Neogene Research Papers - Academia.edu (original) (raw)

A number of motored auger holes have been drilled in 2002 and 2006 in four sand-clay deposits preserved in dissolution pockets within the Dinantian limestones of the watershed north of the Vesdre valley. These deposits of unknown age are... more

A number of motored auger holes have been drilled in 2002 and 2006 in four sand-clay deposits preserved in dissolution pockets within the Dinantian limestones of the watershed north of the Vesdre valley. These deposits of unknown age are currently classified as (Tertiary) SBL in the new geological map of Wallonia. We present detailed lithostratigraphic logs of the deposits and describe the results of sedimentological and mineralogical analyses. In particular, K-Ar dating of neoformed Mn oxides found at the base of one augerhole at Rechain yielded ages ranging from Cenomanian to Santonian, allowing us to place the Rechain and Andrimont deposits within the early Late Cretaceous. This is fully consistent with their topographic location very close beneath the trace of the pre-Cretaceous erosion surface and makes them the westernmost remains of the Hergenrath Member of the Late Cretaceous Aachen Formation. To the west, the Magnee deposit is more "typical SBL", probably correspo...

In this paper, the insectivores, chiropterans and rodents from the middle Miocene site of Can Missert are described. The faunal list of this locality includes the following species: Miosorex grivensis, Desmanella sp., Talpidae indet.,... more

In this paper, the insectivores, chiropterans and rodents from the middle Miocene site of Can Missert are described. The faunal list of this locality includes the following species: Miosorex grivensis, Desmanella sp., Talpidae indet., Vespertilionidae indet., Hispanomys daamsi, Megacricetodon minor, Megacricetodon ibericus, Fahlbuschia crusafonti, Democricetodon brevis nemoralis, Eumyarion medium, Muscardinus hispanicus, Eomuscardinus sp., Paraglirulus werenfelsi and Spermophilinus bredai. H. daamsi is a new Cricetodontine species which is characterized by complete ectolophs and relatively long third lower molars. The rodent association of Can Missert enable one to assign this locality to the late Aragonian, MN 8, being close in age to other localities in the Vallès-Penedès Basin such as Castell de Barberà. However, the proportion in which each species is represented is very different in the two cases. This evidence points to the existence climatic pulses at the end of the Aragonian Mammal-Stage.En este trabajo se describen los insectívoros, quirópteros y roedores del Mioceno medio de Can Missert, en la cuenca del Vallès-Penedès. La lista faunística de esta localidad incluye las siguientes especies: Miosorex grivensis, Desmanella sp., Talpidae indet., Vespertilionidae indet., Hispanomys daamsi, Megacricetodon minor, Megacricetodon ibericus, Fahlbuschia crusafonti, Democricetodon brevis nemoralis, Eumyarion medium, Muscardinus hispanicus, Eomuscardinus sp., Paraglirulus werenfelsi y Spermophilinus bredai. H. daamsi constituye una nueva especie de Cricetodontinae, caracterizada por presentar ectolofos completos y un tercer molar inferior relativamente largo. La asociación de Can Missert permite asignar esta localidad al Aragoniense superior, MN 8, comparable a otras localidades del Vallès-Penedès como Castell de Barberà. Sin embargo, la proporción en que las distintas especies de roedores aparecen representadas en Can Missert es muy diferente de Castell de Barberà, indicando la existencia de importantes pulsos climáticos al final del Aragoniense.

The superfamily Portunoidea including extinct lineages is herein evaluated via cladistic analysis of adult morphological characters and traditional systematics. Nearly every fossil species has been examined via type material, or if this... more

The superfamily Portunoidea including extinct lineages is herein evaluated via cladistic analysis of adult morphological characters and traditional systematics. Nearly every fossil species has been examined via type material, or if this was not possible, through illustrations and original descriptions. The analyses indicate that the superfamily is much more diverse at the family level than has previously been recognized, and three subfamilies, Catoptrinae, Carcininae, and Macropipinae, are herein elevated to family status. One new family, Longusorbiidae; two new genera, Euronectes and Viaophthalmus; and two nomen nova are named herein in addition to the recognition of seven new combinations. The fossil record of each of the resulting families is evaluated and summarized, indicating that the superfamily extends into the Cretaceous but that many of the families are indeed much younger lineages.

