Area balance and strain in an extensional fault system: Strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama. Annual report, March 1996--March 1997

Gilbertown Field is the oldest oil field in Alabama and produces oil from chalk of the Upper Cretaceous Selma Group and from sandstone of the Eutaw Formation along the southern margin of the Gilbertown fault system. Most of the field has been in primary recovery since establishment, but production has declined to marginally economic levels. This investigation applies advanced geologic concepts designed to aid implementation of improved recovery programs. The Gilbertown fault system is detached at the base of Jurassic salt. The fault system began forming as a half graben and evolved in to a full graben by the Late Cretaceous. Conventional trapping mechanisms are effective in Eutaw sandstone, whereas oil in Selma chalk is trapped in faults and fault-related fractures. Burial modeling establishes that the subsidence history of the Gilbertown area is typical of extensional basins and includes a major component of sediment loading and compaction. Surface mapping and fracture analysis indicate that faults offset strata as young as Miocene and that joints may be related to regional uplift postdating fault movement. Preliminary balanced structural models of the Gilbertown fault system indicate that synsedimentary growth factors need to be incorporated into the basic equations of area balance to model strain and predict fractures in Selma and Eutaw reservoirs

Area balance and strain in an extensional fault system: Strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama. Final report, March 1996--September 1998

This project was designed to analyze the structure of Mesozoic and Tertiary strata in Gilbertown Field and adjacent areas to suggest ways in which oil recovery can be improved. The Eutaw Formation comprises 7 major flow units and is dominated by low-resistivity, low-contrast play that is difficult to characterize quantitatively. Selma chalk produces strictly from fault-related fractures that were mineralized as warm fluid migrated from deep sources. Resistivity, dipmeter, and fracture identification logs corroborate that deformation is concentrated in the hanging-wall drag zones. New area balancing techniques were developed to characterize growth strata and confirm that strain is concentrated in hanging-wall drag zones. Curvature analysis indicates that the faults contain numerous fault bends that influence fracture distribution. Eutaw oil is produced strictly from footwall uplifts, whereas Selma oil is produced from fault-related fractures. Clay smear and mineralization may be significant trapping mechanisms in the Eutaw Formation. The critical seal for Selma reservoirs, by contrast, is where Tertiary clay in the hanging wall is juxtaposed with poorly fractured Selma chalk in the footwall. Gilbertown Field can be revitalized by infill drilling and recompletion of existing wells. Directional drilling may be a viable technique for recovering untapped oil from Selma chalk. Revitalization is now underway, and the first new production wells since 1985 are being drilled in the western part of the field

Proceedings of the Fourth Caldwell Conference, St. Catherines Island, Georgia, March 27-29, 2009.

