Early Cretaceous (Valanginian - Hauterivian) calcareous nannofossils and isotopes of the northern hemisphere: proxies for the understanding of Cretaceous climate
Article first published online: 12 MAR 2007
Volume 39, Issue 2, pages 157–172, June 2006
How to Cite
Kessels, K., Mutterlose, J. and Michalzik, D. (2006), Early Cretaceous (Valanginian - Hauterivian) calcareous nannofossils and isotopes of the northern hemisphere: proxies for the understanding of Cretaceous climate. Lethaia, 39: 157–172. doi: 10.1080/00241160600763925
- Issue published online: 12 MAR 2007
- Article first published online: 12 MAR 2007
- received 22 July 2004, revised 6 April 2006.
- Calcareous nannofossils;
- cooling phase;
- stable isotopes
From three boreholes (DSDP Site 535; ODP Site 638; BGS borehole 81/43) of the Central Atlantic and the North Sea Basin 379 samples of early Cretaceous age (Valanginian-Hauterivian) were examined. The localities cover a S-N transect of approximately 3000 km stretching from 17°N to 40°N palaeolatitude. The distribution of calcareous nannofossils and fluctuations of the stable isotopes (δ13C, δ18O) have been recorded and were compared with results of recent studies. We differentiate between high nutrient indicators and oligotrophic taxa and propose a four step scheme to characterize the trophic level of the surface water. (1) High abundances of the fertility group (Biscutum constans/Zeugrhabdotus spp.) combined with a high dominance of B. constans and low abundances of Watznaueria barnesae/W. fossacincta represent a high nutrient environment (eutrophic setting). (2) High abundances of the fertility group combined with a high dominance of Zeugrhabdotus spp. and low abundances of W. barnesae/W. fossacincta reflect enhanced nutrient contents of the surface water (mesotrophic setting). (3) Enhanced abundances of the fertility group combined with high abundances of W. barnesae/W. fossacincta indicate slightly increased nutrient contents of the surface water (meso- to oligotrophic setting). (4) Low abundances of the fertility group and high abundances of W. barnesae/W. fossacincta are of low nutrient affinities (oligotrophic setting). Our estimations of seawater palaeotemperatures in combination with literature data show a distinctive trend for the Valanginian to Hauterivian interval. A general decrease of water temperature from the Valanginian to the early Hauterivian is obvious. This decrease of temperature coincides with the southward migration of the high latitudinal cold water species Crucibiscutum salebrosum to lower latitudes. Our findings shed new light on the evolution of the earliest Cretaceous climate, which may be characterized as a warm greenhouse world with interludes of short cooling.