Reexamination of Sciurotamias gromovi from the upper Miocene of Ukraine stimulated revision of Sinotamias, a problematic Neogene sciurid of uncertain affinities and previously documented only from the middle-upper Miocene of Asia. A... more

Reexamination of Sciurotamias gromovi from the upper Miocene of Ukraine stimulated revision of Sinotamias, a problematic Neogene sciurid of uncertain affinities and previously documented only from the middle-upper Miocene of Asia. A reanalysis of the Ukrainian material and other morphologically similar taxa shows Sinotamias to be a member of the xerine tribe Marmotini. Sciurotamias gromovi and Tamias atsali are shown to be members of Sinotamias. Tamias anatoliensis from the upper Miocene of Turkey is a junior subjective synonym of Sinotamias primitivus. Sinotamias minutus and Sinotamias maximus are excluded from the genus. The latter species is referred to Kherem. Prospermophilus is synonymized with Sinotamias. Phylogenetic analysis of 23 xerine genera using 66 craniodental characters places Sinotamias among the basal Marmotina as a sister group to the living members of the subtribe. The species of the genus are united by obliquely striated lower incisors, posteriorly expanded metaconules of M1-2, and posteriorly tapered ectolophid of m1-2. The late Oligocene-early Miocene Asian genus Plesiosciurus, previously classified in the sciurid subfamily Sciurinae, is instead a member of the Marmotini and is recovered as the sister taxon to Miospermophilus and Sinotamias. The genera Ammospermophilus, Cynomys, Marmota, Miospermophilus, Paenemarmota, Plesiosciurus, Sinotamias, and Spermophilus s.l. form a monophyletic subtribe Marmotina, supported by the absence of the mesoconid in m1-3. Miospermophilus is identified as the basal-most member of this group of genera, suggesting a Nearctic origin for the Marmotina. Sinotamias, considered to be a descendant of Plesiosciurus, appears to have originated in Asia and entered Europe around 8.5 Ma.

The extinct euphractine Prozaedyus was recognized remarking the evident morphological resemblance of the dorsal carapace with the extant piche or pygmy armadillo Zaedyus pichiy. From a phylogenetic viewpoint, Prozaedyus has been... more

The extinct euphractine Prozaedyus was recognized remarking the evident morphological resemblance of the dorsal carapace with the extant piche or pygmy armadillo Zaedyus pichiy. From a phylogenetic viewpoint, Prozaedyus has been interpreted as an early diverging Euphractinae restricted, at the moment, to the late Oligocene and early mid Miocene levels (Deseadan to Laventan SALMAs) of southern South America (Argentina, Chile, and Bolivia). We report here a specimen (MSJ-317) coming from the late Miocene (Loma de Las Tapias Formation;~9 Ma, Chasicoan Stage/Age) of western Argentina (San Juan Province), which represents a new species of Prozaedyus. The specimen includes an almost complete skull with complete dental series, some articulated fragments of the dorsal carapace and several isolated fixed and mobile osteoderms. Absence of teeth in the premaxillae, ornamentation pattern of fixed osteoderms, and presence of small foramina in the posterior and lateral margins of both mobile and fixed osteoderms, are characters that allow its inclusion within the genus Prozaedyus. Differences with the other known species of this genus include smaller size (~35-40%), cranial characters (e.g. position of the infraorbital foramen, palatine suture, morphology of the occipital condyles), and ornamentation pattern of mobile osteoderms. The phylogenetic analysis carried out support its relation as a sister group of the other Prozaedyus species, revealing an ancient divergence for the new taxon, occurred before that of the late Oligocene-early mid Miocene forms, and a distant phylogenetic position from Zaedyus pichiy. This new finding represents the youngest record of the genus, extending its biochron several millions of years, and provides novel information on the poorly know post-Santacrucian forms. Additionally, the cranial anatomy of the new species suggests a carnivore/omnivore habit, similar to extant euphractine armadillos but contrary to the insectivore habit proposed for the other Prozaedyus species.

Teluk Bone memisahkan lengan selatan dan tenggara Sulawesi dan dibagi ke dalam beberapa sub-cekungan dan tinggian. Sejarah pada masa Neogen cekungan ini awalnya kurang diketahui akibat kekurangan data. Dari data seismik, multibeam, dan... more

... d'Algérie et des régions méditerranéenne avoisinantes (Cita et al. 1968 ; Mazzola 1971 ; Cita 1975 ; Iaccarino 1985 ; Hilgen et al. 2000b , 2003). CADRE GÉOGRAPHIQUE ET GÉOLOGIQUE Le Djebel Diss (Fig. 2) est situé à... more

... d'Algérie et des régions méditerranéenne avoisinantes (Cita et al. 1968 ; Mazzola 1971 ; Cita 1975 ; Iaccarino 1985 ; Hilgen et al. 2000b , 2003). CADRE GÉOGRAPHIQUE ET GÉOLOGIQUE Le Djebel Diss (Fig. 2) est situé à l'extrémité sud-occidentale des monts du Dahra, sur ...

