Descripción: Cerro Falkner is composed of granitic rocks underlying volcanic rocks of the Ventana Formation of Paleogene age. Those intrusives are graniodioritic in composition, metaluminous to peraluminous, subalkaline, with characteristics of volcanic arc granites that are concordant with other granitoids of the Cordillera Patagónica Septentrional's northern segment. The age obtained by the K-Ar method on tschemakitic amphiboles (125 ± 20 Ma) points out a minimun age from the lower Cretaceous for the Cerro Falkner's granodiorite. Therefore the use of the term Los Machis Formation (Upper Cretaceous) would be incorrect for these rocks. This age, allows us to relate the granitic rocks on the study area to the lower Cretaceous, coeval with the volcanism of the Divisadero Group.

Descripción: The stratigraphy of Cretaceous marine mudstones in the Fuegian Andes, roughly equivalent to Charles Darwin's clay-slate formation, remains a still unsolved problem. Previous records of Albian, Turonian-Coniacian, and Santonian-Campanian bivalves are combined with new findings of the Late Albian inoceramid Inoceramus anglicus Woods, and the Maastrichtian ammonites Diplomoceras sp., Anagaudryceras sp., Maorites densicostatus (Kilian and Reboul), Maorites sp., and Pachydiscus (Neodesmoceras) sp. to further constrain the Cretaceous stratigraphy of the eastern Fuegian Andes. In addition, new records of distinctive trace fossils and ichnofabric are meaningful for stratigraphic division and delineation of paleoenvironmental settings in these Cretaceous mudstones. The Lower Cretaceous ichnoassemblage of Chondrites targioni (Brongniart) and Zoophycos isp. is consistent with the inferred slope-volcaniclastic apron settings of the Yahgan Formation; Nereites missouriensis (Weller) reflects distal basin plain depositional settings for the Beauvoir Formation. In the Upper Cretaceous, the "Estratos de Buen Suceso" record the earliest extensively bioturbated horizons, reflecting prolonged well-oxygenated bottom conditions. In the Bahía Thetis Formation, organic-rich, channel margin or distal basin slaty mudstones record the last occurrence of inoceramid bivalves in the Austral Basin; the generalized absence of trace fossils is consistent with dysoxic bottom conditions. The thoroughly bioturbated Policarpo Formation, records a marked change in paleoceanographic conditions. The strong contrast in the intensity of bioturbation between the Upper Campanian-Maastrichtian Bahía Thetis Formation, almost devoid of trace fossils, and the highly bioturbated Maastrichtian-Danian Policarpo Formation reflects a change from dysoxic-anoxic to well ventilated conditions, probably associated with a cooling trend of bottom waters in the austral deep oceans.

Descripción: The Cordillera de los Andes is the typical example of a subduction-related orogen. Its present topography is the result of post-Miocene uplift, however, Andean compressional deformation and uplift started in the Late Cretaceous, as increasingly recognized in different sectors of the mountain belt. We present evidences of a Late Cretaceous event of compressional deformation in the southern Central Andes (35oS), reflected in syn-orogenic foreland basin deposits assigned to the Neuquén Group in Argentina and the Brownish-Red Clastic Unit in Chile. Comparison of the facies of these units allows us to recognize a sector proximal to the Late Cretaceous orogenic front, a distal sector with sediment provenance from the forebulge and a western sector where the sediments where deposited within the Late Cretaceous mountain belt. On this basis, we assign the orogenic front to an inverted Jurassic normal fault, the Río del Cobre fault, and reconstruct the structure of the easternmost Late Cretaceous Andes at this latitude. The change in the location of the orogenic front north and south of 35oS allows us to recognize a long-lived change in behavior in Andean evolution in this sector, which correlates with a change in the shape and the deposits of Mesozoic Neuquén basin.

