@misc{HoehnelTagleHofmannetal.2016,
  author    = {Hoehnel, Desir{\´e}e and Tagle, Roald and Hofmann, Axel and Reimold, W. U. and Mohr-Westheide, Tanja and Fritz, Joerg and Altenberger, Uwe},
  title     = {MICRO-XRF ANALYSIS OF ARCHEAN SPHERULE LAYERS AND HOST ROCKS FROM THE CT3 DRILL CORE, BARBERTON GREENSTONE BELT, SOUTH AFRICA},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {51},
  journal   = {Monthly notices of the Royal Astronomical Society},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1086-9379},
  pages     = {A334 -- A334},
  year      = {2016},
  language  = {en}
}
@article{HoehnelReimoldAltenbergeretal.2018,
  author    = {Hoehnel, Desir{\´e}e and Reimold, Wolf Uwe and Altenberger, Uwe and Hofmann, Axel and Mohr-Westheide, Tanja and Oezdemir, Seda and K{\"o}berl, Christian},
  title     = {Petrographic and Micro-XRF analysis of multiple archean impact-derived spherule layers in drill core CT3 from the northern Barberton Greenstone Belt (South Africa)},
  series = {Journal of African earth sciences / Geological Society of Africa},
  volume    = {138},
  journal   = {Journal of African earth sciences / Geological Society of Africa},
  publisher = {Elsevier Science},
  address   = {Oxford},
  issn      = {1464-343X},
  doi       = {10.1016/j.jafrearsci.2017.11.020},
  pages     = {264 -- 288},
  year      = {2018},
  abstract  = {The Archean spherule layers (SLs) of the Barberton Greenstone Belt (BGB, South Africa) and Pilbara Craton (Australia) are the only known evidence of early, large impact events on Earth. Spherules in these layers have been, alternatively, interpreted as molten impact ejecta, condensation products from an impact vapor cloud, or ejecta from impact craters melted during atmospheric re-entry. Recently, a new exploration drill core (CT3) from the northern BGB revealed 17 SL intersections. Spherules are densely packed, sand-sized, and variably rounded or deformed. The CT3 SLs are intercalated with black and brown shale, and laminated chert. The determination of the original number of impact events that are represented by these multiple SLs is central to the present paper. A comprehensive study of the sedimentary and petrographic characteristics of these SLs involved the determination of the size, shape and types of individual spherules, as well as their mineralogy. CT3 SLs consist of K-feldspar, phyllosilicate, siderite, dolomite, quartz, Ti- and Fe-oxides, as well as apatite. In addition, small amounts of carbonaceous, presumably organic material are observed in several spherules at 145 and 149 m depth. Only Ni-rich Cr-spinel (up to 11 wt\% NiO) crystals, rare zircon grains, and alloys of platinum group elements ± Fe or Ni represent primary phases in these thoroughly altered strata. The 0.3 to 2.6-mm-sized spherules can be classified into four types: 1. Spherules crystallized completely with secondary K-feldspar (subtype 1A) or phyllosilicate (subtype 1B); spherules completely filled with Ti- and Fe-oxides (subtype 1C); spherules containing disordered or radially oriented, fibrous and lath-shaped K-feldspar textures (subtype 1D); or subtype 1B spherules that contain significant Cr-spinel (subtype 1E); 2. zoned compositions with these types 1A and/or 1B minerals (subtype 2A); spherules that contain central or marginal vesicles (subtype 2B); subtype 1B spherules whose rims consist of Ti and Fe-oxides (subtype 2C); 3. deformed spherules (subtype 3A) - of all types; (B) subtype 1B spherules are assimilated into groundmass; (C) open spherules or spherules with collapsed rims; and 4. interconnected spherules of type 1A. A few spherules show botryoidal devitrification textures interpreted to result from rapid cooling/devitrification of former melt droplets. SL 15 at a depth of 145 m is unique in being the only grain-size sorted SL; this bed may have been deposited by fallout through a water column. The SL and their host rocks can be easily distinguished by their significant differences in micro-XRF elemental distribution maps. Depending on which aspects of the SLs are primarily considered (such as similar geochemistry, similar layering, SL occurrences abundant at three different depth intervals), the 17 CT3 SLs can be assigned to three or up to 13 individual impact events. Uncertainty about the actual number of impact events represented remains, however, due to the complex folding deformation observed throughout the drill core.},
  language  = {en}
}
@misc{HoehnelReimoldMohrWestheideetal.2016,
  author    = {Hoehnel, Desiree and Reimold, W. U. and Mohr-Westheide, Tanja and Hofmann, Axel and Altenberger, Uwe},
  title     = {PETROGRAPHY OF ARCHEAN SPHERULE LAYERS FROM THE CT3 DRILL CORE, BARBERTON GREENSTONE BELT, SOUTH AFRICA},
  series = {Scientific reports},
  volume    = {51},
  journal   = {Scientific reports},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1086-9379},
  pages     = {A333 -- A333},
  year      = {2016},
  language  = {en}
}
@article{FritzTagleAshworthetal.2016,
  author    = {Fritz, Joerg and Tagle, Roald and Ashworth, Luisa and Schmitt, Ralf Thomas and Hofmann, Axel and Luais, Beatrice and Harris, Phillip D. and Hoehnel, Desiree and {\"O}zdemir, Seda and Mohr-Westheide, Tanja and Koeberl, Christian},
  title     = {Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land, South Africa},
  series = {Quaestiones geographicae},
  volume    = {51},
  journal   = {Quaestiones geographicae},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1086-9379},
  doi       = {10.1111/maps.12736},
  pages     = {2441 -- 2458},
  year      = {2016},
  abstract  = {A Paleoarchean impact spherule-bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro-X-ray fluorescence (lXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer-scale, assisted in the localization and characterization of eight spherule-bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The lXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni-Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3-rich and can be distinguished from the Al2O3-poor marine sediments by distinct Al-OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al-OH-rich spherule layers in Al2O3-poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism.},
  language  = {en}
}