame 2002, calcareous nannoplankton (Dudziak 1984), crustaceans (F6ster etal. 1987, Feldman & Crame 1998, Feldmann & Gazdzicki 1997, foraminifera (Birkenmajer & Luczkowska 1987), echinoids (Jesioneck-Szymanska 1987), cephalopods (Birkenmajer et al. 1987b), gastropods (Karczewski 1987), coral (Roniewicz & Morycowa 1987) and plants (Birkenmajer & Zastawniak 1986). Yroedson & Riding (2002) 0311/5518/2006/0111-22 $3.00 © AAP identified several species of palynomorphs including dinoflagellate cysts and other paleomicroplankton, as well as spores and pollen from both the Cape Melville and the underlying Destruction Bay formations. ...
Seven species of marine bivalves, including six new taxa, are described from the Cape early Miocene Melville Formation which crops out on the Melville Peninsula, King George Island, West Antarctica. The bivalve assemblage includes representatives of the families Nuculidae, Ennucula frigida sp. nov., E. musculosa sp. nov.; Malletidae, Neilo (Neilo) rongelii sp. nov.; Sareptidae, Yoldia peninsularis sp. nov.; Limopsidae, Limopsis psimolis sp. nov.; Hiatellidae, Panopea (Panopea) sp. cf. P. regularis; and Pholadomyoida (Periploma acuta sp. nov.). Species studied come from four sedimentary sections measured in the upper part of the unit. Detailed morphologic features of nucloid and arcoid species are exceptionally well preserved and allow for the first time reconstruction of muscle insertions as well as dentition patterns of Cenozoic taxa. Known geological distribution of the species is in agreement with the early Miocene age assigned to the Cape Melville Formation. The bivalve fauna from Cape Melville Formation is the best known from Antarctic Miocene rocks, a time of complex geologic, paleogeographic and paleoclimatic changes in the continent. The new fauna introduces new taxonomic and palaeogeographic data that bear on the question of opening of sea gateways and distribution of Cenozoic biota around Antarctica.
... Paleogene foraminifera are known only from Seymour Island, where Cretaceous–Paleocene assemblages were reported by Huber (1988), and early Eocene benthic foraminifera by Gaździcki and Majewski (2012). Moreover, Oligocene planktonic (Gaździcki 1989) and Miocene benthic foraminiferal assem− blages (Birkenmajer and Łuczkowska 1987) were described from King George Is− land, South Shetland Islands. Stratigraphically younger, Miocene–Pliocene and Pliocene benthic assemblages were illustrated from James Ross (Jonkers et al. 2002) and Cockburn islands (Gaździcki and Webb 1996) east of the Antarctic Pen− insula. ...
The calcareousmicrofossil assemblage fromMiddleMiocene strata of SHALDRIL
Site NBP0602A−5D consists of benthic foraminifera, ostracods, bivalves, and gastropods, and
is interpreted as shallow−water. It appears to be reworked but its age is probably similar to the
age of the host sediment, which contains only rare, fragmented, agglutinated foraminifera. Most of the calcareous taxa are of uncertain taxonomic affiliation, due to the scarcity of Cenozoic microfossils of this age fromWest Antarctica, and also the very different paleohabitat of this now extinct assemblage.
... The overall nature of the macrobenthic assemblage from Unit D is strongly suggestive of a comparatively deepwater, outer shelf environment (Förster et al. 1987, Feldmann & Crame 1998, and this is supported by both microfaunal and microfloral data (Dudziak 1984, Birkenmajer & ºuczkowska 1987, Troedson & Riding 2002. Further evidence comes from the presence of adeoniform colonies of Aspidostoma, together with the erect, cylindrical-branching form of a vinculariiform bryozoan taxon provisionally assigned to Cellaria (Hara 1994) and another specimen which may belong to the family Calwelliidae MacGillivray, 1887 (Hara 1997(Hara , 1998. ...
