Claudia V. Rubinstein

Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana)

• The advent of embryophytes (land plants) is among the most important evolutionary breakthroughs in Earth history. It irreversibly changed climates and biogeochemical processes on a global scale; it allowed all eukaryotic terrestrial life to evolve and to invade nearly all continental environments. Before this work, the earliest unequivocal embryophyte traces were late Darriwilian (late Middle Ordovician; c. 463-461 million yr ago (Ma)) cryptospores from Saudi Arabia and from the Czech Republic (western Gondwana). • Here, we processed Dapingian (early Middle Ordovician, c. 473-471 Ma) palynological samples from Argentina (eastern Gondwana). • We discovered a diverse cryptospore assemblage, including naked and envelope-enclosed monads and tetrads, representing five genera. • Our discovery reinforces the earlier suggestion that embryophytes first evolved in Gondwana. It indicates that the terrestrialization of plants might have begun in the eastern part of Gondwana. The diversity of the Dapingian assemblage implies an earlier, Early Ordovician or even Cambrian, origin of embryophytes. Dapingian to Aeronian (Early Silurian) cryptospore assemblages are similar, suggesting that the rate of embryophyte evolution was extremely slow during the first c. 35-45 million yr of their diversification. The Argentinean cryptospores predate other cryptospore occurrences by c. 8-12 million yr, and are currently the earliest evidence of plants on land.

Miospore assemblages from the Silurian–Devonian boundary, in borehole A1-61, Ghadamis Basin, Libya

Abstract Well preserved and diversified miospore assemblages have been recorded from a relatively continuous sequence in borehole A1-61 which spans the Silurian–Devonian boundary in the northwestern part of the Ghadamis Basin, Libya. The sequence is represented by early Devonian Lochkovian beds of the Tadrart Formation that transgress onto the Silurian Ludlow-Pridoli beds of the upper part of the ‘Alternances Argilo-greseuses’ Formation. The present work demonstrates a succession of miospore assemblages from closely sampled layers that have been stratigraphically dated as Ludlow–middle Pridoli and early Lochkovian by chitinozoans and acritarchs. Over 80 species of cryptospores and trilete spores have been identified. Modified detailed morphological interpretations are given. The miospore assemblages are correlated with miospore zonation schemes established for the type sequences of the Welsh Borderland, and those previously described from Libya. Early occurrences of some species as Streelispora newportensis on the western Gondwana plate, are put forward by comparison with the Old Red Sandstone continent. Phytogeographic and palaeobotanic implications based on these observations are discussed.

THE ACRITARCH GENUS VERYHACHIUM DEUNFF 1954: TAXONOMIC EVALUATION AND FIRST APPEARANCE

Abstract Veryhachium Deunff 1954, originally described from the Ordovician of western France, is one of the most frequently recorded acritarch genera. Over 250 species and subspecies, from the Cambrian to the Neogene, have been attributed to the genus. This genus has a simple morphology; it displays a triangular, rectangular, or polygonal central vesicle, with a few, simple processes drawn out from the angles of the vesicle in a single plane, and sometimes with supplementary or auxillary processes arising from the vesicle body. Veryhachium has been emended and revised numerous times. The number of valid species is excessive: most are probably synonyms. To facilitate effective classification, only a few morphological categories should be retained. For the Lower Paleozoic, the use of two informal groups is proposed. These are the Veryhachium trispinosum group for triangular specimens, and the Veryhachium lairdii group for rectangular forms. Although generally abundant and widespread throughout the Phanerozoic, Veryhachium is of limited biostratigraphic, paleoecologic, or paleogeo-graphic value. However, its First Appearance Datum (FAD) is of great importance for Ordovician stratigraphy; the first Veryhachium morphotypes appear in the Tremadocian Stage, making the genus an important biostratigraphic marker.

Lochkovian (Early Devonian) acritarchs and prasinophytes from the Solimões Basin, northwestern Brazil

Eighteen core samples from PETROBRAS well 1-JD-1-AM, comprising the upper part of the Jutai Formation, Jandiatuba area, Solimoes Basin, northwestern Brazil, have been studied for marine microphytoplankton. Forty-seven taxa of acritarchs and prasinophytes have been identified. The presence of Demorhethium lappaceum, Duvernaysphaera actinota, Riculasphaera fissa, Thysanoprobolus polykion, Winwaloeusia distracta, ?Cymatiosphaera florida, and numerous Schizocystia spp., among others, suggests a Lochkovian age for the assemblage. Moreover, the occurrence of Polyedryxium fragosulum and Pterospermella chiquitina indicates a possible late Lochkovian age, in agreement with previous age determinations based on chitinozoans and miospores. The significance of Schizocystia as a biostratigraphic marker for the beginning of the Devonian in Gondwana is discussed. The Solimoes Basin assemblage shows close compositional similarity with coeval assemblages from North America, north Gondwana, and the peri-Gondwana region.

