Francisca E. Oboh-Ikuenobe

Sequence stratigraphic interpretations from palynofacies, dinocyst and lithological data of Upper Eocene-Lower Oligocene strata in southern Mississippi and Alabama, U.S. Gulf Coast

Abstract This paper presents new information on the sequence stratigraphy of the Upper Eocene–Lower Oligocene strata in southern Mississippi and Alabama, based on palynological and lithological data from five sections. By integrating lithological characteristics with palynofacies assemblages, several dinocyst paleoecological groups, the Deflandrea group, and the abundance of reworked dinocysts in samples, paleobathymetric curves were reconstructed and used to revise the sequence stratigraphy of the area. We identified a maximum flooding surface in the middle of the Shubuta Clay Formation in southern Mississippi, and dated it as latest Eocene. In southern Alabama, the Eocene–Oligocene boundary was placed within a condensed section representing about 0.19 Ma, and it coincided with the Shubuta Clay–Vicksburg Group contact. This condensed section is equivalent to the accumulation of the upper Shubuta and Red Bluff Formations in southern Mississippi. The Forest Hill–Mint Spring contact, which has been interpreted as a sequence boundary that merged with a transgressive surface, does not correlate with the Tejas A (TA) 4.3/4.4 sequence boundary of Haq et al. (1988) . The Pachuta Marl and lower Shubuta Clay Formations are constituents of a Late Eocene transgressive systems tract in southern Mississippi, but this systems tract extended to the Shubuta Clay–Vicksburg Group contact in southern Alabama. The overlying Early Oligocene highstand systems tract consisted of the upper Shubuta (in Mississippi), and the Red Bluff–Bumpnose–Forest Hill Formations. A thin sandstone in the Mint Spring was interpreted as a deposit of a possible lowstand systems tract above the sequence boundary in one southern Mississippi section. In general, the Mint Spring Marl and Marianna Limestone constituted a transgressive systems tract.

Sequence Stratigraphy and Depositional Facies of Lower Ordovician Cyclic Carbonate Rocks, Southern Missouri, U.S.A.

ABSTRACT Lower Ordovician cyclic carbonate strata of southern Missouri were deposited in a warm, shallow, epeiric sea on a fully aggraded carbonate platform. Sedimentological characteristics distinguish the Jefferson City and Cotter dolomites from the underlying Gasconade and Roubidoux formations. Mixed carbonate-siliciclastic sedimentation characterizes the Roubidoux Formation, with sandstones accounting for up to 60% of sedimentation. The Gasconade, Jefferson City, and Cotter dolomites exhibit an increased occurrence of chalcedonic chert nodules in very similar shape and texture to the gypsum and anhydrite nodules common on modern sabkha supratidal flats. Casts of halite and ghosts of gypsum laths also exist in the Jefferson City and Cotter strata but are rarely found in the underlying units. Facies analysis from drill cores and outcrop sections provides the basis for identifying two major meter-scale cycle types. Type I cycles consist of algal stromatolites, tidal-flat laminites (mechanical and algal), ooid grainstones, wavy peloidal wackestones, and quartz sandstones interpreted as peritidal facies. They are the dominant components of the Roubidoux Formation, Jefferson City Dolomite, and Cotter Dolomite. Type II cycles consist mostly of subtidal facies such as strongly burrowed mudstone, thrombolite boundstone, and stromatolites. Type I cycles are thinner and represent highstand systems tracts, whereas the thicker type II cycles represent transgressive systems tracts and are dominant in the Gasconade Dolomite. The cycle stacking patterns, facies changes, and the intrabasinal correlatability of Fischer plots made from the widely spaced sections argue for a eustatic control on sea-level fluctuation on the platform. Interbasinal correlation with other North American basins is possible using biostratigraphic information and comparison of Fischer plots. Five Missouri sequences correlate with those described for other regions. The continent-wide uniformity in cycle stacking patterns indicates a primarily eustatic control on Lower Ordovician meter-scale cycle development. Regional tectonic and autocyclic controls probably account for general differences in sedimentation pattern among the correlated basins.

