Cretaceous Oceanic Anoxic Event 2 in the Arobes section, northern Spain: nannofossil fluctuations and isotope events

Abstract

The Cenomanian-Turonian boundary interval of the Arobes section, northern Spain, represents the maximum depth of a relatively shallow succession. The investigated section extends within the Rotalipora cushmani and Whiteinella archaeocretacea planktonic foraminiferal zones, and from UC3 up to UC8 nannofloral zones, respectively. The Oceanic Anoxic Event 2 (OAE2) is about 16 m thick and includes a positive d 13 C excursion, from 3 up to 5.5‰. The first peak of d 13 C is situated towards the upper part of the Rotalipora cushmani planktonic foraminiferal zone, while the second peak of d 13 C is situated in the lower part of the Whiteinella archaeocretacea planktonic foraminiferal zone. The plateau, the youngest phase of OAE2, ends slightly above the first occurrence (FO) of the nannofossil Quadrum gartneri. Based on nannofloral fluctuation, an unstable environment is recognized from the last occurrence (LO) of the nannofossil Axopodorhabdus albianus up to the FO of the nannofossil Quadrum gartneri. Mesotrophic, eutrophic and oligotrophic nannofossils have successive peaks throughout the OAE2. In the lower part of OAE2, especially in the trough phase and second build-up, productivity increased. The calcareous dinoflagellate Thoracosphaera spp. peaks up to almost 30% in the lower part of the second build-up phase. The critical nannofloral turnover episode is characterized by impoverished calcareous nannofossil assemblages and temporary disappearances of high-fertility taxa, such as Biscutum constans and Zeugrhabdotus erectus. This shift in nannofloral assemblages starts in the last stages of OAE2; that is, towards the top of the second build-up phase and also covers the main part of the plateau phase of d 13 C.

The Kapanboğazı formation: A key unit for understanding Late Cretaceous evolution of the Pontides, N Turkey

“…4 and 6). Many authors have argued that the Cenomanian-Turonian boundary falls within the UC5c subzone, and hence the first occurrence of the nannofossil Q. intermedium is the youngest Cenomanian nannofloral event (Burnett, 1998;Paul et al, 1999;Hardas and Mutterlose, 2006;Wagreich et al, 2008;Švábenická, 2012;Melinte-Dobrinescu et al, 2013).…”

Isotopic studies in Cretaceous research: an introduction

“…Gaona-Narvaez et al Melinte- Dobrinescu et al (2013) examine the Arobes section, northern Spain, which extends from the Rotalipora cushmani to the Whiteinella archaeocretacea planktonic foraminiferal zones, and from UC3 up to UC8 nannofloral zones, respectively. The data include lithological, and oxygen and carbon stable isotope composition of carbonates.…”