Taphonomy and palaeoecology of the Oligocene flora from Cervera (Catalonia, Spain) and their implication in palaeoclimatic reconstruction

Abstract

The Oligocene flora from Cervera (Eastern Ebro Basin, Catalonia) represents one of the most significant Paleogene palaeobotanical records of the Iberian Peninsula. This flora is studied here from the point of view of taphonomy and palaeoecology. Five plant-bearing beds have been found in the lacustrine facies of the Civit Member (Montmaneu Formation) and Talavera Formation. They contain three different taphonomic and palaeoecological assemblages: (1) an assemblage dominated by small leaves of Rhamnus and leaflets of Rhus and Mimosites, interpreted as wind transported, size-biased remains from open xerophytic woodlands located, away from the lake margins; (2) an assemblage composed of well-preserved whole leaves belonging to the Salicaceae, some species of the Myricaceae and helophytic stem portions without evidence of any selection or traction transport. These were probably supplied to the lake directly from the lakeshores by gravitational fall and would represent elements of a riparian forest; and (3) an assemblage formed by a few leaves belonging to the Lauraceae and some species of the Myricaceae that generally show marked tearing along the veins. These remains reached the lake through transport in river inlets and are assigned to a laurel forest possibly growing beyond the riparian community. This lauracean community would have grown in the lowlands of the Ebro foreland basin rather than at some altitude as suggested by previous authors. The ensemble of remains underwent flotation before being sedimented in the anoxic bottom of the lake centre.The taphonomic biases found in the Cervera leaf assemblages should be taken into account in future palaeoclimatic analyses based on leaf morphology. Specifically, the size-bias of leaves in assemblage 1, which is attributed to wind transport, could provide an exaggerated aridity signal if not corrected appropriately. Also the sampling bias of some previous collections from the same localities has resulted in an over-representation of large well-preserved leaves, mainly belonging to Lauraceae species, which lead to an inflated thermal indication if these were taken into account without determining their taphonomic constraints. This study highlights the need to perform taphonomic studies and define the taphofacies represented in a leaf assemblage before undertaking any palaeoclimatic analysis based on leaf physiognomy, such as CLAMP.