Dispersed Organic Matter in Samples from the Western Continental Shelf of Southern Africa: Palynofacies Assemblages and Depositional Environments of Late Cretaceous and Younger Sediments

Abstract The composition and distribution of dispersed microscopic organic matter particles (phytoclasts) and palynomorphs in sediments and sedimentary rocks reflect factors that influenced their production in their original environments, transport to depositional sites, burial, and post-depositional changes. Thus, they can be used as proxies for reconstructing provenance, temporal and spatial paleoenvironmental conditions, and diagenetic changes. In this study, phytoclasts and palynomorphs in 55 spot samples from Upper Cretaceous, Eocene, Miocene and uppermost Pleistocene sediments on the western continental shelf of Namibia and South Africa were examined. They were used to test lateral depositional facies inferred from unpublished micropaleontological analysis, and to decipher any stratigraphic trends in the distribution of the organic particles in the sediments. Thirteen types of phytoclasts and palynomorphs were identified and analyzed in two ways: visually with basic quantitative techniques and statistically with two multivariate techniques. Three components, namely amorphous organic matter, wood, and black debris, were visually and statistically significant. Average linkage cluster analysis of these three components and discrete changes in the amounts of marine palynomorphs and other terrigenously derived organic material, such as spores and pollen, brown-black fragments, and plant tissues, delineated seven palynofacies assemblages. By contrast, principal components analysis revealed two groups of samples based on the amounts of amorphous organic matter and wood. Five groups of samples (referred to as associations) were identified visually from the pattern of organic matter distribution and compared with the statistical results. A palynofacies depositional model is proposed to re-evaluate the fluvial to inner shelf settings previously inferred for the sediments. Some clear stratigraphic trends were obvious in both sets of results, such as the dominance of amorphous organic matter in Turonian, Coniacian, and uppermost Pleistocene sediments, and higher percentages of black debris in the older sediments. These trends appear to be controlled more by provenance and depositional conditions than by age. The dominance of amorphous organic matter in several uppermost Pleistocene sediments (deposited during a global fall in sea level) were attributed to in-situ physical and biological degradation of mostly marine algal material in an inner shelf setting.

Paleogene palynostratigraphy of the eastern middle Magdalena Valley, Colombia

Abstract This work presents a detailed study of the pollen and spore distribution in the Paleocene‐Eocene Lisama and La Paz Formations on the eastern border of the Middle Magdalena Valley, Colombia. One hundred and forty‐seven samples obtained from cores and outcrops were prepared for palynological research, fifty‐nine of which were rich in pollen and spores. Three hundred spore and pollen taxa were identified. The studied stratigraphic interval is a 2000 m thick coastal and fluvial deposit formed in a variable subsiding tectonic setting. The Lisama Formation is characterized by the dominance of the Proxapertites group. Some typical Paleocene forms start to disappear toward the upper part of the Lisama Formation (e .g. Bombacacidites annae, Ephedripites vanegensis, Retidiporites magdalenensis), and are followed by a barren interval probably linked to intense oxidation during paleosol development (the uppermost 266 m of the Lisama Formation). In the La Paz Formation there is a progressive appearance of ear...

Correlating palynofacies assemblages with sequence stratigraphy in Upper Cretaceous (Campanian) sedimentary rocks of the Book Cliffs, east-central Utah

Some of the most important factors that govern the preservation of depositional sequences in passive margins are the rate of sediment supply, the type of sediment, subsidence history, sea-level changes, and climate. These factors also control the nature of components, such as organic matter, palynomorphs, and other fossils incorporated within the sediments. Because detrital organic matter (palynodebris) behave like sedimentary particles, their distribution in sediments can be used to infer palynofacies, and consequently depositional conditions. This study correlates palynofacies assemblages with sequence stratigraphic interpretations of Upper Cretaceous (Campanian) sedimentary rocks in the Book Cliffs, east-central Utah, namely the Kenilworth, Grassy, and Desert Members of the Blackhawk Formation, Mancos Shale, Castlegate Sandstone, and Buck Tongue of the Mancos Shale. Sedimentological criteria have been used to identify the depositional framework at 8 localities, and 12 palynodebris types have been identified in the sediments: sporomorphs, marine palynomorphs, fresh-water algae, fungal remains, amorphous organic matter, resins, cuticles, parenchyma, degraded bundles, wood, black debris, and degraded debris. The samples and palynodebris were analyzed statistically using average linkage cluster analysis, principal components analysis, and detrended correspondence analysis. Cluster analysis yielded seven palynofacies assemblages, which have been integrated with sedimentological criteria, and correlated with sequence stratigraphic interpretations. Although all the samples are dominated by woody debris, the palynofacies assemblages are defined primarily by marine palynomorphs, degraded bundles, black debris, and sporomorphs, and to a lesser extent by cuticles and resins. Highstand systems tracts and lowstand systems tracts are each represented by major palynofacies assemblages, indicating that there is some correlation with sequence stratigraphy. Two other minor assemblages are indicative of the highstand systems tract. In addition, three assemblages, which are dominated by siltstone and shale samples interbedded with sandstones, are richer in black debris; this is probably due to the effect of oxidation in the depositional environment and, possibly, microbial respiration in the interbedded sandstones. Marine environments are usually characterized by an abundance of marine palynomorphs and palynodebris over sporomorphs and other nonmarine palynodebris, and this characteristic has been used to recognize initial marine flooding events and maximum flooding intervals (condensed sections) in several palynological studies. In this study, however, one possible initial marine flooding event was not easily detected palynologically. In situations such as this, there is a need to integrate palynology with sedimentological and other criteria in order to establish valid regional sequence stratigraphic interpretations.

