Stratigraphic Changes Research Articles

The Wattie Group of the Birrindudu Basin, northern Australia: a witness to the denudation of the Nuna-forming Isan/Chewings Orogeny

The Proterozoic Birrindudu Basin lacks a robust chronostratigraphic framework and remains one of the least explored basins in the Northern Territory, Australia. It shares lithological and chronological similarities with the McArthur Basin and the Tomkinson Province, which together form the ‘greater McArthur Basin’. The sedimentary successions of these basins have been divided into five basin-scale, non-genetic depositional packages—the Redbank, Goyder, Glyde, Favenc and Wilton packages. Of these, the Favenc Package is among the least studied. The Wattie Group in the Birrindudu Basin is interpreted as part of the Favenc Package based on geophysical and sedimentological correlations. New LA-ICP-MS detrital zircon U–Pb data provide new constraints on the age and provenance of the Wattie Group and establish relationships with the other Favenc Package sequences of the greater McArthur Basin. Our new data, combined with published data, yield maximum depositional ages for the formations of the Wattie Group, from oldest to youngest: the Wickham Formation (1623 ± 24 Ma), the Burtawurta Formation (1591 ± 70 Ma), the Hughie Sandstone (1585 ± 28 Ma), the Neave Formation (1611 ± 18 Ma), the Gibbie Formation (1705 ± 55 Ma) and the Seale Sandstone (1550 ± 24 Ma). The detrital zircon age distribution suggests that the Wattie Group primarily received detritus from south and southeastern regions, which we link to denudation and erosion of a southern orogen during the early Mesoproterozoic. A subtle northward shift in sediment source is apparent in stratigraphically younger units. This age-provenance shift is matched with a similar stratigraphic change in petrography, which we interpret as near-complete denudation of southern orogenic topography and a return to sediment sourced from proximal northern sources. Tectonically, we interpret that the Wattie Group represents erosion of topography caused by the Isan/Chewings Orogeny during the last major Nuna amalgamation.

Relocate the base of the Arundian? A re-evaluation from south Cumbrian sections and implications for British and Irish Lower Carboniferous successions

The largely ice-free world of the ‘Chadian’–Arundian (early Visean) is investigated in two successions in south Cumbria to better understand the relationships between transgression, hiatus and the position of the basal Arundian. A detailed foraminiferal biostratigraphy is used to age-constrain the transition from the late ‘Chadian’ to early Arundian. This demonstrates a good synchronous relationship between the sequence stratigraphy of the two successions and the first occurrence of key species (mostly primitive archaediscids, rapidly followed by more evolved forms of the same family), suggesting that there is no significant hiatus and that the record of faunal changes is closely comparable in the key successions. A synthesis of other ‘Chadian’–Arundian boundary successions in Britain and Ireland indicates some key problems with the current Arundian boundary stratotype in practical usage. We propose a stratigraphically higher position for the Arundian boundary in the stratotype, which is more easily correlated to the Bobrikian and Moliniacian substages of eastern Europe and Belgium, respectively, and tied to the first occurrences of foraminifera species, allowing more robust age assessments, free from the confounding factors of inferred lithological or sequence stratigraphic changes.

Long-eccentricity pacing of alluvial stratigraphic architecture in the Eocene Bighorn Basin, Wyoming, USA

Abstract Alluvial stratigraphy builds up over geologic time under the complex interplay of external climatic and tectonic forces and internal stochastic processes. This complexity makes it challenging to attribute alluvial stratigraphic changes to specific factors. Geological records indicate pronounced and persistent climatic changes during the Phanerozoic, while the effects of these changes on alluvial stratigraphy remain insufficiently documented. We provide evidence for 405 k.y. long-eccentricity climate forcing of alluvial stratigraphy in the lower Eocene Willwood Formation of the Bighorn Basin, Wyoming (USA). Two ~90-m-thick intervals, characterized by a relative paucity of sand, dominance of sinuous-river channels, and floodplain sediments with better-developed paleosols, coincide with eccentricity maxima as determined through integrated stratigraphic methods. These intervals are interspersed with three contrasting intervals, marked by relatively high sand content, prevalent braided-river channels, and less-developed paleosols, corresponding to eccentricity minima. A comprehensive genetic model that integrates climate, source-to-sink system, and alluvial dynamics to explain these findings remains to be elucidated. Given the consistent presence of the 405 k.y. eccentricity cycle throughout Earth’s history, it is plausible to infer that its influence may be discernible across a wide array of alluvial stratigraphic records.

