Search

Omission surfaces represent a gap in the sedimentary record on a particular environment, constituting an important tool for basin analyses. Nevertheless, not always these surfaces constitute key sequence-stratigraphic surfaces, and their correct interpretation is highly important for the recognition of genetically related strata. Documentation and interpretation of ichnological data from stratigraphic surface can refine the sedimentological model. The Puesto El Moro Formation (lower Upper Cretaceous) in the Austral-Magallanes Basin, southern Patagonia (Argentina), shows excellent examples of several omission surfaces stacked during a transgressive context associated with the beginning of the foreland stage. Each of these surfaces, interpreted as Tidal Ravinement Surfaces, contain Thalassinoides isp. and Sinusichnus isp., which represent opportunistic colonization by crustaceans into a predominantly firm substrate. In this case study, the vertical recurrence of substrate-controlled trace fossil suites is the result of high-frequency repeated coastal conditions during the transgression; the associated surfaces, which have limited lateral extension, have low potential for correlation at basin scale. [ABSTRACT FROM AUTHOR]

Tracksites representing early human occupation are rare in South America. However, they have been reported in association with mammal and bird tracks from two coastal sites in Buenos Aires Province, Argentina. Both sites are reported in separate papers in this volume. In this paper a brief summary of the better known site is given on the basis of published information and the author's observations. [ABSTRACT FROM AUTHOR]

The Upper Miocene-Lower Pliocene Río Negro Formation (Río Negro Province, Argentina) contains diverse and abundant continental trace fossils. The purpose of this contribution is to recognize distinctive trace fossil assemblages in interdune lakes as response to lake expansion and contraction. The interdune deposits host 23 invertebrate, vertebrate, and plant ichnotaxa that are linked to the hydrological dynamics of the lake. During lake expansion a highly diverse subaqueous trace fossil assemblage reflects an infaunal bivalve population living in a littoral zone with swampy vegetation and semiaquatic mammals. The trace fossil assemblage recorded during Lake Highstand is less diverse and mostly linked to bivalve-generated trace fossils reflecting resting, locomotion, and escape/equilibrium behaviour (comparable to the Mermia ichnofacies). The assemblage during lake contraction exhibits high ichnodiversity and is dominated by vertebrate trace fossils reflecting foraging activities of shorebirds, cursorial birds, and herding semiaquatic mammals and ground sloths frequenting water holes. Flat sandy areas with moist substrates marginal to the interdune lake displayed a moderate ichnodiversity and its distinctive components were armadillo meniscate burrows and footprints in cross-section, as well as subvertical calcareous root casts. Neogene interdune lacustrine deposits reflect a particular zonation of trace fossils in response to changing physical conditions. [ABSTRACT FROM AUTHOR]

This paper contains a taxonomic study of the Permian tetrapod ichnofauna from the Carapacha Basin. Tetrapod traces are analyzed in their environmental context and compared with similar faunas from Europe and North America. This ichnofauna is particularly relevant because of the scarcity of Permian tetrapod tracks from South America and also of Permian tetrapod fossils from Argentina. Ephemeral fluvial and shallow lacustrine deposits compose the sedimentary succession of the basin, which is represented by the Carapacha Formation. Most of the tracks have been collected from the upper member of the formation (Urre-Lauquen Member), mainly from freshwater ephemeral lake deposits as well as from playa-lake mudflats. The deposits of this member have been attributed to the early Late Permian on the basis of a Glossopteris fossil flora. Ichnotaxonomic designations of tetrapod traces are made on the basis of morphologic features that reflect the anatomy of the producer and special attention has been paid to extramorphologic deformations observed in the track assemblage. A total of four footprint ichnotaxa have been recognized, namely Batrachichnus salamandroides (Geinitz, 1861), Hyloidichnus bifurcatus Gilmore, 1927, cf. Amphisauropus isp. and cf. Varanopus isp. These track taxa are associated with two forms of vertebrate swimming traces ( Characichnos isp. and type A swimming trace) and a possible fish trail. Invertebrate trace fossils include abundant arthropod locomotion traces and Scoyenia isp. The ichnofauna is composed of six tetrapod ichnocoenoses that are dominated by tiny amphibian tracks attributed to Temnospondyli ( Batrachichnus and type A swimming trace) and Seymouriamorpha ( Amphisauropus ), and also contain the footprints of small reptiles, mostly Captorhinomorpha and possibly Pelycosauria ( Hyloidichnus and Varanopus ). Even if the ichnofauna of the Carapacha Basin is slightly younger than typical examples from the literature of the Early Permian "red bed ichnofacies" (Hunt et al., 1995b), a comparison is made. However, further detailed case studies are needed to formally define this "red bed ichnofacies" and its prospective subdivisions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This contribution reviews the worldwide record of canid and canid-like (creodont and hyaenid) fossil footprints, the taxonomy of this type of footprints, and reports a new record of canid footprints from the late Pleistocene Pehuen Co site of southern Buenos Aires province, Argentina. On the basis of the comparison of proposed ichnogenera and features of modern canid and felid footprints, a set of ichnogeneric and ichnospecific taxobases are proposed. The ichnotaxonomic review includes Bestiopeda Vialov, 1965; Canipeda Panin and Avram, 1962; Felipeda Panin and Avram, 1962; Pehuencoichnum Aramayo and Manera de Bianco, 1987b; Creodontipus Santamaría et al. 1989–1990; Tetrastoibopus Sarjeant and Langston, 1994; and Quiritipes Sarjeant et al. 2002. A key to discriminate these ichnotaxa is also proposed and the diagnosis of Canipeda emended. The new findings of canid footprints from Pehuen Co are indistinguishable from Pehuencoichnum gracilis Aramayo and Manera de Bianco, 1987b, and this ichnospecies is synonymized under Canipeda gracilis (Vialov, 1965). An emended diagnosis for C. gracilis is proposed. The most likely producer of C. gracilis from Pehuen Co is a medium-sized fox similar to the extant representatives of Lycalopex. [ABSTRACT FROM AUTHOR]

