Nature, 393, 765, 1998 Triton's tenuous atmosphere has been predicted to undergo significant surface-pressure variations in response to seasonal changes in its mean frost temperature, since the principal constituent of the atmosphere, N2, is presumed to be in vapor-pressure equilibrium1-3 with surface frosts. However, whether the frost temperature should be increasing, decreasing, or constant at the present time depends on the unknown thermal properties of the surface and unknown frost-migration patterns. Here we report results from a stellar occultation by Triton observed with the Hubble Space Telescope (HST), which, when combined with previous results, show that: (i) between 1989 and 1997 Triton's surface pressure has been increasing, indicating that Triton is currently undergoing a period of global warming, and (ii) if one accounts for the change of surface pressure with time, the atmospheric structure derived from our occultation data agrees with atmospheric models based on Voyager data4,5. At our inferred rate of surface-pressure increase, the atmosphere is doubling in bulk every five years--significantly faster than predicted by any published model2,3.
Astrophys. J., 483, 837, 1997 We examine two scenarios for formation of the planetary nebula K648: a prompt scenario in which the planetary nebula is ejected and formed immediately after a helium shell flash and a delayed scenario in which a third dredge-up occurs and the envelope is ejected during the following interpulse phase. We present models of both scenarios and find that each can produce K648-like systems. We suggest that the prompt scenario is more favorable but cannot rule out the delayed scenario.
Rev. Mex de Astron. y Astrofis. Conference Series, 7, 30, 1998 A project which aims to understand the abundance patterns of He, C, N, O, Ne, S, and Ar for a small sample of planetary nebulae is described. Abundance ratios of O/H, C/O, and N/O especially show a broad range relative to their solar values, and AGB stellar evolution models used to interpret the patterns indicate that reasonable ranges in progenitor mass and metallicity are adequate to explain the observed abundance spread. Chemical yields of intermediate-mass stars inferred from these same models are used to calculate chemical evolution models of the solar neighborhood. These models indicate that intermediate-mass stars account for roughly half of the 12C and almost all of the 14N in that region.
Planetary Nebulae, IAU Symp. #180, ed. H.J. Habing and H.J.G.L.M. Lamers (Dordrecht: Reidel), p. 236, 1997 We report on our project to re-evaluate carbon and other abundances in PNe spanning the expected PN progenitor mass range. The ultimate goal of this work is three-fold: (i) to determine the abundance of carbon in this sample; (ii) to assess the abundances of sulfur and argon as metallicity indicators in intermediate-mass stars; and (iii) to incorporate our metallicity results into stellar evolution models to predict nucleosynthesis yields as a function of mass and metallicity.
Astron. J., 114, 2611, 1998 Jacoby & Fullton (1998, in preparation) recently surveyed the Galactic globular cluster system for planetary nebulae and identified excellent candidates in the disk clusters Pal 6 and NGC 6441. Velocities, abundances, and central star properties for these two nebulae are derived. There is a 0.5% probability that the nebula in Pal 6 is a chance superposition of a Galactic bulge nebula. Membership for the nebula in NGC 6441, though, is extremely likely based on common velocity, extinction, and proximity to the cluster center. The number of nebulae now known in globular clusters (4) represents a 3.1[sigma] departure from the number expected (16) based on the theoretical stellar death rate (Renzini & Buzzoni 1986) and the depth of the survey. Possible rationales for this apparent discrepancy are discussed. In particular, the small number of observed PN in clusters can be explained by imposing the requirement that cluster PN form from binary progenitors. Statistically, a correlation exists between the presence of PN and the presence of x-ray sources in clusters, suggesting that PN are more likely to be found when the frequency of interacting binaries in a cluster is high. Oxygen abundances for these two PN, plus Ps1 in M15, suggest that the [O/Fe] ratios in cluster stars are not uniform from cluster to cluster. Values range from -0.7 (NGC 6441) to +0.8 (M15), as compared to +0.5 typically measured in low metallicity field stars. © 1997 American Astronomical Society. [S0004-6256(97)02212-7]
Astrophys. J., 493, 247, 1998 This paper is the third in a series reporting on a study of carbon abundances in a carefully chosen sample of planetary nebulae representing a large range in progenitor mass and metallicity. We make use of the IUE Final Archive database containing consistently reduced spectra to measure line strengths of C III] [lambda]1909 along with numerous other UV lines for the planetary nebulae DDDM1, IC 3568, IC 4593, NGC 6210, NGC 6720, NGC 6826, and NGC 7009. We combine the IUE data with line strengths from optical spectra obtained specifically to match the IUE slit positions as closely as possible, in order to determine values for the abundance ratios He/H, O/H, C/O, N/O, and Ne/O. The ratio of C III] [lambda]1909/C II [lambda]4267 is found to be effective for merging UV and optical spectra when He II [lambda]1640/[lambda]4686 is unavailable. Our abundance determination method includes a five-level program whose results are fine-tuned by corrections derived from detailed photoionization models constrained by the same set of emission lines. All objects appear to have subsolar levels of O/H, and all but one show N/O levels above solar. In addition, the seven planetary nebulae span a broad range in C/O values. We infer that many of our objects are matter-bounded, and thus the standard ionization correction factor for N/O may be inappropriate for these PNs. Finally, we estimate C/O using both collisionally excited and recombination lines associated with C+2 and find the well-established result that abundances from recombination lines usually exceed those from collisionally excited lines by several times.
Saunders College Publishing, 1998 It is the fifth edition of Pasachoff's undergraduate astronomy text. It is accompanied by a CD-ROM of photographs that he worked on as well as an Instructor's Manual and other ancillaries. Supported by the publisher, S. Martin is Webmaster and works with Pasachoff in keeping up to date a World Wide Web site with information about the latest advances in astronomy. See http://www.williams.edu/astronomy/jay.
Cambridge University Press, 1997 This is a graduate text. For more information, see http://www.williams.edu/astronomy/corona.)
Cambridge University Press, 1998 This has been published.
Am. J. Physiol., 274, C681-C687 (1998) The myosin heavy chain (MHC) IIB gene is preferentially expressed in fast-twitch muscles of the hindlimb, such as the tibialis anterior (TA). The molecular mechanism(s) for this preferential expression are unknown. The goals of the current study were 1) to determine whether the cloned region of the MHC IIB promoter contains the necessary cis-acting element(s) to drive fiber-type-specific expression of this gene in vivo, 2) to determine which region within the promoter is responsible for fiber-type-specific expression, and 3) to determine whether transcription off of the cloned region of the MHC IIB promoter accurately mimics endogenous gene expression in a muscle undergoing a fiber-type transition. To accomplish these goals, a 2.6-kilobase fragment of the promoter-enhancer region of the MHC IIB gene was cloned upstream of the firefly luciferase reporter gene and coinjected with pRL-cytomegalovirus (CMV promoter driving the renilla luciferase reporter) into the TA and the slow soleus muscle. Firefly luciferase activity relative to renilla luciferase activity within the TA was 35-fold greater than within the soleus. Deletional analysis demonstrated that only the proximal 295 base pairs (pGL3IIB0.3) were required to maintain this muscle-fiber-type specificity. Reporter gene expression of pGL3IIB0.3 construct was significantly upregulated twofold in unweighted soleus muscles compared with normal soleus muscles. Thus the region within the proximal 295 base pairs of the MHC IIB gene contains at least one element that can drive fiber-type-specific expression of a reporter gene.
FASEB, 12(4), 4223 (1998) The myogenic transcription factor MyoD has previously been shown to accumulate in adult fast-twitch muscle. However, whether MyoD plays an active role in the generation of fiber-type, or is simply a result of fiber-type remains to be determined. Hindlimb suspension (HS), a model which induces slow to fast muscle conversion through unweighting, was utilized to determine the physiological pattern of expression of MyoD and the fast myosin heavy chain type IIB (IIBMyHC). Soleus muscles, which do not normally express either MyoD or IIBMyHC, expressed both MyoD and IIBMyHC mRNA after only one week of HS, indicating a correlation of MyoD and IIBMyHC expression. Somatic gene transfer was used to further characterize the relationship between MyoD and IIBMyHC. After injection of a MyoD expression vector into soleus muscles, a significant increase in the expression of IIBMyHC mRNA was observed. The proximal 300 bp of the IIBMyHC promoter contains at least one element required for muscle fiber-type-specific expression. Within this 300 bp region lies an E-box, a putative binding site for MyoD. When 4 bp of this E-box are mutated within the context of the IIB promoter-reporter construct, MyoD induction of reporter gene expression in cotransfected C2C12 cells is reduced 30-fold. This mutation also decreased activity 67-fold as compared to the wild type promoter within the fast twitch tibialis anterior muscle using somatic gene transfer. These data suggest that MyoD can regulate the expression of the IIBMyHC gene, and indicate a probable causative role for MyoD in the observed upregulation of IIBMyHC in HS soleus.
