Late Eocene microspherule count and foraminifera multispecies oxygen and carbon stable isotope data from DSDP Site 94

Dataset abstract Twenty-six 10 cm³ samples from DSDP (Deep Sea Drilling Project) Site 94, Core 15, sections 3 and 4 were examined at 10 cm-intervals (417.84-415.01 meters below seafloor [mbsf]). The sedimentary material was soaked in distilled water and washed under running water through a 63 µm sieve and oven dried at <40 degrees C. Samples were then re-washed and dried using the same method. Foraminifera are abundant and recystallised. Calcite precipitation is observed on microspherules in some samples.

For each sample, a total of three foraminiferal species that correspond to different ecological habitats were selected for isotope analysis. Specimens of Pseudohastigerina micra and P. naguewichiensis were selected from the 125-250 µm size fraction and Turborotalia cocoaensis, and Cibicidoides eocaenus were selected from the >250 µm size fraction. Specimens that had infilling or showed heavy calcification were avoided. All foraminifera were ultrasonicated for 2 seconds prior to isotopic analyses.

To track the number of impact microspherules across the sampled interval, we performed our own microspherules count from the >125 micron size fraction. Microtektites have not been distinguished from microkrystites in this study and thus all recovered spherules should be considered under the broader category of microspherules (both microtektites and crystalline-bearing microkrystites). We recovered a total of 4999 microspherules from the 26 samples. Microspherules are usually <1 mm in size, and occur primarily spherical, although ellipsoid, teardrop and dumbbell forms and fragments have also been found. In most samples the microspherules count is low <50 microspherules. We found a high abundance (>50 microspherules/10 cm³) between samples 15R/3/135-137 cm and 15R/3/89-91 cm (416.36 to 415.90 mbsf). Our peak concentration of microspherules at 15R/3/109-111 cm (416.10 mbsf), where 3395 microspherules were recovered, coincides with the younger of the two late Eocene impacts i.e., the North America microtektite horizon associated with the Chesapeake Bay impact.