The sedimentology, paleoenvironment, and diagenesis of the Asencio Formation of Western Uruguay

Grutas del Palacio and other related Upper Cretaceous continental deposits (SW Uruguay): main sedimentary features and evidence for an old flooded forest

“…For Morrás et al (2010) the columns are composed of ferruginous tongues and the caves would be the result of selective water erosion of the sandstones. Other authors interpreted the column-like structures either as large ferruginized paleorhizospheres (Genise et al, 2011), or as consequence of intense pedogenetic processes (Turner et al, 2017).…”

“…However, the insect nest remnants were so abundant (Frenguelli, 1946;Genise and Bown, 1996) that the rock resembled a monomictic conglomerate (Ford, 1988a), the clasts being hardened insect nests. Today, this stratigraphic unit is considered a local equivalent of the upper part of the Asencio Formation (Palacio Member; Turner et al, 2017;Veroslavsky et al, 2019;this work). Pazos et al (1998) and Alonso-Zarza et al (2011), on the other hand, limited the Asencio Formation to the Palacio Member, while for Morrás et al (2010) part of the Asencio Formation would be due to geochemical weathering of the sandstones of the Mercedes Formation.…”

“…This was probably because of a pedogenetic evolution in a hot and wet tropical climate with a tendency towards monosialitization, i.e., kaolinization processes, so the ferrified crusts were probably generated by a slow process of lateral migration of ferriferous solutions from higher to lower levels. It has been proposed that the ferricretes affecting the Asencio Formation developed over tens of thousands of years in an environment with a mean temperature of 18 ºC and approximate 1,500 mm (per year and square meter) of precipitation for every single stage of generation (Turner et al, 2017). The upper horizons of the Asencio Formation undergone ferrallitization, which would have been generated by metasomatic replacement mechanisms of calcium carbonate to iron oxides due to iron-rich water from the phreatic levels.…”

“…Although new interpretations on the origin of the column-like geoforms of the Asencio Formation have been proposed (e.g., Morrás et al, 2010;Alonso-Zarza et al, 2011;Genise et al, 2011;Turner et al, 2017), a clear and definitive explanation is not forthcoming yet. Some explanations for the ferrification episodes giving rise to pisoliths are available (Veroslavsky and Martínez, 1996;Martínez et al, 2001Martínez et al, , 2015Martínez and Veroslavsky, 2003;Kraus and Hasiotis, 2006;Tófalo and Morrás, 2009;Morrás et al, 2010;Tófalo and Pazos, 2010).…”