FASEB, 12(4), 5942 (1998) The fast-twitch tibialis anterior (TA) muscle has been previously shown to have a 4-fold greater phosphoglycerate mutase (PGAM) activity than in the slow soleus muscle. The purpose of this study was to determine a) whether the expression of this gene can be regulated by unweighting, and b) the level of that regulation. Adult female Sprague-Dawley rats were randomly assigned to either normal (n=6) or hindlimb-suspended (HS: n=6) groups. After four weeks of HS, PGAM enzymatic activity increased significantly within the unweighted soleus muscle (0.109 +/- 0.004 vs. 0.268 +/- 0.058 µmoles/mg/min). This increase in activity was reflected at the protein level by western blot analysis. Pre-translational levels of regulation appear to be important because northern blot analysis showed that the PGAM mRNA was induced 3.5-fold relative to 28S rRNA in the unweighted soleus muscle (0.41 +/- 0.06 vs. 1.50 +/- 0.24 relative AU) nearly to the level found in the TA (2.12 +/- 0.02 relative AU). To determine whether this regulation could be at the transcriptional level, somatic gene transfer into normal TA and soleus muscles was employed. The proximal 400 bp of the PGAM promoter was linked to a firefly luciferase expression vector and co-injected with a normalizing CMV promoter linked to renilla luciferase. These data suggest that PGAM expression is responsive to muscle loading and than an element within the proximal 400 bp of the promoter can direct muscle fiber-type specific expression.
FASEB, 12(4), 2423 (1998) The aim of this project was to identify and characterize the fast muscle fiber-type specific element(s) of the myosin heavy chain type IIB (IIBMyHC) promoter in vivo. Previous data has shown that only the proximal 300 bp of the promoter is sufficient to mimic endogenous IIBMyHC gene expression. Numerous deletion constructs that targeted evolutionarily conserved motifs were generated in the context of the proximal 300 bp. In vivo activity of each promoter deletion construct was determined in the fast-twitch tibialis anterior (TA) muscle and the slow-twitch soleus muscle of the rat hindlimb by the technique of somatic gene transfer. Progressive deletions of two distal AT-rich regions, AT3 and AT2, resulted in a marked decrease of activity in the soleus and TA, suggesting that both elements are required for high levels of activity of the promoter. Deletion of the third proximal AT-rich region, AT1 resulted in a significant increase in activity in both the TA and the soleus muscles, suggesting a negative regulatory role. Deletion of the CArG region resulted in a moderate increase of activity in both the soleus and TA muscles. Transient transfection of these promoter constructs into C2C12 myotubes mirrored activity levels observed in the TA for every construct except for the CArG deletion; while deletion of the CArG element resulted in a moderate increase in promoter activity in vivo, activity in cell culture was very low. In conclusion, these motifs appear not to be involved in determining fiber-type specificity, but likely play a general regulatory role in expression of the IIBMyHC gene.
Tetrahedron Letters, 38, 3817-3820 (1997) Development of a successful synthetic route to the racemic monoterpene 7R-paeonimetaboline-I is reported; extension of this methodology in an approach to synthesis of racemic paeoniflorigenone is also summarized.
Tetrahedron, 53, 13557-13566 (1997) Bioassay-guided fractionation of the chloroform/methanol extract of a dart poison from Indonesian Borneo (Kalimantan), derived from Antiaris toxicaria latex, has led to the isolation of a new cardenolide, toxicarioside A . The structure of 1 was deduced by analysis of spectroscopic data and has led to the first assignment of the 1H- and 13C-NMR shifts for an antiarigenin aglycone. The bioassay employed to isolate cardenolide 1 involves inhibition of Na+/K+-ATPase and mimics the suspected mode of action of these "cardiac-glycoside" toxins.
Tetrahedron, 53, 16959-16968 (1997) Bioassay-guided fractionation of the chloroform/methanol extract of a dart poison from Indonesian Borneo (Kalimantan), derived from Antiaris toxicaria latex, has led to the isolation of two new cardenolides, toxicarioside B  and toxicarioside C . Structures for 2 and 3 were deduced by analysis of spectroscopic data; these materials are isomeric with toxicarioside A  previously isolated in our earlier work with the same poison. The bioassay employed to isolate cardenolides 2 and 3 involves inhibition of Na+/K+-ATPase and mimics the suspected mode of action of these "cardiac-glycoside" toxins.
Chemistry of Materials, 10(4), 1069-1075 (1998) Liquid crystalline properties have been introduced into one-dimensional metal-chain complexes based on Cu(pyridine)2X2, via straightforward derivatization of the pyridyl ligands. When the aliphatic portion of the mesogen is introduced via an ester, no mesophase behavior is observed; however, when an amide group is used as the means of incorporating the flexible portion of the molecule, a mesogenic material results. The structure of these amide derivatized materials is different when obtained from solution vs. from the melt, due to changes in the hydrogen bonding framework formed along the chain. The solution derived material does not display any mesophase behavior, whereas the material derived from the melt does. The thermal behavior of these materials is somewhat complicated by the variety of non-covalent interactions (hydrogen bonds, metal-halide bridging interactions) involved. By including hydrogen bonding groups in the ligands at positions opposite to the metal-coordination site it is possible to significantly affect the environment of the metals in these complexes, presumably via compression of the bridging Cu-X bonds.
Biophysical Chemistry, 75, 1232-1255 (1998) Most hormone concentrations in the body are regulated by negative feedback mechanisms in which the production and release of hormones are regulated according to the concentration of related species. Also, it has been observed that several hormones are released in a variety of pulsatile patterns. In most cases, the mechanism driving these complex patterns is not well understood.
Our model of two cells coupled through negative feedback to their external products demonstrates periodic, aperiodic and chaotic oscillations. The coupling between the cells seems to be responsible for these dynamic behaviors. The variety of dynamic behaviors observed in the model demonstrates that a simple physiological feedback loop mimicking the coupling between circulatory hormones and production centers could be the source of complex hormone release patterns observed in vivo.
The Journal of Chemical Education, 75, 222-223 (1998) A new derivative was developed for the identification of aldehydes in organic chemistry qualitative analysis schemes. The compounds, 3-substituted-1,5-dihydro-2,4-benzodithiepines, are prepared easily, safely, and in high yield from reagents that avoid the toxicity of alternative procedures.
Tetrahedron Letters, 39, 1111-1112 (1998) An efficient, four-step route to the title compound was reported. The key step was an intramolecular hetero Diels-Alder reaction.
Proceedings of TACS `97 (Theoretical Aspects of Computer Science), LNCS 1281, pp. 415-438. Recent years have seen the development of several foundational models for statically typed object-oriented programming. But despite their intuitive similarity, differences in the technical machinery used to formulate the various proposals have made them difficult to compare.
Using the polymorphic typed lambda-calculus as a common basis, we now offer a detailed comparison of four models: (1) a recursive-record encoding similar to the ones used by Cardelli, Reddy, Cook, and others; (2) Hofmann, Pierce, and Turner's existential encoding; (3) Bruce's model based on existential and recursive types; and (4) Abadi, Cardelli, and Viswanathan's type-theoretic encoding of a calculus of primitive objects.
Proceedings of the 38th Symposium on the Foundations of Computer Science, Pp. 496-505, 1997. A grid graph is a finite node-induced subgraph of the infinite two-dimensional integer grid. A solid grid graph is a grid graph without holes. For general grid graphs, the Hamiltonian cycle problem is known to be NP-complete. We give a polynomial-time algorithm for the Hamiltonian cycle problem in solid grid graphs, resolving a long-standing open question. In addition, our algorithm solves a generalization of the Hamiltonian cycle problem that asks for the vertex cycle cover with fewest components, and it does so for quad-quad graphs, a class of graphs that properly includes solid grid graphs.
New York State Museum Bulletin, 491, 75-88 (1998) Proximality-trend analysis records the occurrence of tempestite cycles on storm-dominated coasts. Most authors who use this method link their first-order proximality cycles to the third-order eustatic cycles of Vail et al. Data for the Llandovery Series illustrate a good fit between sea-level curves derived from proximality trends and the Silurian standard sea-level curve. Proximality-trend analysis is therefore deemed to be a valid method for detecting sea-level changes. Caution should be exercised, however, in situations of sediment by-pass and sediment trapping or starvation due to transgression or tectonic movement.
Areas for the Silurian System where this method has been or might be used were identified by literature search and paleoclimatic simulation. The literature search found 63 areas with tempestites that were described mostly in English-speaking countries. This result implies a bias in the literature, but the possibility of limited emphasis on storm deposits in different countries or lack of detailed studies is also possible. The paleoclimatic model predicted many additional sites for tempestite deposition. A closer investigation revealed that most of these were either areas of non-deposition or deeper facies. Kolyma, southeast Australia, south-central Europe, and probably Siberia and Kazakstan, however, are the most likely places to find additional tempestite deposits. The South China Platform and areas on the west side of the Taconic orogen in Laurentia have tempestites, although none were predicted from the climatic simulation. Hurricane nucleation on the epicontinental platform or alternative paleogeographic reconstructions may explain this.
The Mountain Geologist, 35, 55-64 (1998) The Flathead Sandstone of northwestern Wyoming and Montana is a quartz-rich sheet sandstone overlying the Archean igneous and metamorphic basement rocks of the area. It represents the first cycle of deposition as the Cambrian sea transgressed over the craton, and is Middle Cambrian in age. Little detailed work has been done on the Flathead Sandstone, and its provenance and environment of deposition are poorly understood.