Morphological transitions between lobate resurfacing and distal breakout lava flows in flood basalts: insights from analog experiments

Continental flood basalts (CFBs) are dominated by two characteristic lava morphologies. The first type, referred to as ‘compound’ or ‘hummocky pāhoehoe,’ exhibits pillow-like lava flow lobes with cross-sections of ~ 0.5–2 m and thin chilled margins. The second type, referred to as ‘simple’ or ‘sheet lobes’ preserves more massive, inflated flow interiors that are laterally continuous on scales of 100s of meters to kilometers. Previous hypotheses suggest that two factors may contribute to stratigraphic changes in morphology from ‘compound’ to ‘simple’: 1) increased eruption duration or 2) increased extrusion rate. We test the hypothesis that a large increase in extrusion rate would result in flow morphology transitioning from multiple small lobes to inflated sheet lobes due to a shift in flow propagation from intraflow resurfacing-dominated to marginal breakout-dominated. Using polyethylene glycol (PEG) wax extruded into a circular water-filled tank 130 cm in diameter, we produced larger, more complex experiments than previous studies. Our efforts simulated more complex lava fields which change flow morphology with distance from the eruptive vent, characteristic of CFBs. Whereas previous PEG studies linked extrusion rate to near-source surface morphologies, our experiments evaluated how flow propagation mechanisms change with variable extrusion rate and distance from the source. Two flow propagation styles were identified: 1) resurfacing, in which molten material breaks through the surface of a flow and covers the older crust and 2) marginal breakouts, in which molten material extends beyond the crust at the active distal margin of the flow. Flows that propagated via marginal breakouts were found to have lower proportions of resurfaced area and vice versa. We show that significant resurfacing is needed to preserve internal chilled boundaries within a flow and a low-extrusion-rate surface morphology, whereas marginal breakout-dominated flows tend to inflate the pillow-like surface morphology preserving a massive interior at great distances from the vent. Higher and more steady extrusion rates tend to decrease the extent of resurfacing and increase the distance between the source and preserved low-extrusion-rate surface morphologies. We find that an extrusion rate increase equivalent to a jump in the extrusion rate scaling factor, Ψ value, from < 1 to > 5 would be necessary to ensure a switch from resurfacing-dominated lobate morphologies to marginal breakout-dominated propagation style. This amounts to a factor of 125 increase in effusion rate for fissure eruptions and a factor of 625 for point source eruptions, assuming no change in vent geometry. This would be equivalent to an effusion rate of 0.2 m3/s, as documented in 1987–1990 Kīlauea eruptions, increasing to 125 m3/s, which was commonly measured during the 2014 Holuhraun eruption in Iceland and the 2018 eruption at Leilani Estates in Hawai‘i. Thus, we propose that continental flood basalts do not require unusually large effusion rates, but instead were active for a longer and more consistent time period than smaller-volume eruptions.

Study on the geomorphological changes of deep troughs under the influence of reclamation in the Caofeidian

Reclamation projects generally change the hydrodynamics and thus affect the topography of the seabed, which is the main threat to the safety of marine engineering. The Caofeidian Reclamation Project, the largest reclamation project in China to date, involved the reclamation of coastal regions of the Hebei Province. However, the project also created several issues and flaws due to the size of the reclaimed area. Through the comparative analysis in the Caofeidian sea area of multi-phase bathymetric topography, shallow stratigraphic changes, and numerical simulation of sediment dynamics, the characteristics of surface sediments and spatial distribution of erodibility were summarized. New marine geological hazards were discovered, such as submarine landslides and erosion depressions. It was concluded that after the reclamation of the Caofeidian, the south of the deep trough was still in an erosion state, and the erosion rate increased slightly. The shear stress formed by strong tidal currents in the deep trough was greater than the critical erosion shear stress of surface sediments, which caused the erosion transport of sediments. It was the primary dynamic mechanism leading to the long-term erosion state of the deep trough.

Permian-Triassic tectonic evolution of the Ailaoshan orogenic belt in SW China: insights from magmatic records

