MICROBIALITE SHIFTING FACIES: PALEO COASTAL DYNAMICS IN LATE CRETACEOUS LAGOON SYSTEM (YACORAITE FORMATION – NORTHWESTERN ARGENTINA)

FRÍAS-SABA, R.; ALONSO G.; VILLAFAÑE PATRICIO G.; GALLI, C.

La Plata

Congreso; XVIII Reunión Argentina de Sedimentología : IX Congreso Latinoamericano de Sedimentología.; 2023

Asocion Argentina de Sedimentologia

Microbialitic facies reported from Yacoraite Formation (Maastrichtian - Danian) in Maimará locality (Jujuy, Argentina), were developed in a shallow subtidal/lower intertidal environment associated to a lagoon system (Cónsole-Gonella et al., 2017). These facies exhibit diverse architectures, morphologies and structures associated to different paleoenvironmental conditions. The objective of this study is to determine the sedimentary dynamics and changes in the paleo-coastal line, as reflected in lithological facies and the potential recurrence of these changes. Using a multiscale analysis approach, we identified eight facies and three cycles. Cycle 1 is characterized by linked domes and clusters of up to four domes, vertically reaching 20 cm. Their morphology ranges from smooth to colloform, with the mesostructure that changes from continuous laminae to columnar structures. The initial portion of Cycle 2 consists of clusters of up to three domes, vertically reaching 15 cm, with smooth and colloform morphologies and columnar laminated structures. The latter part of Cycle 2 shows isolated domes and clusters of up to five domes, with vertical development up to 65 cm. The morphology and internal structure are colloform and columnar. Cycle 3 is marked by clusters of up to three domes, with vertical development up to 15 cm, exhibiting colloform morphology with columnar structures. The increase in vertical development of microbialites and the transition from smooth to colloform morphologies in Cycle 1 can be attributed to an energy decrease and increase in water depth. The shift from linked domes to clusters suggests greater horizontal accommodation space. The combination of mesostructure and morphologies indicates moderate to high hydrodynamic energy ranging from lower intertidal to upper subtidal environments. Subsequently, a retreat of the water body occurs, resulting in clusters with less vertical development (initial part of Cycle 2). Concurrent with the development of the latter part of Cycle 2, there is a pronounced increase in water depth and decrease in energy, allowing for the vertical growth of stromatolites up to 65 cm. The presence of isolated domes implies greater substrate availability compared to Cycle 1. The mesostructure and morphology in this cycle suggest moderate to high energy, spanning from lower intertidal to mid-subtidal environments. Finally, the development of colloform microbialites up to 15 cm height in Cycle 3 is associated to shallower water depths and moderate to low hydrodynamic energy. These microbialites thrive in lower intertidal to upper subtidal environments. The absence of isolated domes indicates a smaller horizontal accommodation space compared to Cycle 2.