The Miocene lacustrine carbonate factory of the Ñirihuau Formation, Ñirihuau Basin, North Patagonian Andes, Argentina

SANTONJA, C.; BENAVENTE, C.; SURIANO, J.; HEREDIA, A.; FORTUNATTI, N.; RAINOLDI, A.L.; KIETZMANN, D.A.; BECHIS, F.

The Depositional Record

Wiley

Año: 2024

2055-4877

Facies,microfacies and stable isotope analyses of limestone bedsin the northernmost Ñirihuau Basin, North Patagonian Andes, Argentina, documentand constrain the past hydrological, sedimentological and climate conditionsthat prevailed during the deposition of a lacustrine system between ca 15–13 Ma. This palaeoenvironment is recorded in the middle section of theÑirihuau Formation, which holds significance because: 1) it was depositedduring a transition from an extensional to a compressional tectonic regime; 2)it spans the Middle Miocene Climatic Optimum and the beginning of the MiddleMiocene Climatic Transition; and 3) it contains limestone beds interbedded withinan 600 m thick interval of mudstones and siltstones, along with intercalatedsandstone and volcaniclastic bodies. Two detailed sedimentary logs weresurveyed along the Arroyo Las Bayas, at the western and eastern flank of theDavid Syncline. Limestones from both stratigraphic sections were sampled aswell as isolated limestone beds from two other sites. One facies association wasdefined and interpreted as a perennial lake associated with a deltaic systemand dominated by detrital clastic material. It comprises Facies 1 (Marginallacustrine) and Facies 2 (Lower delta plain); in both, the presence ofgrainstones and calcimudstones stands out. Through petrography andcathodoluminescence studies of these continental carbonates, nine microfacieswere identified: a) Intraclastic grainstone, b) Homogeneous calcimudstone, c)Silty grainstone, d) Disrupted micrite, e) Birds-eye micrite, f) Bioclasticmudstone, g) Calcimudstone with sparse detrital grains, h) Fenestral micrite,i) Stromatolitic boundstone. These indicate mainly bio-induced subaqueouscarbonate precipitation and subordinate deposition by tractive flows withshort-distance transport on a littoral lacustrine environment. Most of thesemicrofacies exhibit very early diagenesis (eogenesis) effects. These features,and the geochemistry results, indicate that they were deposited in a palaeolakesystem under temperate to warm and humid conditions.