Arne Deprez

Improving preservation state assessment of carbonate microfossils in paleontological research using label-free stimulated Raman imaging

In micropaleontological and paleoclimatological studies based on microfossil morphology and geochemistry, assessing the preservation state of fossils is of the highest importance, as diagenetic alteration invalidates textural features and compromises the correct interpretation of stable isotope and trace elemental analysis. In this paper, we present a novel non-invasive and label-free tomographic approach to reconstruct the three-dimensional architecture of microfossils with submicron resolution based on stimulated Raman scattering (SRS). Furthermore, this technique allows deciphering the three-dimensional (3D) distribution of the minerals within these fossils in a chemically sensitive manner. Our method, therefore, allows to identify microfossils, to chemically map their internal structure and eventually to determine their preservation state. We demonstrate the effectiveness of this method by analyzing several benthic and planktonic foraminifera, obtaining full 3D distributions of carbonate, iron oxide and porosity for each specimen. Subsequently, the preservation state of each microfossil can be assessed using these 3D compositional maps. The technique is highly sensitive, non-destructive, time-efficient and avoids the need for sample pretreatment. Therefore, its predestined application is the final check of the state of microfossils before applying subsequent geochemical analyses.

Taphonomic impact of ultrasonic treatment on foraminifera from a deep-sea carbonate ooze

The selection and identification of foraminifera in chalky, partially silicified sediments can be problematic, as was experienced with upper Danian (Paleocene) samples from Newfoundland Ridge (IODP Expedition 342 Site 1407). Ultrasound treatment can potentially improve the liberation and identification of foraminifera by removing fine-grained material from the tests, leading to reduced processing time. However, this process is potentially destructive and can alter the composition of foraminiferal assemblages by reducing fragile taxa from the record, similar to the effects of dissolution (Nguyen et al. 2011).

Stable isotope and benthic foraminiferal records of the Latest Danian Event at ODP Site 1262 (Walvis Ridge)

The Latest Danian Event (LDE – aka Top Chron 27n Event) is characterized by a >1h negative benthic foraminiferal CIE in various sections in Egypt, which has been correlated with δ13C shifts of ~0.7h in Zumaia (Spain), Wombat Plateau (ODP 761B, Indian Ocean) and Shatsky Rise (ODP 1209, Pacific Ocean) (Bornemann et al., 2009; Westerhold et al., 2011). A concurrent ~0.5h δ18O excursion suggests a 2◦C bottom water temperature rise during this event at Shatsky Rise, suggesting a hyperthermal nature for this event (Westerhold et al., 2011).