Geology Commons^™

General Geology And Geochemistry Of Metamorphosed Proterozoic Mafic Dikes And Sills, Tobacco Root Mountains, Montana, John B. Brady, Heidi K. Mohlman, Caroline Harris, Sarah K. Carmichael, Lisa J. Jacob, Wilfredo R. Chaparro

Geosciences: Faculty Publications

Just over two billion years ago, basaltic magma intruded rocks of the Pony– Middle Mountain Metamorphic Suite and the Indian Creek Metamorphic Suite that now crop out in the Tobacco Root Mountains of Montana near the northwestern margin of the Wyoming province. Numerous examples can be found of mafic dikes that crosscut layering and gneissic banding, demonstrating that the host rocks were metamorphosed to form the gneissic texture prior to intrusion of the dikes. Although many of the intrusions appear to be sills that followed compositional layering, close inspection reveals low-angle discordance in nearly every case, consistent with rotation of …

Proterozoic Metamorphism Of The Tobacco Root Mountains, Montana, John T. Cheney, John B. Brady, Kara A. Tierney, Kathleen A. Degraff, Heidi K. Mohlman, Jessica D. Frisch, Christine E. Hatch, Michael L. Steiner, Sarah K. Carmichael, Robin G.M. Fisher, Carrie B. Tuit, Kurt J. Steffen, Pamela Cady, Josh Lowell, Leandra L. Archuleta, Jillian Hirst, Karl W. Wegmann, Brian Monteleone

Geosciences: Faculty Publications

Textures and mineral assemblages of metamorphic rocks of the Tobacco Root Mountains are consistent with metamorphism of all rocks during the Big Sky orogeny (1.77 Ga) at relatively high pressure (P >1.0 GPa) followed by differential reequilibration on a clockwise P-T path at lower pressures (0.6–0.8 GPa). The highest pressures are documented by coarse-grained kyanite and orthopyroxene in aluminous orthoamphibolites, which require P ≥ 1.0 GPa. Other higher-pressure mineral assemblages of note include kyanite + orthoamphibole and kyanite + K-feldspar. Abundant textural evidence for partial melting in pelitic and basaltic rocks includes leucosomes, very large (several cm across) porphyroblasts of …

Environmental Indicator Proxies From A Mid-Holocene Coral Reef, Enriquillo Valley, Dominican Republic, Gala M.M. Guerard, Lisa Greer, H. Allen Curran

Geosciences: Faculty Publications

No abstract provided.

Shallow-Water Coral Reefs In Transition: Examples From Belize And The Bahamas, H. Allen Curran, Paulette M. Peckol, Benjamin J. Greenstein, Shannon Ristau, Susan Deyoung

Geosciences: Faculty Publications

Reprinted from: Ronald D. Lewis and Bruce C. Panuska (eds.) Proceedings of the 11th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Gerace Research Center

Assessment Of Selected Reef Sites In Northern And South-Central Belize, Including Recovery From Bleaching And Hurricane Disturbances (Stony Corals, Algae And Fish), Paulette M. Peckol, H. Allen Curran, Emily Y. Floyd, Martha L. Robbart, Benjamin J. Greenstein, Kate L. Buckman

Geosciences: Faculty Publications

The condition of coral. algal. and fish populations in fore reefs. patch reefs, and coral reef ridges was investigated at 13 sites along the northern and south-central Belize barrier reef during May 1999, documenting effects of the 1998 warming episode and Hurricane Mitch. We found high percentages of partial, or even complete, colony mortality of major reef-builders (Acropora palmata, the Montastraea annuluris species complex and Agaricia tenuifolia) that were rarely censused as recruits. A. tenuifolia, formerly a space-dominant coral in reef ridges, had incurred nearly 100% mortality after bleaching. Nearly 45% of the M. annurluris complex …

