Добрый день, Коллеги. Важное сообщение, просьба принять участие. Музей Ферсмана ищет помощь для реставрационных работ в помещении. Подробности по ссылке
A comparative analysis of the Late Cretaceous–Paleocene volcanism was conducted for four areas of Kamchatka: the Pravyi Tolbachik–Levaya Shchapina–Adrianovka interlfuve (the northern part of the Tum-rok Range), the area south of the Ipuin River and Mt. Khrebtovaya (the northern Valaginsky Range), the area of Mt. Savul’ch (the upper reaches of the Kitil’gina River, northern Valaginsky Range), and the Kirganik– Levaya Kolpakova interfluve (the Sredinny Range). New petrochemical, geochemical, and isotopic data on the volcanic rocks from these areas are reported. The examination of this material, together with already published data on volcanic and plutonic rocks of similar composition and age, made it possible to establish the following: (1) the considered basaltoids are ascribed to the subalkali basalt–trachyandesite series with transition toward a meymechite–picrite rock association; (2) the alkali content in the rocks of the Valaginsky–Tumrok–Sredinny ranges increases simultaneously with the increase of the Rb content, while the contents of HFSE and radioactive elements decrease and then again increase. Two trends are identified in the Ybn–Cen diagram: a positive trend spanning most of the volcanic and plutonic rocks and a negative trend defined by the data points of the meyme-chite–picrite association. The first trend reflects the rock evolution during crystallization differentiation, while the second trend was produced by different degrees of melting of initial protolith. The possible geodynamic reconstructions of this volcanism are discussed as well
The Fossil Bluff Group of eastern Alexander Island was deposited in the fore-arc basin of an active magmatic arc, which formed the present-day Antarctic Peninsula. Cephalopods are common throughout the group. Ammonites and belemnites of several localities within the northern half of the outcrop are described, and previously described cephalopods are revised. Nine genera and seventeen species of ammonites (of which Raimondiceras alexandrensis and Blanfordiceras weaveri are new), and two genera and sixteen species of belemnites (including two new subgenera: Belemnopsis {Parabelemnopsis) and B. (Telobelemnopsis), and four new species: B. {Belemnopsis) launceloti, B. (T.) rymilli, B. (T.) bertrami and B. (T.) stephensoni) are described. This detailed study of the cephalopods indicates that the Fossil Bluff Group ranges in age from Kimmeridgian (late Jurassic) to at least Aptian (early Cretaceous), and enables seven ammonite biozones and three belemnite biozones (including two sub-biozones) to be erected within the group. By comparing this new biozonation with other Southern Hemisphere schemes, the positions of the stage boundaries within the succession can be recognized.
In this paper we present new geochronological and thermochronological data from the Turkestan-Alai segment of the southern Kyrgyz Tien Shan, the Ferghana Basin transition and the Trans-Alai Pamir foreland. In the southern and central parts of the Alai Range, towards the Alai Valley, mainly post-collisional granitoids were targeted for zircon U/Pb dating by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), apatite fission-track (AFT) and apatite (U-Th-Sm)/He (AHe) thermochronology. These granitoids, and their thermally metamorphosed contact aureole, yielded Middle Permian zircon crystallization ages of 284 ± 4 to 264 ± 5 Ma. AFT ages (both using the traditional external detector approach as well as using LA-ICP-MS) for these samples are constrained to the Miocene and range between 22.3 ±1.1 and 8.4 ±0.3 Ma, while the AHe ages are somewhat younger, between 12.5 ±0.8 and 5.0 ± 0.3 Ma. This low-temperature thermochronological data suggests an Early Miocene onset of denudation in this area in the Tien Shan orogen, continuing through the Miocene and Pliocene. This denudation is interpreted as a response to reactivation of the mountain belt in the framework of India-Eurasia convergence, and specific to this region, of the Pamir-Tien Shan interaction. On the northern slopes of the Alai Range, at the edge of the Ferghana Basin, a Late Palaeozoic conglomerate yielded a reset Early Cretaceous AFT age of 118 ± 7 Ma, pointing to an older denudation event with respect to those identified in the southern and central parts of the Alai Range. A Mesozoic sediment sample from the same region only contains a Late Triassic age component of ~223 Ma. Mesozoic and Cenozoic age components on the other hand are all detected in the Cenozoic sediments of the Trans-Alai Range, at the transition between the southern Alai Valley and the Pamirs, revealing several Meso-Cenozoic denudation events in the adjoining basement source rocks. The age components in these detrital apatites are ~207 Ma, ~75 Ma, ~18 Ma and ~3 Ma.
The Late Paleozoic Tien Shan fold belt was formed in the course of subduction of the crust underlying the past Turkestan ocean under the Kazakh continent and subsequent collision of the latter with the Alai and Tarim massifs. The onset of subduction is evidenced by development of flysch sequences and olistostromes in the accretionary complex of the South Tien Shan: in the terminal Visean–Serpukhovian (~330–325 Ma ago) in the west and in the second half of the Bashkirian Age (~315 Ma ago) in the east of the Kyrgyz Tien Shan [1].1 The onset of collision between the Kazakh continent and Tarim Massif is dated back to the terminal Late Carboniferous based on the initiation of a foredeep along the northern margin of the latter [6]. The mature collision stage began in the mid-Asselian, when the last sea basins disappeared in the Tien Shan and granitoids intruded in its southern segment [1, 9]. The position and age of the volcanic arc that was forming in the course of convergence between the Kazakh continent and the Tarim Massif remain unclear. Recently, this problem acquired particular significance, since the data available for the territory of China imply subduction under the Tarim Massif and an Early Carboniferous age of collision, i.e., substantially older as compared with that assumed for the Kyrgyz region [7].
