Diego M. Guido

Equisetum thermale sp. nov. (Equisetales) from the Jurassic San Agustín hot spring deposit, Patagonia: Anatomy, paleoecology, and inferred paleoecophysiology

PREMISE OF THE STUDY Dated molecular phylogenies suggest a Cenozoic origin for the crown group of Equisetum. but compression fossil equisetaleans that are morphologically indistinguishable from extant Equisetum and recently discovered anatomically preserved examples strongly suggest an earlier Mesozoic initial diversification. METHODS In situ samples of Equisetum thermale sp. nov. from the Upper Jurassic San Agustín hot spring deposit were collected and studied with the use of polished blocks, thin sections, and light microscopy. KEY RESULTS Equisetum thermale exhibits all the morphological and anatomical characteristics of the extant crown group Equisetum. It shows a mixture of features present in the two extant subgenera, e.g., superficial stomata typical of subgenus Equisetum allied with infrequently ramifying stems typical of subgenus Hippochaete. This appears to ally E. thermale with the least derived extant species in the genus Equisetum bogotense (sister species to the two subgenera). Its association of hydromorphic and xeromorphic characters allowed it to grow as an emergent aquatic in physically and chemically stressed geothermally influenced wetlands, where it formed dense monospecific stands. Equisetum thermale, because it is preserved in situ with intact anatomy, provides clear paleoecological, biological, plus inferred paleoecophysiological evidence of adaptations known in extant species. CONCLUSIONS As the earliest unequivocal member of the genus, E. thermale supports the hypothesis of a Mesozoic origin. Its inferred tolerance of a similar range of stresses (e.g., high salinity, alkalinity, and heavy metal concentrations) to that seen in extant Equisetum suggests early evolution and subsequent maintenance of ecophysiological innovations in the genus.

Jurassic geothermal landscapes and fossil ecosystems at San Agustín, Patagonia, Argentina

Abstract: An extensive, well-preserved, Late Jurassic (c. 150 Ma) geothermal system at San Agustín farm in the Deseado Massif, Patagonia, Argentina, is described. This deposit, along with others previously known from the same region, partially fills a considerable gap between Cenozoic and scattered Palaeozoic hot spring localities reported worldwide. The San Agustín deposit is novel because it represents a large (1.4 km2) and nearly complete geothermal landscape. Siliceous hot spring facies, both subaerial and subaqueous, are exposed side by side in their original spatial and geological context, set amongst intrusive rhyolite domes and fluviolacustrine sediments. The Jurassic hot springs have preserved an entire local ecosystem containing microbes, arthropods, gastropods and plants exhibiting Lagerstätten-style preservation. Plant preservation, in particular, ranges from decayed litter, to seedling sprouts, and to dense stands in life orientation with intact anatomy. The San Agustín deposit shares some ecological, taphonomic and sedimentological characteristics with modern hot springs. As it formed in a pre-angiosperm world, it is akin to the famous hot spring-related Devonian Rhynie cherts of Scotland. It differs in having excellent exposure, and thus will probably contribute to a better understanding of biosignal preservation in extreme environments in the geological record.

Archean (3.33 Ga) microbe-sediment systems were diverse and flourished in a hydrothermal context

Interacting, diverse microbe-sediment systems exist in natural environments today but have not yet been recognized in the oldest records of life on Earth (older than 3.3 Ga) because of lack of distinctive biomarker molecules and patchy preservation of microbial paleocommunities. In an in-situ outcrop- to microbial-scale study, we have differentiated probable phototrophic, chemolithotrophic, and chemo-organotrophic fossil microbial signatures in a nearshore volcanogenic sedimentary setting in 3.33 Ga rocks of the Josefsdal Chert, Barberton greenstone belt, South Africa, while demonstrating the importance of contemporaneous hydrothermal activity. Hydrothermal fluids, as a nutrient source, strongly controlled the development and distribution of the microbial communities and, as a silicifying agent, contributed to their rapid fossilization. We thus show that intricate microbe-sediment systems are deep-rooted in time and that at least some early life may indeed have been thermophilic.

Jurassic hot-spring activity in a fluvial setting at La Marciana, Patagonia, Argentina

Silicified rocks at La Marciana farm, Deseado Massif, Argentinean Patagonia, represent an ancient hot-spring discharging into an active fluvial setting. Their fortuitous burial–erosion history and minimal post-depositional structural modification provide an unparalleled view of a complete, exhumed, late Jurassic geothermal landscape, and thus an opportunity to illuminate hot-spring geological context and palaeoenvironmental gradients. Geological mapping, stratigraphy and petrography revealed hydrothermal eruption events, the spring vent source, structural relationships, dimensions of the discharge apron, and hot-spring facies distributions. Remarkable similarities to Quaternary analogues from the Taupo Volcanic Zone, New Zealand, and Yellowstone National Park, USA, are apparent with respect to scale, spatial distribution of facies, and types of microbial and other palaeoenvironmentally significant fabrics.