Assessment Of Coral Reefs Off San Salvador Island, Bahamas (Stony Coral, Algae And Fish Populations), Paulette M. Peckol, H. Allen Curran, Benjamin J. Greenstein, Emily Y. Floyd, Martha L. Robbart

Geosciences: Faculty Publications

During assessments at 11 shallow reef sites on an Salvador Island, Bahamas in .iunc I998 we found low prevalence of disease, bleaching, and recent partial-colon1 mortality among stony corals (10 cm minimum dixncter). Old partial-colony mortalit) was >50% in Acropora palmata; however, recent tissue losses were low and it had recruits at several sites. Total (recent + old) partial-colony mortality of the Montastraea annularis species complex exceeded 30% on leeward patch reefs and back reefs. Groupers (serranids), snappers (lutjanids), and grunts (haemulids) were rare. Parrotfishes (scarids) were uncommon at most sites and surgeonfishes (acanthurids) were the dominant herbivores. Macroalgae, particularly …

Complex Decapod Burrows And Ecological Relationships In Modern And Pleistocene Intertidal Carbonate Environments, San Salvador Island, Bahamas, H. Allen Curran, Anthony J. Martin

Geosciences: Faculty Publications

Burrowing by thalassinidean shrimp in modern tropical, shallow-subtidal to intertidal carbonate environments is widespread and a powerful agent of bioturbation, particularly within sandy substrates. Deep and intense burrowing by callianassids commonly occurs along the intertidal margins of hypersaline lagoons throughout the Bahamas, such as Pigeon Creek on San Salvador Island, where the sediments of extensive sand flats are thoroughly bioturbated by Glypturusacanthochirus. In addition to dominating the deep-tier infauna, G. acanthochirus is a true ecosystem engineer, and its prodigious burrowing activity results in a highly mounded topography. On sand flats, individual sediment cones commonly coalesce with time to form large …

Effects Of Grand-Cycle Cessation On The Diagenesis Of Upper Cambrian Carbonate Deposits In The Southern Appalachians, U.S.A, Bosiljka Glumac, Kenneth R. Walker

Geosciences: Faculty Publications

The vertical transition from the mainly subtidal alternating shale and carbonate units (or grand cycles) of the Conasauga Group (Middle to Upper Cambrian) to the peritidal dolostone of the Knox Group (Upper Cambrian to Lower Ordovician) marks a major change in the early Paleozoic passive-margin sedimentation of the southern Appalachians. The grand cycles represent an interplay between intrashelf shale basin and carbonate-platform deposition. The end of grand-cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost Conasauga Group strata-the Maynardville Formation. The …

Stable Isotopes Of Carbon As An Invaluable Stratigraphic Tool: An Example From The Cambrian Of The Northern Appalachians, Usa, Bosiljka Glumac, Malkah L. Spivak-Birndorf

Geosciences: Faculty Publications

This study illustrates the usefulness of carbon isotopes in stratigraphic interpretations of poorly fossiliferous strata beyond the resolution possible by biostratigraphy. The Upper Cambrian strata of the lower Gorge Formation in northwestern Vermont have been interpreted as highly condensed continental-slope deposits with a hiatus bracketed by the trilobite fauna of the Dunderbergia zone (Steptoean) and the Saukia zone (upper Sunwaptan). This interpretation was based on information from two thin fossiliferous intervals, the occurrence of one of them being unconfirmed in a recent study. Carbon isotopes provide a means for testing this interpretation because marine carbonate rocks deposited during the Steptoean …

Influence Of Early Lithification On Late Diagenesis Of Microbialities: Insights From Δ 18O Composition Of Upper Cambrian Carbonate Deposits From The Southern Appalachians, B. Glumac

