We have carried out 2-D numerical simulations using the discrete element method (DEM) to investigate density-driven deformation in Martian volcanic edifices and how it affects the development of caldera complexes. These simulations demonstrate that the presence of a dense and weak cumulate body within a volcanic edifice strongly influences the volcano morphology and enhances volcanic spreading. The settling of a cumulate body generates distinctive structural and morphological features characteristic of Olympus Mons and Arsia Mons, including low flank slopes and pronounced summit calderas. We show that gravitational spreading of a cumulate body can play a primary role in the long-term development of calderas. We conclude that a cumulate body that is both shallow and wide could generate a single large depression similar to the Arsia-type caldera, while our simulations of a narrow cumulate body are capable of generating summit subsidence that is similar in dimension to the Olympus Mons caldera.

The evolution and source of the Texas Mud Blanket (300 km3) was determined from 26 new radiocarbon dates and from ∼3000 km of 2D seismic data. Sediment flux (km3/ka) was calculated from this combined dataset. XRD reveals its origins are mostly from the Colorado and Brazos Rivers. Between LGM and 17 ka, sediments filled the deepest accommodation behind a productive reef trend. 17-9 ka was a time of rapid eustatic rise (∼7 mm/year) and low sedimentation (flux=0.4 km3/ka). At ∼9 ka, sediment flux to the mud blanket increased to 41 km3/ka because of ravinement of Brazos and Colorado deltas. By ∼5.5 ka, Texas was experiencing a climatic optimum, which reduced sediment supply from local rivers. During the last 3.5 ka the mud blanket received 172 km3 of fine-grained Colorado and Brazos sediments. The most pronounced trend is the anti-correlation of mud blanket growth and rates of eustatic rise.

The trace element content of calcareous foraminifera provides a powerful tool to the study of glacial-interglacial changes in the physical and chemical properties of the ocean. Foraminifera incorporate barium in direct proportion to its concentration in seawater. Using barium as a nutrient proxy, Ba/Ca in benthic <i>Planulina wuellerstorfi</i> is used to reconstruct changes in thermocline ventilation and mid-depth circulation in the North Atlantic during the last glacial and deglacial time. Rivers are concentrated in barium compared to surface seawater. Therefore, barium in planktonic <i>Neogloboquadrina pachyderma</i> is used to identify deglacial meltwater in the Arctic Ocean. Foraminiferal Li/Ca was analyzed to elucidate factors influencing incorporation behavior, including interspecies differences, temperature, pressure, dissolution, and shell mass. To investigate the use of lithium isotopes as a proxy for paleo-seawater chemistry, <font face="symbol">d</font>^{<small>6</small>}Li was determined in planktonic <i>Orbulina universa</i>. During the last glacial maximum, nutrients in the thermocline and the intermediate water of the North Atlantic was lower than today due to increased ventilation and the presence of nutrient-depleted Glacial North Atlantic Intermediate Water (GNAIW). During deglacial time, GNAIW was replaced by southern component water, resulting in an enrichment of nutrients in the mid-depth Atlantic water. Increased Ba/Ca in the surface Arctic Ocean indicates an increase in meltwater discharge between 12.4 and 11.3 ^{<small>14</small>}C ka BP. This may have triggered an increase in the export of freshwater to the North Atlantic, contributing to a shutdown in GNAIW production, and leading to the onset of the Younger Dryas. A second meltwater event at 9.4 ^{<small>14</small>}C ka BP may be the result of glacial Lake Agassiz draining through the Clearwater spillway to the Mackenzie River. Foraminiferal Li/Ca shows systematic glacial-interglacial variation coincident with <font face="symbol">d</font>^{<small>18</small>}O. The incorporation behavior of lithium in foraminifera does not appear to be dominated by changes in temperature, pressure, dissolution, or shell mass, but is potentially controlled by changes in growth conditions, including calcification rate. Preliminary work indicates that <font face="symbol">d</font>^{<small>6</small>}Li remained constant throughout the Holocene and the last glacial maximum at 30.5 ± 1.1. Further developmental studies are necessary to fully engage lithium isotopes as a tracer of seawater composition.

