Wilson G.S.,University of Otago |
Levy R.H.,Institute of Geological & Nuclear Sciences |
Naish T.R.,Institute of Geological & Nuclear Sciences |
Naish T.R.,Victoria University of Wellington |
And 61 more authors.
Global and Planetary Change | Year: 2012
Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600m and 40Ar/ 39Ar ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with well-dated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of pre-existing strata. The combined age model implies relatively rapid (1m/2-5ky) accumulation of sediment punctuated by hiatuses, which account for approximately 50% of the record. Three of the longer hiatuses coincide with basin-wide seismic reflectors and, along with two thick volcanic intervals, they subdivide the succession into seven chronostratigraphic intervals with characteristic facies:1.The base of the cored succession (1275-1220mbsf) comprises middle Miocene volcaniclastic sandstone dated at approx 13.5Ma by several reworked volcanic clasts;2.A late-Miocene sub-polar orbitally controlled glacial-interglacial succession (1220-760mbsf) bounded by two unconformities correlated with basin-wide reflectors associated with early development of the terror rift;3.A late Miocene volcanigenic succession (760-596mbsf) terminating with a ~1my hiatus at 596.35mbsf which spans the Miocene-Pliocene boundary and is not recognised in regional seismic data;4.An early Pliocene obliquity-controlled alternating diamictite and diatomite glacial-interglacial succession (590-440mbsf), separated from;5.A late Pliocene obliquity-controlled alternating diamictite and diatomite glacial-interglacial succession (440-150mbsf) by a 750ky unconformity interpreted to represent a major sequence boundary at other locations;6.An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150-80mbsf), and;7.A late Pleistocene glacigene succession (80-0mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment. © 2012 Elsevier B.V.
PubMed | University Utrecht, Institute of Geological & Nuclear Sciences, University of Siena, University of Wisconsin - Oshkosh and 14 more.
Type: Journal Article | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2016
Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.
Monien D.,Alfred Wegener Institute for Polar and Marine Research |
Kuhn G.,Alfred Wegener Institute for Polar and Marine Research |
von Eynatten H.,Geoscience Center Gottingen |
Talarico F.M.,University of Siena
Global and Planetary Change | Year: 2012
Bulk chemical fine-grained sediment compositions from southern Victoria Land glacimarine sediments provide significant constraints on the reconstruction of sediment provenance models in the McMurdo Sound during Late Cenozoic time. High-resolution (~. 1. ka) geochemical data were obtained with a non-destructive AVAATECH XRF Core Scanner (XRF-CS) on the 1285. m long ANDRILL McMurdo Ice Shelf Project (MIS) sediment core AND-1B. This data set is complemented by high-precision chemical analyses (XRF and ICP-OES) on discrete samples. Statistical analyses reveal three geochemical facies which are interpreted to represent the following sources for the sediments recovered in the AND-1B core: 1) local McMurdo Volcanic Group (MVG) rocks, 2) Transantarctic Mountain rocks west of Ross Island (W TAM), and 3) Transantarctic Mountain rocks from more southerly areas (S TAM). Data indicate in combination with other sediment facies analyses (McKay et al., 2009) and provenance scenarios (Talarico and Sandroni, 2009) that diamictites at the drill site are largely dominated by local sources (MVG) and are interpreted to indicate cold polar conditions with dry-based ice. MVG is interpreted to indicate cold polar condition with dry-based ice. A mixture of MVG and W TAM is interpreted to represent polar conditions and the S TAM facies is interpreted to represent open-marine conditions. Down-core variations in geochemical facies in the AND-1B core are interpreted to represent five major paleoclimate phases over the past 14. Ma. Cold polar conditions with major MVG influence occur below 1045. mbsf and above 120. mbsf. A section of warmer climate conditions with extensive peaks of S TAM influence characterizes the rest of the core, which is interrupted by a section from 525 to 855. mbsf of alternating influences of MVG and W TAM. © 2010 Elsevier B.V.
Heim C.,Geoscience Center Gottingen |
Lausmaa J.,SP Technical Research Institute of Sweden |
Sjovall P.,SP Technical Research Institute of Sweden |
Toporski J.,WITec GmbH |
And 7 more authors.
Geobiology | Year: 2012
Fracture minerals within the 1.8-Ga-old Äspö Diorite (Sweden) were investigated for fossil traces of subterranean microbial activity. To track the potential organic and inorganic biosignatures, an approach combining complementary analytical techniques of high lateral resolution was applied to drill core material obtained at -450m depth in the Äspö Hard Rock Laboratory. This approach included polarization microscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), confocal Raman microscopy, electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The fracture mineral succession, consisting of fluorite and low-temperature calcite, showed a thin (20-100μm), dark amorphous layer lining the boundary between the two phases. Microscopic investigations of the amorphous layer revealed corrosion marks and, in places, branched tubular structures within the fluorite. Geochemical analysis showed significant accumulations of Si, Al, Mg, Fe and the light rare earth elements (REE) in the amorphous layer. In the same area, ToF-SIMS imaging revealed abundant, partly functionalized organic moieties, for example, C xH y +, C xH yN +, C xH yO +. The presence of such functionalized organic compounds was corroborated by Raman imaging showing bands characteristic of C-C, C-N and C-O bonds. According to its organic nature and the abundance of relatively unstable N- and O- heterocompounds, the organic-rich amorphous layer is interpreted to represent the remains of a microbial biofilm that established much later than the initial cooling of the Precambrian host rock. Indeed, δ 13C, δ 18O and 87Sr/ 86Sr isotope data of the fracture minerals and the host rock point to an association with a fracture reactivation event in the most recent geological past. © 2012 Blackwell Publishing Ltd.
