Comment on 'Tectonic and environmental factors controlling on the evolution of Oligo-Miocene shallow marine carbonate factories along a tropical SE Circum-Caribbean' by Silva-Tamayo et al. (2017)

Silva-Tamayo et al. (2017) study the Chattian to Langhian carbonate succession of the Siamana Formation in the Cocinetas Basin (La Guajira, Colombia). They identify a change in carbonate factory from mixed photozoan-heterozoan and photozoan associations dominated by corals in the Chattian-early Burdigalian to a heterozoan rhodalgal association in the late Burdigalian-Langhian. To validate the regional scale of this shift in carbonate-producing biota along the southeastern Circum-Caribbean realm, Silva-Tamayo et al. compare the Siamana Formation with the San Luis carbonate succession in the Falcón Basin (NE Venezuela) and the Perla carbonates in the Urumaco Trough (Gulf of Venezuela). Referring to Albert-Villanueva (2016) they state that, as in the case of the Siamana Formation, the carbonates of the San Luis Formation also recorded a change in carbonate-producing biota, from a photozoan/heterozoan carbonate factory in the late Oligocene-early Miocene to a heterozoan/rhodalgal carbonate factory in the middle Miocene. Notwithstanding, Albert-Villanueva (2016) interprets the carbonate units cropping out in the Falcón Basin (San Luis and Churuguara formations) as early Miocene in age, and the passage from photozoan to heterozoan carbonate factory as a lateral change of facies within the lower Miocene carbonate platforms of the Falcón Basin

Geology of the Falcón Basin (NW Venezuela)

This paper presents a geological map and cross-section of the Falcón Basin based both on published and unpublished work and on new data collected in the northern and southern basin margins. The geological map covers an area of 4600 km2 at 1:100,000 scale. The cross- section is oriented NNW-SSE, traversing perpendicular to the main structures. In general, the structure of the study area results from the inversion of a graben (Oligocene-early Miocene back-arc basin), that started in the middle Miocene due to the convergence between the Caribbean and South American plates. The map, the cross-section and the observations made in the field have been used to generate a tectonostratigraphic reconstruction of the Falcón Basin. The Oligocene-early Miocene sedimentary succession mapped and described is relevant to the hydrocarbon exploration in the Caribbean and in the Gulf of Venezuela, where new hydrocarbon resources have recently been discovered (i.e. Perla gas field)

Tectonostratigraphic evolution of the Gulf of Venezuela.

Master's thesis in Petroleum Geosciences EngineeringThe Gulf of Venezuela is located at the boundary between the Cretaceous-Cenozoic deformation zone of the South American and Caribbean plates. It is an underexplored area lying between the hydrocarbon-rich Maracaibo Basin and the emergent plays such as the Perla field (Late Oligocene to Early Miocene carbonates) located on the allochthonous terrane. Gravity data, stratigraphy, structural styles, and subsidence plots reveal three main basement provinces in the Gulf of Venezuela: (1) A western Paleozoic basement (Maracaibo province) with continental-affinity similar to those in the Guajira Peninsula and the Maracaibo Basin; (2) a central province covering the area of the Urumaco trough offshore with Meso-Neoproterozoic rocks (Urumaco province); and (3) an easternmost province, with Cretaceous Caribbean arc rocks, related to the Leeward Antilles island arc system (Caribbean province). Two major interpreted strike-slip faults define the boundary between the main provinces. The Cuiza-Río Seco fault is the western flank of the Urumaco trough offshore and represents a structural and stratigraphic abrupt change that is proposed as the boundary between the Maracaibo autochthonous province and the allochthonous provinces. The Pueblo Nuevo fault is proposed to be the continuation onland of a major interpreted strike-slip fault, defining the boundary between the central and easternmost province. In addition, the Cuiza-Río Seco and Pueblo Nuevo faults accommodate strain partitioning as well as the Oca- Ancón fault but at different timing, due to oblique compression of the Caribbean plate against the South American plate. Furthermore, a pop-up structure associated with the Sierra de Perijá is recognized in the southernmost Maracaibo province, allowing to define about ̴ 70-80 km of right-lateral strike-slip displacement along the Oca fault. This fault has a relevant role to the present-day basement configuration, since it has displaced eastwards and segmented the northern part of the basement provinces, resulting in a more complex distribution that needs to be considered to reconstruct the geologic history. Considering the continuation of the Maracaibo block northwards, this region might hold promising opportunities for hydrocarbons exploration, where the Maracaibo Basin petroleum system might extends offshore into the Gulf of Venezuela.The Conjugate Basins, Tectonics and Hydrocarbons Project (CBTH)submittedVersio

