Environmental changes occurred during the Early Danian at the Rio Grande Rise, South Atlantic Ocean
Introduction
The Paleogene is marked by a series of short-term warming events known as hyperthermals (Cramer et al., 2003; Zachos et al., 2001, Zachos et al., 2004, Zachos et al., 2008). These events were associated with increased mean global temperatures and high atmospheric pCO2, which resulted in pronounced shoaling of the lysocline and the carbonate compensation depth (CCD), and an intensification of the hydrological cycle (Zachos et al., 2001; Nicolo et al., 2007; Foster et al., 2018). The Dan-C2 and Lower C29n events, occurred during the early Danian (e.g., Quillévéré et al., 2008; Coccioni et al., 2010, Coccioni et al., 2012; Leighton et al., 2017), are usually characterized as hyperthemals due to the occurrence of abrupt negative carbon isotope excursions (CIEs) and decreased carbonate content (CaCO3) of deep sea sediments (Coccioni et al., 2010).
Investigation of planktonic foraminifera indicates that there was approximately a 4 °C increase in sea surface temperatures at Blake Nose Plateau, North Atlantic Ocean, during the Dan-C2 event (e.g. Quilléveré et al., 2008), coupled with relatively constant bottom waters temperatures, as suggested by the measurements of benthic δ18O. Similarly, in the South Atlantic Ocean, an increase in the bottom water temperatures was not recorded in the benthic δ18O record during the Dan-C2 (Barnet et al., 2019). Therefore, Barnet et al. (2019) suggest that the Dan-C2 does not represent a typical hyperthermal event, but caused an escalating disruption of the carbon cycle in a regional scale. In addition, the ongoing Decan volcanism may have contributed to high atmospheric pCO2 levels and high temperatures during the beginning of the Danian (Schoene et al., 2015), enhancing the sensitivity of climate and carbon to orbital forcing (Barnet et al., 2019).
Considering these different views on the characteristics of the Dan-C2 and Lower C29n events, it is crucial to increase the number of studies addressing these events in order to better understand their impacts on the ocean-climate system. In this study, different proxies are combined to characterize the environmental conditions at the Rio Grande Rise in the South Atlantic Ocean (DSDP Hole 516F), focusing on the first negative δ13C excursions occurred after the K/Pg boundary (earliest Danian).
Section snippets
Studied site
The Danian section of DSDP Hole 516F (Fig. 1a) was investigated in this study, and is located at a water depth of 1313 m on the Rio Grande Rise (30°16.59′S; 35°17.10′W; Barker, 1983). The paleolatitude of Hole 516F is thought to have been 32°S during the Danian (Zachos and Arthur, 1986), at a lower bathyal (1500–2000 m) paleobathymetry (Barker, 1983). The K/Pg boundary is composed of interbedded reddish limestones and reddish brown marly limestones (Barker, 1983), and is positioned at 963.92
Planktonic foraminiferal biostratigraphy
The biostratigraphy of Hole 516F is based on the zonal scheme proposed by Berggren et al. (1995). The Pα [total range of Parvularugoglobigerina eugubina (Luterbacher and Premoli Silva, 1964); Olsson et al., 1999] is found between 963.85 and 963.70 mbsf (Fig. 1, Fig. 2a-c). The base of Subzone P1a [Parasubbotina pseudobulloides Partial-Range Subzone, Berggren and Pearson, 2005 (renamed from Parvularugoglobigerina eugubina-Subbotina triloculinoides Interval Subzone by Berggren et al., 1995)] is
Recognizing the Dan-C2 event
The Dan-C2 event was recognized at DSDP Hole 516F (Fig. 6), based on negative δ13Cbulk excursions, increases in MS, and drops in the CaCO3 content, as seen at the Contessa Highway section (Coccioni et al., 2010) and at Site 1049 (Quillévéré et al., 2008). At Hole 516F, these events are also characterized by the occurrence of red layers (values of 0.63–0.70 μm) and decreased values of brightness (Fig. 6). The onset of Dan-C2 is placed at the negative δ13Cbulk excursion at 65.82 Ma and its top is
Conclusions
Our multiproxy study of the time interval between 66.05 and 65.58 Ma at DSDP Hole 516F, Rio Grande Rise, points to the occurrence of significant environmental changes that were related to the CIEs at the beginning of the Danian. Our data support the following interpretations:
- i.
After approximately 160 kyr into the Danian, briefly before and during the Dan-C2 CIE, a progressive increase in the dissolution of carbonates and a reduction in deep water oxygenation occurred, leading to the formation of
Acknowledgments
The authors are grateful to the International Ocean Discovery Program (IODP) for providing the studied material; to Capes for providing the post-graduate grant for the GK; to VIZLab and Laserca (Universidade do Vale do Rio dos Sinos) for the spectral reflectance measurements; and to Nils Andersen (Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Kiel) for the stable isotope measurements. Criticism by two reviewrs greatly improved the first version of the manuscript. JFS
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