Cerro Barcino Formation Research Articles

The Appendicular Osteology of Patagotitan Mayorum (Dinosauria, Sauropoda)

ABSTRACT Its huge size, excellent preservation, and completeness make Patagotitan mayorum a unique opportunity to explore the anatomy, paleobiological, and phylogenetic aspects linked to gigantism within Sauropoda. In this regard, we describe the appendicular skeleton of this titanosaurian species from the late Albian-aged Cerro Barcino Formation of Chubut Province, Argentina. The diagnosis of Patagotitan mayorum is revised, increasing the number of identified autapomorphies (i.e., lateral surface of the scapular blade with two divergent crests; anterior surface of proximal humerus with paired muscle scars; combined bulges on the deltopectoral area of the humerus; ischium with well-developed and sharp ridge projecting from the ischial tuberosity to the distal blade). Several diagnostic characters of this species correspond to osteological correlates associated to appendicular musculature (e.g., Mm. deltoideus scapularis, deltoideus clavicularis, and teres major; M. coracobrachialis; Mm. supracoracoideus/deltoideus clavicularis and latissimus dorsi; Mm. flexor tibialis 3 and adductor femoris 2), which we discuss in the context of sauropod evolution. In the light of a modification of the scaling equation previously proposed and adjusting the long bone circumference for the humeri of Patagotitan, a new body mass estimate of this species ranges between 42–71 tons, with a mean value of 57 tons. Although considerably less than the value obtained by the original linear equation, the corrected quadratic equation used here provides a mean body mass estimate that is more consistent with those derived from volumetric reconstructions of Patagotitan.

High-resolution chronostratigraphy of the Cerro Barcino Formation (Patagonia): Paleobiologic implications for the mid-cretaceous dinosaur-rich fauna of South America

The Cretaceous Cerro Barcino Formation (Chubut Group) of Central Patagonia, Argentina has yielded a remarkable fossil vertebrate fauna, which form important components of the South American “mid-Cretaceous” fauna, including titanosauriform sauropod dinosaurs, theropod dinosaurs, crocodyliforms, turtles, and lepidosauromorphs. However, a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance. This contribution presents new stratigraphic, sedimentologic, and U-Pb isotopic age data from 11 localities throughout the Patagonian Somuncurá-Canadón Asfalto Basin and analyzes the evolutionary characteristics of the Cerro Barcino fauna within the biostratigraphic context of the Cretaceous of Gondwana.Four new high-precision 206Pb/238U zircon dates by the CA-ID-TIMS method range from 118.497 ± 0.063 Ma to 98.466 ± 0.048 Ma (2σ internal errors) and limits the Puesto La Paloma, Cerro Castaño and Las Plumas members of the Cerro Barcino Formation largely to the Aptian, Albian and Cenomanian stages of the Cretaceous, respectively. Accordingly, the majority of the Cerro Barcino vertebrates fall within a ~118–110 Ma time interval in the latest Early Cretaceous, which makes them the oldest documented component of the “mid-Cretaceous” faunal assemblage of Gondwana. Paleobiologic analyses of the latter assemblage suggests a ~10 m.y. period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers.

Soft-sediment deformation structures in gravelly fluvial deposits: A record of Cretaceous seismic activity in Patagonia?

Cretaceous sedimentary rocks corresponding to the Las Plumas Member of the Cerro Barcino Formation were deposited in the eastern margin of the Somuncurá - Cañadón Asfalto Basin. The analyzed succession records alluvial settings in a fault-proximal scenario and contains a 7 m thick stratigraphic interval bearing soft-sediment deformation structures which include: pebble load casts, pseudonodules, flame structures and contorted bedding. Deformed beds are bounded by undisturbed strata and these features can be traced along the 800 m of exposures. The sedimentological features such as size and shape of SSDS, clast fabric of gravels and depositional paleoenvironment added to the proximity to a fault zone support the interpretation of the described deformation features as formed by liquefaction and/or fluidization triggered by seismic shocks during syn-tectonic deposition.

