Central Andean Basin Research Articles

Lower–Middle Ordovician brachiopods from the Eastern Cordillera of Peru: evidence of active faunal dispersal across Rheic and Iapetus oceans

AbstractNew Floian and early middle Darriwilian brachiopod assemblages of the San José Formation of the Eastern Cordillera of Peru are presented. A new genus and species, Apurimella santiagoi, and two new species, Phragmorthis henrylunae and Nocturnellia ashaninka, are described. The assemblages also contain additional characteristic taxa demonstrating links with other proto‐Andean localities (Peruvian Altiplano, Argentinian Eastern Cordillera, Famatina) as well as with some localities of Baltica (Estonia, Ingria, Norway), Ganderia (Anglesey, Tramore, Indian Bay, Summerford, Miramichi), peri‐Laurentia (Mayo, Svalbard) and Laurentia (Klamath Mountains). Those shared genera indicate dynamic faunal exchanges between the Peruvian Eastern Cordillera and these terranes during the Early–Middle Ordovician transition, suggesting active brachiopod dispersal mechanisms across the Rheic and Iapetus oceans. These connections seem to have still been active by the middle Darriwilian, as suggested by the presence of Phragmorthis in the Darriwilian assemblages of Cuyania and Laurentia. Similarly, the new Peruvian Nocturnellia species is of particular interest, given that this genus is likely to have originated in South China during the Floian, but extended its distribution to Avalonia and to high‐latitude peri‐Gondwana by the Dapingian. It thrived there until the middle Darriwilian, but by that time had also reached the proto‐Andean margin either via Avalonia across the Rheic Ocean or along the Gondwanan coast from high‐latitude settings. All of these occurrences improve our knowledge of Early–Middle Ordovician brachiopod faunas of the northern Central Andean Basin and their relationships with contemporaneous faunas worldwide.

Foraminiferal biostratigraphy of the Pennsylvanian Cerro Prieto Formation, Amotape Mountains, NW Peru: Correlation with the Central Andean basin

Carboniferous-Permian successions in the Amotape Mountains (NW Peru) are poorly dated due to the predominant siliciclastic intervals and the scarcity of fossils. The biostratigraphy of the formations is thus poorly constrained and, in general, limited to major systems or subsystems. The Cerro Prieto Formation was assigned to the Pennsylvanian or middle Pennsylvanian, but at the Caseta de la Antena section, the lower half of the formation contains carbonate horizons where diverse foraminiferal assemblages are recorded. Foraminifers allow to assign the base of the formation to the basal Bashkirian Stage, Morrowan Substage or Globivalvulina-Millerella Zone. This biostratigraphy can be extrapolated to the base of the Tarma Formation in central and south Peru, where this part of the latter formation remains undated. The upper limestone levels at Caseta de la Antena are assigned to the late Bashkirian, Atokan Substage or Eoschubertella-Pseudostaffella Zone. The upper half of the Cerro Prieto Formation, only composed of siliciclastics, might correspond to the uppermost late Bashkirian/lowermost Moscovian, or the mid-upper Atokan, due to fusulinids recorded at the top of the Tarma Formation. Foraminiferal assemblages are rather similar to those recorded from the lower part of the Copacabana Formation in Bolivia, although some differences occur, and apparently rather different from those in south Peru, a fact which suggests a slight biogeographic differentiation between the Amotape Mountains and the Central Andean Belt possibly related to its distinct geological setting.