Fragments of large, bilamellar aspidostomatid bryozoan colonies occur in Early Miocene glaciomarine sedimentary sequences of the Cape Melville Formation, King George Island, South Shetland Islands, West Antarctica. Investigation of the morphological characters of this aspidostomatid cheilostome shows that it represents a new species, which is described herein as Aspidostoma
melvillensis sp. n. A combination of the colony-growth pattern, inferred co-occurring biota and associated sedimentary structures indicates a comparatively deep-water, outer shelf palaeoenvironmental setting. This Miocene occurrence of Aspidostoma
melvillensis sp.n. emphasizes a biogeographical link with adjacent Southern Hemisphere regions during the early Neogene.
Brittle deformation prevails in the ?Late Mesozoic through Recent volcanic pile of King George Island. Tectonic style depends on the scale of the structure. On meso-scale, extensional joints predominate, while on map scale shear deformation (strike-slip faults) prevails over extensional deformation (dykes). Folding affects some parts of the pile being confined to those portions which contain more clastic intercalations. Structural development of the King George Island volcanic pile since at least 77 Ma ago has been dominated by strike-slip tectonic regime. Three stages of development are expressed by three successive sets of extensional joints and as many sets of dykes parallel to them. The structural development of the Antarctic Peninsula region from Late Triassic through Neogene may be explained in terms of long-lived, steady deformation due to continuous subduction. There seems to be an evidence against interpretation of the Bransfield Strait Graben as a back-arc basin. -from Author
The Tertiary strata of King George Island provide evidence for four cold (glacial) and three warm (interglacial) climatic epochs. (1) The Krakow Glaciation (Early/Middle Eocene, about 50 Ma) is evidenced by fossiliferous shallow-water glacio-marine deposits grading upward into marine basaltic hyaloclastites and lava flows. (2) During the Arctowski Interglacial (Middle Eocene - Early Oligocene, 50-32 Ma), primitive terrestrial environments hosted rich warm and moist climate vegetation, and ice-caps covered tops of higher volcanoes. (3) The Polonez Glaciation (late Early Oligocene, 32-30 Ma) was the largest Cenozoic glaciation in Antarctica. The West Antarctic ice-cap crossed Bransfield Strait and reached King George Island where it deposited lodgement tills followed by submarine diamictites and by shallow-marine, glacially-controlled fossiliferous strata with strong contemporaneous volcanic contribution. (4) The Wesele Interglacial (mid-Oligocene, ca 30 Ma) witnessed retreat of glaciers inland. Bransfield Strait and King George Island were dry land undergoing dissection by a primitive river system. (5) The Legru Glaciation (Late Oligocene, 30-26 Ma) was a local glaciation of King George Island, disconnected from continental ice-sheet. Laharic agglomerates alternating with andesitic/basaltic lavas were followed by valley glacier tills. (6) The Wawel Interglacial (Oligocene/Miocene transition, 26-22 Ma) began with recolonization of ice-free land area by temperate (cool and warm) rain forests, followed by a shallow-marine incursion. (7) During the Melville Glaciation (Early Miocene, 22-20 Ma), glacially-controlled fossiliferous marine deposits, corresponding to outer shelf/upper slope of a marginal sea, were laid down. There is a good correlation between the Eocene (Krakow) and Early Oligocene (Polonez) glaciations and low stands of world ocean level. There is no good correlation between low stands of world ocean level and the Late Oligocene (Legru), and the Early Miocene (Melville), glaciations.
Isotopic and palaeomagnetic studies were carried out in the central part of King George Island. Selected mafic to intermediate igneous rocks were sampled for this purpose. Single-grain U-Pb dating of zircons from basalts to dacites was controlled by a whole rock 40Ar- 39Ar data and the magneto stratigraphy. Five magmatic activity phases were distinguished in the SE coast of King George Island. The oldest, late Cretaceous (Campanian) phase represented by basalts of the Uchatka Point Formation are followed by the early to middle Eocene (~53-43 Ma) phase documented by the lava flows whose ages decrease from SW to NE. Next younger magmatic activity phases were recorded by the lava flows or vertical intrusions emplaced in the late Eocene (~37-35 Ma), late Oligocene (~28-25 Ma) and late Pliocene to Holocene. The early to middle Eocene magmatic activity phase was the most extensive, producing the largest volume of magma in the study area. The new age determinations allow a more precise and credible stratigraphic correlation of the interbeds of sedimentary rocks observed in some places within the magmatic succession. The glacial provenance of the Hervé Cove diamictite is not obvious. It might represent a mountain river environment. Intense volcanic activity could be additional factor modelling the climate conditions of Antarctica in Paleogene.
