High-resolution biometry and morphometric characterization of calcareous nannofossils during the Oceanic Anoxic Events 1a and 1d in a global context
Oceanography
Final Report Abstract
Coccolith size data of three species (B. constans, Z. erectus, W. barnesiae) from four different localities of the OAE 1a have been compared. Two sections from the Boreal Realm represent hemi-pelagic and coastal, near shore settings. The western Tethys and the Mid- Pacific localities reflect both open oceanic, pelagic low latitude sites. The different size patterns documented for the Boreal Realm and low latitude sites, suggest the presence of various cryptic species. These explain differences in morphology, that have previously been interpreted as phenotypic variation. Our study shows that at least two cryptic species of B. constans were present in the early Aptian ocean, one producing small coccoliths and the other one producing larger ones. In the pelagic sections (Tethys and Mid-Pacific), both small and large cryptic species are present. In the more proximal North Sea and Lower Saxony Basin (northwest Germany), only the small form occurs. The fundamental difference between the two settings (pelagic vs. proximal/coastal) is the turbidity of the surface waters. This caused us to introduce the „light-attenuation theory“. The high turbidity of the surface waters in the proximal settings was unfavourable for the large-coccolith producing cryptic species, which are not present in the sediment. For the uppermost Aptian OAE 1d the calcareous nannofossils do not show substantial changes with respect to diversity and size. The results for OAE 1d are thus in contrast to those of the OAE 1a, indicating, that both OAEs did not have the same impact on primary producers. This corresponds with different driving mechanisms behind both events, excess atmospheric CO2 in the case of OAE 1a and an orbitally-driven water column stratification collapse for OAE 1d. A single-species study of P. columnata revealed, that this species consists of two morphogroups. Biometric studies allow in this case to quantify the early evolutionary lineage of P. columnata. Absolute ages made it possible to estimate the duration of species formation processes for Prediscosphaera. A small and subcircular morphotyp appears first in the record (116.3 Ma), while the larger and truly circular morphogroup appears at 111.6 Ma. This larger form becomes a permanent component of the assemblage (100.6 Ma), then dominates over the small (from 96.5 Ma onwards) and eventually replaces the small variety completely.
Publications
- (2015). Size variations of coccoliths in Cretaceous oceans - A result of preservation, genetics and ecology? Marine Micropaleontology, 117, 25-39
Lübke, N., Mutterlose, J., Bottini, C.
(See online at https://doi.org/10.1016/j.marmicro.2015.03.002) - (2016). The impact of OAE 1a on marine biota deciphered by size variations of coccoliths. Cretaceous Research, 61, 169-179
Lübke, N., Mutterlose, J.
(See online at https://doi.org/10.1016/j.cretres.2016.01.006) - (2018). A micropalaeontological provenance analysis of masonry and floor tiles from the medieval cathedral of Paderborn (northern Germany). Archaeometry
Lübke, N., Mutterlose, J., Börste, N., Kaplan, U.
(See online at https://doi.org/10.1111/arcm.12394)
