José Carlos García-Ramos

Transgressive–regressive cycles and Jurassic palaeogeography of northeast Iberia

Abstract A correlation and sequence stratigraphy study of Jurassic successions has been carried out in the main sedimentary basins of northeast Iberia, i.e., Asturias, Basque-Cantabrian, and Iberian basins, based on the identification of transgressive–regressive cycles. The development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast Iberia were largely controlled by major tectonic activity at three main intervals, at the beginning of the Jurassic, in the Lower–Middle Jurassic transition, and during the uppermost Jurassic, respectively. During Early Jurassic times, northeast Iberia was the site of a single and large carbonate ramp opened to the north. This carbonate ramp suffered a progressive drowning, evolving from an inner to hemipelagic ramp systems, with the local development of suboxic environments in the deepest areas located to the north. During the Middle Jurassic, different open carbonate platforms were formed including the development of swells in intermediate areas. During the Upper Jurassic, the outer ramp areas were progressively moving to the east Iberian Basin, and the ammonite faunas showing a markedly Tethyan affinity thereafter. Three first order T–R cycles bounded by major discontinuities associated with significant time gaps are identified. They extend respectively from the latest Rhaetian to the Early Aalenian, from the Middle Aalenian to the Early Oxfordian and from the Early Oxfordian to the Late Berriasian. Major transgressive peaks occurred at the Middle Toarcian (Bifrons Zone), at the Late Bajocian (upper Niortense and Garantiana zones) and at the mid-Kimmeridgian (Divisum Zone). Each of the first order cycles includes four second-order T–R cycles. Cycles 1.1–1.4 are identified in the northern basins. Cycles 2.1–2.4 display some differences in age of transgressive peaks from one basin to another. Cycles 3.1–3.4 are mainly identified in the Iberian Basin. The correlation with other separated Boreal and Thethysian basins demonstrates that the number and age of T–R cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development. The transgressive peaks may reflect episodes of eustatic rise during the Jurassic. However, their different age from one basin to another is explained by different subsidence evolution.

Shrinking the World's Largest Dinosaur Tracks: Observations on the Ichnotaxonomy of Gigantosauropus asturiensis and Hispanosauropus hauboldi from the Upper Jurassic of Asturias, Spain

The type material of the ichnospecies Gigantosauropus asturiensis Mensink and Mertmann 1984 is re-examined and shown to represent a sauropod rather than a theropod. This interpretation confirms the recent suggestions of several authors. We describe the trackway in detail but conclude that it is not diagnostic at any taxonomic level, below the general category of sauropod. Thus, G. asturiensis may legitimately be considered a nomen dubium, and the name should be restricted to the original material and not extended to formally describe other poorly preserved specimens. Claims that the largest pes tracks are 1.35 or even 1.5 m in length are incorrect. Pes length ranges from 98–125 cm (mean 110.75 cm). Hispanosauropus hauboldi Mensink and Mertmann 1984 is also of doubtful utility as previously defined. The holotype, a field specimen, which clearly represents a theropod dinosaur, cannot be located, and may be lost to erosion. The paratype is a sauropod track and therefore has no relevance to the ichno-species description. Therefore, we select a new paralectotype and provide a more detailed description of specimens that can be assigned to this ichnotaxon. Hispanosauropus is similar to tracks recently described under the label Megalosauripus. However, the status of this latter ichnogenus, and the spectrum of track types to which it refers, is disputed. Thus, we provisionally restrict the name Hispanosauropus to the original illustrated holotype and a paralectotype from the same locality. On the grounds of morphological similarity, the name may be applied to similar material from elsewhere in the Upper Jurassic of Asturias.

Crocodylomorph Tracks from the Late Jurassic of Asturias (Spain)

Some small and medium-sized crocodylomorph footprints are described from the Late Jurassic (Kimmeridgian) coastal and deltaic units of the northern Spain (Asturias). There are at least four footprint morphotypes. Three of them, with well preserved trackways, are included in the ichnogenus Crocodylopodus (Crocodylopodus isp. and Crocodylopodus meijidei); the fourth one, documented by some isolated large footprints, is referable to the ichnogenus Hatcherichnus. This ichnoassociation confirms the presence of small crocodilians in palaeoenvironments apparently dominated by dinosaurs. The presence of Hatcherichnus seems to confirm the affinity between the Iberian and North American ichnofaunas.