A new species of Carlquistoxylon from the Early Cretaceous of Patagonia (Chubut province, Argentina): the oldest record of angiosperm wood from South America

ABSTRACT An angiospermous wood from the Lower Cretaceous (upper Albian) of the Cerro Barcino Formation, Chubut Group, central Patagonia, Argentina, is described. Its estimated minimum diameter is 40 cm and it is significant as the oldest known angiosperm wood for South America. It has indistinct growth ring boundaries, vessels solitary and in radial multiples, simple perforation plates, alternate intervessel pits, vessel-ray parenchyma pits oval to horizontally elongated, heterocellular rays, non-septate fibres, axial parenchyma absent, and abundant tyloses. Because this Albian wood has non-septate fibres we assign it to Carlquistoxylon, even though it has a general combination of characters similar to that of Paraphyllanthoxylon, which has septate fibres. The number of vessels per radial multiple, vessel tangential diameter and frequency, vessel-ray parenchyma pitting, and absence of axial parenchyma distinguish the fossil described here from the only previously known species of Carlquistoxylon: Carlquistoxylon nacimientense; therefore, a new species is erected. Because of the close similarities between this new specimen and Paraphyllanthoxylon species, comparisons with all the species included in both genera are provided. Systematic affinities for this wood are discussed considering previous discussions for both Paraphyllanthoxylon and Carlquistoxylon affinities. As the oldest described angiosperm wood in South America to date, this specimen provides critical information on the diversity and growth habit of Cretaceous angiosperms from the Southern Hemisphere.

Biostratigraphy and biogeography of charophytes from the Cerro Barcino Formation (upper Aptian–lower Albian), Cañadón Asfalto Basin, central Patagonia, Argentina

Charophytes from the lower Cerro Barcino Formation, Chubut Group, at Paso de Indios, Cañadón Asfalto Basin, include Sphaerochara verticillata, Mesochara symmetrica, Lamprothamnium? barcinencis sp. nov., Clavator harrisii harrisii, C. harrisii zavialensis and Clavatoraxis sp. The charophytes recovered from the basal members of the unit indicate deposition within the upper Aptian–lower Albian stratigraphic interval, as compared with the European charophyte biozonation. This attribution is based on the biostratigraphic significance of the evolutionary species Clavator harrisii that shows the dominance of C. harrisii harrisii in all levels studied and the appearance of C. harrisii zavialensis in the Cerro Castaño Member of the Cerro Barcino Formation. The known distribution of Clavator harrisii in other floras from North and South America, Europe, Asia and Northern Africa provides evidence that it was still a cosmopolitan species in the early Albian and did not show any population fragmentation, in contrast to other coeval cosmopolitan clavatoraceans.

Changing fluvial styles in volcaniclastic successions: A cretaceous example from the Cerro Barcino Formation, Patagonia

The Cretaceous Puesto La Paloma (PLPM) and Cerro Castaño (CCM) members (Cerro Barcino Formation, Chubut Group) are pyroclastic-rich, alluvial successions deposited in the Somuncurá-Cañadón Asfalto Basin during sag and endorheic conditions. The PLPM comprises sheet-like tuffaceous sandstone strata, whereas the overlying CCM includes sheet-to ribbon-channel sandstone bodies intercalated within tuffaceous and fine-grained sediments. In this context, the goals of this contribution were: i) to make a detailed documentation of the contrasting sedimentary palaeonvironments; and ii) to infer the allocyclic controls that governed the sedimentation of both units. The study area is located in the western sector of the basin, where six localities, which were studied.Six facies associations were defined including ash-falls, sheet-floods, shallow lakes, aeolian, fluvial channel-belts, and reworked debris-flows. We defined four stratigraphic intervals for the studied sections, denominated 1 to 4 in chronological order of deposition, which increase their thicknesses toward the Puesto Mesa-Cerro León site. The interval 1 (18–42 m thick) corresponds to the PLPM and includes numerous pedogenized sheet-flood deposits, carbonate-rich lacustrine, aeolian sandy facies, and ash-fall beds. The interval 1 is interpreted as an ephemeral and unconfined alluvial system that interacted with aeolian dunes and dry interdune zones. The interval 2 (20–47 m thick) represents the lower part of the CCM. It shows an alternation of fluvial channel-belt deposits and vegetated floodplain facies with sediments originated from sheet-floods, lakes, and few ash-falls and debris-flows. The mean palaeoflow was toward E-SE, except in the northernmost locality where the drainage was towards SW. Proportion of channel-belt bodies ranges from 10 to 36%, reaching higher values in the northern part of the study area, where they are also thicker. The interval 2 represents a permanent, meandering or locally low-sinuosity, fluvial system, and displays both an increase of lacustrine facies and a decrease of ash-fall deposits. The interval 3 (7.5–27 m thick) corresponds to the middle part of the CCM, and lacks channel-belt bodies. It has the highest participation of sheet-flood and ash-fall deposits. This interval entirely records a pedogenized floodplain setting. In relation to the interval 2, participation of debris-flow deposits remains constant and lacustrine facies subtly increases. The interval 4 (18–148 m thick) represents the upper part of the CCM. It comprises an alternation of channel-belt bodies and pedogenized floodplain facies, the last characterized by sheet-flood, lake, debris-flow, and volcanic ash rain deposits. The mean palaeoflow was toward E-SE, except in the two localities positioned further north where the drainage was towards NE and SSE. Proportion of channel-belt deposits ranges from 6 to 32%. It represents channelized and perennial fluvial systems with meandering and locally low-sinuosity styles. Increase in channel proportion and thicker channel bodies are in the northern part of the study area. Particularly, in Puesto Mesa-Cerro León locality this interval is the thickest and has the highest proportion of thicker channel-belt bodies.We interpret these changes in facies architecture as the response to alternated periods of high (intervals 1 and 3) and low (intervals 2 and 4) primary pyroclastic sediment supply. Moreover, there was a climatic change to wetter conditions (intervals 1 to 2–4); as well as intrabasinal tectonic activity in northern area for intervals 2 and 4 inferred from palaeocurrent data.

