Depositional Events Research Articles

APPLICATION OF AMINO ACID RACEMIZATION TO THE DATING OF FORAMINIFERS AND THE IDENTIFICATION OF REMANIÉ FOSSILS AND REWORKED SEDIMENTS

ABSTRACT The reworking of sediments and fossils is a pervasive element of the stratigraphical record and is frustrated by the fact that the taphonomic nature of fossils may not always reliably indicate the presence of remanié fossils. In this work, the extent of racemization of amino acids, a measure of fossil age based on an increasing ratio of D- to L-amino acids, is used to evaluate the integrity of the sedimentary record in selected case studies, based on the analysis of single foraminifers or samples containing fewer than 10 individuals. The short lifespan of foraminifers (c. 2–24 months), enhances their application for defining the age of sedimentary events, as they more closely relate to the age of the depositional event. The selected case studies range in spatial scale from defining the taphonomically active zone in geologically recent shallow marine sediments, to the application of foraminifers in reef island sediment budgets in Tarawa, to the reworking of foraminifers from Late Pleistocene calcarenites into modern beach sediments. The species Elphidium macelliforme, Amphistegina sp., and Lamellodiscorbis dimidiatus are shown to be particularly suited for amino acid racemization investigations of sediment reworking.

Towards a new generation of fluvial facies models for the interpretation of ancient deposits, based on inter‐annual peak discharge variance of modern rivers

ABSTRACTFluvial facies models based on river planform are flawed and not fully fit for purpose. An alternative approach to classifying fluvial deposits is based on river discharge characteristics. A recent paper showed that the co‐efficient of variance of annual peak discharge (CVQp) correlates well with the characteristics of preserved alluvium for a suite of modern rivers. Here, the database of rivers is expanded and augmented, and the utility of this statistic confirmed. For modern rivers, plotting the running‐value of CVQp for a set interval (for example, 30 years) over a longer discharge record shows that the statistic varies both spatially and temporally. The CVQp can rise abruptly at a given location in response to a single flow event if that event is significantly larger than is common in that river. Such abrupt changes in CVQp are superimposed on longer‐term patterns of more gradual change stimulated by environmental factors or anthropogenic effects such as dam construction. If the period of calculation for CVQp is relatively short, ‘anomalous’ events appear more frequently. Sequential studies of modern rivers indicate that such anomalous events have a high probability of being preserved in the alluvial record of the river, and suggest that, over the timeframes of channel filling and abandonment, they may constitute the dominant (characteristic) portion of the record in high CVQp systems. Since flow events with strongly peaked hydrographs (flashy discharges) are more common in high CVQp systems and leave a record dominated by upper flow regime stratification styles, it follows that the alluvial record of high CVQp rivers will be dominated by upper flow regime stratification. In contrast, in lower CVQp systems the occurrence of an event that changes the running CVQp value significantly may form a distinct event deposit, and the temporarily changed CVQp is unrepresentative for the duration of the channel's life. The dominance of upper flow regime stratification, together with decreased preservation of identifiable macroform structure, increased lateral lithological heterogeneity, and in many cases increased preservation of in situ tree fossils in channel deposits of higher CVQp rivers, forms the basis for a series of new facies models for low, moderate, high and very high/ultra‐high CVQp alluvial systems and deposits. The new models can be applied to ancient successions either in combination with traditional, planform‐based models, or not. These models provide information about ancient palaeoenvironmental conditions, and changes in such conditions over time at various scales via stratigraphic investigations.

Benthic response to event deposition and environmental disturbance in a shoreface to subaqueous delta system: Ichnology of the Silurian-Devonian Furada Formation of Asturias, Spain

Benthic response to event deposition and environmental disturbance in a shoreface to subaqueous delta system: Ichnology of the Silurian-Devonian Furada Formation of Asturias, Spain

A Detailed Sedimentological Analysis of Colour Lake, Axel Heiberg Island, Nunavut