We describe intergradations between the arthropod repichnial trace fossilsDiplichnites gouldi(Gevers et al., 1971),DendroidichnitesDemathieu et al., 1992, andMonomorphichnusCrimes, 1970 with two distinct cubichnial traces,Gluckstadtella cooperiSavage, 1971 andHuilmuichnus santracruzensisnew ichnogenus and ichnospecies. These compound ichnofossils are part of high ichnodiversity arthropod-dominated trace fossil associations from the Late Carboniferous Agua Escondida Formation of the San Rafael Basin (Argentina). The complex ichnotaxonomy ofDiplichnitesand the ichnospeciesD.gouldiare discussed and some possible working solutions are proposed. The most likely producer of the compound trace fossils are the Pygocephalomorpha, a group of Late Paleozoic crustaceans that are recorded in nearby basins from Uruguay and Brazil. The compound trace fossils are used to infer a number of complex behaviors of pygocephalomorphs in a subaqueous setting, including caridoid (tail flip) or more primitive escape reactions, landing followed by resting and transient resting during normal walking. In addition, different gaits can be inferred from well-preservedD.gouldi, which can be correlated with contrasting trackway morphology. [ABSTRACT FROM AUTHOR]

Different traces occur on fossil bones and teeth coming from the Early Miocene Gaiman Formation (Patagonia, Argentina). Most traces were attributed to the action of terrestrial and marine predators and scavengers. However, other traces on bones and teeth from this unit and one tooth from the Eocene La Meseta Formation (Antarctica) are attributed to chemical corrosion by lichens in recent times, that is, in a very late diagenetic time. The living lichens and calcium oxalate deposits occurring on the traces and their particular pattern indicates that they were not produced by vegetal roots. The lichens include reproductive structures which allowed a proper determination. A kind of corrosion pattern (Type 1) on bones and teeth from Patagonia is associated to Sarcogyne orbicularis Korber, Verrucaria sp. Schrad, and Buellia aff. punctiformis (Hoff.) Massal. The lichen Aspicilia aff. aquatica produced rounded holes on an Antarctic tooth (Type 2). On the same tooth, the epilithic lichen Caloplaca sp. Th. Fries did not leave any kind of mark on the enameloid. [ABSTRACT FROM AUTHOR]

Coprinisphaera is one of the most common trace fossils in South American paleosols from the Eocene to the Recent. Nevertheless, an ichnotaxonomical review of this ichnogenus has been lacking until now. The revision of hundreds of specimens of Coprinisphaera from numerous formations in Argentina, Uruguay and Ecuador has resulted in the recognition of two ichnogenera. One of them, Coprinisphaera, includes isolated, spherical, subspherical, pear-shaped and bispherical structures grouped in five ichnospecies: C. ecuadoriensis Sauer, C. murguiai (Roselli), C. kraglievichi (Roselli), C. tonni isp. n., and C. kheprii isp. n. The new ichnogenus and ichnospecies, Quirogaichnus coniunctus, consists of Coprinisphaera-like structures clustered in a common excavated chamber. The ichnotaxobases for the taxonomical arrangement of Coprinisphaera are mostly related to the presence and position of a small chamber (interpreted as the original egg chamber) with respect to a large chamber (provision chamber) and emergence hole. The egg chamber may be included in (1) the provision chamber, leaving no remains in the trace fossils and resulting in cylindrical emergence holes; (2) the wall of the provision chamber, without additional structures; and (3) a mamillate to spherical additional structure, external to the provision chamber, resulting in pear-shaped to bispherical trace fossils. [ABSTRACT FROM AUTHOR]

A new ichnospecies of Arthrophycus Hall 1852, A. minimus , is described from Upper Cambrian-Lower Tremadocian, shallow-marine strata of northwest Argentina. This new ichnospecies consists of small, long, regularly annulated hypichnial elements displaying subcircular to squarish cross-section and a ventral median groove. Side branches are occasionally present, but palmate, fan-like structures and scribbling patterns are absent. We adopt a relatively narrow diagnosis of Arthrophycus , suggesting that roughly annulated, cylindrical structures should not be included in this ichnogenus, unless other diagnostic features (i.e., squarish cross-section, median groove, zipper-like annulations) are also present. Arthrophycus is a common ichnotaxon in Ordovician-Silurian shallow-marine siliciclastic environments. Post-Paleozoic occurrences are removed from Arthrophycus . Arthrophycus has been proposed as a biostratigraphic index fossil in Ordovician-Silurian rocks. The presence of A. minimus in the Santa Rosita Formation of northwest Argentina indicates that Arthrophycus ranges at least from the Upper Cambrian-Lower Tremadocian with probable representatives in the Lower Cambrian and, therefore, its biostratigraphic utility is extended. Arthrophycus minimus represents the first Cambrian occurrence exhibiting not only fine, diagnostic morphologic features, but also the classical Arthrophycus behavioral pattern in dense monoichnospecific assemblages. The exploratory behavioral pattern displayed by A. minimus is simpler than that of the younger ichnospecies, particularly A. brogniartii, A. alleghaniensis, and A. lateralis . This is consistent with the basal position of A. minimus within the arthrophycid lineage. [ABSTRACT FROM AUTHOR]