Miguel López-Blanco

Sedimentary response to thrusting and fold growing on the SE margin of the Ebro basin (Paleogene, NE Spain)

Abstract The Catalan Coastal ranges are the alpine structural unit parallel to the Mediterranean coast in the NE of the Iberian Peninsula. They shape the southeastern margin of the Ebro Foreland basin (the latest stage of the South Pyrenean Foreland trough). The Paleogene sedimentary evolution of this basin margin is closely related to the tectonic evolution of the adjoining Catalan Coastal ranges, a transpressive chain characterized mainly by contractional structures (NNW-verging folds and thrusts). The syntectonic condition of the Paleogene deposits of the Ebro basin is evidenced by facies directly related to the growth of specific structures, thinning, fanning and truncation of the sedimentary units towards the growing structures, as well as to abrupt changes in the composition of the coarse-grained sediments caused by tectonic activity or landslides in the catchment area. A tectonosedimentary evolution of approximately 17 Ma has been deduced: (a) folds and thrusts involving Mesozoic rocks were developed during Ypresian (resulting in the deposition of Mesozoic cover derived breccias); (b) large-scale fold growth mostly from Lutetian to early Bartonian (leading to progressive unconformities, fanning and growth strata); and (c) out-of-sequence basement-involving thrusting during Lutetian and Bartonian (development of large alluvial fans). These events did not take place simultaneously along the 30-km long basin margin studied. There is a clear NE to SW migration of the deformation, as observed along the whole Catalan Coastal ranges and the South Pyrenean Foreland basin.

The Bartonian-Priabonian marine record of the eastern South Pyrenean Foreland Basin (NE Spain) : a new calibration of the larger foraminifers and calcareous nannofossil biozonation

This study presents a combined biostratigraphic (calcareous nannofossils, larger foraminifers) and magnetostratigraphic study of the Middle and Late Eocene marine units of the Igualada area, eastern Ebro Basin. The studied sections of Santa Maria de Miralles and La Tossa encompass the complete marine succession of the Santa Maria Group, where assemblages rich in larger foraminifers have been studied since the early 1950s. A total of 224 paleomagnetic sites and 62 biostratigraphic samples were collected along a 1350m-thick section that ranges from chron C20n to chron C16n (~43Ma to ~36Ma). The resulting magnetostratigraphy-based chronology challenges existing chronostratigraphic interpretations of these units and results in a new calibration of the biostratigraphic zonations. The base of calcareous nannofossil Zone NP19-20 is pinned down to an older age than its presently accepted attribution, whereas the time span assigned to Zone NP18 is significantly reduced. A revised calibration of larger foraminifers indicates that Zone SBZ18, formerly assigned exclusively to the late Bartonian, extends its range to the earlymost Priabonian, the Bartonian stage being almost entirely represented by Zone SBZ17. A division of Zone SBZ18 into two subzones is proposed.

An outcrop-based comparison of facies modelling strategies in fan-delta reservoir analogues from the Eocene Sant Llorenç del Munt fan-delta (NE Spain)

ABSTRACT Sedimentary facies is a key control on petrophysical properties within subsurface reservoirs and facies modelling is a critical aspect of reservoir modelling. Several modelling methods exist and selecting the best approach for a specific case is challenging and time-consuming. Outcrop analogues provide detailed information on architecture, geometry and facies connectivity that is not directly available in the subsurface. By modelling outcrop data it is possible to test and compare different modelling strategies systematically in a case where the geology is well constrained. The Eocene aged, Sant Llorenç del Munt fan-delta complex (NE Spain) is a well exposed, transgressive–regressive fan-delta. Outcrop data were used to test a variety of modelling strategies in which the density of conditioning wells, stratigraphic subdivision, modelling algorithm and trends were all varied. The results of these modelling exercises were compared against themselves and against a close-to-deterministically built Base Case reconstruction using a series of static measures including the distribution of fan-delta front reservoir facies, directional connectivity and reservoir-to-well connectivity. The results highlight the following: (a) the impact of the conditioning well density on improving the stratigraphic architecture reproduction in the different modelling approaches; (b) that surface-based modelling subdivisions including the maximum flooding surface to separate independent grids for modelling the transgressive and regressive sequence sets can be detrimental when compared to using only the top and base of the composite sequence unless additional constraints are included; (c) that an algorithm combining a linear trend and a Gaussian field is the most suitable algorithm for reproducing this type of architecture, but requires defining a 3D trend; and (d) the need for using trends to reproduce the architecture when well data are sparse. These results provide guidelines for modelling analogue fan-delta reservoirs in the subsurface.