Distinguishing climatic and tectonic forcing of turbidite sedimentation, and the bearing on turbidite bed scaling: Palaeocene-Eocene of northern Spain

Abstract

Mineral composition and carbon isotope signals of pelagic limestones and hemipelagic marlstones reveal the driving processes of interbedded turbidites. The Palaeocene to lower Eocene lower bathyal Zumaia series in northern Spain between Zumaia and Getaria (W of San Sebastian) offers this opportunity. This deep-marine series records the transition from a carbonate system (Palaeocene) to a siliciclastic system (early Eocene), mainly controlled by the initiation of Pyrenean uplift in the latest Palaeocene. During the tectonically quiet Palaeocene, varying carbonate turbidite deposition was controlled by climate-dependent production of (foramol association) carbonate debris on the carbonate shelves bordering the basin. The late Palaeocene period was characterized by a cycle of increasing and then decreasing turbidite sedimentation. Increased carbonate production was driven by comparably cool/dry climates in the late Palaeocene Atlantic region, and global marked temperature gradients which enhanced wind-driven Ekman-upwelling of nutrients. In contrast, during warm/perennially humid periods (early Palaeocene and the Palaeocene-Eocene transition) the dynamics of the carbonate turbidite deposition was sluggish, due to decreased carbonate production. In the carbonate system, frequency-size statistics of bed thicknesses show that turbidite generation occurred non-scale invariant. From the earliest Eocene, increasing siliciclastic input from the rising and west advancing Pyrenean chain is observed. After a transitional period, the highly dynamic lower Eocene siliciclastic system evolved on a prograding deep-sea fan under a perennially humid and seasonally wet climate. Several periods of increased tectonic activity and sediment input are recognized by clay mineral assemblages in interturbidite beds. Turbidite bed frequency-size statistics show a power-law distribution, implying that during such periods (particularly NP 12), the depositional system temporarily reached a self-organized critical state. The evolution of the system to critical state appears to be mainly driven by siliciclastic sediment input.