Ainsa Submarine
Fans, Middle Eocene, South Spanish
Pickering, Kevin Thomas1,
Julian Clark2, Nicole Bayliss3, Jordi
Corregidor4 (1) UCL (University College LOndon),
London, United Kingdom (2) Chevron Energy Technology Company, San Ramon, CA (3)
UCL (University College London, Department of Earth Sciences), London, United
Kingdom (4) ERM (Environmental Resources Management), Barcelona, Spain
We present unprecedented detail of the internal
architecture and facies types that characterise the proximal parts of three laterally
offset-stacked sandy submarine fans in the Middle Eocene Ainsa
basin, Spanish Pyrenees, from an integrated outcrop and subsurface study based
on eight wells drilled through ~220-250 m of section with typical inter-well
spacing of ~400 m (including seismic lines, wireline
logs, essentially continuous coring, sandstone petrography, micropalaeontological
and palynomorph analyses). Mapping of the Ainsa, and other, deep-marine clastic
systems shows the lateral stepwise migration of the fans, as a
foreland-propagating clastic wedge. Each fan contains
channels, typically 5-30 m deep and hundreds of metres
wide (~100-600 m). Each discrete fan and channel is initiate
by the development of a mass transport complex (MTC) or mass transport deposit
(MTD), typically a pebbly mudstone horizon. By combining the outcrop and
subsurface data, it is possible to develop a detailed understanding of the
proximal to distal, and axial to lateral, changes in facies
associations, the lateral continuity of beds in a proximal setting, and the
influence of syn-sedimentary tectonics in controlling
fan development. We discuss the interplay between tectonics, eustacy, and basin topography, in driving these
depositional systems at time scales from 2-3 million years for the "tectono-stratigraphic units", to hundreds of thousands
of years, probably at ~400 ka Milankovitch mode (Ainsa depositional system), with discrete fans, channels
and smaller architectural elements at time intervals ranging from in the order
of a hundred thousand years to tens of thousands of years and less.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California