This research project examines sediments in Colour Lake, a non-glacial lake on Axel Heiberg Island in the Canadian High Arctic. Analyzing the mineralogical composition, structural morphology and deposition patterns of the accumulated lake sediments provides information about the depositional environment and can serve as proxies for past environmental conditions. Work focused primarily on a 53 cm long sediment core collected in 2019. The objectives were: (1) to document distinct sediment units and interpret their depositional history by high resolution image analysis and microscopic observations in thin sections; (2) to identify schwertmannite, an iron oxyhydroxy-sulfate mineral within the sediments using scanning electron microscopy and x-ray fluorescence (XRF); (3) to determine this mineral’s relationship with siliciclastic deposits; and (4) to establish sediment chronology by 210Pb and 137Cs dating. Data was organized into pollen charts, incorporating images, scans, sediment stratigraphy, and grain size distributions to better understand sediment layers and their positions within the core. Thirteen lithozones were identified based on observed variations in the core, differing in terms of mud and clay lens distribution, the presence of schwertmannite, lamination patterns (graded or non-graded detrital laminations), the occurrence of biological components, and detrital mineral grain sizes. A recurring lithozone featuring non-graded, amorphous clay with schwertmannite, typically overlying either graded or reverse-graded mud, was observed throughout the core. While the mechanisms responsible for sediment deposition have not been fully explored, they are suspected to be related to hyperpycnal flows and slumping events. An Intervaled Sediment Extruder (ISE) was developed for precise sediment extrusion from a core collected in July for 210Pb and 137Cs dating, which will constrain sedimentation rates and correlate depositional events with past environmental conditions. Future work will focus on linking sediment structures to climatic events, identifying annually laminated layers (varves), and completing dating analyses to better understand past climate variations.

Volcanism and turbidity current events as drivers of the evolution of benthic redox conditions: Organic matter enrichment in the Chang 7 member, Upper Triassic Yanchang formation, Ordos Basin, North China

Depositional events have a significant impact on the terrestrial redox conditions and provide evidence for studying the organic matter enrichment. The objective of this study was to evaluate the influence of volcanic and turbidity current events on benthic redox conditions during the Upper Triassic Chang 7 member (Ch7) of the Ordos Basin. To address these issues, the varying sedimentological settings, paleoredox conditions, and relationships between the redox environment and depositional events were investigated via sedimentary analysis of the profiles, microscopic analysis, organic geochemical analysis, and elemental geochemical data. The fine-grained sediments in the Chang 73 submember (Ch73) consist of abundant organic matter, collophanite, and framboidal pyrite. However, in the upper part of the Ch7 member, there was a decrease in organic matter, a decrease in the number of microorganisms, and an increase in pyrite size, indicating that the oxic environment is not favorable for organic matter enrichment. The element and geochemical proxies show similar vertical variations and redox changes. Volcanic activity can bring substantial amounts of material or elements to the basin. The enrichment of Hg and S exhibited considerable variation, ranging from 8.7 to 274.4 ppb and from 0.16 to 4.53 wt%, respectively, which influenced the organic matter accumulation through the flourishing and death of microorganisms and redox changes in the benthic environment of the terrestrial basin. As the lake basin shrinks, the Ti and Al contents increase with increasing frequency of turbidity current events, and the terrestrial debris transported to the lake basin gradually increases while carrying large amounts of oxygen and affecting sedimentation rates, contributing to the destruction of the reducing conditions of the benthic environment, subsequently, influencing organic matter accumulation. These results will be helpful in understanding the effect of multiple depositional events on organic matter enrichment in lacustrine basins.

Chemostratigraphic characterization of the Lower Paleozoic Amdeh Formation outcrops and correlation to the subsurface Haima Supergroup and Nimr Group, Sultanate of Oman

A chemostratigraphic correlation between the siliciclastic Lower Paleozoic Amdeh Formation outcrops of the Saih Hatat area, just south of Muscat, and the hydrocarbon-bearing Haima Supergroup and Nimr Group of subsurface Oman is presented. The Amdeh Formation is a 3.4 km-thick succession of Cambrian to Ordovician-aged sandstones and shales, divided into five lithological members (Am1–Am5). The Amdeh Formation type section was sampled throughout for inorganic elemental geochemistry, quantitative mineralogy and U–Pb zircon geochronology. A robust chemostratigraphic framework for the equivalent Haima Supergroup and Nimr Group intervals, defined in the subsurface, is utilized to correlate with the Amdeh Formation. The Amdeh is interpreted to be a basinward, fully marine, time equivalent of the subsurface Haradh (and likely also the Karim), Amin, Miqrat, Al Bashair, Barik, Mabrouk, Barakat, Ghudun and Saih Nihayda formations. This correlation is based on the identification of key mineralogical, depositional, provenance and sequence stratigraphic events within the inorganic geochemical data, guided by outcrop observations of depositional facies and key surfaces, and existing biostratigraphy. Positioned beyond the northern edge of the Ghaba Salt Basin, the Amdeh Formation outcrops provide important constraints on subsurface reservoir distribution, palaeogeography and basin evolution, factors that are relevant to deep gas prospectivity.

