Topographic Transition Research Articles

Uplift and denudation history at low-elevation passive margins: Insights from morphostratigraphic analysis in the SE Armorican Massif along the French Atlantic margin

Like other low-elevation passive margins, the French Atlantic margin is characterized by a gradual topographic transition from the coast to low-altitude interior plains or plateaus. Here we propose a morphostratigraphic analysis to constrain long-term landscape evolution and denudation rates, through the characterization of palaeotopographies and related palaeoweatherings in an area restricted to the southeast Armorican Massif. Two regional-scale palaeosurfaces are recognized: (i) the Infraliassic palaeosurface, the truncated weathering profiles of which are sealed by Liassic marine deposits; (ii) the Eocene palaeosurface, underlain by thick kaolinite- and iron-rich palaeosaprolites and by siliceous duricrusts (silcretes). Quantitative constraints on large-scale tectonic uplift and long-term denudation are obtained from these morphostratigraphic markers. Mean uplift and denudation rates calculated on post-Eocene times range between 0.5 and 2 m.Ma -1. These low values imply high landscape stability of the inland margin over most of the Cenozoic.

Assessing Quaternary reactivation of the Main Central thrust zone (central Nepal Himalaya): New thermochronologic data and numerical modeling

Research Article| August 01, 2009 Assessing Quaternary reactivation of the Main Central thrust zone (central Nepal Himalaya): New thermochronologic data and numerical modeling Xavier Robert; Xavier Robert 1Laboratoire de Géodynamique des Chaînes Alpines, Université Joseph Fourrier, CNRS, Grenoble, France Search for other works by this author on: GSW Google Scholar Peter van der Beek; Peter van der Beek 1Laboratoire de Géodynamique des Chaînes Alpines, Université Joseph Fourrier, CNRS, Grenoble, France Search for other works by this author on: GSW Google Scholar Jean Braun; Jean Braun 2Géosciences Rennes, Université de Rennes 1, Rennes, France Search for other works by this author on: GSW Google Scholar Claire Perry; Claire Perry 1Laboratoire de Géodynamique des Chaînes Alpines, Université Joseph Fourrier, CNRS, Grenoble, France2Géosciences Rennes, Université de Rennes 1, Rennes, France *Current address: GEOTOP, Université du Québec à Montréal, Montréal QC H3C 3P8, Canada. Search for other works by this author on: GSW Google Scholar Matthieu Dubille; Matthieu Dubille 1Laboratoire de Géodynamique des Chaînes Alpines, Université Joseph Fourrier, CNRS, Grenoble, France Search for other works by this author on: GSW Google Scholar Jean-Louis Mugnier Jean-Louis Mugnier 1Laboratoire de Géodynamique des Chaînes Alpines, Université Joseph Fourrier, CNRS, Grenoble, France Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (8): 731–734. https://doi.org/10.1130/G25736A.1 Article history received: 07 Jan 2009 rev-recd: 30 Mar 2009 accepted: 02 Apr 2009 first online: 03 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 Xavier Robert, Peter van der Beek, Jean Braun, Claire Perry, Matthieu Dubille, Jean-Louis Mugnier; Assessing Quaternary reactivation of the Main Central thrust zone (central Nepal Himalaya): New thermochronologic data and numerical modeling. Geology 2009;; 37 (8): 731–734. doi: https://doi.org/10.1130/G25736A.1 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 SocietyGeology Search Advanced Search Abstract We study the recent dynamics of the central Nepal Himalaya, focusing on possible reactivation of the footwall of the Main Central thrust, which is marked by an abrupt topographic transition. Different tectonic mechanisms, such as overthrusting of a major crustal ramp, underplating, or out-of-sequence thrusting, have been suggested to explain the morphology and exhumation patterns in this area. We present 25 new apatite fission-track ages collected along a north-south transect in central Nepal, as well as two age-elevation profiles. Ages are consistently younger than 3 Ma old in the Main Central thrust zone and increase continuously to 4–6 Ma old in the south. No jump in apatite fission-track ages is observed across the topographic transition. Apparent exhumation rates from age-elevation relationships vary from 0.46 +0.13/−0.09 km/Ma in the Palung granite south of Kathmandu to 4.4 +4.8/−1.5 km/Ma in the Main Central thrust zone; the latter rate is probably overestimated by a factor of two due to topographic effects. As shown by a new numerical model, these strongly varying exhumation rates can be explained by overthrusting of a crustal ramp, which exerts a primary control on age patterns, and do not require out-of-sequence reactivation of thrusts in the Main Central thrust zone. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Brain and mind operational architectonics and man-made “machine” consciousness