A new Megatheriinae skull (Xenarthra, Tardigrada) from the pliocene of northern venezuela – Implications for a giant sloth dispersal to central and North America

A skull of a ground sloth from the Pliocene San Gregorio Formation documents a northern neotropical occurrence of a megatheriine that addresses issues on intraspecific variation and biogeography. The new specimen is broadly similar in size and morphology to that of Proeremotherium eljebe from the underlying Codore Formation in the Urumaco Sequence, differing in several features such as a longer basicranial area and a more posteriorly projected basioccipital between the condyles. The living sloths species of Bradypus and Choloepus do not have unequivocal anatomical features that indicate sexual dimorphism. Nevertheless, fossil sloths may have shown such dimorphism, and speculations on this subject are part of the considerations that can be made when allocating fragmentary fossils (e.g., in the new skull the presence of a long sagittal crest could indicate a male individual and the absence of an extended crest in Proeremotherium eljebe a female one). We speculate that as early as the late middle Miocene, two main lines of Megatheriinae had clearly separated in two geographic areas, one in the rising Andean area and one at low latitudes on the lowlands of central and northern South America.Fil: Carlini, Alfredo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico de Paleontología de Vertebrados; ArgentinaFil: Brandoni, Diego. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Sánchez, Rodolfo. Museo Paleontológico de la Alcaldia de Urumaco; VenezuelaFil: Sánchez Villagra, Marcelo R.. Universitat Zurich; Suiz

Geochemical study of products associated with spontaneous oxidation of coal in the Cerro Pelado Formation, Venezuela

The aim of this research work is a geochemical, mineralogical, and textural characterization of spontaneously smouldered coal-derived products in northwestern Venezuela (Cerro Pelado Formation, some 10 km from Pedregal city). Several solid samples were collected from this formation, six of unweathering coal, an other six of resulting unmelted rocks forming on a surface coal bed, and the last four of mineralizations found accumulating around gas vents. The fresh coal and the unmelted material were analysed by scanning electron microscopy, X-ray diffraction, and proximate techniques. Products such as magnetite and chabazite-K were identified in the alteration rocks. Likewise, both materials were also studied in order to determine the mobilization of 17 elements into the environment; such elements were analysed through inductively coupled plasma atomic emission spectroscopy on extracts obtained by a sequential extraction method: each sample was firstly extracted with MilliQ water and then the resultant residue was washed. This and the subsequently resulting residues are extracted according to the mentioned procedure by using, respectively, ammonium acetate, chlorhydric acid, peroxide and chlorhydric acid, nitric acid and fluorhydric acid, and nitric acid. The studied elements are classified as highly mobile (Na, Ni, ...), nearly immobile (Ti, P) and partially mobile (Mg, Fe, K,...). In regards to mineralizations around fumaroles associated with smoldering coal seams, Fourier-transform infrared spectroscopy and X-ray diffraction analyses have revealed the presence of salammoniac, mascagnite and other solid combustion compounds formed by reaction of gas emitted from coal oxidation, in addition to previously non-reported sulfur-rich by-products associated with gas fissures, particularly ammonium thiosulfate, a phase first obtained only synthetically in the laboratory. Another objective of the research was to collect and analyse gases escaping from surficial vents. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied coal outcrop, as well as aliphatic hydrocarbons including ethane, propane, butanes, among others. High contents of carbon monoxide, methane and carbon dioxide were also measured for gas samples