First report of a Late Jurassic lizard-like footprint (Asturias, Spain)

This report describes an isolated footprint preserved as a natural cast (convex hyporelief) from the Lastres Fm. (Late Jurassic) of northern Spain. The track consists of a small isolated pentadactyl ectaxonic right manus footprint. It is very asymmetric, plantigrade, with digits and palm deeply marked on the substrate. Digit IV is the longest, digits II and I are nearly equal in length and only a little shorter than III and IV. The footprint morphology is typical of a lizard – like or “lacertoid” track .The general outline of the footprint, the width to length ratio approximately equal to 1, the marked plantigrady and the substantial similarity in length of digits IV-I are coherent with a Rhynchosauroidea manual print. The global record of Rhynchosauroides ichnogenus shows that this specimen represents the latest occurrence of the ichnogenus. The most probable trackmaker was possibly a rhyncocephalian reptile.

The first record of the genus Eurasenia (Ammonitina) from the Upper Jurassic of Asturias (Northern Spain)

Abstract A large ammonite has been found in the predominantly non-marine Lastres Fm. at Villaviciosa, Asturias, Northern Spain. It is identified as Eurasenia sp. aff. manicata ( Schneid ), indicating an Upper Jurassic age, late Lower Kimmeridgian sensu gallico. This is the earliest record in the Upper Jurassic of the northern margin of the Iberian sub-plate. The sedimentary sequence indicates a regime of small and fluvially-dominated near-shore delta systems subjected to episodic marine ingressions.

Rosselia socialis from the Ordovician of Asturias (Northern Spain) and the Early Evolution of Equilibrium Behavior in Polychaetes

ABSTRACT Stacked specimens of Rosselia socialis from the Middle to Upper Ordovician Castro Formation of Asturias, northern Spain represent an example of an infaunal community able to move upwards simultaneously to avoid burial due to sedimentation from unidirectional currents. This ichnofabric is similar to those described from younger deposits and attributed to equilibrium structures produced by polychaetes belonging to the Order Terebellida. Although high density of specimens has been documented in Cambrian Rosselia suites, the Ordovician occurrence from Asturias is so far the oldest example of a Rosselia ichnofabric recording synchronous equilibrium behaviour of a whole community. Despite uncertainties derived from their patchy fossil record and potential for behavioral convergence, trace-fossil evidence seems to indicate that some groups of polychaetes were efficient burrowers since the early Cambrian. Rosselia ichnofabrics reflect an increased complexity of the trophic web and the ability of infaunal polychaete communities to colonize sandy, relatively high-energy settings by the early Paleozoic.

First Record of Gregarious Behavior in Robust Medium-Sized Jurassic Ornithopods: Evidence from the Kimmeridgian Trackways of Asturias (N. Spain) and Some General Considerations on Other Medium-Large Ornithopod Tracks in the Mesozoic Record

ABSTRACT At least four parallel trackways of medium-sized and robust ornithopods are described from the Upper Jurassic Tereñes tracksite in Asturias (N. Spain). While the tracks and trackways of small and gracile ornithopods are common in the Jurassic record, large ornithopods are very rare in this period. Ornithopod gregarious behavior has been recorded from many Cretaceous ichnoassemblages, but there are few examples from the Jurassic, and these always relate to small individuals. The Asturian tracks are quite different from known ichnogenera, but they are not sufficiently well preserved to propose a new one. Medium-large Jurassic ornithopods with robust feet such as Draconyx or Cumnoria are the best candidates to be the trackmakers.

