Middle Eocene to early Oligocene magnetostratigraphy of ODP Hole 711A (Leg 115), western equatorial Indian Ocean

Abstract

Ocean Drilling Program (ODP) Site 711, located in the western equatorial Indian Ocean near the Seychelles Archipelago on Madingley Rise, is an important site for studying middle Eocene to early Oligocene climatic evolution. This site is ideal for studying the impact of Neo-Tethyan gateway closure on Indian Ocean currents and circulation to further understand global climate changes through the greenhouse to icehouse transition. Middle Eocene-to-lower Oligocene strata recovered within Hole 711A (Cores 711A-14X to 21X) primarily consist of clay-bearing nannofossil oozes/chalks, with layers rich in radiolarians. Here, we report a high-resolution magnetostratigraphic record and a new integrated age model for the middle Eocene-to-lower Oligocene section of Hole 711A. Correlation of the polarity pattern to the geomagnetic polarity timescale provides a record from Chron C19r (middle Eocene) to C12r (early Oligocene). Our results extend the existing polarity record down into the middle Eocene and confirm published results from the lower Oligocene section of the hole. Overall, these new results from Hole 711A have important implications for identifying and dating global climate change events, and for reconstructing calcite compensation depth history at this site.Supplementary material:Magnetostratigraphic data used for construction of age models for Hole 711A included in this study are available at: www.geolsoc.org.uk/SUP18595

Middle Eocene-Lower Oligocene calcareous nannofossil biostratigraphy and paleoceanographic implications from Site 711 (equatorial Indian Ocean)

“…1 -Calcareous nannofossil biohorizons identified in Hole 711A. The age of the bioevents is defined using available magnetostratigraphic records (Savian et al, 2013) by applying a linear interpolation between nearest reversal boundaries.…”

Magnetoestratigrafia aplicada à datação de eventos climáticos durante o Eoceno e Oligoceno

“…Estes eventos concordam com as datações mais precisas obtidas em testemunhos marinhos coletados pela ODP (Coxall et al, 2005;Bohaty et al, 2009). A intensidade da NRM das amostras analisadas do testemunho ODP 711A mostram variações significativas entre 5.23×10 -5 e 1.77×10 -1 A/m com média de 5.27×10 -3 A/m (Savian et al, 2013). O portador magnético das amostras estudas é a magnetita.…”

“…Outro evento importante ocorreu em aproximadamente 40 Ma, denominado por uma "aberração" por Zachos et al (2001) devido ao aumento abrupto de temperatura (4-5 °C) por aproximadamente 500.000 anos (Bohaty et al, 2003). Os carbonatos pelágicos das Formações Scaglia Variegata e Scaglia Cinerea encontrados na seção de Monte Cagnero (Itália) (Figura 1), que representa a margem norte da Neo-Tétis Ocidental, é particularmente marcante pela sua continuidade e preservação e, desta forma, pode ser também considerada como uma seçãotipo a ser utilizada para o estudo deste eventos climáticos e correlações globais (Coccioni et al, 2008 Savian et al, 2013).…”

Magnetic methods and the timing of geological processes

“…We introduce applications that use magnetic direction and geomagnetic polarity reversals to infer geodynamo processes, tectonics, diagenesis and climate change. (Firth et al 2012;Savian et al 2013;Jovane et al 2013), and a composite integrated magnetostratigraphic sequence from Italy is provided for the entire Palaeogene Period (Coccioni et al 2012).…”