Multivariate Statistical Analyses of Palynodebris from the Middle Miocene of the Niger Delta and their Environmental Significance

Fourteen types of palynodebris have been identified in Middle Miocene reservoir sediments from the Niger Delta. They include palynomorphs, cuticle, parenchyma, resins, black debris, woody fragments and degraded components. The palynodebris types were interpreted by Principal Components Analysis and Average Linkage Cluster Analysis. Four assemblages of samples emerged and they have been grouped into two palynofacies associations because of their correlation with mudstone and muddy heterolithic lithofacies and sandstone lithofacies, respectively. The significant palynodebris components are black debris, parenchyma, resins and amorphous organic matter. The size, shape and texture of all the components were integrated with sedimentological features, palynomorph and foraminiferal assemblages to recognize seven, possibly eight, deltaic sub-environments of deposition in the reservoir

Sedimentology, Palynology, and Sea Level Fluctuations Recorded from Two Pennsylvanian Cores from Northwestern Missouri

Two cores from Buchanan and Andrew Counties in the Forest City Basin, northwestern Missouri, yielded approximately 1,200 feet of sedimentary rock deposited during the Pennsylvanian Period (approximately 300 million years ago), a period characterized by rapid fluctuations in sea level. The cores were logged from the Excello Formation in the Upper Desmoinesian Series upward to the Iatan Formation at the top of the Missourian Series. Lithofacies were identified from rock composition, grain size, color, bedding thickness, sedimentary structures, and fossils. Petrographic thin sections were taken from selected rock types and the results were used to complement the visual descriptions. Limestones are the dominant lithofacies, but elastic rocks and coal beds are also present. A preliminary palynological investigation of dispersed organic matter (palynodebris), spores, and pollen from organic-rich lithofacies provided additional information on the depositional environments. The two cores were correlated primarily on the basis of the sedimentologic, and then integrated with palynologic results. Several formations are characterized by fades changes. This study also examined the possible influences of sea level fluctuations on the sedimentary rocks, and it appears that coal beds, underclays, and shales are correlative with sea level falls

Correlation Between Sequoia Type Pollen and Lower Oligocene Transgressive Deposits in the Eastern Gulf Coast

Two taxodiaceous conifer pollen species form the dominant components among sporomorphs of the Lower Oligocene Vicksburg Group in the eastern Gulf Coast. The two species, Sequoiapollenites lapillipites and Sequoiapollenites sp. 1, are very prominent in the Mint Spring Marl and Marianna Limestone at two localities in SE Mississippi and SW Alabama. These two lithostratigraphic units constitute the transgressive systems tract of the Tejas A Gulf Coast (TAGC)-4.4 sequence. Thus, the concentration of these two Sequoia type pollen species may be used as a marker for these transgressive deposits in the eastern Gulf Coast

Base-Level Buffers and Buttresses: A Model for Upstream versus Downstream Control on Fluvial Geometry and Architecture within Sequences

The effects of downstream base-level control on fluvial architecture and geometry are well explored in several broadly similar sequence-stratigraphic models. Cretaceous Dakota Group strata, U.S. Western Interior, have characteristics reflecting combined downstream and upstream base-level controls that these models cannot address. Particularly, three layers of amalgamated channel-belt sandstone within this group thicken and are continuous for distances (≤ 300 km) along dip that stretch the reasonable lengths for which these models are intended to apply. As well, architecture in up-dip reaches records repeated valley-scale cut-and-fill cycles. This contrasts with equivalent strata down dip which record channel-scale lateral migration with no such valley-scale cycles apparent. We here introduce the concept of buffers and buttresses to address these observations. We assume that river longitudinal profiles are each anchored down dip to some physical barrier (e.g., the sea strand, etc.) that we refer to as a buttress. Buttress shift is considered the primary downstream control on base level. Profiles extrapolated up dip from the buttress over any modeled duration of buttress shift can range widely because of high-frequency variability in upstream base-level controls (e.g., discharge, etc.). All these potential profiles however are bounded above by the profile of highest possible aggradation, and below by the profile of maximum possible incision. These upper and lower profiles are buffers, and they envelop the available fluvial preservation space. Thickness of the buffer zone is determined by variability in upstream controls and should increase up dip to the limit of downstream profile dominance. Dakota valley-scale surfaces record repeated cut-and-fill cycles driven by up-dip controls and are confined between thick stable buffers. Equivalent strata down dip record lateral reworking within a thinner channel-scale buffer zone that was positioned by downstream controls. Regression exposed slopes similar to the buffer zone, thus buffers were stable for long distances and durations. This prompted dip-extensive lateral reworking of strata into upstream valley-scale and downstream channel-scale sheets. Buffers and buttresses provide a broadly applicable model for fluvial preservation that captures upstream vs. downstream base-level controls on geometry and architecture. The model lends general insights into dip-oriented variations in fluvial architecture, production of sheet vs. lens geometry, total preservation volumes for fluvial systems, and variations in these factors related to contrasting climatic conditions and basin physiography. The model can be amended to existing sequence stratigraphic approaches in order to capture dip-oriented variations in sequence architecture