A new Megatheriinae skull (Xenarthra, Tardigrada) from the pliocene of northern Venezuela : Implications for a giant sloth dispersal to central and North America

A skull of a ground sloth from the Pliocene San Gregorio Formation documents a northern neotropical occurrence of a megatheriine that addresses issues on intraspecific variation and biogeography. The new specimen is broadly similar in size and morphology to that of Proeremotherium eljebe from the underlying Codore Formation in the Urumaco Sequence, differing in several features such as a longer basicranial area and a more posteriorly projected basioccipital between the condyles. The living sloths species of Bradypus and Choloepus do not have unequivocal anatomical features that indicate sexual dimorphism. Nevertheless, fossil sloths may have shown such dimorphism, and speculations on this subject are part of the considerations that can be made when allocating fragmentary fossils (e.g., in the new skull the presence of a long sagittal crest could indicate a male individual and the absence of an extended crest in Proeremotherium eljebe a female one). We speculate that as early as the late middle Miocene, two main lines of Megatheriinae had clearly separated in two geographic areas, one in the rising Andean area and one at low latitudes on the lowlands of central and northern South America.Facultad de Ciencias Naturales y Muse

The Tropics as Reservoir of Otherwise Extinct Mammals: The Case of Rodents from a New Pliocene Faunal Assemblage from Northern Venezuela

We report a new vertebrate assemblage from the Pliocene Vergel Member of the San Gregorio Formation in northwestern Venezuela, which includes Crocodylia and Testudines indet., toxodonts, at least four species of xenarthrans of the Dasypodidae, Pampatheriidae, Glyptodontidae and Megatheriidae, and rodents. The last are Cardiatherium, cf. Caviodon (Hydrochoeridae), Neoepiblema (Neoepiblemidae), and what is here described as a new genus of a low-crowned octodontoid. cf. Caviodon is the first cardiomyine for northern South America. The rodent assemblage resembles in its ecological composition those of the late Miocene (Huayquerian) from the "Mesopotamian” of Argentina and the Acre region in Brazil, with partially overlapping systematic composition. The stratigraphic position of the San Gregorio Formation and mammals other than caviomorphs suggest a late Pliocene age for these sediments, implying the endurance of rodent taxa beyond their biochron in southern South Americ

Systematics of the South American Native Ungulates and the Neogene Evolution of Mammals from Northern South America

