COMPARATIVE GENESIS OF BIOCONCRETIONS: PALEOENVIRONMENTAL IMPLICATIONS. The aim of this study is to describe and morphogenetically and environmentally compare bioconcretions found in a continental environment at Quequén Salado with those found in a coastal environment at Playa Chica; both localities are in Buenos Aires Province. The first section —on the bank of the Quequén Salado river— is a 1.80 m thick bed of a late Pleistocene—Holocene siltstone with a sand to clay grain-size. These bioconcretions reach up to 25 cm long and variable diameters ranging from 1 to 5 cm. They are vertically oriented with ascending branches and associated with frustules of freshwater diatoms. The second analyzed profile is located at Playa Chica, on the northern shores of the Río Negro. The 2.40 m thick layer with bioconcretions is divided into 5 to 10 cm with subhorizontally laminated rhythmite-like beds at very low angle. The BC are yellowish to dark-reddish brown in color, subcircular, well-consolidated, accompanied by marine to brackish-water diatoms, euryhaline ostracods and foraminifera. Regarding the origin of the bioconcretions it was possible to establish that the Quequén Salado concretions were originated in a seasonally flooded, fluvial environment dominated by groundwater fluctuations. The Playa Chica bioconcretion deposits show wet periods with a stable water table. The sequence of several bioconcretion layers with successive growth is evidence of changing conditions with flooding and drainage of marine water levels in the basin, within a period of increasing aridity.

VERTEBRATE TAPHONOMY OF UPPER CRETACEOUS VERTEBRATES FROM THE LONCOCHE FORMATION IN CALMU-CO (MENDOZA, ARGENTINA): PALEOENVIRONMENTAL AND PALEOGEOGRAPHICAL IMPLICATIONS. This paper presents a taphonomic study of vertebrate fossils from the Loncoche Formation (late Campanian—early Maastrichtian) found in the Calmu-Co area in Mendoza, Argentina. Four environmental stages were recognized in this site, (1) saline lacustrine systems; (2) fluvial systems; (3) deltaic systems; (4) shallow fluvial and lacustrine systems. The vertebrates found in the deltaic environment comprise disarticulated parautochthonous—allochthonous concentrations (taphofacies 1) of fishes (Chondrichthyes, Teleostei, Lepisosteidae and Ceratodontidae), turtles (Chelidae), dinosaurs (Titanosauria) and plesiosaurs (Plesiosauria). The disarticulated and fragmentary feature of these mixed concentrations (terrestrial, freshwater, marine) suggest a mixture of remains from littoral environments and fluvial systems. The above interpretation is based on the taphonomic attributes of these concentrations, which showed a high degree of weathering, abrasion and time-averaging. On the other hand, disarticulated parautochthonous concentrations (taphofacies 2) of dinosaurs were registered in the fluvial environment. These remains showed processes of fragmentation and abrasion due to hydraulic transport. Fossil-diagenetic processes include events of permineralization and cementation of vascular canals and fractures, phenomena of deformation and lithostatic compression. These evidences indicate that the Atlantic marine ingression (Maastrichtian—Paleocene) which covered northern Patagonia, spread until Calmu-Co, in the western Neuquén Basin.

REVIEW OF THE PALEOFLORA OF THE NESTARES FORMATION (EARLY JURASSIC), NEUQUÉN AND RÍO NEGRO PROVINCES, ARGENTINA. In this contribution the paleoflora of the Nestares Formation, exposed along both banks of the Limay River, close to the Alicurá dam (northwest of the Northpatagonian Massif) was reviewed. A sedimentological profile was measured, four fossil-bearing levels were identified and the systematic study allowed the identification of 18 taxa, 12 of which were previously described for this site= Neocalamites carrerei (Zeiller) Halle, Marattia muensteri (Goeppert) Zeiller, Goeppertella diazii Arrondo and Petriella, Kurtziana brandmayri Frenguelli, K. cacheutensis (Kurtz) Frenguelli, Taeniopteris sp., Otozamites albosaxatilis Herbst, O. ameghinoi Kurtz, O. bechei Brongniart, O. hislopii (Oldham) Feistmantel, Ptilophyllum acutifolium Morris in Grant, Elatocladus confertus (Oldham and Morris) Halle and six that are new for this formation= Equisetites frenguellii Orlando, Archangelskya protoloxsoma (Kurtz) Herbst, Sagenopteris nilssoniana (Brongniart) Ward, Nilssonia taeniopteroides Halle, O. bengalensis Oldham and Morris, and Elatocladus planus (Feistmantel) Seward. These records are added to 6 other previously studied taxa, including Cladophlebis mendozaensis (Geinitz) Frenguelli, C. oblonga Halle, Gleichenites cf. sanmartini Halle emend. Herbst, Scleropteris vincei Herbst, Araucarites phillipsi Carruthers, Podozamites elongatus (Oldham and Morris) Halle, providing an updated list of 24 taxa for this unit. The compositional similarity with other Early Jurassic paleofloras from Argentina indicates a Sinemurian age.

SUBSURFACE MIOCENE PALYNOMORPHS FROM SANTIAGO DEL ESTERO, ARGENTINA. The palynological assemblage recovered from the YPF.SE. LH.x-2 Los Horcones well, Santiago del Estero Province, is dominated by Amaranthaceae/ Chenopodioideae and freshwater green algae, together with subordinate Nothofagaceae and Malvaceae. Marine dinoflagellates and foraminiferal linnings are also present in the upper half of the sampled section. This assemblage may have developed in a lacustrine environment. A mostly herbaceaous and shrubby vegetation may have surrounded the water-body. The climate may have been warm—temperate and relatively arid. The palynoflora could be related to the marine ingression that affected northwestern Argentina during the middle Miocene (15–13 My).

PRESENCE OF CAIMAN LATIROSTRIS (DAUDIN, 1802) (CROCODYLIA, ALLIGATORIDAE) IN THE PIQUETE FORMATION (PLIOCENE-EARLY PLEISTOCENE) OF SALTA PROVINCE, ARGENTINA: PALEOENVIRONMENTAL AND SYSTEMATIC IMPLICATIONS. This paper describes the remains of an alligatorid from levels of the Piquete Formation (Pliocene—early Pleistocene) of Rosario de la Frontera, southern of Salta province, Argentina. The specimen is referred to the species Caiman latirostris (Daudin, 1802) based on their morphology. The results of a phylogenetic analysis suggest a close relationship with species bearing a prominent rostral ridge of the genus Caiman Spix, 1825. The validity of other remains assigned to the species is discussed, constituting this record the most complete and best preserved. Based on the ecological requirements of C. latirostris paleoenvironmental interpretations are made by analogy with the currently inhabited environment of this taxon.