Claudia J. del Río

TERTIARY MARINE MOLLUSCAN ASSEMBLAGES OF EASTERN PATAGONIA (ARGENTINA): A BIOSTRATIGRAPHIC ANALYSIS

Pectinids are the most abundant and widely distributed taxa in the Tertiary marine beds of Patagonia. Along with other very common molluscan species, they characterize five assemblages, from oldest to youngest: 1) the Oligocene Panopea sierrana– Parinomya patagonensis Assemblage; 2) the Late Oligocene–Early Miocene Jorgechlamys centralis–Reticulochlamys borjasensis Assemblage; 3) the Early Miocene Reticulochlamys zinsmeisteri–Struthiolarella patagoniensis–Pleuromeris cruzensis Assemblage; 4) the Early Miocene Pseudoportlandia glabra–Antimelatoma quemadensis Assemblage; and 5) the latest Early Miocene–earliest Middle Miocene Nodipecten sp.–Venericor abasolensis–Glycymerita camaronesia Assemblage. A brief analysis of the origin and composition of these Tertiary Patagonian molluscan faunas is provided. Striking compositional changes occurred through time, recorded mainly in the Late Paleocene, Late Eocene, Late Oligocene–Early Miocene, and Late Miocene.Abstract Pectinids are the most abundant and widely distributed taxa in the Tertiary marine beds of Patagonia. Along with other very common molluscan species, they characterize five assemblages, from oldest to youngest: 1) the Oligocene Panopea sierrana– Parinomya patagonensis Assemblage; 2) the Late Oligocene–Early Miocene Jorgechlamys centralis–Reticulochlamys borjasensis Assemblage; 3) the Early Miocene Reticulochlamys zinsmeisteri–Struthiolarella patagoniensis–Pleuromeris cruzensis Assemblage; 4) the Early Miocene Pseudoportlandia glabra–Antimelatoma quemadensis Assemblage; and 5) the latest Early Miocene–earliest Middle Miocene Nodipecten sp.–Venericor abasolensis–Glycymerita camaronesia Assemblage. A brief analysis of the origin and composition of these Tertiary Patagonian molluscan faunas is provided. Striking compositional changes occurred through time, recorded mainly in the Late Paleocene, Late Eocene, Late Oligocene–Early Miocene, and Late Miocene.

Nature and Origin of Spectacular Marine Miocene Shell Beds of Northeastern Patagonia (Argentina): Paleoecological and Bathymetric Significance

Abstract Biofacies and taphonomic analysis has allowed for the reconstruction of the paleoenvironmental history of accumulation of a series of spectacular mollusk-dominated shell-concentrations from the Puerto Madryn Formation and the benthic assemblages that inhabited the Miocene sea in northern Patagonia, Argentina. An upward-shallowing from open mid-shelf to more restricted shoreface-foreshore environments has been recognized. Transgressive, Maximum Highstand and Regressive phases are recognized based on the integrated approach of assemblages and lithofacies arrangement. Eleven mollusk-dominated fossil assemblages were defined and grouped into Associations A, B, and C. Transgressive and Maximum Highstand phases preserve three main shell beds that record an upwards change from dynamic to complete bypassing conditions. These were deposited in tidal current-dominated mid- and inner-shelf environments and belong within Association A. The top bedding surface records the maximum depth attained by the sea. The Regressive Phase is characterized by three upward-deepening cycles comprised of foreshore-shoreface sandbar deposits containing Association C. Sandbars are capped by environmentally condensed shell-beds of Association B and record deposition from the shoreface (wave-breaking zone) to mid-shelf environments, all above storm-wave base. Based on these fossil assemblages, seven benthic life associations can be identified. The deepest ones inhabited the mid-to-inner shelf and were represented by suspension-feeders from gravel-substrata swept by strong tidal currents and by suspension-feeders from lower energy firm bottoms. Lower shoreface sandy bottoms, close to fairweather wave base and affected by weak tidal currents, were inhabited by epifaunal suspension-feeders, whereas sandy bottoms close to the fairweather wave-breaking zone were characterized by semi-infaunal deposit feeders and suspension feeders. The shallowest living assemblages inhabited intertidal and foreshore settings and were represented by soft-bottom infaunal suspension feeders, as well as by firm bottom, vagile carnivorous and suspension-feeding epifauna.