The Neogene vertebrate fossil record of Greece is famous for its rich mammal assemblages, which were documented as early as the 19th century. In contrast, the equally diverse but comparatively understudied coeval reptile faunas have only... more

The Neogene vertebrate fossil record of Greece is famous for its rich mammal assemblages, which were documented as early as the 19th century. In contrast, the equally diverse but comparatively understudied coeval reptile faunas have only recently gained research attention, both as an important source of information on palaeobiogeographical radiations, and as a potential centre for the early cladogenesis of Europe’s modern herpetofauna. Snake remains have been particularly enigmatic because, despite their ubiquity, they are almost always poorly preserved. Nonetheless, these isolated specimens, consisting almost entirely of vertebrae, reveal a range of taxa including typhlopids, boids, pythonids, colubrids sensu lato, elapids and viperids. To date, only two species have been formally named: the endemic pythonid Python euboicus and the gigantic viperid Laophis crotaloides. Both of these taxa were described in the
19th century and their holotypes are now lost, yet L. crotaloides arguably remains one of the most mysterious snake fossils from Europe. Derived from the early Pliocene (MN 15) of Megalo Emvolon in Northern Greece, L. crotaloides was thought to be a gigantic viper in its initial description. The holotype comprised 13 vertebrae, which although figured only as a schematic diagram, have proven sufficient to identify more recently recovered material, including a large precloacal vertebra (centrum length 16.3 mm) from the type locality. Size estimates based on the new specimen suggest a body length possibly exceeding 3 m, and a mass range of up to 26 kg that would place it amongst the largest venomous snakes ever to have lived. The presence of a gigantic viperid within the late
Neogene ecosystems of mainland Greece concurs with the distribution of other largebodied Mio-Pliocene snakes, including the elapid Naja sp. and an indeterminate species of Vipera. Conversely, their palaeoenvironmental coincidence with cool, dry climates is puzzling and prompts speculation about the ecological and/or physiological factors that must have favoured large ectothermic predators in such an atypical setting.

Surprisingly few natural hydrocarbon seeps have been identified in Australia's offshore basins despite studies spanning thirty years. Early studies of natural hydrocarbon seepage around the Australian margin were generally based on the... more

Surprisingly few natural hydrocarbon seeps have been identified in Australia's offshore basins despite studies spanning thirty years. Early studies of natural hydrocarbon seepage around the Australian margin were generally based on the geochemical analysis of stranded bitumens, water column geochemical ‘sniffer’ sampling, synthetic aperture radar or airborne laser fluorosensor. Later studies involved the integration of these remote sensing and geochemical techniques with multi-channel and shallow seismic. A review of these earlier studies indicates that many seepage interpretations need to be re-evaluated and that previous data sets, when placed in a global context, often represent normal background hydrocarbon levels. Low Recent burial and subsidence rates are not favourable for high rates of seepage. There are also difficulties in proving seepage on high energy, shallow carbonate shelves, where seabed features may be rapidly re-worked and modern marine signatures are overprinted on authigenic seep carbonates. Thus, the relatively few sites of proven natural hydrocarbon seepage in Australia's offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting. Active thermogenic methane seepage on the Yampi Shelf, the only proven documented occurrence in Australia, is driven by deposition of a thick Late Tertiary carbonate succession and Late Miocene tectonic reactivation. Therefore, to increase the success of detecting and correctly interpreting natural hydrocarbon seepage, data need to be analysed and integrated within the context of the local geological setting, and with an understanding of what is observed globally.