New insights into the conodont biostratigraphy and paleobiogeography of the Katkoyeh Formation (Lower–Upper Ordovician) at the Katkoyeh Section, East-Central Iran

The Katkoyeh Formation comprises most of the Ordovician strata in the Kerman Province of East-Central Iran. However, determining its depositional timing remains challenging due to conflicting biostratigraphic ages, regional stratigraphic gaps, and tectonic complexities in the area. To enhance the understanding of the Katkoyeh Formation, a new conodont sampling was conducted at the Katkoyeh type section, which revealed 1,937 conodont elements belonging to 31 species of 26 genera. They allow the recognition of the Juanognathus variabilis Range Zone (middle–upper Floian) and the Icriodella superba Range Zone (Katian–?Hirnantian) in the Katkoyeh Formation, leading to better biostratigraphic and intercontinental correlations of the Ordovician strata in East-Central Iran with the Precordillera, the Famatina System, and the Central Andean Basin of northwestern Argentina, as well as with North American Midcontinent and North Atlantic basins, and South China. Moreover, the oral structure of Juanognathus variabilis Serpagli is reassessed based on the new Iranian records, recognizing 7 morphotypes in its apparatus structure, referred to the M, Pa, Pb, Sa, Sba, Sbb and Sc positions.

Ordovician chitinozoans and review on basin stratigraphy, biostratigraphy and paleobiogeography of northern Argentina along the Proto-Andean margin

Ordovician strata exposed across the Cordillera Oriental and the Sierras Subandinas in northwestern Argentina were part of a large retroarc foreland basin developed along the Proto-Andean margin within the Central Andes in South America. A revised chitinozoan biostratigraphy along and across-strike for the Tremadocian, Floian, Dapingian, Katian and Hirnantian stages, calibrated with other fossil groups in the basin, allow pinpointing the most characteristic events that affected the basin fill testing global versus local controls in accommodation, and suggesting comparisons with other peri-Gondwanan records. According to the chitinozoan data, the glacially-related Ordovician deposits in northwestern Argentina are restricted to the Hirnantian, and unconformably overlie late Katian deposits. In the Caspalá area (Cordillera Oriental), an interval with synsedimentary deformation and reworked chitinozoans correlate with glacially-related deposits in other sites of the eastern part of the basin (Río Capillas and Mecoyita areas). A glacial waning stage is determined by a thin interval of organic‐rich black shales with sparse dropstones at the top of the Zapla Formation, containing Spinachitina oulebsiri associated with Desmochitina gr. minor, which together are typical latest Hirnantian components in other regions of Gondwana. Our study strengthens the foreland systems tract for the Ordovician Central Andean Basin with a volcanically fed interarc and foredeep depozone to the west (Puna region); a lower-accommodation forebulge depozone in the central area (mostly the Cordillera Oriental region); and a backbulge depozone (Sierras Subandinas and Sierras de Santa Bárbara) extending as far as the eastern Paraná Basin (reaching Paraguay and Brazil). Contemporaneous unconformities driven by global sea-level fluctuations were amplified or reduced due to deepening-narrowing or widening-shallowing, allowing contrasted accommodation, respectively associated to loading and relaxation. Ordovician chitinozoans from the Central Andean Basin indicate Northern, Western and peri-Gondwanan affinities, although locally some more cosmopolitan species described in Baltica, Avalonia and South China, are also recorded.

Lower Tremadocian (Ordovician) lingulate brachiopods from the Central Andean Basin (NW Argentina) and their biogeographical links

Lower Tremadocian (Ordovician) lingulate brachiopods from the Central Andean Basin (NW Argentina) and their biogeographical links

The Central Andean Basin as a dispersal centre: Biogeographic patterns of olenid trilobites during the late Cambrian – Early Ordovician

