Tafonomía y paleoecología del ecosistema acuático de Las Hoyas (Barremiense superior, Serranía de Cuenca).

The freshwater ecosystem of Las Hoyas contains one of the most significant records of aquatic organisms described from the Early Cretaceous worldwide. The benthos was formed by a diverse assemblage of animals such as aquatic insects, ostracods, cray-fishes, and juvenile and small adult fishes, which depended on the ground cover of charophytes and aquatic angiosperms for shelter and food. The nekton was mainly composed o f crustaceans and a large variety of fishes. Phytoplankton is represented by two chlorophytes and zooplankton is represented by planktonic pupae of dipterans. Cheirolepidiaceous conifers, matoniaceous tree-ferns and herbaceous schizaeacean ferns were growing in swamps. Among tetrapods with aquatic habitats modern amphibians and reptiles were found. In spite of the exceptional preservation, the fossil record of Las Hoyas includes sedimentological, taphonomic and palaeoecological biases. Form the palaeoecological point o f view, mass mortality levels contain thousands of individuals of crayfish associated with freshwater plant remains. These levels are attributed to eutrophication events of the otherwise oligotrophic lake. Other mass-mortality levels include hundreds of juvenile teleostean individuals associated with small shrimps. Changes in the water-table and related temperature changes, variation of acidity or input of toxic substances may account for this type of mass mortality

Taphonomy

Trabajo presentado en el II International Symposium on Lithographic Limestones celebrado en Cuenca.-- Field trip guide book.The taphonomic anal ysis of the Las Hoyas site is still at an early stage. This analysis is necessary since it is considered a prerequisite for paleoecological reconstructions (Shipman, 1981). Besides, taphonomic analysis has its own aims; in this case they could be summarized as the establishment of the temporal succession of processes which led to the formation of the site.Peer reviewe

Sedimentología y evolución paleogeográfica de la cubeta de Las Hoyas (Cretácico inferior, Serranía de Cuenca)

[ES] La cubeta de Las Hoyas (Serranía de Cuenca, Cordillera Ibérica) sufrió un relleno sedimentario complejo durante el Cretácico inferior. En un contexto de rift intracontinental, la cubeta de Las Hoyas se encontraba localizada sobre un bloque subsidente controlado por directrices tectónicas ONO-ESE y NO-SE. La variación a lo largo del tiempo del equilibrio entre la tasa de sedimentación y la tectónica sinsedimentaria activa, en interacción con una serie de factores intra y extracuencales (producción de carbonatos, llegada de aportes siliciclásticos, clima...) determinó una historia sedimentaria en tres episodios en los que la paleogeografía de esta cubeta estuvo dominada por diferentes arnbientes. En un primer Episodio se instaló una llanura aluvial distal. Un segundo Episodio está definido por la instalación en todo el área de un ambiente lacustre abierto. El tercer y último Episodio está representado por un ambiente de llanura aluvial distal con áreas lacustres marginales dominantes.[EN] Las Hoyas sub-basin (Serranía de Cuenca, Iberian Ranges) had a very complex sedimentary infilling during the Lower Cretaceous. This basin was settled on a subsident block, in a intracontinental rift context. This block was controlled by WNW-ESE and NW-SEtectonic lineations. lts sedimentary history was developped in three stages and was outlined by the interaction and the equilibrium among severa! factors: sedimentation rate, diferential subsidence, carbonate production, siliciclastic supply, climate... During the three stages the paleogeography was dominated by differents environments. During the first one a distal alluvial plain was installed in the area. A lacustrine environment was developped during the second stage. The third síage is represented by the installation of a distal alluvial plain dominated by marginal lacustrine areas.Peer reviewe

Involvement of microbial mats in delayed decay: an experimental essay on fish preservation

Microbial mats have been implicated in exceptional fossil preservation. Few analyses have addressed how these complex-multilayered biofilms promote fossil preservation. The sequence of changes during decay of neon tetra fish were tracked up to 27 months, and their decomposition in mats was compared against nonmat sediments (control fish). Statistically significant differences in quantitative variables (length, width, and thickness) are provided (ANOVA test, in all cases, P, 0.001). Changes in the qualitative features (body-head, fins, scale connection, and eye and body coloration) were phenetically analyzed resulting in two clusters and highlighting that notable differences in decay began at day 15. Mat fish how a delayed decomposition maintaining the external and internal body integrity, in which soft organs were preserved after 27 months as shown by Magnetic Resonance Imaging. We discuss how the organization, structure, and activity of this community are interrelated, favoring exceptional preservation. Microbial mats entomb the fish from the earliest stages, forming a Ca-rich coat over the carcass while embedding it in an anoxic condition. This quick entombment provides important protection against abiotic and/or biotic agents

El registro estratigráfico del rifting Jurásico Superior-Cretácico Inferior en la región del Alto Tajo-Serranía de Cuenca (Cordillera Ibérica, España): Evidencias genéticas y estructurales para su revisión y nueva propuesta litoestratigráfica