NEW BIOSTRATIGRAPHIC PROPOSAL FOR THE LOWER PALAEOZOIC TUCUNUCO GROUP (SAN JUAN PRECORDILLERA, ARGENTINA) BASED ON MARINE AND TERRESTRIAL PALYNOMORPHS

Abstract. This is an exhaustive analysis of the palynomorph assemblages, organic-walled marine phytoplankton and miospores from the Tucunuco Group. This group includes the La Chilca and Los Espejos formations and is exposed in the Central Precordillera of San Juan. Four localities were included in this study, i.e., Río Jáchal, Río de las Chacritas, Cerro La Chilca and Quebrada Ancha. Previous data concerning several fossil groups, such as graptolites, conodonts and brachiopods, suggest a mainly Llandovery—Wenlock? age for the La Chilca Formation and a Wenlock to locally Lochkovian age for the Los Espejos Formation. Marine palynomorphs are predominant in the two formations in all the studied sections. Although terrestrial palynomorphs are the minor component, trilete spores are abundant, diverse and biostatigraphically relevant in the Los Espejos Formation. Correlations using marine palynomorph assemblages and miospore biozones recognized worldwide allow constraining the age of the two stratigraphic units. Based on marine phytoplankton, the middle—upper part of the La Chilca Formation is assigned to the Wenlock. In the Los Espejos Formation, palynomorph assemblages allow the recognition, from the base to the top, of the Wenlock with doubts, the Ludlow, and the Pridolí. The Lochkovian has been documented exclusively in the northern part of the basin. This confirms the presence of the Silurian/Devonian boundary in the upper part of the Los Espejos Formation. A north-south correlation panel of the studied sections is presented.

Upper Silurian miospores from the Precordillera Basin, Argentina: biostratigraphic, palaeonvironmental and palaeogeographic implications

This study is concentrated on Ludlow (to Pridoli?) miospores from the Los Espejos Formation at the Quebrada Ancha locality, Central Precordillera, San Juan Province, Argentina. The Ludlow age is in agreement with the age based on acritarchs. The assemblage of continental palynomorphs is composed of 43 miospore species (29 trilete spores and 14 cryptospores). A new synonymy is proposed: Chelinospora poecilomorpha is here considered a junior synonym of Clivosispora verrucata . In addition, specimens belonging to C. verrucata var. verrucata and C. verrucata var. convoluta are included in a new morphon. This study represents the second Late Silurian miospore assemblage described from South America; the first was from the Urubu River, Amazon Basin, northern Brazil. The Quebrada Ancha assemblages allow a reasonably good correlation with biozones established for the Upper Silurian from the Cantabrian Mountains, northern Spain. The dendrogram analysis between coeval miospore assemblages from different localities shows a strong palaeogeographic affinity with the miospores recovered from northern Brazil and North Africa. Miospore assemblages from Spain show influences from Baltica and North Africa, demonstrating their intermediate position between these two continental plates. Conversely, dissimilarities recognized between Libya and Tunisia are most probably owing to local ecology and/or environmental conditions.

Tremadocian acritarchs from northwestern Argentina

Abstract A Tremadocian acritarch assemblage is described from the Santa Rosita Formation, Cordillera Oriental, Salta Province, northwestern Argentina. The microplankton corresponds to trilobite-bearing strata assigned to the lower to upper Tremadocian from the middle part of the Santa Rosita Formation. The 26 acritarch species comprising the assemblage (six identified to species, ten identified as cf. and ten left in open nomenclature) are poorly preserved and not very abundant. Nevertheless, the assemblage appears to be related to the Mediterranean Paleoprovince located along the periphery of Gondwanaland, and thus represents a high paleolatitudinal microplankton assemblage.