ABSTRACT The Ailaoshan orogen in SW China records the evolution of the Ailaoshan Paleo-Tethyan ocean and the amalgamation history between the South China and Indochina blocks, an important process for the formation of Southeast Asia. However, its tectonic evolution remains ambiguous with various competing models. We have carried out an integrated geochronological–petrological–geochemical study for the granites, dacites-rhyolites, granodiorites and trachyandesites in this orogen to give new constraints on this issue. The 255–254 Ma granites and the 250–248 Ma dacites-rhyolites show similar geochemical features and are characterized by strongly peraluminous nature, continental crust-like trace element patterns and negative zircon εHf(t) values (−14.4 to −6.6), indicating they derived from partial melting of ancient crust. The 229 Ma hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.96–1.01) and belong to high-K calc-alkaline I-type granites. They show depleted whole-rock Sr-Nd and zircon Hf isotope compositions (initial 87Sr/86Sr = 0.7027 to 0.7038, εNd(t) = 4.0 to 4.1, εHf(t) = 9.3 to 11.5), suggestive of derivation from partial melting of juvenile mafic crust. The 226 Ma trachyandesites are characterized by high MgO (4.1–4.6 wt.%), high Mg# (56) and arc-type geochemical affinities with enriched isotope compositions (initial 87Sr/86Sr = 0.7108 to 0.7111, εNd(t) = −7.7 to −7.5, εHf(t) = −6.3 to −3.5). These features indicate that their parental magmas derived from partial melting of enriched lithospheric mantle metasomatized by oceanic sediment-derived melts. These new data, in conjunction with spatial-temporal-temperature variations of igneous rocks, metamorphic records and stratigraphic changes in the region, suggest that the Ailaoshan Paleo-Tethyan ocean closed at the Early Triassic (ca. 250 Ma) which was followed by the Late Triassic postcollisional slab breakoff, and the ocean experienced westward unipolar subduction during its evolution with no assumed eastward subduction.

Stratigraphic change in flow transformation processes recorded in early post‐rift deep‐marine intraslope lobe complexes

AbstractThe Early Jurassic Los Molles Formation in the Neuquén Basin of western Argentina is a rare example of well‐exposed syn‐rift to post‐rift stratigraphy. In the Chachil Graben, the onset of the early post‐rift stage is marked by drowning of a carbonate system and the development of two deep‐marine intraslope lobe complexes. This field‐based study in the Chachil Graben involved field mapping and correlating eleven stratigraphic logs, and petrographic analysis to document how grain size and texture within intraslope lobe sandstones change from the lobe centre to their frontal pinch‐out. Eight different bed‐scale facies are identified and inferred to be formed by turbulent (turbidites; Type A and B beds), transient turbulent–laminar (transitional flow deposits; Type C, D, E and F beds), laminar gravity flows (debrites; Type G) and post‐depositional clastic injections (injectites; Type H beds). Fifteen lobes form two stacked lobe complexes that show stratigraphic evolution from a lower argillaceous sandstone‐dominated lobe complex, built by transitional flow deposits, to an upper coarser‐grained, sandier lobe complex largely constructed by turbidites. Petrographic analysis quantified sandstone mineralogy, matrix content, grain size and sorting, revealing that both lobe complexes are volcanic arc‐sourced. This study proposes that the differences in the character of the two lobe complexes are due to maturation of sediment transport routes through progressive healing of the intraslope relief, with a concomitant decrease in substrate erosion and flow bulking. Also proposed here is a model for intraslope lobe complex development that accounts for the impact of flow‐confinement on flow behaviour and transformation induced by the inherited topography. Bed type distribution suggests that high‐density flows terminate more abruptly against confining slopes and produce greater depositional variability than lower‐density flows. This integrated petrographic, architectural and sedimentary process model provides new insights into how post‐rift intraslope lobe systems may act as hydrocarbon reservoirs, aquifers and carbon storage sites.

Measuring and evaluating colorimetric properties of samples from loess-paleosol sequences

Colorimetric measurements are valuable in studying paleoenvironmental changes in sediment archives such as loess-paleosol sequences. These measurements allow for the identification of climate-sensitive minerals such as hematite, goethite, and secondary carbonates, as well as the observation of stratigraphic changes influenced by paleoclimate variations. Herein, a detailed workflow protocol emphasizing mineral abundance extraction by determining true band amplitudes is presented. Moreover, we present a protocol for colorimetric measurements that eliminates container bias, allowing the analysis and re-analysis of stored sediment quickly and inexpensively. Finally, we introduce a new R-package ('LESLIE') for graphical data display and enhancement. The protocol and its validation are demonstrated on the Suhia Kladenetz loess-paleosol sequence of northern Bulgaria.•A detailed workflow protocol eliminating container bias in colorimetric measurements and extracting mineral abundances is presented.•The protocol is independently validated with aid of Attenuated Total Reflectance Fourier Transform mid-infrared (ATR-FTIR) spectroscopic experiments.•Stratigraphic color enhancement using the R-package 'LESLIE' is facilitated by a user-friendly R-shiny application.