Petrographic analysis and stratigraphic evidence are used to distinguish the various marine and continental environments present during deposition of the formation in the Clarks Fork area. Point-count data indicate a craton interior provenance with some evidence for basement uplift. The composition of the sandstone is consistent with derivation from the underlying granitic rocks. However, a portion of the samples contain grains of chert and metamorphic quartz, suggesting contribution from an older sedimentary and/or metamorphic source.
Internal structures, textures, and mineralogic composition point to both marine and fluvial facies in the Flathead Sandstone. Fluvial facies are distinguished by pebble lag deposits, submature textures, and feldspathic composition. Structures evident within the fluvial facies are trough cross-stratification, cut-and-fill structures, and thin horizontal bedding. Marine facies are on average medium-grained, texturally mature quartz arenites, some of which display horizontal feeding traces or vertical burrows. Sedimentary structures include thick horizontal bedding, low-angle planar and trough cross-bedding, and hummocky cross-stratification.
The interlayering of marine and terrigenous deposits in the Clarks Fork area indicates that on a local scale many factors cause departures from the ideal transgressive sequence. Sediment flux resulting from tropical storms and aggravated by the unvegetated nature of the Paleozoic craton, as well as relief on the nonconformity, contributed to a complex and dynamic shelf and shoreline during the Middle Cambrian.
Proceedings of the UNESCO-IUGS-IGCP 348/368 International Field Workshop on Proterozoic Geology of Madagascar, Gondwana Research Group, 13-14 (1997) The Itremo Group is a remnant of a Proterozoic sedimentary basin, which was deformed and metamorphosed during the amalgamation of Gondwana. The basin was of continental affinity, representing either a passive margin setting or possibly an epicontinental seaway. U-Th-Pb analyses of zircon grains were made on the sensitive high resolution ion microprobes (SHRIMP I and SHRIMP II) at the Research School of Earth Sciences (RSES) at the Australian National University, Canberra. The zircons are clearly detrital. They show the effects of extensive mechanical abrasion, with all original facets and faces destroyed. They are also highly variable in terms of color, transparency and size. Although the grains are highly rounded and the surfaces are extensively pitted, small platelets of new zircon growth are present. This new growth shows no sign of any abrasion and in fact covers pre-existing pitted surfaces and thus must have formed in situ. Numbers of grains from all age sub-populations show radiogenic Pb-loss, a significant part of which appears to be late Proterozoic, presumably reflecting lead loss and zircon growth during metamorphism and deformation associated with Gondwana assembly. Of these, the grain which showed the most severe Pb-loss (MAD 113, Grain 15; Fig. 4) was analyzed several times in different areas in order to try and establish the time of alteration. In section this opaque zircon is a patchwork of holes and Fe-oxide inclusions and gives a blotchy cathodoluminescence image with no hint of any igneous or original internal structure. The four analyses on this grain all have relatively high common Pb contents and have variable U/Pb ages (Table 3), plotting along the concordia curve between 800 and 400 Ma (Fig. 4). A weighted mean 207Pb/206Pb age calculated on these four points gives 833 1 112 Ma (2s), this being equivalent to regressing the data and assuming zero-age Pb-loss. We interpret this date to represent the time of metamorphism of the rocks and the time at which the zircon was altered, both structurally and isotopically.
Concordant detrital zircon ages range from 2732 1 12 Ma to 1855 1 11 Ma, indicating that the provenance included rocks of mid-Proterozoic to Archean age. The youngest concordant ages form a tight cluster at around 1.85-1.88 Ga, providing a maximum age for the sequence. The Itremo Group bears lithologic similarities to Proterozoic sequences in Africa and India, with which it has been tentatively correlated. Likely source areas for the Itremo Group include the Tanzanian craton in Africa and the Dharwar craton of India, and these possibilities can be tested by examining the match between the detrital zircon ages and the basement ages. Statistical analysis of highly concordant (>80%) grains with minimal common Pb suggests seven distinct age populations are significant. The distribution of these age populations is very similar to the distribution of ages for the Tanzanian Craton but bears little resemblance to recorded ages from the Dharwar Craton. This suggests a source for the Itremo Group in Africa rather than India. Because most of the published ages for the Tanzanian and Dharwar cratons are Rb-Sr isochron ages, and may not represent crystallization ages in all cases, the robustness of this conclusion remains to be tested.
Gondwana Research Group Miscellaneous Publication, 5, 106 pp. (1997) This volume contains a compilation of edited abstracts presented at an international geological symposium held in Antananarivo, Madagascar, in August of 1997.
New Mexico Bureau of Mines and Mineral Resources Map-GM-73, Scale 1:24,000 (1997) The White Rock quadrangle (Fig. 1) exposes a diverse suite of Miocene through Holocene rocks that record volcanism, sedimentation, and erosion along the axis of the Rio Grande rift in the southern Espa-ola Basin. Rocks were derived from volcanic sources in the Cerros del Rio and the Jemez Mountains and from eroded metamorphic and intrusive rocks exposed in the Sangre de Cristo Range. In Miocene time, before the Rio Grande developed as axial drainage for the Espa-ola Basin, the map area was on the west and southwest margin of a large alluvial-fan complex. Sometime before about 3 m.y. ago (Ma), perhaps in early Pliocene time, the Rio Grande began to run through the vicinity of White Rock Canyon (Manley, 1979). Since middle Pliocene time, the river has flowed near its present location, shifting less than 10 km (6.2 mi) laterally in response to volcanic activity along the river and to the construction of a volcaniclastic fan (Puye Formation) from the Jemez Mountains. The symmetry and age of slump complexes along the Rio Grande indicate that the river has not changed course appreciably since before middle Pleistocene time. Middle Pliocene fan construction; location, age, and chemistry of volcanic rocks erupted at maars and other vents along the Rio Grande; and the Quaternary history of White Rock Canyon are portrayed in this map (scale 1:24,000) and discussed in the accompanying text.
Geological Society of America Abstracts with Programs, 30(1), 70 (1998) Middle to late Holocene terraces and alluvial fans expose sequences of buried soils developed in sandy alluvium along tributaries to the Rio Grande in the Puye 7.5' quadrangle, northern New Mexico. Regional lowering of base level by 100 m since ~500 ka has driven downcutting along tributaries, punctuated by periods of aggradation and equilibrium best recorded by late Pleistocene and Holocene surfaces. 14C ages of disseminated charcoal suggest that channels and alluvial fans aggraded from 2 to 7 m above modern arroyo levels from 3.5 ka to after 2.0 ka. Aggradation in one channel began before 5 ka. Sparse cultural and vegetation evidence indicates that channel downcutting began after 1500 AD and probably after 1800 AD.
Aggradational sequences contain numerous buried soil profiles, including one 3 m sequence of 9 buried soils. Field evidence shows that buried soils are a few cm to decimeters thick and consist mainly of A/C profiles, Bw horizons and weakly developed Bt horizons that contain carbonate coatings along fractures and pores. 14C ages and laboratory analyses from such buried soil profiles allow us to estimate the rate of development of pedogenic characteristics such as organic matter accumulation, which is as high as 6.9 percent in buried A horizons, and extractable Fe, CaCO3, and fines content. The degree of soil development at dated sites and continuity of aggradational profiles allows us to estimate the age of nearby undated deposits and surfaces. Preliminary results suggest that the pattern of aggradation and incision and rates of soil development near the Rio Grande is similar to those measured at upstream sites near Los Alamos.
Geological Society of America Special Paper, 321, 23-46 (1997) Siberia and Laurentia were independent Silurian continents that accumulated extensive carbonate deposits on broad epicontinental shelves attached to limited land areas. Siberian Anabar was a domed lowland, but Taconia in eastern North America was an elongate highland thrust up as a result of oceanic foreshortening in the Proto-Atlantic. Both lands shed quartzitic detritus into coastal environments, permitting accurate map reconstructions of their shorelines. The greater topographic relief of Taconia sheltered the inboard carbonate platform from the most severe storms, but Anabar stood in the direct path of hurricanes that swept across the flanking carbonate shelf and stimulated deposition of cyclic storm beds.
During the middle Aeronian and early Telychian, Siberia was imprinted by two global highstands in sea level that can be well correlated to Laurentia and other paleocontinents, such as Avalonia and Baltica, on the basis of stratigraphic discontinuities in beds with rich concentrations of the brachiopod Pentamerus oblongus. An earlier highstand recorded by widespread distribution of the brachiopod Virgiana decussata in North America is masked by a prolonged Rhuddanian deepening event on Siberia. Thicker Silurian deposits in Siberia as opposed to North America and especially Siberia's extensive Rhuddanian shales and interbedded fine limestones, attributed to a deep-shelf setting, may be explained by comparatively low hypsography.