Geosciences: Faculty Publications

This paper documents a difference in isotopic compositions between Upper Cambrian microbial and non-microbial micritic deposits and proposes implications for diagenesis of calcimicrobial deposits. The δ 18O values (-10.98 to -8.71; average -9.88‰ VPDB) of calcimicrite comprising shallow subtidal microbialites from the southern Appalachians are more negative than: (1) the calcimicrite from associated subtidal non-microbial deposits (-8.98 to -7.16; average -7.82), suggesting a different diagenetic history; and (2) estimates of Late Cambrian marine calcite values (-5 to -3 ‰), indicating postdepositional modifications. Early diagenetic calcification of microbial deposits promoted the formation of growth cavities and borings rimmed with marine fibrous …

Ichnology Of Holocene Carbonate Eolianites Of The Bahamas, H. Allen Curran, Brian White

Geosciences: Faculty Publications

No abstract provided.

Behavioral Plasticity Of Modern And Cenozoic Burrowing Thalassinidean Shrimp, M. F. Miller, H. Allen Curran

Geosciences: Faculty Publications

No abstract provided.

Resilience And Recovery Of Coral Reefs From Large-Scale Disturbances: Contrasting Patterns For San Salvador Island, Bahamas, And Belize, Paulette M. Peckol, H. Allen Curran, Martha Robbart, Benjamin J. Greenstein

Geosciences: Faculty Publications

Benjamin J. Greenstein and Cindy K. Carney (eds)

San Salvador, Gerace Research Center

A Sea-Level Lowstand (Devil's Point Event) Recorded In Bahamian Reefs: Comparison With Other Last Interglacial Climate Proxies, Brian White, H. Allen Curran, Mark A. Wilson

Geosciences: Faculty Publications

Reprinted from: Benjamin J. Greenstein and Cindy K. Carney (eds.) Proceedings of the 10th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Gerace Research Center

Coastal Effects Of Hurricane Floyd On San Salvador Island, Bahamas, H. Allen Curran, Priscilla Delano, Brian White, Meredith Barrett

Geosciences: Faculty Publications

Hurricane Floyd, a Category 4 storm with winds up to I 55 mph, made a close encounter with San Salvador Island on September 13-14, 1999. In addition to inflicting severe damage to homes, tourist facilities, businesses, and infrastructure on the island, the storm also caused considerable beach erosion and coastal modification, mostly on the western and northern coasts. This paper reports and documents with photos the findings of a survey of coastal erosion effects on four areas of the San Salvador coastline: Coast Guard Beach, Rocky Point south to Cockburn Town and Fernandez Bay, South of Sugarloaf toward Grotto Bay, …

Carbonate Deposition And Sequence Stratigraphy Of The Terminal Cambrian Grand Cycle In The Southern Appalachians, U.S.A, Bosiljka Glumac, Kenneth R. Walker

Geosciences: Faculty Publications

The cessation of shale and carbonate deposition of the Conasauga Group grand cycles (Middle to Upper Cambrian) and the establishment of the widespread peritidal carbonate deposition of the Knox Group (Upper Cambrian to Lower Ordovician) represent a prominent change in sedimentation along the early Paleozoic passive continental margin in the southern Appalachians. To evaluate the causes for this change, this study focuses on the Maynardville Formation, which is the uppermost carbonate unit of the Conasauga Group. The Maynardville consists of: (1) a lower subtidal faciès succession, which is underlain by the Nolichucky Shale and resembles the rest of the Conasauga …

Stable Isotope And Crystal Chemistry Of Tourmaline Across Pegmatite - Country Rock Boundaries At Black Mountain And Mount Mica, Southwestern Maine, U.S.A, Darby Dyar, Charles V. Guidott, Daniel P. Core, Katherine M. Wearn, Michael A. Wise, Carl A. Francis, Kathleen Johnson, John B. Brady, J. David Robertson, Laura R. Cross