Biotic interaction between spionid polychaetes and bouchardiid brachiopods: Paleoecological, taphonomic and evolutionary implications

Shells of Bouchardia rosea (Brachiopoda, Rhynchonelliformea) are abundant in Late Holocene death assemblages of the Ubatuba Bight, Brazil, SW Atlantic. This genus is also known from multiple localities in the Cenozoic fossil record of South America. A total of 1211 valves of B. rosea, 2086 shells of sympatric bivalve mollusks (14 nearshore localities ranging in depth from 0 to 30 m), 80 shells of Bouchardia zitteli, San Julián Formation, Paleogene, Argentina, and 135 shells of Bouchardia transplatina, Camacho Formation, Neogene, Uruguay were examined for bioerosion traces. All examined bouchardiid shells represent shallow-water, subtropical marine settings. Out of 1211 brachiopod shells of B. rosea, 1201 represent dead individuals. A total of 149 dead specimens displayed polychaete traces (Caulostrepsis). Live polychaetes were found inside Caulostrepsis borings in 10 life-collected brachiopods, indicating a syn-vivo interaction (Caulostrepsis traces in dead shells of B. rosea were always empty). The long and coiled peristomial palps, large chaetae on both sides of the 5th segment, and flanged pygidium found in the polychaetes are characteristic of the polychaete genus Polydora (Spionidae). The fact that 100% of the Caulostrepsis found in living brachiopods were still inhabited by the trace-making spionids, whereas none was found in dead hosts, implies active biotic interaction between the two living organisms rather than colonization of dead brachiopod shells. The absence of blisters, the lack of valve/site stereotypy, and the fact that tubes open only externally are all suggestive of a commensal relationship. These data document a new host group (bouchardiid rhynchonelliform brachiopods) with which spionids can interact (interestingly, spionid-infested sympatric bivalves have not been found in the study area despite extensive sampling). The syn-vivo interaction indicates that substantial bioerosion may occur when the host is alive. Thus, the presence of such bioerosion traces on fossil shells need not imply a prolonged post-mortem exposure of shells on the sea floor. Also, none of the Paleogene and Neogene Bouchardia species included any ichnological evidence for spionid infestation. This indicates that the Spionidae/ Bouchardia association may be geologically young, although the lack of older records may also reflect limited sampling and/or taphonomic biases.

The Maastrichtian – Danian at General Roca (Patagonia, Argentina): a reappraisal of the chronostratigraphy and biostratigraphy of a type locality

The Late Cretaceous – Early Paleogene succession exposed in the type area of the Roca Formation (General Roca, Rio Negro Province), has been sampled in detail. Analyses of the calcareous nannofossil assemblages indicate the Late Maastrichtian – Early Danian interval (CC26-NP4 zones; MARTINI 1971), which is the first proved evidence of the Late Maastrichtian in the mentioned type area. Moreover, the “Rocanense” invertebrate fauna has been placed in a high resolution biostratigraphic scheme based on the nannofossil zones, and three assemblages have been recognized.

Palaeontology of the Cerros Bayos section, Roca Formation (Danian), La Pampa Province, Argentina

del Río, C.J., Martínez, S.A., Stilwell, J.D. & Concheyro, A., September, 2007. Palaeontology of the Cerros Bayos section, Roca Formation (Danian), La Pampa Province, Argentina. Alcheringa 31, 241-269. ISSN 0311-5518. New mollusc and echinoid faunas are recorded from exposures of the Roca Formation at Cerros Bayos (La Pampa Province) and assigned to the Maastrichtian – Danian (CC26 – NP3 Zones of Martini 1971) on the basis of the associated nannofossil assemblages. The macroinvertebrate assemblages show increased diversity and abundance of molluscs from Zones NP1 to NP3. One new Danian echinoid, the spatangoid Bolbaster argentinensis sp. nov., is described. At least 19 molluscan genera are recognized; 14 of these, together with seven species, are identified for the first time from Danian exposures of La Pampa Province. An equivocal record of Pyropsis tumida Wilckens, 1905 may extend the range of this tudiclid gastropod from the latest Cretaceous into the Danian. The Cerros Bayos exposures substantially increase our knowledge of diversity trends and biotic recovery immediately following the Cretaceous – Paleogene boundary event, and provide clues to the composition of the little-studied earliest Paleogene faunas in southern Patagonia. Claudia J. del Río [cdelrio@macn.gov.ar], Museo Argentino de Ciencias Naturales B. Rivadavia, CONICET, A. Gallardo 470-C1405DJR Buenos Aires, Argentina; Sergio A. Martínez [smart@fcien.edu.uy], Instituto de Geología y Paleontología. Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay; Jeffrey D. Stilwell [jeffrey.stilwell@sci.monash.edu.au], School of Geosciences, Monash University, Clayton VIC 3800, Australia; Andrea Concheyro [andrea@gl.fcen.uba.ar], Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II. 1428 Buenos Aires, CONICET and Instituto Antártico Argentino, Argentina; received 25.11.2005, revised 8.9.2006.

