Cecilia del Papa

The Corte Blanco garnetiferous tuff: A distinctive late Miocene marker bed in northwestern Argentina applied to magnetic polarity stratigraphy in the Río Yacones, Salta Province

Abstract We introduce the Corte Blanco Tuff, a white garnetiferous air fall unit, as a distinctive Neogene marker bed. Three whole-rock K/Ar ages from rocks at the source of this unit indicate that it was erupted 8.73 ± 0.25 Ma from the La Pava-Ramadas Caldera on the Argentine Puna. Ash spread eastward across the foreland provinces of the Eastern Cordillera and Sierras Subandinas. Recognition of this dated marker unit in these provinces provides the first, easily identified, late Miocene time line in the vast, densely vegetated region to the east of the Puna. We encountered the unit in seven localities from all three morphostructural provinces in NW Argentina. A depositional gap in the air fall material is present between 20 and 150 km to the east of the caldera. Recognition of the Corte Blanco Tuff in the Rio Yacones, near Salta, allowed an interpretation to be made of a magnetic polarity stratigraphy section erected in marginally suitable Neogene detrital strata of the Rio Guanaco Formation. We interpret the strata we examined to have been deposited between 10.5 and 6.4 Ma and report a 10° clockwise rotation since the strata were deposited. This is the first numerically dated section in the Rio Guanaco Formation of NW Argentina. These results reveal that uplift of the Eastern Cordillera was in progress at this time.

Gymnogeophagus eocenicus, n. sp. (Perciformes: Cichlidae), an Eocene Cichlid from the Lumbrera Formation in Argentina

ABSTRACT A new cichlid referable to the extant genus Gymnogeophagus is described from the Eocene Lumbrera Formation of the Salta Group, northwestern Argentina. †Gymnogeophagus eocenicus, n. sp., presents the synapomorphies that support the genus: absence of supraneurals and a presence of a forward spine in the first dorsal pterygiophore. The existence of an early to middle Eocene—aged species presenting the synapomorphies and the appearance of a modern genus requires the acceptance of an extensive differentiation from the basal cichlid lineages. Extant Gymnogeophagus species are restricted to the La Plata drainage and a few coastal drainages of southern Brazil and Uruguay. The occurrence of an Eocene fossil in the geographical area corresponding to the present distribution of the genus suggests the patterns of distribution and endemism of the Neotropical fish fauna have a very old history in the continent.

PROTEROCARA ARGENTINA, A NEW FOSSIL CICHLID FROM THE LUMBRERA FORMATION, EOCENE OF ARGENTINA

Abstract The Lumbrera Formation is the uppermost unit of the Santa Bárbara Subgroup of the Salta Group, exposed in northwestern Argentina. It consists of fine clastic sediments of characteristic brick red color with an intercalation of green mudstone levels, which are called Faja Verde. The specimen described here was collected from the middle part of the Faja Verde II at the Alemania locality in sediments dated as Eocene. The material comprises a specimen, preserved as part and counterpart, which is assigned to a new genus and species: Proterocara argentina, gen. et sp. nov. The phylogenetic analysis to establish its position within Cichlidae was based on a matrix with 51 taxa and 91 characters. The most parsimonious tree shows P. argentina as sister group of the clade formed by the subfamilies Cichlasomatinae and Geophaginae based on three characters: articulating process of premaxilla moderately distinct, first hemal arch on last abdominal vertebra, and 13–14 pectoral-fin rays. Two autapomorphies are recognized for P. argentina: ascending arm of premaxilla as long as dentigerous arm, and dorsal lateral line on caudal fin between caudal rays D2 and D3. Extant members of the family Cichlidae live mostly in lentic freshwater bodies, corroborating the lacustrine paleoenvironment assigned to this formation.

Sedimentation on a ramp type lake margin: Paleocene–Eocene Maı́z Gordo Formation, northwestern Argentina

Abstract The Maiz Gordo Formation was deposited in a sag basin during late Paleocene to early Eocene time and formed by rocks deposited in a lacustrine basin of mixed carbonate-clastic sedimentation. Percentages of carbonate rocks decrease from the inner lake zones to the margins. Several different subenvironments were identified which were either spatially related or occurred during a time of varied climatic conditions. The paleontologic record used as an environmental indicator reveals that the climate varied from arid conditions at the base of the sequence to more humid conditions toward the top. Temperatures were moderate to warm throughout. Sag basin formation was characterized by a slowly subsiding basin with low surrounding relief, which produced a lacustrine basin characterized by ramp margins with sedimentation of low/high energy type.

