Abstract The Navidad district, Argentina, is an advanced exploration project with an estimated measured and indicated resource of 19,670 tons (t; 632 million ounces) Ag, 1.32 Mt Pb, and significant contents of Cu and Zn in eight separate to semicontinuous deposits. The mineralization is hosted by volcanic and sedimentary rock units of the Middle to Late Jurassic Cañadón Asfalto Formation and formed in an active continental rift environment. Navidad is an intermediate sulfidation epithermal silver deposit, which is located at the center of a northeast-trending belt of polymetallic deposits within the northern Patagonia Massif. The generally stratiform mineralization is localized within permeable horizons that are abruptly capped by impermeable units. The mineralization is zoned at the district scale about well-defined hydrothermal upflow zones defined by phreatic breccia and greater intensity of intermediate argillic alteration mineral assemblages. Proximal mineralization to the upflow zones is characterized by fine-grained, Ag- and Pb-bearing pyrite, complex sulfide textures, and Ag/Pb ratios as low as 6.6. Proximal mineralization precipitated due to rapid cooling of the hydrothermal solutions and by mixing between acid-sulfate and bicarbonate waters, as evidenced by the presence of hypogene kaolinite, alunite, barite, and abundant calcite. Distal deposits were formed following the lateral migration of hydrothermal fluids for as much as several kilometers from the central upflow zones. Distal mineralization is characterized by fine- to medium-grained sulfide mineralization with acanthite as the most important silverbearing mineral in a medium- to coarse-grained calcite-barite gangue. The Ag/Pb ratio for distal mineralization is as high as 187.8. No gold occurs within the Navidad deposits.

Abstract This review advances understanding of the palynostratigraphy of the Late Triassic–Early Jurassic by correlating the established palynozonations for the northern and southern hemispheres. Previous palynological studies have contributed greatly to our understanding of the biostratigraphy, paleoclimatology and paleogeography of the Upper Triassic. In general, palynology is a good tool for interregional cross-correlation of marine and non-marine successions because palynomorphs, unlike most of other fossils, commonly are present in continental and marine environments. Currently, however, biostratigraphical resolution based on Upper Triassic palynomorph assemblages is rather low, primarily because of the rarity of successions that are independently dated (i.e. via ammonoids, conodonts, isotopes, paleomagnetism) to correlate the palynomorph assemblages, but also for other reasons, such as microfloristic provincialism, palaeoenvironmental conditions and differential preservation of palynomorph assemblages. During the last few decades many palynological studies have attempted to integrate and improve the biostratigraphical correlations and paleoclimatologic reconstructions across the Triassic–Jurassic boundary. Several authors have recognized specific microfloral assemblages with well-defined and recognizable suites of palynomorphs that enhance the importance of palynomorphs in the definition of Triassic–Jurassic stages. Comparison of the palynomorph assemblages from different biostratigraphical stages demonstrates that a change occurred in the palynofloral composition of the Tethyan domain between the Carnian and the earliest Hettangian that was gradual and without abrupt changes.