Depositional architecture of a wave-dominated clastic shoreline (Pilmatué Member, Argentina): Linking dynamics and stratigraphic record of bartrough systems

ISLA, MANUEL F.; CORONEL M.D.; SCHWARZ E.; VEIGA G.D.

MARINE AND PETROLEUM GEOLOGY

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2020

0264-8172

Bar-trough morphologies are almost ubiquitous within wave-dominated clastic shorelines. Despite these barred configurations have been widely described, mostly by GPR-based and core studies on recent environments, there still exist some uncertainties about their interpretation in the ancient record. The lack of detailed outcrop-based approaches clarifying the facies distribution and architecture of the record of bar-trough configuration causes inconsistences on reconstructing the morphology of recent and deep time clastic shorelines. Existing facies models for wave- and storm-dominated clastic shorelines have some limitations regarding the morphological interpretation of ancient systems and it is common to fall in a simplification about the dominant processes and transport dynamics. One of the most poorly understood aspects about bar-trough settings is just the necessary conditions for bar generation and preservation. This work presents a detailed characterization and interpretation of the sedimentary record of an ancient bar-trough morphology. This was achieved through the analysis of nearshore (i.e. upper-shoreface and foreshore) deposits corresponding to a particular parasequence in the Lower Cretaceous Pilmatué Member of the Agrio Formation (Neuquén Basin, Argentina). A high-resolution facial and architectural analysis was performed combining detailed sedimentary logs with mapping of bounding and internal surfaces. Results led to interpret those deposits as a bar-trough configuration mainly composed of large-scale trough cross-bedded sandstones as the result of longshore currents exerting a strong influence over the sediment transport and distributing large amounts of sediment along the shore. The thorough analysis of nearshore deposits from different points of view led to reconstruct not just the dominant processes for transport and deposition, but also to incorporate aspects about the short- to- mid-term evolution of these prograding systems. The evolution model proposed for bar-trough clastic shorelines successions relate the lack of bar-related deposits with major storms and shoreline erosional processes.