岐阜県中津川市，小秀山北西斜面に分布する流紋岩質溶岩 (小秀山流紋岩) のK-Ar年代

The distribution of foraminifera in the Uscari, Rio Banano, Moin Formations of the Limon Basin, Costa Rica, is the subject of this study. Heterostegina antillea and Lepidocyclina (L.) waylandvaughani place the basal Uscari Formation of Quebrada Terciopelo in Zone N3 of the latest Oligocene. The overlap of Orbulina universa and Globorotalia fohsi peripheroronda places the type section Uscari Formation in the early Middle Miocene (zones N9 to N10). The overlapping ranges of planktonic foraminifera and the ostracods Radimella ovata in the sandstones places that unit in Zone N18 of Early Pliocene. Globorotalia truncatulinoides excelsa indicates a Pleistocene age for the Moin Formation. The algal-foraminiferal limestones of the basal Uscari Formation were deposited on a shallow shelf receiving volcaniclastic sediment from the emerging islands of the Central American arc. During the Late Oligocene and Early Miocene the Linon Basin quickly subsided. In the Quebrada Terciopelo reference section of the Uscari Formation, Early Miocene foraminiferal indicators of a middle to upper bathyal environment include Siphogenerina transversa and Melonis pompilioides; late early and early Middle Miocene faunas (Uvigerina peregrina, Bolivina pseudoplicata, and Buliminella bassendorfensis indicate progressive shoaling. For the Early Miocene Rio Reventazon section of the Uscari Formation, species such as Cibicides wuellerstorfi and Melonis pompilioides indicate depths near 2000 meters. The type section of the Uscari Formation in Quebrada Uscari is dominated by an outer shelf assemblage containing Hanzawaia concentrica and Fursenkoina pontoni. The Early Pliocene sandstones of the Rio Banano Formation were deposited on a shallow, current-swept continental shelf. These rocks contain a mixture of open marine, nearshore, and a few reefal species, including Cibicidoides floridanus, Amphistegina gibbosa, Articulina mayori, and Elphidium discoidale. The claystones of the Pleistocene Moin Formation contain outer shelf to upper slope species, such as Gyroidina soldani, Cibicidoides floridanus, and Cassidulina curvata. The foraminiferal record of the Rio Banano sandstones suggests land was emergent in the southern Limon Basin, separating the Caribbean and Pacific basins, by 5 mybp, before such an event occurred in Panama.

Miocene of the S.E. United States: A model for chemical sedimentation in a peri-marine environment

Aim We propose a phylogenetic hypothesis for the marine‐derived sciaenid genusPlagioscionin the context of geomorphology and adaptation to freshwaters of South America, and assess the extent to which contemporary freshwater hydrochemical gradients influence diversification within a widely distributedPlagioscionspecies,Plagioscion squamosissimus.Location Amazon Basin and South America.Methods Using nuclear and mitochondrial DNA sequence data, phylogenetic analyses were conducted on the five nominalPlagioscionspecies, together with representatives fromPachyurusandPachypops, using character and model‐based methods. Genealogical relationships and population genetic structure of 152P. squamosissimusspecimens sampled from the five major rivers and three hydrochemical settings/‘colours’ (i.e. white, black and clear water) of the Amazon Basin were assessed.Results Phylogenetic analyses support the monophyly ofPlagioscionin South America and identify two putative cryptic species ofPlagioscion. Divergence estimates suggest that thePlagioscionancestor invaded South America via a northern route during the late Oligocene to early Miocene. WithinP. squamosissimusa strong association of haplotype and water colour was observed, together with significant population structure detected between water colours.Main conclusions Our analyses ofPlagioscionare consistent with a biogeographic scenario of early Miocene marine incursions into South America. Based on our phylogenetic results, the fossil record, geomorphological history and distributional data of extantPlagioscionspecies, we propose that marine incursions into western Venezuela between the late Oligocene and early Miocene were responsible for the adaptation to freshwaters inPlagioscionspecies. Following the termination of the marine incursions during the late Miocene and the establishment of the modern Amazon River,Plagioscionexperienced a rapid diversification.Plagioscion squamosissimusarose during that time. The formation of the Amazon River probably facilitated population and range expansions for this species. Further, the large‐scale hydrochemical gradients within the Amazon Basin appear to be acting as ecological barriers maintaining population discontinuities inP. squamosissimuseven in the face of gene flow. Our results highlight the importance of divergent natural selection through time in the generation and maintenance of sciaenid diversity in Amazonia.