To build a true conscious robot requires that a robot's "brain" be capable of supporting the phenomenal consciousness as human's brain enjoys. Operational Architectonics framework through exploration of the temporal structure of information flow and inter-area interactions within the network of functional neuronal populations [by examining topographic sharp transition processes in the scalp electroencephalogram (EEG) on the millisecond scale] reveals and describes the EEG architecture which is analogous to the architecture of the phenomenal world. This suggests that the task of creating the "machine" consciousness would require a machine implementation that can support the kind of hierarchical architecture found in EEG.

Channel network extraction from high resolution topography using wavelets

The availability of high resolution topography from LIDAR offers new opportunities for objectively extracting the channels directly from a DEM using local topographic information, instead of inferring them indirectly based on global criteria, such as area or area‐slope threshold relationships. Here we introduce the use of wavelet filtering to delineate threshold curvatures for defining valleys and threshold slope‐direction‐change for defining probable channeled portions of the valleys. This approach exploits the topographic signatures uniquely found in high resolution topography, and reveals the fuzzy topographic transition in which local weakly convergent areas lie at the transition between hillslopes and valleys.

Spring phytoplankton bloom and associated lower trophic level food web dynamics on Georges Bank: 1-D and 2-D model studies

Abstract A coupled biological–physical model was developed and tested in one-dimensional (1-D, vertical) and two-dimensional (2-D, cross-sectional) domains to examine the spring phytoplankton bloom and associated lower trophic level food web dynamics on Georges Bank (GB). The biological model consists of nine compartments: dissolved inorganic nutrients (nitrate, ammonium and silicate), phytoplankton (large and small size classes), zooplankton (large and small size classes), and detrital organic nitrogen and biogenic silica. The 1-D model results showed that in the shallow central bank, the timing and duration of spring blooms are closely linked to the light intensity and its downward penetration, while the intensity of blooms is regulated by initial nutrient concentrations and zooplankton grazing pressure. In the deeper flank area, the bloom dynamics is directly controlled by the seasonal development of stratification. The interactions between the shallow and deep regions of the bank were examined by a 2-D model, which showed that the cross-sectional gradients of biological quantities were caused mainly by the shallow-deep topographic transition and tidal mixing. Between the shallow and deep regions, a possible phytoplankton maximum concentration area was seen in the model at the time before the formation of the tidal-mixing front. Once the tidal-mixing front was established during late spring, the model showed a relatively high concentration of phytoplankton near the front as the result of the tidally driven up-front nutrient flux. Both the 1-D and 2-D models captured the basic seasonal cycles of the nutrients and phytoplankton in the central bank, but failed to reproduce those patterns in the deep flank regions, where horizontal advection might play a significant role.

Timing in cognition and EEG brain dynamics: discreteness versus continuity

This article provides an overview of recent developments in solving the timing problem (discreteness vs. continuity) in cognitive neuroscience. Both theoretical and empirical studies have been considered, with an emphasis on the framework of operational architectonics (OA) of brain functioning (Fingelkurts and Fingelkurts in Brain Mind 2:291-29, 2001; Neurosci Biobehav Rev 28:827-836, 2005). This framework explores the temporal structure of information flow and interarea interactions within the network of functional neuronal populations by examining topographic sharp transition processes in the scalp EEG, on the millisecond scale. We conclude, based on the OA framework, that brain functioning is best conceptualized in terms of continuity-discreteness unity which is also the characteristic property of cognition. At the end we emphasize where one might productively proceed for the future research.