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

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

The Permian-Triassic Boundary in the Kurdistan Region of Northern Iraq

The well-preserved Upper Permian-Lower Triassic succession in the Kurdistan region of northern Iraq has provided an opportunity to study the Permian-Triassic boundary. This study presents the first ever stable isotope data for these rocks. One hundred and sixty-five samples from the Ora-Beduhe and CZO sections located within the Ora structure in the Thrust Zone were studied for lithological, stable isotope, trace fossil and invertebrate fossil variations.  Carbon and oxygen isotopic signals (d13C, d18O) and %CaCO3 indicate dramatic changes within the CZO section (between samples 29 and 30) where d13C records a negative excursion of 6‰ VDP in a portion of the section previously interpreted as late Permian. The P-T boundary matching the lithic changes and extinction of Permian fauna, in addition to another boundary or contact were identify between (samples 16 and 17) which is marked due to severe decreasing in late Permian fauna and appearance of early Triassic. Paleontological record suggests a gradational extinction pattern for the boundary in northern Iraq. Faunal changes are consistent with other regional and global studies for the Permian-Triassic boundary. Keywords: Permian-Triassic boundary, Kurdistan, Northern Iraq, Stable Isotopes, Neo-Tethy

Organic Matter Assessment And Paleoenvironmental Changes Of The Middle Jurassic Main Source Rocks (Khatatba Formation) In The North Western Desert, Egypt: Palynofacies And Palynomorph Perspectives

The Middle Jurassic in the north Western Desert, Egypt, was a time of complex tectonics and increased environmental perturbations attributed to the predominant sedimentation of organic carbon-rich fine siliciclastic and carbonate deposits of the Khatatba Formation. Although some studies have addressed the hydrocarbon potential and source rock characteristics of the Khatatba Formation, a regional-scale investigation of the prevalent paleoenvironmental conditions and organic matter characteristics is still necessary. In this study, the Khatatba Formation is investigated for detailed palynofacies analysis and palynomorph composition to assess organic matter kerogen types and reconstruct the depositional paleoenvironmental patterns on a regional scale. For this purpose, 116 drill cuttings were collected from five wells in the Matruh, Shushan, and Dahab-Mireir Basins. Moderately diverse assemblages of spores, pollen, and dinoflagellate cysts are reported. Age-diagnostic dinoflagellate cysts, including Adnatosphaeridium caulleryi, Dichadogonyaulax sellwoodii, Korystocysta gochtii, Wanaea acollaris, and Pareodinia ceratophora, along with occasional records of Systematophora areolate and Systematophora penicillate, defined a Bajocian–Callovian age. Based on particulate organic matter (POM) composition, four palynofacies assemblages (PFAs) are identified. PFA-1 is the most common within the Khatatba Formation in the five studied wells. It contains high proportions of phytoclast fragments versus low contents of amorphous organic matter (AOM) and palynomorphs and is defined by a gas-prone kerogen Type III. PFA-2 is comprised of moderate abundances of AOM and phytoclast characteristics of oil-prone kerogen Type II. PFA-3 is dominated by phytoclasts and moderate to low proportions of AOM and palynomorphs of kerogen Type III, whereas PFA-4 consists of AOM and palynomorphs defining kerogen Type II. PFA-1 indicates predominant deposition in proximal active fluvio-deltaic sources to marginal marine conditions with enhanced contributions of terrestrial/riverine influx. PFA-2 and PFA-3 reveal deposition under an enhanced dysoxic to anoxic proximal inner neritic shelf due to the abundant occurrences of spores and coastal to shallow marine dinoflagellate cysts. PFA-4 suggests deposition under enhanced suboxic to anoxic distal inner neritic conditions because of enhanced AOM and abundant proximate and some chorate dinoflagellate cysts. Thus, the Middle Jurassic experienced a predominantly marginal to shallow water column in this part of the southern margin of the Tethyan Ocean where the Matruh, Shushan, and Dahab-Mireir Basins were located