The biogeographic histories of two cosmopolitan groups of Olenida: Hypermecaspididae and Parabolinella (Olenidae) are studied herein. Different biogeographical models were compared, and the results were discussed in a palaeogeographic and palaeoceanographic context. Dispersal pathways were proposed for both groups, identifying potential environmental factors that affected their distribution. Calibrated phylogenetic hypotheses for each taxon were used to compare different models of geographical evolution with R package BioGeoBEARS. Time-stratified analyses were carried out, using different distance matrices, for three intervals (Furongian, Early Ordovician and Middle Ordovician). Numbers and types of biogeographical events were estimated under the best-fitting models by using Biogeographic Stochastic Mapping (BSM). For both groups, the best-fit model incorporated jump dispersal, indicating that this was an important speciation strategy. Vicariance was unimportant for these trilobites, which would have been favoured by the stable conditions of their habitat. Ocean currents were key in the dispersal patterns of Parabolinella, but not in those of Hypermecaspididae. The main strategy used for both groups would have been “island hopping”, taking advantage of the microterranes and volcanic island arc chains surrounding Laurentia, Baltica, Avalonia, and Gondwana. Creeping also operated as a dispersal mechanism in Parabolinella. This genus originated in the late Miaolingian, when the more uniform sea conditions would have favoured its dispersal capabilities. On the other hand, Hypermecaspididae diversified mainly in the Early Ordovician, when cooling seas and changes in ocean circulation patterns generated more segmented habitats, affecting chances of dispersal, and favouring jump-founder events. Despite these differences, in both clades founder and dispersal events were more abundant from the western margin of Gondwana, which constituted an important dispersal centre during the Furongian and Early Ordovician.

Using Constrained Optimization (CONOP) to examine Ordovician graptolite distribution and richness from the Central Andean Basin and their comparison with additional data from North America and Baltoscandia

Ordovician graptolite fossils represent one of the first abundant, well-documented records of marine zooplankton. An accurate assessment of their stratigraphic ranges, biogeography, and taxon richness is crucial to studies on the Great Ordovician Biodiversity Event. Unfortunately, our understanding of graptolite richness from high paleo-latitudes is poor and recent work has demonstrated that many high paleo-latitude taxa are often misidentified endemic species. Hence, high paleo-latitude localities likely contain a hidden graptolite richness.This work uses CONOP9 to construct a range chart and correlation model from the graptolite occurrences at thirty-eight Ordovician stratigraphic sections from the Central Andean Basin of South America, and parts of Laurentia and Baltoscandia. Thirteen graptolite biozones spanning the early Tremadocian (Tr1)–middle Dapingian interval (Dp2) are identified. Some taxa in the Central Andean Basin composite exhibit unusual ranges and occur in biostratigraphically unexpected positions in the composite range chart. In order to examine the possible causes of these unusual ranges, sections from Baltica and Laurentia were added to the analyses. These additional data facilitated results that were more consistent with the generally accepted positions of certain taxon.The first raw taxon richness curve of graptolites from the Central Andean Basin obtained with CONOP9 shows a diversification phase in the early Floian that continues to a peak in the late early Floian. A second peak occurs at the beginning of the middle Floian. A decreasing trend is observed from the top of the Didymograptellus bifidus Biozone to the “Isograptus victoriae” Biozone. These results generally agree with the graptolite richness curves published for the same interval in Baltica, Australasia, and the Yangtze region of SW China, but differs from the patterns observed for the Jiagnan and Yiyang regions of SE China. The rarified regional taxon richness curve, obtained with CONOP64, is also in agreement with global curves previously proposed by different authors.

Palaeobiogeographic distribution of Silurian and Devonian bivalves in the Bolivian central Andean basin, western Gondwana

