First find of the Upper Tithonian ammonite genus Blanfordiceras from the Miers Bluff Formation, Livingston Island, South Shetland Islands

Article (PDF Available)inNeues Jahrbuch fur Geologie und Palaontologie Monatshefte · June 2002with 87 Reads
Abstract
The first find of a macrofossil, the age-diagnostic Upper Tithonian ammonite Blanfordiceras sp. (aff. wallichi) is reported from the Miers Bluff Formation (MBF). The presence of this genus is indicative of the Antarctica-specific Blanfordiceras ammonite zone from the middle Upper Tithonian. This zone is an approximate time equivalent of the Mediterranean Paraulacosphinctes transitorius zone. The new Late Tithonian age of the MBF (Hurd Peninsula, Livingston Island) allows to suggest that the MBF is partly synchronous with the Anchorage Formation (Byers Peninsula, Livingston Island), the Nordenskjöld and the Latady Formations (Antarctic Peninsula), and thus plays an important role for the Upper Jurassic to Cretaceous depositional history and structural evolution of the South Shetland Islands and of the Antarctic Peninsula.
  • ... Its base is unexposed and is overlaid by Cretaceous (?) volcanic deposits (Pallàs et al., 1992). The fossil record assigns a Late Jurassic age to the deposit (Pimpirev et al., 2002). Hervé et al. (2006b) reported two U-Pb detrital zircon data, and a crystallization age of an intrusive body, in order to determinate the maximum possible sedimentation age and an upper age limit, respectively. ...
    ... The results for the sedimentary samples were of Middle Jurassic and Middle Triassic, while for the igneous data wasEarly Cretaceous (Valanginian). Although the results are in agreement with the Late Jurassic fossil age indicated by Pimpirev et al. (2002), the Middle Triassic maximum sedimentation age opens the possibility of a wider time interval, suggesting that a progressive migration of the TPG environment from the continental margin might have taken place. ...
  • ... The present study, however, summarizes newly ob- tained macro-and nannofossil data that prove a Tithonian-Maastrichtian age for the MBF ( Pimpirev et al. 2002;Stoykova et al. 2002). ...
    ... aff. wallichi (Gray 1832), that indicates a late Tithonian age for the lowermost, unexposed part of the formation ( Pimpirev et al. 2002). ...
    Conference Paper
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    The age of the sedimentary sequences of Hurd Peninsula (here referred to the Miers Bluff Formation (MBF)), has been considered so far as Triassic, coeval of the Trinity Group. Recently, a Tithonian ammonite species was found in a non-in situ block, coming from the lowermost unexposed part of the Formation. Our micropaleontological study reveals the occurrence of calcareous nannofossils in six sections. The recorded nannofossil association comprises the following species: Micula decussata, Calculites obscurus, Arkhangel-skiella cymbiformis, Prediscosphaera cretacea, Lucianorhabdus coyeuxii, Cyclagelosphaera reinhardtii, Braarudosphaera bigelowii, Ceratolithoides aculeus, Broinsonia cf. parca, Thoracosphaera sp. indet., Nephrolithus sp. indet., Cretorhabdus sp. indet., Watznaueria sp. indet. It determines a Campanian-Maastrichtian age for the middle and upper part of MBF. Two calcareous nanofossil species, Prediscosphaera cretacea and ?Fasciculithus sp. indet., found in the Burdick Peak section suggest a Late Maastrichtian to (?) Paleocene age of the uppermost part of the MBF. The sediments of the MBF are possibly coeval of a part of Marambio Group (James Ross Island and Seymour Island) and Williams Point beds (Livingston Island).
  • ... Terrestrial palynomorphs reported by Xiguang et al. (2002) suggest a Late Triassic (probably Norian–Rhaetian ) age, but these may have been introduced to the sequence by later processes like reworking of older sediments. The debate broadened with the finding of Campanian nannofossils (Pimpirev et al., 2006; Stoykova et al., 2002) and a late Jurassic ammonite (Pimpirev et al., 2002). Absolute age determinations have not yielded reliable ages. ...
    ... Alternatively, the coastal structures (Area II) may be ascribed to a mega-slump that displays a different orientation from the principal stratigraphic unit. The remarkable age difference between the Upper Jurassic Blanfordiceras fossil (Pimpirev et al., 2002 ) discovered on the northwestern side of dike HP-1A and the upper Cretaceous nannofossils found at a distance of a few hundred meters on its southeastern side (Stoykova et al., 2002) cannot be explainedFig. 3 . ...