Detrital K-feldspar as a novel archive of continental crustal evolution using coupled in situ Rb[sbnd]Sr dating and Pb isotope analysis

Here we present in situ RbSr and Pb isotopic analysis of K-feldspar from the Shap Granite, (Cumbria, UK) and detrital K-feldspar from the associated Shap Wells Conglomerate Formation, to investigate the potential of the detrital K-feldspar record as an archive of crustal composition. We use a unique, collision cell – multi collector inductively coupled plasma tandem mass spectrometer to make the in situ isotope measurements, using ‘chemical resolution’ of 87Rb+ and 204Hg+ isobaric interferences on 87Sr+ and 204Pb+, achieved with SF6 and NH3 reaction gases, respectively. Using this technique, we successfully demonstrate that the majority of detrital K-feldspar RbSr ages, as well as initial Sr and Pb isotope ratios, from the Shap Wells Conglomerate are within uncertainty of those for parental Shap Granite K-feldspar (398 ± 1 Ma, n = 6). Some detrital K-feldspar grains record perturbed RbSr ages, reflecting post depositional alteration events. The majority of samples with disturbed RbSr ages carry distinct petrographic features evident in SEM imaging, prior to in situ dating, which indicates a means to help screen for reliable ages.We further illustrate the potential value of combined RbSr and Pb isotopic information preserved in K-feldspar to estimate the timing and chemical composition of juvenile continental crust formed in the past. Where UPb has been fractionated during juvenile crust formation, the initial Pb isotope ratio provided by the K-feldspar yields model crustal U/Pb (diagnostic of tectonic setting) and extraction age. The contrast in the U/Pb composition of juvenile crust formed in intraplate or subduction settings allows the model U/Pb ratios of the detrital K-feldspars to be used to constrain the style of juvenile crust formation. Additionally, the initial 87Sr/86Sr isotope ratio measured in detrital K-feldspar can be combined with the calculated crustal extraction age and RbSr K-feldspar age to model the Rb/Sr of the juvenile crustal protolith.

Post-glacial stratigraphy and late Holocene record of great Cascadia earthquakes in Ozette Lake, Washington, USA

Ozette Lake is an ~100-m-deep coastal lake located along the outer coast of the Olympic Peninsula (Washington, USA); it is situated above the locked portion of the northern Cascadia megathrust but also relatively isolated from active crustal faults and intraslab earthquakes. Here we present a suite of geophysical and geological evidence for earthquake-triggered mass transport deposits (MTDs) and related turbidite deposition in Ozette Lake since ca. 14 ka. Comprehensive high-resolution bathymetry data, seismic reflection profiles, and sediment cores are used to characterize the post-glacial stratigraphic framework and examine paleoseismic evidence in the lacustrine sediments. Stacked sequences of MTDs along the steep eastern flanks of the lake appear to grade basin-ward from thick, chaotic, blocky masses to thin, parallel-bedded turbidite beds. The discrete turbidite event layers are separated by fine-grained (silt and clay) lake sedimentation. The event layers are observed throughout the lake, but the physical characteristics of the deposits vary considerably depending on proximity to primary depocenters, steep slopes, and subaqueous deltas. A total of 30–34 event deposits are observed in the post-glacial record. Radiometric dating was used to reconstruct a detailed sedimentation history over the last ~5.5 k.y., develop an age model, and estimate the recurrence (365–405 yr) for the most recent 12 event layers. Based on sedimentological characteristics, temporal overlap with other regional paleoseismic chronologies, and recurrence estimates, at least 10 of the dated event layers appear to be sourced from slope failures triggered by intense shaking during megathrust ruptures; the recurrence interval for these 10 events is 440–560 yr. Thus, Ozette Lake contains one of the longest and most robust geological records of repeated shaking along the northern Cascadia subduction zone.

