Late Miocene Research Papers - Academia.edu (original) (raw)

The NNE-SSW striking Giudicarie Fault System (composed of the Northern and Southern Giudicarie Fault and the Meran-Mauls Fault) represents a distinctive bend and offset in the Periadriatic Fault System (PFS). It terminates the E-W... more

The NNE-SSW striking Giudicarie Fault System (composed of the Northern and Southern Giudicarie Fault and the Meran-Mauls Fault) represents a distinctive bend and offset in the Periadriatic Fault System (PFS). It terminates the E-W striking Tonale Fault Zone to the east, and the ESE-WNW striking Pustertal-Gailtal Fault to the west. Along the Giudicarie Fault System Oligocene tonalitic bodies occur, subsumed under the term 'Oligocene Tonalitic lamellae'. Along the southern part of the Northern Giudicarie Fault only a few < 50 m thick and 200 m long lenses crop out, often strongly affected by brittle deformation. So far no tonalitic bodies have been found between the locality Rumo (Val di Non) and Pawigl (south of Meran), i.e. for some 20 km. From Pawigl to the NE the lenses are more continuous, up to 150 m thick and less affected by brittle deformation. Fission Track analyses was carried out on samples from tonalitic lenses along the Northern Giudicarie Fault and the Meran ...

The fern genus Dryopteris (Dryopteridaceae) is represented in the Hawaiian Islands by 18 endemic taxa and one non-endemic, native species. The goals of this study were to determine whether Dryopteris in Hawai’i is monophyletic and to... more

The fern genus Dryopteris (Dryopteridaceae) is represented in the Hawaiian Islands by 18 endemic taxa and one non-endemic, native species. The goals of this study were to determine whether Dryopteris in Hawai’i is monophyletic and to infer the biogeographical origins of Hawaiian Dryopteris by determining the geographical distributions of their closest living relatives. We sequenced two chloroplast DNA fragments, rbcL and the trnL-F intergenic spacer (IGS), for 18 Hawaiian taxa, 45 non-Hawaiian taxa, and two outgroup species. For individual fragments, we estimated phylogenetic relationships using Bayesian inference and maximum parsimony. We performed a combined analysis of both cpDNA fragments employing Bayesian inference, maximum parsimony, and maximum likelihood. These analyses indicate that Hawaiian Dryopteris is not monophyletic, and that there were at least five separate colonizations of the Hawaiian Islands by different species of dryopteroid ferns, with most of the five groups having closest relatives in SE Asia. The results suggest that one colonizing ancestor, perhaps from SE Asia, gave rise to eight endemic taxa (the glabra group). Another colonizing ancestor, also possibly from SE Asia, gave rise to a group of five endemic taxa (the exindusiate group). Dryopteris fusco-atra and its two varieties, which are endemic to Hawai’i, most likely diversified from a SE Asian ancestor. The Hawaiian endemic Nothoperanema rubiginosum has its closest relatives in SE Asia, and while the remaining two species, D. wallichiana and D. subbipinnata, are sister species, their biogeographical origins could not be determined from these analyses due to the widespread distributions of D. wallichiana and its closest non-Hawaiian relative.

We report on the earliest modern mongooses of Africa, from the late Miocene (ca. 7 Ma) of the hominid locality TM 266, Toros-Menalla, Chad. The material is based on fragmentary dentitions of three individuals. The main diagnostic feature... more

We report on the earliest modern mongooses of Africa, from the late Miocene (ca. 7 Ma) of the hominid locality TM 266, Toros-Menalla, Chad. The material is based on fragmentary dentitions of three individuals. The main diagnostic feature of the Chadian species is the great development of the shear in the carnassials, which distinguishes the Chadian specimens from all extant herpestids

Three specimens of a fossil catfish, collected from the Upper Miocene of Toros-Menalla (Western Djurab, Chad), are identified as members of Auchenoglanis (Claroteidae, Auchenoglanidinae) based on the shape and the ornamentation of the... more

Three specimens of a fossil catfish, collected from the Upper Miocene of Toros-Menalla (Western Djurab, Chad), are identified as members of Auchenoglanis (Claroteidae, Auchenoglanidinae) based on the shape and the ornamentation of the bones of the skull, including a markedly developed parieto-supraoccipital broadly connected with the first nuchal plate. The description is based on a comparison with living specimens of the two valid species of the genus, providing details on their bony anatomy. The fossil fish is a new species, Auchenoglanis soye sp. nov. Original features include supraoccipital process more than twice as wide as long, straight posterolateral border of the sphenotic, parurohyal with a median anterior process, and lateral articular surfaces of the second dorsal spine lateral to the foramen. Auchenoglanis fish are known since the Late Miocene and are endemic to the Nilo-Sudanese province. The fossil record was previously limited to a few isolated spines identified as Auchenoglanis sp., and A. soye sp. nov. is the first fossil species described for the genus. On the basis of preliminary observations of the ichthyofauna from Toros-Menalla, the scarcity of Auchenoglanis in the fossil record might be due to the low abundance of a fish with a rather high ecological valence.

