MICROBIALLY INDUCED WRINKLE STRUCTURES IN ANCIENT LAKE DEPOSITS: AN EXAMPLE FROM THE MIOCENE RIO SALÍ FORMATION, TUCUMAN, ARGENTINA

ALONSO MURUAGA, P.J.; GARCÍA-LÓPEZ, D.A.; MADOZZO JAÉN, C. ; ARMELLA, M.A.

Corrientes

Simposio; III Simposio del Mioceno-Pleistoceno del Centro y Norte de Argentina; 2015

The Río Salí Formation (Choromoro Group, middle Miocene) consists of fine-grained clastic, carbonatic, and evaporitic bedsthat record sedimentation in a variety of lacustrine environments, mainly developed in intermountain valleys in the NorthwesternPampean Ranges of the Tucumán Province. The lower member of this unit, composed of fine-grained sandstones,mudstones, and limestones together with local occurrence of stromatolites deposited in an open lacustrine setting, providesan opportunity to document microbially induced wrinkle structures and explore their paleoecological affinities. Thesestructures are preserved in sandstone and siltstones layers interbedded with limestones, occurring on the upper beddingplanes or at the lower surfaces of the beds. The study samples are characterized by the arrangement of linear to sinuouslycurved, frequently bifurcated ridges, usually 1 mm high and 2-1 mm wide, separated by parallel depressions and locally resemblingsmall scale interference ripples. This pattern is classified as typical Kinneyia wrinkle structure. The development ofthese structures in the bedding planes is related to microbial activity, and its identification allows unlocking paleoenvironmentalparameters that indicate microbial colonization in a moist substrate and quiet water conditions in subaqueoussettings, probably associated to littoral areas of ephemeral lakes. In addition, the recognition of microbial colonization bringspaleoecological information, particularly on the food web, given the participation of microbial communities in the primary productivity.Understanding the paleoecological parameters that controlled the formation of these structures may facilitateexploration of other paleontological and biological signatures in ancient lake deposits.