Regeneration Dynamics and Genetic Variability of Sugar Maple (Acer Saccharum [Marsh.]) Seedlings at the Species' Northern Growth Limit, Lake Superior Provincial Park, Canada

The transition from deciduous to boreal forest is abrupt regionally and topographically in Lake Superior Provincial Park, Ontario, Canada. The northern range limit of Acer saccharum is coincident with the forest transition to boreal forest. The goal of our study was to characterize the distribution of A. saccharum seedlings at the transition zone to determine variability in seedling demographics and genetics with topographic position and along a short north-south gradient. Seedling density, size, age, and growth were evaluated in permanent plots across the regional transition zone, and at the south-facing, ridge top and north-facing limits across the topographic transition. Growth over 5 yrs. was determined by measuring the distance between terminal bud scars, and compared with regional climate data. Genetic material was collected and analyzed from two of these sites. No significant differences were detected in density or growth of Acer saccharum across the regional transition but mean age increased and height decreased as the limit was approached. Across the topographic transition, ridge top seeding densities were greater than the south-facing or north-facing limits. Genetic variability is great with no cohort preference for topographic position detected.

A Study Topographic Characters and Transition of Paddy Fields and Ponds in Yokohama

横浜市域のエコロジカル・ネットワーク計画の基礎研究として, 水田及び池の特質と推移について検討した。約100年前, 水田は谷戸田と河川沿い水田がほぼ同面積で約7400haあり, 池は谷戸奥の農業用の溜池を中心に約140ヶ所あった。現在では, 水田は約600haに減少するとともに, 池は溜池がほとんどなくなり, 53ヶ所が公園化等により残されているに過ぎない。その保全再生が今後の大きな課題である。

Extension of a Pulmonary Blastoma Into the Left Atrium

Extension of a Pulmonary Blastoma Into the Left Atrium

A Study on Topographic Characters and Transition of “yato” in Yokohama

自然共生都市の重要な生態的拠点となる谷戸に関する基礎研究として, 横浜市域における谷戸生態系の成立過程, 谷戸地形の分布と特徴及びその現況について検討した。横浜市域の谷戸地形は, 縄文海進期に概成される。谷戸の農業開発による二次自然としての谷戸生態系の成立は中世以降である。○○谷戸と呼ばれる小字地名も数多く残されている。1次谷戸数は3751か所で全市に分布する。横浜は「谷戸の発達した都市」といってもよい。近年住宅開発等によって谷戸地形そのものや土地利用に大きな変化が見られる。現在の1次谷戸は, 2467ケ所である。そのうち, 自然的土地利用の多い谷戸は944ケ所となっている。

The shape of Mars before Global Surveyor: Results from reanalysis of the Viking control point network

Three‐dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of Viking Orbiter image data are studied with respect to the shape and large‐scale morphology of Mars. Spheres, spheroids, spherical functions, and a Digital Terrain Model (DTM) of 50 km grid spacing are fitted to the data. Prominent topographic features in the terrain model include the Tharsis volcanoes, Olympus Mons, Alba Patera and prominent mare and highland regions as well as the major impact basins. While the global dichotomy is clearly visible in our data, our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale. Rather, it suggests a smooth topographic transition from southern to northern hemisphere. This model is unique among existing topographic data sets for Mars, as it combines global coverage, a spatial resolution sufficient to resolve regional topography, and absolute elevation data more accurate than in previous control point network analyses. Formal errors and a comparison with the first released topographic profiles obtained by Mars Global Surveyor's Laser Altimeter (MOLA) suggest that 70% and 90% of the DTM grid elements represent the topography of the planet to better than 1000 m and 2000 m, respectively.