A cyclostratigraphic framework of the Upper Carboniferous Westoe and Cleaver formations in the southern North Sea Basin as a methodology for stratigraphic reservoir characterisation

Abstract Orbital driven climate control on sedimentation produces regional, stratigraphically repetitive characters and so cyclostratigraphic correlation can improve correlation and identify stratigraphic trends in borehole sections. This concept is commonly used to correlate marine and lacustrine strata. However, in the alluvial domain, its use is more challenging because internal, local dynamics controlling sedimentation may interfere with the expression of cyclic climate forcing. Intervals of low net-to-gross may be important for successful application in this domain as they tend to better document regional changes. This study applies climate-based stratigraphic correlation concepts to improve well correlations, characterise vertical sand distribution, and identify potential reservoir targets in a generally low net-to-gross interval. Coarsening upward sedimentary repetitions (cyclothems) are identified and correlated with high certainty in nineteen well sections in the upper Carboniferous Westoe and Cleaver formations of the Silverpit Basin. Local sedimentary dynamics provide variability in the character of the cyclothems and several types of cyclothem are classified. Correlation of sections using cyclothems recognised on wireline logs is done twice: once manually and once semi-automatically. The semi-automated correlation is based on calculation of deviation curves which depict stratigraphic changes that are less dependent on absolute wireline values and follow vertical trends more clearly. The correlations provide composite stratigraphies that are analysed using vertical proportions curves. Both approaches yield similar results in terms of stratigraphic trends. However, for detailed correlation of wells, the manual correlation is better at accounting for any local variability within the system. The same two zones of higher net-to-gross ratios are found using both correlation methods. These are linked to palaeoclimatic changes driven by long eccentricity and the proposed climate stratigraphic model has predictive value for identifying sandstone occurrence. The climate-based stratigraphic correlation improves the assessment reservoir distribution and properties on small (10–20 m thickness) and large (100–200 m thickness) stratigraphical scales.

Taphonomy and paleoecology of the Lontras Shale Lagerstätte: Detailing the warming peak of a Late Paleozoic Ice Age temperate fjord

Fjords are considered biodiversity hotspots and aquatic critical zones, being extremely sensitive to climate change due to close oceanic, terrestrial, and glacial interactions. These ecosystems have received a great deal of attention in research on current and future anthropic impacts. Despite this, there is no analog in the geological record that presents icehouse-greenhouse biological and climatic changes. Here we present an analog, through a detailed taphonomic survey of the Lontras Shale Lagerstätte (Itararé Group, Paraná Basin, Brazil), related to a climatic optimum of the end of the Late Paleozoic Ice Age (Late Pennsylvanian), in which a temperate outer paleofjord with a rich well-preserved biota was installed. In the monotone layers of black shale, we find subtle variations of the dominant skeletal type, rates of fragmentation and disarticulation, and other taphonomic aspects that define distinct taphofacies. Each of them is the result of distinct time-averaging related to mass mortality events, turbidity, and depositional hiatus periods at different scales and intensities, mixing the ecologic census with short-term and long-term within-habitat assemblages. In addition, the rich paleobiota was reconstructed with autochthonous and allochthonous benthic fauna, many marine nektonic organisms, and intense continental contribution of terrestrial bioclasts, that proliferated and were exceptionally preserved by the establishment of an anoxic temperate outer fjord. The taphofacies show an evolution in a high-frequency sequence within a highstand systems tract, linked to climatic improvement. Furthermore, taphonomic detailing can be used as a comparison of deep marine and deep lacustrine taphofacies, in addition to serving as an analog for the short-time scale biological, biogeochemical, climatic, and stratigraphic changes associated with the icehouse–greenhouse transition in the past, present, and future.

Geochemistry of the Cretaceous Mowry Shale in the Wind River Basin, Wyoming

The siliceous nature of the Mowry Shale distinguishes it from many of the well-studied organic-rich mudstones of the Cretaceous Western Interior Seaway. Available models of organic enrichment in mudstones rarely incorporate detailed biomarker, bulk organic, inorganic, and mineralogy data. Here, we used these data to evaluate how variations in organic matter source, productivity, dilution, and preservation modulated organic matter accumulation during the deposition of the Mowry Shale, while also demonstrating the benefits of this integrated approach. An organic stable carbon isotope vertical profile for the Mowry Shale is presented to test whether the Mowry Shale was deposited during oceanic anoxic event 1d (OAE 1d), thereby contributing to organic enrichment in the Mowry Shale. Samples were analyzed from three thermally immature drill cores collected from the Wind River Basin, Wyoming to advance our understanding of the conditions that led to the formation of the Mowry Shale. Results from bulk organic and inorganic geochemistry and biomarkers show that redox-driven preservation is closely coupled with stratigraphic changes in organic matter content in intermediate to distal settings of the Mowry Shale. Biogenic silica dilution decouples productivity and organic enrichment, such that the interval that was deposited during the highest productivity is offset from the interval containing maximum organic content. These findings contrast with previous studies that identified productivity as the primary driver of organic enrichment in distal settings of the Mowry Shale. The middle and lower Mowry Shale contain primarily marine organic matter, whereas the relative contribution of terrestrial organic matter increases in the upper Mowry Shale and overlying Frontier Formation as relative sea level declined and the western shoreline prograded eastward. Finally, the organic stable carbon isotope profile of the Mowry Shale together with recent radioisotopic dating suggest that the Mowry Shale postdates OAE 1d by ∼1−2 million years (m.y.), providing another example of temporal offset between organic matter accumulation in the Cretaceous Western Interior Seaway compared to other regions that record global OAEs.

