Cordillera Region Research Articles

Identification of the sources of inertia-gravity waves in the Andes Cordillera region

Abstract. Four major sources of inertia-gravity waves are known in the Earth atmosphere: upper-tropospheric jet-streams, lower-tropospheric fronts, convection and topography. The Andes Cordillera region is an area where all of these major sources are potentially present. By combining ECMWF and NCEP-NCAR reanalysis, satellite and radiosoundings data and mesoscale WRF simulations in the Andes Cordillera region, we were able to identify the cases where, respectively, the jet-stream source, the convective source and the topography source are predominantly in action. We retrieve emitted wave parameters for each case, compare them, and analyse possible emission mechanisms. The WRF mesoscale model shows very good performance in reproducing the inertia-gravity waves identified in the data analysis, and assessing their likely sources.

Crustal thickening in an active margin setting (Philippines): The whys and the hows

A synthesis of crustal thickness estimates was made recently utilizing available field, geochemical, seismicity, shear wave velocity and gravity data in the Philippines. The results show that a significant portion of the Philippine archipelago is generally characterized by crust with a thickness of around 25 to 30 kilometers. However, two zones, which are made up of a thicker crust (from 30 to 65 km) have also been delineated. The Luzon Central Cordillera region is characterized by thick crust. Another belt of thickened crust is observed in the Bicol-Negros-Panay-Central Mindanao region. This paper examines the interplay of tectonic and magmatic processes and their role in modifying Philippine arc crust. The processes, which could account for the observed crustal thicknesses, are presented. The contributions of magmatic arcs as compared to the contribution of the emplacement and accretion of ophiolite complexes to crustal thickness are also discussed.

The fossil record of the desert-adapted South American rodent Tympanoctomys (Rodentia, Octodontidae). Paleoenvironmental and biogeographic significance

New mandibular remains of one specimen of the desert-adapted South American rodent Tympanoctomys from the Pleistocene of central Argentina are described. These materials, together with a hemimandible previously analyzed by Ameghino, represent the limited paleontological record of the genus, and the first undoubted record of a living genus of the Octodontinae subfamily. The taxonomic, paleoenvironmental and biogeographic significance of these materials is discussed. The sediments yielding the new remains, at the coastal region of Mar del Plata, represent one of the glacial events that deposited the Pichileufu Drift in the Cordillera region of Argentina (between isotopic stages 23 and 25). We propose that, as a consequence of the glaciation, favorable habitats for populations of Tympanoctomys would have extended eastwards. Consequently, the present distributional pattern of the genus may be considered a relict.

Engineering the Philippine uplands: Gender, ethnicity, and scientific forestry in the American colonial period

The policy discourses and “technologies of rule” of the U.S. colonial state in the Philippines (1898–1946) rationalized people, territories, and natural resources in a way that conveyed implicit gender and ethnic biases. Through its ethnological surveys, the colonial government firmed up boundaries of ethnic identities and habitats by classifying people into ethnic categories and partitioning their territories into officially recognized administrative units. The Kalanguya, an upland group living in southern portions of the Cordillera region, have not been “pulled out” of anonymity by these surveys or state-sponsored ethnological studies. Thus, they have not benefitted from state-allocated resources such as protected reserves nor have they been granted seats in public office like other upland groups. For their part, upland women were seen as belonging to the private sphere of domesticity, despite their contributions to upland livelihoods and subsistence, while upland men were centrally located within the orbit of public state transactions. As a result, upland women were never recognized by forestry officials as resource managers in their own right, nor were they treated as capable political subjects with rights to own and make claims to resources in the uplands. Forestry agents also classified and determined which varieties of forest resources were suitable for commerce and they delineated certain spaces for private disposition and others, especially the forest and uplands, as falling under state control. The U.S. colonial state's social engineering in the uplands privileged men over women as gatekeepers of resources by defining how resources would be used and by rendering particular groups like the Kalanguya as anonymous in the ethnographic landscape.

