Narrow Contact Zone Research Articles

Studies of the Pinus rigida-Serotina Complex I. A Study of Geographic Variation

Pinus rigida and P. serotina, two closely related taxa which inhabit the eastern United States, have been described historically as varieties and subspecies of P. rigida and as separate species. These taxa are allopatric except for a narrow contact zone coincident with the Delmarva Peninsula and southeastern New Jersey. In this contact zone intermediate specimens have been encountered, and these have been interpreted both as belonging to clinally intermediate populations of a single continuum and as natural hybrids between two sympatric taxa. The present study was undertaken to provide additional information about the relationship of P. rigida and P. serotina and the composition of populations in the contact zone. A number of populations were sampled from the natural ranges of the two taxa and from the transition zone. Bud and seed characteristics, along with cone length, were found to be quite similar in the two taxa. Other features, such as needle length, peduncle length, cone diameter, and serotiny differed. All of these characters varied clinally within each taxon, and these clinal patterns converged toward the transition zone. The natural populations of this zone were shown to possess characteristics of a single taxon that were morphologically intermediate between nearby populations of the two taxa. They were interpreted as being intermediate populations of a single geographically variable complex. Evidence was detected of a local steepening of the morphological gradation through the transition zone, and this evidence was interpreted as supporting a system of secondary intergradation, rather than primary radiation. The authors follow Clausen (1939) in denoting the taxa as subspecies: P. rigida subsp.

Contact metasomatism and ore deposition, Tem Piute, Nevada

Ore at Tem Piute occurs in a thermally zoned, contact-metasomatic garnet-pyroxene skarn zone separating barren limestone and hornfels from unmineralized quartz monozonite. The scheelite is more abundant in garnet areas and the sulfides in the diopsidic bands.Two unusual features are the number of different ore minerals and the thermally controlled mineralogical zoning across the aureole. Pyrrhotite (and associated marcasite), magnetite and, locally, molybdenite and ilvaite are concentrated close to the quartz monzonite in the inner portion of the contact aureole. Sphalerite together with lesser amounts of galena, bismuthinite, cosalite, galenobismutite and native bismuth, occur close to the limestone contact in the outer portion of the skarn aureole, tungsten-copper-silver deposit. The ore minerals 1 occur in a banded1 Used in the same sense as in the standard texts on ore mineralogy and ore microscopy, i.e., there is no implication of commercial value. Here fluorite is the characteristic gangue. This partitioning of the minerals is in response to thermal differences across the aureole. Certain minerals such as pyrite, chalcopyrite, and scheelite, are uniformly distributed throughout the aureole. All available pyrrhotite is at least in part monoclinic and thus not directly suitable for geothermometry; there are indications, however, that some annealed monoclinic pyrrhotites may yield valid crystallization temperatures. Annealed samples indicate an apparent temperature of deposition in the inner part of the aureole of between approximately 455 degrees C and 510 degrees C. Such temperatures are reasonable but, in view of the possibility of compositional changes having occurred during the initial change from the hexagonal state, the values must be viewed with caution. Some of the sulfo-salts in the outer portion of the aureole, based on thermochemical calculations, formed below 235 degrees + or - 25 degrees C. Thus, the indication is that the ore minerals were deposited at rather low temperatures for a contact-metasomatic ore deposit and that there was a surprisingly high-temperature gradient across this narrow contact zone.

The Facies Front of the Devonian Slave Point-Elk Point Sequence in Northeastern British Columbia and the Northwest Territories

Abstract The facies front of the Slave Point – Elk Point sequence is the narrow zoneof contact between the carbonate Slave Point, Sulphur Point and Pine Pointformations and the equivalent shales of the Horn River formation. The faciesfront trends approximately north-northeast in British Columbia andeast-northeast in the Northwest Territories. The shales lie to the northwest ofthe front and the carbonates to the southeast. The facies front of the Slave Point Elk Point sequence is in the order of 1000 miles in length. It extends over a maximum known stratigraphic interval ofabout 1,300 feet. In parts of the Northwest Territories, the interval overwhich the facies front is developed is considerably less due to the influence of a positive tectonic feature known as the Tathlina High. In most areas, the Slave Point and Sulphur Point formations pass to shalequite abruptly and tend to behave as a unit in this respect. The zone in whichthe Pine Point formation passes to shale is much broader than that in which the two overlying formations pass to shale. Three main tectonic divisions of the facies front are recognized. It is probable that the major morphological features of the front result from structural control. Drilling has shown that, in many areas, the dolomitized Slave Point formation at the facies front contains abundant reserves of natural gas. There are sufficient grounds for believing that the underlying formations at the front also contain significant hydrocarbon reserves. Introduction In the eastern part of northeastern British Columbia and in northern Alberta, the Slave Point Elk Point sequence consists of a series of evaporites and carbonates, mainly Givetian in age. When traced to the northwest, the evaporites are lost from the sequence and the Slave Point – Elk Point rocksconsist of a series of limestones and dolomites with occasional interbedded shales. Beyond a relatively narrow zone of profound lithologic change whichtrends east-northeast across the southern part of the Northwest Territories and north-northeast across northeastern British Columbia, the upper three-quarters of the Slave Point – Elk Point sequence is represented by a series of shales.

