Continental-Marine Correlations and Climate Signals in the Palaeogene Foreland of the South Pyrenees, Spain

Abstract

Continental to marine correlations have always been a challenge regarding to sequence stratigraphy. The longstanding debate is about how surfaces and sedimentary packages translate from one environement to another and the various origins that have been put forward to explain them: eustastic sea level changes, sediment supply variations, subsidence pulses or tectonic variations. In the deep water system of the lower-middle Eocene Ainsa basin, in the southern Pyrenees (Spain), as well as in its fluvial counterparts in the Tremp-Graus basin, stratigraphic cyclicity in the form of repetitive packages of sand and shale alternations of intermediate timescales (10^4 to 10^6 years) has long been recognized and has typically been imputed to eustatic changes, with a modulation by active tectonics. Most of the studies have so far focused either on the deep water system or on their fluvial counterparts without a detailed effort at the correlation between both. Our objective is to evaluate the role of eustatic variations, that are well known to have taken place at these periods, in generating or modifying such cyclicities and to understand the link, at high resolution, between the continental and marine deposits. This is particularly important in order to understand how sea-level fluctuations are tided to depositional environments over multi-millennial times-scales and how the deep-sea sedimentary record can be used to reconstruct the Earth's history of surface response to climate change. To address these issues, a mapping and multi-proxy approach was undertaken in the Tremp-Graus and Ainsa basins. We focus on the middle Eocene Castissent formation, a major fluvial excursion and its deep marine time-equivalent; the turbiditie systems of Fosado, Arro and Gerbe. Through a study of carbon and oxygen stable isotopes on the bulk rock and on the organic matter, geochemistry of major and trace elements performed on two sections representing the distal marine and the continental part of the basin, we attempt to trace environmental signals across the whole source-to-sink system. These analyses coupled with thorough physical mapping on the field allow us to discuss hypotheses on the timing of deposition of the different continental sedimentary packages with repect to the marine ones.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016