The algal microfossil Bolboforma reticulata Daniels and Spiegler is recorded from the Oligocene-Miocene glacio-marine sediments of King George Island, South Shetland Islands, Antarctica. The record extends the geographic extent of the species to Antarctica. -Author
A plant fossil assemblage (micro-and macrofl ora) from the northern sector of Nelson Island (Rip Point) is abborded on its composition and age. The macrofl ora shows few ferns and a conifer remain (cf. Papuacedrus) and dominant angiosperm fossil leaves represented by laurophyll (probable Elaeocarpaceae/Anacardiaceae affi nity), acrodromophyll (Melastomaceae?) and protophyll
(Nothofagaceae) morphotypes. The absence of marginal characters in great part of the leaf remains incentivate their treatment by morphological groups, trying to guarantees at least the stablishment of its relation with other extant and fossil assemblages and the reconstructions of the geological process implied in its preservation. The microfl ora shows a distinct composition, with many fern and fungal spores and pollen grains of gymnosperms, with a minor component in angiosperms (Proteacea, Aquifoliacea and
primitive Nothofagus). The presence of Classopollis and “ancestral” forms of Nothofagidites pollen grains indicate a Campanian-
Lower Maastrichtian age to the Rip Point succession, where the occurrence of a probable Papuacedrus and Melastomataceae related
forms have a strong evolutive value and phyllogenetic implications, could being its anciest know record. Leaves of deciduous Nothofagus dominate the macrofl ora and probably include juvenile forms. Fungi spores and foraminifera indicate a near-coast lake environment to the deposit, and the fl oristic composition, the remobilization of the leaf remains from a vegetation growing on the slopes of the proximal volcanoes. Comparable extant analogues grows today in rain forests of southern South America and New Zealand, and allows to infer a wet temperate to subtropical climate to the north of Antarctic Peninsula in the end of Cretaceous.
Ostatnie dekady to okres znaczących zmian zachodzących w ekosystemie Antarktydy. Zjawiska takie jak zmniejszanie się zasięgu lodu oraz jego grubości maja bardzo dynamiczny charakter w rejonie Półwyspu Antarktycznego. Wyniki zachodzących zmian obserwowane są zarówno w parametrach fizycznych, jak i chemicznych wszystkich warstw wód oceanicznych. Zmiany te nie pozostają bez wpływu również dla organizmów żywych, w szczególności tych zamieszkujących ekosystemy przybrzeżne, w tym strefy pływowe.
W celu śledzenia i identyfikacji zmian środowiskowych zachodzących w ekosystemie Antarktydy, w sezonie letnim 2011 został zapoczątkowany projekt, którego priorytetem jest zgromadzenie możliwie najpełniejszej wiedzy o bioróżnorodności i parametrach fizycznych równi pływowej w okolicach polskiej stacji polarnej na wyspie Króla Jerzego. W celu realizacji badań wyznaczono trzy transekty (prostopadłe do linii wody) rozciągające się od niskiego do wysokiego poziomu pływu. Próby zebrano na trzech wysokościach równi pływowej w odniesieniu do wysokości pływu, tj. na poziomie niskiego, średniego i wysokiego poziomu pływu. Próby makrofauny i flory zebrano przy użyciu ramki o wymiarach 50 x 50 cm, natomiast próby meiofauny zebrano rdzeniem o średnicy 4,5 cm. Dodatkowo na każdej z lokalizacji poboru prób zainstalowano czytniki temperatury wody. Czytniki te rejestrowały temperaturę przez okres trzech miesięcy letnich, co 5 minut.
