Sedimentology of the Late Cretaceous in the Western Aude Valley, Southern France

Abstract

The closure of the Tethys seaway between Iberian and European plates and early stage development of the Pyrenees produced continental sedimentation in the Western Aude Valley south of Carcassonne. Although timing is difficult in continental deposits, fluvial sedimentation occurred in much of Campanian time and changed gradually to lacustrine/ palustrine by Maastrichtian time. The aim of this poster is to assess sedimentary changes laterally and over time. Sedimentary logs over an area of 16 x 30 km have been measured to correlate main bodies of sandstone and initiation of carbonate sedimentation. Siliciclastic deposits can be grouped into 4 facies: trough cross-bedded conglomerate, massive conglomerate, trough cross-bedded sandstone and horizontally bedded sandstone. They suggest that they were formed in a high energy, low sinuosity braided river system with significant topography and coarse sediment supply. Breaks in coarse sedimentation, characterized by paleosols and fluvial stromatolites, suggest episodic high-energy sedimentation and are consistent with semi-arid climate hypothesized for the Campanian. Above coarse Campanian sediments are Maastrichtian-aged thick marls and several-metre sandstone beds. Marl deposits indicate generally lower-energy conditions and contain dinosaur bones whereas sandy beds can be rich in dinosaur egg fragments and Microcodium associated with vegetation. Fine-grained carbonates and marls continue to the end of the Cretaceous. The presence of charophyte stems and gyrogonites, lack of desiccation cracks and medium gray colour with some preserved organic matter suggest lacustrine carbonates. Above and often interbedded with gray carbonate is mottled pink, yellow and cream limestone with roots, nodules and desiccation cracks interpreted to be marginal lacustrine to palustrine. The interbedded nature of these deposits suggests fluctuating water level controlling lacustrine/palustrine cycles and episodic high-energy clastic input. Relatively thin gray carbonate may mean perennial lakes were shorter-lived whereas palustrine conditions persisted over a longer time. The Tethys seaway existed in the area until Santonian time, but was closed by the Campanian due to the IberiaEurope collision creating a continental basin. Early stage of Pyrenean uplift and moderate topographic relief promoted fluvial deposition in the basin. Palaeocurrents and clast types will be assessed to differentiate among potential source mountains to the north (Montagne Noire), east (Massif de Mouthoumet) and/or south (Pyrenees). Over time, sediment transport energy decreased suggesting lower topography and, possibly, sufficient uplift to the south to confine lacustrine deposits. Infill logging next field season will attempt to define Campanian and Maastrichtian sediment sources, lake boundaries, dinosaur nesting areas and the transition to early Paleocene deposits.