New York State Museum Bulletin, 491, 3-13 (1998) Rocky shores and coastal valleys undergo subaerial and/or some degree of intertidal erosion. Burial of coastal topography with rise in sea-level results in the formation of unconformities. If the tectonic component of relative sea-level change can be identified, the minimum eustatic rise may be determined from the maximum topographic relief covered by marine strata. Data of this kind are reviewed for a dozen Silurian rocky-shore localities and from four regions that preserve Silurian paleovalleys. Paleocontinents on which these coastal features are known include Gondwana, Laurentia, Avalonia, Baltica, and North and South China.
All purported global rises in Silurian sea-level are associated with burial of Silurian coastal topography. The best documented examples are for the Rhuddanian (+70 m) and Aeronian (+65 m) events in the Early Silurian. Other unconformities that resulted from onlap across Silurian rocky shores are correlated with the early and late Telychian, middle Sheinwoodian, early Gorstian, middle Ludfordian, and Pridoli transgressions. Available descriptions of these features are less informative with regard to the extend of paleotopographic relief. The regional relief of karst surfaces buried during the late Llandovery and early Pridoli in Laurentia is 30-53 m. Improved understanding of this topic relies on more thorough outcrop observations, greater use of subsurface data, and better dating of the time of formation of rocky shores and paleovalleys.
New York State Museum Bulletin, 491, 63-73 (1998) The east Siberian Silurian was deposited in a cratonic basin with facies that range from deep-water graptolitic to shallow foreshore and lagoonal with linguloids and fish. A detailed regional stratigraphy and analysis of local and regional tectonic and sedimentary cycles allow determination of bathymetry, submarine relief, and eustasy. Shoreline features were overlapped by transgressive sediments, and this allows interpretation of topography marginal to the basin and a quantitative measurement of sea-level rise. On the carbonate margins of the shallow shelf where rich, benthic faunal assemblages are regularly overlapped by pelagic assemblages, eustatic fluctuations are most clearly identifiable. The Moyero, Turukhansk, and Middendorf regions are most representative of this situation and allow creation of a sea-level curve for east Siberia. This standard is supported by local events that show the appearance of pelagic assemblages only on the deeper part of the shallow shelf. The deep-shelf sea-level curve is less dramatic. It is recognized only by the quantitative characters of graptolite and rarer pelagic brachiopod and ostracode faunas. The sea-level record of the east Siberian Silurian includes nine highstands, which are clearly recognized and conform to the eustatic standard. These highstands are: 1) late Moyerocaninan (late Rhuddanian), 2) late Khaastyrian (middle Aeronian), 3) early Agideian (early Telychian), 4) late Agideian (late Telychain), 5) early Khakomian (late Sheinwoodian), 6) late Tukalian (early Gorstian), 7) early Postnichian (late Ludfordian), and 8) late Postnichian (Pridoli). Another early Moyerocanian highstand (1a) is related to the earliest, most extensive, and most rapid Silurian transgression after latest Ordovician regression.
New York State Museum Bulletin, 491, 89-143 (1998) This report summarized Early Silurian (Llandovery-early Wenlock) sequences, events, and biostratigraphy of the Appalachian foreland basin (AFB) in eastern North America. The four Llandovery and the early Wenlock eustatic cycles are recognized throughout the AFB. They form third-order depositional sequences that are synchronous with current biostratigraphic resolution, and display marked similarities along the northeast-southeast depositional strike. Sequence I (Rhuddanian-early Aeronian) is siliciclastic-dominated (Medina [New York, Ontario], Tuscarora [Pennsylvania, Maryland, Virginia], and Clinch [Tennessee] Formations), with a transgressive sandstone that overlies the Ordovician at the Cherokee Unconformity. Gray sandy shales that reflect tectonically induced, early Rhuddanian marine incursion generally occur in the lower third of Sequence I. Sequence II (middle-late Aeronian; lower Clinton Group [New York]; lower Rose Hill Shale [central Appalachians]; middle member of Rockwood and Red Mountain Formations [Tennessee, Alabama]) is characterized by fine-grained siliciclastics, carbonates, and ferruginous to phosphatic shell-rich beds that mark flooding surfaces. Sequence III (lower-middle Telychian) comprises green-maroon shales and ferruginous to phosphatic sandstones (Sauquoit-Otsquago [New York], middle Rose Hill [central Appalachians], upper member of Rockwood-Red Mountain Formations, in part [Tennessee, Alabama]). The Sequence II-III boundary appears conformable in the central Appalachians, where sandstones of a lowstand wedge or shelf margin systems tract (Cabin Hill Member) occur in the Rose Hill Shale. The thin, distinctive Sequence IV (late Telychian-earliest Wenlock) overlies a prominent, regional angular unconformity that truncates parts of Sequences I-III in the northwestern part of the basin (New York, Ontario, Ohio, Kentucky). Center Member sandstones of the Rose Hill may again record lowstand progradation in the basin center. Oolitic ironstones (e.g., Westmoreland Iron Ore [New York]) and carbonates mark the transgressive systems tract and condensed section of Sequence IV. Overlying dark gray, fossiliferous shales (Williamson-Willowvale [New York], uppermost Rose Hill [central Appalachians], and upper Rockwood-Red Mountain [southern Appalachians]) record the deepest water facies (Benthic Association 3-5) in most sections. Sequence V (early Wenlock-Sheinwoodian) records renewed influx of coarser-grained siliciclastics (Herkimer-Keefer Sandstones) that possibly reflects foreland basin flexure and regression. Overlying dark gray shales (Rochester-Miffintown) record middle Wenlock highstand.
Proximal ferruginous and distal phosphatic shell-rich beds are regional markers in the AFB Lower Silurian. An association with condensed sections indicates that they record sediment starvation during transgressions. Chamositic precursors of hematites and phosphorites formed near sediment redox boundaries, but oolitic hematites seem to occur in more agitated, better-oxygenated settings than phosphorites. Ironstone and phosphorite development was favored by tectonic quiescence. Global sea-level maxima are coeval with the major marine incursions of the transgressive or highstand systems tracts of the large-scale depositional sequences in the AFB. Sea-level maxima are marked by ferruginous or phosphatic shelly beds.
Geochimica et Cosmochimica Acta, 61, 2467-2474 (1997) Comparison of results from the isotope dilution and the single-grain zircon evaporation methods on highly discordant samples shows that the evaporation method can yield accurate crystallization ages on some zircon populations that display complex discordant patterns. Three granite gneiss samples from the Western Gneiss Region, Norway, which crystallized at approximately 1660 Ma and experienced profound Pb-loss in zircon during Caledonian metamorphism at 400 Ma were analyzed by both the isotope dilution (Tucker et al., 1990) and evaporation methods. 207Pb/206Pb evaporation ages on one sample agree with the isotope dilution crystallization age. Two other samples produced a range of anomalously young 207Pb/206Pb evaporation ages. Analyses at the highest evaporation temperatures from one of these two samples were consistent with crystallization ages determined by the isotope dilution method, but it would be difficult to interpret them correctly without independent age information. The anomalously young results are generally easy to recognize by the pattern of increasing 207Pb/206Pb ages with increasing evaporation temperature. A more serious problem, however, is that some grains produced 207Pb/206Pb age plateaus over a range of increasing evaporation temperatures that cannot be correlated with any documented geologic event in the region. The evaporation analyses yielding the youngest 207Pb/206Pb ages also display the most common Pb suggesting that common Pb may diffuse into the zircon grains during loss of radiogenic Pb.
A pegmatite from Massachusetts, U.S.A., contains zircons with visible xenocrystic cores. The 207Pb/206Pb evaporation ages at lower temperatures agree well with the 299 Ma crystallization age determined by the isotope dilution method on the zircon rims (R.D. Tucker, unpublished data). At higher evaporation temperatures, a range of older 207Pb/206Pb ages are produced by mixing of Pb evaporated from both the zircon rims and xenocrystic cores. Large changes in the 206Pb/208Pb ratio accompany the increase in 207Pb/206Pb ages and indicate mixing of two distinct zircon domains. Thus, in addition to providing useful 207Pb/206Pb age information, the evaporation method may help distinguish between discordance produced by diffusional Pb loss and mixing of two domains of differing age.
New England Intercollegiate Geologic Conference, Guidebook for Fieldtrips, B3-I-20 (1997) In southern Vermont, the Green Mountain massif and the Chester, Athens, Wilmington, and Jamaica domes are cored by Middle Proterozoic Grenvillian basement and mantled by Late Proterozoic to Early Paleozoic metasedimentary and metaigneous rocks. Anyone wishing to understand the complex structural history of this area must first be able to distinguish correctly basement from cover rocks. Another vital task is to decipher the facies relationships between coeval sequences of cover rocks. Participants on this trip will visit key localities in the Green Mountain massif and Chester dome for studying the complex nature of basement-cover contacts and see first-hand how difficult it can be to distinguish between fault and unconformity interpretations of contacts. We will compare basal cover sequences found in the region and try to reconstruct their original distribution. We will also develop, in detail, the problem of distinguishing basement from cover rocks and examine, critically, the evidence for assigning some exposures of the Gassetts schist and related rocks to the Grenvillian basement, as has been done in recently published U.S.G.S. maps.