The Mobilization of Human Resources by Non-Governmental Organizations in the Bolivian Andes

In the tropical Andes, a long tradition exists in the utilization and mobilization of rural resources. In certain periods, agriculture and settlement patterns were well adapted to the specific local environmental conditions; at other times, constraints of the natural environment, of historical burdens, and of current social, economic, and political problems contributed to widespread conditions of poverty and underdevelopment. This paper examines the development issues and the activities of non-governmental organizations (NGOs) and a number of affiliated agencies in two representative regions of highland Bolivia: the northern Altiplano and the eastern Cordillera region in the Departamento de Cochabamba. Based on documentation of the agencies and on numerous talks and formal interviews with representatives of the NGOs and the campesinos, an attempt was made to identify the major problems and constraints of specific micro-regions, as well as the perceived development priorities, and the strategies of the agencies and local communities to implement the development process. Although the NGOs may use different approaches and methods, it became obvious that the key to successful and sustained development lies in programs and projects that take into account the specific local environmental conditions, the cultural traditions of the indigenous communities, and the felt needs of the local people. Based on these premises, an effective partnership may be established between NGOs and the campesinos which can lead to a mobilization of local human and material resources and to appropriate sustainable forms of rural development.

Predatory arthropods in cabbage terraces under different conditions in the Cordillera Region of Luzon, Philippines

AbstractPredatory arthropods on cabbage terraces were studied by square flooding and by pitfall trapping in January 1992, following a transect through the Cordillera Region of Luzon, with decreasing numbers of insecticidal sprays per year. Predator numbers were sampled along this transect per 4 m2 and with 15 pitfall traps per site. The dry biomass of predators was also measured. The four sites studied were classified as two pairs, one with high input of insecticides and low predator numbers, low biomass and diversity, the other with low insecticidal input and high predator numbers, high biomass and diversity. The number of ant (Hymenoptera: Formicidae) genera per 15 pitfall traps increased along the transect, showing that ants might be used as indicators of the insecticidal intensity for growing vegetables in the Luzon Cordillera Region. Compared with Europe, the potential abundance and diversity of predators in the Philippines proved to be very high. The reasons for the large differences between sites concerning abundance and diversity of predators are discussed, together with conclusions drawn from the findings presented.

Evolution of Lake Whitefish (Coregonus clupeaformis) in North America during the Pleistocene: Evidence for a Nahanni Glacial Refuge Race in the Northern Cordillera Region

Lake whitefish (Coregonus clupeaformis) could have survived through (at least) the Illinoisan and Wisconsinan Pleistocene glacial maxima in an area in the vicinity of the present Nahanni National Park in the Northwest Territories of Canada according to the geological evidence. This possibility was addressed by an analysis of the genetic makeup of 43 lake whitefish populations in the Northwest Territories, the Yukon Territory, British Columbia, and Alberta. Populations in the lower Liard, Tetcela, Fraser, and upper Peace River systems as well as the headwaters of the Athabasca River were distinguished from both the Bering glacial refuge race populations inhabiting the Yukon and upper Liard River basins in the Yukon Territory and the Mississippi–Missouri glacial refuge race populations inhabiting most of the Northwest Territories, Alberta, and areas further to the east by a specific combination of electrophoretic mobility alleles. This evidence supports the hypothesis of the survival and subsequent dispersal of lake whitefish from a Nahanni glacial refugium. Possible dispersal routes and the limited extent of introgression among races are discussed.

Role of crustal thickening and extensional collapse in the tectonic evolution of the Sevier-Laramide orogeny, western United States