South America was isolated from other continents during most of the Cenozoic and it was home of an endemic mammalian fauna. Among the most characteristic faunal elements are the South American native ungulates (SANUs), a group of ungulate-grade mammals that were widespread and highly diverse in the continent. Despite of significant advances, the phylogenetic interrelationships of SANUs are not fully resolved, and remain a major challenge in palaeomammalogy. The evolutionary history of SANUs and other endemic mammals is recorded mostly in higher latitudes; however, most of the mammal diversity today is found in lower latitudes, and there is a need to increase the record of Neotropical fossils in order to better understand the evolution of diversity gradients in mammals. The aim of this dissertation is to study exceptional new fossils that serve to address the phylogenetic relationships of one of the main SANU clades (Notoungulata) with other placentals, and review the systematics and diversity of Neogene mammals based on the documentation of new fossil assemblages from northern South America. Chapter one presents the description of the oldest notoungulate skeleton with associated dental and postcranial remains: Thomashuxleya externa (Isotemnidae, Notoungulata) from the middle Eocene of Patagonia, Argentina. The exceptionally complete specimen is the basis of an estimate of body size of approximately 235 kg; the fossil is integrated in an examination of the phylogenetic hypotheses for the relationships of Notoungulata with other placentals. An analysis combining morphological and molecular data favours a limited number of hypothetical trees, but it cannot definitely arbitrate between affinities of Thomashuxleya with Afrotheria or Laurasiatheria. When constrained as monophyletic with the Pleistocene notoungulate Toxodon (known for collagen sequences), Thomashuxleya is reconstructed on the stem to Euungulata (Perissodactyla + Artiodactyla) or as sister to Perissodactyla. The isolation of South America finished with the formation of the Isthmus of Panama, which established a land connection with North America and facilitated the faunal exchange between the two continents, a biotic event known as the Great American Biotic Interchange (GABI). Chapter two presents a biogeographic analysis of the mammalian faunas in South America from the Miocene to the Pliocene, and a revision of the temporal and geographic distribution of mammals during the GABI. It shows that the tropical and temperate faunas can be clearly differentiated since at least the middle Miocene, and documents a strong sampling bias in the fossil record towards higher latitudes and younger localities, which represents a challenge to paleontological studies of the GABI. Chapter three and four represent contributions towards filling this temporal and geographic gap in the Neotropical fossil record based on the description of new material from the Cocinetas (northern Colombia) and Falcó (northwestern Venezuela) basins Chapter three describes new remains of giant rodents (Neoepiblemidae, Caviomorpha) from the Urumaco Formation (late Miocene), in the Falcón basin. It documents the presence of at least two taxa of neoepiblemids in the assemblage, Phoberomys and Neoepiblema. Furthermore, the dental variation observed suggests that several of the Phoberomys species previously described represent different ontogenetic stages of only few taxa. Chapter four describes Neogene SANU material from the Cocinetas and Falcón basins, and it provides a phylogenetic analysis for Astrapotheriidae and Toxodontidae. In the Cocinetas basin, the middle Miocene fauna of the Castilletes Formation includes Hilarcotherium sp. nov. (Astrapotheriidae), cf. Huilatherium (Leontiniidae), and Neodolodus cf. colombianus (Proterotheriidae). The late Pliocene fauna of the Ware Formation includes Toxodontinae indet. and the oldest record of Camelidae indet. (Artiodactyla) in South America. In the Falcón basin, the Pliocene faunas of the Codore and San Gregorio Formations include Toxodontidae gen. et sp. nov. and Protherotheriidae indet. These new data add evidence to the tropical provinciality documented for Astrapotheria, Leontiniidae during the middle Miocene. The Pliocene faunas from the Ware and San Gregorio formations are characterized by the predominance of native South American taxa, despite their proximity to the Isthmus of Panama. Only one North American ungulate herbivore immigrant is present (Camelidae indet.). The Pliocene faunas also document an important landscape change in the region and suggest that ecological processes. Key words Mammalia, Notoungulata, Litopterna, Astrapotheria, Caviomorpha, Neotropics, Patagonia, Argentina, Colombia, Venezuela, Phylogeny, Biogeography, Eocene, Miocene, Pliocene, Great American Biotic Interchange and biotic interactions could have affected the diversity dynamics and biogeographic patterns of SANUs during the GAB

Gravity Data Analysis and 3D Modeling of the Caribe-South America Boundary (76°– 64° W)

A new gravity data compilation for Venezuela reprocessed and homogenized. Analysis of the gravity maps using different techniques. In this work, results of independent detailed geophysical surveys were used in conjunction with the reprocessed gravity data in the construction of 3-D density model to study of the tectonic of the Caribbean-South America plate boundary

Arguments for and against the Pacific origin of the Caribbean Plate: discussion, finding for an inter-American origin

Arguments in support of the Pacific origin for the Caribbean Plate are discussed along with others that point to an inter-American origin. Entry of a Pacific-derived plate would have involved unlikely, geometrically complex and highly diachronous events. They would have included changes in direction of subduction, changes in direction of plate migration, major (1000s of km) plate migration, major rotation of large parts of a volcanic arc, major rotations of the Maya and Chortis blocks and diachronous development of flysch/wildflysch deposits as the entering plate interacted with neighbouring elements. The internal structural conformity of the Caribbean Plate and of the Maya and Chortis blocks with regional geology of Middle America shows that no major migrations or rotations have occurred. Coeval, regional deposits of Albian shallow water limestones, Paleocene– Middle Eocene flysch/wildflysch deposits, Middle Eocene limestones, and a regional Late Eocene hiatus show an inter-American location, not a changing Pacific-Caribbean location. Neogene displacement of the Caribbean relative to North and South America amounts to no more than 300 km