The tectonic relationships of the Hillabee Chlorite Schist and the adjacent rock units in southern Cleburne County, Alabama

Southern Cleburne county Alabama contains two defined litho-tectonic blocks separated by a large displacement thrust fault. The Talladega block is composed of low grade metamorphic rocks. Sericite Phyllites and Quartzites are the main composition units. Metamorphic and tectonic events have created four defined structural events that are mapped in the block. The Hillabee Chlorite Schist, a low grade metamorphic unit lies conformable and the youngest unit in the Talladega block. Geochemical analysis indicates the origin to be in an island arc environment. The Coosa Block is thrust over the Talladega clock. The Hollins line fault is the contact between the Talladega and Coosa Blocks. The Coosa Block is composed of high grade Amphibolites facies rocks. Mica Schist with garnet and kyanite are interbedded with Amphibolites composing this block. Deformation along the Hollins line Fault creates a sercite phyllite in the high grade metamorphic Coosa Block unit. These phyllites include garnet that defines the contact between the two blocks and the placement of the Hollins line fault. (Published By University of Alabama Libraries

Finite element models for the deformation of the Askja volcanic complex and rift segment, Iceland

The Askja volcanic complex and rift segment of Iceland's Northern Volcanic Zone has been continuously subsiding at an usually high rate for more than two decades. InSAR data compiled over the last decade reveal two patterns of deformation: (1) a radially symmetric pattern of subsidence local to Askja's caldera and (2) an elongated pattern of subsidence tracking the rift segment. Microgravity data suggest a mass loss from a shallow reservoir and seismicity data reveal a relatively shallow brittle-ductile transition. A simple model combining two vertically-aligned and contracting Mogi sources, one shallow (~3 km) and one deep (~20 km), in an elastic half space generally predicts the observed InSAR deformation. Subsidence along the Askja fissure swarm has also been attributed to effects of plate spreading across rheologically weak fissure swarms. The shallow contracting Mogi source and microgravity data are consistent with magma migration out of the shallow reservoir. Interpretations of the deep contracting source are more uncertain. We present an alternative model that combines magma extraction from a shallow, fluid-filled cavity with a plate spreading model having rheologic partitioning expected for the rift segment. This 3D finite element model (FEM) simulates an elastic upper crust and viscoelastic lower crust. Inspired by a model configuration presented by Pedersen et al. (2009), the simulated brittle-ductile transition shallows beneath the rift, in accord with seismicity data. The FEM is driven by plate spreading at a constant rate and specified mass flux from the shallow cavity. The magnitude of flux is a calibration parameter estimated from InSAR data via inverse methods. Preliminary results suggest this alternative model generally predicts the both deformation patterns. However, the simulated shallow brittle ductile transition, combined with kinematic loading of plate spreading, accounts for much of the regional deformation originally attributed to magma migration out of a deep reservoir. This suggests that the estimated characteristics of magma extraction from the deep reservoir should be re-examined. The FEM accounts for multiple types of observations (both local and regional subsidence patterns, microgravity data, seismicity data, and plate spreading) associated with active deformation of the Askja volcano complex and rift segment. (Published By University of Alabama Libraries

Estimating nonlinear source parameters of volcano deformation: an application of FEM-based inverse methods and InSAR

Migration of magma within an active volcano produces a deformation signature at the Earth's surface. The internal structure of a volcano and specific movements of the magma control the actual deformation that is observed. Relatively simple models that simulate magma injection as a pressurized body embedded in a homogeneous elastic half-space (e.g., Mogi) can predict the characteristic radially-symmetric deformation patterns that are commonly observed for episodes of volcano inflation or deflation. Inverse methods, based on half-space models, can precisely and efficiently estimate the non-linear parameters that describe the geometry (position and shape) of the deformation source, as well as the linear parameter that describes the strength (pressure) of the deformation source. However, although such models can accurately predict the observed deformation, actual volcanoes have internal structures that are not compatible with the elastic half-space assumptions inherent to Mogi-type models. This incompatibility translates to errors in source parameter estimations. Alternatively, Finite Element Models (FEMs) can simulate a pressurized body embedded in a problem domain having an arbitrary distribution of material properties that better corresponds to the internal structure of an active volcano. FEMs can be used in inverse methods for estimating linear deformation source parameters, such as the source pressure. However, perturbations of the non-linear parameters that describe the geometry of the source require automated re-meshing of the problem domain - a significant obstacle to implementing FEM-based nonlinear inverse methods in volcano deformation studies. I present a parametric executable (C++ source code), which automatically generates FEMs that simulate a pressurized ellipsoid embedded in an axisymmetric problem domain, having an a priori distribution of material properties. I demonstrate this executable by analyzing Interferometric Synthetic Aperture Radar (InSAR) deformation data of the 1997 eruption of Okmok Volcano, Alaska as an example. This executable facilitates an inverse analysis that estimates the non-linear parameters that describe the depth and radius of the spherical source, as well as the linear strength parameter that best accounts for the InSAR data. The strong radial symmetry and high signal-to-noise ratio of the InSAR data, along with known seismic tomography data, provide robust constraints for estimated parameters and sensitivity analyses. (Published By University of Alabama Libraries