Characterization of a moderately halo-acidophilic bacterium isolated from Lake Brown, western Australia

Compared to prevalent alkaline to neutral hypersaline environments, acidic hypersaline environments have been scarcely studied. However, they hold interest to many researchers in that these environments have similar geological and geochemical characteristics as those found in lithified strata on Mars. Fieldwork indicated that Lake Brown, located in Western Australia, possessed pH values of 3.1-4.5 and salinity between 13.0-23.0%. Water column, groundwater, and sediment samples were collected from the lake during the austral winter of 2005. These samples were analyzed with both traditional culture and molecular methods. Modified growth media and minimal media were designed to match the composition (Cl, Na, Mg, SO4, K, Ca, and Br) of Lake Brown surface and ground waters for the enrichment of microorganisms. One of the isolates obtained, Brown 1, can grow in media that possesses pH values of 3-7 with optimal growth at pH 4, salinity that ranged from 5% to saturation with optimal growth at 5% and could grow under temperatures that ranged from 20°C to 65°C with optimal grow occurring at 37°C. The isolates optimum growth conditions are similar to those found in Lake Brown. The isolate is a Gram-negative rod that forms yellow colonies on 17% Phytogel. Its 16S rRNA gene can be amplified with bacterial primers but not with archaeal primers. Its 16S rRNA gene sequence suggests that the isolate is a gamma proteobacterium. Studies on organisms isolated from environments such as Lake Brown, an acid hypersaline lake, can provide an opportunity to both expand our knowledge of terrestrial extremophiles and gain insight on the possible forms of life that might have existed on Mars.

NEW SPECIES OF DINOFLAGELLATE CYSTS FROM THE PALEOCENE OF THE ANAMBRA BASIN, SOUTHEAST NIGERIA

Abstract Six new species of dinoflagellate cysts and one new combination from the Paleocene to ?lowermost Eocene succession in the Alo-1 well, southeast Nigeria, are proposed herein. The new species are Achomosphaera quadrata, Diphyes bifidum, Ifecysta fusiforma, Ifecysta heterospinosa, Palaeocystodinium rafii, and Wilsonidium stellatum. Furthermore, Fibrocysta lappacea (Drugg 1970) Stover & Evitt 1978 is transferred to Ifecysta, and the diagnosis of Ifecysta is emended.

A portrait of Late Maastrichtian and Paleocene Palynoflora and Paleoenvironment in the Northern Mississippi Embayment, Southeastern Missouri

Upper Cretaceous and lower Paleogene sedimentary rocks in southeastern Missouri record the northwest extension of the Mississippi Embayment, yet very little information exists about them due to rarity of outcrops and borehole material. This has hindered a clearer understanding of the depositional conditions before and after the terminal Cretaceous impact event. Access to freshly excavated sediments of the Owl Creek, Clayton and Porters Creek formations and to material from several US Geological Survey boreholes has provided a wealth of data to study this time interval in the area. In this study, detailed palynomorph and palynofacies data have been used to infer palynostratigraphy and paleovegetation. Characteristics of lithology, ichnofossils, invertebrate fossils, foraminifera and well logs have provided the framework for reconstructing the depositional history. Palynomorphs indicate Late Maastrichtian, Danian and Thanetian—Selandian ages for the Owl Creek, Clayton and Porters Creek formations, respectively. Although the Cretaceous—Paleogene (K—Pg) boundary itself is marked by an unconformity, the basal part of the overlying Clayton Formation was apparently deposited as a single megatsunamite following the Chicxulub impact event. Palynofloras suggest mixed coastal and inland subtropical forest vegetation dominated by angiosperm taxa, although abundant records of gymnosperm pollen production occurred at various times during the deposition of the Porters Creek. While terrestrially derived organic components dominate the four palynofacies assemblages (A–D) identified by cluster analysis, lithologic, ichnofacies, macrofossil and dinoflagellate cysts suggest that assemblages C and D, which are characterized by higher percentages of amorphous organic matter, represent more distal marine depositional environments.