W 27 próbach makrofauny oznaczono osiem grup organizmów: Gastropoda, Bivalvia, Amphipoda, Isopoda, Bryozoa, Nemertini, Polychaeta i Pantopoda. Największym bogactwem gatunkowych charakteryzowały się Amphipoda, natomiast Pantopoda reprezentowane były zaledwie przez jeden gatunek. Pod względem liczebności na wszystkich stacjach dominowały Gastropoda, które charakteryzowały się także znaczną biomasą, Największą zanotowano dla gatunku Nacella concinna. Wśród osobników meiofauny zanotowano łącznie 14 taksonów. Taksonami dominującym były Nematoda, Harpacticoida oraz Turbellaria. Wraz z wysokością względem poziomu pływu zaobserwowano spadek wszystkich parametrów zespołów meio- i makrofauny, tj. ilości gatunków, zagęszczenia oraz biomas. Średnie temperatury na równie pływowej wahały się pomiędzy 1.89 a 3.26° C. Zaznaczyły się wyraźne wahania w amplitudzie temperatur i były one znacznie wyższe na poziomie wyso-kiego pływu. Amplituda pływów podczas okresu badań wynosiła maksymalnie 1.9 m.
Przeprowadzone badania wykazały wysoką bioróżnorodność, liczebność jak i biomasę w ekstremalnie dynamicznym środowisku, jakim jest antarktyczna równia pływowa. Zmienność parametrów biocenozy takich jak bioróżnorodność, liczebność i biomasa była spowodowana wyraźnym gradientem w warunkach fizycznych (pływu i co się z tym wiąże temperatury). Wraz ze zmianą fizycznej dynamiki tego środowiska włączając w to takie parametry jak temperatura wody, intensywność falowania i obecności lodu będę prawdopodobnie zmieniać się również parametry biologiczne. Dlatego systematyczny monitoring podstawowych komponentów biologicznych ekosystemu równi pozwoli na śledzenie zmian zachodzących w szybko zmie-niającym się środowisku polarnym.
Pokrywa lodowa Oceanu Arktycznego kurczy się i przewiduje się, że będzie on wolny od lodu w miesiącach letnich już za 30 lat. Niewątpliwie będzie to mieć ogromny wpływ na biologiczną część ekosystemu morskiego. Nowe gatunki pojawiają się już teraz, podczas gdy prawdziwie arktyczne mogą zniknąć. Jak dotąd ciągle niedostatecznie rozumiemy procesy kontrolujące bioróżnorodność rejonów polarnych, a to one podlegają przecież najgwałtowniejszym zmianom. W niniejszej pracy ukazujemy znaczenie twardego, mobilnego podłoża dla płytkiego litoralu Arktyki. Kraby pustelniki użyte zostały w tym celu jako organizmy modelowe. Istnieją bowiem pewne dowody w literaturze z niższych szerokości geograficznych, że ten rodzaj podłoża ma pozytywny wpływ na lokalną pulę gatunkową. Poprzez zapewnienie dodatkowych niszy może zwiększać lokalną różnorodność gatunkową organizmów poroślowych.
Postawiona hipoteza badawcza zakładała, że obecność krabów pustelników również w Arktyce będzie prowadzić do zwiększenia lokalnego bogactwa gatunkowego. W celu jej realizacji zebrano 50 krabów pustelników z gatunku Pagurus pubescens Krøyer, 1838 i P. bernhardus (Linnaeus 1758), 50 ślimaków należących do 11 gatunków (głównie głównie Buccinum undatum Linnaeus, 1758 i B. glaciale Linnaeus, 1758) i ~ 50 kamieni w każdym z sześciu miejsc (czterech w Isfjordzie na Zachodnim Spitsbergenie oraz dwóch w północnej Norwegii). Muszle krabów pustelników skolonizowane były przez większą liczbę gatunków niż nawet znacznie większe ślimaki i kamienie. Z 99 taksonów znalezionych na wszystkich trzech podłożach aż 26 występowało tylko i wyłącznie na muszlach używanych przez kraby. Przeciętna muszla kraba była siedliskiem dla 4-11 gatunków podczas gdy muszla ślimaka 2-8 gatunków, a kamień zaledwie dla 2-5 gatunków.