2013.01 The tectonic evolution of the Indian Plate, which started in Late Jurassic about 167 million years ago (approximately 167Ma) with the breakup of Gondwana, presents an exceptional and intricate case history against which a variety... more

2013.01 The tectonic evolution of the Indian Plate, which started in Late Jurassic about 167 million years ago (approximately 167Ma) with the breakup of Gondwana, presents an exceptional and intricate case history against which a variety of plate tectonic events such as: continental breakup, sea-floor spreading, birth of new oceans, flood basalt volcanism, hotspot tracks, transform faults, subduction, obduction, continental collision, accretion, and mountain building can be investigated. Plate tectonic maps are presented here illustrating the repeated rifting of the Indian plate from surrounding Gondwana continents, its northward migration, and its collision first with the Kohistan-Ladakh Arc at the Indus Suture Zone, and then with Tibet at the Shyok -
Tsangpo Suture. The associations between flood basalts and the recurrent separation of the Indian plate from Gondwana are assessed. The breakup of India from Gondwana and the
opening of the Indian Ocean is thought to have been caused by plate tectonic forces which were localized along zones of weakness caused by mantle plumes (Bouvet, Marion, Kerguelen, and Reunion Plumes). The sequential spreading of the Southwest Indian Ridge/Davie Ridge, Southeast Indian Ridge, Central Indian Ridge, Palitana Ridge, and Carlsberg Ridge in the Indian Ocean were responsible for the fragmentation of the Indian Plate during the Late Jurassic and Cretaceous times. The Reunion and the Kerguelen Plumes left two spectacular hotspot tracks on either side of the Indian Plate. With the breakup of Gondwana, India remained isolated as an island continent, but reestablished its biotic links with Africa during the Late Cretaceous during its collision with the Kohistan-Ladakh Arc ( approximately 85Ma) along the Indus Suture. Soon after
the Deccan eruption, India drifted northward as an island continent by rapid motion carrying Gondwana biota, about 20cm/year, between 67Ma to 50Ma; it slowed down dramatically to 5cm/year during its collision with Asia in early Eocene (approximately 50Ma). A northern corridor was established between India and Asia soon after the collision allowing faunal interchange. This is reflected by mixed Gondwana and Eurasian elements in the fossil record preserved in several continental Eocene formations of India. A revised India-Asia collision model suggests that the Indus Suture represents the obduction zone between India and the Kohistan-Ladakh Arc, whereas the Shyok Suture represents the collision between the Kohistan-Ladakh Arc and Tibet. Eventually, the Indus-Tsangpo Zone became the locus of the final India-Asia collision, which probably began in early Eocene ( approximately 50Ma) with the closure of Neotethys Ocean. The post-collisional tectonics for the last 50 million years is best expressed in the evolution of the
Himalaya-Tibetan Orogen. The great thickness of crust beneath Tibet and Himalaya and a series of north vergent thrust zones in the Himalaya and the south-vergent subduction zones in Tibetan Plateau suggest the progressive convergence between India and Asia of about 2500km since the time of collision. In the early Eohimalayan phase ( approximately 50 to 25Ma) of Himalayan Orogeny (middle Eocene-late Oligocene), thick sediments on the leading edge of the Indian Plate were squeezed, folded, and faulted to form the Tethyan Himalaya. With continuing convergence of India, the architecture of the Himalayan - Tibetan Orogen is dominated by deformational
structures developed in the Neogene Period during the Neohimalayan phase ( approximately 21Ma to present), creating a series of north-vergent thrust belt systems such as the Main Central Thrust, the Main Boundary Thrust, and the Main Frontal Thrust to accommodate crustal shortening. Neogene molassic sediment shed from the rise of the Himalaya was deposited in a
nearly continuous foreland trough in the Siwalik Group containing rich vertebrate assemblages. Tomographic imaging of the India-Asia Orogen reveals that Indian lithospheric slab has been subducted subhorizontally beneath the entire Tibetan Plateau that has played a key role in the uplift of the Tibetan Plateau. The low-viscosity channel flow in response to topographic loading of Tibet provides a mechanism to explain the Himalayan-Tibetan Orogen. From the start of its
voyage in Southern Hemisphere, to its final impact with the Asia, the Indian Plate has experienced changes in climatic conditions both short-term and long-term. We present a series of
paleoclimatic maps illustrating the temperature and precipitation conditions based on estimates of Fast Ocean Atmospheric Model, a coupled global climate model. The uplift of the Himalaya-Tibetan Plateau above the snow line created two most important global climate phenomena-the
birth of the Asian monsoon and the onset of Pleistocene glaciation. As the mountains rose, and the monsoon rains intensified, increasing erosional sediments from the Himalaya were carried down by the Ganga River in the east and the Indus River in the west, and were deposited in two great deep-sea fans, the Bengal and the Indus. Vertebrate fossils provide additional resolution for the timing of three crucial tectonic events: India-KL Arc collision during the Late Cretaceous,
India-Asia collision during the early Eocene, and the rise of the Himalaya during the early Miocene.

