How did the climate fluctuate in Early Jurassic ? Investigations of belemnites from South Germany give the answer

Methods

Summary

The investigated fossils were collected in Southern Germany near Aselfingen. The investigated fossils are belemnite rostra. A belemnite is a squid-like carnivorous animal closely related to the modern cuttlefish. The belemnitida is an Order of Belemnoidea, which is a cohort of the Subclass Coloidea of the Class Cephalopoda. The fossils were sampled by drilling into the rostra, with a handheld drilling machine with a 1.2 mm drill bit. Each drill hole makes a subsample position. The specific belemnite fossils were selected in stratigraphic order. Most of the processed samples originate from the Pliensbachian, representing about 15 meters of the complete succession. First, a small part of the selected position was removed to avoid possible impurities. Aliquots of at least 2 mg calcitic powder were taken. Sampling of rims and apical lines were avoided. If possible the dorsal side was sampled, because the distance between the growth bands are larger in a number of specimen. The drilled powder was collected on pieces of greaseproof paper and subsequently filled into 3.5 ml glass vials.

All 225 subsamples were balanced precisely between 300 μg and 700 μg for ICP and subsequently diluted in 2 % HNO₃ to a Ca concentration of 25 μg/g. Then the samples were measured to match the calibrated solution in a Perkin Elmer Optima 7000 DV ICP-OES in the laboratory at UCPH. The last step of the preparation was for the Isoprime Gas Source Isotope Ratio Mass Spectrometer measurements of oxygen and carbon ratios. The 225 samples were balanced in aliquots of 400 μg to 700 μg into new glass vials after ionizing. The corrected and normalized data were then ready for management and further processing. The corrected data are specified in relation to the PDB standard using the Carrara Marble “LEO” with double

standard deviations for δ¹³C and δ¹⁸O.