Flow characteristics as inferred from core and outcrop data of a turbidite channel-fill: The Solitary Channel (Miocene, Tabernas Basin, SE Spain)

A conventional outcrop description, plus digital outcrop model interpretation, core and the corresponding CT Scan data from two behind-the-outcrop wells, allowed for detailed quantification of sedimentary structures as well... [ view full abstract ]

A conventional outcrop description, plus digital outcrop model interpretation, core and the corresponding CT Scan data from two behind-the-outcrop wells, allowed for detailed quantification of sedimentary structures as well as for a notion of their tree-dimensional arrangements on a bed-by-bed basis.

The Solitary Channel (SC) fill is made up of sandstones (88%) with minor conglomerates (6%) and siltstones (5%). Among the sandstones 93% range between very-fine- to medium-grained. Normal grading is thoroughly observed, and single normal graded units are up to 30 cm thick. Most normal graded beds exhibit distribution grading, either on all of the bed or better developed at its top. Few centimetre thick, inverse graded units exist, mostly at the base of thick normal graded units. With few exceptions, sandstones exhibit some structure. This can be just preferred orientation of nonspherical particles but the most abundant structure is plane-parallel lamination/bedding. In finer grades most of these laminae are thin, evidenced from color changes within centimetric lamina-sets; some are continuous in core, others seem to die out laterally into areas with no distinct structure. In coarser grades the lamination/bedding is apparent to the eye only by subtle grain-size variations. Ripple cross-lamination is rare, it occurs as single-trains, with low and almost linear crests.

Lateral transitions have been observed that can easily be described in terms of Ta and Tb Bouma divisions and can be linked to a specific near-bed sedimentation processes that occur at the base of the turbidity flow. Preferred grain-orientation can be interpreted as a consequence of traction, although the overall structureless context of the matrix indicates high sedimentation rates in channel-axis. A decreasing sediment concentration towards channel margins explains the dominance of parallel lamination, as well an increase in lamina definition. Virtual absence of ripples despite of favourable grain-sizes, can be interpreted as the combined effect of: fast decay of flow velocity, and grain-shape effects on bedload sediment transport.

Ichnological analysis give us an additional insight into channel sub-environments as well as into qualitative sedimentation rates, improving the facies interpretation and their three-dimensional relationships.Three ichnofabrics were identified that exhibit increased inchonodiversity and bioturbation intensity from channel-axis towards margin. A fourth ichnofabric is exclusive of the sandy-mudstones below the SC. Several firmground omission surfaces (Glossifungites ichnofacies) were found in the channel-fill associated to erosive events.

The authors acknowledge financial support to ExxonMobil and project SEROS (CGL2014-55900-P) and CORELAB for CT-Scans (Geology Faculty University of Barcelona).