A fragmentary isolated vertebra from the early Pliocene of Megalo Emvolon (also known Karabournou) in Northern Greece is referred to the gigantic extinct viper Laophis crotaloides Owen. This taxon was originally named on the basis of 13... more

A fragmentary isolated vertebra from the early Pliocene of Megalo Emvolon (also known Karabournou) in Northern Greece is referred to the gigantic extinct viper Laophis crotaloides Owen. This taxon was originally named on the basis of 13 vertebrae recovered from Megalo Emvolon in 1857, and subsequently lodged in the collection of The Natural History Museum in London. Unfortunately, the type remains have since been lost and the species thus ignored or relegated to a nomen dubium, in spite of its estimated body length having potentially exceeded 3.5 metres. The incomplete and isolated nature of the new Laophis specimen hinders resolution to lower taxonomic levels. However, the fossil can be unequivocally placed within Viperidae because of its proportionally wide cotyle and condyle (the latter being markedly robust), probable presence of a hypapophysis, and most notably its dorsally tilted prezygapophyseal facets. Moreover, a multivariate quantitative approach supports previous assertions of large body size with an estimated maximum length and body mass, comparable to, if not larger than Lachesis muta, the largest extant viperid - a size that distinguish Laophis as amongst the largest extinct or extant venomous snakes ever known. The presence of a colossal viperid within the late Neogene ecosystems of mainland Greece is also significant because it concurs with the distribution of other gigantic Mio-Pliocene reptiles, including the large elapid Naja sp., another substantial but indeterminate species of Vipera, the varanid lizard Varanus marathonensis, and the colossal tortoises Cheirogaster. Similar coeval taxa have been found throughout the Balkan peninsula, southwestern Europe, and Asia Minor, and coincide with the onset of widespread climatic cooling during the late Miocene–late Pliocene. The spread of savannah grasslands throughout Mediterranean Europe during this time has been used to explain increased body sizes in herbivorous tortoises via dietary selection for greater consumption of C4 vegetation. However alternative ecological and/or physiological factors must be sought for large ectothermic predators, which would have had to effectively compete within a trophic system otherwise dominated by a broad range of mammalian carnivores.

A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern... more

A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern Idaho and northern Nevada, USA. The facies association contrasts with those typical of silicic volcanism elsewhere and records unusual, voluminous and particularly environmentally devastating styles of eruption that remain poorly understood. It includes: (1) large-volume, lithic-poor rhyolitic ignimbrites with scarce pumice lapilli; (2) extensive, parallel-laminated, medium to coarse-grained ashfall deposits with large cuspate shards, crystals and a paucity of pumice lapilli; many are fused to black vitrophyre; (3) unusually extensive, large-volume rhyolite lavas; (4) unusually intense welding, rheomorphism, and widespread development of lava-like facies in the ignimbrites; (5) extensive, fines-rich ash deposits with abundant ash aggregates (pellets and accretionary lapilli); (6) the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre; (7) a bimodal association between the rhyolitic rocks and numerous, coalescing low-profile basalt lava shields; and (8) widespread evidence of emplacement in lacustrine-alluvial environments, as revealed by intercalated lake sediments, ignimbrite peperites, rhyolitic and basaltic hyaloclastites, basalt pillow-lava deltas, rhyolitic and basaltic phreatomagmatic tuffs, alluvial sands and palaeosols. Many rhyolitic eruptions were high mass-flux, large volume and explosive (VEI 6–8), and involved H2O-poor, low-δ18O, metaluminous rhyolite magmas with unusually low viscosities, partly due to high magmatic temperatures (900–1,050°C). SR-type volcanism contrasts with silicic volcanism at many other volcanic fields, where the fall deposits are typically Plinian with pumice lapilli, the ignimbrites are low to medium grade (non-welded to eutaxitic) with abundant pumice lapilli or fiamme, and the rhyolite extrusions are small volume silicic domes and coulées. SR-type volcanism seems to have occurred at numerous times in Earth history, because elements of the facies association occur within some other volcanic fields, including Trans-Pecos Texas, Etendeka-Paraná, Lebombo, the English Lake District, the Proterozoic Keewanawan volcanics of Minnesota and the Yardea Dacite of Australia.