Geology, 26, 215-218 (1998) Tectonic models of the Ordovician Taconian orogeny in western New England usually invoke a collision between the Laurentian margin and a magmatic arc identified as the Bronson Hill arc. However, in central Massachusetts and southern New Hampshire, rocks in the Bronson Hill arc are 454 to 442 Ma and therefore younger than much of the Taconian deformation and metamorphism in western New England and eastern New York, which began by 470 Ma. U-Pb and single-grain evaporation zircon ages combined with geochemical analyses reveal the presence of an older magmatic arc, the Shelburne Falls arc, that formed west of the Bronson Hill arc at 485 to 470 Ma. The Shelburne Falls arc formed above an east-dipping subduction zone by the Early Ordovician. The Taconian orogeny was the result of the collision between Laurentia and the Shelburne Falls arc beginning ca. 475 to 470 Ma. The younger Bronson Hill arc formed above a west-dipping subduction zone that developed along the eastern edge of the newly accreted terrane during the final stages of and subsequent to the Taconian orogeny. The Taconian orogeny ended when plate convergence between Laurentia and Iapetus was accommodated by the newly developed west-dipping subduction zone instead of by crustal shortening in the Taconian thrust belt. The tectonic history of the New England Appalachians is inconsistent with a Middle Ordovician collision between Laurentia and the proto-Andean margin of Gondwana.
Geological Society of America, Abstracts with Programs, 29, A-378 (1998) The tectonic history of the New England Appalachians indicates that Iapetus existed adjacent to Laurentia from the Late Proterozoic until just before the Devonian Acadian orogeny. Following Late Proterozoic rifting and the inception of Iapetus, a passive margin developed adjacent to Laurentia and sedimentation of coeval shallow water shelf and deep water slope-rise sequences persisted until the Early Ordovician. By 470 Ma the passive margin of Laurentia was drawn into an east-dipping (present-day reference frame) subduction zone above which the Shelburne Falls arc formed. West-directed thrusting of the Taconian orogeny followed collision of Laurentia with the Shelburne Falls arc. The Taconian orogeny ended at approx. 455 Ma when a west-dipping subduction zone developed east of the newly accreted Shelburne Falls arc and accommodated plate convergence. The younger Bronson Hill arc developed above this new west-dipping subduction zone from about 455 to 440 Ma (Tucker and Robinson, 1990). Subduction of oceanic crust at this time led to back-arc rifting which extended the crust between the Shelburne Falls and Bronson Hill arcs creating the Connecticut Valley trough. Accumulation of thick sediments and rift volcanics in the trough indicate that the Connecticut Valley trough was active through the Silurian. Collision between Avalonia and Laurentia began in Newfoundland in the Silurian and the intervening ocean basin closed scissors-like towards the south; oceanic crust of Iapetus was subducted under both Laurentia and Avalonia. Thus, the history of this portion of the Appalachians is not compatible with a continent-continent collision involving the proto-Andean margin of Gondwana having occurred in the Ordovician.
Geological Society of America, Abstracts with Programs, 30, 29 (1998) The Cavendish Formation (Doll et al., 1961) in southeastern Vermont contains quartzite, dolomitic marble, calc-silicate rock, and pelitic schist. On the Centennial geologic map of Vermont it is shown to be younger than the Middle Proterozoic Mount Holly Complex and older than the Late Proterozoic to Cambrian Tyson and Hoosac Formations. More recently, it has been interpreted as equivalent to the Tyson and Hoosac Formations (e.g. Thompson et al., 1990). In a radical departure from these interpretations, Ratcliffe et al. (1996) reassigned rocks of the Cavendish Formation located in the Chester dome and elsewhere in southeastern Vermont to the Mount Holly Complex based on an inferred intrusive relationship between the meta-sediments and a 1.4 Ga tonalite. This new age assignment, if correct, requires a completely new structural interpretation of the region.
Detrital zircon grains extracted from a quartzite layer from Cavendish Gorge near the inferred intrusive contact with the tonalite constrain the age of the Cavendish Formation. Grain shapes vary from euhedral to nearly spherical. Virtually all of the grains have pitted surfaces and show at least some rounding of edges and terminations. Single grain evaporation analyses of ten grains and sensitive, high-resolution ion microprobe analyses of 14 grains yield ages ranging from 943 to 1290 Ma. The youngest grains, which are less than 980 Ma, are consistent with derivation from granitic plutons which post-date the Grenville orogenic cycle. Thus, the Cavendish Formation should not be assigned to the Mount Holly Complex.
Geological Society of America, Abstracts with Programs, 30, 63 (1998) During the Ordovician Taconian orogeny, the Late Proterozoic to Cambrian Greylock Schist was thrust westward onto Cambrian and Ordovician rocks of the Stockbridge and Walloomsac Formations. The complex repetitions of the Greylock Schist and Stockbridge and Walloomsac Formations on Mount Greylock were interpreted by Ratcliffe et al. (1993) to be the result of recumbent folding of a single large thrust. We believe the repetitions are best explained as large carbonate thrust slivers of the Stockbridge Formation, which were dragged up along imbricate thrusts within the Greylock Schist as it overrode the Stockbridge Formation. The late crenulation cleavage in the Greylock Schist, which overprints an earlier schistosity, is most strongly developed near fault contacts and is only weakly developed in the cores of hypothesized recumbent folds. This suggests that the crenulation cleavage formed during faulting and that the faults were not folded after displacement ceased. Textural evidence indicates that retrograde reactions occurred after thrusting and crenulation cleavage development. Some rocks on Ragged Mountain contain abundant garnet inclusions in albite porphyroblasts but only a few corroded garnet grains in the matrix, suggesting that the eastern-most thrust sheet on the Greylock massif reached garnet grade during thrusting but cooled after emplacement.
The Walloomsac Formation is typically distinguished by the presence of graphite, and faults are drawn at the boundary between graphitic and non-graphitic schist. We suggest that the presence or absence of graphite is not a useful stratigraphic marker on Mount Greylock. Graphitic and non-graphitic lilthologies are intercalated and found in areas mapped as Walloomsac Formation and Greylock Schist. Much of the mapped Walloomsac Formation on Mount Greylock is probably Greylock Schist that has been infiltrated by fluids migrating along fault zones which precipitated graphite.
Geological Society of America, Abstracts with Programs, 30, 82 (1998) The Siluro-Devonian tectonic history of the eastern margin of the Northern Appalachians involves two oblique collisions. During the Late Ordovician to Late Silurian (445-420 Ma) Ganderia (medial New England terrane) and Avalonia accreted piecemeal to Laurentia. The subduction zone was retreating to the southeast (present coordinates); hence most of the Laurentian plate was under extension. Although minor in volume, Silurian subduction related arc/backarc volcanism (450-425 Ma; Silurian phase of Notre Dame arc) occurs along the whole length of the Northern Appalachians on the Laurentian margin. Final collision between Ganderia/Avalonia and Laurentia at ca. 420 Ma was accompanied by slab-break off, which induced a substantial amount of bimodal magmatism in the collision zone that lasted until c. 400 Ma.
Outboard west-directed subduction of the Rheic Ocean beneath Avalonia produced the Early Silurian coastal volcanic arc (CVA). The CVA is very weakly developed in Newfoundland consistent with a convergence vector nearly parallel to the trace of the Chedabucto Fault. Available data suggest that the Avalonian margin of Laurentia collided dextrally oblique with a Gondwanan promontory or microcontinent (Meguma; lower plate) during the Earliest Devonian, which shut-off the CVA arc. This collision coincides with a major change in plate motion of Laurentia.
The shut down of magmatism in Avalonia from c. 400-370 Ma in an overall convergent setting is attributed to the development of a Laramide-style orogen (Acadian Orogeny) and development of a flat-slab subduction zone beneath Laurentia. The flat-slab subduction is attributed to the overriding of a plume by Laurentian's margin, which yielded northwesterly younging deformation, thick-skinned basement uplifts in the foreland, LP-HT metamorphism and intra-crustal magmatism. The vestiges of this plume are thought to reside beneath the Magdalen Basin.
Geological Society of America Memoir, 191, 397-418 (1997) The Silurian Cadillac Mountain intrusive complex occurs along the coast of Maine and consists of the Cadillac Mountain granite (CMG), a gabbro-diorite unit and three smaller granitic units that were emplaced at a shallow depth into coeval volcanic rocks. Multiple infusions of basaltic magma were injected into and ponded on the floor of the CMG magma chamber, producing the gabbro-diorite unit. Fractionation and mixing of these infusions generated layers of mafic to intermediate magma enriched in incompatible elements that were trapped beneath silicic magma. Granitic rocks that crystallized before the basaltic infusions (lower CMG) are relatively hydrous with two feldspars and early hornblende and biotite (I-type). Granitic rocks that crystallized after the basaltic infusions (upper CMG) are hypersolvus with late interstitial hornblende, greatly enriched in high-field-strength elements, and have higher Ga/Al (A-type). Mafic enclaves in the upper CMG originated from the incompatible-rich intermediate magma that developed at the base of the chamber. The CMG provides a record of the thermal and chemical transformation of resident granitic magma from I-type to A-type due to interactions between resident silicic magma and basaltic infusions. It demonstrates that A-type characteristics can be produced by processes in high-level magma chambers and need not reflect the original conditions of melting or the chemical character of the source rocks for the granitic magma. The processes that operated in the CMG may be important in the generation of other A-type granites that occur in areas of bimodal magmatism.