The palaeobiogeographic distribution of the Ludlow‒Přídolí and Devonian Bivalves in the Bolivian Central Andean Basin of Western Gondwana, has been established from the study of twenty-five genera, twenty-two of which are considered cosmopolitan and three endemics. Taking into account the total studied genera, seven correspond to Protobranchia, such as Praectenodonta, Praenucula, Notonucula, Nuculites, Palaeoneilo, Phestia and Solemya. The Autobranchia are diverse; representing the remaining eighteen genera and are represented by the groups Praecardiidae (Praecardium, Cardiola and Dualina), Ambonychiidae (Mytilarca), Pteriomorphia (Leptodesma (Leptodesma), Ptychopteria (Ptychopteria) and Ptychopteria (Actinopteria)), Pectinidae (Pseudaviculopecten), Heteroconchia (Pleurodapis, Cardiomorpha and Paracyclas), Grammysiidae (Grammysia, Andinodesma, Grammysioidea, Sanguinolites and Pholadella) and Modiomorphidae (Modiomorpha and Sphenotomorpha). Three dendrograms based on the Jaccard affinity coefficient, and three palaeogeographic maps were built, in three intervals of time: Ludlow to early Lochkovian, late Lochkovian to Emsian and Eifelian to Frasnian.The greatest affinity found in the Ludlow-early Lochkovian, in Central Andean Basin was with North Gondwana Basins (Florida and North African Basins) with 62% and with Nova Scotia (Canada) with 58%. During late Lochkovian to Emsian, the greatest affinity found was with South Africa and Paraná Basins with 65% and Uruguay with 40%. During Eifelian to Frasnian times, the affinities remained with South Africa with 74% and Paraná Basins with 73%, Laurentia kept 33% and Amazonas Basin with 24%. According to the distribution of Bivalves, the basin shows a strong influence of equatorial and low palaeolatitude fauna, especially during the Ludlow to the early Lochkovian and during the Eifelian to Frasnian. From this part of Gondwana, between the Ludlow‒Přídolí and the early Lochkovian, sixteen genera are studied throughout the basin, which thirteen are considered cosmopolitan and only three endemics (Notonucula, Pleurodapis and Andinodesma). In contrast, from late Lochkovian to Emsian, eleven cosmopolitan genera colonize a contracted basin, three of which are genera from equatorial palaeolatitude arriving to Western Gondwana in this period (Phestia, Solemya and Pholadella). During the interval from Eifelian to Frasnian, eighteen genera are registered, among which sixteen are cosmopolitan and only two endemics. Those endemic genera appear earlier in the basin (Notonucula and Pleurodapis). The Bivalves do not appear to have been dependent on temperatures or palaeolatitudes between Ludlow to Frasnian. Discussions about dispersal versus vicariant distributions were presented, and different palaeoenvironmental strategies developed by Bivalves were analyzed.

Estimating the body mass of the late pleistocene megafauna from the south America intertropical region and a new regression to estimate the body mass of extinct xenarthrans

The palaeobiogeographic distribution of the Ludlow‒Přídolí and Devonian Bivalves in the Bolivian Central Andean Basin of Western Gondwana, has been established from the study of twenty-five genera, twenty-two of which are considered cosmopolitan and three endemics. Taking into account the total studied genera, seven correspond to Protobranchia, such as Praectenodonta, Praenucula, Notonucula, Nuculites, Palaeoneilo, Phestia and Solemya. The Autobranchia are diverse; representing the remaining eighteen genera and are represented by the groups Praecardiidae (Praecardium, Cardiola and Dualina), Ambonychiidae (Mytilarca), Pteriomorphia (Leptodesma (Leptodesma), Ptychopteria (Ptychopteria) and Ptychopteria (Actinopteria)), Pectinidae (Pseudaviculopecten), Heteroconchia (Pleurodapis, Cardiomorpha and Paracyclas), Grammysiidae (Grammysia, Andinodesma, Grammysioidea, Sanguinolites and Pholadella) and Modiomorphidae (Modiomorpha and Sphenotomorpha). Three dendrograms based on the Jaccard affinity coefficient, and three palaeogeographic maps were built, in three intervals of time: Ludlow to early Lochkovian, late Lochkovian to Emsian and Eifelian to Frasnian.The greatest affinity found in the Ludlow-early Lochkovian, in Central Andean Basin was with North Gondwana Basins (Florida and North African Basins) with 62% and with Nova Scotia (Canada) with 58%. During late Lochkovian to Emsian, the greatest affinity found was with South Africa and Paraná Basins with 65% and Uruguay with 40%. During Eifelian to Frasnian times, the affinities remained with South Africa with 74% and Paraná Basins with 73%, Laurentia kept 33% and Amazonas Basin with 24%. According to the distribution of Bivalves, the basin shows a strong influence of equatorial and low palaeolatitude fauna, especially during the Ludlow to the early Lochkovian and during the Eifelian to Frasnian. From this part of Gondwana, between the Ludlow‒Přídolí and the early Lochkovian, sixteen genera are studied throughout the basin, which thirteen are considered cosmopolitan and only three endemics (Notonucula, Pleurodapis and Andinodesma). In contrast, from late Lochkovian to Emsian, eleven cosmopolitan genera colonize a contracted basin, three of which are genera from equatorial palaeolatitude arriving to Western Gondwana in this period (Phestia, Solemya and Pholadella). During the interval from Eifelian to Frasnian, eighteen genera are registered, among which sixteen are cosmopolitan and only two endemics. Those endemic genera appear earlier in the basin (Notonucula and Pleurodapis). The Bivalves do not appear to have been dependent on temperatures or palaeolatitudes between Ludlow to Frasnian. Discussions about dispersal versus vicariant distributions were presented, and different palaeoenvironmental strategies developed by Bivalves were analyzed.