An out-of-Africa dispersal route has been proposed for many organisms, including modern man. However, counter examples of in-to-Africa dispersal routes are less common. In the present article, the phylogenetic relationships within the... more

An out-of-Africa dispersal route has been proposed for many organisms, including modern man. However, counter examples of in-to-Africa dispersal routes are less common. In the present article, the phylogenetic relationships within the Labeoninae, a subfamily of cyprinid fishes distributed in Asia and Africa, were analyzed to investigate the biogeographic processes governing the modern distribution of these Asian and African cyprinids. The mitochondrial DNA cytochrome b gene was used as a molecular marker. The phylogenetic analysis indicated that the subfamily Labeoninae is a monophyletic group, with some Asian labeonins located at the basal position. Two subclades were found that contained both African and Asian species, which highlighted a need for further biogeographic analysis. Based on this analysis, it is proposed that the centre of origin of the Labeoninae was in East Asia. Molecular clock estimation suggests that the Labeoninae arose by the Early Miocene (~23 MYA) during the period of the second Tibetan uplift. Subsequently, two dispersal events of labeonins from Asia into Africa occured in the Early Miocene (~ 20 MYA) and Late Miocene (~9 MYA) and serve as examples counter to out-of-Africa dispersal.

High-grade metamorphic rocks of the upper amphibolite to granulite facies in the Higher Himalayan crystalline (HHC) were studied for their appropriateness for palaeomagnetic investigations. Sampling and fieldwork was accomplished on a... more

High-grade metamorphic rocks of the upper amphibolite to granulite facies in the Higher Himalayan crystalline (HHC) were studied for their appropriateness for palaeomagnetic investigations. Sampling and fieldwork was accomplished on a south-north transect at ˜87°E in the Khumbu region south of Everest. Paragenesis of iron-sulphides and oxides was found to be variable due to different source rocks and metamorphic conditions in this area. Unblocking temperature ranges, isothermal remanence acquisition, low-temperature magnetic properties and microscopic observations confirm the presence of pyrrhotite and magnetite. Two remanence components were separated with unblocking temperature intervals of 250-330 °C and 370-550 °C, which can be attributed to characteristic remanent magnetizations (ChRM) of monoclinic pyrrhotite (ChRMpyr) and magnetite (ChRMmag), respectively. Mainly the ChRMpyr showed a consistent demagnetization behaviour, probably residing in pyrrhotite particles within the single domain to pseudo-single domain range. Normal and reverse polarities were observed, partly co-existing within the unblocking spectrum of single specimens; this (i) supports a thermoremanent (TRM) origin of the ChRMpyr and (ii) indicates that the time span of remanence acquisition was long enough to average out palaeosecular variation. The age of the ChRMpyr can be related to the last metamorphic cooling event at the Early to Late Miocene boundary (16 Ma). The ChRMmag is probably a secondary chemical or thermochemical remanence acquired by hydrothermal processes during retrogression. ChRMpyr and ChRMmag directions are similar suggesting that pyrrhotite and magnetite were magnetized approximately contemporaneously. Separation of the sampling area into three sectors reveals a south-north trend with (i) variable block rotations in the southernmost part close to the Main Central Thrust (five sites), (ii) no rotation in the area between Lukla and Namche (10 sites) and (iii) a significant clockwise rotation (N= 5 sites, D/I= 42.3°/29.4°, k= 20.7, α95= 17.2°) along the Imja Khola north of Namche. We interpret the clockwise rotation as an apparent rotation due to tilting by crustal doming in the Everest region. This doming obviously occurred north of a fault zone located at around Namche and was not affecting the region south of it. The clockwise sense of the apparent vertical-axis rotation indicates that the area north of Namche is located at the western side of the dome structure where westward tilting around a subhorizontal axis occurred (best fit: tilt direction 277°, tilt angle 51°).

