RT Journal Article
T1 Fossilization of ammonites and sedimentary events in deep environments of carbonate platform (highest Middle to lowest Upper Oxfordian, Iberian Range, Spain).
A1 Fernández López, Sixto Rafael
A1 Meléndez Hevia, Guillermo
AB In the Ricla area (Zaragoza, Aragonese Branch ofthe Iberian Range), at the top of the Yátova Formation, grey-reddishwackestone limestones grade into yellow-green siliciclastic limestonesof the Aldealpozo Formation. These changes of facies between the twosuccessive formations are associated with syndepositional palaeoreliefsdeveloped during the Late Oxfordian. The uppermost deposits of theYátova Formation represent an Oxfordian condensed section, from theupper Bifurcatus Zone (Middle Oxfordian) and Hypselum Zone (UpperOxfordian). These deposits are interpreted as developed in an openmarine, moderately deep carbonate platform, showing uniform lowenergyconditions with extremely reduced carbonate and terrigenousbackground sedimentation, and very low sedimentation rates. The lowdiversity of the benthic fauna, scarce development of sponge biohermsand ammonite populations inhabiting the platform are palaeobiologicalcriteria which corroborate these palaeoenvironmental conditions.Ammonite assemblages are composed of Sub-Mediterraneantaxa. Over 900 ammonite specimens have been collected from the upperBifurcatus and Hypselum zones. Oppeliidae (45,2%) and Perisphinctidae(37,9 %) are dominant. Aspidoceratidae (14,3%) are common. Haploceratidae(2,2%) are scarce. Two phylloceratids and a lytoceratid havebeen found. Ammonoids are commonly preserved as concretionary calcareousinternal moulds of reelaborated elements. Resedimented shellsare scarce. The degree of packing of ammonite remains and the stratigraphicalpersistence display high values. Taphonomic features indicativeof sedimentary starving in deep carbonate platform environments are: 1)high concentrations of reelaborated ammonites, 2) taphonic populationof type two, 3) phragmocones completely filled with sediment, and 4)homogeneous concretionary internal moulds, bearing no signs of abrasion,bioerosion or dense encrusting by organisms (such as serpulids,bryozoans or oysters). In conclusion, the occurrence of these ammoniteassociations confirms the development of an advanced deepeningphase, within a 3rd order deepening/shallowing cycle, in the Aragoneseplatform, during the late Bifurcatus to Hypselum zones.
PB Università degli studi di Milano. Dipartimento di Scienze della Terra "A. Desio"
SN 0035-6883
YR 2004
FD 2004-03
LK https://hdl.handle.net/20.500.14352/50813
UL https://hdl.handle.net/20.500.14352/50813
LA eng
DS Docta Complutense
RD 4 abr 2025