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

<p>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. </p

Table_2_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.XLSX

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Table_1_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.XLSX

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_2_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.JPEG

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_3_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.JPEG

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_1_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.JPEG

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_2_Composition of planktonic foraminifera test-bound organic material and implications for carbon cycle reconstructions.jpeg

IntroductionForaminiferal shells are extensively used to reconstruct the marine environment in the geological past. The foraminifera test-bound organic material (FBOM), sheltered by the test from potential diagenetic alteration and contamination, has great feasibility to improve our understanding of carbon and nitrogen cycling. The FBOM δ13C has been proposed as a proxy for reconstructing past environmental conditions. However, to fully exploit the proxy potential of FBOM, its molecular composition and the influence of the latter on the FBOM δ13C need to be assessed.MethodHere we use a novel combination of gas chromatography-mass spectrometry, flame ionization detection (GC-MS/FID) and liquid chromatography organic carbon and nitrogen detection (LC-OCD/ OND) analyses to study the FBOM chemical composition.ResultsOur results indicate that polysaccharides and proteins dominate FBOM, as proposed by earlier studies, with no evidence of detectable lipids (alkyl lipids, trimethylsilyl ethers of fatty alcohols, trimethylsilyl esters of fatty acids and steranes derivatives were targeted).DiscussionPrevious studies suggested that FBOM δ13C may be used to reconstruct past atmospheric CO2 concentrations. However, our results indicate that the use of FBOM δ13C to reconstruct CO2 carries an approximate uncertainty of ±21 ppm for past atmospheric CO2 abundance. We suggest that FBOM δ13C can be used as a novel proxy to reconstruct particulate organic material (POM) δ13C. This is also supported by the recently confirmed minor fractionation between POM and FBOM δ13C.</p

Table_1_Composition of planktonic foraminifera test-bound organic material and implications for carbon cycle reconstructions.xlsx

IntroductionForaminiferal shells are extensively used to reconstruct the marine environment in the geological past. The foraminifera test-bound organic material (FBOM), sheltered by the test from potential diagenetic alteration and contamination, has great feasibility to improve our understanding of carbon and nitrogen cycling. The FBOM δ13C has been proposed as a proxy for reconstructing past environmental conditions. However, to fully exploit the proxy potential of FBOM, its molecular composition and the influence of the latter on the FBOM δ13C need to be assessed.MethodHere we use a novel combination of gas chromatography-mass spectrometry, flame ionization detection (GC-MS/FID) and liquid chromatography organic carbon and nitrogen detection (LC-OCD/ OND) analyses to study the FBOM chemical composition.ResultsOur results indicate that polysaccharides and proteins dominate FBOM, as proposed by earlier studies, with no evidence of detectable lipids (alkyl lipids, trimethylsilyl ethers of fatty alcohols, trimethylsilyl esters of fatty acids and steranes derivatives were targeted).DiscussionPrevious studies suggested that FBOM δ13C may be used to reconstruct past atmospheric CO2 concentrations. However, our results indicate that the use of FBOM δ13C to reconstruct CO2 carries an approximate uncertainty of ±21 ppm for past atmospheric CO2 abundance. We suggest that FBOM δ13C can be used as a novel proxy to reconstruct particulate organic material (POM) δ13C. This is also supported by the recently confirmed minor fractionation between POM and FBOM δ13C.</p

Image_7_Composition of planktonic foraminifera test-bound organic material and implications for carbon cycle reconstructions.jpeg

IntroductionForaminiferal shells are extensively used to reconstruct the marine environment in the geological past. The foraminifera test-bound organic material (FBOM), sheltered by the test from potential diagenetic alteration and contamination, has great feasibility to improve our understanding of carbon and nitrogen cycling. The FBOM δ13C has been proposed as a proxy for reconstructing past environmental conditions. However, to fully exploit the proxy potential of FBOM, its molecular composition and the influence of the latter on the FBOM δ13C need to be assessed.MethodHere we use a novel combination of gas chromatography-mass spectrometry, flame ionization detection (GC-MS/FID) and liquid chromatography organic carbon and nitrogen detection (LC-OCD/ OND) analyses to study the FBOM chemical composition.ResultsOur results indicate that polysaccharides and proteins dominate FBOM, as proposed by earlier studies, with no evidence of detectable lipids (alkyl lipids, trimethylsilyl ethers of fatty alcohols, trimethylsilyl esters of fatty acids and steranes derivatives were targeted).DiscussionPrevious studies suggested that FBOM δ13C may be used to reconstruct past atmospheric CO2 concentrations. However, our results indicate that the use of FBOM δ13C to reconstruct CO2 carries an approximate uncertainty of ±21 ppm for past atmospheric CO2 abundance. We suggest that FBOM δ13C can be used as a novel proxy to reconstruct particulate organic material (POM) δ13C. This is also supported by the recently confirmed minor fractionation between POM and FBOM δ13C.</p

DataSheet_1_Composition of planktonic foraminifera test-bound organic material and implications for carbon cycle reconstructions.pdf

IntroductionForaminiferal shells are extensively used to reconstruct the marine environment in the geological past. The foraminifera test-bound organic material (FBOM), sheltered by the test from potential diagenetic alteration and contamination, has great feasibility to improve our understanding of carbon and nitrogen cycling. The FBOM δ13C has been proposed as a proxy for reconstructing past environmental conditions. However, to fully exploit the proxy potential of FBOM, its molecular composition and the influence of the latter on the FBOM δ13C need to be assessed.MethodHere we use a novel combination of gas chromatography-mass spectrometry, flame ionization detection (GC-MS/FID) and liquid chromatography organic carbon and nitrogen detection (LC-OCD/ OND) analyses to study the FBOM chemical composition.ResultsOur results indicate that polysaccharides and proteins dominate FBOM, as proposed by earlier studies, with no evidence of detectable lipids (alkyl lipids, trimethylsilyl ethers of fatty alcohols, trimethylsilyl esters of fatty acids and steranes derivatives were targeted).DiscussionPrevious studies suggested that FBOM δ13C may be used to reconstruct past atmospheric CO2 concentrations. However, our results indicate that the use of FBOM δ13C to reconstruct CO2 carries an approximate uncertainty of ±21 ppm for past atmospheric CO2 abundance. We suggest that FBOM δ13C can be used as a novel proxy to reconstruct particulate organic material (POM) δ13C. This is also supported by the recently confirmed minor fractionation between POM and FBOM δ13C.</p