391 p. : ill. (chiefly col.), maps (chiefly col.) ; 26 cm. "Issued March 23, 2011."This edited volume addresses the geoarchaeology of St. Catherines Island (Georgia). The field of geoarchaeology has typically been defined as either geology pursued within an archaeological framework or (sometimes the reverse) as archaeology framed with the help of geological methodology. Either way, the formalized objectives of geoarchaeology define a broad range of pursuits, from placing archaeological sites into relative and absolute temporal context through the application of stratigraphic principles and absolute dating techniques, to understanding the natural processes of site formation, to reconstructing the landscapes that existed around a site or group of sites at the time of occupation. The editors of this volume have generally followed the lead of G.R. Rapp and C.L. Hill (2006, Geoarchaeology : the earth-science approach to archaeological interpretation) by stressing the importance of multiple viewpoints and methodologies in applying geoscience techniques to evaluate the archaeological record. In the broadest sense, then, Geoarchaeology of St. Catherines Island applies multiple earth science concepts, techniques, or knowledge bases to the known archaeological record and the processes that created that record. This volume consists of 16 papers presenting the newest research on the stratigraphic and geomorphological evolution of the St. Catherines Island landscape. Of particular interest are presentations addressing the relative timing and nature of sedimentation, paleobiology, sea level change, stream capture, hydrology, and erosional patterning evident on St. Catherines Island (and to some degree the rest of the Georgia Bight). These papers were initially presented at the Fourth Caldwell Conference, cosponsored by the American Museum of Natural History and the St. Catherines Island Foundation, held on St. Catherines Island (Georgia), March 27-29, 2009. Table of contents: Why this archaeologist cares about geoarchaeology : some pasts and futures of St. Catherines Island / David Hurst Thomas -- Evolution of late Pleistocene-Holocene climates and environments of St. Catherines Island and the Georgia Bight / Fredrick J. Rich, Anthony Vega, and Frank J. Vento -- Geoarchaeological research at St. Catherines Island : defining the geological foundation / Gale A. Bishop, Brian K. Meyer, R. Kelly Vance, and Fredrick J. Rich -- Development of a late Pleistocene-Holocene genetic stratigraphic framework for St. Catherines Island : archaeological implications / Frank J. Vento and Patty A. Stahlman -- Ichnological diagnosis of ancient storm-washover fans, Yellow Banks Bluff, St. Catherines Island / Anthony J. Martin and Andrew K. Rindsberg -- Quaternary vegetation and depositional history of St. Catherines Island / Fredrick J. Rich and Robert K. Booth -- Recent shoreline erosion and vertical accretion patterns, St. Catherines Island / Donald B. Potter Jr. -- Role of storm events in beach ridge formation, St. Catherines Island / Harold B. Rollins, Kathi Beratan, and James E. Pottinger -- Drainage changes at Ossabaw, St. Catherines, and Sapelo sounds and their influence on island morphology and spit building on St. Catherines Island / Timothy M. Chowns -- Vibracores and vibracore transects : constraining the geological and cultural history of St. Catherines Island / Gale A. Bishop, David Hurst Thomas, Matthew C. Sanger, Brian K. Meyer, R. Kelly Vance, Robert K. Booth, Fredrick J. Rich, Donald B. Potter, and Timothy Keith-Lucas -- Application of ground penetrating radar to investigations of the stratigraphy, structure, and hydrology of St. Catherines Island / R. Kelly Vance, Gale A. Bishop, Fredrick J. Rich, Brian K. Meyer, and Eleanor J. Camann -- Postsettlement dispersal and dynamic repopulation of estuarine habitats by adult Mercenaria mercenaria, St. Catherines Island / Robert S. Prezant, Harold B. Rollins, and Ronald B. Toll -- The foundation for sea turtle geoarchaeology and zooarchaeology : morphology of recent and ancient sea turtle nests, St. Catherines Island, Georgia, and Cretaceous Fox Hills Sandstone, Elbert County, Colorado / Gale A. Bishop, Fredric L. Pirkle, Brian K. Meyer, and William A. Pirkle -- Sea turtle habitat deterioration on St. Catherines Island : defining the modern transgression / Gale A. Bishop and Brian K. Meyer -- Modeling indigenous hunting and harvesting of sea turtles and their eggs on the Georgia Coast / Gale A. Bishop, David Hurst Thomas, and Brian K. Meyer -- Geomorphology, sea level, and marine resources : St. Catherines Island / Harold B. Rollins and David Hurst Thomas -- Appendix 1. Noncultural radiocarbon record from St. Catherines Island : a compendium -- Appendix 2. Vibracore record from St. Catherines Island : a compendium.Conference sponsored by the American Museum of Natural History and the St. Catherines Island Foundation

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

Abstract: Rock outcrops of the sedimentary–stratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sediment–water or sediment–air interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. Some true substrates are notable for their sedimentary, palaeontological and ichnological signatures that provide windows into key intervals of Earth history, but countless others occur routinely throughout the sedimentary–stratigraphic record. They frequently reveal patterns that are strikingly familiar from modern sedimentary environments, such as ripple marks, animal trackways, raindrop impressions or mudcracks: all phenomena that are apparently ephemeral in modern settings, and which form on recognizably human timescales. This paper sets out to explain why these short‐term, transient, small‐scale features are counter‐intuitively abundant within a 3.8 billion year‐long sedimentary–stratigraphic record that is known to be inherently time‐incomplete. True substrates are fundamentally related to a state of stasis in ancient sedimentation systems, and distinguishable from other types of bedding surfaces that formed from a dominance of states of deposition or erosion. Stasis is shown to play a key role in both their formation and preservation, rendering them faithful and valuable archives of palaeoenvironmental and temporal information. Further, the intersection between the time–length scale of their formative processes and outcrop expressions can be used to explain why they are so frequently encountered in outcrop investigations. Explaining true substrates as inevitable and unexceptional by‐products of the accrual of the sedimentary–stratigraphic record should shift perspectives on what can be understood about Earth history from field studies of the sedimentary–stratigraphic record. They should be recognized as providing high‐definition information about the mundane day to day operation of ancient environments, and critically assuage the argument that the incomplete sedimentary–stratigraphic record is unrepresentative of the geological past

Construction of ichnogeneric names

Ichnologists have over used the root ichn- “trace”, employing it in new terms and new ichnogenera alike, to the point where it can be difficult to express one self clearly without using it several times in one sentence. The root derives from Ancient iχνος (ichnos), which means “foot print” or “track”, or by extension a “trace”, any sign of an animal’s activity. Perhaps it is time to explore the use of other roots to create new ichnologic terms and genera. Alternative Latin and Greek roots are given here, as well as ad vice on how to construct new ichnogenera in a technically correct and aesthetically pleasing manner