Early Devonian organic-walled phytoplankton and miospores from the Precordillera Basin of San Juan, Argentina: biostratigraphic and paleobiogeographic implications

ABSTRACT The palynological assemblages of the Talacasto and Punta Negra formations, from the Argentinean Precordillera, were analysed. Marine phytoplankton is dominant in both stratigraphic units. ?Cymatiosphaera florida, Evittia sommeri, Palacanthus ledanoisii, Riculasphaera fissa, Schizocystia pilosa, Tysanoprobolus polykion and Winwaloeusia distracta are among the most age-significant phytoplankton species of the Talacasto Formation, while Amicosporites sp. cf. A. streelii, Dictyotriletes emsiensis Morphon, Dictyotriletes favosus and ?Knoxisporites riondae prove the most biostratigraphically significant miospore species. A Lochkovian to probably late Pragian age is interpreted based on the marine and terrestrial palynomorphs. The lower part of the Punta Negra Formation contains phytoplankton species such as Cordobesia oriental, Cordobesia uruguayensis, Duvernaysphaera stellata, Navifusa bacilla, Polyedryxium fragosulum and Pterospermella sp. cf. P. pernambucensis as well as the miospores Acinosporites sp. cf. A. lindlarensis and Apiculatasporites microconus, which suggests an early Emsian age. Taxa such as Cordobesia, Schizocystia and Winwaloeusia support affinities of the Argentinean assemblages with Gondwana.

The palaeobiogeographical spread of the acritarch Veryhachium in the Early and Middle Ordovician and its impact on biostratigraphical applications

The genus Veryhachium Deunff, 1954, is one of the most frequently documented acritarch genera, being recorded from the Early Ordovician to the Neogene. Detailed investigations show that Veryhachium species first appeared near the South Pole in the earliest part of the Tremadocian (Early Ordovician). The genus was present at high palaeolatitudes (generally>60° S) on the Gondwanan margin during the Tremadocian before spreading to lower palaeolatitudes on the Gondwanan margin and other palaeocontinents (Avalonia and Baltica) during the Floian. It became cosmopolitan in the Middle and Late Ordovician. Although useful for distinguishing Ordovician from Cambrian strata, the diachronous first appearance data of Veryhachium morphotypes mean that they should be used with caution for long-distance correlation.

EARLY DEVONIAN MARINE AND TERRESTRIAL PALYNOMORPHS FROM THE CHACOPARANÁ BASIN, URUGUAY --- Preprint doi:10.5710/AMGH.15.12.2017.3164

Abstract. Fragmentary anuran remains in the Ameghino Collection in the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” were recently considered as belonging in Ceratophryidae (the clade of the South American horned frogs) and coming from middle—late Oligocene sediments exposed south of Lake Colhue Huapi, Chubut, Argentina. However, both the taxonomic placement and the geographic and stratigraphic origin attributed to this material are problematic. A new study of these remains show they possess several features that allow their attribution to the extant genus Ceratophrys Wied-Neuwied. The available information on the collection locality of this material is dubious —namely Gran Barranca, where rocks range from the middle Eocene to early Miocene in age. Additionally, details of the history of this collection and the specimen itself suggest that its provenance should better be considered unknown.The Neogene sedimentary basins from the Colombian Pacific coasts were formed in forearc basins associated with the uplift of the Andes. Some marine sequences in this area remain unexplored and lack of biostratigraphic information. In addition, the available high-resolution biostratigraphic and biochronologic data from this region are limited almost exclusively to research in the open sea by the Integrated Ocean Drilling Programs (IODP). Ladrilleros-Juanchaco section is a continuous and well-exposed marine terrigenous sedimentary sequence with abundant Miocene microfossils. In this section, we carried out biostratigraphic and biochronologic studies through calcareous nannofossils, planktonic foraminifera, and diatoms identifying seventeen astronomically calibrated and standard calcareous microfossil biohorizons and two tropical diatom biozones. This information allowed the establishment of a chronologic framework between the Base of Praeorbulina glomerosa and Catinaster coalitus Base, corresponding to 16.27 and 10.79 Ma, respectively (Burdigalian–Tortonian). Low-latitude planktonic foraminifera and calcareous nannofossil bioevents show a high correlation, whereas variations between diatom biozones and calcareous nannofossil biohorizons were observed since the lowest occurrence of diatoms at ~12.2 Ma. Furthermore, using an interpolated age between the Sphenolithus heteromorphus Top and Fohsella praefohsi Base bioevents, it is interpreted that the Reticulofenestra pseudoumbilicus (>7μm) Base common took place around 13.6 Ma, which is correlated with other sites revealing that it can be considered as a good bioevent for the base of the Serravallian in these tropical areas.