Fossil assemblages, lithofacies, taphofacies and interpreting depositional dynamics in the epicontinental Oxfordian of the Prebetic Zone, Betic Cordillera, southern Spain

The study of six sections within the External Prebetic (Pozo Cañada, Fuente Álamo, Chinchilla de Montearagón and Riogazas-Chorro II) and the Internal Prebetic (Navalperal and Rı́o Segura), comprises the first results of a taphonomic study to be incorporated into the ecostratigraphic interpretation of the Oxfordian in the Prebetic Zone, Betic Cordillera, southern Spain. A taphonomic analysis was made of 9350 specimens (including fragments) of macroinvertebrate fossils: ammonoids (64%), benthic organisms (26%), and belemnoids and nautiloids (10%). The taphonomic features analysed were: (a) state of preservation (ratio of moulds with/without shell and type of mould filling); (b) fossil size; (c) position within the bed; (d) corrasion (see [Brett, C.E., Baird, G.C., Palaios 1 (1986) 207–227]; (e) fragmentation; (f) epibionts and encrustment; (g) disarticulation; (h) uncoupling and (i) deformation. Analysis of the relative significance of these features, and their relation to the lithofacies, allows us to characterise and distinguish three major taphofacies: (a) taphofacies I, characterised by the greater average size of the specimens recorded, higher values of corrasion, encrustation and colonisation, and by the fact that a high proportion of the specimens are in a quasi-horizontal position; (b) taphofacies II, characterised by a higher proportion of smaller specimens and a greater variety of azimuthal orientation, although the quasi-horizontal position is always predominant and corrasion values are low; (c) taphofacies III, with predominantly small specimens, the highest proportion of quasi-horizontal orientation and fragmentation, and no evidence of corrasion. The taphofacies are stratigraphically and palaeogeographically distributed. In interpreting the taphofacies, the exposure time of skeletals is an essential parameter, and is related to the controlling effect of the sedimentation rate. This latter depends on factors such as the tectonic–eustatic dynamics, the relative distance from the shore, and the bottom physiography.