Palaeoenvironmental significance of Miocene larger benthic foraminifera from the Xisha Islands, South China Sea

Extant camelids (llamas and camels) are unique among wild mammals in their regular employment of a pacing gait. They also have a unique foot morphology, assumed to be an adaptation for this mode of locomotion: their feet are secondarily digitigrade, with the loss of hooves and the addition of a broad foot pad. We examined 22 measurements of the metapodials and phalanges of camelids and ruminants with bivariate and multivariate analyses, including 18 genera of extinct camelids from the Tertiary of North America. Extant camelids and ruminants were clearly distinguishable from each other. Most extinct camelids showed some morphological features typical of extant forms, five out of eighteen clustered with the extant camelids. Pacing may have evolved independently within the subfamilies Camelinae and Protolabinae. Additionally, evolutionary change towards a condition resembling that of extant camelids also occurred within the subfamilies Stenomylinae and Miolabinae. These parallel changes in camelid locomotor anatomy occurred in the late Oligocene or early Miocene, preceding the formation of widespread open grassland habitats in the late Miocene.

Research Article| May 01, 1965 Atera Fault and Its Displacement Vectors ARATA SUGIMURA; ARATA SUGIMURA Geological Institute, Faculty of Science, The University of Tokyo, Tokyo, Japan Search for other works by this author on: GSW Google Scholar TOKIHIKO MATSUDA TOKIHIKO MATSUDA Earthquake Research Institute, The University of Tokyo, Tokyo, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information ARATA SUGIMURA Geological Institute, Faculty of Science, The University of Tokyo, Tokyo, Japan TOKIHIKO MATSUDA Earthquake Research Institute, The University of Tokyo, Tokyo, Japan Publisher: Geological Society of America Received: 19 Mar 1964 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1965, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1965) 76 (5): 509–522. https://doi.org/10.1130/0016-7606(1965)76[509:AFAIDV]2.0.CO;2 Article history Received: 19 Mar 1964 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ARATA SUGIMURA, TOKIHIKO MATSUDA; Atera Fault and Its Displacement Vectors. GSA Bulletin 1965;; 76 (5): 509–522. doi: https://doi.org/10.1130/0016-7606(1965)76[509:AFAIDV]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The northwest-southeast-trending Atera fault, which is expressed geomorphologically and geologically, cuts many terraces of the Kiso River in central Japan. The authors measured the vertical and horizontal displacement of the fault from the offset of the terrace surfaces and faces (scarps). Seven displacement vectors were calculated in the fault plane. They show that (1) the horizontal displacement is about five times larger than the vertical; (2) the faulting, to date, has been consistently left lateral; (3) the rate of faulting seems to have been almost consistent (about 2–4 m/1000 yrs.). It is noted that the Neo Valley fault is subparallel to the Atera fault, and that its displacement is also left lateral. Data on recent strike-slip fault displacements in central Japan, in part from this specific study, show a regular pattern of geographic distribution of strains. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Miocene, Pliocene, and Pleistocene strata were deposited in two embayments in the central Atlantic Coastal Plain, the Salisbury to the north and Albermarle to the south. Both embayments underwent local tectonics, and no single area within either has a continuous section. Deposition in both embayments began in early Miocene time. In the Salisbury embayment, the early deposits were largely biogenic (Fairhaven Member of the Calvert Formation), and the center of deposition was located in Maryland. Relatively continuous clastic deposition commenced in the late early Miocene and continued through the middle Miocene (Plum Point Marl Member of the Calvert Formation and the Choptank and St. Marys formations). Deltaic deposition began in the northern part of the embayment, as seen in the Calvert and Kirkwood formations and influenced environments west of the delta lobe. The center of deposition in the Salisbury embayment shifted southward into Virginia during late Miocene time (“Virginia St. Marys” beds) and continued there through the early and middle(?) Pliocene (Yorktown Formation); only the southeastern part of the embayment received sediments in the late Pliocene and early Pleistocene (uppermost part of the “Yorktown” Formation). Environments throughout this time were largely inner shelf (less than 60-m depths), and some marginal-marine to nonmarine intervals. The Albemarle embayment in North Carolina received largely biogenic and biochemical deposition during the early and early middle Miocene (Pungo River Formation). This was followed by uplift in the late middle and late Miocene. Clastic sedimentation started near the Miocene-Pliocene boundary and continued with minor hiatuses throughout much of the Pliocene and into early Pleistocene (Yorktown, uppermost part of the “Yorktown,” Duplin, Croatan, and Waccamaw formations). Some Pungo River strata formed in middle-shelf environments as deep as 100 m; most younger strata were deposited in inner-shelf environments (less than 60-m depth), but some in marginal-marine intervals.

