The flux of extraterrestrial spinels to Earth associated with He-3 anomalies in Cenozoic and Ordovician sediments

Samuele Boschi

Research output: ThesisDoctoral Thesis (compilation)

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The main goal of this thesis is to reconstruct the flux of extraterrestrial matter to Earth in specific time intervals of our past in order to add an astronomical dimension to the understanding of Earth's history. To accomplish this, extraterrestrial chrome-spinel grains have been extracted and analysed. Moreover, analyses of other proxies of extraterrestrial matter e.g. iridium in Cenozoic sediments, have been carried out. Relict spinel grains from extraterrestrial material dispersed in sediments can be used to reconstruct variations in the flux of the different meteorite types to Earth through the ages. Falls of meteorites are rare on Earth’s surface and those that fall decay rapidly due to weathering. However, almost all types of meteorites contain a tiny fraction of spinel minerals that survive weathering and they can be recovered after a laboratory acid-dissolution treatment of large limestone samples. The spinel approach can give detailed information on the types of extraterrestrial matter that fell on Earth at specific times in the geological past. Variations in flux and types of meteorites may reflect breakups in the asteroid belt of the parent bodies for different meteorite types known and not yet known as well as possible large-scale orbital pertubations of planets and other celestial bodies in the solar system. Other goals of this thesis are: (1) describe the Popigai impactoclastic layer in a new Italian section; (2) study the detrital rounded zircon grains from lower Paleocene pelagic limestones of the Bottaccione section in order to constrain the origin of co-occuring terrestrial chrome spinels; (3) resolve whether the mid-Ordovician L-chondritic parent body breakup directly affected Earth's climate and biota. (4) search for extraterrestrial spinels and classify the terrestrial chrome spinels recovered in the late Miocene Monte dei Corvi section. The late Eocene marine sedimentary rocks at Massignano, Italy, were analysed for equilibrated, ordinary chondritic chromite (EC) content, yielding 28 EC grains (>63 μm) in a total of 1168 kg of rock. Most of these EC grains occur in the ∼40 cm interval immediately above the Popigai ejecta layer. Element analyses reveal that grains in the lower half of this interval have an apparent H-chondritic composition, whereas L-chondritic grains dominate in the upper half. We argued that the grains may originate from the regoliths of the Popigai and the Chesapeake Bay impactors, respectively. The Popigai ejecta layer was recovered for the first time in a new Italian location at Monte Vaccaro. Due to the low content of diluting terrestrial chrome spinels in this section, it is ideal to investigate the small size fraction (32-63 μm), and thus resolving the late Eocene event in greater detail. The early Paleocene interval at the Bottaccione section shows a dominance of H-chondritic grains that is possibly is related to na H-chondritic parent body breakup during the late Cretaceous epoch. In the same interval detrital zircons were recovered and U-Pb analyses suggest that the mostly eolian terrigenous material originated from arid regions in northern Africa and southern Europe. In the Monte dei Corvi section (late Miocene), no extraterrestrial grains >63 μm could be recovered from an interval rich in 3He. The L-chondritic parent body breakup (LCPB) occurred in the mid-Ordovician and was probably connected to ice-age conditions at that time. The ice age conditions are indicated by an eustatic sea-level fall related to global cooling triggered by the dust from the LCPB breakup.
Original languageEnglish
  • Schmitz, Birger, Supervisor
  • Terfelt, Fredrik, Assistant supervisor
Award date2019 Dec 13
ISBN (Print)978-91-7895-304-2
ISBN (electronic) 978-91-7895-305-9
Publication statusPublished - 2019 Nov 11

Bibliographical note

Defence details
Date: 2019-12-13
Time: 13:15
Place: Rydberg Lecture Hall, Department of Physics, Sölvegatan 14A, Lund
External reviewer(s)
Name: Folco, Luigi
Title: Professor/Dr.
Affiliation: Pisa University, Pisa, Italy

Subject classification (UKÄ)

  • Astronomy, Astrophysics and Cosmology
  • Geology


  • Chromite
  • He-3 anomaly
  • Cenozoic
  • mid-Ordovician
  • asteroid breakup
  • ordinary chondrites
  • Popigai ejecta
  • iridium anomaly
  • Zircons
  • ice age


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