A new genus and species of Heroini (Perciformes: Cichlidae) from the early Eocene of southern South America

The Lumbrera Formation is the uppermost unit of the Salta Group, which crops out in northwestern Argentina. The paleoenvironment of the Lumbrera Formation is interpreted as a perennial lake deposited under temperate climatic conditions during the early to middle Eocene. Its fossil content is made up of palynomorphs, insects, crocodiles, turtles, lizards, and mammals, besides an ichthyofauna formed by cichlids, poeciliids and dipnoans. †Plesioheros chauliodus is described based on a single individual from this formation, which was fossilized as a lateral view impression (missing anal and caudal fins). It can be distinguished from other cichlids by a moderately deep body, enlarged anterior dentary teeth bearing subapical cusp, a low abdominal vertebral count (10), five canal openings in the dentary, and XI + 12 dorsal-fin rays. A phylogenetic analysis, using the matrix by Kullander (1998), recovered †Plesioheros within Heroini. This species was recovered most closely related to Australoheros and to the deep-bodied South American heroins. The occurrence of an Eocene Heroini, as well as of other cichlid lineages in the same stratigraphical level, is evidence of an ancient diversification in this family. This ancient age supports the hypothesis that the Cichlidae originated on Gondwana.

Fossil mammals of the Quebrada de los Colorados Formation (late middle Eocene) at the locality of La Poma, Salta Province, Argentina

Abstract An anatomical and taxonomic analysis of the mammalian record in the locality of La Poma in Salta Province, Argentina, is here presented. This record consists in two specimens exhumed in levels of the Quebrada de los Colorados Formation referred to the middle late Eocene. The first specimen is represented by a partial skull preserving mostly the rostrum and some dental pieces and was identified as a member of Leontiniidae, although it does not bear enough information for generic or specific determination. The second specimen is represented by more complete material, preserving much of the dentition. It was identified as a new species of the genus Pampahippus, traditionally included in the paraphyletic family Notohippidae. The leontiniid here studied presents several plesiomorphic features identified in other taxa of northwestern Argentina, and this material represents a new example of a pre-Deseadan basal morphotype within the family. Regarding the new species of Pampahippus, it shows clear signs of rising hypsodonty, representing the first case for a notoungulate lineage in the Paleogene of northwestern Argentina. http://www.zoobank.org/urn:lsid:zoobank.org:pub:45D87764-5B63-4487-BAAC-74F8D490AE18

A New Eocene Dasypodid with Caniniforms (Mammalia, Xenarthra, Cingulata) from Northwest Argentina

The aim of this work is to present a new genus and species of Dasypodidae from the Lumbrera Formation (“lower Lumbrera”), early-middle Eocene of Salta Province, northwest Argentina. The new taxon, documented by one specimen, consists of an incomplete skull and jaw with teeth housed in their alveoli, postcranial remains, and isolated osteoderms. Lumbreratherium oblitum, gen. et sp. nov., is characterized by heterodont dentition, with a caniniform as the first tooth, diastema between caniniform and first molariform, teeth with closed roots, and a peculiar morphology of the osteoderms. A phylogenetic analysis indicates that Lumbreratherium oblitum, gen. et sp. nov., and Pucatherium parvum belong to a monophyletic clade in a basal position within the Cingulata. The singularity of the morphological characteristics of these Paleogene armadillos of northwest Argentina reinforces the hypothesis of an intertropical origin of mammal clades different from those of the Paleogene in more austral regions of Argentina.

SEM and TEM evidence of mixed-layer illite-smectite formed by dissolution-crystallization processes in continental Paleogene sequences in northwestern Argentina

Abstract In the northernmost Calchaquí Valley (Salta, Argentina), the Paleogene continental sediments show a transition from smectite, at the top, to R3 I-S (>90% illite) through R1 I-S (65-80% illite), in contrast to the remaining sectors, containing smectite up to the bottom. Samples at the base of the succession were characterized by high-quality step-scan X-ray diffraction (XRD), scanning electron microscopy (SEM) and analytical high-resolution transmission electron microscopy (HRTEM). Analysis by SEM demonstrated dissolution of primary phases (feldspars, micas and quartz) and crystallization of illite, I-S and kaolinite. As this alteration is not pervasive, an intermediate fluid/rock ratio could be inferred. The lattice-fringe images of the samples from upper parts of the sequence show abundant I1-rich areas, whereas in the lower parts of the sequence, illite packets and I3 I-S coexist and compositions evolve towards muscovite (tetrahedral-charge increase, principally compensated by Mg-by- Al substitution in octahedral sites and by a slight decrease in Ca in interlayer sites). As burial temperatures were probably similar in all the samples, depth was not responsible for the illite formation at the bottom. The TEM textures suggest that illitization proceeded mainly by dissolution-crystallization. The active faults close to the northern Calchaquí Valley probably promoted the circulation of hot, deep fluids, favouring illitization.