The Fosado Turbidite Channel Complex (Eocene, South-Central Pyrenees,
Spain)
A. Obradors-Latre1*, E. Remacha2 & M. Poyatos-Moré2,3
1
UCD School of Geological Sciences, University College Dublin.
Departament de Geologia, Universitat Autònoma de Barcelona, 08193-Bellaterra, Spain
3
Stratigraphy Group, School of Earth, Atmospheric and Environmental Sciences, University
of Manchester, UK
2
*corresponding authors:
arnau.obradors-latre@ucdconnect.ie
miquel.poyatos-more@manchester.ac.uk
In the Eocene of the South-Central Pyrenean foreland basin, the lower part of the Castissent
tectono-sedimentary unit (TSU-3) is formed by the Fosado-Torla turbidite system. In this
system, the Fosado Turbidite Channel Complex (FTCC) is a distinctive base-of-slope largescale sandstone-rich body filling the lower part of the Atiart submarine canyon. Excluding a
very general stratigraphic framework, little is known about this channel complex. Therefore,
the aim of this project is to provide a first more detailed study concerning chrono- and
lithostratigraphy, architecture and the main types of facies associations of this multi-storey
channel system.
The Atiart canyon is a large-scale submarine erosional feature formed in middle Ypresian
(Cuisian) times, within the Chron C22r, ca. 50.2 Ma. Its incision and fill was tectonically
controlled by the Foradada fault and by the syn-sedimentary activity of the Atiart thrust.
Later, the onset of Los Molinos thrust and the effects of the Samper out-of-syncline thrust
(located in the hanging wall of the Atiart thrust) controlled the development of the upper
unconformity of the Fosado-Torla system, expressed in the lower Charo canyon. Both the
Atiart and the lower Charo unconformities define a third-order scale depositional sequence
known as Castissent-1 depositional sequence. The FTCC is located in the hanging wall of
Los Molinos thrust, passing transitionally upward into a thick mud-dominated slope
succession.
The Fosado channel-overbank complex is a multi-storey and relatively sand-rich unit,
reaching up to 240 m in thickness, and comprising five unconformity-bounded high-frequency
units. Each unit contains channel sandstone bodies overlying hyperconcentrated-flow
deposits which form the lower part of the high-frequency cycles. Channel bodies commonly
show lateral accretion followed by vertical aggradation, and these may therefore be related to
high-sinuosity channels, laterally associated to thin-bedded overbank deposits. Finally, the
channel bodies are succeeded by thin-bedded drapes which cap the high-frequency units.
Lower sandstones of the higher units show a pronounced aggradational pattern and consist
of depositional channels with well-developed channel margin facies.
Lastly, the mudstone wedge that evolved above the FTCC comprises local minor
hyperpycnal channel-overbank systems which are interpreted as slope deposits and which
pass basinward into thin-bedded lower slope fine-grained lobes.