Evolution of submarine channel morphology in intra-slope mini-basins: 3D-seismic interpretation from offshore Niger delta

The morphological characteristics of a submarine channel system, within buried intra-slope mini-basins in the offshore Niger Delta have been investigated on 3D seismic data. The studied submarine channel named Amaku Channel Levee System (ACLS) initiated after avulsion of a feeder channel called Amaku Major System (AMS). The ACLS runs across three folds (A, B, and C), related to mobile shale deformation, being underlain by mass transport complexes (MTCs), lobes, and levees. From three defined channel reaches (upper, middle, and lower reaches), we have used seismic facies description, channel architecture characterization and quantitative analyses to decipher the spatial and temporal evolution of the channel levee system. Our results reveal that the western channel margin was controlled by structural barriers associated with mobile shale deformation, while the eastern channel margin was influenced by depositional barriers linked to levees and mass transport complexes (MTCs). We argue that the depositional barriers are in some cases more efficient than the structural barriers in controlling channel pathways, since pre-channel sediments confine the channel elements and divert them against positive reliefs. Seismic observations show that channels migrate from folds to structural lows causing flow stripping processes. Downstream variations of morphological parameters (such as sinuosity, width, and levee width), indicate that pre-existing deposits prevented these basin-ward migrations, driving straightening and narrowing of the channel system. This study reveals that submarine channels can undergo dramatic morphological and stratigraphic changes in structurally complex areas because of the configuration of sidewall reliefs, which is controlled, in turn, by the interplay between structural deformation and pre-channel deposition.

Investigation of the maturation effects on biomarker distributions in bituminous coals

Biomarkers in coal can evolve dramatically in terms of their concentration and distribution during coalification, limiting their use in source allocation of coal-derived pollution. Here we analyzed a broad range of aliphatics (i.e., 26 n-alkanes, 6 isoprenoids, 32 terpanes, 19 steranes) and 77 polycyclic aromatic compounds (PACs) in the Permo-Carboniferous and Late Triassic coals from the Chinese Huainan and Da Baoding coalfields, respectively. These coals, classifying as high volatile bituminous B to low volatile bituminous with vitrinite reflectance (Rr) values ranging from 0.71 to 1.74 %, show variable organic geochemical features owing to the combined effects of thermal maturity and organofacies. Changes in the n-alkanes and isoprenoids indicate the loss of aliphatic fractions associated with maturation owing to cracking of the long-chain alkanes. The stratigraphic changes in the pristane to phytane ratios (Pr/Ph), Pr/n-C17, and Ph/n-C18 reflect a control exerted by the depositional environment in the Huainan coals. In addition, principal component analysis (PCA) recognizes the Pr/n-C17, Ph/n-C18, carbon preference index (CPI), and odd-to-even predominance 2 (OEP 2) as organofacies sensitive indices. Intercomparison of the PAC distributions suggest different maturation pathways for the coals from the Huainan and Da Baoding coalfields. The demethylation processes related to coalification preferentially occur on the polymethyl substitutes that occur to a greater degree in the Da Baoding coals than in the Huainan coals. Nine PAC indices display distinctive patterns when plotting against Rr. The DMP-2 vs DBT:DBF cross-plot explicitly separates the Huainan and Da Baoding coals into three distinctive zones representing different depositional environments and sources of organic matter. Moreover, PCA explicitly discriminate the maturation sensitive indices (i.e., MNR, DNR-1, TrMN-1, TrMN, TeMN, MPR, and MPI-1) from organofacies sensitive indices (i.e., DMP-2 and DBT:DBF).