A number of Neogene fossil localities are known from Greece, including classic sites such as Pikermi and Samos, where systematic excavations have been conducted since the nineteenth century. Large mammals have always been the main focus... more

A number of Neogene fossil localities are known from Greece, including classic sites such as Pikermi and Samos, where systematic excavations have been conducted since the nineteenth century. Large mammals have always been the main focus of these excavations, rendering other groups, such as snakes, poorly studied or totally ignored. Nevertheless, fossil snakes appear to be ubiquitous at many localities, but they frequently consist of isolated vertebrae, thus preventing identification to species level. Only two extinct species have been named to date from these localities: Python euboicus, a proportionally large pythonid from the Lower Miocene of Euboea Island, and Laophis crotaloides, a gigantic viperid from the Lower Pliocene of northern Greece, both described in the nineteenth century. Unfortunately, the holotypes of both taxa are lost, and frustratingly, whereas no additional material has ever been found of the former, a large precloacal vertebra has only recently been attributed to L. crotaloides. Previously undescribed material ranging in age from Early Miocene to Late Pleistocene of more than 50 different localities throughout Greece, reveals a rich diversity of taxa consisting of typhlopids, pythonids, colubrids sensu lato, elapids, viperids and several indeterminate forms. The biogeographic importance of the Greek localities, the large number of endemic fossil mammals, and the relatively rich extant snake fauna, make it highly likely that a thorough review of existing collections and new field work, will shed new light on the palaeobiogeography, palaeoecology, systematics and evolution of European snakes.

The Miocene elephantoid Choerolophodon from SE Europe-SW Asia is studied, based on the Greek localities of Thymiana, Axios Valley, Pikermi, Samos and Nikiti-2. Although this genus is well documented in Greece, there is no recent taxonomic... more

The Miocene elephantoid Choerolophodon from SE Europe-SW Asia is studied, based on the Greek localities of Thymiana, Axios Valley, Pikermi, Samos and Nikiti-2. Although this genus is well documented in Greece, there is no recent taxonomic study and its biostratigraphy and palaeoecology had never been examined in detail. Three choerolophodont species are recognized in SE Europe–SW Asia: the Middle Miocene C. chioticus (late Orleanian, MN 5), and the Late Miocene C. anatolicus (early Vallesian, MN 9) and C. pentelici (late Vallesian–Turolian, MN 10–MN 13). The latter species is divided into a primitive morph, dated to the late Vallesian and possibly earliest Turolian, and an advanced morph from the Turolian. At the end of the Miocene Choerolophodon disappeared. With respect to the geographical distribution of Choerolophodon, the genus is very well documented in SE Europe–SW Asia but it is unknown from Central, Western and Northern Europe, a fact which is attributed to ecological factors. The phylogenetic relationships of all known choerolophodont species from the Miocene of the Old World are examined using a cladistic analysis, and their proposed biogeography is discussed. Finally, the palaeoecology of Late Miocene Choerolophodon from Northern Greece is studied through a dental microwear analysis, revealing that Choerolophodon foraged mainly on grasses, a type of vegetation widespread in open environments. These palaeoecological results are in agreement with previous environmental reconstructions for the Late Miocene of Greece.

Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending to a cave-forming zone from below in leaky confined conditions, where deeper groundwaters in regional or intermediate flow systems... more

Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending to a cave-forming zone from below in leaky confined conditions, where deeper groundwaters in regional or intermediate flow systems interact with shallower and more local groundwater flow systems. This is in contrast to more familiar epigenic speleogenesis which is dominated by shallow groundwater systems receiving recharge from the overlying or immediately adjacent surface.Hypogenic caves are identified in various geological and tectonic settings, formed by different dissolutional mechanisms operating in various lithologies. Despite these variations, resultant caves demonstrate a remarkable similarity in patterns and meso-morphology, which strongly suggests that the hydrogeologic settings were broadly identical in their formation. Hypogenic caves commonly demonstrate a characteristic suite of cave morphologies resulting from rising flow across the cave-forming zone with distinct buoyancy-dissolution components. In addition to hydrogeological criteria (hydrostratigraphic position, recharge–discharge configuration and flow pattern viewed from the perspective of the evolution of a regional groundwater flow system), morphogenetic analysis is the primary tool in identifying hypogenic caves.Cave patterns resulting from ascending transverse speleogenesis are strongly guided by the permeability structure in a cave formation. They are also influenced by the discordance of permeability structure in the adjacent beds and by the overall hydrostratigraphic arrangement. Three-dimensional mazes with multiple storeys, or complex 3-D cave systems are most common, although single isolated chambers, passages or crude clusters of a few intersecting passages may occur where fracturing is scarce and laterally discontinuous. Large rising shafts and collapse sinkholes over large voids, associated with deep hydrothermal systems, are also known.Hypogenic caves include many of the largest, by integrated length and by volume, documented caves in the world. More importantly, hypogenic speleogenesis is much more widespread than it was previously presumed. Growing recognition of hypogenic speleogenesis and improved understanding of its peculiar characteristics has an immense importance to both karst science and applied fields as it promises to answer many questions about karst porosity (especially as deep-seated settings are concerned) which remained poorly addressed within the traditional epigenetic karst paradigm.