The effects of crustal thickening and extensional collapse of continental crust, combined with variations in plate-convergence forces, provide a coherent explanation for evolution of the Cretaceous-early Tertiary Sevier-Laramide orogeny. Crustal thickening of the Sevier-Laramide hinterland region was triggered by the combination of compressive plate-convergence forces and subduction-induced conductive heating of the crust. Eastward progradation of the locus of Sevier-Laramide deformation through time reflects the progressive widening of the region of crustal thickening. The region of maximum crustal thickening migrated outward until about 80 to 75 Ma, when it encountered excessively strong lithosphere of the Colorado Plateau. The locus of deformation was then transmitted laterally across both a hinterland that had attained maximum crustal thickness and the rigid Colorado Plateau, into the Laramide Rocky Mountain foreland. An episode of vigorous extensional collapse of orogenically thickened crust affected the southern Cordillera between about 75 and 35 Ma. Early Tertiary waning of plate-convergence rates and continued subduction-induced conductive heating of thickened crust allowed extensional collapse along the southern Cordillera region to drive the Colorado Plateau block northward. The result was the late Laramide phase of Rocky Mountain foreland deformation. Because of this, compressive deformation in the central and southern Laramide Rocky Mountain region continued through Eocene time, rather than ceasing at 56 Ma, as it did in the northern Cordillera.

Isotopic variations in continental basaltic lavas as indicators of mantle heterogeneity: Examples from the western U.S. Cordillera

The nature and significance of Sr and Nd isotopic variations in late Cenozoic basalts from the western U.S. Cordillera region are examined in the light of major and trace element characteristics of two end member suites from the Lunar Crater (LCVF) and the Snake River Plain (SRP) volcanic fields. Like many other late Cenozoic Basin and Range basalts, those from LCVF are mildly alkalic and have isotopic (Sr, Nd) compositions similar to those of many oceanic island basalts (OIB). SRP basaltic lavas are tholeiitic and have lower incompatible trace element contents and systematically higher 87Sr/86Sr and lower 143Nd/144Nd isotopic ratios compared to LCVF lavas. These two suites are unlikely to have any genetic relation to one another but are representative of the range of isotopic variations observed in the region. We specifically address the question of how such isotopic diversity arises. For example, (1) could all of these magmas be generated from isotopically similar source materials and then be variably contaminated by crustal material during ascent, or (2) do their isotopic compositions reflect actual heterogeneities within the underlying mantle? To answer these questions, processes of contamination were evaluated using combined major and trace element and isotopic data, and it is concluded that isotopic distinctions between SRP and LCVF basalts cannot be entirely due to contamination. Indeed, they seem to reflect compositional differences in the respective magma source regions. We interpret the LCVF magmas to represent partial melts of dominantly “asthenospheric” mantle (i.e., similar to OIB sources) which, in the case of the Basin and Range province, has presumably upwelled beneath a region of major lithospheric extension. In contrast, isotopically distinct SRP basalts could be derived from ancient or enriched mantle that most likely resides in the continental lithosphere. Thus lateral and/or vertical heterogeneities inferred to exist in the mantle beneath the western United States can be reconciled with geodynamic models that are consistent with regional tectonic evolution.

THE RED TURNIP BEETLE, ENTOMOSCELIS AMERICANA (COLEOPTERA: CHRYSOMELIDAE): DISTRIBUTION, TEMPERATURE ADAPTATIONS, AND ZOOGEOGRAPHY

AbstractMost of the range of the red turnip beetle, Entomoscelis americana Brown, lies within the Western Cordillera and Interior Plains physiographic regions of North America between latitudes 45°N and 68°N. Entomoscelis americana is associated mainly with three types of vegetation: forests, forest–grasslands, and grasslands. Temperature adaptations in the egg, larval, pupal, and adult stages that permit E. americana to occupy its present range are outlined. Host plant abundance may be the main factor preventing eastward extension of its range. Climate and host plant abundance together appear to limit E. americana to low altitude locations north of 60°N latitude. Eight of the temperature adaptations of the egg and adult stages together seem to limit southward extension of the range. Entomoscelis Chevr. appears to have a Holarctic distribution, with 11 species in the Palearctic region and one (E. americana) in the Nearctic region. The stock giving rise to E. americana may have migrated to North America during the Pleistocene when the Bering land bridge was in existence. Entomoscelis americana likely spent the Wisconsinan glacial period south of the ice in the Western Cordillera and (or) in central United States.