Ichnotaxonomy as a science

If ichnotaxonomy is to be scientific, then its results must be repeatable. While some ichnotaxa are identified consistently, others are not, suggesting that ichnotaxonomy is not a mature science. When researchers disagree on the identification of a specimen, it suggests that closer examination is needed: an intermediate stage in the scientific method. But when ichnologists publish different names for the same trace fossils, multiple trials of classification have yielded different results, suggesting a failure of the hypotheses that led to the names. The burgeoning of invertebrate ichnology from the 1960s onward was made possible by demonstrating its utility to the petroleum industry; in part, this was accomplished by simplifying the ichnotaxonomy of common trace fossils to the point where a specialist was not required to make use of them in sedimentology and stratigraphy. The biological aspect of trace fossils, albeit of great interest, was downplayed in favour of a severely geometric approach. Ironically, this has had the effect of obscuring basic relationships of trace fossils and their palaeoenvironments that could be of great use to sedimentologists. Previous researchers have emphasized the value of a uniform approach in ichnotaxonomy. To accomplish this, ichnologists should take inspiration from the taxonomy of body fossils. Making ichnotaxonomy more replicable will take time and effort among investigators. In the long run, this can be accomplished by a holistic approach that includes close observation of trace fossils, standardized procedures of description and diagnosis, reinvestigation of type material, attention to bioprint (morphological traits that reveal the anatomical and ethological characteristics of the tracemakers; Rindsberg and Kopaska-Merkel, 2005), avoidance of taphonomic and human bias, and above all, cooperation

The use of the terms trace, mark and structure

Mark, trace and structure have been in consistently used in ichnology for many years; we wish to clarify the origins and to prescribe correct usage of these terms. The origins of the words are ancient and complex; in the twentieth century they were given clear definitions as ichnologic terms. Seilacher (1953) defined a mark (German Marke) as a physical (abiogenic) sedimentary structure, as in the common terms sole mark, flute mark, but not bite mark or scratch mark. Trace has been defined many times; we recommend the consensus definition of Bertling et al. (2006) as “a morphologically recurrent structure resulting from the life activity of an individual organism (or homotypic or ganisms) modifying the substrate”; this in cludes dwelling trace, feeding trace, bite trace. Structure, as implied in another consensus paper (Frey, 1973), is a neutral term for geologic patterns resulting from either biogenic or abiogenic processes. Use of the three terms in a clear consistent manner will aid communication both among ichnologists and between ichnologists and their colleagues in other fields

Trilobites in early Cambrian tidal flats and the landward expansion of the Cambrian explosion

The timing of the early invasion of the continents, the routes to the land, and the environmental breadth of the Cambrian explosion are important topics because they are at the core of our understanding of early evolutionary breakthroughs. Illuminating some aspects of these problems are trilobite trace fossils in tidal-flat deposits from the lower Cambrian Rome Formation in the southern Appalachian Mountains of Tennessee (USA). Morphologic details and size range of the trace fossils suggest production by olenellid trilobites, which occur as body fossils in the same unit. The occurrence of this ichnofauna, together with physical structures indicative of periodic subaerial exposure (desiccation cracks) and deposition within the intertidal zone (flat-topped ripples), shows that trilobites forayed into the upper intertidal zone during the Cambrian. Our finding supports the migration of subtidal organisms into marginal-marine, intertidal settings at the dawn of the Phanerozoic, suggesting that trilobites contributed to the establishment of the intertidal ecosystem during the Cambrian. The sequence of events involved in the colonization of early Paleozoic tidal flats is consistent with the idea that most terrestrial taxa originated from marine rather than freshwater ancestors, and that direct routes to the land from marginal-marine ecosystems were involved in the colonization of continental environments early in the Phanerozoic.Fil: Mángano, M. Gabriela. University of Saskatchewan; CanadáFil: Buatois, Luis A.. University of Saskatchewan; CanadáFil: Astini, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Rindsberg, Andrew K.. University of West Alabama; Estados Unido

Area balance and strain in an extensional fault system: Strategies for improved oil recovery in fractured chalk, Gilbertown Field, southwestern Alabama -- Year 2. Annual report, March 1997--March 1998

Gilbertown Field is the oldest oil field in Alabama and has produced oil from fractured chalk of the Cretaceous Selma Group and glauconitic sandstone of the Eutaw Formation. Nearly all of Gilbertown Field is still in primary recovery, although waterflooding has been attempted locally. The objective of this project is to analyze the geologic structure and burial history of Mesozoic and Tertiary strata in Gilbertown Field and adjacent areas in order to suggest ways in which oil recovery can be improved. Indeed, the decline of oil production to marginally economic levels in recent years has made this type of analysis timely and practical. Key technical advancements being sought include understanding the relationship of requisite strain to production in Gilbertown reservoirs, incorporation of synsedimentary growth factors into models of area balance, quantification of the relationship between requisite strain and bed curvature, determination of the timing of hydrocarbon generation, and identification of the avenues and mechanisms of fluid transport