Japan Trench event stratigraphy: First results from IODP giant piston coring in a deep-sea trench to advance subduction zone paleoseismology

The International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology, represents the first utilization of giant piston coring (GPC) within scientific ocean research drilling. This allowed for a Mission Specific Platform (MSP) multi-site, multi-hole, shallow subsurface coring in an ultra-deep water subduction zone trench. The primary objective of the expedition was to investigate the concept of submarine paleoseismology in the Japan Trench, which involves studying long-term records of deposits in the deep sea that can provide insights into past earthquake events. In this paper, we compile and interpret initial shipboard data and results to (1) establish first-order event stratigraphic correlation of thick event beds (> 50 cm in thickness) between sites, (2) test previously published event-stratigraphic predictions of earthquake-related event deposits as proposed based on high-resolution hydro-acoustic subbottom profiler (SBP) data, and (3) derive SBP-scale event deposits age estimates to (4) discuss the advantages and limitations of giant piston coring for scientific drilling operations and the potential of new event stratigraphy results for advancing submarine paleoseismology.The findings of the study identified a total of 77 SBP-scale event beds across 15 sites along a trench-parallel transect spanning over 600 km. These event beds exhibit clear expressions in SBP data, with approximately 49 % matching precisely with SBP units previously identified by Kioka et al. (2019a). For the remaining 51 % of SBP-scale event beds, thin, acoustically-transparent bodies were observed between high-amplitude horizons, for which SBP-based seismic interpretation alone would not be definitive. Consequently, the study concluded that the SBP-scale event-stratigraphy observed in IODP 386 cores validates the event-bed mapping conducted by Kioka et al. (2019a) and improves SBP interpretation for event beds in the 0.5 to 1 m thickness range.The initial age constraints obtained from shipboard radiolarian biostratigraphy enable us to provide rough estimates of event ages by linearly interpolating between previously dated events occurring less than 2000 years ago and a datum around 11,000 years ago reported in four boreholes from trench basins in the Southern, Central, and Northern Japan Trench. Inter-site stratigraphic correlation reveals distinct SBP-scale event stratigraphies for the trench segments located to the north and south of the structurally complex “boundary area” at approximately 39.3–39.4°N, which is hypothesized to potentially act as a persistent rupture barrier for megathrust earthquakes. We observe more frequent but thinner event deposits in the Southern and Central Japan Trench, and fewer but thicker event beds in the Northern Japan Trench. This spatial variation may be related to the different seismogenic behavior of the various asperities along the Japan Trench megathrust and/or to differences in the response of slope sediments to earthquake shaking. However, here-presented investigations at the SBP-scale level are deemed too simplistic for robust application of the “submarine paleoseismology” approach. The extensive and high-quality dataset from IODP GPC, coupled with the encouraging initial correlation results presented here, leads us to hypothesize that further detailed studies can identify and characterize event deposition dynamics at the micro-facies level, refine sediment provenance, and constrain precise event ages necessary for evaluating synchronicity in paleoseismological interpretation. These studies will also enable robust exploration of along-strike correlations or variations, facilitating the extraction of paleo-earthquake signals from Japan Trench event stratigraphies.

Sedimentary signatures of large earthquakes along the submerged Enriquillo–Plantain Garden transpressional plate boundary, northern Caribbean

Abstract The Enriquillo–Plantain Garden fault (EPGF), the southern branch of the northern Caribbean left-lateral transpressional plate boundary, has ruptured in two devastating earthquakes along the Haiti southern peninsula: the Mw 7.0, 2010 Haiti and the Mw 7.2, 2021 Nippes earthquakes. In Jamaica, the 1692 Port Royal and 1907 Great Kingston earthquakes caused widespread damage and loss of life. No large earthquakes are known from the 200-km-long Jamaica Passage segment of this plate boundary. To address these hazards, a National Science Foundation Rapid Response survey was conducted to map the EPGF in the Jamaica Passage south of Kingston, Jamaica, and east of the island of Jamaica. From the R/V Pelican we collected >50 high-resolution seismic profiles and 47 gravity cores. Event deposits (EDs) were identified from lithology, physical properties, and geochemistry and were dated in 13 cores. A robust 14C chronology was obtained for the Holocene. A Bayesian age model using OxCal 4.4 calibration was applied. Out of 58 EDs that were recognized, 50 have ages that overlap within their 95% confidence ranges. This allowed for their grouping in multiple basins located as much as 150 km apart. The significant age overlap suggests that EDs along the Enriquillo–Plantain Garden plate boundary resulted from large and potentially dangerous earthquakes. Most of these earthquakes may derive from the EPGF but also from thrust faulting at this strain-partitioned transpressional boundary. The recent increase in Coulomb stress on the EPGF from the Mw 7.2 Nippes earthquake in southwestern Haiti and the discoveries reported here enhance the significance for hazard in the Jamaica Passage.