The Central Andean Basin as a Dispersal Centre: Biogeographic Patterns of Olenid Trilobites During the Late Cambrian – Early Ordovician

The Central Andean Basin as a Dispersal Centre: Biogeographic Patterns of Olenid Trilobites During the Late Cambrian – Early Ordovician

Silurian and Devonian Heteroconchia Cardiomorphi Bivalves from Bolivia

Heteroconchia Cardiomorphi bivalves from Silurian and Devonian beds of the Central Andean Basin of Western Gondwana are herein presented. This paper is not only a systematic updated revision of three Heteroconchia Cardiomorphi genera, but it also includes the description of new findings and first reports of some taxa in the basin. They were collected in nine scattered outcrops in the Interandean and Subandean regions of Bolivia. A total of 22 specimens, well- to regularly-preserved was studied. The genus Pleurodapis, is reported for the first time from Ludlow–Pridoli successions of Alarache, southern Subandean as Pleurodapis sp. A. The cosmopolitan genus Paracyclas is reported in the Central Andean Basin for the first time, from the Middle Devonian of Subandean as Paracyclas? sp. The species Pleurodapis multicincta and Cardiomorpha oblonga, are described from the central Subandean and the Interandean regions for the first time in the basin. This research is also a contribution to understand the distribution and the richness of Silurian and Devonian bivalves in Central Andean Basin and their relations with the surrounding basins of Gondwana.

Thermal history of the Northwestern Argentina, Central Andean Basin, based on first-ever reported graptolite reflectance data

The thermal maturity from the Early Paleozoic strata in Northwestern Argentina was studied using reflected light microscopy and Rock-Eval analyses. The graptolites were collected from the Acoite and Lipeón formations, at the Los Colorados section, Cordillera Oriental, and the Huaytiquina, and Muñayoc sections, Puna highland, corresponding to the "Coquena" Formation and the Cochinoca-Escaya Magmatic-Sedimentary Complex. Rock-Eval parameters were unreliable due to the low TOC, S1, and S2 values. The Cordillera Oriental region sediments have low maturity based on low reflectance (%GRo= 0.63%–1.11%) and anisotropy of graptolites. In contrast, the higher graptolite reflectance of samples from the Muñayoc and Huaytiquina sections (%GRo= 5.57%–6.62%), in the Puna region, indicates considerably higher maturity. This could result from the combination of hydrothermal fluids with a temperature range from 336 °C to 358 °C, associated volcanism, and deformation related to tectonics events, which produced a higher geothermal gradient in the Puna. The Los Colorados section's thermal maturity modeling shows a better fit considering erosion episodes at the Late Paleozoic and Early Cenozoic. However, more studies about geothermal parameters and stratigraphy are necessary to corroborate these preliminary models and propose new approaches for the Puna region.

