Callovian and the Callovian - Oxfordian transition sedimentary record in NE Iberian Chain: Taphonomic analysis and palaeogeography

Resumen

A comparative study is made on Callovian to middle Oxfordian sequences along the Northeastern Iberian Chain (E. Spain). In the NW areas, from Veruela-Ricla to Tosos (SW-S of Zaragoza), Callovian deposits are represented by expanded carbonate sequences (mudstone and marls with a variable content in clastics) ranging from early Bullatus to Athleta Biozone. Farther East in the near area of Moneva-Ariño (Sierra de Arcos) and in the area of Calanda (SE of Zaragoza), this stratigraphic interval is represented by a strongly condensed, 2-4 m thick, highly incomplete sequence. Bullatus to early Anceps biozones are partly represented under bioclastic or oolitic packstone facies. The Callovian-Oxfordian transition interval deposits are represented by a decimeter-thick ironooid fossiliferous limestone condensed sequence (low values of sedimentation rate) formed by expanded sediments (high values of instant rate of sediment accumulation). Ammonite recorded associations frequently show traces of reelaboration and clear evidence of taphonomic condensation. The palaeogeographic evolution of the platform is reconstructed on the basis of extensive sedimentologic studies and on the analysis of taphonomic gradients shown by ammonite associations. Such taphonomic gradients clearly show a shallowing trend of the platform during the Callovian, which would take place earlier in the SE areas (Sierra de Arcos-Calanda) from Gracilis Biozone onwards, and later, from Coronatum Biozone onwards, in the NW areas (Veruela-Ricla to Tosos), the SE area acting as a shallow to temporarily emerged palaeogeographic threshold. The shallowing process would lead to the widespread emersion of the platform from latest Callovian (Lamberti Biozone) to earliest Oxfordian (Mariae and Cordatum biozone, p.p.)