Abstract Megatracksites, popularly known as ‘dinosaur Freeways’ are regionally extensive, stratigraphically restricted track-bearing sequences mainly associated with coastal plain facies, but in rarer cases with fluvio-lacustrine palaeoenvironments. Nine convincing, dinosaur-dominated examples are reported from the Mesozoic of North America, Europe, Africa and Central Asia, with a tenth tetrapod-dominated example reported from the Permian. Some, like the Moab Megatracksite (Utah) are labelled as Type 1 and restricted to ‘single surfaces’ or units only c . <1.0 m thick. Others (Type 2) represent relatively thin track-bearing packages ( c. 1.0– c. 10.0 m in thickness). Type 3 megatracksites represent imprecisely correlated, laterally extensive track-bearing facies. Most Type 1 and 2 examples including a Permian, four Jurassic and three Cretaceous examples display genetic sequence stratigraphic similarities, mainly associated with transgressive marginal marine facies. A Triassic megatracksite from Colorado and Utah is associated with a terrestrial fluvio-lacustrine system, and another from Spain is a lacustrine example. Type 1 megatracksites are defined by correlating multiple tracksites (assemblages) in stratigraphically restricted zones, across distances of c. 10 km– c. 100 km or more. Tetrapod megatracksites, ichnocoenoses and ichnofacies are all large-scale ichnological phenomena, which despite variability and different definitions can be integrated to various degrees. Because sequence stratigraphic, sedimentological and ichnological studies often proceed along separate, specialist lines a more integrated approach to the study of sedimentary geology and tetrapod ichnology is advocated in areas where megatracksites have been reported.

The Faciès Rognacien is a sequence of highly bioturbated and pedogenically modified palustrine carbonates that were deposited under oxic conditions around the Cretaceous-Tertiary (K-T) boundary in the northeastern Pyrenean foreland basin (SW France). The sedimentary structures and early diagenetic features identified (mottling, nodule formation, brecciation, pseudomicrokarst, cracking, charophytes, Microcodium ) suggest deposition in a palustrine environment between the subarid and intermediate climate type. Sedimentological and paleoecological analysis enables us to distinguish two facies associations, the lacustrine pond facies and the freshwater marsh facies associations. The majority of the carbonates are attributed to the freshwater marsh facies. The lacustrine pond facies occurs only in isolated paleolows, and is identified on the basis of its paleobiological content (charophytes, ostracodes). This suggests that the palustrine carbonates of the Faciès Rognacien were deposited in a seasonal wetland (carbonate-producing freshwater marsh), rather than in the marginal zone of a large, shallow lake. In this wetland paleoenvironment, all carbonates underwent widespread pedogenesis, and small, ephemeral ponds are of limited distribution, most likely recording deposition in paleolows. La Faciès Rognacien es una secuencia formada por carbonatos palustres muy bioturbados y modificados pedogénicamente, que se depositó bajo condiciones óxicas en la cuenca de antepaís Pirenaica (SW de Francia). Su edad está entorno al límite K-T. Las estructuras sedimentarias y los rasgos diagenéticos tempranos (caráceas, Microcodium , moteado, formación de nódulos, brechificación, pseudomicrokarst, fisuración) indican que esta secuencia se depositó en un ambiente palustre de clima subárido a intermedio. Los análisis sedimentológicos y paleontológicos permiten distinguir dos asociaciones de facies: charcas lacustres y zonas pantanosas de agua dulce. Las facies de charcas aparecen aisladas en paleodepresiones y tienen un contenido paleobiológico característico (caráceas, ostrácodos). Esto sugiere que los carbonatos palustres de esta secuencia se depositaron en humedales estacionales más que en las zonas marginales de grandes lagos someros. En estos humedales todos los carbonatos sufrieron modificaciones pedogénicas importantes.