Effects of Climate, Tectonism, and Variations in Sea Level on Formation of Cretaceous Coals of North America: ABSTRACT

Extensive deposits of Cretaceous coal-bearing strata are present in western North America, extending from the North Slope of Alaska to northern Mexico. Most of the Cretaceous sediments were derived from the active Cordillera region and were deposited in foreland basins on the western margin of the Western Interior seaway. A multidisciplinary study is in progress to document and attempt to explain the temporal and spatial distribution of the Cretaceous coals. The study examines the effects of variations of paleoclimate, tectonics, and relative sea level on a continentwide scale. In addition, coal quality is related to the regional depositional settings. Many aspects of coal quality (for example, maceral composition, ash content, sulfur content) are determined by the flora and hydrology of the mire in which the original peat accumulated. The existence of Cretaceous coals throughout the length of the Western Cordillera provides a unique opportunity to determine variations in mire type with climate over a range of 50/degrees/ of paleolatitude, and to examine the effects of these variations on coal quality. The relationships between coal beds and associated clastic facies should also be expected to change with varying mire types. Recent developments in their understanding of foreland basin evolution, Cretaceous seamore » level changes, and peat-forming environments make this an optimal time to begin a regional synthesis of North America's Cretaceous coals. Results of this study should aid the development of better predictive models of coal quality and seam thickness. These models will take into account the effects of major controls on sedimentation (climate, tectonics, sea level changes) rather than just the local depositional environment.« less

COCORP: Northwest Cordillera and Southern Appalachian regions

The Consortium for Continental Reflection Profiling (COCORP) announces the availability of seismic reflection data sheets, map sheets, and digital tapes for two regions: (1) the Northwest Cordillera area covering 532 line‐km consisting of Washington lines 1–5, 7, 8; Idaho lines 1, 2; and Montana lines 1, 2; and (2) the Southern Appalachian area covering 1073 line‐km consisting of Florida lines 1, 2, 4; and Georgia lines 10–21, 24. The COCORP operation is part of the U.S. Geodynamics Program sponsored by the National Academy of Sciences and funded by the National Science Foundation. The executive group of the consortium consists of representatives from Cornell University, Dartmouth College, Princeton University, Rice University, and the University of Wisconsin. Cornell University is the operating institution.

Silurian graptolites from N Greenland

Summary Recent collections of Silurian graptolites from N Greenland have yielded much new information on the biostratigraphy of the area. The graptolites occur mainly in slope and trough sediments, some of which are now incorporated in the N Greenland foldbelt. The full sequence of graptolite zones established in Britain cannot be recognized. The oldest Silurian graptolites indicate a lower Llandovery atavus or cyphus Zone age and above this an intermittent succession of graptolite faunas are found throughout the Llandovery, Wenlock, Ludlow and into the Pridoli ( transgrediens Zone only). There are differences between the zones recognized in the western and eastern parts of N Greenland. The spiralis Zone appears to be the most extensive, occurring all over N Greenland. The graptolite sequences in N Greenland correspond most closely with those reported from the nearby Canadian Arctic Archipelago, but are easily correlated with the graptolite faunas from the Cordillera region, especially from the northern part. Differences of faunal assemblages are tentatively correlated with changes in sedimentary environments, possibly indicating a difference in the spatial distribution of species in a living graptolite community.

Icebergs and Glacial-Marine Sediment of Central Arctic Ocean: ABSTRACT

Mechanism of one variety of glacial-marine sediment transportation and deposition is inferred from observation of the activity of ice island T-3. This iceberg carries a significant sediment load. As T-3 moves with the Arctic pack ice, several meters of ice melt annually, releasing sediment to the ocean floor. The sediment accumulates at rates measured in a few mm per 1,000 years but in remarkably homogenous layers. This uniform sedimentation in a seemingly heterogeneous environment is unexpected. The uniformity results from clockwise rotation of the pack ice that transports T-3-sized icebergs at rates up to several km/day in constant patterns. T-3 currently is in at least its third traverse of the Amerasian Basin during the past 30 years. The consistent Arctic surface cur ents have brought T-3 over the same areas during the different cycles. There has been little change in central Arctic sedimentation since at least the late Miocene. Late Cenozoic layers of glacial-marine sediment on the Alpha Cordillera have been organized into thirteen lithostratigraphic units. Even thin units can be correlated over several hundred thousand square kilometers. A textural classification of Arctic glacial-marine sediment recognized four classes, all forming since the late Miocene in the Alpha Cordillera region. Quantities of glacial ice, bearing sediment derived from similar source areas and transported in similar patterns by constant ocean basin currents, account for the uniform glacial-marine sediment in the Arctic Ocean. End_of_Article - Last_Page 911------------