Geological Society of America Abstracts with Programs, 29(6), A-407 (1997) The first large-scale mapping of the northeastern Wet Mountains shows that Mid-Proterozoic amphibolite-grade gneisses are intruded by several generations of granite. They lie near the hypothesized terrane boundary separating Yavapai and Mazatzal rocks in Colorado. The oldest lithologies include metasediments (biotite gneiss, biotite-hornblende gneiss and minor cpx-bearing hornblende gneiss) and less voluminous metabasalts (amphibolite). The metasediments are a good match with NASC on REE plots and lie near the sub-greywacke-arkose border on an Al203-Fe203-SiO2 diagram. An active continental margin/island arc setting is plausible for these rocks. The interlayered basalts are enriched in LILE relative to N-MORB and slightly depleted in HFSE. They plot as calc-alkaline and as a mature island arc or continental-margin arc. This contrasts with amphibolites to the north of the Arkansas River, which are tholeiitic and with the bimodal volcanic suites to the west near Salida. All these assemblages resemble Yavapai rocks. Metamorphic conditions in a sillimanite-biotite-cordierite rock in the northern Wets were 575oC and 4-6 Kb; garnet-biotite assemblages yielded temperatures of 450oC and 525oC. These rocks were isoclinally folded and contain NW-WSW striking foliations. Mineral lineations plunge generally downdip to the NE or NNE, coincident with hinge lines of folds. Fabrics suggest top-to-SW shear, followed by down-NE extension crenulation. One syntectonic granite has yielded a preliminary U-Pb age of 1725 Ma ± 87 Ma (M.E. Bickford, Syracuse U.).
The metamorphic suite was intruded by gneissic granodiorite of probable Boulder Creek age. Younger foliated granite bodies of possible Silver Plume age cut the other units. They assimilated country rock and may have induced a thermal metamorphic overprint that produced unaligned biotite and possibly reset garnet-biotite thermometers. These granites can be distinguished from the Boulder Creek granitics by their higher Al2O3 content and FeO and trace element compositions. Foliation patterns within these still-like bodies define Km-scale folding suggesting that NW-SE contraction post-dated intrusion.
EOS, Transactions Amer. Geophysical Union, 78(46), 786 (1997) Early Proterozoic ortho-amphibolites in central Colorado were sampled along a 100 km north-south transect from the southern Front Range through the Arkansas River Canyon to the northern Wet Mountains. Those from the Front Range commonly occur as concordant layers in pelitic metasedimentary hosts, while in the Wet Mountains they occur as layers, pods, and blocks in highly deformed biotite-quartz feldspar gneisses of mixed heritage and as xenoliths in granitic plutons. The intervening Arkansas Canyon amphibolites are locally interlayered with felsic metavolcanics, some of which retain relict pyroclastic fabrics. Amphibolites in all areas pre-date the oldest generation of granitic plutons in the region (1.72-1.69 Ga).
New major and trace element analyses of 35 samples by XRF and INAA data for 19 samples indicate significant geochemical differences between the north and the south. Front Range samples are basalts with tholeiitic affinities; they are generally lower in total alkalies and most high-field-strength elements and are less enriched (normalized to N-MORB) in large-ion lithophile elements than are those to the south. Amphibolites from the Arkansas Canyon and northern Wet Mountains are calc-alkaline, ranging from basalts to trachy-basalts and basaltic trachy-andesites. When plotted on a variety of tectonic discriminant diagrams using minor elements and immobile trace elements, all plot as volcanic arc basalts. Because of their spatial separation and geochemical differences, the north and south may represent parts of two different island arc systems - one more highly evolved than the other - that were accreted to the rapidly growing North American craton late in the Early Proterozoic.
EOS, 79(17), 355 (1998) The Arkansas River canyon of central Colorado contains a significant and previously overlooked Early Proterozoic bimodal metavolcanic suite in the section extending 50 km upstream (west) from the Royal Gorge to the Pleasant Valley fault near the town of Howard.. The felsic and mafic units are interlayered with a well-exposed series of biotite-quartz-feldspar gneisses, quartzites, and metapelites. The layered rocks were deformed during regional sillimanite-grade metamorphism prior to the intrusion of the Garrell Peak pluton, which cross-cuts the metavolcanic units and gives them a minimum age of 1.65 Ga. The predominantly aphyric felsic units are characterized by primary fragmental texture and locally by relict flattened pumice lapilli. Amphibolites represent mafic flows and gabbroic sills; no pillow structures were observed.
Trace element data for 17 felsic samples by XRF and 12 by INAA show enrichment in both LILEs and HFSEs, and depletion in Sr, P, Ti, and Sc in MORB-normalized spider plots. REE diagrams show LREEs at about 100x chondrite and only slightly enriched over HREEs (LaN/YbN<5), along with small to moderate negative Eu anomalies. Geochemically these rocks closely resemble the less deformed Early Proterozoic aphyric metarhyolites near Salida, 15 km west of the western edge of the studied section (Boardman and Condie, 1986). The ranges and averages of most trace elements in these rocks are consistent with those for mature island arcs and active continental margins, both of which are components of regional tectonic models for Colorado showing rapid accretion of arc systems onto an enlarging continental margin during the Early to Middle Proterozoic.
Keck Research Symposium in Geology Proceedings, 11, 112-116 (1998) Students in this project obtained the first detailed lithologic and structural data from the Arkansas River Canyon, constructed the first geological maps, and used geochemical analyses to model rock origins. Their work will be used in coming years to constrain models of crustal growth in the region because existing tectonic models have not incorporated findings from these study areas. Thus, the fundamental field and laboratory data are the most significant aspect of the project. Currently, debate exists over the possibility of a large terrane boundary separating Mazatzal and Yavapai rocks occurring in this region. These data will complement planned geophysical projects which will explore the deeper crust.
Mapping north of Howard revealed a continuation of the low-grade, bimodal volcanic and sedimentary sequence described by Boardman for the Salida area. South of the Arkansas River, the rocks are somewhat higher grade and considerably injected by plutons of several ages. The bimodal volcanic sequence continues east possibly to the north end of the Wet Mountains, but is not observed in small exposures ten miles to the south. Extensive ductile deformation and at least two periods of metamorphism and plutonism have affected these rocks.
Journal of Knot Theory and Its Ramifications, 6, 32, 149-161, (1997) The concept of stick number for knots and links is addressed under various restrictions concerning the length of the sticks, the angles between sticks, and placements of the vertices. In particular, we focus on the effect of composition on the various stick numbers. Ultimately, we determine the traditional stick number for an infinite class of knots, which are the (n,n-1)-torus knots together with all of the possible compositions of such knots. The exact stick number was previously known for only seven knots.
Mathematics Teacher, 90, 8, 640-646, 652, (November, 1997) This article explains how teachers can use the mathematical theory of knots to involve their students with mathematics in the classroom.
W.H. Freeman and Co., New York, NY, Japanese Translation, (January, 1998)
Mathematical Sciences Research Institute, CD-ROM, 1, (Spring, 1998) A CD-ROM version of a presentation given in the Conversations Series at the Mathematical Sciences Research Institute, Berkeley, CA, Dec. 11, 1996.
Chaos, Solitons and Fractals, special issue Vol. 9 No 4/5, April/May 1998 This volume consists of nineteen articles on current research in the field of knot theory and its applications.
Mathematical Intelligencer, 20 (1998)
CR-Geometry and Determined Systems, Advanced Studies in Pure Mathematics, 25, 110-121, (1997) Vector-valued forms arise in the study of various higher codimensional geometries. This note gives an overview of how the invariant theory of the Levi form (a vector-valued form) can be used to understand higher codimensional CR-structures.
Journal of Algebra, 201, 573-583, (1998) Until recently it was thought that excellent rings cannot have local generic formal fibers. In this paper, however, we construct a class of excellent rings that in fact do possess this property. In addition, we show that the dimension of the generic formal fiber ring can be controlled.
A. K. Peters, (1998) Starting with an extrinsic approach to curvature, this book provides a short, intuitive, direct introduction to Riemannian geometry, including topics from general relativity, global geometry, and current research on norms more general than area.
Proc. Royal Soc., 127A, 819-822, (1997) We discuss existence and lower semicontinuity for clusters of materials minimizing an energy given by a collection of norms [[script_phi]]ij on the interfaces between regions Ri and Rj. Following Ambrosio and Braides, we exhibit a problem for which the triangle inequality holds but existence fails, and we state a new sufficient condition for lower semicontinuity, which may be necessary.
The Christian Science Monitor, biweekly, starting June 14, 1996 Biweekly column with questions, answers, and prizes, based on the call-in show, both available via The Christian Science Monitor, both available via Morgan's web page at www.williams.edu/Mathematics/fmorgan.
The Mathematics Teacher, 90, 746-750, (December, 1997) This is a write-up of my famous contest, for use by high school teachers.