Pennsylvanian (Desmoinesian) sedimentary rocks within the Paradox Basin Four Corners area of the western United States afford a unique opportunity to study the development of sedimentary successions in a complex marine to nonmarine depositional setting. The close association of thick intervals of nonmarine fan-delta facies adjacent to and in time equivalent position to marine carbonate-evaporite facies suggests complex relationships between the factors affecting deposition. Development of an effective scheme to differentiate the depositional signatures from within these sedimentary successions is the primary goal of this study. To achieve this goal, two objectives were pursued. The first was to calibrate the diverse range of rock-types in the Hermosa Group to in-situ wellbore measurements. To facilitate this process, a neural network evaluation procedure coupled with standard petrophysical evaluation techniques were employed to aid in facies succession prediction and lateral facies correlation. This process proved to be as accurate as standard wireline analysis procedures and was able to account for variations not as detectable in conventional scheme. The second objective was to correlate the stratigraphy of the Hermosa Group from outcrops of the Animas Valley to the subsurface along the southern Paradox Basin. The key to understanding the depositional sequences within the Middle Pennsylvanian section is to determine spatial and temporal relationships between the evaporites and black-shale deposits associated with carbonate algal mound buildups and juxtaposed terrigenous clastic fan-delta depositional facies. Once the relationships of these facies successions are delineated, then a three dimensional architectural framework can be manipulated to examine all possible lateral facies successions. By utilizing these analyses, several members of the Paradox Formation were shown to be laterally equivalent and physically continuous with parts of the previously designated undifferentiated Honaker Trail Formation of the San Juan Dome region. The study required a rigorous integration process utilizing a digital workstation environment combining large and more diverse datasets than previously utilized for improved correlation control. Techniques for evaluation of facies successions involved core (42), subsurface wells (4000+), and measured sections (12+) were employed.

The Arkoma Basin is one of several foreland basins formed in association with the Ouachita orogeny. The Arkoma Basin has been studied in depth with regard to stratigraphy, depositional environments, structure and its relationship to the Appalachian-Ouachita orogenic event. This study focuses on the variability of the deltaic deposits within the Arkoma Basin and the significance of the variables to both the delta complex and the overall tectonic setting. The specific characteristics to be investigated include variations in paleocurrent directions, bed thicknesses, bed geometries, organic contents, sand/shale ratios, mineral assemblages and fossil assemblages. In the case of the Arkoma deltaic deposits, bed thickness is a function of the duration and rate of the depositional event, assuming no scour has occurred. Bed geometry is controlled by the location of the deposit within the delta complex. The organic content, and thus trace fossil abundance, is controlled by the course of the river, as well as wave and tidal influences on the delta. The mineral assemblages are determined by the composition of the parent rock as well as the effects of weathering as the sediments are transported. Paleoflow in a deltaic system is controlled by the course of the river as well as specific branching of distributary channels. Traditional QFL data have been unable to resolve the conflict over source area. Two source areas have been proposed for this system: 1) a northern cratonic source and 2) an eastern Appalachian source. Detrital tourmaline chemistry provides an alternative method for determining provenance in this system. Tourmaline analysis suggests an eastern Appalachian source is more probable.

The Mississippi River has undergone at least seven cyclic avulsions during the Holocene epoch. The latest avulsion, down the Atchafalaya River into the Gulf of Mexico, has produced two bayhead deltas prograding into Atchafalaya Bay. The Wax Lake Delta, typical of other Mississippi sub-deltas, has a natural anastomosing channel pattern. In contrast, the Atchafalaya Delta, situated in the eastern side of the Bay, has experienced sporadic and limited growth due to the dredging of a navigation channel below natural depth. Channel bifurcation, and sediment transport processes and responses, were investigated in the Wax Lake Delta, using channel flow velocities, suspended sediment concentrations, cross-channel bottom profiles, and short push-core stratigraphy during flood and non-flood conditions. Center channel flow velocities averaged 2 to 2 1/2 times higher during flood conditions than during non-flood conditions. Velocities maintained near constant values from proximal to distal, then decreased near distributary channel mouths. Cross-channel flow velocities reached a maximum above the thalweg. During non-flood conditions, flow velocities, inversely proportional to tidal fluctuations, were greatly reduced during strong southerly winds; however, tidal and wind influences were negated by flood condition flow velocities. Homogeneous suspended sediment concentrations of coarse silt to very fine sand (mean grain size) were found throughout the system, indicating well-mixed, turbulent flow. Suspended sediment concentrations were up to 20 times higher during flood than during non-flood conditions. Most calculated boundary shear stresses were greater than critical boundary shear stresses, indicating little deposition was occurring in distributary channels during sample collection. Bedload sediment size remained near constant throughout the system in all samples from proximal to distal end, indicate sediment moves efficiently through the deltaic system with very little grain size fractionation in suspended or bedload sediments. Downstream sediment fluxes vary directly with velocity. Thus, the thalweg transports the highest volume of sediment per unit time even though the sediment concentrations per unit volume are homogeneous. Sediment deposition per unit time is greatest at the distributary mouth channel thalweg, where velocities slow, creating a distributary mouth bar and subsequent channel bifurcation. This process has been termed sediment flux controlled deposition.