Descripción: Ciénaga del Río Huaco Formation was deposited during the Cretaceous in the Precordillera Central (La Rioja and San Juan provinces). The unit forms part of a thick red-bed sequence including rocks of different ages (from Late Paleozoic to Tertiary) and problematic identification. In the La Troya river area, the red bed sequence is composed of the Panacán (Permian), Santo Domingo (Late Triassic- Early Jurassic), Ciénaga del Río Huaco (Cretaceous) and Puesto La Flecha Formations (Oligocene- Early Nfiocene). In the past, all these formations were included in the same stratigrapbic unit and only in recent years the different formations could be separated mainly based on their fossil contain. In the case of Ciénaga del Rio Huaco Formation, the finding of microfossils (palynomorphs and ostracods) allowed to infer a Late Cretaceous age for these rocks. However, a radiometric age of 108,1 ± 4,4 Ma presented in this paper, clearly suggest that the unit was deposited at the end of the Early Cretaceous. This age is the first Cretaceous absolute age in the Precordillera Central and enhances the time constraints of of the Cretaceous Basin.

Descripción: The paleoenvironmental and paleoclimatic significance of Cretaceous flora in the Neuquén Basin is summarized. Berriasian-Barremian terrestrial palynological assemblages are dominated by Araucariaceae and Cheirolepidiaceae, with subordinated podopcarps, ferns, lycopsids and bryophytes that progressed in a mild and humid climate. Tithonian-Barremian dinoflagellates mostly possess Mediterranean affinities. Upper Barremian evaporitic strata represent the final cycle of marine deposition related to the Pacific ocean in the basin. In the Aptian appear the first angiosperm pollen grains. Aptian-Cenomanian terrestrial palynological assemblages are characterized by the presence of northern Gondwana forms such as Afropollis and elaterate pollen grains. Tempskyaceae and Ginkgoales are also present in the late Early Cretaceous. Turonian-lower Campanian continental strata mostly include petrified wood and charophytes. Upper Campanian-Maastrichtian strata yield a rich terrestrial palynological assemblage composed by Nothofagaceae, Podocarpaceae, Cheirolepidiaceae, Araucariaceae, Salviniales and angiosperms, but also dinoflagellates that reflect the beginning of a marine transgression related to the Atlantic ocean. The presence of locally abundant cycads and palms suggests a warm and relatively humid climate towards the end of the Cretaceous.

Descripción: We present here new paleointensity and geochronology results from Early Cretaceous volcanic rocks of Sierra Chica de Cordoba (Argentina). The new K-Ar isotopic ages of 5 samples range from 136 to 122 Ma. Twenty five samples from 7 individual flows yielded acceptable paleointensity estimates. The mean paleointensity values per flow are ranging from 53.0±1.9 to 25.4±2.6 μT and the corresponding Virtual Dipole Moments (VDMs) are ranging from 9.3±1.3 to 4.6±0.5 (1022 Am2). This corresponds to the mean value of 7.3±1.7x1022 Am2, which is compatible to the present geomagnetic axial dipole. Currently available selected paleointensity data from 80 to 130 Ma suggest that geomagnetic field strength frequently fluctuated before and during the Cretaceous Normal Superchron while the magnetic polarity maintained stable. The mean paleointensities derived from Cordoba lavas agree remarkably well with those obtained from the Parana Magmatic Province (133-132 Ma). This reinforces the hypothesis about the unreliability of ‘Mesozoic Dipole Low'. © 2006, The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan, The Geodetic Society of Japan, The Japanese Society for Planetary Sciences. All rights reserved.