Benthic ecology of the high arctic deep sea

An analysis is made of 75 quantitative benthic samples collected by Mini-LUBS, and 28 qualitative benthic samples collected with the “small biological trawl”, from Fletcher's Ice Island, T-3, while it was drifting over the Alpha Cordillera region of the High Arctic Ocean during October, 1969 through February, 1970 and in March, 1972. The depth range was 1000 to 2500 m. Benthic foraminiferans account for about 53%, bivalves for 27%, sponges for 7%, and polychaetes for 5% of the total biomass. Other groups make up the remaining 8%. The weight ratio of macro- to meiofauna is 1:1. Numerically, excluding Foraminifera, polychaetes comprise 42%, nematodes 16%, sponges 11%, and bivalves 8% of the total fauna. The remaining 23% is composed of 13 other taxa. Biomass in the Amerasian Basin at depths of 1000 to 2000 m is extremely low (0.04 g/m); it is comparable to depths of 5000 to 6000 m in the oligotrophic red-clay area of the mid-Pacific Ocean, and is 40 times less than biomass at comparable depths from Antarctica and off Peru. Diversity, as calculated by the Shannon-Weaver method, is low, suggesting that the Arctic ecosystem is young, as reported in earlier studies (Dunbar, 1968; Menzies et al., 1973). Although the H' values are low, no biocoenoses of oligomixity in the deep Arctic are revealed, contrary to previous statements and beliefs. There may be fewer major benthic groups in the Arctic Ocean than in other parts of the world oceans. Following the conventional terminology of Petersen (1913) and Thorson (1957), we have called the High Arctic biocoenoses of the Alpha Cordillera region a Thenea abyssorum-Spirorbis granulatus community.

Geomagnetic depth sounding and upper mantle structure in the Cordillera region of western North America

This report describes recent geomagnetic depth-sounding investigations on the inland (Cordillera) anomaly first reported by Schmucker at latitude 32°N. It includes Hyndman's profile at latitude 49.5°N and two subsequent profiles at latitudes 35°N and 51°N. All three profiles crossed the transition between the ‘high-I’ and ‘low-I’ zones. Characteristic parameters have been derived from power spectral analysis of the data. The attenuation in the normalized vertical component at the western stations increases with frequency, from 0.97±0.65 db at 0.025 c/ks (10-hour period) to 8.10±1.25 db at 0.35 c/ks (45-minute period). The attenuation is uniform along all three profiles, confirming that the same conductivity structure exists in the southwest United States and in southern British Columbia. Quantitative analysis indicates a rise of highly conducting material (10−11 emu ± 20%) to within 25–35 km of the surface under the western region.

Brazer Dolomite (Mississippian), Randolph Quadrangle, Northeast Utah

The Brazer dolomite in its type area consists of about 850 feet of dolomite with a few beds of quartz sandstone and limestone near the top. Although poorly fossiliferous, the lower two-thirds of the formation has yielded a fauna of Early Mississippian age that suggests correlation with the Mission Canyon limestone of the type Madison group. The upper third of the formation contains a meager fauna of uncertain affinities, interpreted as Late Mississippian in age. Inasmuch as the Brazer can not be recognized on a lithologic or faunal basis outside the type area, it is recommended that the name be restricted to the Mississippian dolomite sequence in the Crawford Mountains. New nomenclature should be devised for the Upper Mississippian limestone-sandstone facies, previously c lled Brazer, in the northern Cordillera region.