8Adequate characterization of depositional architecture is of great importance when 9 studying fluvial outcrops as reservoir analogs. The complex three-dimensional (3D) 10 distribution and lateral/vertical relationships of sandstone bodies require a high degree of 11 stratigraphic control in order to make a proper assessment of the distribution and connectivity 12 of the reservoir facies. This demands the use of reliable correlation datums. Unfortunately, 13 clear marker beds (e.g., ash/coal layers and paleosols) are not always available in fluvial 14 outcrops, and when present they are often covered by vegetation or debris that prevents their 15 tracking over long distances. 16A new method to achieve highly accurate and semiautomatic correlations within 17 fluvial DOMs (Digital Outcrop Model) is presented in response to the need for further 18 correlation procedures, especially in the absence of suitable datums. The method is based on 19 the hypothesis that the average depositional paleosurface of a sedimentary system can be 20represented by a plane at outcrop scale. If this assumption is valid, this plane can be used as a 21Virtual Datum to identify along the DOM the sediments that were deposited simultaneously. 22The method was tested and applied successfully within two kilometer-scale outcrops 23 of the Huesca Fluvial Fan (Early Miocene, N Spain), where the Virtual Datum provided 24 accurate correlations regardless of stratigraphic or topographical complexities. Moreover, the 25 entire sedimentary successions were automatically subdivided into the desired stratigraphic 26 intervals by only moving the Virtual Datum vertically. These intervals can be subsequently 27 isolated to facilitate the detection of subtle variations and trends of their fluvial properties. 28

This paper presents a geological map and cross-section of the Falcón Basin based both on published and unpublished work and on new data collected in the northern and southern basin margins. The geological map covers an area of 4600 km 2 at 1:100,000 scale. The crosssection is oriented NNW-SSE, traversing perpendicular to the main structures. In general, the structure of the study area results from the inversion of a graben (Oligocene-early Miocene back-arc basin), that started in the middle Miocene due to the convergence between the Caribbean and South American plates. The map, the cross-section and the observations made in the field have been used to generate a tectonostratigraphic reconstruction of the Falcón Basin. The Oligocene-early Miocene sedimentary succession mapped and described is relevant to the hydrocarbon exploration in the Caribbean and in the Gulf of Venezuela, where new hydrocarbon resources have recently been discovered (i.e. Perla gas field).

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