A new fossil vertebrate site dating to the late Miocene yielding bird remains was recently discovered at Ruwais in Abu Dhabi, United Arab Emirates. The fossils from the new locality come from the Baynunah Formation which is largely... more

A new fossil vertebrate site dating to the late Miocene yielding bird remains was recently discovered at Ruwais in Abu Dhabi, United Arab Emirates. The fossils from the new locality come from the Baynunah Formation which is largely composed of fluvial deposits. The bird remains from Ruwais and other late Miocene localities with Baynunah Formation deposits are here described. The taxa and material represented are Struthioformidae eggshell, and Anhinga sp. and Ardeidae postcranial skeletal material. The presence of a modern genus in the Miocene has prompted a discussion here of the maximum age of modern genera in the fossil record, which in many cases appears to be Neogene. The latter can in turn lead to the identification of modern species because a past member of a modern genus falls within the size range of a modern species.

October Field is one of the most prolific offshore oil fields in the Gulf of Suez of Egypt. It consists of a number of marine platforms and produces oil from different reservoirs of different geological ages from the Lower Cretaceous to... more

October Field is one of the most prolific offshore oil fields in the Gulf of Suez of Egypt. It consists of a number of marine platforms and produces oil from different reservoirs of different geological ages from the Lower Cretaceous to the Miocene. The aim of this study was to enhance a seismic-log evaluational procedure to evaluate the Miocene-aged Asl and Hawara Formations which encounter the main hydrocarbon and source rock potentials in the area North of October Oil Field. The well logging data, the borehole seismic data, and the velocity surveys are all used in this study. A number of synthetic seismograms are constructed and interpreted together with the deduced seismic impedance and reflection coefficient data for many wells in the study area. In addition, a comprehensive velocity analysis is performed using the seismic times and the computed average and interval velocities. These seismic-derived parameters are primarily used in recognizing and locating precisely the marl and sand sections of Asl Formation which show low to middle amplitudes. Furthermore, a quantitative well logging analysis is carried out over Asl and Hawara Formations to shed light over their hydrocarbon potentiality. Good oil saturation is exhibited by the Asl sand section which reaches to more than 90% in the southern parts of the study area. The petrophysical characters of this sand are very good in terms of good effective porosity (9% to13%), low shale volume (V sh S h > 85%). The sections of the Asl marl and the Hawara shale on the other hand are considered completely wet. An integrated model making use of the seismic- and log-derived properties is applied over the two studied formations for better understanding the reservoir of interest. Many relations are constructed between velocity, seismic impedance, and the rock pore spaces on one hand and between the velocity, lithology, and fluid content on the other hand. This study revealed that the sand section attains very good oil-bearing potentiality in the study area and proved that the application of an integrated model of the log- and seismic-derived properties led to an enhanced evaluation of the Asl and Hawara Formations, good discrimination between their lithological components besides precise differentiation from the overlying Middle to Late Miocene sections. يعد حقل أكتوبر للزيت أحد أهم حقول البترول البحرية Off-shore المنتجة للزيت في خليج السويس بمصر، فهو يتكون من مجموعه من الأرصفة البحريةPlatforms و ينتج من عده خزانات ذات عصور جيولوجية مختلفة تتراوح من الطباشيري السفلي إلي الميوسين. تهدف هذه الدراسة إلي تطبيق نموذج تقييمي يعتمد علي خواص مشتقه من البيانات السيزمية و تسجيلات الآبار و ذلك لتقييم تكويني "عسل" و "هواره" ذا العصر الميوسيني، حيث يحوي هذان التكوينان علي الجهود الهيدروكربونيةHydrocarbon Potentiality و المصدرية الرئيسية للزيت في منطقه شمال حقل أكتوبر. استخدم في هذه الدراسة العديد من تسجيلات الآبار بالإضافة إلي البيانات السيزمية البئرية و بيانات تسجيلات السرعة. كما تم إنشاء و تفسير مجموعه من السيزموجرامات التخليقية Synthetic seismograms مع كل من الممانعة الصوتية و معامل الانعكاس للعديد من الآبار في منطقه الدراسة. بالاضافه إلي هذا تم عمل تحليل كمي للسرعة باستخدام الزمن السيزمي و السرعات المتوسطة و الفترية المقاسة. هذا وقد استخدمت المعاملات المشتقة من البيانات السيزمية بصفه أساسيه و بدقه في تعيين و تحديد نطاقات المارل و الحجر الرملي لتكوين "عسل" ذات السعه القليلة إلي متوسطة Low to middle amplitude . بالاضافه إلي ذلك تم عمل تحليل كميQuantitative analysis متكامل لتكويني "عسل" و "هواره" باستخدام تسجيلات الآبار و ذلك لإلقاء الضوء علي الجهد الهيدروكربونية لكل منهما. وقد أظهر التحليل الكمي احتواء تكوين "عسل علي تشبعات جيده من الهيدروكربونات تصل إلي أكثر من 90%. كما أوضح أن الخواص البتروفيزيقية لهذا الخزان جيده جده و خاصة في الأجزاء الجنوبية من منطقه الدراسة حيث تتراوح المسامية الفعالةEffective porosity ما بين 9% و 13% و التشبع بالزيت إلي أكثر من 85%، في حين يتضاءل حجم الطفلةShale volume إلي اقل من 5%. و من ناحية أخري اعتبرت صخور الطفل و المارل الخاصة بتكوين "هواره" و الجزء العلوي من تكوين "عسل" نطاقات مشبعه كاملا بالماء Wet zones. تم تطبيق نموذج متكاملIntegrated model يجمع ما بين الخواص السيزمية و البتروفيزيقية و ذلك لفهم طبيعة و خواص التكوينين قيد الدراسة بصوره أفضل. و في هذا الصدد تم إنشاء العديد من العلاقات بين السرعة و الممانعة السيزمية و المسامية الصخرية من ناحية، و بين السرعة والمكونات الصخرية و المحتوي من السوائل من جهة أخري. بصفه عامة أكدت هذه الدراسة علي الخواص الهيدروكربونية المميزه لنطاق الحجر الرملي الخاص بتكوين "عسل" و خاصة في الأجزاء الجنوبية من منطقه الدراسة، كما أثبتت أن تطبيق النموذج المتكامل الذي يجمع ما بين الخواص السيزمية والاخري البتروفيزيقية المشتقة من تسجيلات الآبار قد أدي إلي تحسين تقييم التكوينات المدروسة بدرجه كبيره، فضلا عن تحديد مكوناتهما الصخرية بصوره أوضح، بالاضافه إلي فصلهم الدقيق عن رواسب الميوسين التي تعلوهم.

