Portail de Conférences / Conference Portal, STRATI2010 - 4th "French" Congress on Stratigraphy

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POSTER: Depositional environments in the "Lo Hueco" palaeontological site (Upper Cretaceous, Cuenca, Spain)

Manuel Segura, Fernando Barroso-Barcenilla, Oscar Cambra-Moo, Beatriz Carenas, José Francisco García-Hidalgo

Building: Bâtiment Esclangon
Room: Main Hall / Hall principal
Last modified: 2010-07-01

Abstract


The exceptional fossil site of "Lo Hueco" is close to the village of Fuentes, in the centre of the province of Cuenca, in the middle east of Spain. It was discovered in 2007, during the trench works of the Madrid-Levante highspeed railway, in Upper Cretaceous marly mudstones lying below Cenozoic conglomerates. This site comprises a stratigraphic interval in "Garumnian" facies (an informal term for marls, clays and gypsums, mainly of reddish coloration, deposited in shallow marine, coastal or continental environments in southwestern Europe during Latest Cretaceous and Early Palaeogene times) corresponding to the upper part of the heterolithic and poorly known "Villalba de la Sierra" Formation. To date, "Lo Hueco" has provided more than 8,500 macroremains from different taxa, including plants, invertebrates and vertebrates. The vertebrate fossil assemblage is mainly composed of titanosaur sauropod dinosaurs (some of them with nearly complete skeletons), but also of actinopterygian and teleostean fishes, amphibians, panpleurodiran (bothremydids) and pancryptodiran turtles, squamate lizards, eusuchian crocodiles, pterosaurs, and euornithopod (rhabdodontids) and theropod (mainly dromaeosaurids) dinosaurs. The collected fossil sample represents a singular accumulation not only for the Iberian record but also for the entire Upper Campanian-Lower Maastrichtian European vertebrate record.

The stratigraphic succession of "Lo Hueco" is composed, from base to top, of the following levels separated by transitional boundaries. An interval of green marly mudstones (V), 2 m of grey marly mudstones (G1), 2.75 m of red marly mudstones (R1), 1.5 m of grey marly mudstones (G2), 2.25 m of red marly mudstones (R2) and an interval of brown marly mudstones (M). Laterally, these levels can show differences in thickness of up to 0.75 m. This stratigraphic succession changes slightly in three areas of the outcrop. In its eastern area, a first sulphated interval (S1) can be distinguished, which has some points that are especially enriched with mudstones and carbonates. This sulphated interval reaches, at least, 1 m of height, and interrupts the V level by means of a net boundary. In the southern area of the outcrop, a channel structure (C) can be seen, which follows a N120ºE direction and is composed of sandy conglomerates, sandstones and sandy mudstones. This elongated structure reaches up to 10 m of width and 3 m of height in transverse section, and interrupts the V, G1 and R1 levels by means of an erosive surface. In the north-eastern area of the outcrop, a second sulphated interval (S2) can be distinguished, which has some points that are especially enriched with mudstones and carbonates. This irregular sulphated interval reaches up to 1.5 m of height, and, at least, interrupts the G2 level by means of a net boundary.

Concerning the environmental interpretation of "Lo Hueco", the entire succession seems to correspond to a near coast muddy flood plain crossed by sandy channels, which suffered successive depositional intervals (mainly clayey but, occasionally, also chalky or sandy) and syn- or early post-depositional periods of sulphatation and ferruginization. This continental plain (with abundance of terrestrial plants, invertebrates and vertebrates) apparently registered intermittent intervals of aquatic influence (burrows, bivalves, fishes, bothremydid and pancryptodiran turtles, crocodiles), clearly evident in the G1 and G2 levels, the C structure and the S1 and S2 intervals, and of partial or total desiccation (roots), especially manifest in R1 and R2. The same aquatic influence probably was mainly of fresh water (unionid bivalves), but occasionally also was of marine or brackish water (Thalassinoides, herringbone or chevron bedding, pancryptodiran turtles). This aquatic influence seemingly suffered notable oscillations in volume and energy. Apparently, during the high energy intervals, some of the registered sediments and organisms were transported and fragmented, mainly across a channel (C structure), but also across its overbank zones (G1 and G2 levels). During the diminishing energy intervals, some of the registered sediments and organisms were orientated, parallel and perpendicular to the axis of the channel, and deposited on the overbank zones and inside the channel. During the low energy intervals, mainly on the overbank zones, relatively isolated water masses could be formed, acting maybe as miring areas. Progressively, these areas might give place to trampling areas (oblique or infilled breakages in vertebrate remains near the C structure). Finally, during the intervals without aquatic influence, the environment of "Lo Hueco" site was partially or totally dried up and vegetation settled over the muddy plain (R1 and R2 levels).