THE FAMILY VOLUTIDAE (MOLLUSCA–GASTROPODA) IN THE TERTIARY OF PATAGONIA (ARGENTINA)

Abstract Volutes are widely distributed in the Cenozoic record of Patagonia and Tierra del Fuego, where they are represented by the South American endemic genera Adelomelon Dall, 1906, Pachycymbiola Ihering, 1907, Odontocymbiola Clench and Turner, 1964, and Miomelon Dall, 1907. These taxa have been restricted to the southwestern Atlantic and southeastern Pacific Oceans from Tertiary times to the Recent, and since their earliest record in the ?Middle Eocene–Late Oligocene–earliest Miocene they have evolved adaptations to variations in water depth and temperature. These ecological adaptations were less marked for Adelomelon and Pachycymbiola, which have achieved a similar geographical pattern since the Tertiary, but they were strongly modified in Miomelon. In the Atlantic, Miomelon migrated southwards from the shallow and warm-temperate waters that it typically inhabited during the Tertiary, to deeper, colder waters of the Recent Magellanic Province and Subantarctic region, where it is restricted at present. A detailed discussion of the validity of Tertiary genus Proscaphella Ihering, 1907 herein concludes it to be a synonym of Miomelon Dall, 1907. Seven species are redescribed and illustrated: Adelomelon pilsbryi (Ihering), A. cannada (Ihering), A. (Pachycymbiola) ameghinoi Ihering, ?Pachycymbiola feruglioi (Doello Jurado), Miomelon gracilior (Ihering), M. dorbignyana (Philippi), and M. petersoni (Ortmann); and four new ones are described: Miomelon castilloensis, Pachycymbiola chenquensis, P. camachoi, and P. arriolensis.

REVISION OF THE LARGE NEOGENE PECTINIDS (MOLLUSCA: BIVALVIA) OF EASTERN SANTA CRUZ AND CHUBUT PROVINCES (PATAGONIA: ARGENTINA)

The systematic position of endemic Early Miocene pectinid taxa of Patagonia contained in the uppermost horizons of the San Julián and Monte León formations and in the basal and middle beds of the Chenque Formation is revised. Two new genera are proposed: Reticulochlamys new genus with R. proximus (Ihering) as its type species and Jorgechlamys new genus with J. juliana (Ihering) as its type species. Two new species are described: Reticulochlamys zinsmeisteri new species from the Monte León Formation and Reticulochlamys borjasensis new species from the Chenque Formation.Abstract The systematic position of endemic Early Miocene pectinid taxa of Patagonia contained in the uppermost horizons of the San Julian and Monte Leon formations and in the basal and middle beds of the Chenque Formation is revised. Two new genera are proposed: Reticulochlamys new genus with R. proximus (Ihering) as its type species and Jorgechlamys new genus with J. juliana (Ihering) as its type species. Two new species are described: Reticulochlamys zinsmeisteri new species from the Monte Leon Formation and Reticulochlamys borjasensis new species from the Chenque Formation.

IHERINGINUCULA, A NEW GENUS OF THE FAMILY NUCULIDAE (MOLLUSCA: BIVALVIA) FROM THE TERTIARY OF PATAGONIA (ARGENTINA)

ABsTcr-Iheringinucula, a new Tertiary genus of the family Nuculidae, is proposed. This taxon is known only from the Patagonian region (Argentina), and its range is from the late Eocene to the early Miocene. Two species are known: Iheringinucula tricesima (Ihering) from the Monte Le6n Formation (upper Oligocene-lower Miocene) and Iheringinucula crassirugata new species from the San Julian Formation (upper Eocene-lower Oligocene?) and the Monte Le6n Formation.

The genus Swiftopecten Hertlein, 1936, (Bivalvia: Pectinidae) in the Tertiary of southern South America

The presence of Swiftopecten Hertlein, 1936, in Patagonia (Argentina), a region situated in the southeastern extreme of the South American continent, is the oldest and southernmost fossil record of the genus. Furthermore, its occurrence during the Late Eocene in the circum-Antarctic region suggests that its origin was in the Southern Hemisphere; it has been known from Japan and the eastern Pacific, ranging from Miocene to Holocene (Moore, 1984). Swiftopecten iheringii new species, from the Late Eocene-Early Miocene sedimentary sequence of Patagonia, is described and illustrated.

A new Early Miocene species of Ophiocrossota (Ophiuroidea) from Southern Patagonia, Argentina

The first South American species of Ophiocrossota CLARK, 1928, O. kollembergorum n. sp., is described, extending the known geographical range of the genus to Argentina. The new species is characterized by its large radial shields, proximally in contact within, but separated distally by the triangular plates, and by its large and elongate oral shields, that cover most of the interradial area. Zusammenfassung: Die erste sudamerikanische Art von Ophiocrossota CLARK, 1928 wird be- schrieben, und ihre bekannte geografische Verbreitung damit bis nach Argentinien ausgedehnt. Die neue Art zeichnet sich aus durch ihre grossen Radialschilde, welche proximal in Kontakt, aber distal durch die dreieckigen Platten abgetrennt liegen und durch ihre grossen und langlichen Mundschilde, welche die Interradialflache beinahe ganz bedecken.