Iron species and sulfur isotopic compositions of authigenic pyrite in deep-sea sediments at southern Hydrate Ridge, Cascadia margin (ODP Leg 204): implications for non-steady-state depositional and diagenetic processes

Two accretionary sediment sequences from Sites 1245 and 1252 recovered during Ocean Drilling Program (ODP) Leg 204 at southern Hydrate Ridge were investigated to explore the response of geochemical partitioning of iron and sulfur isotopic composition of authigenic pyrite to non-steady-state depositional and diagenetic scenarios. Five iron species were characterized by a modified sequential extraction procedure that covers almost all iron-bearing minerals in sediment cores, including: (1) iron-bearing carbonates, mainly siderite; (2) ferric (hydr)oxides, probably ferrihydrite and/or lepidocrocite; (3) magnetite; (4) iron-bearing silicates; and (5) pyrite. Highly reactive iron has been accumulated for a long-term steady-state history and its pyritization, to varying degrees, is limited by availability of dissolved sulfide. This causes pyrite and siderite occurred in the same sedimentary layer and shows an inverse relationship between their concentrations. From this, their proportions to highly reactive iron can be chosen for evaluating the degree of sulfidization. A significant change in sulfur isotopic composition of pyrite (-42.4 to +16.8‰ VCDT) indicates that the steady-state conditions are dramatically limited, where the δ34S values higher than -20‰ may result from an upward shift of SMT zone close to the seafloor or a sudden, massive depositional event. To explain the downcore sulfidization effects and pyrite δ34S values, we developed two categories of conceptual scenarios based on variations in sedimentation rate and methane flux. The geochemical features similar to those derived from each scenario were searched in the sediment columns and the non-steady-state events behind the scenarios were proved to be consistent with the real observations. Thus, iron species and pyrite δ34S values can be regarded as a proxy to differentiate different non-steady-state depositional and diagenetic controls on the sedimentary record.

Not all shell beds are made equal: Recognizing singular event‐concentrations in megalakes

ABSTRACTEvent deposition accounts for a large part of the preserved sedimentary record. Tempestites, tsunamites and turbidites are among the most common event deposits in marine and lacustrine systems. While facies models exist for these deposits, the challenge lies in the fact that diverse triggers can give rise to analogous depositional processes and comparable taphonomic features, making it difficult to pinpoint the precise trigger for an event bed. Hence, five distinct modern‐type shell concentrations are studied in Permian strata from the Paraná Basin, West Gondwana, to access the parameters to discriminate event phenomena, and their associated depositional and taphonomic processes. During this time interval, the basin underwent continuous continentalization due to orogenic events, leading to the entrapment of epeiric marine waters and the transformation of the system into a megalake, supporting a diverse and endemic freshwater bivalve fauna. While sedimentation was primarily influenced by meteorological events, certain stratigraphic intervals were also affected by tectonically active periods and meteor impact events. The different products are categorized into bioclastic sandstone, shell bed, shell‐rich phosclast rudstone and shell‐rich conglomerate that are interpreted as proximal and distal tempestites and tsunamites, respectively. Finally, the products and the processes that lead to the deposition of tempestites and tsunamites are compared to establish diagnostic signatures that may be applied to differentiate these event concentrations in analogous settings from the geological record.

Single-grain luminescence and combined U-series/ESR dating of the early Upper Palaeolithic Lagar Velho Rock Shelter, Leiria, Portugal