Osteology and phylogenetic relationships of Tyrannotitan chubutensis Novas, de Valais, Vickers-Rich and Rich, 2005 (Theropoda: Carcharodontosauridae) from the Lower Cretaceous of Patagonia, Argentina

The theropod clade Carcharodontosauridae is a broadly distributed group of large allosauroid theropods. The carcharodontosaurids recorded in the Albian–Cenomanian of Gondwana are the youngest and most derived members of this clade. Tyrannotitan chubutensis, from the Cerro Castaño Member of Cerro Barcino Formation (Albian; Chubut Group), Central Patagonia, Argentina, is of prime interest among Gondwanan carcharodontosaurids as it represents the oldest record of the group. Here we offer a detailed osteological comparative description of the holotype and paratype of Tyrannotitan chubutensis together with a new diagnosis of the species. The new information results in a better understanding of this taxon and Carcharodontosauridae. Furthermore, a comparative study of the anatomy of the pectoral girdle of Giganotosaurus is reinterpreted as very similar to that of Tyrannotitan and Mapusaurus. We also present a phylogenetic analysis of Carcharodontosauridae that recovers Tyrannotitan as a derived carcharodontosaurid, being the sister group of the clade formed by Giganotosaurus and Mapusaurus, all nested in the clade Giganotosaurini.

New remains and new insights on the Gondwanan meiolaniform turtle Chubutemys copelloi from the Lower Cretaceous of Patagonia, Argentina

New cranial and postcranial remains of the Gondwanan meiolaniform turtle Chubutemys copelloi Gaffney, Rich, Vickers-Rich, Constantine, Vacca and Kool 2007 from the Lower Cretaceous Puesto La Paloma Member of the Cerro Barcino Formation (Chubut province, Patagonia, Argentina) are presented, described, and compared in this contribution. Carapace and plastral remains, pectoral and pelvic girdle, cervical and thoracic vertebrae, and the left maxilla and jugal are the new recovered elements from C. copelloi. These new remains were found in 2008 in Turtle Town locality, the same site where the holotype and referred specimens of C. copelloi had been found in 1997. The facies analysis of the sedimentary succession in Turtle Town and surrounding areas suggests a paleoenvironment constituted by a broad alluvial plain with influx of volcanic ash-falls, whose deposits were disturbed by pedogenesis or reworked by current flows that supplied water and sediment in ponded areas. The presence of a very thin shell, broad vertebrals (broader than pleurals), the presence of a shallow nuchal notch with the vertebral 1 almost reaching the anterior border of the carapace, the presence of costo-peripheral fontanelles, and the presence of an ectepicondylar canal in the humerus, are the most notable features provided by the new remains. A cladistic analysis has been performed to test the phylogenetic position of C. copelloi. This phylogeny corroborates the basal position of C. copelloi among Meiolaniformes. The plausible phylogenetic relationships of the clade Meiolaniidae with other Gondwanan (e.g., Otwayemys cunicularius Gaffney, Kool, Brinkman, Rich, and Vickers-Rich 1998) or Laurasian Lower Cretaceous taxa (e.g., sinochelyids) are also discussed in this contribution. Taxa included in Meiolaniformes have been mainly found in Gondwana and as the most basal taxon was found in Patagonia, paleobiogeographic studies suggest this clade originated in South America. Due to the basal position of C. copelloi among Meiolaniformes the discovery of more and previously unknown remains of this species sheds light on the origin and early evolution of this curious clade.