Forelimb and hindlimb articulation, reconstructed musculature, and function were examined in Apatosaurus, Diplodocus, and Camarasaurus. A technique was developed using a Microscribe three-dimensional digitizer to capture external morphological data for skeletal reconstruction and determination of taxonomically useful features. The appendicular musculature of Alligator mississippiensis was dissected to determine form, function, origin, and insertion of muscles to aid in reconstruction of sauropod musculature. Contrary to the literature, M. caudofemoralis longus was found to originate primarily from the lateral surfaces of the proximal chevrons instead of the bodies and transverse processes of the caudals, demonstrating that chevron morphology is indicative of the size, shape, and extent of M. caudofemoralis longus in fossil archosaurs. Apatosurus and Diplodocus were found to have narrower chests than Camarasaurus with forelimbs situated directly under their bodies. Forelimb posture differences between taxa were indicated by the position of the humeral head, morphology of the distal humeral condyles, and the orientation of the posterior process of the ulna. The scapulae in all three taxa were oriented subhorizontally. Hindlimb articulation was found to be related to the shape of the femur and pelvis width. The medial condyles of the femur were longer than the lateral condyles in diplodocids, producing a narrow stance, while the femoral condyles of Camarasaurus were coequal in length, producing a relatively wide stance. This stance would have resulted in wider Camarasaurus trackways than those of diplodocids. Limb motion was restricted to a single plane. Rotation of the brachial and antebrachial joint was constrained by osteology with the brachial joint limited to between 33º and 40º of rotation, and the antebrachial joint limited to no more than 55º of rotation. Femoral joint rotation was limited to between 30º and 37º based on changes in the length of M. caudofemoralis longus, and rotation of the femerotibial joint was restricted by osteology to between 47º and 55º. M. caudofemoralis longus was relatively larger in Diplodocus than in either Camarasaurus or Apatosaurus based on chevron morphology. These results indicate that tripodal rearing, as sometimes proposed for diplodocids, was not common, based on stance and M. caudofemoralis longus contraction length.

Pennsylvanian age Jackfork Group cores from the DeGray Lake Dam and outcrop from the east wall of the DeGray Lake Spillway, Arkansas, provide an opportunity for a detailed study on the transport and depositional characteristics of a fine-grained, deep-water depositional system. Two phases of resedimentation processes are responsible for deposition of the sediments in the cores and the outcrop. Primary resedimentation processes transport terrigenous sediments from the shelf or basin edge into the middle fan environment, while secondary resedimentation alter the sediments after they are initially deposited in the environment. Debris flows, slurry flows, and high and low density turbidity currents are all of the primary flows that can be identified in the cores and outcrop. It is likely that most of these flows (termed sediment gravity flows) were derived from slides and slumps that originated up-slope. Slides, slumps, creep, and debris flows have occurred on localized slopes on the sea floor, creating a secondary phase of deposition. Each of these events is recorded in rather small-scale intervals in the cores and outcrops, but their accumulated influence is significant. Core and outcrop can be placed into separate depositional packages based on changes in lithofacies characteristics. These packages are compared from core to outcrop, and those that are most similar are correlated. The cores and outcrop show bedding trends and other sedimentary characteristics that indicate they were deposited within the framework of a middle submarine fan. The middle fan is characteristic of thick-bedded channel axis sands, thick- to thin-bedded channel margin sands, thin-bedded levee/overbank sands and muds, and very thin-bedded distal overbank silty muds. In some cases, more than one subenvironment is suggested as an appropriate interpretation for a depositional package. This is due to the fact that the divisions between these subenvironments are gradual and many deposits may fall into a transitional realm. Core and closely spaced outcrops studied together offer several benefits over studying each separately. The cores provide new data from the subsurface that is applied to a well known outcrop. Fresh core faces show more fine-scale details that are hard to see in the spillway, which has many heavily weathered and covered sections. The spillway east outcrop, although tilted, provides more spatial variation, which can be correlated back to the cores. Bedding trends and contacts are better exposed in outcrop due to artificial breaks in the cores caused by drilling and recovery.

