Actualistic, sedimentological, and experimental approaches to the study of vertebrate trace taphonomy in the Kenya Rift Valley have permitted the characterization and even quantification of factors that influence trace morphology and preservation potential in semi-arid lake margins. Several important taphonomic factors were identified from the modern lake-marginal sediments of saline, alkaline Lake Bogoria and freshwater Lake Baringo in the Baringo-Bogoria basin (1º N and 36º E). The investigation of these factors, considering vertebrate ecology and sedimentology of the deposits, together with the study of early and later diagenetic processes that cement substrates, provided a framework for the paleoecological interpretation of three Pleistocene fossil footprint localities, also in the Baringo-Bogoria basin. The most important taphonomic factors appear to be related to the semi-arid climate (e.g., high evaporation:precipitation ratio), frequent lake level changes, the closed nature of the lake basins, bedrock geology (mainly volcaniclastic) within the catchment, and the chemical composition of lake and pore waters. Notable factors that cause the alteration, destruction, and stabilization of traces include efflorescent salt crystallization, which may temporarily cement substrates or destroy traces during crystal growth in the capillary fringe; substrate wetting and drying, which can induce soil-crusting and the shrinking and swelling of smectitic clays; and the presence of benthic microbial mats and biofilms, which may temporarily stabilize substrates or contribute to their early cementation by mediating carbonate precipitation. Experiments to quantitatively and statistically test the effects of salt efflorescence, the rate and temperature of substrate drying (e.g., sun-baking), and swelling and non-swelling clays supported field observations. Preservational processes interpreted from Pleistocene footprint-bearing sediments include the early cementation of substrates by carbonates (e.g., calcite), and during prolonged, stable dry phases, the precipitation of zeolitic cements and Mn- and Fe-oxide minerals. ****PLEASE NOTE: This thesis is formatted to be printed double-sided.

Thesis (M.S.)--Ohio University, August, 2009. / Title from PDF t.p. Includes bibliographical references.

No description available.

No description available.

The Upper Cretaceous Medicine Hat Member (Niobrara Formation) in western Canada contains abundant reserves of biogenic natural gas. In the Medicine Hat gas field area of southeast Alberta, nineteen cored intervals were examined and classified based on primary physical and biogenic sedimentary structures. Core analysis and stratigraphic mapping determined that the Medicine Hat Member strata consist of stacked, regionally extensive, lobate geobodies that prograde to the north. Employing spot-minipermeametry, the effect of biogenic rock fabrics on the reservoir characteristics was assessed. X-ray micro-computed tomography was conducted on four samples from a reservoir interval to visualize the geometry and distribution of burrow-associated heterogeneity. The results demonstrate that planiform bioturbate textures locally enhance the storage and transmission of natural gas in Medicine Hat reservoirs.

Recognition of large biogenic sedimentary structures (burrows, nests), their differentiation from physical structures (small storm-surge channels, synsedimentary deformation, buried objects), as well as imaging bioturbation in real time remain key challenges in sedimentology and ichnology. To address these issues, this study focused on laboratory and field ground-penetrating radar (GPR) experiments using both traditional time-lapse mode (TLM) and a time-triggered mode (TTM). In three sets of laboratory experiments, substrate consisted of dry, well-mixed, moderately sorted, medium sand common for upper beach (berm/foredune) and aeolian settings. Targets simulating burrowing organisms were placed on a basal layer (L1) buried by ~20-cm-thick cover horizon (L2), both with near identical mean grain size (1.69 and 1.65 ϕ, respectively). Improvements were made to the experimental design, including an experiment with a saline balloon (vertical pull) and a ground-coupled antenna, at varied moisture levels (0%, 3.7%, and 29.5%). High-frequency (2300 MHz) surveys were captured in TTM while manually extracting the target (variable deformation rate; total time window: 20 seconds). Velocities of simulated deformation calculated from time-triggered radargrams have the potential to be used in the field and laboratory to quantify rates of subsurface bioturbation not available by direct observation. Sediment disruption was quantified using standard ImageJ-aided grayscale analysis to detect truncations (breaks in reflection continuity), with an increase of 10-28% relative to undeformed substrate. Similarly, area-based mean grayscale values increased between 8-16% for damp and saturated TLM surveys, respectively. Complementing the laboratory experiments, this research produced one of the first GPR databases of post-emergence sea turtle nests, ichnologically understudied and relatively complex biogenic structures. A simulated structure (Deauville Beach, DE) and two in situ post-emergence sea turtle nests (Sandbridge Beach, VA) were imaged with an 800 MHz antenna, complemented with sediment texture and magnetic susceptibility analyses. The Delaware experiment provided a reference dataset for a full ethological sequence of nesting and emergence, for comparison with few available studies. At Sandbridge, a clear anomaly was identified at the recent Kemp’s Ridley (Lepidochelys kempii) nesting site, including a V-shaped truncation (width: 0.3-0.5 m; depth: ~0.75-0.9 m). At another location, an older (2020) loggerhead (Caretta caretta) nest was imaged and characterized in a similar aeolian ramp setting, which is characterized by a unique combination of upper berm and aeolian granulometric statistics. Numerous ghost crab burrows, with some imaged during surveys, place sea turtle nests into the Psilonichnus ichnofacies, with overprinting representing a contemporary ichnocoenosis rather than a facies shift. This research has wide-ranging implications for: 1) nest recognition in ancient sequences through identification of diagnostic aeolian ramp packages with diagnostic deformation structures; 2) distinguishing nests from morphologically similar paleo-channels based on overall metrics (tiered components) and fill structure, and 3) conservation of endangered species, with novel applications for nest characterization and potential hatchling emergence monitoring. / Geology