Most submarine canyons are erosive conduits cut deeply into the world’s continental shelves through which sediment is transported from areas of high coastal sediment supply onto large submarine fans. However, many submarine canyons in... more

Most submarine canyons are erosive conduits cut deeply into the world’s continental shelves through which sediment is transported from areas of high coastal sediment supply onto large submarine fans. However, many submarine canyons in areas of low sediment supply do not have associated submarine fans and show significantly different morphologies and depositional processes from those of ‘classic’ canyons. Using three-dimensional seismic reflection and core data, this study contrasts these two types of submarine canyons and proposes a bipartite classification scheme.The continental margin of Equatorial Guinea, West Africa during the late Cretaceous was dominated by a classic, erosional, sand-rich, submarine canyon system. This system was abandoned during the Paleogene, but the relict topography was re-activated in the Miocene during tectonic uplift. A subsequent decrease in sediment supply resulted in a drastic transformation in canyon morphology and activity, initiating the ‘Benito’ canyon system. This non-typical canyon system is aggradational rather than erosional, does not indent the shelf edge and has no downslope sediment apron. Smooth, draping seismic reflections indicate that hemipelagic deposition is the chief depositional process aggrading the canyons. Intra-canyon lateral accretion deposits indicate that canyon concavity is maintained by thick (>150 m), dilute, turbidity currents. There is little evidence for erosion, mass-wasting, or sand-rich deposition in the Benito canyon system. When a canyon loses flow access, usually due to piracy, it is abandoned and eventually filled. During canyon abandonment, fluid escape causes the successive formation of ‘cross-canyon ridges’ and pockmark trains along buried canyon axes.Based on comparison of canyons in the study area, we recognize two main types of submarine canyons: ‘Type I’ canyons indent the shelf edge and are linked to areas of high coarse-grained sediment supply, generating erosive canyon morphologies, sand-rich fill, and large downslope submarine fans/aprons. ‘Type II’ canyons do not indent the shelf edge and exhibit smooth, highly aggradational morphologies, mud-rich fill, and a lack of downslope fans/aprons. Type I canyons are dominated by erosive, sandy turbidity currents and mass-wasting, whereas hemipelagic deposition and dilute, sluggish turbidity currents are the main depositional processes sculpting Type II canyons. This morphology-based classification scheme can be used to help predict depositional processes, grain size distributions, and petroleum prospectivity of any submarine canyon.

During the Neogene, northern South America maintained a very diverse reptilian fauna. Especially crocodyliforms were diverse, with almost 30 species and a disparity of morphotypes greater than that seen in any other crocodylian fauna,... more

During the Neogene, northern South America maintained a very diverse reptilian fauna. Especially crocodyliforms were diverse, with almost 30 species and a disparity of morphotypes greater than that seen in any other crocodylian fauna, extant or otherwise. Our knowledge of the impressive Neotropical South American Cenozoic record of reptiles is based largely on three units: the Middle Miocene Honda Group of Colombia and the Upper Miocene Solimões and Urumaco Formations, respectively of Brazil and Venezuela. Additional insight into the Neotropical reptilian fossil record derives from several smaller or lesser-known Upper Oligocene to Lower Pliocene deposits in several countries on the continent. In this chapter we review turtle and crocodyliform faunas found in these deposits. The Miocene development of the faunas in Amazonia corresponds to a shift from lake-dominated to fluvial-dominated ecosystems in the Late Miocene. They also show that full marine conditions at the time were limited to coastal areas around the continent and apparently did not extend into the contintent’s interior.