Nieves Meléndez

Extensional fault control on the sedimentation patterns in a continental rift basin: El Castellar Formation, Galve sub-basin, Spain

In the Galve sub-basin, the sedimentary record of the Upper Hauterivian–Lower Barremian El Castellar Formation is divided into two stages by a marlstone interval with gypsum. Stage 1 shows a great variety of subenvironments and facies (alluvial, palustrine and lacustrine) whereas in stage 2 an extensive, shallow carbonate lake developed. Sedimentation was controlled by a system of south-dipping, ENE–WSW listric normal faults, laterally bounded by NNW–SSE steeper transfer faults. Faults controlled sedimentation from a basin scale (basin margins and main characteristics and evolution of sediments) to a regional and a local scale (thickness and facies distribution of the synrift series as well as the location and evolution of lakes and minor alluvial fans). The changes between stages 1 and 2 are related to the passing from an independent movement of faults to the movement of all the extensional faults as a whole, at a sole detachment level. The interval with gypsum was caused by underground water flow changes associated with the interrelation and connection of the faults in the transition period. These changes have been correlated with the transition from the rift initial stage to the rift climax stage, which took place in the Hauterivian–Barremian transition.

A preliminary note on the first tetrapod trackways from the lithographic limestones of Las Hoyas (Lower Cretaceous, Cuenca, Spain)

Although famous as a fossil lagerstatte that has produced numerous well-preserved vertebrates, recent discoveries indicate that the lithographic limestones of Las Hoyas (Calizas de la Huerguina Formation) also contain vertebrate trackways. We herein report on at least two distinctive tetrapod track types tentatively assigned to crocodilians and to turtles. Turtle tracks are isolated while the crocodile ones are forming a trackway showing an animal walking with a very regular step and stride length on an emergent surface. It is interesting to note the similarity between the inferred turtle tracks from Las Hoyas and those from the Late Jurassic lithographic limestones of Cerin, France. The occurrence of tracks in both environments suggests that the ichnofaunas are similar.

Climatic control on Lower Cretaceous sedimentation in a playa-lake system of a tectonically active basin (Huérteles Alloformation, Eastern Cameros Basin, North-Central Spain)

The Berriasian Huérteles Alloformation is the fourth alloformation in which the Tithonian-Berriasian Depositional Sequence is divided in Eastern Cameros Basin. This depositional sequence can be recognized in several basins East of The Iberian Plate. Huérteles Afm. was deposited in a trough with a NW-SE orientation and strong subsidence. In this trough the sedimentary record exceeds 1000 m in thickness for this alloformation. The Basin shows a marked asymmetry, with the highly subsident trough displaced to the NE.The sedimentary system consists of a playa complex, in which several subenvironments can be distinguished. The proximal or bajada environments were located to the west. The terrigenous materials, that constitute the sediments of these areas, come from the erosion of materials previously deposited in the Basin. To the East the environments were mainly saline lakes, that received siliciclastic materials from the Northeast, where the main border fault system was situated.The vertical sequence in the central part of the Basin (where a perennial saline lake was located) shows a marked cyclicity, with primary sequences about 10 m thick. These consist of laminated limestones in their lower part, and carbonate breccias at the top. These primary sequences represent the filling of a lake, with relatively dilute waters at first, passing gradually into a saline lake. This reflects a transition from humid to arid climatic periods.Additionally there is another cyclicity of a higher rank indicated by sequences about 300 m thick These major sequences are formed by primary sequences. The minor primary sequences are mainly composed of laminated limestones in the lower part of the major sequences, and the carbonate breccias dominate in the upper part of the major sequences. These major sequences may indicate longer periods of climatic variation, that varied from a relatively humid to an arid climate. This sequential arrangement was accentuated by the strong tectonic activity during sedimentation, that produced large slump structures where evaporites were more abundant.

Sedimentological analysisof the Lower Cretaceous lithographic limestones of the “Las Hoyas” fossil site (Serrania de Cuenca, Iberian Range, Spain)

Abstract The lithographic limestones of the Las Hoyas fossil site (Lower Cretaceous) were deposited in a meromictic lake.The climate (subtropical), the active synsedimentary tectonics, the high organic productivity and the high sedimentation rate were the main controls on lake dynamics. The variety of microfacies recognized reflects a complex behaviour of the lake that produced the exceptional fossil record at this site. The main factors and processes that favoured the exceptional preservation of the fossils seem to be: the morphology of the lacustrine basin, the anoxia of the bottom of the lake, the very fast burial of the rests by turbidity deposits, the development of microbial mats, as well as, the early diagenetic mineralization of the rests, that were buried in carbonate sediments.