Taphonomic tools to evaluate sedimentation rates and stratigraphic completeness in Rosso Ammonitico facies (epioceanic Tethyan Jurassic)

A combined multidisciplinary approach has been applied to calculate minimum values of the stratigraphic completeness and, secondarily, sedimentation r ates in 9.2 m thick Rosso Ammonitico facies from central Apennines (Italy) and 11 m thick deposits of the same facies in Southern Spain. Middle - Uppe r Toarcian expanded sedimentation in Valdorbia section (Umbria-Marche Apenn ines) and extremely condensed Oxfordian - Tithonian sedimentation at Puerto Escano section (External Subbetic) have been investigated using combined t aphonomic, ichnologic and sedimentologic data and analyses. At Valdorbia, i nfaunal tiering is largely preserved and 27 horizons of infaunal-tiering tr uncation and casting reveal strong erosional activity forced by tempestite/ turbidite events. Therefore, microstratigraphic gaps could be evaluated wit hout biostratigraphic control. In this expanded section, 13 horizons of fir m- and hardgrounds have been recorded showing simple or gradational tiering . Conversely, in the condensed Puerto Escano section, taphonomic analysis r eveals 25 horizons of bioclasts truncation (mainly in ammonites), and 56 ho rizons of firm-hardgrounds intensively bioturbated. In Valdorbia rather tha n in Puerto Escano section, the evaluation of flattening in burrows and sph erical bioclasts reveal a measurable mechanical compaction and dissolution. In addition, Rosso Ammonitico at Valdorbia section favoured the calculatio n of decompaction coefficients (nd) for each lithology easier than in Puert o Escano section. In condensed and essentially hiatal Rosso Ammonitico, mot tled deposits due to intense bioturbation dominate and tiering cannot be re cognizable. This fact is accentuated by usual overprinting of elementary de positional events, which in turn hampered the accurate calculation of missi ng deposits. Therefore, in condensed Rosso Ammonitico the latter was only a vailable in terms of minimal missing-record trough the analysis of truncate d bioclasts.