Israel J. Math, 102, 269-282, (1997) We construct rank-one infinite measure preserving transformations satisfying each of the following dynamical properties: 1) Continuous + L° spectrum, conservative k-fold Cartesian products but nonergodic Cartesian square; 2) ergodic k-fold Cartesian products; 3) nonconservative Cartesian square. We show how to modify the construction of 1) to obtain type III [lambda] transformations with similar properties.
Real Analysis Exchange, 23, 1, 259-266, (1998) We use a set in the unit interval to construct measure preserving transformations that are lightly mixing on intervals but not ergodic, and ergodic measure preserving transformations that are lightly mixing on intervals but not lightly mixing, and give some applications.
New York J. of Math, 3A, 99-115, (1998) We characterize mildly mixing group actions of a noncompact, locally compact, second countable group G using orbit equivalence. We show an amenable action of G is mildly mixing if and only if G is amenable and for any nonsingular ergodic G-action, the product G-action x is orbit equivalent to. We extend the result to the case of finite measure preserving noninvertible endomorphisms; i.e., when G =N.
Pure and Applied Chemistry, 69, 2099 (1997)
The photoisomerization of rhodopsin in 200 femtoseconds is among the fastest and most efficient photochemical reactions known. We have developed a microscopic model to study rhodopsin's dynamics which retains the collective quantum mechanics of the pi electrons in the conjugated system. Our model is a generalization to three dimensions of Su, Schrieffer, and Heeger's model for polyacetylene (CH)x. Model parameters are inferred from comparison with experiments and ab initio calculations. The spatial structure and vibrational modes of the rhodopsin chromophore 11-cis retinal are calculated and shown to agree quite well with NMR and Raman spectroscopy measurements. Dynamics following photoexcitation are studied.
Physica A, 236, 220 (1997) A simplified model of reptation is presented. The master equation of the model is systematically solved by expansion in powers of the strength of the driving field. From the explicit form of the probability distribution, exact conclusions can be drawn about the average shape of the polymer, its drift velocity, and the zero field diffusion constant. Correlations between segments of the chain are calculated and turn out to be large, even in the weak driving field limit. The results are compared with simulations of the model.
Technical Digest of the Conference on Lasers and Electro-Optics, May 1998. pp. 158-159 We have studied period doubling, period tripling, and quasiperiodicity in the pulse train of a mode-locked Ti:sapphire laser. The exchange of energy between pulses in these regimes is accompanied by spatial dynamics and can be modeled by coupling of transverse modes.
Physical Review Letters, 78, 5022 (1997) The "entanglement of formation" of a mixed state P of a bipartite quantum system can be defined as the minimum number of singlets needed to create an ensemble of pure states that represents P. We find an exact formula for the entanglement of formation for all mixed states of two qubits having no more than two nonzero eigenvalues, and we report evidence suggesting that the formula is valid for all states of this system.
Physical Review Letters, 80, 2245 (1998) The entanglement of a pure state of a pair of quantum systems is defined as the entropy of either member of the pair. The entanglement of formation of a mixed state P is the minimum average entanglement of an ensemble of pure states that represents P. An earlier paper conjectured an explicit formula for the entanglement of formation of a pair of binary quantum objects (qubits) as a function of their density matrix, and proved the formula for special states. The present paper extends the proof to arbitrary states of this system and shows how to construct entanglement-minimizing decompositions.
Journal of Personality and Social Psychology, 74, 159-169, 1998. Preschool antecedents of the use of defense mechanisms were longitudinally studied using data from 90 nursery school children who were again evaluated at age 23. Defense use was determined by coding Thematic Apperception Test (H.A. Murray, 1943) stories with a method previously shown to be reliable and valid. The findings indicated continuity between preschool personality and subsequent defense use for male participants but little continuity for female participants. Young men's use of the age-inappropriate defense of denial was predicted by indications at ages 3-4 of low ego resiliency and psychological difficulties in the areas of emotion, intellect, impulse control, and social interactions.
Journal of Personality, 66, 335-357, 1998 To investigate the effect of a threat to gender identity on the use of defense mechanisms, college students were given false feedback regarding their sex-role identity. Male and female students who were given gender-contrary feedback showed a marked increase in the use of the defense of identification, as compared to students who were given gender-consistent feedback. Further, both affect change and the use of identification was a function of the degree of discrepancy between feedback condition and conscious gender identity
Journal of Research in Personality, 32, 156-172, 1998 The identity status, narcissism, and use of defense mechanisms of 89 college seniors who had previously been assessed as they entered college (Cramer, 1995) was determined. As compared to earlier follow-up studies, fewer students were found in the Foreclosed status, and more students remained in Moratorium. Support was found for the previously made predictions that change in identity status would be associated with change in defenses and narcissism. Students who advanced to higher identity statuses made less use of defenses and showed higher narcissism.
Journal of Applied Developmental Psychology, 19, 417-439, 1998 The existence of negative attitudes toward overweight body builds is demonstrated in two groups of preschool children aged 3 to 5 years (ns = 30 and 83), using four different measures of body size stigmatism. Although this stigmatism was stronger in the older children, it was clearly present in the 3 year olds. There was little support for the position that stigmatism would be greater for outgroup members. Rather, the cultural stereotype that `fat is bad' was pervasive across gender, regardless of the child's own body build. In fact, overweight preschoolers demonstrated stronger stigmatism that did those who were not overweight. The findings suggest that efforts to counteract body size stigmatism should begin in the early preschool years.
Family Process, 37, 35-49, 1998 Children's attributions about the causes of family arguments affect both their interpretations of the meaning of and their adjustment to such events. Children's attributions about family arguments are, therefore, of importance in family therapy, especially for therapists who work from a cognitive or constructivist perspective. In an exploratory study, we examined children's attributions about family arguments in two arenas: marital arguments and parent-child arguments. Ninety-two children, aged 5-12, listened to an audio-taped argument and answered a series of structured questions concerning different attributions about the causes of such arguments. Descriptive analyses of the most and least endorsed attributions provided an overall map of the "stories" children tell about the causes of family arguments, and showed that, in general, they are more likely to endorse multiple, interacting causes than internal, blaming attributions. Additionally, children of all ages made somewhat different attributions concerning mothers vs. fathers in marital arguments. Implications for family therapy and suggestions for future clinical research are discussed.
Family Process, 37, 17-33, 1998 One important clinical task in family therapy involves transforming the client's construction of the presenting problem from an individual, intrapersonal view to an interpersonal, relational, or systemic one (Sluzki, 1992). To study the transformation process in initial sessions, we sampled 8 families in which the referring parent requested help for a child's problem. The 8 therapists, trained and experienced in Sluzki's (1992) narrative approach, attempted to facilitate a transformation in the parents' initial construction of the problem. In 4 sessions, the transformation was independently judged to be successful by the therapist and observers, while in 4 other sessions the transformation was judged to be unsuccessful. Videotapes of the 8 interviews were analyzed qualitatively, and the parent's' verbatim descriptions of the problem were coded using the Cognitive Constructions Coding System (Friedlander, 1995). We compared the successful and the unsuccessful sessions and developed a conceptual model of the successful transformation process that included client performances as well as therapist operations (Greenberg, 1986). While many elements in the model are consistent with Sluzki's (1992) "blue print" transformation, several new elements were added. Practical implications are described, along with limitations and recommendations for future research.
Developmental Psychology, 33, 764-770, 1997. Two-year-old children were required to use non-literal words or actions to complete scenarios in which a doll acted as the agent of a series of make-believe events. An experimenter encoded the doll's imaginary intentions either verbally or through pretend actions. No gender differences were observed, but older 2-year-olds performed reliably better than younger 2-year-olds. In addition, episodes that required children to enact the conclusion to events that began with doll-directed actions proved difficult to comprehend. Discussion focused on the implications of children's understanding of independent agency for joint sociodramatic play and on the problem of intersubjectivity in children's understanding of an adult's non-literal intentions.
Journal of Personality and Social Psychology, 73 (1), 31-44, 1997 The authors argue that self-image maintenance processes play an important role in stereotyping and prejudice. Three studies demonstrated that when individuals evaluated a member of a stereotyped group, they were less likely to evaluate that person negatively if their self-images had been bolstered through a self-affirmation procedure, and they were more likely to evaluate that person stereotypically if their self-images had been threatened by negative feedback. Moreover, among those individuals whose self-image had been threatened, derogating a stereotyped target mediated an increase in their self-esteem. The authors suggest that stereotyping and prejudice may be a common means to maintain one's self-image, and they discuss the role of self-image maintenance processes in the context of motivational, sociocultural, and cognitive approaches to stereotyping and prejudice.