FIRST REPORT OF FUNGI AND FUNGUS-LIKE ORGANISMS FROM MESOZOIC HOT SPRINGS

ABSTRACT Herein we provide the first report of the diversity of fungi and fungus-like organisms within a Mesozoic hot spring ecosystem. The Jurassic San Agustín hot spring deposit (Patagonia, Argentina), represents only the second known Phanerozoic hot spring ecosystem with an associated microflora and contains diverse, exceptionally preserved microorganisms. Preserved propagules include flask-shaped pycnidia produced by extant coelomycetes, shield-like and nearly round thyriothecia of extant Microthyriales in the ascomycetes, variously shaped spore-like bodies representing chytrid and chytrid-like zoosporangia and other life cycle forms, and additional fungal and fungus-like remains (spores, hyphal fragments, reproductive structures) of uncertain affinity. Many of these microorganisms are associated with variously decayed organic remains, most commonly of horsetails. This expands the fungal fossil record and provides a unique opportunity to learn about the biology of Mesozoic microorganisms.

A new metallogenical association (Sn-Cd-In-Zn-Ag-Au) in the Deseado auroargentiferous province, Deseado Massif, Patagonia, Argentina

A new metallogenical association (Sn-Cd-In-Zn-Ag-Au) is reported for the low sulphidation epithermal Deseado Auroargentiferous Province, in Patagonia, Argentina. The anomalous presence of Sn, Cd and In, together with anomalies of Zn and Ag, and also high contents of Cu, Mn, Pb, W and Bi in a complex sulphur-rich mineralogy, represent a new metallogenical association. This assemblage could be related to a higher temperature mineralization or a different type into the epithermal range. The presence of this new metallogenical association increases the mining potential of the region, extending exploration targets in this metallogenical province and must be considered during future exploration duties in the region.

Indium distribution and correlations in polymetallic veins from Pingüino deposit, Deseado Massif, Patagonia, Argentina

ABSTRACT The Pingüino deposit is characterized by the presence of indium-rich polymetallic vein mineralization representing an atypical epithermal occurrence for the low sulphidation epithermal mineralization from the Deseado Massif, Patagonia, Argentina. Polymetallic veins display high In, Zn, Pb, Ag, Cd, Au, As, Cu, Sn, W and Bi values represented by complex sulphide mineralogy. Mineralization developed in two main stages: a Cu-Au-In-As-Sn-W-Bi stage, and a Zn-Pb-Ag-In-Cd-Sb stage. Correlation coefficients are used to estimate the degree of inter-relation between metals concentrations in each stage and specifically to determinate the behaviour of indium. Indium concentrations show a wide range (3.4–1184 ppm In) and, based on the correlation coefficients of ore geochemistry, in the first stage indium is associated mainly with Sn, present in ferrokesterite and cassiterite, while the highest indium values are related to the late mineralization stage, closely associated with Zn and Cd and present in the Fe-rich sphalerite, the most important In-bearing mineral in the deposit.

First Glimpse of the Silicified Hot Spring Biota from a New Jurassic Chert Deposit in the Deseado Massif, Patagonia, Argentina

Abstract. Jurassic hot-spring chert deposits in the Deseado Massif, Patagonia, Argentina, have been known for over two decades, but the associated biota has only begun to be documented recently, and thus far only from a small number of localities. Here we report the discovery of a large complex of well-exposed Upper Jurassic epithermal siliceous deposits represented by organic-rich cherts preserved within the geothermal system from La Bajada, Santa Cruz, Argentina. The chert samples analyzed so far contain exceptionally well-preserved, in situ and transported, tri-dimensionally silicified plants, animals and microorganisms. Plants include equisetaleans (Equisetum thermale), ferns and gymnosperms. Among them, well-preserved in situ osmundaceous rhizomes in different developmental stages are the dominant component of the taphoflora. Conifers are represented by wood, seeds, leaves and pollen tentatively assigned to the families Araucariaceae and Cheirolepidiaceae. The assemblage also contains vegetative and reproductive structures of fungi, oomycetes, cyanobacteria, algae, testate amoebas, ciliates and numerous remains of unresolved taxonomic affinity. Microorganisms are preserved isolated in the chert matrix or directly associated with plants and other organic remains in mutualistic, parasitic and saprotrophic engagements. Also present are numerous coprolites and arthropod remains that, along with the named microorganisms, are indicative of trophic relationships in the ecosystem. Altogether, this fossil assemblage suggests that distal paleoenvironments within the geothermal system are preserved at La Bajada. The diversity, abundance, and exceptional preservation of fossils in the La Bajada ecosystem provides a unique window into the geological past that offers a substantial contribution to the reconstruction of middle Mesozoic terrestrial ecosystems.