A high-resolution hydroclimate record of the last three millennia from a cored stalagmite at Desoto Caverns (Alabama, USA)

Late Holocene climate changes in the Southeast USA are poorly documented due to the paucity of high-resolution paleo-records. This study provides high-resolution records of rapid hydroclimate changes in the Southeast over the last three millennia. The records are based on stable isotope rainfall proxies whose time series are constrained by precise U/Th dates from a stalagmite sampled at DeSoto Caverns. The average growth rate of the stalagmite was 149 µm/yr prior to 1400 years and it has been growing with an average growth rate of 42 µm/yr in the last 1400 years. During the past three thousand years stable isotope time series document six wet episodes (at ~ 2950, 2450, 1675, 1200, 700 and 70 years ago) alternating with six drier periods (at ~ 3100, 2800, 1900, 1500, 800 and 300 years ago). The biannually resolved 18O record agrees well with the contemporaneous SST record from the Sargasso Sea cores suggesting that changes in moisture availability in the Southeast are likely linked to subtropical North Atlantic SST variability. Power spectra analysis of the stalagmite-based oxygen isotope record reveals statistically significant periodicities at 24±1 and 36±1 year that are consistent with those observed in the contemporaneous atmospheric 14C production record. The 24 years periodicity is also consistent with the 24-year NAO Index periodicity. On the basis of our analysis we propose that the hydroclimate in the Southeast USA over the last three millennia was intimately linked to NAO variability powered by solar activity fluctuations. (Published By University of Alabama Libraries

Biostratigraphy, paleogeography, and paleoenvironments of the Upper Cretaceous (Campanian) northern Mississippi Embayment

Most paleogeographic and paleoenvironmental reconstructions of the northern Mississippi Embayment during the Late Campanian (Late Cretaceous) illustrate a generalized gulf between central Mississippi and Arkansas stretching northward into southern Illinois. The most detailed reconstruction shows a large river flowing from the Appalachians to the northeastern edge of the gulf with a river delta covering most of the northern embayment and stretching from southern Illinois to west-central Alabama. Lack of age constraints, incorrect stratigraphic correlations, paucity of detailed geologic maps and subsurface data, and misunderstanding of the basin geometry have led to inaccurate or vague paleogeographic interpretations of the Upper Cretaceous northern Mississippi Embayment. This project correlates the marine and nonmarine biostratigraphy, identifies the upper Campanian lithofacies, interprets the paleoenvironment of each lithofacies, and maps these interpretations to create a paleogeographic model of the northern Mississippi Embayment during the Late Campanian. Biostratigraphic indicators used in this project include foraminifera, calcareous nannoplankton, palynomorphs, ammonites, and other mollusks. Uppermost Campanian units correlated in this project include the uppermost Demopolis Chalk and lowermost Ripley Formation in Alabama and Mississippi; a basal volcaniclastic deposit of the subsurface Demopolis Chalk in Mississippi; the Coon Creek Formation lower facies in Tennessee; the Coffee Sand in northern Tennessee, Kentucky, Illinois, and Missouri; the smectite clays (proposed name of Glenallen Clay) in Missouri; the lower Nacatoch Sand and upper Saratoga Chalk in Arkansas; and the Saratoga and Demopolis Chalks undifferentiated calcareous clay in the central embayment subsurface. Paleoenvironments identified in the study area include molluscan-rich clastic shelf; barrier bar complex; carbonate shelf; estuaries and tidal flats; depression marshes and lakes; and volcanoes with clastic and carbonate rims. (Published By University of Alabama Libraries

Upper Jurassic (Oxfordian) Smackover facies characterization at Little Cedar Creek Field, Conecuh County, Alabama