The existing radiocarbon (14C) dating framework for Lagar Velho is broadly consistent but provides limited constraint on several geoarchaeological complexes (GCs) and does not favour detailed chronological comparisons across all sectors of the site; including the stratigraphically disconnected child burial complex in the east area and the broader archaeological sequence in the central-west area. In this study, we undertake a complementary chronological assessment of Lagar Velho Rock Shelter using single-grain quartz OSL, single-grain quartz TT-OSL and combined U-series/ESR dating of fossil teeth, with the aim of establishing more comprehensive reconstructions of archaeological events and placing the human occupation sequence in a firmer regional climatic context. Expanding on the original chronological study, we also compare the published 14C datasets against widely used sample quality indicators (i.e., organic preservation and contamination proxies) to ensure reliable comparisons with our new luminescence and combined U-series/ESR ages. Eight 14C samples pass our combined chronological and stratigraphic hygiene criteria and are included in the final dating evaluations. Ten of the twelve optical dating samples produce homogeneous equivalent dose (De) datasets indicative of suitable daylight exposure. The replicate single-grain TT-OSL De datasets exhibit more pronounced scatter, consistent with enhanced potential for insufficient bleaching of TT-OSL residual doses in some karst settings. The fossil enamel samples dated using U-series/ESR span relatively low natural dose ranges, necessitating the inclusion of maximum dose (Dmax)-adjusted dose response curve fitting and additional background noise subtraction to avoid De biases of up to 13%. Stratigraphically consistent ages (n = 26) spanning the full archaeological infill sequence are obtained using the four different dating methods, providing a robust interpretive framework and underscoring the significant role of single-grain OSL and combined U-series/ESR dating for refining early Upper Palaeolithic histories of Iberia. Bayesian modelling of the combined chronological dataset reveals a site accumulation history spanning 35,750–23,440 cal. BP and provides improved age constraints on all GCs; particularly the al, bs, tc, gs and ls deposits that were previously undated or imprecisely constrained. The age of the child burial complex is refined to 29,410–28,280 cal. BP, potentially occurring within Greenland Interstadial 4. Comparison of the modelled GC ages from the east and west-central areas enables improved temporal correlations of depositional events across stratigraphically disconnected sectors of the site. This analysis suggests that the child burial complex and the Late Gravettian occupation are statistically indistinguishable based on current dating evidence. The new dating assessments reveal three periods of human occupation at Lagar Velho: the Late Gravettian (including the shorter duration child burial event) 31.6–26.0 ka from the end of Heinrich Stadial (HS) 3 until the emergence of HS2; the Terminal Gravettian 26.5–24.5 ka coinciding with HS2; and the Middle Solutrean 25.2–23.4 ka extending from HS2 to the end of Greenland Stadial 3. The timing of these occupations during late Marine Isotope Stage (MIS) 3 and early MIS 2 highlights the significance of central western Portugal for supporting regional human populations during periods when much of Europe was experiencing extreme cold, aridity and expanded glacial coverage.

Uranium enrichment driven by paleomarine condition and event deposition: Insights from the lower Cambrian Niutitang Formation organic-rich shales in northeastern Guizhou, South China

Organic-rich shale related uranium (U) mineralization has attracted widespread attention as a strategic and clean alternative to fossil energy and a paleoceanic redox proxy. A comprehensive study of mineralogy, organic geochemistry and elemental geochemistry of the lower Cambrian Niutitang Formation organic-rich shales in northeastern Guizhou, South China was conducted to address this issue. SEM-EDS results showed that the U occurrence state in the Niutitang Formation shales is dominated by nanoscale U minerals, mainly including coffinite, brannerite, U-bearing apatite and U-bearing xenotime. Various states of U are closely associated with organic matter, apatite, pyrite and clay minerals. Based on geochemical indexes, paleomarine condition and event deposition jointly drove the U enrichment in the Niutitang shales, in which hydrothermal activities and/or volcanic eruptions increased U fluxes in seawater and euxinic environment with high primary productivity provided a favorable condition for U reduction. The adsorption, complexation and reduction of UO22+ by organic matter and the formation of uranyl phosphate complexes by the combination of phosphate and UO22+ accelerated U immobilization and enrichment from bottom water to sediments. The microbial activities (e.g., BSR) in this process created favorable euxinic conditions and released inorganic-phase P to provide available ligands for UO22+. The U enrichment models of the lower Cambrian Niutitang shales in northeastern Guizhou were established. This paper provides a new insight into the U enrichment mechanism in organic-rich shales, and may also have implications for the applicability of U as redox proxy and the exploration of organic-rich shale related U deposits.

In situ forest with lycopsid trees bearing lobed rhizomorphs from the Upper Devonian of Lincheng, China.

The earliest forests in the Devonian were reported from only four localities worldwide. The tree lycopsids, sometimes as the primary elements of Devonian forests, had evolved several types of rooting systems. In recent years, we found and excavated a Late Devonian (Famennian, 374-359 Ma) lycopsid forest from Zhejiang Province, China. The fossil forest occurs at seven locations of Lincheng Town of Changxing County and mainly consists of in situ small tree lycopsid (Heliodendron longshanense gen. et sp. nov.) stems usually connected to lobed cormose rhizomorphs. The four short lobes of each rhizomorph often branch once and bear roots arranged radially. Allometry is observed between the trunk diameter of Heliodendron and the length of its rhizomorphic lobes, indicating that the trunk develops later than the rhizomorph in tree lycopsid plants. The Devonian witnessed the transformation from clastic nonlycopsid dominated forests to Carboniferous swampy forests dominated by giant lycopsid trees. These trees form a multigenerational community, as shown by the in situ preserved stems at various levels within the same area due to frequent sedimentation events.