Geosciences: Faculty Publications

Major element and stable isotope chemistry of tourmaline from two complexly-zoned rare element pegmatites has been studied to gain insights into the processes by which the pegmatites were formed. Two locations in the Oxford Pegmatite Field of western Maine, U.S.A., were chosen for this study: Black Mountain, an isolated body located in sillimanite zone, highly sulfidic metapelites and quartzite; and Mount Mica, which is bounded by schists and pegmatite and aplitic granite bodies commonly having gradational contacts with each other. At each locality, tourmaline was sampled from the surrounding country rocks into the contact and wall zones through to the …

A Late Cambrian Positive Carbon-Isotope Excursion In The Southern Appalachians: Relation To Biostratigraphy, Sequence Stratigraphy, Environments Of Deposition, And Diagenesis, Bosiljka Glumac, Kenneth R. Walker

Geosciences: Faculty Publications

A positive carbon-isotope excursion is recorded within the Upper Cambrian sedimentary succession in the southern Appalachians that consists of the Nolichucky Shale, the Maynardville Formation, and the Copper Ridge Dolomite. The lower part of the succession contains Aphelaspis zone fauna (Early Steptoean). The extensively dolomitized and poorly fossiliferous nature of the upper part of the succession precludes any detailed biostratigraphic determinations. Correlation with similar positive carbon-isotope excursions in coeval successions elsewhere suggests that this excursion represents a perturbation in the global cycling of carbon. Comparison of excursions at different localities in North America provides a means for the application of …

Ichnology Of Holocene Carbonate Eolianites On San Salvador Island, Bahamas: Diversity And Significance, H. Allen Curran, Brian White

Geosciences: Faculty Publications

Reprinted from: H. Allen Curran and John E. Mylroie (eds.), Proceedings of the 9th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Bahamian Field Station

Bahamian Coral Reefs Yield Evidence Of A Brief Sea-Level Lowstand During The Last Interglacial, Brian White, H. Allen Curran, Mark A. Wilson

Geosciences: Faculty Publications

The growth of large, bank-barrier coral reefs on the Bahamian islands of Great Inagua and San Salvador during the last interglacial was interrupted by at least one major cycle of sea regression and transgression. The fall of sea level resulted in the development of a wave-cut platform that abraded early Sangamon corals in parts of the Devil's Point reef on Great Inagua, and produced erosional breaks in the reefal sequences elsewhere in the Devil's Point reef and in theCockburnTown reef on SanSalvador. Minor red caliche and plant trace fossils formed on earlier interglacial reefal rocks during the low stand. The …

Comparison Of Recent Coral Life And Death Assemblages To Pleistocene Reef Communities: Implications For Rapid Faunal Replacement On Recent Reefs, Benjamin J. Greenstein, Lora A. Harris, H. Allen Curran

Geosciences: Faculty Publications

Marine ecologists and paleoecologists are increasingly recognizing that the Pleistocene and Holocene fossil record of coral reefs is the exclusive database from which an assessment of the long-term responses of reef communities to environmental perturbations may be obtained. The apparent persistence of coral communities in the face of intense fluctuations in sea level and sea surface temperature during glacial and interglacial stages of Pleistocene time is in marked contrast to dramatic fluctuations in reef community structure documented by short-term monitoring studies. We compared the taxonomic structure of live and dead coral communities on a modem patch reef currently undergoing a …

Ophiomorpha Nodosa In Estuarine Sands Of The Lower Miocene Calvert Formation At The Pollack Farm Site, Delaware, Molly F. Miller, H. Allen Curran, Ronald L. Martino

Geosciences: Faculty Publications

No abstract provided.