Descripción: This paper reports the presence of Maastrichtian rocks in the north of the Precordillera (La Rioja province). The Cretaceous succesion (122 m thick) is a classical red bed sequence composed of sandstones, mudstones, marls and thin levels of evaporites. According to lithological features 6 facies associations have been recognized that mainly characterize a lacustrine system developed under arid to semiarid conditions. Probably as a result of an increase in aridity, eolian sediments were deposited at the top of the Cretaceous unit. At least two transgressive-regressive events have been recognized in the lacustrine sequence. The best developed is the first event formed by fossiliferous black shales corresponding to the maximum flooding stage. These rocks have yield remains of calcareous microfossils, palynomorphs and gastropods. The former comprise charophytes, with Platychara compressa (Knowlton) an Tectochara sp. A Musacchio, anda ostracods, with Ilyocypris wichmanni punctata Musacchio y Simeoni, Eucandona? sp., Cypridopsis and Ovo cytheridea? rionegrensis Musacchio.. Palinomorphs form a monospecific assemblage of algae colonies corresponding to Pediastrum. The lithological features, stratigraphic location and fossiliferous remains clearly suggest a regional correlation with the Ciénaga del Rio Huaco Formation. This correlation considerably enlarge the regional distribution of the Cretaceous sediments which were previously limited to the Precordillera of San Juan province. © 2005 Asociación Geológica Argentina.

Descripción: Nearly all data regarding land-plant turnover across the Cretaceous/Paleogene boundary come from western North America, relatively close to the Chicxulub, Mexico impact site. Here, we present a palynological analysis of a section in Patagonia that shows a marked fall in diversity and abundance of nearly all plant groups across the K/Pg interval. Minimum diversity occurs during the earliest Danian, but only a few palynomorphs show true extinctions. The low extinction rate is similar to previous observations from New Zealand. The differing responses between the Southern and Northern hemispheres could be related to the attenuation of damage with increased distance from the impact site, to hemispheric differences in extinction severity, or to both effects. Legacy effects of the terminal Cretaceous event also provide a plausible, partial explanation for the fact that Paleocene and Eocene macrofloras from Patagonia are among the most diverse known globally. Also of great interest, earliest Danian assemblages are dominated by the gymnosperm palynomorphs Classopollis of the extinct Mesozoic conifer family Cheirolepidiaceae. The expansion of Classopollis after the boundary in Patagonia is another example of typically Mesozoic plant lineages surviving into the Cenozoic in southern Gondwanan areas, and this greatly supports previous hypotheses of high latitude southern regions as biodiversity refugia during the end-Cretaceous global crisis. © 2012 Barreda et al.

Descripción: A new ammonoid species of the Andean endemic genus Andiceras Krantz is here described from upper Tithonian-lower Berriasian levels of the Vaca Muerta and Chachao Formations of the Mendoza Group, in north-western Mendoza Province, Argentina. Andiceras planulatus sp. nov. lies between the last beds with representatives of the Substeueroceras koeneni Assemblage Zone of late Tithonian age and the first bed yielding elements of the Argentiniceras noduliferum Assemblage Zone of early Berriasian age, according to the traditional Andean ammonoid zonation scheme. The particular stratigraphic position of Andiceras planulatus, together with its easily recognizable morphology makes this species a good potential biostratigraphic marker for the Jurassic-Cretaceous boundary in the Andean region.

Descripción: This paper discusses the general atmospheric circulation over Patagonia on the basis of the principal palaeoclimate forcings: continental drift, orography, variations in the greenhouse gases in the Earth's atmosphere, evolution of the atmosphere and the oceans, changes in the orbit of the Earth, albedo feedbacks, and the land surface. These processes affect climate on time scales of millions to hundreds of thousands of years. Additionally, orbital forcing has had a major influence on climate during the Quaternary. The palaeo-atmospheric circulation of Patagonia is analyzed for the Early to Late Jurassic, the Cretaceous, the Late Palaeocene-Eocene Thermal Maximum, the Tortonian-Oligocene cooling, the Pliocene, the Quaternary including the Last Glacial Maximum, the Holocene Optimum, and the last millennium changes. Alternative palaeo-atmospheric circulations from climatic modelling scenarios through the ages are reviewed and compared with proxy data. Detailed and updated reference information on the topics analyzed is also provided. © 2011 The Linnean Society of London.

Descripción: Results of a detailed geologic survey of the Río Borbollón area, located in the Cordillera Principal of the province of Mendoza are presented. The stratigraphic record of the area corresponds to a Jurassic-early Cretaceous sedimentary succession, the products of Neogene igneous activity and Quaternary deposits. The Tres Esquinas and La Manga Formations of Jurassic age were recognized for the first time in the study area. The main structural features of the area are described and interpreted based on the obtained data and previous works. A balanced structural cross section of the Malargüe fold and thrust belt at 34°15'S depicts the structural style and the amount of orogenic shortening in this region of the Andes.