Stochastic representation and conditioning of process-based geological model by deep generative and recognition networks

Accurate and realistic geological modelling is the core of oil and gas development and production. In recent years, process-based methods are developed to produce highly realistic geological models by simulating the physical processes that reproduce the sedimentary events and develop the geometry. However, the complex dynamic processes are extremely expensive to simulate, making process-based models difficult to be conditioned to field data. In this work, we propose a comprehensive generative adversarial network framework as a machine-learning-assisted approach for mimicking the outputs of process-based geological models with fast generation. The main objective of our work is to obtain a continuous parametrization of the highly realistic process-based geological models which enables us to calibrate the models and condition the models to data. Numerical results are presented to illustrate the capability of our proposed methodology.

Impact of Hurricane Irma on coral reef sediment redistribution at Looe Key Reef, Florida, USA

Abstract. Understanding event-driven sediment transport in coral reef environments is essential to assessing impacts on reef species, habitats, restoration, and mitigation, yet a global knowledge gap remains due to limited quantitative studies. Hurricane Irma made landfall in the Lower Florida Keys with sustained 209 km h−1 winds and waves greater than 8 m on 10 September 2017, directly impacting the Florida Reef Tract (FRT) and providing an opportunity to perform a unique comprehensive, quantitative assessment of its impact on coral reef structure and sediment redistribution. We used lidar and multibeam derived digital elevation models (DEMs) collected before and after the passing of Hurricane Irma over a 15.98 km2 area along the lower FRT including Looe Key Reef to quantify changes in seafloor elevation, volume, and structure due to storm impacts. Elevation change was calculated at over 4 million point locations across 10 habitat types within this study area for two time periods using data collected (1) approximately 1 year before the passing of Irma and 3 to 6 months following the storm's impact as well as (2) 3 to 6 months after and up to 16.5 months after the storm. Elevation change data were then used to generate triangulated irregular network (TIN) models in ArcMap to calculate changes in seafloor volume during each time period. Our results indicate that Hurricane Irma was primarily a depositional event that increased mean seafloor elevation and volume at this study site by 0.34 m and up to 5.4 Mm3, respectively. Sediment was transported primarily west-southwest (WSW) and downslope, modifying geomorphic seafloor features including the migration of sand waves and rubble fields, formation of scour marks in shallow seagrass habitats, and burial of seagrass and coral-dominated habitats. Approximately 16.5 months after Hurricane Irma (during a 13-month period between 2017 and 2019), net erosion was observed across all habitats with mean elevation change of −0.15 m and net volume change up to −2.46 Mm3. Rates of elevation change during this post-storm period were 1 to 2 orders of magnitude greater than decadal and multi-decadal rates of change in the same location, and changes showed erosion of approximately 50 % of sediment deposited during the storm event as seafloor sediment distribution began to re-equilibrate to non-storm sea-state conditions. Our results suggest that higher-resolution elevation change data collected over seasonal and annual time periods could enhance characterization and understanding of short-term and long-term rates and processes of seafloor change.

Rapid morphosedimentary development of a shallow subtropical embayment in response to extreme episodic flooding

Variability in supply of terrestrial sediments to the coastal zone impacts sediment transport processes and ecological dependencies. This study investigated surface sediment distribution and transportation within a 2020 km2 shallow embayment following a period of flood induced sediment supply. Extensive field sampling of 221 common sites between 2015 and the 2019 follow-up survey presented, identified significant reduction in fine sediment fractions, evident through a 367 km2 decrease in surface mud coverage. Wind-wave sediment transport processes controlled the spatial distribution of fine sediments, exporting 23 million tonnes of mud from the shallow sedimentation zones. In a broader context, sensitive benthic habitats such as seagrass meadows exhibited signs habitat recolonisation coinciding with areas of reduced mud content. Despite these promising short-term outlooks, the developed fine sediment budget suggests ongoing terrestrial sedimentation will exhaust key sediment sinks within Moreton Bay, effectively reducing the system's ability to buffer future sedimentation events.