Isotope Geochemistry Of Proterozoic Talc Occurrences In Archean Marbles Of The Ruby Mountains, Southwest Montana, U.S.A, John B. Brady, John T. Cheney, Amy Larson Rhodes, Angela Vasquez, Chris Green, Mathieu Duvall, Ari Kogut, Lewis Kaufman, Dana Kovaric

Geosciences: Faculty Publications

Talc occurs as massive, economic deposits in upper amphibolite facies marbles of Archean age in southwestern Montana. Previous workers have demonstrated that the talc is a replacement of the marble that resulted from interaction with a large volume of fluid. δ18O (SMOW) values for dolomite and calcite range from 20-25‰ for the unaltered Archean marbles to as little as 8-10‰ in the talc deposits, suggesting that the metasomatic fluids had low δ18O values. In contrast, δ13C values for calcite and dolomite are similar for all samples (-2 to +2‰ PDB). Therefore, it is likely that the metasomatic fluids were oxygen-rich …

Status Of Coral Reefs In The Northern Areas Of The Wider Caribbean, Judy Lang, Pedro Alcolado, Juan Pablo Carricart-Ganivet, Mark Chiappone, H. Allen Curran, Phil Dustan, Gudrun Gaudian, Francisco Geraldes, Steve Gittings, Robbie Smith, Wes Tunnell, Jean Wiener

Geosciences: Faculty Publications

Published on behalf of the (GCRMN) Global Coral Reef Monitoring Network by the Australian Institute of Marine Science

How Much Ecological Information Is Preserved In Fossil Coral Reefs And How Reliable Is It?, B. J. Greenstein, H. Allen Curran

Geosciences: Faculty Publications

The coral reef fossil record is the exclusive database from which analyses of the response of coral communities to environmental change over geological time scales may be gauged. However, few studies have attempted to ascertain whether the reef fossil record is a reasonably accurate representation of a once living coral community. To address this issue, we have performed a systematic comparison of the taxonomic composition and diversity present in exposure of Pleistocene patch reef and reef tract facies found in the Bahamas to that observed for life and death assemblages currently present in analogous modern reefs of the Florida Keys. …

Fernandez Bay, San Salvador, Bahamas: A Natural Laboratory For Assessment Of The Preservation Of Coral Reef Community Structure, Benjamin J. Greenstein, Lora A. Harris, H. Allen Curran

Geosciences: Faculty Publications

Reprinted from: James L. Carew (ed.), Proceedings of the 8th Symposium on the Geology of the Bahamas: San Salvador, Bahamian Field Station

Ichnology Of An Intertidal Carbonate Sand Flat: Pigeon Creek, San Salvador Island, Bahamas, H. Allen Curran, Austin B. Williams

Geosciences: Faculty Publications

Reprinted from: James L. Carew (ed.), May 30–June 3, 1996, Proceedings of the 8th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Bahamian Field Station.

Bahamian Sangamonian Coral Reefs And Sea-Level Change, Brian White, H. Allen Curran, Mark A. Wilson

Geosciences: Faculty Publications

Reprinted from James L. Carew (ed.) May 30–June 3, 1996, Proceedings of the 8th Symposium on the Geology of the Bahamas and Other Carbonate Regions: Bahamian Field Station, San Salvador, Bahamas.

A Memorial And Dedication: Susan Jenks Gaffey (1946–1995), H. Allen Curran, Michael J. Gaffey

Geosciences: Faculty Publications

Reprinted from: James L. Carew (ed.), Proceedings of the 8th Symposium on the Geology of the Bahamas and Other Carbonate Regions: San Salvador, Bahamian Field Station

Guide To Bahamian Ichnology: Pleistocene, Holocene, And Modern Environments: A Field Trip Guide, H. Allen Curran, Brian White, Mark A. Wilson

Geosciences: Faculty Publications

This guide was prepared for the Fourth International Ichnofabric Workshop (IIW- 4) to be hosted by the Bahamian Field Station and held on San Salvador Island on March 15-22, 1997. About 35 scientists representing 15 countries are registered to attend the workshop.

The focus of discussion in the infonnal scientific sessions will be the uses of ichnofabric analysis in sedimentary geology. An ichnofabric is the texture or internal structure created within a sedimentary substrate from the bioturbating activity of organisms. Ichnofabric analysis is a new and emerging area of ichnology (the study of trace fossils), and its methods are proving …