The Carboniferous Lower Atoka outcrops in the Arkoma Basin of Central Arkansas contain turbidite deposits in a channelized and unchannelized submarine fan setting. The objectives of the study were to determine depositional characteristics and reservoir performance of these fine-grained submarine fan deposits. Four outcrops (Highway 5, Perryville, Chula, and Danville) were studied and described in detail emphasizing sedimentary facies, vertical succession of beds, sedimentary structures, and other small-scaled features that cannot be resolved in subsurface deposits. Five distinct sedimentary facies were recognized: Facies A - massive sandstones, Facies B - thin-bedded sandstones with a mudstone drape, Facies C - interbedded thin sandstones and mudstones, Facies D - chaotic deposits, and Facies E - mudstone. Facies and sedimentary characteristics of the outcrops provide clues as to which deepwater sub-environment the facies were deposited. On the basis of field criteria, the outcrops were characterized as channelized, channel or channel margin deposits, or unchannelized, sheet sand deposits. Channel deposits are massive fine-grained sandstones (facies A), with occasional scouring at the base and rip-up clasts throughout. Channel margin deposits consist predominately of interbedded thin sandstones and mudstones (facies C) with many of the sandstone beds containing small-scaled ripples and laminations. Sheet sand deposits are from lower-energy flows with the presence of more sedimentary structures, less scouring and a higher net-to-gross than the channelized deposits. Highway 5 and Perryville outcrops were deposited in a middle fan environment as channel and channel margin deposits. Danville and Chula outcrops were deposited in a lower fan setting as sheet sands. There are several potential source terranes for these deposits determined from point counting and detailed analysis of tourmaline crystals, which suggest that the main source consisted of sedimentary and metasedimetary rocks from the Appalachians with possible sediment transport from the craton interior: the Illinois Basin.

While the composition and origin of brines in deep sedimentary basins has been extensively discussed, the composition and origin of low salinity waters is not as well documented. Since the 1960s, the presence of deep, low-salinity waters has been observed in some sedimentary basins and is commonly present in overpressured sections. The episodic release of low salinity, overpressured fluids upward into sediments containing high salinity formation waters likely occurs at <100-year intervals. Because there is a growing body of evidence that suggests mixing formation waters of varying salinity could induce the dissolution and precipitation of minerals, it is important to have detailed information about chemical compositions of both end-member fluids to adequately predict such mixing results. This study concludes that low salinity waters (<35 g/l) are generally not unique in major solute composition when compared to high salinity waters (>35 g/l). On log-log plots, monovalent cations plot along 1:1 slopes with respect to salinity and total anionic charge, while divalent cations plot along 2:1 slopes. However, this study concludes that more compositional variability exists at salinities less than seawater and lower anionic charge values. Also, major cations and Cl correlates better with anionic charge than with salinity. While Cl plots on a 1:1 slope as a function of salinity in all waters in southwest Louisiana, other basins in this study begin to show variability at salinities <10,000 mg/l. Spatial analyses from this study suggest the origin of low salinity fluids in southwest Louisiana present at depths greater than 2500 m, are not likely meteoric in origin. Southwest Louisiana water compositions are most likely controlled by rock-buffering with ambient mineral phases. A calculation performed as part of this study showed that the smectite to illite transition could reduce salinity up to 43% in shales. Considering this and the documented presence of illite along the Gulf Coast as well as the stability of illite in the waters presented in this study, it is reasonable to conclude deep, low-salinity waters in southwest Louisiana originate in substantial part from the smectite to illite transition.