Sedimentary architecture of an ancient linear megadune (Barremian, Neuquén Basin): insights into the long-term development and evolution of aeolian linear bedforms

Abstract

Linear aeolian bedforms are the most abundant bedform type in modern Earth sand seas and are very common in our Solar System. Despite their abundance, the long-term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood. The aims of this paper are to study the exposed record of an ancient linear megadune in order to discuss the factors that impact the development and sedimentary architecture of aeolian linear bedforms. The outcrops of the ancient Troncoso Sand Sea (Barremian, Neuquen Basin, Argentina) provide a unique opportunity to access a preserved megadune record with an external body geometry that unequivocally confirms its linear morphology. Architectural analysis of the bedform record reveals significant differences for several aspects of cross-stratified set bodies and bounding surfaces and allows for the identification of three architectural complexes. Insights from deterministic models, analysis of set body relative chronology and distribution suggest that complexes result from distinctive phases in bedform development. It also clearly shows that the megadune’s construction was achieved by expansion from a core, where the oldest deposits are located, and that its development was characterized by sustained growth and strong longitudinal dynamics. Factors that impact the development and architecture of linear bedforms are identified, discussed, and compared to bedforms of transverse dynamics. Finally, a scheme of expected styles of sedimentary architecture for linear bedforms is presented. This case study shows how growth can be a critical factor conditioning linear bedform architecture and indicates how the preservation of certain styles of sedimentary architecture in the geological record may not be as unusual as previously thought.