Sedimentary Record Research Articles

Archive and library special collections as proxy data: reconstructing the American chestnut blight through digitized collections

This paper discusses the design and implications of a study that explored the potential for archives and library special collections to serve as historical environmental proxy data to support the reconstruction of the spatiotemporal spread of the American chestnut blight in Tennessee. By collecting, reconciling, and analyzing heterogeneous mundane primary source materials from 1904 to 1950, the major period of infection and tree loss, the case study reached beyond conventional evidence to ask new questions of nontraditional sources. QGIS and Python were used to reconcile and model nonstandardized and ambiguous natural-language keywords derived from these sources to identify trends and patterns that may not be evident from traditional document analysis. The paper argues that the contributions made by textual and visual information fragments found in these materials support an expansion of the term “proxy data” beyond what is currently understood as paleoclimate archives, i.e., physical, chemical, and biological materials preserved within the geologic record (USGS 2022). Such socially constructed records found in archives and library special collections offer additional qualitative and quantitative information about historical climate change to support modeling variable fluctuations over time. They can also provide a rich and dynamic context for the natural causes and human interventions that, in combination, act on the environment. However, the study also identifies significant limitations in the digital accessibility of relevant archival sources and a lack of specificity in their descriptions. These need to be addressed if integrating such source material into scientific studies is to become more widespread and scalable.

Radiogenic heat production provides a thermal threshold for Archean cratonization process

A striking feature of the Yilgarn craton at the current erosional level is an abundance of late K-rich granites with radiogenic heat production elevated far above global crustal averages. Extrapolated back in time, the total thickness and contribution to crustal heat production and heat flow from these granites were greater, implying that the deeper crustal sources must also have had elevated radiogenic heat production. Through back-calculated and time-integrated one-dimensional thermal modeling underpinned by geological and geochemical constraints for the model crustal columns, we find that elevated radiogenic heat production provided a significant internal driver for prolonged crustal melting and eventual cratonization of the Yilgarn craton. Our results show that elevated thermal gradients driven by high heat production thermally primed the mid- and deep crust at or above the threshold for large-volume partial melting over long periods of time, as evidenced in the magmatic rock record. This would have been amplified by any additional heat that may have been provided by the mantle melting processes that punctuated the geological history. Over time, advective movement of progressively more radiogenic heat production to the shallower crust would have resulted in two complementary outcomes: progressively refractory deep crust and long-term cooling. The widespread granite “bloom” at 2650−2600 Ma records the final time at which the crust was fertile enough to melt in large volumes and the thermal gradient was hot enough to intersect the solidus. The magnitude of radiogenic heat production in the Yilgarn craton has been underestimated in previous studies, resulting in an underappreciation of the importance of its contribution to internal drivers of magmatism and ultimately cratonization.

Holocene onshore/offshore tephra correlation of Mt. Etna, Sicily

The volcanic history of Mt. Etna is mainly known from studies of subaerial deposits and stratigraphy. However, little is known about the offshore deposits, which can provide a more detailed insight into geological and sedimentological processes affecting the flanks of Mt. Etna. During RV Meteor Cruise M178, eight gravity cores were taken offshore across the continental margin east of the volcanic edifice to re-evaluate the volcanic history of pre-historic eruptions and mass wasting events in the area. In total, we investigated 87 marine tephra layers in order to build a marine tephrostratigraphic framework. Based on major element compositions of glass shards, sediment componentry, and petrographic characteristics, 27 layers were identified as primary pyroclastic flow and fall deposits, i.e., directly related to an explosive volcanic eruption. However, most of the remaining tephra layers are interpreted to represent deposits of secondary density currents and are not necessarily related to a volcanic eruption. The marine dataset is complemented by twelve onshore samples taken from major explosive eruptions. Applying geochemical fingerprinting of volcanic glass shard compositions, we correlated eleven marine tephra deposits to seven well-known Mt. Etna eruptions (FV, FF, FG, FL, FS, TV, and M1 eruptions) within the last 12 kyr, which provide valuable time markers in the marine sediment record. Furthermore, we correlated ten marine tephra layers between the marine cores (four individual eruptions) and identified another six primary layers in single cores. In total, we discovered 17 widespread volcanic events in the marine record, including four previously unknown eruptions between 10 and 7.7 ka, which indicate that Mt. Etna was more active than previously thought during this time period.