The Shape of Mars and the Topographic Signature of the Hemispheric Dichotomy

Reanalysis of occultation data from the Mariner 9 and Viking Orbiter spacecraft to determine the shape of Mars indicated that the hemispheric dichotomy is not a fundamental feature of the shape of the planet. It is a consequence of an approximately 3-kilometer offset between Mars's center of mass and center of figure, and the boundary, along most of its length, consists of broad, gradual surface slopes over distances of thousands of kilometers. This result was supported by analysis of high spatial resolution Earth-based radar topographic profiles. Any successful model for the origin of the dichotomy must explain a planet with an ellipsoidal shape and a long wavelength gradual topographic transition between the northern and southern hemispheres.

Winter water mass distributions in the western Gulf of Mexico affected by a colliding anticyclonic ring

The winter water mass distributions in the western Gulf of Mexico, affected by the collision of a Loop Current anticyclonic ring, during January 1984 are analyzed. Two principal modes of Gulf Common Water (GCW) formation, arising from the dilution of the Caribbean Subtropical Underwater (SUW), are identified. Within the western gulf continental slope to the east of Tamiahua, the GCW is formed by the collision of anticyclonic rings. During these collision events, the SUW, entrapped at the core (200 m depth) of these features, is diluted by low salinity (36.1≤S≤36.3‰) water from the uppermost layer of the main thermocline. The end product of this mixture is GCW, which is further diluted by low salinity coastal water within the western gulf continental shelf. The second GCW formation mode is associated to the northerly wind stress which propagates over the western gulf during winter. During January, 1984, this wind stress gave rise to a 175 m mixed layer. This convective mixing destroyed the static stability of the summer thermocline and allowed for the partial dilution of the SUW with low salinity (S≤36.3‰) water from the western gulf continental shelf. Within the western gulf's upper 2000 m, the following water masses were identified to be present: GCW, SUW, Tropical Atlantic Central Water and associated dissolved oxygen minimum stratum, Antarctic Intermediate Water remnant, a mixture of the Caribbean Intermediate Water and the upper portion of North Atlantic Deep Water (NADW), and the NADW itself. The topographic distribution of these water masses' strata was dictated by the cyclonic-anticyclonic baroclinic circulation that evolved from the anticyclone's collision to the east of Tamiahua. Between the cyclonic and anticyclonic domains, the maximum pressure differential of these water masses' core occurrences was 150 to 280 dbar. The topographic transition zone defined by these strata occurred between the cyclonic and anticyclonic domains and coincided unambiguously with the anticyclone's collision zone. Within the continental shelf, we identified low temperature (12°C) and low salinity (31‰) coastal waters contributed by river runoff. Driven by the northerly wind stress, these coastal waters were advected toward the south hugging the coastline. The coastal and continental shelf waters demarcated a sea surface temperature, salinity, and dissolved oxygen discontinuity region that coincided with the horizontal baroclinic flow transition zone associated to the anticyclone's collision.

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Topography plays a major role in the morphology, geochemistry, and mineral inclusion profiles of placer gold from the East Fork of the San Gabriel River. These trends are consistent with a significant change in topographic gradient over a short distance, and coincident with the break in slope along the range-front of the San Gabriel Mountains. Placer gold from above this topographic transition is more rounded and 3-dimensional, with elevated silver in the alloy of the native gold, little evidence of gold enrichment rims, and abundant inclusions of brittle and reactive minerals. Below the topographic transition, placer gold assumes a distinctly flattened form, with lower silver alloy content, thin gold enrichment rims, and rare inclusions of relatively inert minerals. This relationship is observed for placer gold shed from two inferred lode sources within the river catchment, with placer gold from each of these sources being traceable as a unique population over at least 8 km of the river. Significantly, these placer gold properties are distinctive enough to fingerprint gold from specific portions of the placer deposit. These identifying characteristics, with virtually identical morphology and chemical trends, are observed in the large nuggets of the Mel Fisher collection of purported San Gabriel gold. These similarities appear to confirm the provenance of the collection, including identification of the specific locations where each nugget originated.