Trace-element and phosphorus contents in sediment associated with Cretaceous oceanic anoxic events

• Main Author: Westermann, S.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Université de Lausanne, Faculté des géosciences et de l'environnement 2010
• Subjects: oceanic anxoic event (OAE); Valanginian; Aptian; Cenonamian-Turonian; western Tethys paleoceanographic change; redox-sensitive traceelement; phosphorus; 13C; acid extraction methods; événement océanique anoxique; Ualanginien; Aptien; Cenonamien-Turonien; domaine ouest-téfhysien changements paléocéanographiques; redox-sensitive éléments traces reodx-sensibles; phosphore; méthode d'attaque acide; Southern Ocean; Pacific
• Online Access: https://serval.unil.ch/notice/serval:BIB_1C0D04E016ED; https://serval.unil.ch/resource/serval:BIB_1C0D04E016ED.P001/REF.pdf; http://nbn-resolving.org/urn/resolver.pl?urn=urn:nbn:ch:serval-BIB_1C0D04E016ED6

ABSTRACT : During my SNSF-funded Ph.D. thesis project, I studied the evolution of redox conditions and organic-carbon preservation in the western Tethyan realm during three major positive excursions in the Cretaceous δ13C record, corresponding to the Valanginian, Early Aptian and Late Cenomanian. These periods were characterized by important global environmental and climate change, which was associated with perturbations in the carbon cycle. For the period of the Valanginian δ13C excursion, total organic carbon (TOC) contents and the quality of preserved organic matter are typical of oxic pelagic settings in the western Tethys. This is confirmed by the absence of major excursions in the stratigraphic distribution of RSTE during the δ13C shift. Published TOC data from other parts of the Valanginian oceans indicate that dys- to anaerobic zones were restricted to marginal seas within the Atlantic and Southern Ocean, and to the Pacific. Phosphorus (P) and mineralogical contents suggest a stepwise climatic evolution during the Valanginian, with a humid and warm climate prior to the δ13C shift leading to an increase in continental runoff. During the δ13C shift, a decrease in detrital input and P contents suggests a change in the climate towards more and conditions. During the early Aptian oceanic anoxic event (OAE 1a), a general increase followed by a rapid decrease in P contents suggests enhanced nutrient input at the beginning of OAE 1a. The return to lower values during OAE 1 a, associated with an increase in RSTE contents, may have been related to the weakened capacity to retain P in the sedimentary reservoir due to bottom-water oxygen depletion. In basinal settings, the RSTE distribution indicates well-developed anoxic conditions during OAE la, whereas in the shallower-water environments, conditions were oxic to suboxic, rather than anoxic. Furthermore, in the deeper part of the Tethys, two distinct enrichments have been observed, indicating fluctuations in the intensity of water column anoxia during the δ73C ...