Mars is a mirror – Understanding the Pahrump Hills mudstones from a perspective of Earth analogues

ABSTRACTMudstone‐dominated lacustrine strata in the Pahrump Hills area of Gale Crater, Mars, have the most extensive data set of physical and geochemical observations yet collected. Although sparse by Earth standards, a source‐to‐sink portrayal of the sedimentary system that differs substantially from previous work has been extracted by integrating sedimentology, stratigraphy, mineral and elemental analyses, geochemical modelling, laboratory experiments and Earth analogues in a sequence‐stratigraphic and palaeogeographical framework. Approximately 3.5 Ga, these 15 m thick strata contain five facies that range from fine to coarse detrital mudstone with abundant sediment‐incorporative evaporite pseudomorphs. The section is dominated by first‐cycle grains of minimally weathered primary igneous minerals but with four distinct compositions. Bedding in the mudstones comprises planar‐parallel beds, current ripples and wave‐induced structures, with common and widespread truncation. The absence of primary desiccation and synaeresis cracks is probably due to minimal clay‐mineral content, as supported by laboratory experiments. Evaporite minerals formed on and within detrital muds shortly after accumulation by evapoconcentration and cooling. The succession contains 16 parasequences in five depositional sequences with all the sequence‐stratigraphic elements known from terrestrial strata. Two of the sequence boundaries are unconformities that record significant shifts in the behaviour and palaeogeographical configuration of the fluvio‐lacustrine system. This contrasts with the previous view that all facies are genetically related. Most of the variability in rock composition can be attributed to stratigraphic changes in provenance that integrate changing drainage basin configurations, type of exposed bedrock and changes in weathering regime. These strata are interpreted as evaporative lake deposits that accumulated in an underfilled lake basin with closed surface hydrography but through‐flowing groundwater. Lake waters were saline to hypersaline, and lake levels, shorelines and salinities fluctuated greatly at various temporal scales.

Petrographic and chemical-technological characteristics coal seamsof the lower carbon,formation C12 of the kalmiusblock

Purpose. To establish the petrographic and chemical-technological features of the coal seams of formation C12 of the Kalmius block. Method. General scientific and applied research methods were used to fulfill the tasks. With the help of petrographic methods, the macroscopic and microscopic characteristics of the composition of coal were studied in detail, and the degree of its recovery and metamorphism was determined. With the help of chemical and technological methods, a comprehensive description of the composition and quality of coal is provided. The use of modern methods of analysis and interpretation made it possible to provide a generalized characteristic of coal seams, to reveal the peculiarities of their composition and quality. Findings. For the first time, regional ("provincial") features of the composition and quality of the coal formation C12 for Lower Donbass were revealed. Their typical petrographic composition was determined on the Kalmius block square. It was established that the coal of formation C12 differs from coal of formation C13 both in terms of gross petrographic composition and maceral composition. In addition, they are characterized by different degrees of recovery. It is proved that in the stratigraphic section, from the layers of the lower world to the layers of the upper world, the number of maceral groups of inertinite and liptinite increases, and the groups of vitrinite decrease. Lateral regularities of changes in the composition and quality of coal are determined. It was established that, compared to coal formation C13, higher values of sulfur content, heat of combustion, thickness of the plastic layer, and the Rog index are characteristic of coal formation C12. The elemental composition of the coal seams formation C12 is characterized by higher values of carbon and hydrogen content and significantly lower values of the amount of oxygen. Changes in the petrographic composition of Lower Carboniferous coal were revealed. The originality. For the first time, changes in the typical petrographic composition of coal in the Lower Carboniferous stratigraphic section of Southern Donbas, which indicate different conditions of formation of peatlands, were established. Practical implementation. The regional ("provincial") features of the region's coal have been clarified, lateral and stratigraphic changes in its composition and quality indicators have been determined, the grade composition of coal according to the new current standard in Ukraine has been established, and the technological value of formation C12 coal has been calculated.

Uranium isotope reconstruction of ocean deoxygenation during OAE 2 hampered by uncertainties in fractionation factors and local U-cycling

A δ238U record of changing ocean anoxia during OAE 2 is reconstructed using seawater derived U in pelagic marine sediments in the Portland #1 core in the south-central region of the Western Interior Seaway of North America. The peak negative excursion of 1.4‰ in authigenic sedimentary δ238U values is consistent with expansion of marine anoxia during the event, but the size of the shift is much larger than the negative excursions recorded in two other published records: (1) a pelagic chalk succession at Eastbourne (0.3‰) in the Paris-Anglo basin, and a black shale succession at Demerara Rise (0.15‰) in the proto-North Atlantic Ocean. By incorporating the estimated fractionation factors of processes governing removal of U into modern marine sediments, proxy data on pore fluid oxygen penetration into the sediment, faunal information on circulation in the Western Interior Seaway, and an ocean U box model, we identify and discuss the complications that hampered our effort to find a consensus value for the change in the δ238U value of the ocean U reservoir during OAE 2. These include: (1) strong local controls governing post-depositional uptake of seawater-derived U isotopes in marine sedimentary successions, and (2) local U cycling effects in epicontinental seas, which can work together or alone to mask the true change in the δ238U value of the ocean U reservoir during ocean anoxic events. Correcting the Portland record for stratigraphic changes in fractionation factors reduced the magnitude of the excursion to 0.9‰. Using an ocean U box model, this corresponds to 21% of the area of the seafloor covered by anoxic bottom waters during OAE 2. However, since the study setting represents an epicontinental sea that was located thousands of kilometers from the open ocean, we cannot exclude the possibility that the shift in seawater δ238U values was amplified by local U cycling effects, or that smaller negative excursions recorded elsewhere in the proto-North Atlantic Ocean were diminished by fractionation factor uncertainty and/or local U cycling in those settings.