Descripción: The Andes located in the central Neuquén (38°-39°S), which belong to the southern Central Andes (35°-39°S), have recorded a similar chronology of uplift than the neighbor northern Patagonian Andes (39°-46°S), Both areas have been formed trough successive phases of contraction in the Late Cretaceous, Middle Eocene and Late Miocene respectively. However, the Neuquén Andes have experienced two discrete phases of orogenic relaxation, during the Late Oligocene and Pliocene-Quaternary, which make then distinctive respect to the area located to the south. Field studies have shown new evidences of an episodic behavior of the fold and thrust belt in Neuquen, corresponding to compressive phases followed by stages of crustal collapse, at least since the Middle Cretaceous. The study of two main morphostructural units in the arc and retroarc area at 37°-39°S, the Alto de Copahue Pino Hachado, and its continuation to the north in the Chilean Andes (Laguna de la Laja), and the Loncopué trough respectively exemplify this particular behavior. A structural and a stratigraphie study in those areas have given a new evolutionary framework for the Neuquén Andes. © 2005 Asociación Geológica Argentina.

Descripción: Late Cretaceous and Paleogene sedimentary rocks of the Austral Basin crop out on the south-eastern margin of Lake Viedma. In the Barrancas Blancas section, 28 m of yellowish sandstone and mudstone of the La Asunción Member of the Anita Formation are transitionally covered by 390 m of greyish sandstone and mudstone of the Cerro Fortaleza Formation. The former represent a prograding barred nearshore system, whereas the latter correspond to paralic, fluvial and fluvial-tidal sedimentation. The evolution of the depositional sequences, sedimentary palaeoenvironments, sandstone provenance and palaeocurrents indicate that the sediments were deposited during the back-arc (sag) stage of the basin. At Cerro Piramides, Tertiary sedimentary rocks rest with fault contact on top of the Cerro Fortaleza Formation. The limited thickness (<1m) preserved of greenish sandstone of the Man Aike Formation precludes any attempt to interpret its depositional environment. Conglomerate, sandstone and mudstone (locally carbonaceous) of the Río Leona Formation (75 m) rest with erosional contact on the former. These rocks represent a rapid transition from a high energy to low energy fluvial systems that eventually graded into marginal marine environments represented by the fossiliferous sandstones of the Centinela Formation (<3m). The facies arrangement, evolution of the palaeoenvironments, and palaeocurrents suggest that these sediments were deposited during the foreland basin stage. © 2003 Asociación Geológica Argentina.

Descripción: A continental sequence of red beds and interbedded basaltic layers crops out in the Sierra Chica of Cordoba Province, Argentina (31.5°S, 64.4°W). This succession was deposited in a half-graben basin during the Early Cretaceous. We have carried out a palaeomagnetic survey on outcrops of this basin (147 sites in seven localities). From an analysis of IRM acquisition curves and detailed demagnetization behaviour, three different magnetic components are identified in the volcanic rocks: components A, B and X are carried by single- or pseudo-single-domain (titano) magnetite, haematite and multidomain magnetite, respectively. Component A is interpreted as a primary component of magnetization because it passes conglomerate, contact, tilt and reversal tests. The carrier of the primary magnetization, fine-grained (titano) magnetite, is present in basalts with a high degree of deuteric oxidation. This kind of oxidation is interpreted to have occurred during cooling. Components B and X are discarded because they are interpreted as recent magnetizations. In the sedimentary rocks, haematite and magnetite are identified as the carriers of remanence. Both minerals carry the same component, which passes a reversal test. The calculated palaeomagnetic pole, based on 55 sites, is Lat. 86.0°S, Long. 75.9°E (A95=3.3, K=35). This palaeomagnetic pole supersedes four with anomalous positions reported in previous papers.