Na Zachodnim Spitsbergenie dominującym gatunkiem epibiontów był Semibalanus balanoides (Linnaeus, 1758), podczas gdy w północnej Norwegii dominowały młodociane postacie serpulidów (Serpulidae). W obydwu miejscach kolejnym najliczniejszym gatunkiem był Circeis armoricana Saint-Joseph, 1894. Z wyjątkiem dwóch miejsc muszle krabów pustelników podtrzymywały również większą ilość osobników. Badania dowodzą, że (1) kraby pustelniki mają wyraźnie większe znaczenie dla różnorodności biologicznej, niż by można było sądzić na podstawie ich powierzchni oraz, to że (2) poprzez wykorzystywanie pustych muszli ślimaków wykazują duży potencjał do tworzenia i modyfikowani siedlisk, w których bytują a w związku z tym (3) są dobrymi przykładami tzw. inżynierów środowiska także w stosunkowo ubogiej w gatunki Arktyce.
Celem nowego projektu jest poznanie podstawowych zależności ekologicznych kontrolujących populacje szkarłupni w środowiskach polarnych – w Arktyce i Antarktyce. Takie tło, w powiązaniu z bardziej wyrafinowanymi analizami pozwala zabrać głos w aktualnie najważniejszych debatach naukowych jak obieg i depozycja węgla/węglanów w oceanie czy ‘zakwaszanie oceanów’.
Projekt opiera się na klasycznych metodach jak też na nowatorstwie badania mas szkieletów. Materiał został pozyskany na przełomie 2010 i 2011 roku podczas XXXIV ekspedycji naukowej do stacji im H. Arctowskiego. Opróbkowaniem objęto niemal całą Zatokę Admiralicji. Za pomocą nurkowania swobodnego (scuba-diving) wykonano zdjęcia, obserwacje terenowe oraz zebrano okazy do badań laboratoryjnych. Masy szkieletów odczytano w wyniku ważenia wysuszonych szkieletów (ok. 10 osobników/gatunek) po odsączeniu ich na menzurkach z filtrem (po rozpuszczaniu materii organicznej w podchlorynie sodu). Otrzymane krzywe kalibracyjne użyliśmy do szacowania parametrów ze zdjęć jak też do porównań np. liczebność vs rozmiary vs biomasa vs masa szkieletów. Konieczne do tego było poznanie liczebności, bioróżnorodności, biomasy, rozmiarów oraz wagi szkieletów w skali osobnika, ramki (0,5m x 0,5m), gatunku, gromady i większej.
Stwierdzono 23 gatunki szkarłupni na 90 m2 dna. Przeciętnie na 1 m2 dna notowano 7 osobników należących do dwóch gatunków szkarłupni. Największą biomasę w Zatoce Admiralicji spośród szkarłupni osiągają jeżowce. Najwyższą bioróżno-rodność stanowią rozgwiazdy. Masy szkieletów wskazują na znaczne różnice pomiędzy gatunkami. W przeliczeniu na m2 dna morskiego jeżowce wytwarzają najwięcej węglanów (średnio 13 g Ca, Mg, SrCO3/m2). Analiza zdjęć potwierdza wybitnie nierównomierne rozmieszczenie szkarłupni (patchiness), co tłumaczy znaczące różnice w produkcji węglanów pomiędzy poszczególnymi wycinkami dna morskiego. Porównania z danymi literaturowymi mówią, że produkcja węglanów w Antarktyce jest mała i dostarczają dowodu na hipotezę sugerującą wzrost kalcyfikacji w kierunku środowisk tropikalnych. Analiza zdjęć potwierdza nieregularne rozmieszczenie reprezentantów szkarłupni na dnie morza oraz wyraźnie zazna-czającą się strefowość zgrupowań szkarłupni regulowaną czynnikami oceanograficznymi (topografia/litologia dna, energe-tyczność środowiska, niszczenie przez lód).
Szkarłupnie z Zatoki Admiralicji są przedmiotem wartościowych badań od ponad 20 lat (Presler, Jażdżewski, Siciński, Pabis i inni). Nasze analizy dostarczają nowych wniosków, szczegółowych przeliczników (rozmiar/sucha masa/ mokra masa/masa bezpopiołowa/masa szkieletu), jak też ujawniły obecność nieznanego do tej pory gatunku rozgwiazdy w Zatoce Admiralicji (dr Piotr Presler inf. e-mail).