Pharmacology, Biochemistry and Behavior, 59, 819-827. This study examined the effects of exposure to prenatal stress on young and adult rats, and whether the concomitant administration of an anxiolytic neurosteroid, allopregnanolone (3-alpha-hydroxy-5 alpha-pregnant-20-one), could ameliorate some of the behavioral dysfunctions associated with prenatal stress. Pregnant dams were assigned to one of five treatment groups on gestational day 14. These groups were exposed to either 1) restraint for 45 min. three times daily; 2) a vehicle injection twice daily; 3) 5 mg/kg allopregnanolone twice daily; 4) restraint with allopregnanolone injections; or 5) nonhandled controls. Assays for plasma allopregnanolone concentrations indicated that exogenous allopregnanolone injections significantly raised circulating levels to a comparable degree in gestational day 20 dams and their fetuses. At 7 days of age, however, subjects prenatally exposed to allopregnanolone either alone or with restraint now had lower circulating levels compared to the other groups, suggesting some negative compensatory change. Behavioral results suggested that the effects of prenatal stress on affective behaviors (ultrasonic vocalizations emitted after a brief maternal separation at 7 days of age, and plus-maze behavior at 70 days of age) could be reversed by coadministration of allopregnanolone. When locomotor activity was assessed at 16 and 60 days of age, no comparable reversal effect was observed. In fact, the allopregnanolone groups had results similar to those of the restraint alone group. Thus, for some neuronal systems, allopregnanolone may exert either a direct teratogenic effect or an indirect effect due to neurosteroid-induced behavioral changes in the pregnant dam.
Journal of Social Issues, 53 (3), 487-502, 1997 We exposed some mock jurors to pretrial publicity (PTP) biased against the defendant a few days before they read the trial transcript and rendered individual verdicts. Exposure to the PTP prejudiced the jurors toward voting "guilty," unless they read information within the PTP that indicated that the defendant was African American and that raised suspicion about the racist motives underlying the PTP's reporting. Information designed to raise more generic, nonracist suspicion did not have this effect. In addition, participants were less likely to vote to convict the defendant if he was African American than if his race was unspecified, and non-White participants were less likely to vote to convict the defendant than were White participants. We discuss these issues and results in the context of the O.J. Simpson trial, specifically, and of the psychology and law literatures more generally.
Personality and Social Psychology Bulletin, 23(11), 1215-1226, 1997 Mock jurors learned incriminating information about a defendant in the context of pretrial publicity (Study 1) or testimony introduced in the trial but ruled inadmissible (Study 2). Despite the judge's instructions that they disregard the information, jurors' verdicts were affected significantly by the information, unless the jurors were made suspicious about the motives underlying the introduction of this information. That is, jurors given reason to be suspicious about why the incriminating information was introduced into the media or the trial offered verdicts that did not differ from those made by jurors who were not exposed to the incriminating information. The potential role of suspicion in weakening the biasing effects of a variety of nonevidentiary factors on jurors' verdicts is discussed, as is the role of suspicion in social-cognitive processes more generally.
Pharmacology and Therapeutics, 74: 27-38, 1997 This review discusses some of the major findings implicating the autonomic nervous system in the regulation of immune function. The sympathetic nervous system, the primary focus of this line of research, directly innervates the major lymphoid organs, and physiological release of sympathetic neurohormones at these sites has been documented. Leukocytes have been shown to express receptors for catecholamines, as well as neuropeptide Y, and studies in vitro and in vivo have indicated that occupation of these receptors by the appropriate ligands produces functional changes in immunological cells. Finally, altered sympathetic regulation may underlie some of the immunological abnormalities observed in chronic stress, clinical depression, and aging.
Journal of Personality and Social Psychology, 72, 1284-1296, 1997 Counterfactual thoughts of "what might have been" have been shown to influence emotional responses to outcomes. The present investigation extends this research by proposing a model of how categorical cutoff points, or arbitrary values that impose qualitative boundaries on quantitative outcomes induce counterfactual thoughts and influence individuals' satisfaction. In particular, just making a cutoff for a category is hypothesized to elicit downward counterfactual comparisons, boosting satisfaction, whereas just missing a cutoff prompts upward counterfactual thoughts, decreasing satisfaction. In some circumstances, this asymmetry can reverse the usual relationship between objective outcome and satisfaction, causing those who do objectively better to feel worse than those they outperform. This hypothesis is supported by the results of one naturalistic study and two scenario experiments.
Personality and Social Psychology Bulletin, 24, 529-536, 1998. Confidence has been found to vary with temporal proximity to an upcoming task: Peoples' confidence that they will do well tends to diminish as the "moment of truth" draws near. We propose that this phenomenon stems in part from individuals using their pre-task arousal as a cue to their level of confidence. Arousal that is part and parcel of "gearing up" to perform a task may be misattributed to diminished confidence. Consistent with this reasoning, participants in two experiments who were encouraged to misattribute their arousal to a neutral source ("subliminal noise") expressed greater confidence in their ability than did participants not able to do so--a result that would not be obtained if arousal was simply a reflection, and not a cause, of diminished confidence.
Archives of Neurology, 55, 349-355 (1998) To determine the validity and reliability of a rapidly administered neurocognitive screening battery consisting of 4 brief tests (Enhanced Cued Recall, Temporal Orientation, Verbal Fluency, and Clock Drawing) to distinguish between patients with probable Alzheimer's disease (AD) and healthy controls subjects. Sixty successive referrals to the Memory Disorders Clinic at Southwestern Vermont Medical Center, Bennington, who were diagnosed as having probable AD and 60 community-dwelling volunteers of comparable age, sex distribution, and education. Interrater and test-retest reliability, inter-group comparisons between patients with AD and control subjects on the 4 individual tests, and determination of probability of dementia for patients with AD and control subjects using the entire battery of tests. Mean time of administration was 7 minutes 42 seconds. Mean scores for patients with AD and control subjects on all 4 individual tests were significantly different (for each, P<.001). When the 4 tests were combined in a logistic regression, the battery had a sensitivity of 100% and a specificity of 100%. A series of 1000 repeated random samples of 30 patients with AD and 30 control subjects taken from the overall sample of 60 patients with AD and 60 control subjects had a mean sensitivity of 92% and a mean specificity of 96%. The battery was equally sensitive to patients with mild AD as demonstrated by correctly classifying all 13 patients with AD using Mini-Mental State Examination scores of 24 or higher. Neither age nor education was a statistically significant factor when added as a covariate. Test-retest reliabilities for individual tests ranged from 083 to 0.93. Test-retest reliability for the entire battery was 0.91. Interrater reliability for the entire battery was 0.92. The 7 Minute Screen appears highly sensitive to AD and may be useful in helping to make initial distinctions between patients experience cognitive changes related to the normal aging process and those experiencing cognitive deficits related to dementing disorders such as AD. It has reasonable interrater and test-retest reliability, can be administered in a brief period, and requires no clinical judgment and minimal training.
Psychology and Aging, 13 (2), 186-192 (1998). Human participants who, 5 years earlier, participated in studies of acquisition of the classically conditioned eyeblink response to a tone conditioned stimulus (CS) and an air puff unconditioned stimulus (UCS), returned to the laboratory to test for retention of the conditioned response (CR). Retention consisted of 20 tone CS-alone presentations. Young adult participants (23-31 years of age at the time of retention testing) showed good retention of the CR (45%), middle-aged participants (45-52 years) showed reduced retention (28%), and older participants (69-78 years) showed little evidence of retention (<5%). Retention testing was followed by reacquisition of the CR in which the CS and the UCS were again paired. The ability to reacquire the CR also showed a decline with age. The data suggest that the CR can be retained over long intervals and that the degree of retention is age dependent.
Neurology, 50 (supp 4), A162, (1998) The purpose of this study was to evaluate the utility of the 7 Minute Screen in a primary care practice. The 7 Minute Screen is a rapidly administered neurocognitive screening battery consisting of 4 brief tests (Temporal Orientation, Enhanced Cued Recall, Verbal Fluency, and Clock Drawing) that distinguish between patients with probable Alzheimer's disease (AD) and normal healthy controls. The validity and reliability of the 7 Minute Screen were previously established in 60 successive referrals to the Memory Clinic, Southwestern Vermont Medical Center, Bennington, VT who were diagnosed with AD and 60 community-dwelling age education matched controls. The battery was demonstrated to have a sensitivity of >90% and a specificity of >90% when the results of the four tests were combined in a logistic regression. (Solomon et al., Arch. Neurol, in Press). This study was conducted over the course of 7 weeks in a primary care practice. One hundred and thirty-seven successive admissions over the age of 60 provided informed consent, gave a brief history, and underwent brief mental status testing and the 7 Minute Screen. This sample represented 96% of all patients over the age of 60 seen in the practice during that time period. Of the 137 patients, 124 patients screened negative on the 7 minute screen (i.e. low probability of dementia) and 13 patients screened positive (i.e. probability of dementia). A random sample of 26 patients with a low probability of dementia underwent history, physical and comprehensive neuropsychological evaluation. Twenty-five of these patients had no evidence of Alzheimer's disease or other dementia; one patient demonstrated mild cognitive impairment. Of the 13 patients who screened positive, 11 agreed to return for further evaluation consisting of history and physical neuropsychological testing, laboratory evaluation, and CT scan. Ten of the 11 patients were subsequently diagnosed with probable AD. The 7 Minute Screen correctly identified 10 of 11 patients with probable AD and 25 of 26 patients with normal cognitive abilities.