ALBERT

Description: Deep marine successions of early Campanian age from DSDP site 516F drilled at low paleolatitudes in the South Atlantic reveal distinct sub-Milankovitch variability in addition to precession and eccentricity related variations. Elemental abundance ratios point to a similar 5 climatic origin for these variations and exclude a quadripartite structure - as observed in the Mediterranean Neogene - of the precession related cycles as an explanation for the inferred semi-precession cyclicity in MS. However, the semi-precession cycle itself is likely an artifact, reflecting the first harmonic of the precession signal. The sub-Milankovitch variability is best approximated by a ~ 7 kyr cycle as shown by 10 spectral analysis and bandpass filtering. The presence of sub-Milankovitch cycles with a period similar to that of Heinrich events of the last glacial cycle is consistent with linking the latter to low-latitude climate change caused by a non-linear response to precession induced variations in insolation between the tropics.

Description: "In order to assess the potential of the honeycomb oyster Pycnodonte vesicularis for the reconstruction of palaeoseasonality, several specimens recovered from the late Maastrichtian Neuquén Basin (Argentina) were subject to a multi-proxy investigation, involving scanning techniques, trace element and isotopic analysis. Combined CT scanning and light microscopy reveals two major calcite micromorphologies in P. vesicularis shells (vesicular and foliated calcite). Micro-XRF analysis and cathodoluminescence microscopy show that reducing pore fluids were able to migrate through the vesicular portions of the shells (aided by bore holes) and cause recrystallization and precipitation of secondary carbonate in the porous micromorphology, thus rendering the vesicular portions not suitable for palaeoenvironmental reconstruction. In contrast, stable isotope and trace element compositions show that the original chemical composition of the shell is well-preserved in the denser, foliated portions, which can therefore be reliably used for the reconstruction of palaeoenvironmental conditions. Stable oxygen and clumped isotope thermometry on carbonate from the dense hinge region yield sea water temperatures of 11°C, while previous TEX86H palaeothermometry yielded much higher temperatures. The difference is ascribed to seasonal bias in the growth of P. vesicularis, causing warm seasons to be underrepresented from the record, and TEX86H palaeothermometry being potentially biased towards warmer surface water temperatures. Superimposed on this annual mean is a seasonality in d18O of about 1 per mil, which is ascribed to a combination of varying salinity due to fresh water input in the winter and spring season and a moderate temperature seasonality. Attempts to independently verify the seasonality in sea water temperature by Mg/Ca ratios of shell calcite are hampered by significant uncertainty due to the lack of proper transfer functions for pycnodontein oysters. The multi-proxy approach employed here enables us to differentiate between well-preserved and diagenetically altered portions of the shells and provides an improved methodology for reconstructing palaeoenvironmental conditions in deep time. While establishing a chronology for these shells was severely complicated by growth cessations and diagenesis, cyclicity in trace elements and stable isotopes allowed a tentative interpretation of the potential annual seasonal cycle in the late Maastrichtian palaeoenvironment of the Neuquén basin. Future studies of fossil ostreid bivalves should target dense foliated calcite rather than sampling bulk or vesicular calcite. Successful application of clumped isotope thermometry on fossil bivalve calcite in this study indicates that temperature seasonality in fossil ostreid bivalves may be constrained by the sequential analysis of well-preserved foliated calcite samples using this method.

Description: This dataset contains X-ray diffraction data of powder drilled from the shell of A. benedeni benedeni specimen SG-125. This measurement was carried out in order to determine whether the originally aragonitic shell of this specimen contained any calcite of diagenetic origin. The spectrum of this specimen was compared to that of a modern aragonitic shell measured in-house (XRD_Fresh_Aragonite_Cerastoderma_edule.csv), and a calcite mineral from an external database (RRUFF database, ID R040070; Lafuente et al. 2015). The bivalve shells were collected in 2013 from a shell bed at the top of the Oorderen Member of the Lillo Formation of the Pliocene in Belgium. The collection site was a construction-related temporary outcrop at the Deurganck Dock Lock (now Kieldrecht Lock) in the city of Antwerp, located at 51°16′44″N 4°14′52″E. X-ray diffraction analysis was carried out in spring 2021 at the department of Earth Sciences at Utrecht University, the Netherlands, on a Bruker D8 diffractometer that was calibrated with a corundum crystal. Measurement conditions were as follows: 40 kV voltage, 40 mA current, 1.5418 Å (CuKα) radiation, 0.165 mm divergence slit, 2.5° primary soller slit, no secondary soller slit, 15-70° 2theta measuring range, 0.02° 2theta step-size, 0.85 s counting time, 15 rpm sample rotation. Reported are the angle (in degrees 2theta) and the corresponding intensity (in counts per second).

Description: This dataset (XRF_Benedeni_benedeni_SG-125_126_127_crosslines_cal.csv) contains micro-X-ray fluorescence elemental data of the shell of A. benedeni benedeni specimens SG-125, SG-126, and SG-127. The bivalve shells were collected in 2013 from a shell bed at the top of the Oorderen Member of the Lillo Formation of the Pliocene in Belgium. The collection site was a construction-related temporary outcrop at the Deurganck Dock Lock (now Kieldrecht Lock) in the city of Antwerp, located at 51°16′44″N 4°14′52″E. These measurements were carried out in order to screen for diagenetic alteration, which results in enrichment of certain elements (e.g., Fe and Mn). The specimens were measured in spring 2021 at the Analytical, Environmental, and Geochemistry Research Group (AMGC) of the Vrije Universiteit Brussel, Belgium), on a Bruker M4 Tornado µXRF scanner. This instrument is equipped with a 30 W Rh anode metal-ceramic X-ray tube operated at 50 kV and 600 µA, and polycapillary lens focussing. The measurement was carried out following the methods described in de Winter and Claeys (2017) and Kaskes et al (2021), and consisted of multiple line scans oriented perpendicular to the growth direction. Also provided is an image file (XRF_Benedeni_benedeni_crosslines_locations.png) which shows the location of these line scans on the shell cross sections.

Description: This dataset (.crc and .cpr files) contain electron backscatter diffraction maps of thin sections of A. benedeni benedeni specimens SG-125, SG-126, and SG-127. Also included are .BMP files for each map. The bivalve shells were collected in 2013 from a shell bed at the top of the Oorderen Member of the Lillo Formation of the Pliocene in Belgium. The collection site was a construction-related temporary outcrop at the Deurganck Dock Lock (now Kieldrecht Lock) in the city of Antwerp, located at 51°16′44″N 4°14′52″E. These measurements were carried out in order to determine the microstructures of the shells of A. benedeni benedeni, as well as to screen for minor diagenetic alterations. The specimens were measured in spring 2021 at Department of Earth Sciences of Utrecht University, the Netherlands, on an Oxford Instruments Symmetry EBSD detector attached to a Zeiss Gemini 450 SEM. Thin sections of the samples were mechanically polished with 0.3 µm aluminium oxide suspension and finished with chemical Syton® polish. The thin sections were covered with a thin (several nm) carbon coating to keep charge build-up during the measurements at a minimum.