West Gondwana

The San Luis Formation is one of the lithostratigraphic units constituting the early Paleozoic crystalline base-ment of the Sierras de San Luis, which are part of the Sierras Pampeanas of central Argentina. The low-grademetamorphic overprint of the San Luis Formation makes it a key unit for the modelling of its sedimentaryenvironment, which belongs to a deep-marine environment. This formation crops out in two belts named asEastern and Western, whose stratigraphic correlation has not been clarified. Five samples from both belts of theSan Luis Formation show U-Pb age distributions of detrital zircons with dominant peaks that are characteristic oforogenic systems of the West Gondwanan landmasses. However, detrital zircon age spectra and maximum de-positional ages differ substantially in each belt of the San Luis Formation. While the Western belt displayspolymodal age patterns with its most prominent age peaks at∼635 Ma, a second most important populationappears at 535–575 Ma with subordinate groups at 720–775 Ma and 1.7–2.2 Ga; the Eastern belt shows analmost unimodal age pattern dominated by an age peak at∼535 Ma, with very subordinate peaks at∼620 Ma,∼780 Ma and∼1,017 Ma. Regarding the maximum depositional age, two different ages have been recognizedin the Western belt,∼555 Ma at its bottom and∼530 Ma at its top; whereas in the Eastern belt the maximumdepositional age is∼515 Ma. The age spectra of detrital zircons from the San Luis Formation record the evo-lution of the nearby Pampean orogen. At an early stage of exhumation, the Pampean orogenic system chieflyliberated recycled sedimentary detritus containing zircons with Neoproterozoic (∼635 Ma), Mesoproterozoic(∼1,000 Ma) and subordinate amounts of Paleoproterozoic (∼2,200 Ma) ages. Upon advanced unroofing andactive erosion, the Pampean sequences sourcedfirst-cycle detritus with latest Neoproterozoic to early Cambrianages (555–525 Ma). A major conclusion is that the San Luis Formation accumulated in at least two stages,fillingsuccessive deep-marine basins that were marginal to the Pampean orogen during and after its latestNeoproterozoic to Cambrian development

For 130 years dinosaurs have been divided into two distinct clades – Ornithischia and Saurischia.

This dissertation looks at the earliest evolution of the clade Dinosauria by focusing upon the interrelationships of the major subsidiary clades within it. It does this following examination, comparison and description of early dinosaur material, and by utilising modern phylogenetic analysis techniques, to rigorously and objectively test the fundamental groupings within the clade Dinosauria using a newly compiled dataset of early dinosaurs and other dinosauromorphs (= close dinosaur relatives). The current consensus on how the principal clades within Dinosauria (Theropoda, Sauropodomorpha and Ornithischia) are related to one another is challenged by the results of these analyses. This study finds, for the first time, a sister-group relationship between Ornithischia and Theropoda, here termed Ornithoscelida. Consequently, a new definition for Dinosauria is presented, as the historic definition would exclude all members of Sauropodomorpha from the clade. As well as this, I propose revisions to the definitions of each of the principal dinosaurian sub-divisions and propose a new timeframe and geographic setting for the origin of Dinosauria. These new hypotheses force re-evaluations of early dinosaur cladogenesis and character evolution, suggest the independent acquisition of hypercarnivory in multiple dinosaur groups and offers an explanation for many of the anatomical features previously regarded as striking convergences between theropods and early ornithischians.

As well as presenting new anatomical data on many early dinosaurs and dinosauromorphs, including a comprehensive re-description of the postcranial anatomy of Lesothosaurus diagnosticus (Chapter 2), and a new anatomical dataset of early dinosaurs (the largest ever compiled), this thesis goes on to implement the new dataset to investigate a number of important outstanding questions about early dinosaur evolution and provides new lines of enquiry for future workers to pursue. The results of this thesis reveal the oldest known members of the dinosaurian clades Theropoda and Sauropodomorpha (Chapter 6), as well as a new clade within Ornithischia; a taxon previously thought to represent a derived theropod has been recovered as a potential ‘missing link’ between theropods and ornithischians using the new dataset.
This work now provides a unique tool for the assessment of the phylogenetic affinities of early dinosaurs and dinosauromorphs and, once published, will hopefully become the benchmark dataset for palaeontologists working in this area.

The illaenid trilobite Vysocania is widely represented in the Upper Ordovician of the Czech Republic, Portugal and Spain, and is one of the most characteristic taxa in the high-latitude peri-Gondwana palaeobiogeographical region to which it is endemic. Three species of the genus that were formerly assigned to Stenopareia and Zetillaenus, from the Czech Republic and Spain respectively, are herein revised, and a new species is described from the Czech Republic. The genus Octillaenus, of which a new species is described from the Upper Ordovician of Morocco, is considered to have arisen from Vysocania through paedomorphic (neotenic) processes. The relationships between Vysocania, Octillaenus, Stenopareia and Zetillaenus are reviewed and the criteria used in the definition of these taxa discussed. Species assigned to Vysocania are V. vaneki (type-species), V. iberica, V. moraveci sp. nov. and V. panderi; species assigned to Octillaenus are O. hisingeri (type-species) and O. marocanus sp. nov. Vysocania appears for the first time in the lower Berounian (Sandbian) and has its last undoubted record in the upper Berounian (upper Katian); Octillaenus is presently restricted to the Kralodvorian (upper Katian). •

This paper presents an analysis of the spatiotemporal distribution and composition of a volcanosedimentary complex, which has recorded a significant episode of carbonate productivity embedded in a thick and monotonous, turbiditic-dominated rift succession. The studied nucleation of a microbial–skeletal carbonate factory is middle Cambrian in age and situated at Sidi-Saïd-Maâchou, an uplifted rift shoulder of the Moroccan Coastal Meseta located at the junction of several graben segments, where an alkaline basaltic magma was extruded along fissures or intruded as sills and dikes. The geometry and facies of the skeletal calcarenite sheets, composed of hiatal shelled accumulations separated by microbial mats, is comparable to those of the Brèche à Micmacca recorded across the lower-middle Cambrian transition in the Anti-Atlas and High Atlas. The patchy and diachronous distribution of these 'anomalous' carbonate factories, spatially and temporally associated with volcanic episodes, marks the northward migration of active rifting structures throughout the Moroccan margin of West Gondwana.

