Pere Busquets

Neogene structures overprinting Palaeozoic thrust systems in the Andean Precordillera at 30°S latitude

Field studies along a 30°S latitude transect of the Precordillera in NW Argentina indicate that Neogene to recent deformation caused high-angle faulting that uplifted and breached a Palaeozoic east-verging thrust stack. Palaeozoic structures crop out in the higher linear ranges, and intramontane Neogene basins occur in the intervening valleys. The Palaeozoic rocks include three tectonic units with contrasting structural styles and differences in stratigraphy. The Western Allochthon includes clastic Ordovician rocks metamorphosed to lower greenschist facies and folded by large-scale asymmetric, east-verging folds with a well-developed axial planar cleavage. This unit overthrusts a Siluro-Devonian flysch-type succession of the Central Imbricate thrust system and associated fault propagation folds in which the thrusts merge into a basal thrust beneath Ordovician carbonates. Middle to Upper Carboniferous sediments unconformably overlie structures of this imbricate system. In the Frontal Unit minor thrust faults are interpreted to explain the low-angle unconformity within Palaeozoic rocks. Neogene deformation causes only a minor overprint of the Palaeozoic structure, and large-scale folding in the Frontal Unit appears to be mostly of Neogene age. The new data indicate that Neogene intracontinental shortening may be smaller than previously proposed, providing new perspectives on the present orogenic architecture along this Andean section.

Marine and Transitional Middle/Upper Eocene Units of the Southeastern Pyrenean Foreland Basin (NE Spain)

The stratigraphic basis of this work has allowed the use of larger foraminifers in the biostratigraphic characterisation of the new Shallow Benthic Zones (SBZ). This part of the volume presents a description of the sedimentary cycles formed by the transgressive-regressive systems of the Lutetian and Bartonian in the southeastern sector of the Ebro Foreland Basin.Concerning the Lutetian deposits studied in the Amer-Vic and Emporda areas, four sedimentary cycles have been characterised. The first and second are found within the Tavertet/Girona Limestone Formation (Reguant,1967;Palli,1972), while the third and fourth cycles cover the Coll de Malla Marl Formation (Clavell et al.,1970), the Bracons Formation (Gich,1969,1972), the Banyoles Marl Formation (Almela and Rios,1943),and the Bellmunt Formation (Gich,1969,1972). In the Bartonian deposits studied in the Igualada area,two transgressive-regressive sedimentary cycles have been characterised in the Collbas Formation (Ferrer,1971),the Igualada Formation (Ferrer,1971),and the Tossa Formation (Ferrer,1971). The Shallow Benthic Zones (SBZs)recognised within the Lutetian are the following:SBZ 13, from the Early Lutetian, in the transgressive system of the first cycle;SBZ 14,from the Middle Lutetian, in the second cycle and the lower part of the transgressive system of the third cycle; SBZ 15,from the Middle Lutetian, in the remaining parts of the third system; SBZ 16, from the Late Lutetian,throughout the fourth cycle.The association of larger foraminifers in the first and second cycles of the Bartonian in the Igualada area has been used as the basis for the definition of SBZs 17 and 18 recognised in the Bartonian of the western Tethys.

Interplay between longitudinal fluvial and transverse alluvial fan systems and growing thrusts in a piggyback basin (SE Pyrenees)

Abstract The integration of sedimentological and structural data in the western end of the Ripoll syncline allows a clearer understanding of the palaeogeography of the area between the oblique termination of the Pedraforca thrust sheet and the frontal Vallfogona thrust during middle Eocene times. In this region, a 2.5-km thick clastic succession corresponding to the Bellmunt and Milany sequences infilled the Ripoll syncline. This succession evolved from fluvio-deltaic to alluvial. The long-lived and west prograding longitudinal fluvio-deltaic system was parallel to the axis of the syncline. The fluvio-deltaic deposits are found interfingered with others, which correspond to transverse alluvial fans of northern provenance, which are increasingly important towards the top of the section. The persistent and uniform WSW palaeoflow direction of the fluvio-deltaic system together with the position of open marine conditions to the south indicate that the southern boundary of the system was constrained by a tectonic barrier which is attributed to the emergence of the Vallfogona thrust. The ramp of this thrust above the foreland basin strata formed the Ripoll piggyback basin from middle Lutetian times on, several millions years earlier than previously proposed. The western end of the Ripoll syncline is thus an example of a complex partitioning of a foreland basin over time and space by structures of differing growth duration and different trend. The interaction of the oblique system of thrusts, corresponding to the eastern termination of the Pedraforca thrust sheet and the Vilada anticline, and the frontal system of the Vallfogona thrust controlled the position of the Bellmunt river-dominated delta, which acted as the outlet of the Ripoll piggyback basin.