The Upper Jurassic (Oxfordian) Smackover Formation is a shallow-marine carbonate unit in the subsurface of the U.S. Gulf Coast, spanning from south Texas to west Florida. This field case-study focuses on Little Cedar Creek Field located in southeastern Conecuh County, Alabama. The objectives of this study are to 1) construct a 3-D depositional model for the Smackover Formation at Little Cedar Creek Field; 2) establish a sequence stratigraphic framework for the construction of the depositional model; 3) characterize and map lithofacies with high resource potential based on the depositional model; and 4) demonstrate the use of the depositional model to maximize hydrocarbon recovery in the field area Little Cedar Creek Field is located near the up-dip limit of the Smackover Formation. The top of the Smackover is found at depths between 10,000 to 12,000 feet, and the formation ranges in thickness from 60 to 120 feet. The Smackover Formation overlies the Callovian-Oxfordian Norphlet Formation and underlies the Kimmeridgian Haynesville Formation. The petroleum reservoirs in Little Cedar Creek Field, unlike most Smackover fields in the eastern Gulf region, are composed predominantly of limestone, not dolomite, and do not possess a Buckner Anhydrite top seal immediately above the reservoir. Beginning from the top of the Smackover, the facies are: (S-1) Peritidal lime mudstone-wackestone; (S-2) tidal channel conglomeratic floatstone-rudstone; (S-3) peloid-ooid shoal grainstone-packstone; (S-4) subtidal lime wackestone-mudstone; (S-5) microbially-influenced packstone-wackestone; (S-6) microbial (thrombolite) boundstone; and (S-7) transgressive lime mudstone-dolostone. Production is from both the thrombolite boundstone and shoal grainstone facies, though pressure and fluid data indicate no communication between the two reservoirs. The data indicate that the microbial communities developed on subtle topographic highs overlying the transgressive lime mudstone-dolostone in a shallow-water, low-energy, hypersaline environment, parallel to the southwest-northeast trending paleoshoreline. The Conecuh Embayment, formed by the Conecuh and Pensacola Ridges to the northwest and southeast, respectively, created low-energy, tranquil conditions that promoted the development of these opportunistic microbial organisms. (Published By University of Alabama Libraries

Pressure-temperature-time paths, prograde garnet growth, and protolith of tectonites from a polydeformational, polymetamorphic terrane: Salmon River Suture Zone, West-Central Idaho

The metamorphic rocks of the Salmon River suture zone (SRSZ) in west-central Idaho provide a unique glimpse into mid-lower crustal processes during continental growth by island arc accretion. The SRSZ, which separates island arc terranes of the Blue Mountains Province (BMP) from the Mesozoic margin of North America, contains medium to high grade tectonites that record multiple metamorphic and deformation events. The SRSZ is divided by the Pollock Mountain thrust fault (PMtf) into two structural blocks: the higher-grade Pollock Mountain plate (PMp), and the lower-grade, underlying Rapid River plate (RRp). Previous studies interpreted pre-144 Ma metamorphism within the SRSZ related to assembly of the BMP. Counter-clockwise P-T paths for metamorphism within the RRp [peak=8-9 kbar ~600°C, retrograde=5-7 kbar, 450- 525°C] were inferred to include prograde garnet growth during pre-144 Ma loading followed by garnet growth during rapid cooling due to lithospheric delamination. The PMp was interpreted to have subsequently been buried to increasing depth and metamorphosed again at 128 Ma as a result of the BMP docking with North America. New P-T-t paths for the RRp and PMp constructed from geochronology, geothermobarometry, pseudosections, and petrography suggest that after loading, slow cooling rates caused diffusion in garnet rims, which produced counter-clockwise P-T paths. Garnet Sm-Nd ages of 112.5±1.5 Ma from the RRp, and 141-124 Ma from the PMp suggest that metamorphism within the SRSZ is diachronous and that crustal thickening was protracted occurring between 141-112 Ma. P-T-t paths between both plates indicate that the PMp reached peak metamorphism prior to peak metamorphism of the RRp. This suggests that the PMp was buried prior to the development of the PMtf. The RRp was subsequently buried along the PMtf, which was followed by development of the Rapid River thrust fault, which juxtaposed RRp schists onto the Wallowa terrane of the BMP. This model suggests that metamorphism in the SRSZ was controlled by individual thrust faults instead of recording collisions between terranes and is consistent with a prolonged burial of rocks in the SRSZ followed by slow cooling that does not require lithospheric delamination to account for retrograde P-T estimates. (Published By University of Alabama Libraries

Coseismic and postseismic deformation of the great 2004 Sumatra-Andaman Earthquake