Discoveries in Chad by the Mission Paléoanthropologique Franco-Tchadienne have substantially changed our understanding of early human evolution in Africa. In particular, the TM 266 locality in the Toros-Menalla fossiliferous area yielded... more

Discoveries in Chad by the Mission Paléoanthropologique Franco-Tchadienne have substantially changed our understanding of early human evolution in Africa. In particular, the TM 266 locality in the Toros-Menalla fossiliferous area yielded a nearly complete cranium (TM 266-01-60-1), a mandible, and several isolated teeth assigned to Sahelanthropus tchadensis and biochronologically dated to the late Miocene epoch (about 7 million years ago).

Most of the economic ore deposits of Ecuador are porphyry-Cu and epithermal style gold deposits associated with Tertiary continental arc magmatism. This study presents major and trace element geochemistry, as well as radiogenic isotope... more

Most of the economic ore deposits of Ecuador are porphyry-Cu and epithermal style gold deposits associated with Tertiary continental arc magmatism. This study presents major and trace element geochemistry, as well as radiogenic isotope (Pb, Sr) signatures, of continental arc magmatic rocks of Ecuador of Eocene to Late Miocene (~50–9 Ma, ELM) and Late Miocene to Recent (~8–0 Ma, LMR) ages. The most primitive ELM and LMR rocks analyzed consistently display similar trace element and isotopic signatures suggesting a common origin, most likely an enriched MORB-type mantle. In contrast, major and trace element geochemistry, as well as radiogenic isotope systematics of the whole sets of ELM and LMR samples, indicate strikingly different evolutions between ELM and LMR rocks. The ELM rocks have consistently low Sr/Y, increasing Rb/Sr, and decreasing Eu/Gd with SiO2, suggesting an evolution through plagioclase-dominated fractional crystallization at shallow crustal levels (SiO2. We explain the adakite-type geochemistry of LMR rocks, rather than by slab melting, by a model in which mantle-derived melts partially melt and assimilate residual garnet-bearing mafic lithologies at deeper levels than those of plagioclase stability (i.e., >20 km), and most likely at sub-crustal levels (>40–50 km). The change in geochemical signatures of Tertiary magmatic rocks of Ecuador from the ELM- to the LMR-type coincides chronologically with the transition from a transpressional to a compressional regime that occurred at ~9 Ma and has been attributed by other investigations to the onset of subduction of the aseismic Carnegie ridge. The major districts of porphyry-Cu and epithermal deposits of Ecuador (which have a small size,

The study provides a regional seismic interpretation and mapping of the Mesozoic and Cenozoic succession of the Lusitanian Basin and the shelf and slope area off Portugal. The seismic study is compared with previous studies of the... more

The study provides a regional seismic interpretation and mapping of the Mesozoic and Cenozoic succession of the Lusitanian Basin and the shelf and slope area off Portugal. The seismic study is compared with previous studies of the Lusitanian Basin. From the Late Triassic to the Cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence. The