ARCHITECTURE OF FLUVIAL/AEOLIAN DEPOSITS IN THE AVILÉ MEMBER (HAUTERIVIAN), NORTHERN NEUQUÉN PROVINCE, ARGENTINA

VEIGA, G.D.; SPALLETTI, L.A.

Simposio; VII Symposium on Mesozoic Terrestrial Ecosystems; 1999

The Avilé Member is an up to 100 m-thick sandy and heterolitic unit that sharply intercalates between deep shelf marls and black shales of the Lower and Upper Members of the Agrio Formation. This Member is widely distributed all over the northern Neuquén Province and southern Mendoza, and was usually described as a continental unit product of a sudden sea level fall. In the Pampa de Tril region, the Avilé Member is 40 m thick and is composed of three sections. The lower section is characterised by amalgamated sets of planar and trough cross-bedded sandstones. Planar sets range from 1 to 6 m thick and are interpreted as aeolian dunes. Frequent intercalations of trough cross-bedded and minor plane-bedded sandstones represent wet (fluvial-dominated) interdunes. The middle section of the Avilé Member is composed of tabular-planar cross-bedded aeolian sandstones (up to 4 m thick). They are associated with massive and cross-laminated (climbing-rippled) sandstones that grade up to heterolitic intervals, interpreted as interdune deposits produced by fast and non-channelised floods. Lenticular sandstone bodies (1-2 m thick and 10 m wide) with sharp erosional lower boundaries and abundant mud-intraclasts, associated with tabular m-thick fine-grained intercalations, characterise the upper portion of this unit. These facies asociations represent fluvial channels incised on floodplain deposits. Both paleocurrent patterns and lateral accretion deposits suggest a high-sinuosity fluvial system. The facies and architectural analysis suggest a close interaction between aeolian and fluvial processes. The depositional environment was characterised by smooth topographies and semiarid conditions. The vertical arrangement of facies associations suggests the evolution from aeolian-dominated to fluvial-dominated depositional systems. Towards the top of the Avilé member, the development of a more permanent and evolved fluvial network indicates a slight palaeoclimatic change to more humid conditions.