Abstracts, 28th IAS Meeting of Sedimentology 2011, Zaragoza, Spain T1a. Ancient and modern lacustrine and palustrine records

What vertebrate fossil assemblages reveal about the palustrine and lacustrine environments of the El Castellar Formation (Lower , Maestrazgo Basin)

J.M. Gasca, J.I. Canudo & M. Moreno-Azanza

Grupo -IUCA (http://www.aragosaurus.com), Paleontología, Facultad de Ciencias, Universidad de Zaragoza, 50009- Zaragoza, Spain ([email protected], [email protected], [email protected])

The El Castellar Formation is an synrift unit within the Wealden facies of the Iberian Peninsula. More than one hundred vertebrate fossil sites are known in this formation. Most of these sites are situated in the Galve sub-basin (Teruel, Spain). This is a small rift basin, which formed part of the larger Cretacic Maestrazgo Basin. It is located in the eastern part of the Iberian Chain (NE Spain). In the Galve sub-basin the sedimentary record of the El Castellar Formation is divided into two stages. The lower El Castellar Formation is an alluvial unit with great lithological heterogeneity, mainly consisting of lutites, sandstones and conglomerates. The upper El Castellar Formation comprises burrowed palustrine-lacustrine limestones and marls typical of a lacustrine system in phases of expansion and retraction. The upper El Castellar Formation is lower in age, as indicated by the presence of the charophyte Atopochara trivolvis triquetra. As a whole, the faunal list of the upper El Castellar Formation is composed of 48 vertebrate taxa including 6 chondrichthyans, 4 osteichthyans, 4 lissamphibians, 2 lacertids, 2 testudines, 4 crocodylomorphs, 1 pterosaur, 19 and 6 . This represents one of the most diverse Mesozoic vertebrate assemblages in Iberia. The taphonomic modes are quite different between the fossil localities of the lower and upper El Castellar Formation. localities with macro-remains of disarticulated skeletons have been found in the lower unit, related to debris-flow hosted bonebeds and avulsion deposits. By contrast, the most common vertebrate localities within the upper unit comprise accumulations of disarticulated micro-remains. These vertebrate microfossil assemblages display taphonomic differences associated with the particular environment. The main variations can be observed in the lithology (marls and limestones), the abundance of vertebrate remains and the relative abundance of the different taxa. On the basis of these features we consider that some localities represent a palustrine fringe with organic debris (grey marls which represent a fossiliferous level with notable lateral continuity), scattered ponds (dark grey marls with limited lateral continuity, and an unusually high concentration of vertebrate and carbonaceous plant remains) or lacustrine deposits (grey limestones with only chondrichthyan and osteichthyan vertebrate assemblages). Moreover, most of the vertebrate localities are located in a similar stratigraphic position, immediately overlying a discontinuous gypsum bearing level identifiable at basin-scale. This short fossiliferous interval within the basal part of the upper El Castellar Formation has previously been interpreted as a low-energy shallow lake. Several subenvironments are thus represented, which are part of a common wetland. This palaeoenvironment might have supported a lentic ecosystem with an extraordinary vertebrate diversity.

Acknowledgements: This paper forms part of the project CGL2007-62469 and CGL2010-16447 and is subsidized by the Spanish Ministry of Science and Innovation, the European Regional Development Fund, and the Government of Aragón (“Grupos Consolidados” and “Dirección General de Patrimonio Cultural”).

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