Deep-water coral occurrences in the Strait of Gibraltar

This study reports for the first time on the occurrences of deep-water coral species in the Spanish territorial waters of the Strait of Gibraltar. Based on an extensive dataset of 334 grab samples, 16 species of calcareous corals have been identified in water depths between 13–443 m. Scleractinian corals form the dominant benthic community between 140–330 m water depth. The corals appear on the seabed both as solitary individuals and as patches on small biological topographic build-ups. The most common coral species Lophelia pertusa and Madrepora oculata are associated with coarse-grained calcareous sediments and mound structures. In the shallowest part of the study area (<150 m) algae and bryozoans are dominant and only a few coral species are observed. This zonation and the occurrence of the azooxanthellate corals in the Strait of Gibraltar relates to light availability and perhaps also to the complex interaction between the outflow of Mediterranean water and surficial inflow of Atlantic water into the Mediterranean Sea.

An inventory of the marine and transitional Middle/Upper Eocene deposits of the Southeastern Pyrenean Foreland Basin (NE Spain)

In the southeastern Ebro Foreland Basin, the marine deposits of Lutetian and Bartonian age show excellent outcrop conditions, with a great lateral and horizontal continuity of lithostratigraphic units. In addition, the rich fossil record -mainly larger foraminifers-, provides iostratigraphic data of regional relevance for the whole Paleogene Pyrenean Basin, that can be used for the Middle Eocene biocorrelation of the western Tethys. This contribution is a sedimentary and biostratigraphic synthesis of the basic outcrops and sections of the Lutetian and Bartonian marine and transitional deposits in the southeastern sector of the Ebro Foreland Basin.

Eocene siliceous sponges from the Ebro Basin (Catalonia, Spain)

The Eocene (Bartonian) marls of the La Guixa Member and Gurb Member, Vic Marls Formation (Ebro Basin, Catalonia, Spain), contain a very rich and diversified siliceous sponge fauna. The fauna is dominated by hexactinellids; lithistids and other demosponges are rare. It consists of 16 species representing 16 genera. Eleven new species and two new genera are proposed for these sponges: Reguantella cavernosa nov. gen. nov. sp., Regadrella concinna nov. sp. (both Hexactinellida, Lyssacinosa), Eurete clava nov. sp., Pleuroguettardia iberica nov. sp., Aphrocallistes almeriae nov. sp., Hexactinella informis nov. sp. (all Hexactinellida, Hexactinosa), Brachiolites munterensis nov. sp., Centrosia viquensis nov. sp., Callicylix eocenicus nov. sp., Rhizocheton robustus nov. sp. (all Hexactinellida, Lychniscosa), Propetrosia pristina nov. gen. nov. sp. (Demospongia, Haplosclerida). Some genera of sponges in this fauna are still extant, but, in general, the predominant ones are very close in morphology, and, without doubt, closely related to the Late Cretaceous sponges. This fauna also differs considerably, in terms of composition, from most other described faunas of Tertiary sponges from the Mediterranean region, which are dominated by lithistid sponges. Lithistid sponges are rare in this investigated assemblage, which seems most similar to an as yet undescribed Eocene fauna from Italy. There is ecological differentiation in the proportions of particular sponges in various outcrops and/or stratigraphical levels that is clearly associated with water-depth-related controlling factor(s): Munter, Tona and Sta. Cecilia represent the deepest facies, Gurb is intermediate, and St. Roc and Vespella are the most shallow. The exact bathymetric position of the sponge fauna is difficult to estimate, but it seems that 100 m (but probably 200 m and more in the case of the deepest parts) of water depth may be inferred for this facies.

Nurse logs: An ecological strategy in a late Paleozoic forest from the southern Andean region

ABSTRACTDecaying logs on the forest fl oor can act as “nurse logs” for new seedlings, helping with the regeneration of the vegetation. Fossil evi-dence of this ecological strategy is exceptionally well preserved in the Argentinean Andes, where an ~300 m.y. old permineralized for-est was found at 3000 m elevation in San Juan Province. The fossil trunks, some of them in life position, are intercalated between volca-nic rocks and sediments deposited in fl ooded environments (probably coastal lagoons). More than 100 specimens studied allow us to suggest the dominance of only one tree species in the forest. The fi rst issue of the research was to determine the means used by the vegetation to survive in such adverse environmental conditions. Fossil evidence supports the hypothesis of regeneration via nurse logs. Little rootlets preserved inside the wood of several specimens indicate that seedlings developed on these logs. Important additional information provided by the fossils is the presence of aerenchymatic tissue in the rootlets. Aerenchyma tissue is a common feature developed in plants living in fl ooded environments; therefore its recognition in the fossil forest helps in the ecological interpretation.INTRODUCTION

New correlation between charophyte and larger Foraminifera biozones (Middle Eocene, Southeastern Pyrenees)