Linkages between the southern Patagonia Pre-Permian basements: new insights from detrital zircons U-Pb SHRIMP ages from the Cerro Negro District

The Patagonian basement rocks are dominated by Precambrian to Early Paleozoic metamorphic rocks intruded by Paleozoic granitoids. Recently discovered basement rocks in the Cerro Negro District are characterized mainly by quartz-muscovite-chlorite schists; the metamorphic grade reaches greenschist facies (biotite-garnet grade) with a regional S1 schistosity subparallel to the original sedimentary structure S0 and a secondary non-penetrative S2 foliation. New detrital zircon U-Pb geochronology shows that maximum depositional ages for detrital zircons are Devonian, ages of 379 ± 4Ma. These results suggest that the Cerro Negro basement rocks are the youngest basement in the Deseado Massif, overlapping some detrital zircon ages in the eastern Andean Metamorphic Complex in the Andean region. Most of detrital zircons are igneous in origin with a major peak around ~396Ma, provably sourced from the Devonian granitoids of the Rio Deseado Complex (El Laurel and Bahia Laura granites) and equivalent northern Patagonia granitoids (e.g. Colan Conhue and Lago Lolog granites). Secondary peaks correspond to Ordovician to Silurian ages, being the Rio Deseado Complex and La Modesta Formation (and their igneous contributors) the possible sources of the zircons. The minor oldest peaks yield Cambrian-Neoproterozoic; Mesoproterozoic and Paleoproterozoic-Archean ages, evidencing a common source from the interior of Gondwana. The results provide new insights about the relationships between the pre-Permian metasedimentary rocks of the extra-Andean and Andean region during Mid-Paleozoic ages.

Millerocaulis zamunerae sp. nov. (Osmundaceae) from Jurassic, geothermally influenced, wetland environments of Patagonia, Argentina

Sagasti, A.J., García Massini, J., Escapa, I.H., Guido, D.M. & Channing, A., August 2016. Millerocaulis zamunerae sp. nov. (Osmundaceae) from Jurassic geothermally influenced wetland environments of Patagonia, Argentina. Alcheringa 40, xxx–xxx. ISSN 0311-5518 A new species of Millerocaulis Erasmus ex. Tidwell emend. Vera is defined based on several permineralized stems recovered from geothermally influenced chert deposits in the Middle–Late Jurassic La Matilde Formation (Santa Cruz, Argentina). Millerocaulis zamunerae sp. nov. is characterized by the presence of an ectophloic dictyoxylic siphonostele, inner parenchymatic and outer sclerotic cortices, homogeneous sclerotic ring in the petiole bases, two masses of sclerenchyma lining the concavity of the petiolar vascular bundle, petiolar inner cortex with sclerenchyma strands in the outermost petiole cycles and stipular wings having one large and several smaller sclerenchyma bundles. Millerocaulis zamunerae inhabited geothermal wetlands and other hot-spring-related sedimentary facies associated with the La Bajada epithermal deposit. Reference to active geothermal wetlands, analogous living plants and other fossil hot spring ecosystems suggest the plant’s tolerance of physico-chemical stressors including elevated temperature, pH, salinity and phytotoxic metals/metalloids. Millerocaulis zamunerae thrived in wetlands preserved in the Jurassic geothermal systems of Santa Cruz Province, the same kind of environment in which Equisetum thermale Channing et al. was recorded previously. Ana Julia Sagasti [anajusagasti@gmail.com] División Paleobotánica, Facultad de Ciencias Naturales y Museo. Becaria Doctoral Consejo Nacional de Investigaciones Científicas y Técnicas, Paseo del Bosque S/N B1900FWA La Plata, Buenos Aires, Argentina. Juan García Massini [massini112@yahoo.com.ar] Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET. Entre Ríos y Mendoza S/N, 5301 Anillaco, La Rioja Argentina. Ignacio H. Escapa [iescapa@mef.org.ar] Museo Paleontológico Egidio Feruglio, Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Fontana 140, U9100GYO, Trelew, Chubut, Argentina. Diego M. Guido [diegoguido@yahoo.com] Instituto de Recursos Minerales (INREMI), Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata. Consejo Nacional de Investigaciones Científicas y Técnicas. Calle 64 y 120, La Plata (1900), Argentina. Alan Channing [channinga@gmail.com] School of Earth & Ocean Sciences, Cardiff University, Cardiff CF10 3AT, UK.