Descripción: As a result of a microfacial study in the outer and middle ramp deposits of the Vaca Muerta Formation (lower Tithonian-upper Valanginian), four ichnotaxa of crustacean microcoprolites are described: Palaxius azulensis Kietzmann isp. nov., Palaxius caracuraensis Kietzmann isp. nov., Helicerina? isp. A. aff. Helicerina siciliana and Helicerina isp. B. They represent one of the first records of crustacean microcoprolites for the Neuqun Basin and Argentina. Helicerina is reported for the first time from the Upper Jurassic and Lower Cretaceous of South America. It is inferred that Palaxius ichnospecies were produced by callianassids, while Helicerina ichnospecies could be produced by decapods of Mecochiridae, Erymidae, and/or Nephropidae affinity. Two assemblages of crustacean microcoprolites are recognised, a middle Tithonian to lower Berriasian Palaxius-dominated assemblage and an early to late Valanginian Helicerina-dominated assemblage.

Descripción: Magmatism related to the growth and migration of the Andean arc was developed from the 36°40'S to the 38°20'S latitude, in the northwestern sector of the Neuquén Province, by the end of the Mesozoic. Hypabyssal and extrusive facies, which outcrop in the Pichaihue area, were described based on petrologic studies. The first ones are composed of andesites that are emplaced as lacoliths, dikes or sills intruding the Mesozoic sedimentary sequences. In addition, basalts outcrops were recognized. The extrusive facies consist of breccia or massive lavas and little domes. The geochemistry reveals an arc-like calc-alkaline signature with a normal crust and trace-element patterns which suggest a similar source. Based on regional knowledge, three groups are proposed: Cerro Mocho dikes with Ti anomalies and higher Sm/Yb; extrusive facies of the Upper Cretaceous- Paleocene (Rivera Andesite); and the hypabyssal facies of thr Eocene (Colipilli Dikes). Finally, the occurrences of these rocks in this segment of the Andes indicate an important shift to the East of the Upper Cretaceous-Eocene volcanic arc that reveals its easternmost position.

Descripción: The Larsen Basin is the depositional area including all the upper Mesozoic-lower Cenozoic sedimentary rocks on the continental shelf of the northern Antarctic Peninsula. The western boundary between the basin fill and the rocks forming its technical basement, is not exposed, and was defined on the basis of aeromagnetic data. On petrological grounds, the Mesozoic marine sedimentary rocks exposed on western Tabarin Peninsula, at the north-eastern extremity of the Antarctic Peninsula, are assigned to the lower part of the Aptian-Eocene regressive megasequence that forms the basin filling. These rocks are faulted against sediments of the Antarctic Peninsula magmatic arc, suggesting that post- depositional tectonic movements probably occurred. This compressional deformation is assigned to mid-Cretaceous times, when the Coniacian partial basin inversion was accompanied by westward-verging deformation at the western basin margin. Although the original extent of the basin cannot be discerned from these data, the lithostratigraphical evidence and geographical position of the basin sediments, together with terrestrial magnetic data, confirm that the Larsen Basin extends onto the southern part of Tabarin Peninsula, and indicate that the western limit of the basin is located northward of the previously proposed limit. © 2004 Asociación Geológica Argentina.