The ichnogenus Tubotomaculum: an enigmatic pellet-filled structure from Upper Cretaceous to Miocene deep-marine deposits of southern Spain

Abstract The trace-fossil name Tubotomaculum has been extensively used to refer to spindle-shaped pellet-filled tubes present in Upper Cretaceous to Miocene deep-marine deposits of the western Mediterranean region. However, it has never been formally diagnosed, and accordingly it was regarded as a nomen nudum. In this paper, we formally introduce the ichnogenus Tubotomaculum, including the new ichnospecies Tubotomaculum mediterranensis. Bioglyphs, represented by scratch traces that may be present on the basal and lateral surfaces of the structure, suggesting production by crustaceans. The functional meaning of these structures challenges the simple model of a mining strategy. Instead, the storing of pellets to use them as a bacteria-enriched resource during times when organic detritus was scarce is suggested. The association with chemoautothrophic bacteria in modern analogs of Tubotomaculum provides a crucial piece of evidence to support the cache model. Integration of information from modern environments and the fossil record points to a connection between Tubotomaculum, mud volcanism, fluid venting, and hydrocarbon seeps. The presence of bioglyphs suggests firmgrounds that may have resulted from bottom current scouring of the sea sediment, leading to erosional exhumation of previously buried compacted sediment, which was therefore available for colonization by the infauna. However, an alternative scenario involves enriched fluids related to mud-volcanism resulting in reducing conditions that favored carbonate precipitation and nodule formation just a few centimeters below the sediment-water interface.

The Mesozoic Vertebrate Radiation in Terrestrial Settings

In the last three decades vertebrate ichnology went through a renaissance due the discovery of new tracksites and the application of rigorous analytic methods (e.g., synapomorphy analyses). This finally allowed full hypothesis testing and a better integration of vertebrate ichnology in paleobiologic, paleoecologic and paleobiogeographic studies. In this chapter we provide a review of recent advances in vertebrate ichnology, focusing on Mesozoic terrestrial reptiles.

Trace Fossils Assemblages from the Cenozoic “Flysch Units” of the Campo de Gibraltar Complex (Southern Spain)

ABSTRACT Ichnological analysis of deep-sea trace fossil assemblages from the Cenozoic turbiditic succession of the Campo de Gibraltar Complex (Cádiz Province, southern Spain) is presented. A relatively diverse and abundant trace fossil assemblage is recognized, with 20 ichnogenera belonging to the nongraphoglyptid assemblage and 12 to the graphoglyptid assemblage. Nongraphoglyptid traces are dominated by Chondrites, Halopoa, Helminthopsis, Lophoctenium, Nereites, Ophiomorpha, Phycosiphon, Planolites, Scolicia, Thalassinoides and Zoophycos, while Gordia and Tubotomaculum are common, and Cladichnus, Gyrophyllites, Polykampton, Rotundusichnium, Rutichnus, Spirophycus and Stelloglyphus are scarce or rare. Except for Helminthopsis and Spirophycus, all ichnotaxa are post-depositional structures, with feeding forms (pacichnia and fodinichnia) dominant. The graphoglyptid assemblage consists of agrichnia, predepositional trace fossils, with abundant Desmograpton, and Paleodictyon; in turn, Helminthorhaphe, Megagrapton and Urohelminthoida are common, and the rest, including Belorhaphe, Cosmorhaphe, Glockerichnus, Helicolithus, Lorenzinia, Paleomeandron and Spirorhaphe, are scarce or rare. Trace fossil assemblages can be attributed to the Nereites ichnofacies, with dominance of the Nereites ichnosubfacies, but the Ophiomorpha rudis ichnosubfacies and the Paleodictyon ichnosubfacies could be associated to different depositional settings into the deep-marine basin-floor and the deep-sea fan. Together with the tectonic activity and climate, variations in the petrology of the source area, inducing differences in clay mineral composition, may influence the input and deposition of organic matter, affecting graphoglyptid composition. The graphoglyptid assemblage is dominated by winding and meandering structures, some branched, as well as networks; while radial structures and spiral structures are scarce and little diversified. The studied successions are of special interest for interpreting paleoenvironmental and evolutionary changes affecting graphoglyptid assemblages from Paleocene to Miocene in the Campo de Gibraltar Complex.