<p> The Lower Cretaceous (Upper Albian) Viking Formation of central Alberta contains numerous linear sandbodies and fewer large irregularly-shaped sandbodies. Most studies to date have focused on individual sandbodies, leaving their interrelationships largely unknown. Developing a high-resolution allostratigraphy for the Viking of central Alberta allows mapping of regional bounding discontinuities and the definition of distinct allomembers. Placement of the Viking hydrocarbon fields within this framework permits an understanding of the exact stratigraphic relationships of the various fields. </p> <p> Examination of 120 cores and numerous well log correlations suggests the existence of four regionally mappable bounding discontinuities (BDl-4) which separate five distinct allomembers (I-V). Sandbodies within these allomembers were deposited in a variety of sedimentologically distinct environments. These include 'regional Viking' offshore to shoreface sandstones, prograding highstand shoreface sediments, transgressive incised shoreface sediments, and forced regressive, onlapping shoreface 'tongues'. The series of linear trending hydrocarbon fields from Joffre to Chain are also stratigraphically distinct. The sandbodies exist at five separate stratigraphic horizons and therefore are not all part of the same incised shoreface deposits. </p> <p> The four regional bounding discontinuities are interpreted as transgressive surfaces of erosion formed by four separate drops and subsequent rises of relative sea level. These fluctuations were greater than 30m and each complete cycle occurred over roughly 375,000 years. </p> / Thesis / Master of Science (MSc)

No description available.

Bioturbation in supratidal carbonate substrates has only recently received attention from ichnologists, relying primarily on traditional ground-based techniques. This study is the first high-resolution geophysical investigation of three decapod species inhabiting adjacent coastal biotopes on San Salvador Island. Extensive (&gt;2 km) 800 MHz georadar surveys captured a diverse suite of &gt;120 burrows of ghost (Ocypode quadrata), blackback (Gecarcinus lateralis) and blue (Cardisoma guanhumi) land crabs. Site-specific post-processing protocols were used to establish characteristic attributes that distinguish unfilled burrows from other discordant anomalies based on signal polarity structure. Variably oriented 2D and quasi-3D (~0.75-1.25 wavelength line separation) images allow the diagnostic signature of G. lateralis burrows to be distinguished from those of O. quadrata based on: 1) higher density of point-source diffractions (0.9-1.9/m vs. 0.01-0.06/m) and 2) shallower inclination angle (21-46° vs. &gt;60°). C. guanhumi burrows are differentiated by: 1) larger diameter; 2) presence of an end chamber (where the radar signal is not attenuated by saline groundwater); 3) low electromagnetic signal velocity (~9 cm/ns vs. ~11 cm/ns) in organic-rich muddy substrate and 4) rapid signal decay. The migrated inclination angle (a) and the effective range (t0; time window of strongest reflectors) offer the best combination that differentiates between the three end-member structures and matrix properties. This study establishes GPR as a viable non-invasive subsurface imaging technique, with potential implications for: 1) identification of shifting ichnocoenoses, as exemplified by intense hurricane impacts (2015/2016); 2) recognition and mapping of similar biogenic structures in buried or lithified carbonates and, 3) quantification of a near-surface ichnofabric index and the dual porosity/permeability structure of prospective hydrocarbon reservoirs. Furthermore, the basic attributes of subsurface visualization can be readily extended to other mesoscale biogenic structures in evaporite and siliciclastic media. / Geology

The Ediacaran Period, stretching from 635–542 million years ago, is one of the most dynamic intervals in the history of life. It witnessed the rapid transition from a microbially-dominated world, which had existed undisturbed for almost three billion years, to a Phanerozoic biosphere that is greatly modified by the interactions between macro-organisms and Earth surface systems. Ediacaran successions worldwide contain enigmatic assemblages of fossilised soft-bodied organisms. Determining the biological affinities of these fossils represents one of the major challenges in modern palaeontology. This thesis addresses some of the fundamental questions surrounding the Ediacara biota of the Avalon region from taphonomic, ontogenetic and palaeoenvironmental perspectives. Up-to-date stratigraphic ranges are produced for Avalonian macro-organisms, documenting spatial and temporal trends in their occurrence. New fossil assemblages are described, which include populations of juvenile rangeomorphs, and one of the earliest examples of community succession in the fossil record. The previously unexplained fossil Ivesheadia Boynton and Ford 1996 is re-described as a taphomorph, preserving the remains of Ediacaran macro-organisms that had died and undergone microbial decay on the seafloor prior to burial. This hypothesis implies considerable time-averaging of Avalonian palaeocommunities, and consequently suggests that the preserved fossil assemblages do not represent census populations of living organisms at the time of burial. Microbial decay is experimentally demonstrated to replicate aspects of Ivesheadia-type morphology, supporting the arguments presented herein for the preservation of microbially-induced taphomorphs during the Ediacaran. Finally, the discovery of the oldest evidence for metazoan locomotion, from 565Ma horizons at Mistaken Point in Newfoundland, suggests that motile macro-organisms were present amongst the Ediacara biota, ~20Myrs before the Cambrian boundary. This portrayal of Ediacaran palaeobiology views the deep-marine Avalonian ecosystems as diverse assemblages of both macro- and micro-organisms. Such palaeoenvironments preserve rare evidence of organisms capable of locomotion, and are likely to have included metazoans.