Contradictory coeval vertical facies changes in upper Miocene heterozoan carbonate–terrigenous deposits (Sierra de Gádor, Almería, SE Spain)

ABSTRACT While spatial facies patterns can be observed in modern systems, only vertical facies successions can usually be examined in ancient deposits. Lateral facies relationships (depositional models) and relative sea-level changes throughout time are traditionally deduced from correlation of vertical facies successions along transects perpendicular to inferred paleo-shorelines. Establishing vertical facies successions and their corresponding time-equivalent proximal to distal facies patterns are, therefore, paramount in reconstructing ancient carbonate depositional systems and their response to sea-level change. In the present study of well-exposed panoramics of late Tortonian (8.1 Ma) mixed heterozoan carbonate and terrigenous deposits in La Chanata area in Sierra de Gádor, Almería, SE Spain, we show that frequent changes in facies width make it difficult to predict how variation in sea level impacts the facies distribution. The following facies are recognized: shoreline conglomerates directly overlie an erosion surface on the basement; terrigenous coralline-algal packstones extend basinwards from the conglomerates and are interpreted as shallow-water deposits stabilized by seagrass. There exist three types of facies consisting of relatively well-preserved, parautochthonous bioclasts, which occur generally seawards of the packstones: a) branching-coralline rudstones that formed from rhodolith (maërl) beds, both shorewards and basinwards from seagrass meadows where b) foliose-coralline rudstones to floatstones accumulated, and c) lenses of Heterostegina rudstones to floatstones changing laterally to any of the coralline algal facies. The factory facies of a–c show a patchy distribution with no definite arrangement in shoreline-parallel belts. The evolution of the depositional system is as follows: after filling paleovalleys in the erosion surface, deposition took place on a homoclinal ramp. The hybrid heterozoan carbonate–terrigenous deposits show a general retrogradation altered by one episode of proximal facies progradation. The width of facies across the ramp changes markedly in different episodes of relative sea-level rise: in several episodes of transgression, terrigenous coralline-algal packstones spread across the ramp locally overlying more distal facies, such as branching-coralline rudstones, thus generating regressive vertical patterns during relative sea-level rise. In other transgressive episodes packstones disappear, and the a–b factory facies pass laterally into conglomerate. The stratigraphic changes in facies width might be due to changes in general energy caused by climate variations or, alternatively, to the amount of relative sea-level rise. Large sea-level rise would result in relatively deep and calm conditions, thus favoring little fragmentation of large bioclasts during accumulation of the factory facies. Conversely, little change in accommodation would have resulted in higher-energy environments with concomitant increased physical erosion of the coralline-algae factories, thus resulting in mostly sand-size bioclasts in the packstones. In this environmental context, vertical change from distal to proximal facies can result from relative sea-level rise with increased mobilization and lateral expansion of proximal facies across the ramp. This outcome challenges the adequacy of using vertical lithofacies successions to reconstruct relative sea-level change in carbonate depositional systems.

Geochemistry and sedimentary photopigments as proxies to reconstruct past environmental changes in a subtropical reservoir

Sediment cores were used to establish past environmental impacts associated with eutrophication, erosion and metal contamination in the subtropical Atibainha reservoir (São Paulo State, Brazil). We hypothesize that: (1) the levels of nutrients, determined by a spectrophotometric method, reflect the contributions of these elements over time and (2) changes in sedimentation rates, determined by 210Pb geochronology, and metal flows, determined by ICP-AEOS, are related to anthropic activities. Stratigraphic changes in the analysed variables were used to divide the sediment cores into three intervals, according to PCA and cluster analysis (Euclidian distances, Ward's method). Interval I, composed by the period prior to operation of the reservoir, was influenced by organic matter levels. Interval II, between 1967 and 1993 (PC2: 14.94% of the total variability), a period of minor impacts, was mainly influenced by Mn (eigenvalue of 0.71) and Zn (0.74). Interval III, which included sediment deposited between 1993 and 2015 (PC1: 60.28% of the total variability), was influenced by the highest levels of the pigments lutein (0.86), zeaxanthin (0.90) and fucoxanthin (0.65), together with total nitrogen (0.78) and sedimentation rate (0.91), suggesting changes in the phytoplankton community composition probably associated to the intensification of eutrophication and erosion processes. Despite the limitations of applying paleolimnological techniques in reservoirs and the use of pigments as proxies in regions with higher temperatures, it was observed that the anoxic conditions and the aphotic environment in the hypolimnion acted to preserve pigments associated with the groups Chlorophyta (lutein), Cyanobacteria (zeaxanthin) and Bacillariophyta (fucoxanthin). The isolated analysis of nutrients was not sufficient to make conclusive inferences regarding the eutrophication history, since the levels of TP tended to decrease over time, in contrast to an increase in the levels of TN. Despite intensification of eutrophication and erosion, associated to anthropic activities, no signs of metal contamination were recorded.