Danisik M.,University of Tübingen |
Danisik M.,Curtin University Australia |
Migon P.,Wrocław University |
Kuhlemann J.,University of Tübingen |
And 4 more authors.
Geomorphology | Year: 2010
A combination of zircon (U-Th)/He (ZHe), apatite fission track (AFT) and apatite (U-Th-[Sm])/He (AHe) thermochronology is used to constrain the long-term exhumation and erosional history of the Karkonosze Mts. in north-eastern Bohemian Massif by analyzing samples from the highly elevated summit planation surface. ZHe ages from the south-eastern part of the planation surface are 285 ± 19, 295 ± 20 and 308 ± 21 Ma, indicating that the area remained at temperatures below ∼ 190 °C since the Permian. In contrast, ZHe ages in the western part of the planation surface are mid-Cretaceous, proving that this part was residing at temperatures above ∼ 190 °C prior to exhumation. The exhumation occurred in the Late Cretaceous, as evidenced by AFT and AHe ages, ranging from 82 ± 5 to 90 ± 8 Ma and from 77 ± 5 to 91 ± 6 Ma, respectively. Modelled cooling trajectories are characterized by a two-stage cooling history: fast cooling through the apatite partial annealing zone and helium partial retention zone to surface conditions between ∼ 90 and ∼ 75 Ma, and slow cooling or even thermal stagnation from ∼ 75 Ma to present. Although our data do not allow us to resolve the age of the planation surface completely, we narrowed down the number of explanatory options and propose two alternative solutions for the formation of the planation surface: (i) the planation surface represents the remnant of a Permian peneplain, which was buried by Mesozoic sediments of the Central European Basin System and was re-exposed in the Late Cretaceous; or, (ii) the planation surface formed after ∼ 75 Ma, after termination of a period of massive erosion documented by thermochronological data and by the sedimentary record in adjacent basins. Cenozoic relief production and uplift of the planation surface, evident from regional landforms and the sedimentary record, is not recorded by thermochronological data. This shows that erosion on the uplifted planation surface since ∼ 75 Ma was less than ∼ 1.2 km. © 2009 Elsevier B.V.
Heron D.P.L.,Royal Holloway, University of London |
Meinhold G.,University of Cambridge |
Meinhold G.,Geoscience Center Gottingen |
Elgadry M.,Libyan Petroleum Institute |
And 2 more authors.
Basin Research | Year: 2015
This paper presents new stratigraphic and sedimentological data of the Ordovician, Silurian, and Mesozoic succession exposed on the western flank of Al Kufrah Basin. Field data (logged sections, photographs, palaeocurrent analyses) are presented from the Jabal Eghei region. This region lies ca. 200 km E of the closest stratigraphic tie point at Mourizidie on the eastern flank of the Murzuq Basin. The succession starts with the Hawaz Formation (Middle Ordovician) comprising >100 m of cross-bedded and bioturbated sandstones that are interpreted as deposits of tidal currents in an open shelf setting. The contact between the Hawaz and Mamuniyat formations is an erosional unconformity, incised during advance of Late Ordovician ice sheets towards the NE. The Mamuniyat Formation comprises >150 m of massive and graded sandstones tentatively assigned to the Hirnantian, and contains an intraformational, soft-sediment striated surface that is interpreted to record re-advance of ice sheets over Jabal Eghei. The outcrop section suggests the sandstone would form an excellent reservoir in the subsurface. The Mamuniyat Formation is overlain by the Tanezzuft Formation (uppermost Ordovician-lowermost Silurian). This includes sandy limestone/calcareous sandstone, a Planolites horizon, and then 50 m of interbedded shale, silt and fine-grained, graded and hummocky cross-stratified sandstone recording deposition from both shallow marine turbidity currents and storm flows. A striated pavement in the lower part of this sequence is overlain by calcareous lonestone-bearing intervals (interpreted as ice-rafted debris). These features testify to late phases of glacial advance probably post-dating the regional Hirnantian glacial maximum. The basal Silurian 'hot shale' facies is not developed in this area, probably because late glacial advance suppressed the preservation of organic matter. The upper part of the Tanezzuft Formation is truncated by an unconformity above which palaeosol-bearing fluvial deposits (undifferentiated Mesozoic) occur. © 2014 The Authors.
Danisik M.,Curtin University Australia |
Danisik M.,University of Waikato |
Kadlec J.,Academy of Sciences of the Czech Republic |
Glotzbach C.,Leibniz University of Hanover |
And 8 more authors.