[EN] The Southwestern Iberian Domain (Southiberian Basin) corresponds to one of the five palaeogeographic domains into which the Iberian Basin was divided during the Late Jurassic-Early Cretaceous rifting stage. Although it was already known that this domain was clearly separated into two sub-basins, Cuenca and Valencia, the same lithostratigraphic scheme was assumed to be applicable to the whole domain. In the last decades, new data have been incorporated to the knowledge of the Serranía de Cuenca and the Alto Tajo region, showing that this area underwent a separated palaeogeographic evolution and developed a different stratigraphic record. Evidences of such independence are, among others, the development of a Late Jurassicearly Barremian unconformity with unique features in the Iberian Basin and herein described for the first time. Syn-rift sedimentation was controlled by an intricate extensional geometrical and kinematic pattern of multiple and small half-graben basins, and it is represented by just two unconformity-bounded units, late Barremian and Aptian in age respectively. This work reviews, clarifies, and simplifies old and confusing stratigraphic nomenclatures and proposes a specific lithostratigraphic scheme for the Alto Tajo-Serranía de Cuenca region. It includes the new upper Barremian Tragacete Formation and the redefinition of La Huérguina Formation in terms of lithofacies, lower boundary, age and environmental interpretation.[ES] El Dominio Ibérico Suroccidental (Cuenca Suribérica) corresponde a uno de los cinco dominios paleogeográficos en los que se ha dividido la Cuenca Ibérica (actual Cordillera Ibérica) durante el ciclo de rifting intracontinental Jurásico Superior-Cretácico Inferior. Aunque se sabe que el Dominio Ibérico Suroccidental estuvo compartimentado en dos sub-cuencas diferentes, Cuenca y Valencia, hasta la actualidad se ha asumido que el relleno sedimentario de ambas era asimilable y se ha aceptado un único esquema litoestratigráfico para ambas. Varias décadas de estudio e integración de datos estructurales, estratigráficos, sedimentológicos y paleontológicos del área de la Serranía de Cuenca y el Alto Tajo (Cuenca y Guadalajara) han revelado que esta región sufrió una evolución paleogeográfica independiente y posee un registro estratigráfico particular, que no se refleja en los esquemas estratigráficos disponibles para el Dominio Suroccidental. Evidencias de esta singularidad son (1) el desarrollo de una discontinuidad estratigráfica Jurásico Superior-Barremiense inferior con características únicas en el contexto de la Cuenca Ibérica y descrita por primera vez en este trabajo; (2) el registro más tardío (Barremiense superior) del comienzo de la sedimentación sinrift en la Cuenca Ibérica. La sedimentación sinrift estuvo muy condicionada por el desarrollo de un complejo patrón extensional y cinemático que compartimentó la cuenca en múltiples cubetas de tipo graben y semi-graben, y está representada por dos unidades limitadas por discontinuidades. La primera unidad es Barremiense superior y está compuesta por dos unidades litoestratigráficas con rango de formación constituidas por sedimentos continentales que se superponen y presentan cambio lateral de facies: la Formación Tragacete, que se define formalmente por primera vez en este trabajo, y la Formación La Huérguina, que se redefine formalmente aquí en términos de litofacies, límite inferior, edad y ambientes sedimentarios. También se descarta la presencia y validez en el área de estudio de la Formación El Collado, hasta la actualidad considerada cambio lateral de facies de la Formación La Huérguina en su definición inicial. La segunda unidad es Aptiense y está compuesta por la Formación Contreras que cambia lateralmente de facies al Miembro Malacara (Formación El Caroch), y por el Miembro El Burgal (Formación El Caroch). Sobre ambas unidades limitadas por discontinuidades se apoya discordante el Grupo Utrillas (Albiense), no existiendo registro en esta cuenca de otras unidades aptienses y albienses recogidas en los esquemas estratigráficos tradicionales del Dominio Suroccidental. Además, en este trabajo se revisan y clarifican las diversas nomenclaturas que se han venido usando en las últimas décadas en trabajos publicados y mapas geológicos nacionales de la serie MAGNA correspondientes a esta región.This work is a contribution to project CGL2013-42643 of the Spanish Ministry of Economy and Competitiveness.Peer reviewe

Cenomanian vertebrates from Algora (central Spain): New data on the establishment of the European Upper Cretaceous continental faunas

The palaeontological area of Algora (Guadalajara Province, central Spain) provides the largest concentration of vertebrate macroremains for the Cenomanian of south-western Europe. The available faunal list for Algora, based on the analysis of scarce remains collected in geological surveys carried out more than thirty years ago, was never updated. Therefore, and despite the great potential of this site to reveal novel information about the composition of the vertebrate fauna from the base of the Upper Cretaceous in the continent, the previous determination of many of the taxa recognized there is identified here as inaccurate or erroneous (e.g., the identification of two actinopterygian fishes, a single crocodyliform, the helochelydrid turtle Helochelys danubina and carcharodontosaurid dinosaurs). Recent fieldwork campaigns have provided numerous remains, including those of clades poorly represented so far, as well as others hitherto unknown at this site. The new faunal list proposed here included the lepisosteoid Obaichthys africanus, the helochelydrid aff. Plastremys lata, the pleurodiran Algorachelus peregrina, an indeterminate elasmosaurid, a non-eusuchian neosuchian and a eusuchian crocodyliform, a likely abelisaurid theropod and a lithostrotian sauropod. The study of these taxa provides new information about the palaeobiogeography and temporal distributions of some lineages, and increases knowledge about the poorly-known transition between the Lower and the Upper Cretaceous faunas in Europe. This faunal replacement, in which several well-represented lineages in the uppermost Cretaceous were established, is recognized as strongly conditioned by climate changes that took place between the end of the Early Cretaceous and the beginning of the Late Cretaceous