The North American Mesquites Prosopis Sect. Algarobia (Leguminosae)

Bentham (1875) included nearly all the plants of Prosopis Sect. Algarobia DC. emend. Burk. (Leguminosae) in one polymorphic species, P. juliflora (Sw.) DC., distributed from Chile and Argentina to the United States. His treatment has been followed by most North American authors, e.g. Sargent (1902). Most of these authors have recognized in the United States the varieties glandulosa (Torr.) Coekerell and velutina (Woot.) Sarg. The discovery of an older name, P. chilensis (Mol.) Stuntz, based on Chilean plants, was followed by nomenclatural transfers of these varieties. In the same section, Burkart (1940) can recognize a number of species, among others P. chilensis sens. str., P. jutliflora sens. str., P. articutlata S. Wats., P. glandulosa Torr. and P. velutina Woot. That members of this section have indistinct morphic boundaries is probably due, says Burkart, to hybridization. Burkart cited, and presumably saw, rather few North American collections. Benson (1941) agrees that P. chilensis is not conspecific with the North American mesquites, but can recognize only one species in the United States, P. juliflora, with three varieties, glandulosa, veluttina, and torreyana. The oftenremarked taxonomic difficultv of this section needs no further emphasis than to point out these divergences in treatment. Field and herbarium studies of mesquites have been undertaken to determine whether considerable discontinuities exist between populations of mesquites, and whether combinations of certain characters show geographic localization. Some recent work of this nature has been done by Graham (1960) in northeastern Mexico. Graham demonstrates the existence of a narrow contact zone or zone of morphic inter(gradation between the lonI-leaved P. glanidulosa and a kind of "short-leaf" mesquite (included in P. laevigata in this paper). The characters which Graham finds to be siQmifieant are quanititative foliage characters. Benson (1941) distincuished the mesquites of the United States mainly on the basis of quantitative foliage characters. Preliminary studies on all the members of this section likewise indicate that foliage characters are geographically segregated and are of prime taxonomic value. Characters of fully mature fruits are also geomraphically segregated, and well correlated with those of foliage, but such fruits are so infrequently present in the field or on herbarium specimens that their taxonomic value is secondary. Quantitative inflorescence characters, such as absolute length of raceme, or raceme-length relative to leaf-length, may prove to be distinctive, but their evaluation is difficult. Quantitative characters of the flowers are very difficult to evaluate because of the proterogynous development (Burkart 1940) ; measurements have to be taken at comparable stages of developmnent, since the genitalia differ so greatlv in relation. to each other at different stages. The geography of some of the quantitative foliage characters is presented on the nmap, Fig. 2. The data were taken from herbariuim sheets. They do not

INTROGRESSIVE HYBRIDIZATION BETWEEN TWO SOUTHEASTERN TREEFROGS

Natural interspecific hybridization in anuran amphibians is not rare, and a number of examples are recorded. There are, however, few conclusively proven instances of introgressive hybridization in the restricted sense of gene exchange between species. The best known case is that of the toads Bufo woodhousei fowleri and Bufo terrestris americanus (A. P. Blair, 1941; Volpe, 1952; and others). A related example is reported by A. P. Blair (1955) between Bufo w. woodhousei and Bufo microscaphus, and Wasserman (1957) provides evidence of introgression in the spadefoot toads Scaphioputs hurteri and Scaphio pus couchi. Most other presumed examples are based largely on simple identification of hybrids with no evidence for introgression, or belong to the borderline category of closely related contiguously allopatric forms that interbreed freely along a narrow zone of contact. This paper deals with a clear case of interspecific gene exchange between the green treefrog, Hyla cinerea, and the barking treefrog, Hyla gratiosa, near Auburn, Alabama. Both species are widely distributed over the southeastern coastal plain. H. gratiosa ranges from North Carolina along the coastal plain (exclusive of southern Florida) to southeastern Louisiana, extending locally above the fall line, and onto the Cumberland Plateau. H. cinerea ranges from Maryland to south-central Texas, up the Mississippi Basin to southern Illinois, and into southern Florida. The two forms are, therefore, sympatric over the greater

Contact metamorphism at Rye Patch, Nevada

Research Article| August 01, 1944 Contact metamorphism at Rye Patch, Nevada CHARLES J. VITALIANO CHARLES J. VITALIANO Search for other works by this author on: GSW Google Scholar GSA Bulletin (1944) 55 (8): 921–950. https://doi.org/10.1130/GSAB-55-921 Article history received: 07 Jul 1943 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation CHARLES J. VITALIANO; Contact metamorphism at Rye Patch, Nevada. GSA Bulletin 1944;; 55 (8): 921–950. doi: https://doi.org/10.1130/GSAB-55-921 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 In the Rye Patch area in the west-central part of the Humboldt Range, Nevada, Triassic (?) limestones interbedded with silty layers have been intruded by igneous rocks, the principal type being a quartz monzonite. The quartz monzonite is surrounded on the north, east, and south by an aureole of contact metamorphism. On the western side faulting has cut the intrusion so that any metamorphic rocks which may have been formed are not seen at the surface. A long narrow contact zone east of the aureole extends northward a considerable distance.Metamorphic changes range from recrystallization of limestone to complete replacement by contact silicates. The contact-metamorphic minerals include garnet, diopside, epidote, clinozoisite, idocrase, tremolite, recrystallized calcite, quartz, and minor scheelite.The sediments are deformed by the intrusion into a small northerly trending arch. Aplite dikes and quartz veins appear related to the arching and also to the formation of scheelite. 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.