Swiss Journal of Geosciences | Year: 2011
A combination of four thermochronometers [zircon fission track (ZFT), zircon (U-Th)/He (ZHe), apatite fission track (AFT) and apatite (U-Th-[Sm])/He (AHe) dating methods] applied to a valley to ridge transect is used to resolve the issues of metamorphic, exhumation and topographic evolution of the Nízke Tatry Mts. in the Western Carpathians. The ZFT ages of 132. 1 ± 8.3,155.1 ± 12.9, 146.8 ± 8.6 and 144.9 ± 11.0 Ma show that Variscan crystalline basement of the Nízke Tatry Mts. was heated to temperatures &210°C during the Mesozoic and experienced a low-grade Alpine metamorphic overprint. ZHe and AFT ages, clustering at ~55-40 and ~45-40 Ma, respectively, revealed a rapid Eocene cooling event, documenting erosional and/or tectonic exhumation related to the collapse of the Carpathian orogenic wedge. This is the first evidence that exhumation of crystalline cores in the Western Carpathians took place in the Eocene and not in the Cretaceous as traditionally believed. Bimodal AFT length distributions, Early Miocene AHe ages and thermal modelling results suggest that the samples were heated to temperatures of ~55-90°C during Oligocene-Miocene times. This thermal event may be related either to the Oligocene/Miocene sedimentary burial, or Miocene magmatic activity and increased heat flow. This finding supports the concept of thermal instability of the Carpathian crystalline bodies during the post-Eocene period. © 2011 Swiss Geological Society.
Liebke U.,University of Tübingen |
Antolin B.,University of Tübingen |
Appel E.,University of Tübingen |
Basavaiah N.,Indian Institute of Geomagnetism |
And 4 more authors.
Geological Society Special Publication | Year: 2011
Palaeomagnetic, rock magnetic and geochronological investigations were carried out on the Abor volcanics of Arunachal Pradesh, NE India. A Late Palaeozoic formation age for part of the Abor volcanics cannot be excluded based on K-Ar whole rock dating. Low-temperature thermochronometers - zircon (U-Th)/He and fission track analyses - yield a maximum burial temperature of c. 150-170 ° during Late Miocene. ZFT thermochronology of the Yinkiong and Miri Fms. indicates a post-Paleocene and post-Jurassic deposition age, respectively. This infers that the volcanic rocks intercalating or intruding them are not part of the Late Palaeozoic sequence but represent one or more, latest Cretaceous to Tertiary event(s). Therefore the Abor vol-canics are connected to at least two separate events of volcanism. From palaeomagnetic sites, two characteristic magnetic remanence components were separated: a low-coercivity-component demagnetized below 20 mT and a high-coercivity-component demagnetized between 15 and 100 mT. Fold tests support a secondary origin of both components. Thermochronological and rock magnetic analyses indicate a low-grade overprint event between India-Asia collision and Miocene, which probably represents the time of remanence acquisition. The high-coercivity-component shows a trend of clockwise declinations, which is likely related to vertical-axis rotations of the eastern Himalayas due to eastward extrusion of the Tibetan Plateau. © The Geological Society of London 2011.
Le Heron D.P.,Royal Holloway, University of London |
Meinhold G.,University of Cambridge |
Meinhold G.,Geoscience Center Gottingen |
Bergig K.A.,Libyan Petroleum Institute
Basin Research | Year: 2013
The Murzuq Basin is one of the most petroliferous basins of North Africa. Its remote eastern flank has been largely ignored since early reconnaissance work in the 1950s and 1960s. This article presents new stratigraphic and sedimentological data on the Neoproterozoic through Devonian succession from the Mourizidie and Dor el Gussa regions. The Neoproterozoic to Cambrian Mourizidie and Hasawnah formations in the eastern part of the Mourizidie region dip to the east and north-east, resting directly on late Precambrian metasediments and granitoids. These strata record the initial progradation of sand-dominated braidplain systems upon peneplained Precambrian basement. Rhyolite clasts in the Hasawnah Formation may record tectonically driven uplift and unroofing in the southern Tibesti Massif or tectonomagmatic rejuvenation to the south of this massif. In the western part of the Mourizidie region, Late Ordovician through Silurian strata (Mamuniyat and Tanezzuft-Akakus formations) directly overlie late Precambrian metasediments and granitoids, and dip at a low angle towards the west into the Murzuq Basin. Elsewhere at the eastern Murzuq Basin flank, in Dor el Gussa, Late Ordovician glaciogenic sediments rest with angular unconformity upon shallow marine sandstones of Cambrian-Ordovician age. This angular unconformity may also occur in the Mourizidie region and indicates widespread tectonism, either as a result of a Middle-Late Ordovician orogenic event, far-field tectonism related to the opening of the Rheic Ocean along the northern margin of Gondwana or alternatively crustal depression associated with the growth of Late Ordovician ice sheets. Unconformity development was also probably associated with glacial incision. Following ice sheet retreat, isostatic rebound during deglaciation resulted in uplift of tens to hundreds of metres, locally removing all Cambrian and Ordovician formations. Rising sea levels in the Silurian led to deposition of the Tanezzuft Formation on Precambrian basement in the northwestern Mourizidie region. © 2012 The Authors. Basin Research © 2012 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.