Zagrożenie antropogenicznymi zmianami oceanów najwcześniej i o największej magnitudzie dotknie środowiska polarne, co wyznacza rangę podejmowanych badań. Wydaje się to prawdziwe biorąc pod uwagę niewielką ilość węglanów produkowanych przez ich mieszkańców. Ich wartość zaś podkreśla wyczerpujący charakter pracy, począwszy od badań terenowych, poprzez prace laboratoryjne i analizy statystyczne aż po kompilację i analizę literatury plasując je ze skali mikro w kontekście globalnym. Nie bez znaczenia jest także wysoka rozdzielczość pozyskanych danych, co czyni je unikatowymi. Naszą aspiracją jest zaproponowanie punktu odniesienia dla wszystkich przyszłych badań szkarłupni i biogenicznych węglanów. Jest to możliwe dzięki obszernej bazie danych i ilustracji, która będzie dostępna publicznie razem z publikacją prezentowanych wyników.
Jesteśmy wdzięczni wszystkim, którzy umożliwili i ułatwili nam prace terenowe podczas pobytu na Stacji Arctowskiego. Dziękujemy też kolegom z Zakładu Ekologii Morza za pomoc, cenne rady, dyskusje i miłą atmosferę podczas prac labora-toryjnych. Dziękujemy dr. Piotrowi Preslerowi oraz prof. Markowi o’Laughlinowi za bezcenne konsultacje taksonomiczne.
The foraminiferal fauna in Pliocene (3.5–2.6 Ma) sediments excavated in a trench 4 m deep, in Heidemann Valley, Vestfold Hills,
East Antarctica is examined and described. Sediments accumulated in shallow, fully marine conditions in a glacial valley during
the last major glacial event in the Vestfold Hills. The section correlates well with the Cockburn Island Formation (Pecten Conglomerate), sediments of Wright Valley, Dry Valleys, and marine event M10 recognized as far south as Amery Oasis, 500
km to the southwest of Heidemann Valley. The foraminiferal fauna generally is dominated by infaunal cassidulinid and elphidiid
species. Assemblages vary dramatically, even between samples collected very close to each other, and no simple relationship
with the position in sections or the valley can be determined. It is a shallow-water, fully marine fauna virtually free of
agglutinated forms and with a low planktonic component Planoglabratella webbi is described as new.
Stratigraphic positions of Late Cretaceous and Tertiary floras have been established on King George Island, West Antarctica, based on K-Ar dating of associated volcanics. The oldest dated floras, of Late Cretaceous and Paleocene ages, provide evidence for a warm climate phase preceding the early Eocene glacial event termed the Kraków Glaciation. Late Eocene through early Oligocene floras indicate another warm period termed the Arctowski Interglacial, which post-dates the Kraków Glaciation. The youngest floras, of Oligocene-Miocene boundary age, indicate a temperate (or cool-temperate) climate, corresponding to the Wawel Interglacial which separated late Oligocene glacial and interglacial epochs (Polonez Glaciation, Wesele Interglacial and Legru Glaciation) from early Miocene glaciation (Melville Glaciation).
Petrological and geochemical data are reported for a series of Late Cretaceous-Middle Miocene volcanic, hypabyssal and intrusive rocks from King George Island (KGI) and from nearby Ridley Island, South Shetland Islands. Major element data indicate a calc-alkaline, basic to intermediate composition for the analysed samples. Although emplaced on a continental margin, the KGI rocks generally display low abundances of incompatible trace elements, close to those typically observed in calc-alkaline suites erupted in intraoceanic island arcs. A few samples have a significant negative Ce anomaly. Many incompatible elements define smooth positive trends on interelemental variation diagrams which suggests that magmas erupted at different times on KGI maintained a rather constant composition in terms of incompatible element ratios. Geochemical modelling, based on Sr isotope ratios and incompatible element ratios, suggests that the primary calc-alkaline magmas of KGI were all generated in an upper mantle modified by addition of small amounts of pelagic sediments dragged down by subduction processes.