Descripción: A composite section, 1400 m thick, is established for the Upper Cretaceous-Paleogene strata in the fold and thrust belt of the Andes Fueguinos, south of 54° 30′S. The basal Policarpo Formation, > 350 m thick, consists of tuffaceous sandstones and bioturbated sandstones and siltstones. The ammonites Maorites densicostatus and Diplomoceras sp.; foraminifera common to the Gaudryina healyi Zone; and the dynocysts Manumiella seelandica and Operculodium cf. azcaratei indicate a Maastrichtian age. The Paleocene to lower Eocene include four new formations. The Cabo Leticia Formation, c.150 m, Paleocene, consists of gravity flows deposits: brecchias; conglomerates; and massive, tuffaceous sandstones. La Barca Formation, c. 220 m, includes two members: LB1, tuffaceous sandstones and intercalated carbonaceous siltstones; and LB2, black mudstones with Palaeocystodinium golzowense and Spiroplectammina spectabilis. P. golzowense and the Bulimina karpatica Assemblage in LB1 indicate a late Paleocene age. Punta Noguera Formation, 380 m, is dominated by glauconite rich, massive, tuffaceous sandstones with interbedded turbidite packages. The dynocyst group Apectodinium, Deflandrea robusta, Palaeocystodinium sp., and Odontodinium askinae; the foraminifera Alabamina creta, Charltonina acutimarginata, Valvulineria teurensis and the first ocurrence of Elphidium and Cribrorotalia suggest an age near the Paleocene/Eocene boundary. The Cerro Ruperto Formation, 200 m, is dominated by glauconite rich, silty very fine sandstones and siltstones; dominance of Deflandrea dartmooria indicate an early Eocene age. Resting on angular unconformity, the Río Bueno Formation, c. 60-80 m, consists of carbonate rocks; its member RB1, rhythmically bedded grainstones, with the planktic foraminifera Planorotalites australiformis and Subbotina linaperta is of early middle Eocene age; and its member RB2, regular alternation of grainstones and bioturbated marls and micrites, with Elphidium saginatum and Bulimina cf. bortonica, is assigned to the mid middle Eocene. The sedimentary and stratigraphic features of the Maastrichtian/Eocene have a strong tectonic control, suggesting that the foreland phase of evolution of the basin has been active at least since the Maastrichtian.

Descripción: In this paper the ichnology of the marine intervals of the Neuquén Basin is reviewed, taking into account an stratigraphic framework and discussing previous works on ichnology that contain some ichnogenus (Lapispira) that are firstly documented in South America in Jurassic rocks of the Río Atuel area, and other ichnogenera that constitute well preserved records in the Jurassic tidal influenced deltas of the Lajas Formation. The trace fossil record includes Asterosoma, Asteriacites, Dactyloidites, Diplocraterion, Gyrochorte, Palaeophycus, Polykladichnus, Schaubcilindrichnus, Siphonichnus, Thalassinoides, Teichichnus and rare traces in shallow marine deposits like Helmin-thorhaphe and root traces indicative of a very complex facies scheme. A special mention deserves the traces from the carbonates of the La Manga Formation at Bardas Blancas, that contain ichnogenera like Dactyloidites, Gyrochorte, Jamerosonichnites and Thalassinoides recorded in tempestites. The Lower Cretaceous record documented in the Mulichinco and Agrio Formation is composed of Asteriacites, Gyrochorte, Lockeia, Ophiomorpha, and possibly Bergaueria, documented in the Mulichinco Formation at Vega de Escalone locality. Other ichnofossils described in the Agrio Formation are Gyrochorte, Ophiomorpha, Thalassinoides, Teichichnus among others of dubious assignation recorded at Bajada del Agrio and other areas of the basin. New material coming from both units includes subaqueous vertebrate scratchs (Characichnos?) both from Vega de Escalone and Puerta Curaco. Arthropod trackways include both some with differentiated (Diplichnites?) and other specimen with undifferentiated appendages. In the case of the Agrio Formation at Cerro Rayoso, teropod tracks are indicatives of subaerial exposure in sections expected to be fully marine. Complex traces assigned to Hillichnus produced by tellinacean bivalves are the only record of such bivalves in the basin. Those ichnogenera are good examples that precede body fossil records and along with the scratch marks suggest very shallow and occasional subaerial exposition in areas of the basin unexpected according to paleogeographic maps. Finally a brief analysis of the further work in the turbidites of the Molles Formation or the exploration of bioerosion and meiofauna records suggest that the knowledge about the ichnology of the Neuquén Basin is in its infancy if it is compared with the stratigraphic, paleontologic (biostratigraphic) and sedimentologic studies and also remains unexplored related to changes in permeability of reservoirs of bioturbated deposits documented from cores.