    Article
    The Antarctic Peninsula has been part of a magmatic arc since at least Jurassic times. The South Shetland Islands archipelago forms part of this arc, but it was separated from the Peninsula following the Pliocene opening of the Bransfield Strait. Dikes are widespread throughout the archipelago and are particularly accessible on the Hurd Peninsula of Livingston Island. The host rocks for the dikes are represented by the Miers Bluff Formation, which forms the overturned limb of a large-scale fold oriented 63/23 NW. The orientation of minor structures indicates a fold axis oriented NNE–SSW (24/0). Structural analysis of the dikes and their host rocks shows that the tectonic regime was similar to other parts of the archipelago and that only minor changes of the stress field occurred during dike emplacement.
  • ... 1). It is a turbiditic deposit originally correlated with the TPG (Trouw et al., 1997), but now considered to be a younger sedimentary succession, on the basis of the occurrence of a Tithonian ammonite (Pimpirev et al., 2002) and the youngest detrital zircon population of ca. 170 Ma (Hervé et al., 2006). ...
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    Metasedimentary rocks in the Antarctic Peninsula and south-western Patagonia record detrital zircon evidence for significant Permian magmatic events along the Palaeo-Pacific margin of south West Gondwana. However, it is unclear where and how this magmatism formed due to the lack of outcropping Permian igneous sources at similar latitudes. Combined U-Pb, O, and Lu-Hf isotope analyses of detrital zircon grains in Permo-Triassic metasedimentary rocks indicate that the Permian magmatism resulted from the interaction of crust- and mantle-derived sources in an active continental margin. Permian detrital zircons from the Trinity Peninsula Group in the Antarctic Peninsula range from crustal signatures in the northern part (δ18O of ~8‰, initial εHf of ~-6) to mantle-like values in the south (δ18O of ~5‰, initial εHf of ~+3). Zircons from the northern domain have isotopic features similar to those from the Patagonian Duque de York Complex. They also share a secondary Ordovician component of ca. 470Ma. The Middle Jurassic Cape Wallace Beds in Low Island record a ca. 250Ma igneous source, with stronger crustal signatures (δ18O and initial εHf values of 7.5 to 10.8‰ and -3.2 to -14.2, respectively). In contrast, zircons from the upper Jurassic Miers Bluff Formation on Livingston Island and Cretaceous sediments on James Ross Island have similar Permian U-Pb ages, O and Hf trends to their Trinity Peninsula Group counterparts, suggesting reworking after the late Jurassic. Our results provide evidence for a Permian subduction-related magmatic arc, partly located in Patagonia and extending to West Antarctica. The southerly decrease in δ18O coupled with increasing initial εHf indicate fewer sedimentary components in the magma source and is consistent with a glaciated cold and dry climate. These conditions are comparable with West Antarctica climate settings, located close to the South Pole during the Carboniferous and Permian.
  • ... The intrusion of the diorite places an upper age limit of 137.7 ± 1.4 Ma, which is Early Cretaceous (Valanginian) for the succession at the sampled area. This interval is in agreement with the Late Jurassic (Tithonian) sedimentation age indicated by the ammonite described by Pimpirev et al. (2002) from rocks in the vicinity. The data obtained from sample VF 15 is not in disagreement with the above established time brackets for deposition of the MBF, but its Middle Triassic maximum sedimentation age opens the possibility that a wider time interval may be represented in the MBF. ...
    Article
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    Detrital zircon populations from two sandstone samples from the lower member (Johnsons Dock Member) of the Miers Bluff Formation at Hurd Peninsula have been dated by the Sensitive High Resolution Ion Microprobe (SHRIMP) U–Pb method. In one of the samples, zircons as young as early Middle Jurassic (Bajocian) age are present. In the second sample, the youngest detrital zircons are Middle Triassic in age. The detrital zircon age spectra indicate that Permian, early Palaeozoic and Meso- to Neoproterozoic zircon bearing rocks were present in the source areas of the Miers Bluff Formation. The sedimentary rocks are intruded by the Hespérides Point Intrusive diorite stock which yielded a U–Pb zircon crystallization age of 137.7 ± 1.4 Ma (Early Cretaceous, Valanginian). These results indicate that sedimentation of the Johnsons Dock Member of the Miers Bluff Formation is bracketed in time between the Bajocian and the Valanginian. The Miers Bluff Formation has been correlated with the Trinity Peninsula Group from the Antarctic Peninsula, based on sedimentological and structural similarity. Since the Trinity Peninsula Group is older than Middle Jurassic a direct chronological correlation is not supported by our new U–Pb zircon data. However, we suggest that the tectonic setting may have migrated in time with deposition of the pre-Middle Jurassic TPG on the peninsula, to Livingston Island where the maximum age for deposition of the MBF is Bajocian (about 170 Ma).
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