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

ALONSO MURUAGA, PABLO J.; GARCÍA-LÓPEZ, DANIEL A.; MADOZZO JAÉN, CAROLINA; ARMELLA, MATÍAS A.

Corrientes

Workshop; 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 beds that record sedimentation in a variety of lacustrine environments, mainly developed in intermountain valleys in the Northwestern Pampean 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, provides an opportunity to document microbially induced wrinkle structures and explore their palaeoecological affinities. These structures are preserved in sandstones and-siltstones layers interbedded with limestones, occurring on the upper bedding planes or at the lower surfaces of the beds. The study samples are characterized by the arrangement of linear to sinuously curved, frequently bifurcated ridges, usually 1 mm high and 2-1 mm wide, separated by parallel depressions and locally resembling small scale interference ripples. This pattern is classified as typical Kinneyia wrinkle structure. The development of these structures in the bedding planes is related to microbial activity, and its identification allows unlocking palaeoenvironmental parameters that indicate microbial colonization in a moist substrate and quiet water conditions in subaqueous settings, probably associated to littoral areas of ephemeral lakes. In addition, the recognition of microbial colonization brings paleoecological 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 facilitate exploration of other paleontological and biological signatures in ancient lake deposits.