Causes of lineage decline in the Aplodontidae: Testing for the influence of physical and biological change

This paper describes a juvenile rhinocerotid skull from Eschenbach (eastern Switzerland). Computed tomography revealed the presence of the unerupted adult teeth P4 and M3 and enabled their three dimensional virtual reconstruction. The morphological features of this skull (postglenoid and posttympanic apophyses in contact, deep nasal notch, very slight occipital elevation, molar lingual cingulum absent, strong molar crochet) ascribe it to an evolved form of Diaceratherium lemanense (POMEL 1853) when compared with other European specimens. The diacerathere lineage is restricted to the Western European basins, except for the occurrences of the primitive D. cf. lamilloquense in the late Oligocene deposits of Nong Ya Plong (Thailand, Asia) and Diaceratherium askazansorense in the early Miocene of the Askazansor Formation (south-western Betpakdala, southern Kazakhstan, Asia). The Eschenbach locality represents a new biostratigraphical pinpoint at the Aquitanian (early Miocene), probably at the base of the MN2a Mammal Zone (Granitischer Sandstein Formation, upper part of the Lower Freshwater Molasse, USM, eastern Swiss Molasse Basin). A review of the European diacerathere record is proposed from the First Appearance Data of D. lamilloquense (MP29, La Milloque) to the Last Appearance Data of D. cf. aurelianense (MN4b, Eggingen-Mittelhart). During this time interval, the diacerathere lineage points to climatic stress and environmental changes. An ecological and spatio-temporal evolution in three phases between the “Terminal Oligocene Crisis” (disappearance of the ronzothere lineage) and the “Proboscidean Datum Event” at the late early Miocene (first European occurrence of the overtaking Brachypotherium) is suggested: 1) the Diaceratherium genus arrive in Europe during the latest Oligocene (the faunal renewal phase); 2) high diversity of the diacerathere group during the Aquitanian (the diversification phase); 3) wide geographical expansion of the last representatives (D. aurelianense) of the lineage during the Burdigalian (the stabilisation & geographical expansion phase).

The Owen Ridge south of Oman represents oceanic crust that was uplifted by compressional tectonic forces in the early Miocene.Build-out of the Indus Fan led to deposition of a thick sequence of turbidites over the site of the Ridge during the late Oligocene and early Miocene.Early Miocene uplift of the Ridge led to a pelagic cap of nannofossil chalks.Two short sequences of turbidites from the pre-and syn-uplift phases were chosen for detailed grain size analysis.The upper Oligocene section at Site 731 is composed of thin (centimeter-decimeter scale) graded mud turbidites separated by relatively thick (decimeter-meter scale) intervals of homogeneous, non-bioturbated clayey siltstones.These finer intervals are unusually silt-rich (about 60%) for ungraded material and were probably deposited as undifferentiated muds from a series of turbidity current tails.By contrast, the lower Miocene section at Site 722 is comprised of a sequence of interbedded turbidites and hemipelagic carbonates.Sharp-based silt turbidites are overlain by burrow-mottled marly nannofossil chalks.The Oligocene sequence may have accumulated in an overbank setting on the middle fan-the local topographic position favoring frequent deposition from turbidity current tails and occasional deposition from the body of a turbidity flow.Uplift of the Ridge in the early Miocene led to pelagic carbonate deposition interrupted only by turbidity currents capable of overcoming a topographic barrier.Further uplift eventually led to entirely pelagic carbonate deposition.

A 60-million-year Cenozoic history of western Amazonian ecosystems in Contamana, eastern Peru

Studies of depth-related benthic foraminiferal biofacies permit the construction of paleobathymetric maps of the La Honda and San Joaquin basins of central California. These maps support the hypothesis that the La Honda and San Joaquin basins were contiguous during the late Oligocene and early Miocene and subsequently were separated by about 320–330 km of right-lateral displacement on the San Andreas fault. Furthermore, these estimates of displacement support the notion that right-lateral slip occurred along the San Andreas fault during the early Miocene.

A new record of Notocetus vanbenedeni (Squalodelphinidae, Odontoceti, Cetacea) from the Early Miocene of Peru

Caribbean reefs underwent significant biotic change during the Late Oligocene and Early Miocene. This was a critical time in the evolution of the modern Caribbean fauna characterized by increasing endemism resulting from regional extinction of lineages that survive in the modern Indo-Pacific. An understanding of the dynamics and potential causes of the Oligocene/Miocene transition, however, is hampered by the relative lack of well-preserved Oligocene to early Miocene coral faunas in the Caribbean. Here we examine new exposures in the Culebra Formation of Panama that contain a well-preserved coral fauna of Early Miocene age. Taxonomic, stratigraphic, and paleoecologic study of the Culebra Formation exposed along the Gaillard Cut of the Panama Canal allows us to infer the paleoenvironments and reef coral communities from the Panama Canal Basin during this critical interval. The Culebra Formation consists of a deepening upward sequence with shallow-lagoon sediments at the base, overlain by fringing reef facies in the middle of the section, and open-shelf to bathyal facies at the top of the section. We recovered 31 species of reef corals from a combination of new and old collections. Comparison of our collections with other Late Oligocene to Middle Miocene reef coral assemblages confirms that there was a major faunal turnover after deposition of the Upper Oligocene Antigua Formation. This turnover consisted of a large number of extinctions followed by an increased rate of first occurrences so that regional diversity did not change appreciably. Improved stratigraphic resolution at this and other Caribbean localities is required to understand fully the dynamics of change during the Oligocene/ Miocene transition.

A timescale and phylogeny for “Bandicoots” (Peramelemorphia: Marsupialia) based on sequences for five nuclear genes