Initiation of the Unazuki Belt, Southwest Japan, during the Carboniferous as an island arc system along the North China Craton

The Unazuki Belt, Southwest Japan, is a part of the Hida Belt, which is characterized as a plutono-metamorphic complex with a continental affinity formed between the late Paleozoic and early Mesozoic. The Unazuki Belt is known to be an important tectonic unit for the tectonic correlation between the proto-Japan and East Asian continents as it records Permo–Triassic tectono-thermal events, however, comprehensive chronology of the Unazuki Belt including the timing of the initiation of this Belt is yet unclear. The present study reveals certain Carboniferous magmatic and sedimentation events from the Unazuki Belt and their tectonic implications for the first time as follows. Zircon U–Pb age dating results and whole-rock geochemical compositions show that the protoliths of metagranite and metatrachyandesite in the Unazuki Belt formed at 328.2 ± 4.4 Ma and 332.8 ± 2.2 Ma, respectively, in an arc tectonic setting. Most metasedimentary rocks of the Unazuki Belt have the youngest detrital zircon grains of ~ 300 Ma with the Carboniferous single cluster at ~ 340–300 Ma without any Pre-360 Ma detrital zircon grains. However, one metasedimentary rock with Precambrian detrital zircons (~ 20%) has the youngest detrital zircon age of ~ 252 Ma, and ~ 66% of detrital zircons show a Permian age. Most of the εHf(t) values of zircon grains from all the studied Unazuki Belt samples, including the metasedimentary and metaigneous rocks with Carboniferous ages (~ 360–300 Ma) are positive (+ 6– + 18), whereas those of the zircon grains with Permian ages (~ 280–260 Ma) show wide variations between + 16 and -23. The whole-rock geochemical compositions of the ~ 300 Ma metasedimentary rocks of the Unazuki Belt show an island arc tectonic setting, whereas those of ~ 252 Ma metasedimentary rock have a continental arc affinity. These new data suggest that (1) igneous and sedimentary rocks in the Unazuki Belt formed in the island arc tectonic setting separated from the margin of continental crust during the Carboniferous but shifted to the continental arc tectonic setting during the latest Permian, (2) the collision between the island arc and continental arc may have caused the intermediate-P/T metamorphism during the Permian in the Unazuki Belt. The Carboniferous island arc tectonic setting in the Unazuki Belt indicates that the Hida Belt, including the Unazuki Belt, formed not at the margin of the South China Craton where Carboniferous subduction is absent but on the continuous subduction zone located along the eastern margin of the North China Craton, including the eastern margin of the northern Korean Peninsula where Carboniferous subduction occurred.Graphical

Random and time-persistent depositional processes in turbidite successions: an example from the marine deep-water Aoshima Formation (Neogene, Kyushu Island, southwest Japan)

ABSTRACT The deposits of flood- and earthquake-derived subaqueous sediment gravity flows represent a significant fraction of lacustrine and deep-sea sedimentary successions, thus providing a valuable record of such natural disasters. The magnitude of these events and the thickness of the associated deposits are considered to follow a lognormal or power-law frequency distribution, whilst that of time intervals between subsequent events appear to be best approximated by a Poisson model, indicative of a random, time-independent phenomenon. However, the debate on whether the sedimentary record of these natural disasters is governed by randomness alone or whether there is some underlying stratigraphic ordering is still unsettled and requires detailed time-series analysis. This study consists of a time-series analysis of mudstone- and sandstone-dominated turbidite successions offshore a fan-delta system in the Neogene Aoshima Formation that belongs to the sedimentary fill of the forearc basin of southwest Japan. The formation consists of a monotonous alternation of very fine- to medium-grained sandstones capped by hemipelagic mudstones and, more rarely, by turbidite mudstones. The results show that the autocorrelation function of the time series suggests quasi-periodic variability in the upper sandstone-dominated part, whereas the lower mudstone-dominated part shows a white-noise-like pattern. Rescaled range analysis shows that the number of events per unit time in the lower part is characterized by a random time series, such as Brownian noise with a Hurst exponent of 0.5. In contrast, the thickness of event beds of the lower part and the thickness and the number of events of the upper part are persistent time series with a Hurst exponent > 0.5. These results suggest that the number of turbidite depositional events in the mudstone-dominated part indicates random timing, whereas its thickness time series and the sandstone-dominant part are not governed by simple stochastic processes but are affected by sea-level changes, sediment transport dynamics, and other factors such as, for example, seafloor topography.