Huevos De Saurópodos Del Aptiano-Albiano, Formación Cerro Barcino (Patagonia, Argentina): Un Enigma Paleoambiental y Paleobiológico

SAUROPOD EGGS FROM THE APTIAN-ALBIAN CERRO BARCINO FORMATION, CHUBUT (PATAGONIA, ARGENTINA): A PALEOENVIRONMENTAL AND PALEOBIOLOGICAL ENIGMA. Here are described the first eggs and eggshell fragments from the Lower Cretaceous Chubut province. The two eggs and eggshell materials come from the Huaniman locality at the north-central region of Chubut. In this paper, we provide a paleontological description of the materials to infer their paleoenvironmental setting and we offer a morphological comparison with other South American dinosaur eggs. The egg materials were found in fine tuffaceous sandstone from a proximal floodplain deposits associated to sinuous and multi-episodic river channels, belonging to the Cerro Castaño Member (Aptian-Albian; Cerro Barcino Formation). The eggshell morphology is similar to that of megaloolithid eggs (a paraphyletic group in egg parataxonomy) known from Patagonia such as Auca Mahuevo, Neuquen, positively identified as sauropod titanosaurs on the basis of in ovo embryos, and Salitral Moreno, Rio Negro. However, the new specimens from Chubut exhibit structural features of the eggshell not previously reported such as a horizontal network of pore canals clearly visible near and beneath the outer nodular eggshell surface, similar in morphology but differently placed than in the Auca Mahuevo eggs —where it overlays the membrana testacea. This morphological feature and the 1.5 mm thick eggshell may illustrate a novel adaptation to this specific nesting environment. Although only two isolated eggs were found in Huaniman, this discovery suggests the potential for the existence of a more substantial nesting site in the area.

Fluvial styles, palaeohydrology and modern analogues of an exhumed, Cretaceous fluvial system: Cerro Barcino Formation, Cañadón Asfalto Basin, Argentina

Superb surface exposures of a fluvial palaeochannel-belt 2–5 km wide and 13 km long occur in Cretaceous sedimentary rocks of the Cerro Barcino Formation (Las Plumas Member), Chubut Group, Cañadón Asfalto Basin, Argentina. The exceptional plan-view exposures of fluvial sandbodies allowed identification of a large number of WNW–ESE sinuous ridges that represent high-sinuosity, braided and low-sinuosity fluvial palaeochannels, crevasse and chute palaeochannels, and crevasse-splay deposits. Predominance of low-sinuosity palaeochannels and low values of the width/thickness ratio of most them suggest high stability of their margins, probably controlled by the cohesiveness of tuffaceous floodplain deposits. Morphological and sedimentological observations provide evidence of abrupt lithofacies changes in palaeochannel fills, fine-grained intercalations in multi-storey palaeochannels and occurrence of different fluvial styles, implying temporal/spatial variations in palaeodischarge and/or slope conditions. Comparison of the near-identical plan view morphology of the Cretaceous palaeochannel belt with the nearby Chubut River, plus the comparison of palaeohydrological data of the exhumed palaeochannels with hydrological data from this modern analogue, gives evidence of a very similar fluvial behaviour. This provides an integrative tool to be employed in the study of other ancient fluvial successions, including the reconstruction of palaeofluvial hydrological parameters in planetary geology.