Silurian and Devonian Modiomorphidae Bivalves from Bolivia

Modiomorphid bivalves from the Silurian and Devonian beds of the Central Andean Basin of Western Gondwana are herein presented. This paper is not only a systematic updated revision of certain species of modiomorphids but also includes the description of newly found ones in Bolivia. They were collected from 17 scattered outcrops along Eastern Cordillera, Eastern Altiplano, Interandean, and Subandean regions of Bolivia. A total of 55 specimens, well- to regularly-preserved, were studied. The Sphenotomorpha orientalis new species from the Interandean of Mataral is described. The genus Sphenotomorpha is reported for the first time from Ludlowian layers of the Central Andean Basin with Sphenotomorpha sp. A. Other species described and systematically discussed are Modiomorpha concentrica, Modiomorpha cf. pimentana, Sphenotomorpha ulrichi and Sphenotomorpha cf. bodenbenderi? Forms classified as Modiomorphidae indet. A, B, and C are studied and some discussions about their previous and current taxonomic designations are herein presented. The biostratigraphic distribution of the two cosmopolitan genera, Sphenotomorpha, 1916, and Modiomorpha, 1869, is proposed. From the Eifelian to the Frasnian, endobyssal forms, such as Modiomorpha concentrica, coexisted with foot forms like Modiomorphidae indet. C and Sphenotomorpha sp. B, which would have developed a discreet byssus. This research contributes to the still inaccurately known Silurian and Devonian palaeogeography of the Central Andean Basin.

First Middle Ordovician conodont record related to key graptolites from the western Puna, Argentina: perspectives for an integrated biostratigraphy and correlation of the Central Andean Basin

Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindström) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.

Phragmolites (Gastropoda) from the Late Ordovician of the Peruvian Altiplano

AbstractPhragmolites lissoni new species is described from 11 specimens found in the Sandbian Calapuja Formation near Calapuja in Peru. The deposits are part of the Central Andean Basin. This is the hitherto only systematically described Ordovician gastropod from Peru. The species is from a brachiopod-dominated siliciclastic sequence and is associated with bryozoans. Most specimens are preserved as external molds, but latex casts yield excellent details of shell ornamentation and are used as a basis for evaluating this feature in the genus. The characteristic ornamentation of Phragmolites should be called corrugated lamellae, and the individual elements on these should be referred to as flutes. A descriptive terminology for these is suggested. The development and shape of the corrugated lamellae and flutes could be biomechanical process. A second component in lamellar formation is the alternation between regular incremental growth and formation of a lamella. Phragmolites is mainly found in shallow-water carbonate facies from tropical latitudes in the Sandbian and a mid-latitude presence in Peru is unexpected. Brachiopods from the same section in Calapuja show affinities with faunas of the Mediterranean margin of Gondwana but also weak links with Avalonia. Phragmolites is found abundantly in deeper-water facies in Laurentia, and a broad tolerance to facies and temperature and possible planktotrophy might have allowed a wide geographical dispersal of the genus. The scant record of Ordovician gastropods in the Central Andean Basin precludes comparison with the disparate record of the Ordovician gastropod taxa from the Precordillera, which do not include Phragmolites.UUID: http://zoobank.org/References/fbd7a43e-a610-42fd-a31d-b1a16fa69c9b

Stratigraphical distribution of the Ordovician graptolite Azygograptus Nicholson & Lapworth in the Central Andean Basin (northwestern Argentina and southern Bolivia)

We analyzed new occurrences of Azygograptus lapworthi from the Cordillera Oriental, Argentina. The bearer sandstones levels, corresponding to the Acoite Formation, are overlying the deposits, in which the Didymograptellus bifidus Biozone (Lower Ordovician, upper Floian, Fl3) was previously recognized, and are overlain by younger pelitic levels yielding Xiphograptus lofuensis (Middle Ordovician, early Dapingian, Dp2). Previous records from the Central Andean Basin are also reviewed in detail and accurately correlated, allowing us to conclude that the Azygograptuslapworthi Biozone corresponds to the Middle Ordovician (lower Dapingian, Dp1). This biostratigraphic framework documents that the transition between the Lower and Middle Ordovician deposits occurs in the uppermost levels of the Acoite Formation in the Argentine Cordillera Oriental. It is additionally integrated with up to date conodont records to establish a high-resolution regional correlation, with equivalent deposits from the Puna of northwestern Argentina and Cordillera Oriental of Bolivia, and to discuss new insights for global correlation.