ANDREWS, J. T., AUSTIN, W. A., BERGSTEN, H. & JENNINGS, A. E. Palaeoceanography of North Atlantic margins: an introduction KNUDSEN, K. L. & AUSTIN, W. E. N. Late glacial foraminifera Canadian North Atlantic margins ANDREWS, J. T., OSTERMAN, L. E. JENNINGS, A. E., SYVITSKI, J. P. M., MILLER, G. H. & Weiner, N. Abrupt changes in marine conditions, Sunneshine Fiord, eastern Baffin Island, NWT during the last deglacial transition: Younger Dryas and H-0 events JENNINGS, A. E., TEDESCO, K. A., ANDREWS, J. T. & KIRBY, M. E. Shelf erosion and glacial ice proximity in the Labrador Sea during and after Heinrich events (H-3 or 4 to H-0) as shown by foraminifera SYVITSKI, J. P. M., LEWIS, C. F. M. & PIPER, D. J. W. Palaeoceanographic information derived from acoustic surveys of glaciated continental margins: examples from eastern Canada
Layered intrusions have received continuous interest since the publication of the treatise on ‘Layered Igneous Rocks’ by Lawrence Wager and Malcolm Brown, updated in books edited by Ian Parsons in 1987 and Grant Cawthorn in 1996. The study of these fossilized magma chambers keep inspiring a number of scientists with a range of interests including petrology and igneous differentiation, geochronology, geochemistry, mineralogy, rock textures and fabric, fluid dynamics, and ore deposits. The goal of this book is to further our understanding of magma chamber processes and crystal-liquid relationship during magma cooling magma. Physical and chemical processes are now better quantified thanks to the development analytical and computing tools such as compositional mapping, 3D X-ray computed tomography, in situ analyses for trace elements and isotopes, development of new experimental facilities, and progress in instrument sensitivity <...>
Cinq ans après la parution de deux premiers Tomes, consacrés à l'étude de la Stratigraphie et de la Paléontologie du Bassin côtier de Tarfaya (1966), voici que nous présentons aujourd'hui le Tome III, consacré également à la Paléontologie de cette province, dont le Crétacé s'est révélé d'une richesse inouïe en fossiles.
Ce Tome III comporte une série d'importantes études sur les Mollusques du Crétacé, notamment celle du Général M. Collignon sur les Gastéropodes, celle de Madame S. Freneix sur les Lamellibranches, celle de J. Sornay sur les Inocerames. Il s'y ajoute une quatrième étude sur les Echinides du Moghrebien par J. Roman.
La particularité des formations crétacées de cette région consiste dans le fait que l'érosion, au lieu de dissoudre les coquilles des fossiles, les dégage au contraire patiemment en dissolvant peu à peu la roche encaissante. Cette action est due sans doute d'une part au climat, caractérisé par de très faibles précipitations, et au contraire par des brouillards matinaux intenses, d'autre part au fait que toutes les eaux de la région sont plus ou moins salées. Quoiqu'il en soit, on y récolte des fossiles de toute beauté en excellent état de conservation, ce qui est d'ailleurs attesté par les planches de photographies.
Le genre Acrioceras a été proposé par A. HYATT en 1 900 pour 1 'Ancyloceras tabarelli ASTIE ammonite à coquille tripartite, admettant une partie initiale spiralée, une hampe et une crosse mais de taille bien inférieure à celle des véritables Ancyloceras. Durant longtemps, le nombre des espèces attribuées à Acrioceras est demeuré des plus réduits, limité en fait au générotype et à un taxon voisin, également proposé par ASTIER : A. terveri . Dans le cadre de sa révision des ammonites «déroulées>> du Crétacé inférieur du Sud-Est de la France, S. SARKAR[ 1 9 5 5] a multiplié les créations typologiques à partir du matériel déposé dans les collections publiques. <...>
Le Toarcien du sous-bassin nord-lusitanien (Portugal) a fourni plus de 2 800 coquilles appartenant au nouveau genre Soaresirhynchia (Rkynehoneilacea, Wellerellidae). Sîolmo-rhynchia Buckman étant mieux défini depuis la révision de son espèce-type, S. stoiidota (Prosser, 1993), les espèces toarciennes jusqu'ici rapportées à ce genre, doivent en être écartées. Elles sont désormais attribuées à Soaresirhynchia nov. gen. Outre Fespèce-type Rhynchonelia bouchardi Davidson, il s'agit de Rhynchoneila rusîica (Dubar), de R. flamandi (Dubar), de R. clesiana (Lepsius) et de R. renzi nov. sp . Leur révision paléon-tologique constitue F objet de ce travail, chapitre II (sauf celle de R. clesiana non représentée au Portugal). R, renzi, nomen nudum de Choffat, dont Facception est connue grâce aux collections de cet auteur à Lisbonne et qui a fréquemment été citée par Mouterde et al., est décrite et figurée pour la première fois <...>
The Apuan Alps are commonly defined by geologists with the term “tectonic window”, an area where geological processes have brought to the surface rocks that usually lie buried deep under other rock formations. The Apuan Metamorphic Complex is today divided into two tectonic units: the Apuan Unit and the Massa Unit to which belong the mineral deposits object of this study <...>