The 26 December 2004 M9.2 Sumatra-Andaman earthquake (SAE) induced a devastating tsunami when it ruptured over 1300 km of the boundary between the Indo-Australian plate and Burma microplate (Vigny et al., 2005; Bilek, 2007). Three months later on 28 March 2005, the M8.7 Nias earthquake (NE) ruptured over 400 km along the same trench overlapping and progressing to the south of the M9.2 rupture (Banerjee et al., 2007). The spatial and temporal proximity of these two earthquakes suggests that the SAE mechanically influenced the timing of the NE. I analyze the coseismic and postseismic deformation, stress, and pore pressure of the 2004 SAE using 3D finite element models (FEMs) in order to determine the mechanical coupling of the SAE and NE. The motivation for using FEMs is two-fold. First, FEMs allow me to honor the geologic structure of the Sumatra-Andaman subduction zone, and second, FEMs simulate the mechanical behavior of quasi-static coseismic and postseismic deformation systems (e.g., elastic, poroelastic, and viscoelastic materials). The results of my study include: 1) Coseismic slip distributions are incredibly sensitive to the distribution of material properties (Masterlark and Hughes, 2008), 2) Slip models derived from tsunami wave heights do not match slip models derived from GPS data (Hughes and Masterlark, 2008), 3) These FEMs predict postseismic poroelastic deformation and viscoelastic deformation simultaneously (Masterlark and Hughes, 2008), 4) Pore pressure changes induced by the SAE triggered the NE via fluid flow in the subducting oceanic crust and caused the NE to occur 7 years ahead of interseismic strain accumulation predictions (Hughes et al., 2010; Hughes et al., 2011), 5) Global Conductance Matrices provide a way to smooth an underdetermined FEM for arbitrarily irregular surfaces, and 6) FEMs are capable and desired to model subduction zone deformation built around the complexity of a subducting slab which is usually ignored in geodetic studies (Masterlark and Hughes, 2008; Hughes et al., 2010). Rapidly advancing computational capabilities recently placed FEMs at the forefront of earthquake deformation analyses. The results and conclusions of this study will strongly influence future analyses of coseismic and postseismic deformation, stress, pore pressure, and tsunami genesis. (Published By University of Alabama Libraries

Stromatoporoids and the Upper Devonian Alamo Impact Breccia of southeastern Nevada

Eleven species in 10 genera of stromatoporoids were identified from within and below the Alamo Breccia of southeastern Nevada, in an effort to determine the excavation depth of a bolide impact that occurred during the Late Devonian, approximately 382 Ma. The specimens identified in this study are taxa that are also known from Iowa, Canada, and other parts of the world. Actinostroma cf. A. clathratum, Clathrocoilona cf. C. involuta, Stictostroma maclareni, Trupetostroma bassleri, and Arctostroma contextum were identified from stromatoporoid-bearing beds located in the Guilmette Formation below the Alamo Breccia. Atelodictyon sp. 1, Hammatstroma albertense, and Hermatoporella sp. 1 were identified from both below and within the Alamo Breccia. The remaining species: Actinostroma sp. 1, Atopostroma distans, and Habrostroma turbinatum were identified from within the Alamo Breccia. Based on the results of this study, a definite depth of penetration cannot be obtained. However, using stromatoporoid biostratigraphy, it is most likely that the bolide impacted no deeper than rocks of Emsian age. (Published By University of Alabama Libraries

Upper crustal shortening and forward modeling of the Himalayan fold-thrust belt along the Budhi-Gandaki river, central Nepal

Geologic mapping along the Budhi-Gandaki River in central Nepal reveals 6 significant structures: 1) South Tibetan Detachment system; 2) Main Central thrust; 3) Ramgarh thrust; 4) Lesser Himalayan duplex including the Trishuli thrust; 5) Main Boundary thrust; and 6) Main Frontal thrust system. A balanced cross-section between the South Tibetan Detachment system and Main Frontal thrust reveals that the region has a minimum total shortening of 76% or 420 km. The breakdown of the accommodation of shortening on each thrust is as follows: Main Central thrust - 115 km; Ramgarh thrust - 120 km; Lesser Himalayan duplex including the Trishuli thrust - 156 km; Main Boundary thrust - 10 km; Main Frontal thrust system - 19 km. In order to validate the balanced cross-section, a reconstruction program was used to forward model the system. By moving faults with appropriate amounts of displacement over a reasonable configuration of undeformed stratigraphy from the hinterland to foreland, the deformation of the Himalayan thrust belt along the Budhi-Gandaki River cross-section is reproduced. The forward modeling program moves hanging wall rock over stationary footwall rock using each individual fault identified in the balanced crosssection. Hanging wall rock deforms as it is thrust over footwall structures. Using forward modeling, the cross-section has a shortening estimate of 412 km or 75%. The two shortening estimates are virtually identical indicating the balanced cross-section along the Budi-Gandaki River is viable and admissible. (Published By University of Alabama Libraries