Large scale facies change in the middle Eocene South-Pyrenean foreland basin: The role of tectonics and prelude to Cenozoic ice-ages

Abstract

The present study reports a sedimentological analysis of the Guara Limestone Formation deposited during the Lutetian in the Sierras Exteriores, in the South-Pyrenean foreland basin. We provide a detailed facies analysis of the carbonates to precise the paleoenvironmental context during their deposition. We show that those limestones are mainly composed of shallow-water foraminifers and were deposited in relative shallow-water environments (b120 m) during the whole Lutetian (SBZ 13 to SBZ 16). The Guara Limestone Formation represents the last occurrence of carbonate platform in the South-Pyrenean foreland basin and disappeared definitely at the Lutetian to Bartonian transition. The demise of carbonate producers at the end of the Lutetian could be related to an increase of continental erosion, due to tectonic and/or climatic forcing. We illustrate that in the Jaca basin, this event correlates with a marked increase in subsidence rate. However, this deformation event is local and the carbonate systems in the Pyrenean foreland resisted to many deformation events during the whole basin history before. Paleobathymetric reconstructions in the Jaca basin, where shallow marine sections outcrop, suggest an increase of the amplitude of high-frequency sea-level cycles. This increase is contemporaneous with several climatic evidences, which suggest the appearance of early ice-sheets near the Lutetian-Bartonian boundary. The demise of carbonate producers seems, therefore, to be the result of a major environmental shift in the basin accompanying increased subsidence rates, switching from low nutrient oligotrophic conditions -favourable for shallow water benthic foraminifers -to eutrophic conditions due to the increase of erosion and terrigenous nutrient input associated with higher-frequency sea-level changes and river destabilization.

The Qs problem: Sediment volumetric balance of proximal foreland basin systems

“…At approximately the same time, the Ebro Basin foredeep became internally drained (Costa et al ., ). Oxygen isotope data from marine molluscs in the Ebro pro‐foreland basin suggest a significant growth of topographic relief (<2 km) between 49 and 41 Ma in the central Pyrenees (Huyghe et al ., ). The present‐day highest peak is at 3404 m, and present‐day rivers drain transversely across the fold–thrust belt to the Ebro River.…”

“…Consequently, the local slope of the river profile becomes a simple function of catchment length with a constant of proportionality equal to the steepness index k s . The value of k s is problematical, and varies with mean uplift rate U (Lague & Davy, ), as expected from the linear relation between topographic relief and uplift rate (Hurtrez et al ., ): where k is an erodibility coefficient (equal to 2·8 × 10 −6 in Huyghe et al ., ), and n is the slope exponent in the stream power law (Howard & Kerby, ; Whipple & Tucker, 1999), taken as ca 1. Assuming that uplift rate is balanced by erosion for the catchment as a whole, the steepness index can be calculated from Eq.…”

Middle Eocene to Late Oligocene Antarctic glaciation/deglaciation and Southern Ocean productivity

“…The approximately coincident δ 18 O shift toward positive values is likely connected to global cooling rather than to ice sheet growth [ Pagani et al ., ; Bohaty et al ., ]. This event (labelled Cooling A by Villa et al ., ) has also been recognized in the Spanish Pyrenees and related to a transition from a carbonate to deltaic sedimentary system [ Huyghe et al ., ], which suggests a possible global‐scale nature for this climatic event.…”

Orbital forcing as principal driver for fine-grained deep-marine siliciclastic sedimentation, Middle-Eocene Ainsa Basin, Spanish Pyrenees

“…In the Tremp Basin, high-frequency climatic changes have been identified within the fluvial and deltaic sediments of the Montañana Group (e.g., Weltje et al, 1996;Nijman, 1998). In the Jaca Basin, Huyghe et al (2012) described cyclic carbonates and explained them as due to high-amplitude, high-frequency (b 100 kyr) glacio-eustatic sea-level changes. Also, Kodama et al (2010) deduced orbitally-induced changes in magnetite content in the Arguis Formation, which they interpreted as caused by periodic variations in precipitation, fluvial discharge and terrigenous supply during the rainy season.…”