Drastic Vegetation Change in the Guajira Peninsula (Colombia) during the Neogene

Dry biomes occupy ~35% of the landscape in the Neotropics, but these are heavily human-disturbed. In spite of their importance, we still do not fully understand their origins and how they are sustained. The Guajira Peninsula in northern Colombia is dominated by dry biomes and has a rich Neogene fossil record. Here, we have analyzed its changes in vegetation and precipitation during the Neogene using a fossil pollen and spore dataset of 20 samples taken from a well and we also dated the stratigraphic sequence using microfossils. In addition, we analyzed the pollen and spore contents of 10 Holocene samples to establish a modern baseline for comparison with the Neogene as well as a study of the modern vegetation to assess both its spatial distribution and anthropic disturbances during the initial stages of European colonization. The section was dated to span from the latest Oligocene to the early Miocene (~24.2 to 17.3 Ma), with the Oligocene/Miocene boundary being in the lower Uitpa Formation. The early Miocene vegetation is dominated by a rainforest biome with a mean annual precipitation of ~2,000 mm/yr, which strongly contrasts with Guajira\u27s modern xerophytic vegetation and a precipitation of ~300 mm/yr. The shift to the dry modern vegetation probably occurred over the past three millions years, but the mechanism that led to this change is still uncertain. Global circulation models that include the vegetation could explain the ancient climate of Guajira, but further work is required to assess the feedbacks of vegetation, precipitation, and CO2

Fingerprinting the Cretaceous-Paleogene boundary impact with Zn isotopes

Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; however, none fingerprint volatilization, a key process that occurs during large bolide impacts. Stable Zn isotopes are an exceptional indicator of volatility-related processes, where partial vaporization of Zn leaves the residuum enriched in its heavy isotopes. Here, we present Zn isotope data for sedimentary rock layers of the K-Pg boundary, which display heavier Zn isotope compositions and lower Zn concentrations relative to surrounding sedimentary rocks, the carbonate platform at the impact site, and most carbonaceous chondrites. Neither volcanic events nor secondary alteration during weathering and diagenesis can explain the Zn concentration and isotope signatures present. The systematically higher Zn isotope values within the boundary layer sediments provide an isotopic fingerprint of partially evaporated material within the K-Pg boundary layer, thus earmarking Zn volatilization during impact and subsequent ejecta transport associated with an impact at the K-Pg

Sedimentology of Acid Saline Lakes in Southern Western Australia: Newly Described Processes and Products of an Extreme Environment

Naturally acid saline systems with pH values between 1.7 and 4 are common on the Yilgarn Craton of southern Western Australia. a combination of physical and chemical processes here yield a previously undescribed type of modern sedimentary environment. Flooding, evapoconcentration, desiccation, and eolian transport at the surface, as well as influx of acid saline groundwaters, strongly influence these lakes. Halite, gypsum, kaolinite, and iron oxides precipitate from acid hypersaline lake waters. Shallow acid saline groundwaters affect the sediments of the lakes and associated mudflats, sandflats, channels, and dunes by precipitating early diagenetic halite, gypsum, iron oxides, clays, jarosite, and alunite. These modern environments would likely yield a rock record composed mostly of bedded red siliciclastic and reworked gypsum sand, alternating with less common beds of bottom-growth gypsum and halite, with alteration by early diagenetic features diagnostic of acid saline waters. This documentation of sedimentary processes and products of modern acid saline environments is an addition to the comparative sedimentology knowledge base and an expansion of the traditional models for classifying brines. Implications include better interpretations of terrestrial redbeds and lithified martian strata, improved acid remediation methods, new models for the formation and occlusion of pores, and the new setting for finding previously undescribed extremophiles