A correlation between the charophyte index-species Raskyella peckii and the biozonation of larger foraminifera (Shallow Benthic Zones SBZ 13 and SBZ 18) is proposed, which results in a widening to about 6 MA of the present known chronostratigraphic range of the charophyte species. The new range is Early Lutetian to Late Bartonian. This leads to a significant modification in charophyte biozonation including a redefinition of the charophyte biozone of Raskyella peckii as a partial range zone and the elimination of the biozone of Maedleriella embergeri (Early Lutetian). In addition, the new chronostratigraphic range of Raskyella peckii overlaps the range of the related species Raskyella vadaszi, covering the gap which separated both species. Gaps in the fossil record of Raskyellaceae gave rise to the hypothesis of a polyphyletic origin for this fossil family. The new, continuous chronostratigraphic range suggests that at least the genus Raskyella appears to be monophyletic and did not originate from different characean ancestors.

The relationship between carbonate facies, volcanic rocks and plant remains in a late Palaeozoic lacustrine system (San Ignacio Fm, Frontal Cordillera, San Juan province, Argentina)

The San Ignacio Fm, a late Palaeozoic foreland basin succession that crops out in the Frontal Cordillera (Argentinean Andes), contains lacustrine microbial carbonates and volcanic rocks. Modification by extensive pedogenic processes contributed to the massive aspect of the calcareous beds. Most of the volcanic deposits in the San Ignacio Fm consist of pyroclastic rocks and resedimented volcaniclastic deposits. Less frequent lava flows produced during effusive eruptions led to the generation of tabular layers of fine-grained, greenish or grey andesites, trachytes and dacites. Pyroclastic flow deposits correspond mainly to welded ignimbrites made up of former glassy pyroclasts devitrified to microcrystalline groundmass, scarce crystals of euhedral plagioclase, quartz and K-feldspar, opaque minerals, aggregates of fine-grained phyllosilicates and fiammes defining a bedding-parallel foliation generated by welding or diagenetic compaction. Widespread silicified and silica-permineralized plant remains and carbonate mud clasts are found, usually embedded within the ignimbrites. The carbonate sequences are underlain and overlain by volcanic rocks. The carbonate sequence bottoms are mostly gradational, while their tops are usually sharp. The lower part of the carbonate sequences is made up of mud which appear progressively, filling interstices in the top of the underlying volcanic rocks. They gradually become more abundant until they form the whole of the rock fabric. Carbonate on volcanic sandstones and pyroclastic deposits occur, with the nucleation of micritic carbonate and associated production of pyrite. Cyanobacteria, which formed the locus of mineral precipitation, were related with this nucleation. The growth of some of the algal mounds was halted by the progressive accumulation of volcanic ash particles, but in most cases the upper boundary is sharp and suddenly truncated by pyroclastic flows or volcanic avalanches. These pyroclastic flows partially destroyed the carbonate beds and palaeosols. Microbial carbonate clasts, silicified and silica-permineralized tree trunks, log stumps and other plant remains such as small branches and small roots inside pieces of wood (interpreted as fragments of nurse logs) are commonly found embedded within the ignimbrites. The study of the carbonate and volcanic rocks of the San Ignacio Fm allows the authors to propose a facies model that increases our understanding of lacustrine environments that developed in volcanic settings.

Cold-Water coral distribution in an erosional environment: The strait of Gibraltar gateway

Publisher Summary The sill of the Strait of Gibraltar is the morphological, oceanographical, and ecological gateway between the Atlantic Ocean and the Mediterranean Sea for the post-Messinian crisis period. The seabed is composed of synorogenic Betic-Rif clayey flysch overlaid by Pliocene and/or Quaternary calcareous conglomerates and coral accumulations, as well as current transported sand and mud in the deepest parts. The Strait of Gibraltar is one of the busiest maritime zones in the world and is thus affected by invasive species, but the benthic community is poorly studied. Furthermore, the study zone is affected by benthic trawl fisheries on the shelf and near-shelf areas and by the laying of submarine cables. Overall, the naturalness of the study area is considered to be largely unmodified. Based on the Benthic Terrain model scheme, a morphological classification has been made of the bathymetric MBES data, indicating several morphological habitats in the area that can cause fragmentation in the main ecosystem. This classification is based on the rugosity, slope, curvature, depth, bathymetric positioning index (BPI) with annulus neighborhood of 1,125, 300, 120, and 60 m, and the range of standard deviation of the depth over a distance of 45 m based on a bathymetric grid of 15 m. The predicted textural distribution map is based on the rugosity, slope, and objectively classified morphological zones identified in combination with textural information of the sampled stations used in a maximum-likelihood statistic algorithm provided by ArcGIS. Coral distribution is based on grab samples and the layers of the derived morphological grids.