Outcrop and core integrative ichnofabric analysis of Miocene sediments from Lepe, Huelva (SW Spain): Improving depositional and paleoenvironmental interpretations

Abstract

Ichnofabric analysis was conducted in Miocene sediments from Lepe (Huelva, SW Spain) based on integrative outcrop and core research, to improve interpretations of depositional and paleoenvironmental conditions, with special attention to sequence stratigraphy. Seven intervals were differentiated in outcrops based on stratigraphic and ichnological features, consisting of two ichnofabrics: Ophiomorpha-Thalassinoides-Spongeliomorpha ichnofabric characterizes intervals 1, 2, 6, 7 and 8, while Palaeophycus-Planolites-Phycosiphon ichnofabric characterizes intervals 3, 4 and 5. Fourteen ichnofabrics were differentiated in core, mainly in view of lithological features, including ferruginous material, grain size, mottled background, ichnotaxa, and Bioturbation Index. A comparison between outcrop and core ichnofabrics through the upper 13.5 m, corresponding to the uppermost Tortonian-lowermost Messinian interval, revealed certain similarities as well as some differences. A continuous siliciclastic deposition with punctual variations in the sedimentation rate can be interpreted that, associated with favorable paleoenvironmental parameters such as aerobic conditions and nutrient availability, allow the maintenance of a well-developed and diverse macroinvertebrate trace maker community. Softgrounds are dominant, but punctually loosegrounds and even firmgrounds could develop. The ichnofabric distribution shows long-scale patterns in outcrop and core, and short-scale patterns exclusively in core. Long-scale patterns reflect the last phases of a transgressive system tract, with a “maximum flooding zone” at the end, and then a highstand normal regression. High-frequency, short-scale, repetitive patterns in ichnofabrics from core, mainly between ichnofabrics 6 and 8 (below) and 9 (above), can be linked to “local flooding surfaces”, subdividing the “maximum flooding zone” into parasequences.