Changes in Coral Skeleton Growth Recorded by Density Band Stratigraphy, Crystalline Structure, and Hiatuses

Next-generation high resolution brightfield microscopy, x-radiography, and microcomputed tomography (microCT) analyses indicate that coral skeleton high density band (HDB) and low density band (LDB) stratigraphic sequences record dynamic changes in coral growth history. HDB-LDB sequences were studied within three small heads of Orbicella annularis, an ecological keystone species in the Caribbean Sea, collected from the leeward fringing reefs on Curaçao. Results indicate that HDB layers are formed by the thickening of exothecal and endothecal dissepiments, costae, and theca located at the margin and external to individual skeletal cups (corallites). Conversely, septa and columellas located inside individual corallites do not change in thickness. HDB-LDB stratigraphic sequences were laterally traced from the center to the margins of individual coral heads, demonstrating that shifts took place in the trajectory of coral skeleton growth. Normal HDB layers in the center of individual coral heads are formed at the same time (age-equivalent) as surfaces of erosion and no skeleton growth (hiatuses) on the margins of the heads. These hiatus surfaces within HDB-LDB stratal geometries indicate that multiple marine ecological and environmental processes affect the orientation, size, shape, and geometry of coral skeletons during coral growth history. The presence of these hiatus surfaces in other large coral heads would strongly impact sclerochronology and the interpretation of multiple environmental factors including sea surface temperature (SST).

Late Holocene environmental change in Celestun Lagoon, Yucatan, Mexico

Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence of sea-level rise and coastal geomorphic change on these estuaries obscures climate signals, thus requiring careful development of paleoenvironmental histories to interpret the paleoclimate archives. We used foraminifera assemblages, carbon stable isotope ratios (δ13C) and carbon:nitrogen (C:N) mass ratios of organic matter in sediment cores to infer environmental changes over the past 5300 years in Celestun Lagoon, Yucatan, Mexico. Specimens (> 125 µm) from modern core top sediments revealed three assemblages: (1) a brackish mangrove assemblage of agglutinated Miliammina and Ammotium taxa and hyaline Haynesina (2) an inner-shelf marine assemblage of Bolivina, Hanzawaia, and Rosalina, and (3) a brackish assemblage dominated by Ammonia and Elphidium. Assemblages changed along the lagoon channel in response to changes in salinity and vegetation, i.e. seagrass and mangrove. In addition to these three foraminifera assemblages, lagoon sediments deposited since 5300 cal yr BP are comprised of two more assemblages, defined by Archaias and Laevipeneroplis, which indicate marine Thalassia seagrasses, and Trichohyalus, which indicates restricted inland mangrove ponds. Our data suggest that Celestun Lagoon displayed four phases of development: (1) an inland mangrove pond (5300 BP) (2) a shallow unprotected coastline with marine seagrass and barrier island initiation (4900 BP) (3) a protected brackish lagoon (3000 BP), and (4) a protected lagoon surrounded by mangroves (1700 BP). Stratigraphic (temporal) changes in core assemblages resemble spatial differences in communities across the modern lagoon, from the southern marine sector to the northern brackish region. Similar temporal patterns have been reported from other Yucatan Peninsula lagoons and from cenotes (Nichupte, Aktun Ha), suggesting a regional coastal response to sea level rise and climate change, including geomorphic controls (longshore drift) on lagoon salinity, as observed today. Holocene barrier island development progressively protected the northwest Yucatan Peninsula coastline, reducing mixing between seawater and rain-fed submarine groundwater discharge. Superimposed on this geomorphic signal, assemblage changes that are observed reflect the most severe regional wet and dry climate episodes, which coincide with paleoclimate records from lowland lake archives (Chichancanab, Salpeten). Our results emphasize the need to consider coastal geomorphic evolution when using epikarst estuary and lagoon sediment archives for paleoclimate reconstruction and provide evidence of hydroclimate changes on the Yucatan Peninsula.