Gyrophyllites cristinae isp. nov. from Lower Ordovician Shallow-Marine Deposits of Northwest Argentina

The lower Paleozoic marine siliciclastic succession of the Central Andean Basin, northwestern Argentina, provides a valuable record of the onset of the Great Ordovician Biodiversification Event in western Gondwana. A new ichnospecies of rosette trace fossil, Gyrophyllites cristinae, is documented from lower and upper Tremadocian (Tr1 and Tr2) deposits of this basin. It is characterized by five to six non-overlapping petaloid lobes and can be easily differentiated from the other four formally defined ichnospecies. Gyrophyllites cristinae occurs at the top of hummocky cross-stratified sandstone regularly interbedded with mudstone. These deposits are interpreted as reflecting the alternation of high-energy storm events and low-energy fair-weather conditions immediately below the fair-weather wave base, representing deposition in offshore transition environments. Gyrophyllites has been traditionally interpreted as the product of worms of uncertain taxonomic affinity that mined the sediment in search for food (fodinichnia). The occurrence of Gyrophyllites cristinae in these Ordovician deposits records post-storm colonization. Storms may have increased oxygenation and supplied fresh organic detritus that were exploited by worm-like, surface detritus- or shallow deposit-feeders exploring the uppermost silt-rich fine-grained sediments.

Broeggeria Walcott and other upper Cambrian and Tremadocian linguloid brachiopods from NW Argentina

The Broeggeria assemblage is a peculiar brachiopod association that has been recorded mainly from Tremadocian black shales of Baltoscandia, the Anglo‐Welsh Basin, Nova Scotia, South Urals and Kazakhstan. Here, we report a low diversity brachiopod association dominated by Broggeria omaguaca n. sp. from upper Tremadocian open‐shelf mudstones of northwestern Argentina. The dark‐grey transgressive muddy interval bearing the Broeggeria assemblage starts with an erosive flooding surface marked by a glauconite‐rich bed containing reworked bioclasts, which overlies storm‐dominated shoreface sandstones. Lithologic and taphonomic evidence indicates that the fauna from the mudstones represents a palaeocommunity inhabiting oxygen‐depleted bottoms. Besides Broeggeria omaguaca, which by far is the more abundant linguloid, the assemblage includes the obolids Palaeoglossa elongata (Harrington) and Libecoviella aff. tilcarensis Benedetto and Muñoz, and the punctate orthide Lipanorthis andinus Benedetto. Associated trilobites are abundant and low diversity, the more common being the large asaphid Asaphellus jujuanus Harrington. Coeval strata exposed in the Santa Victoria area contain rare specimens of Broeggeria omaguaca associated with Leptembolon argentinum Benedetto and Muñoz and Palaeoglossa elongata. Comparable dysoxic black shales of Furongian age bearing the olenid trilobite Parabolina (Neoparabolina) frequens have yielded a monospecific association of Lingulella n. sp. The records of Broeggeria at global scale support its late Cambrian origin in the Anglo‐Welsh Basin (Avalonia) and its rapid migration into the Karatau–Naryn terrane (a part of the Kazakhstanian collage). By the early Tremadocian, Broeggeria spread to Belgium and to the neighbouring Megumia terrane, migrating later (mid‐late Tremadocian) to Baltica, Southern Urals, Kazakhstanian terranes, Perunica and the Central Andean Basin. By the late Floian/early Dapingian, Broeggeria colonized palaeoequatorial deep shelves (Spitsbergen). Copyright © 2017 John Wiley & Sons, Ltd.

