End-Signature of Deep-Marine Basin-Fill, as a Structurally Confined Low-Gradient Clastic Slope: the Middle Eocene Guaso System, South-Central Spanish Pyrenees

Sutcliffe, Clare¹, Kevin Pickering² (1) University College London, London, United Kingdom (2) U.C.L. (University College London), London, United Kingdom

Few studies consider the way in which systems change their architectural style as basins infills through time, despite mounting evidence that small changes to controls can lead to multiple architectural styles of deep-water sandy systems.

We present an example of sheet-like sandbodies with internal complexity (due to the stacking of multiple shallow erosional channels), which represent the final stages of deep-marine basin infill. Mapping of the Guaso system (Eocene deep marine system, south central Pyrenees, Spain), from outcrops, aerial photo interpretation, and logging shows the absence of deep erosional structures, a marked deviation from the older systems (mainly canyon and channel) below.

The first-order control on the basin-scale accommodation space was tectonically-driven phases of subsidence. As there are 20 -25 discrete deep-marine sandbodies within the Ainsa basin, that accumulated over ~ 10 million years, they were most likely controlled by a eustatic driver such as the Milankovitch-type cyclicity at ~ 400 ka. The critical end-signature of deep-marine basinal deposition was that the tectonic driver on subsidence was effectively removed, or at least much reduced. At this stage, the next eustatic sea-level fall was insufficient to cause the cutting of canyons or relatively deeply-incised slope channels, as had been the case with earlier clastic systems. Such clastic slopes, with their characteristic depositional architecture, probably characterize the end-signature for the infill of shallowing-up deep-marine basins where a tectonic driver on subsidence is removed, leaving eustasy as the principal control on sediment flux.