The Talampaya Formation is the basal unit of the Ischigualasto-Villa Union rift system and has been traditionally assigned to the Triassic based on stratigraphic relationships. A median UePb age of 252.38 (þ0.09/0.22) Ma was obtained from volcanic zircons collected from a tuff bed close to the top of this unit at the Bordo Atravesado locality in the Cuesta de Miranda area (La Rioja, Argentina). This radiometric age is very close to the accepted PermianeTriassic boundary indicating that, at least in this locality, sedimentation occurred during the Late Permian but may have extended into the earliest Triassic. This new evidence indicates that the onset of the extensional event that gave rise to the rift basins in western Argentina started during the Permian. Detailed sedimentological studies of the 260 m thick Talampaya Formation allowed subdividing the succession into seven facies associations grouped into three evolutionary stages indicating that sedimentary environments initially evolved from alluvial fans to a braided river system. Subsequent intrabasinal volcanism associated with sediment deposition by low-to moderate-sinuosity rivers is recorded in the lower third of the column. The middle and upper part of the unit captures the evolution from ephemeral fluvial systems with an eolian interval to an ephemeral clastic lake with intermittent volcanic ash deposits. These changes indicate a progressive lowering of the landscape and a transition towards arid or semiarid conditions.

ABSTRACT In this study, we utilize multiple thermochronometric methods, including apatite and zircon fission track, (U-Th)/He, and zircon U-Pb, to evaluate the cooling history and provenance of sedimentary strata of the late Carboniferous to Late Permian eastern Paganzo basin and adjacent basement rocks (Argentina). The strata in the study area represent a long-lived, composite basin system that is interpreted to have experienced multiple periods of deformation, and to have received sediment from a number of different source terranes. These strata are well exposed in the Sierra de Chepes of west-central Argentina. New thermochronometric data and field observations, together with published data from the surrounding mountains, allow us to reconstruct: (1) the cooling history of the underlying basement rocks and the highlands surrounding the basin, (2) the thermal history of the source areas that provided sediment to the basin, and (3) the timing of structural inversion of the basin. Our data suggest that parts of the Sierra de Chepes were rapidly exhumed in Late Devonian-Carboniferous times; these exhuming areas supplied sediment to the adjacent basin. In contrast, the overlying red-bed strata originated from a slowly exhuming region located farther east or north of the basin within the Pampean orogenic belt or the Famatinian belt, respectively. Burial by latest Carboniferous and younger strata and an elevated geothermal gradient resulted in heating of the underlying Upper Carboniferous strata and underlying granitoid basement to temperatures between 80 degrees C and 140 degrees C. During Triassic time, the eastern Paganzo basin was structurally inverted; this event was marked by rapid cooling and may be related to regional extension and the development of rift basins to the west. The basement and the Upper Paleozoic strata of the eastern Paganzo basin in the study area have remained below 50 degrees C since latest Jurassic-Early Cretaceous times and are characterized by very slow cooling. Results of this study provide a thermochronometric view along an similar to 330 m.y. path defining the geologic evolution of the eastern Paganzo basin and the upper crust of west-central Argentina.

In this study, we utilize multiple thermochronometric methods, including apatite and zircon fission track, (U-Th)/He, and zircon U-Pb, to evaluate the cooling history and provenance of sedimentary strata of the late Carboniferous to Late Permian eastern Paganzo basin and adjacent basement rocks (Argentina). The strata in the study area represent a long-lived, composite basin system that is interpreted to have experienced multiple periods of deformation, and to have received sediment from a number of different source terranes. These strata are well exposed in the Sierra de Chepes of west-central Argentina. New thermochronometric data and field observations, together with published data from the surrounding mountains, allow us to reconstruct: (1) the cooling history of the underlying basement rocks and the highlands surrounding the basin, (2) the thermal history of the source areas that provided sediment to the basin, and (3) the timing of structural inversion of the basin. Our data suggest that parts of the Sierra de Chepes were rapidly exhumed in Late Devonian–Carboniferous times; these exhuming areas supplied sediment to the adjacent basin. In contrast, the overlying red-bed strata originated from a slowly exhuming region located farther east or north of the basin within the Pampean orogenic belt or the Famatinian belt, respectively. Burial by latest Carboniferous and younger strata and an elevated geothermal gradient resulted in heating of the underlying Upper Carboniferous strata and underlying granitoid basement to temperatures between 80 °C and 140 °C. During Triassic time, the eastern Paganzo basin was structurally inverted; this event was marked by rapid cooling and may be related to regional extension and the development of rift basins to the west. The basement and the Upper Paleozoic strata of the eastern Paganzo basin in the study area have remained below 50 °C since latest Jurassic–Early Cretaceous times and are characterized by very slow cooling. Results of this study provide a thermochronometric view along an ∼330 m.y. path defining the geologic evolution of the eastern Paganzo basin and the upper crust of west-central Argentina.