Palynofacies Analysis and Submicron Pore Modeling of Shale-Gas Plays

The present study combines palynological applications with advanced microscopic techniques to characterize the Utica, Haynesville and Fayetteville shale-gas source rocks. This unprecedented approach could offer an alternative way to measure the total organic carbon (TOC) content using the 2D subsurface Scanning Electron Microscope (SEM) images. This approach is considered to be a faster and inexpensive method compared to conventional geochemical analyses. Palynofacies analysis provided valuable information about kerogen type and its degree of thermal maturation, which are key parameters in shalegas exploration. Moreover, it qualitatively allowed the estimation of important organic geochemical parameters such as vitrinite reflectance (Ro %) and numerical thermal alteration index (TAI). New high resolution microscopic solutions have successfully been exploited for source rock characterization at both microand nano-meter scales. In-situ Focused Ion Beam (FIB) and Scanning Electron Microscope (SEM) technologies provided new insights into rock fabrics such as porosity, permeability, tortuosity, anisotropy and kerogen content. Serial sectioning and sequential imaging using dual beam SEM/FIB instrument were implemented successfully to characterize the 2D kerogen content and 3D submicron-pore structures. Moreover, pores were found in organic matters with the size of nano level and occupy 40−50% of the kerogen body. A successful example of reconstructed 3D pore model from Fayetteville Shale is presented. Introduction Qualitative and quantitative characteristics of shale-gas source rock are used by petrophysicists, geochemists and reservoir engineers. These include submicron pore structure and organic matter analyses, which are important in the derivation of rock capillarity, wettability and storativity. Shale-gas source rocks hold large quantities of hydrocarbon reserves that have made significant impact on North American oil and gas market since early 2000s. The ambiguity behind gas storativity and deliverability can be demystified through the understanding of the relationship between organic matter content and porosity. Conventional standalone analyses are inadequate and not suited for unconventional gas rock characterization. The proposed combined approach provides important information for evaluating and appraising shale-gas plays. Palynofacies analysis identifies intervals of exploratory interest in terms of hydrocarbon content. It can also be used as a proxy to estimate organic geochemical values that are very expensive to obtain and thus, significantly reduces exploration and production costs. Pore imaging and modeling allows the evaluation of gas storage quantity and deliverability in shale-gas plays, which enables the development of optimized processes for hydrocarbon recovery. Palynofacies analysis as defined by Tyson (1995) is: “the palynological study of depositional environments and hydrocarbon source rock potential based upon the total assemblage of particulate organic matter.” In the present study, palynofacies analysis was carried out on five samples recovered from the Haynesville, Utica and Fayetteville shale-gas source rocks in order to evaluate their kerogen type and degree of thermal maturation. Three of the five studied samples are from the Utica Shale (two samples from Dolgeville member and one sample from the Indian Castle Member), while the fourth and fifth samples are from Haynesville and Fayetteville shales. The data obtained were used to qualitatively estimate some key organic geochemical parameters such as vitrinite reflectance (Ro %) and numerical thermal alteration index (TAI). Samples were also analyzed for TOC content in order to fully understand their source potential.

Palynology of the Eocene Esmeraldas Formation, Middle Magdalena Valley Basin, Colombia

The palynology of the Eocene Esmeraldas Formation in the Middle Magdalena Valley Basin, Colombia was analyzed in order to constrain the age of the unit. This formation is a very important oil reservoir in the Middle Magdalena Valley Basin, which is a product of the fragmentation of a Cenozoic foreland basin by the uplift of the Northern Andes. The lateral continuity of the formation, as well as its correlations with lithostratigraphic units in adjacent basins is not clearly understood. The Los Corros Fossil Horizon, a molluscan horizon in the upper part of the Esmeraldas Formation, has been used to trace the top of the formation. This horizon is not laterally continuous over the basin and its age is still debatable. Data from 82 samples from an outcrop section in the Nuevo Mundo Syncline area and from seven previously studied wells have been integrated with a palynological zonation of northern South America in order to date the Esmeraldas Formation. The age ranges from the late Early Eocene to the Late Eocene. The Esmeraldas Formation is correlative with the upper Picacho Formation and the lower part of the Concentracion Formation in the Eastern Cordillera, and the upper Mirador Formation and the base of the Carbonera Formation in the Llanos Foothills. The Los Corros Fossil Horizon is Late Eocene and is time-correlative with a marine transgression in the central Llanos Foothills. A non-metric multidimensional scaling analysis suggests that floras from the Middle Magdalena Valley were different from those in the Llanos Foothills area during the Middle to Late Eocene. This is apparently due to taphonomic effects. The results of this study will contribute to a better understanding of the overall evolution of the Middle Magdalena Valley Basin.