DAWSONITE IN TUFFS AND LITHARENITES OF THE CERRO CASTANO MEMBER, CERRO BARCINO FORMATION, CHUBUT GROUP (CENOMANIAN), LOS ALTARES, PATAGONIA, ARGENTINA

Dawsonite, NaAlCO 3 (OH) 2 , occurs as a replacement, cement, and fracture filling in continental, zeolitized and silicified vitric tuffs and litharenites of the Cenomanian Cerro Castano Member, Cerro Barcino Formation, Chubut Group, Patagonia, Argentina. Analcime is the only associated zeolite; it replaces the vitric masses and also fills fractures and cavities. Dawsonite and analcime display an inverse ratio. Textural relationships indicate that dawsonite is a pseudomorph after oligoclase, quartz, vitric shards, and vitric masses; it coexists with diagenetic quartz cement and postdates analcime, calcite, and hematite cements. Unaltered crystals of high sanidine postdate all other cements generated. Silicification of the tuffs is likely to have occurred in various stages during the diagenetic history of the sequence. Hypabyssal bodies of alkaline basic rocks of the El Buitre – El Canquel Formation, which intruded regionally the Cerro Castano Member during Eocene time, are interpreted to be responsible for the introduction of CO 2 gas at high partial pressures, together with sodium, which led to dawsonite formation. Diagenetic quartz, at a late stage of silicification, is related to the transformation of oligoclase and analcime to dawsonite, also releasing Na and Ca into the system. The δ 13 C (PDB) values of dawsonite, in the range −1.2 to −2.4‰, attest to alkaline igneous activity in the Cerro Castano Member during the Eocene and, in addition, set a limit on the age of the dawsonite.

New chelid turtles of the lower section of the Cerro Barcino formation (Aptian-Albian?), Patagonia, Argentina

A new chelid species ( Prochelidella cerrobarcinae nov. sp.) are described from the Aptian-Albian? Puesto La Paloma Member, Cerro Barcino Formation, northern of Chubut Province, Argentina. The basal section of this member, which bears the turtle remains, is composed of tuffaceous mudstones with plane parallel lamination, asymmetrical ripples and a chert intercalation suggesting sub-aqueous deposition in a relatively shallow lacustrine environment. Pr. cerrobarcinae nov. sp. is represented by post-cranial remains of several specimens that not only represents the oldest pleurodiran chelid record in the world but, together with the chelid remains of Albian Lightning Ridge, New South Wales, Australia, indicates that chelid diversification began well before the final fragmentation of southern Gondwana.

The osteology of Chubutisaurus insignis del Corro, 1975 (Dinosauria: Neosauropoda) from the ‘middle’ Cretaceous of central Patagonia, Argentina

ABSTRACT Titanosauriform sauropods were one of the most widely distributed groups of dinosaurs during the Cretaceous. In contrast to most derived forms from the Upper Cretaceous, the most basal taxa of the group are poorly known. Thus, studies on these forms are of special interest for understanding the origin and early evolution of Titanosauria. Chubutisaurus insignis del Corro, 1975, is known from postcranial remains found in the Bayo Overo Member of the Cerro Barcino Formation (Chubut Group), which is commonly regarded as Aptian–Cenomanian in age. Phylogenetic analyses that include Chubutisaurus recovered this taxon as the sister group to Titanosauria. Nevertheless, most published studies have not included this taxon, probably due to its brief description and fragmentary remains. Fieldwork conducted in the quarry where the holotype was found yielded new materials that are regarded as part of the same specimen. These new materials, together with additional undescribed, and briefly described elements, originally collected by G. del Corro, are described here. The new information allows the recognition of a more extensive diagnosis of this taxon. The phylogenetic analysis presented here resolves Chubutisaurus as the most basal somphospondylian.

The first crocodyliform from the Chubut Group (Chubut Province, Argentina) and its phylogenetic position within basal Mesoeucrocodylia

A new crocodyliform specimen is presented here found in the Cerro Castaño Member of the Cerro Barcino Formation (Chubut Group). The material consists of cranial and postcranial remains that represent a new taxon that has strong affinities with Peirosauridae, but also shares derived features present in Araripesuchus. The phylogenetic relationships of this new taxon were tested through a cladistic analysis depicting it as a member of the Peirosauridae. The inclusion of Barcinosuchus within this clade of basal mesoeucrocodylians is supported by the presence of hypapophyses up to the third or fourth dorsal vertebrae, anterolateral facing edge on postorbital, quadrate dorsal surface divided in two planes by a ridge; mandibular symphysis tapering anterirorly in ventral view, lateral surface of dentary convex anterior to mandibular fenestra, distal body of quadrate well developed, anteroposteriorly thin and lateromedially broad. The new specimen broadens the temporal and geographical distribution of Peirosauridae during the Cretaceous of Gondwana, representing the southern-most and the most ancient record of the group in Patagonia. The new material also provides insights on the postcranial anatomy of peirosaurids, a group that has been so far studied almost exclusively from cranial material.

