Establishing a new and detailed mid-Cretaceous palaeoceanographic record for the SE Pacific domain from Peru - Phase 2
Final Report Abstract
The overall goal of this DFG project was to investigate the mid-Cretaceous environmental change from the SE Pacific domain as this region, despite its sheer size, was only poorly investigated so far compared to far better studied Tethyan area. This study has clearly established that the numerous rapid environmental changes observed in the middle Cretaceous of the Tethyan realm are also recorded in the SE Pacific realm, further reinforcing the notion that they are all of global nature, even the “lesser” and less well understood OAE 1c and 1d events. Of major interest here is however, the observation that the paroxysmal event of the Middle Cretaceous, the OAE 2, which occurs at the Cenomanian-Turonian transition, had not impacted the shallow-marine carbonate factory in Peru, contrary to the OAE 1b sub-event Leenhardt, which has triggered a transient carbonate demise in northern Peru. This highlights the importance of local conditions for mediating the response of carbonate factory to global environmental perturbations. Thus, since the Cenomanian in Northern Peru was characterized by an oyster-dominated carbonate factory, adapted to and thriving in nutrientrich water, it did not suffer from the increased nutrient levels induced by the OAE 2 event. The contemporaneous development of Perouvianella peruviana facies in central Peru further exemplifies the role of local factors in mediating global environmental signals. Indeed, the uplift of the Marañon Massif has protected this part of the Peruvian Western Platform from nutrient inputs derived from the Brazilian shield weathering, allowing the development of an oligotrophic environment during OAE 2. Furthermore, a consequence of vigorous neritic carbonate production during the Cenomanian-Turonian transition is the preservation of a thick carbonate sequence (ca. 50m) that has allowed us to obtain very high-resolution C-isotope record for this time interval. This is of notable interest since the OAE 2 is most of the time only recorded in condensed sections throughout the world. We have then been able to confirm that the onset of OAE 2 is characterized by a small negative carbon isotope excursion, similarly to the other anoxic events of the Mesozoic. Finally, thanks to the background work established within the frame of this DFG project, we are now in a position to use the Peruvian samples we have collected for further geochemical analyses. We are thus currently establishing collaboration with the research group of Philip Pogge Von Strandmann (University College London), specialized in Li isotope analyses. We aim here at using the Peruvian carbonate-rich successions for reconstructing the evolution of global continental weathering rates throughout the middle Cretaceous, and therefore better understand the effect of protracted elevated greenhouse gas levels in the atmosphere on the Earth’s exogenic dynamic. We believe the outcome of our work is contributing to our overall knowledge of the SE Pacific Cretaceous palaeoceanography.
Publications
- (2015). Record of Albian to early Cenomanian environmental perturbation in the eastern sub-equatorial Pacific. Paleogeogr. Paleoclimatol. Paleoecol. 423, 122-137
Navarro-Ramirez, J.P., Bodin, S., Heimhofer, U., and Immenhauser, A.
(See online at https://doi.org/10.1016/j.palaeo.2015.01.025) - (2016). Ongoing Cenomanian - Turonian heterozoan carbonate production in the neritic settings of Peru. Sed. Geol. 331, 78-93
Navarro-Ramirez, J.P., Bodin, S., and Immenhauser, A.
(See online at https://doi.org/10.1016/j.sedgeo.2015.10.011) - (2017). Response of western South American epeiric-neritic ecosystem to middle Cretaceous Oceanic Anoxic Events. Cret. Res. 75, 61-80
Navarro-Ramirez, J.P., Bodin, S., Consorti, L., and Immenhauser, A.
(See online at https://doi.org/10.1016/j.cretres.2017.03.009)