Molluscan fossils accompanied by familiar SSF have been recovered from Early Cambrian limestone erratics in the Early Miocene glaciomarine Cape Melville For− mation of King George Island, West Antarctica. The molluscan fauna comprises the hyoliths Conotheca, Microcornus, Parkula, Hyptiotheca ," Hyolithes", the helcionelloids ?Pararacornus, Yochelcionella, Anabarella, the low dextrally coiled Pelagiella and the high helically coiled Beshtashella, as well as the problematic mollusc Cupitheca. Most of described species are recorded here for the first time from Antarctica. The lithological and fossil contents of the erratics are almost the same as from autochthonous successions the Shackleton Limestone in the Argentina Range and Transantarctic Mountains. Early Cam− brian outcrops around the Weddell Sea are a probable source of the erratic boulders. The Antarctic fauna is very similar to that from uppermost Botomian and Toyonian carbonate deposits in the Cambrian Basins of South Australia. These faunal and facies similarities be− tween Antarctica and Australia confirm their neighbouring position and common biotic and basin evolution on the Cambrian Gondwana margin.
Adamussium jonkersi sp. nov. is described from the Late Oligocene Destruction Bay Formation, Wrona Buttress area, King George Island (South Shetlands), West Antarctica. The unit, characterized by volcanic sandstone, is a shallow marine succession deposited in a moderate- to high-energy environment. The thin-shelled pectinids, collected from the lower part of the unit, are preserved mostly as complete valves. Shell thickness, sculpture pattern and umbonal angle suggest a free-living, inactive swimming life habit.
On Hurd Peninsula (Livingston Island) neotectonic features, such as faults, affect the landforms and emerged marine levels. A detailed local study of these features provides information on the recent structural and geomorphological evolution of the area. We suggest that Hurd Peninsula is divided into several tectonic blocks separated by faults. Movement of the faults determines the relative altitude of these blocks and, in consequence, their susceptibility to glacial, periglacial or marine processes. Although some of the tectonic movements reflected in the landforms may have been inherited from former phases of deformation, some of the neotectonic faulting has a maximum lower Miocene age. A new method of correlation of emerged beach levels is suggested and the possibility of analysing the effects of neotectonic deformations from their analysis is discussed. The application of the methods tested here to other areas of the South Shetland archipelago could provide insights into the timing and mechanisms of recent tectonic evolution.
Authigenic pyrite framboids in sedimentary facies of the Mount Wawel Formation (Eocene), King George Island, West Antarctica
Pyrite framboids occur in loose blocks of plant-bearing clastic rocks related to volcano-sedimentary succession of the Mount Wawel Formation (Eocene) in the Dragon and Wanda glaciers area at Admiralty Bay, King George Island, West Antarctica. They were investigated by means of optical and scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and isotopic analysis of pyritic sulphur. The results suggest that the pyrite formed as a result of production of hydrogen sulphide by sulphate reducing bacteria in near surface sedimentary environments. Strongly negative Δ ³⁴ S VCDT values of pyrite (-30 - -25 ‰) support its bacterial origin. Perfect shapes of framboids resulted from their growth in the open pore space of clastic sediments. The abundance of framboids at certain sedimentary levels and the lack or negligible content of euhedral pyrite suggest pulses of high supersaturation with respect to iron monosulphides. The dominance of framboids of small sizes (8-16 μm) and their homogeneous distribution at these levels point to recurrent development of a laterally continuous anoxic sulphidic zone below the sediment surface. Sedimentary environments of the Mount Wawel Formation developed on islands of the young magmatic arc in the northern Antarctic Peninsula region. They embraced stagnant and flowing water masses and swamps located in valleys, depressions, and coastal areas that were covered by dense vegetation. Extensive deposition and diagenesis of plant detritus in these environments promoted anoxic conditions in the sediments, and a supply of marine and/or volcanogenic sulphate enabled its bacterial reduction, precipitation of iron monosulphides, and their transformation to pyrite framboids.
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