Chubutemys, a New Eucryptodiran Turtle from the Early Cretaceous of Argentina, and the Relationships of the Meiolaniidae

Abstract Chubutemys copelloi is the oldest nonmarine cryptodire from South America represented by a skull. The skull and associated postcranial fragments are from the Aptian Cerro Costano Member of the Cerro Barcino Formation of Chubut, Argentina. Chubutemys has a processus trochlearis oticum, showing that it is a cryptodire, and an enclosed canalis caroticus internus extending to the posterior margin of the pterygoid, showing that it is a eucryptodire. The skull of Chubutemys is similar to that of other primitive eucryptodires, particularly Dracochelys, but also to Hangaiemys, Judithemys, Sinemys, and Ordosemys. Chubutemys differs from all these, however, in possessing a solidly roofed skull, formed by long, wide parietals, rather than a posterior emargination. Chubutemys also differs from these taxa in having no cheek emargination. A phylogenetic analysis using PAUP* analyzed 104 parsimony-informative characters resolving into one most parsimonious cladogram of 224 steps, a consistency index of 0.55, an...

Provenance and anatomy of Genyodectes serus, a large-toothed ceratosaur (Dinosauria: Theropoda) from Patagonia

ABSTRACT The type material of Genyodectes serus, the first unquestionable non-avian theropod dinosaur to be described from South America, is redescribed in detail and its provenance and systematic position are discussed. Although no detailed information about the provenance of the specimen exists, it is probably derived from the lower part of the Cerro Barcino Formation (Chubut Group; Aptian-Albian) at Canadón Grande, central Chubut Province, Argentina. Genyodectes is characterized by closely-spaced premaxillary teeth that are arranged in an overlapping en-echelon pattern and extremely transversely compressed maxillary teeth, the longest of which exceed the minimal height of the dentary in apicobasal length. Although systematic information is limited by the fragmentary nature of the material, the combination of fused interdental plates, maxillary and dentary teeth with a pronounced flat or even slightly concave area adjacent to the serrated carinae, premaxillary teeth that are considerably shorter than the maxillary teeth and strongly compressed and very long maxillary teeth indicates neoceratosaurian and, more specifically, ceratosaurid affinities for Genyodectes. Thus, this taxon adds a further lineage of neoceratosaurs to the already diverse South American record of this group.

Dinosaur remains from the Lower Cretaceous of the Chubut Group, Argentina

Some fragmentary dinosaur remains from the uppermost Hauterivian–Barremian La Paloma Member of the Cerro Barcino Formation of northern Chubut, Argentina are described. Together with the fauna from the La Amarga Formation of Neuquén, Argentina, this material represent the oldest known Cretaceous dinosaur fauna from South America. It includes remains of a probable titanosaurian sauropod and an abelisaurian, probable abelisaurid, theropod. This is the oldest record of titanosaurs from South America and the oldest record of abelisaurids globally. The presence of both small-bodied noasaurids in the La Amarga Formation and medium-sized–large abelisaurids in the Cerro Barcino Formation, in the middle Lower Cretaceous of Argentina, indicates that abelisaurian diversification began well before the final fragmentation of Gondwana. Whereas this explains the wide distribution of abelisaurs in the Late Cretaceous, reasons other than vicariance must be invoked for their apparent absence in the ‘middle’ Cretaceous of Africa.

South American reference pole for the mid-Cretaceous: Further constraints in the interpretation of Andean paleomagnetic data

A paleomagnetic study of the Aptian Cerro Barcino Formation in central Patagonia showed the presence of a stable magnetization with a positive tilt test. The obtained pole position (lat 85°S, long 181°E, α 95 = 5.6°, N = 11) differs from reliable Early and Late Cretaceous South American cratonic poles. The Cerro Barcino pole overlaps coeval poles from the Chilean Andean fore arc previously interpreted to record crustal block rotations. This new result indicates that previously published Andean tectonic models must be reviewed.