Plectorthoid brachiopods from the Lower Ordovician of north-western Argentina; phylogenetic relationships with Tarfaya Havlíček and the origin of heterorthids

The re-study of species previously attributed to the genus Nanorthis from the Tremadocian of north-western Argentina has led to the recognition of the new genera Gondwanorthis (type species Nanorthis calderensis Benedetto), to which the Iranian species Nanorthis bastamensis Ghobadi Pour, Kebriaee-Zadeh & Popov is also referred, and Lampazarorthis (type species Eoorthis bifurcata Harrington), which includes Nanorthis brachymyaria Benedetto and Lampazarorthis alata sp. nov. New extensive collections from the Cordillera Oriental support reassignment of the upper Tremadocian species Nanorthis purmamarcaensis to the genus Tarfaya. The species Nanorthis carinata Laurie, from Tasmania, is reassigned here to Tarfaya. According to the present taxonomic revision, Nanorthis is not cosmopolitan but is a pan-tropical genus, confined to Laurentia, the Laurentian-derived Precordillera terrane, and probably to Baltica, Siberia and Kazakhstanian terranes, whereas Gondwanorthis and Tarfaya are Gondwanan and peri-Gondwanan endemic taxa. Cladistic analysis of early orthoids, plectorthoids and dalmanelloids, including those recorded from mid to high latitude Gondwana successions, portrays Gondwanorthis and Lampazarorthis as a sister group basal to the tarfayid + heterorthid clade, whereas the South American and North African Incorthis appears as a basal member of this clade. Morphological and stratigraphical evidence provided in this study, along with the results of the cladistic analysis, supports the view that heterorthids could have arisen from the tarfayids by the end of Floian. The enlargement and incipient bilobation of the cardinal process in Tarfaya grandis leaves this species as a potential ancestor of Tissintia, which occurs in Darriwilian beds of the Central Andean Basin (Bolivia), but could have been present in this basin since the late Floian. We speculate that punctae in the Heterorthidae evolved independently from a Tarfaya-like ancestor, and that the transition from an impunctate to a punctate shell may have occurred repeatedly through rhynchonelliform evolution.http://zoobank.org/urn:lsid:zoobank.org:pub:FFE818F6-FA92-4B26-AE76-077617C3D9EA

The eoorthid brachiopod Apheoorthina in the Lower Ordovician of NW Argentina and the dispersal pathways between the Andean and Mediterranean regions of Gondwana

The eoorthid brachiopod Apheoorthina is reported for the first time from the Lower Ordovician of NW Argentina. It is represented by a species similar to A. ferrigena from the Tremadocian of the Prague Basin, increasing the faunal affinities between the Central Andean Basin and the South European microcontinents, in particular the Bohemian region (Perunica). Nine out of the fourteen brachiopod genera reported from the Tremadocian of the Central Andean Basin (~64%) are shared with the Mediterranean region, four of which (~28%) have been recorded in the Prague Basin, and two (Kvania and Apheoorthina) are restricted to the Central Andes and Perunica. Dispersal pathways around Gondwana are analyzed in the light of major factors affecting large-scale distribution of brachiopods (environment, larval capacity for dispersal, oceanic currents). The presence in Apheoorthina aff. ferrigena of a well-preserved larval protegulum measuring 420 μm in width and 210 μm in length strongly suggests that this species had planktotrophic larvae capable of long-distance dispersal. According to recent ocean-atmosphere general circulation models for the Ordovician Period, the Central Andean margin was dominated by the cold-water Antarctica Current. Despite the complex non-zonal pattern produced by current deflections around the peri-Gondwanan microcontinents, the general westward circulation sense favoured larval dispersal from the Andean region to North Africa, Avalonia, the Armorican Terrane Assemblage, and Perunica. On the other hand, the eastwards flowing Gondwana Current connected the North Gondwana waters with the South American epicontinental seas, which could explain the reversed migration of some brachiopods.