Multi-century geological data thins the tail of observationally based extreme sea level return period curves

Estimates of extreme sea-level return periods guide flood hazard mitigation. Return period estimates calculated from tide gauge records, which are relatively short (typically less than 100 years), can fail to capture the rarest and most potentially impactful extreme events. Here, we employ a two-dimensional Poisson point process model to fuse water-level data from tide gauges with data from multi-century geologic records of extreme overwash events. Experiments with synthetic data show that including geologic data reduces the uncertainty of 1% and 0.1% average annual chance water levels by about half, relative to using tide gauge data alone. Similar uncertainty reductions occur with two case studies of geologic data (Mattapoisett Marsh, Massachusetts and Cheesequake, New Jersey) and their neighboring tide gauges (Woods Hole, Massachusetts and the Battery, New York). The analysis also reveals non-stationarity at Cheesequake and The Battery, arising from either climatic changes or changes in the fidelity of the geological record, with substantially higher 1–10% average annual chance water levels since 1900 compared to prior centuries.

Geology and landforms of Two Peoples Bay Nature Reserve, Western Australia

Context Underlying geology strongly influences landforms, soil composition, and hydrogeology in Two Peoples Bay Nature Reserve, Western Australia, which was mapped by P. E. Playford in 1982. Aims To review the mapping of the Reserve, with the aim to better understand the geological history and landforms of the area. Methods In 2024, I. M. Tyler and K. A. Evans reviewed P. E. Playford’s mapping in the field, viewed aerial photography and geophysical imagery, and reviewed research published since 1984. Key results The oldest rocks are 1290 Ma granitic gneiss and an 1180 Ma granite intrusion. Amalgamation of the Meso- to Neoproterozoic Rodinian Supercontinent put the Albany−Fraser Orogen at the heart of east Gondwana for ~1.0 billion years. At 165 Ma, that plate configuration began to break up, and from 83 Ma, the Eucla Basin opened. Cenozoic landforms and surficial deposits record northward plate movement and collision with south-east Asia at around 23 Ma, causing tectonic uplift, sea-level change, and climate change. The middle to upper Eocene Plantagenet Group was deposited in a shallow marine embayment with Maardjitup Gurlin/Mount Gardner, forming an island. The uplifted Eocene sea floor was lateritized in the Miocene and is presently covered by Holocene eolian sand dunes, peaty swamps and lakes. Maardjitup Gurlin/Mount Gardner was connected to the mainland by Pleistocene eolianite deposits. Conclusions The influence of plate tectonics on the geological evolution of an area is profound, from the origin and composition of the oldest rocks to the present landscape and the youngest surficial deposits. Implications Understanding the geological history of an area is essential to understanding landscape evolution and the natural history of the flora and fauna that inhabit it.

Climate and land-cover controls of aquatic carbon dynamics since the last glacial maximum: Evidence from stable carbon isotopes of subfossil Cladocera

Lake metabolism and associated emissions of CO2 in lakes are heavily subsidized by terrestrial carbon. However, how land-cover change and long-term climate interact to influence landscape biogeochemistry remains unclear. A ∼26,000-year sediment record from a lake in Southwest China shows how terrestrial-aquatic carbon dynamics responded to climate changes, atmospheric CO2 levels, and changing land-cover (vegetation composition) prior to cultural disturbances. Decoupled and coupled variations in the δ13C of Zooplankton (Bosmina) and sedimentary organic carbon from the Last Glacial Maximum tracked changes in atmospheric CO2 and the δ18O records of monsoonal intensity (Dykoski et al., 2005; Wang et al., 2005), highlighting a primary climatic control on coupled terrestrial-aquatic carbon dynamics. Zooplankton and algal production, alongside Bosmina δ13C-inferred lake CO2 concentrations, exhibited synchronous variations with the intensification of the southwest monsoon from ∼10 cal kyr BP, reflecting both increased aquatic production and enhanced terrestrial carbon export driven by forest expansion. These results highlight the critical role of monsoon-driven hydrological changes in regulating terrestrial organic matter inputs to lakes and shaping aquatic carbon dynamics at timescales of 102–103 year.

Charcoal morphotypes as indicators of fire fuel types and fire events along eight centuries in east‐central Mexico

ABSTRACTThe study of fire and charcoal production in tropical mesophytic ecosystems provides valuable insights into the ecological and climatic history of these systems. The diverse vegetation produces charcoal in various forms and sizes, which influences its dispersion and provides key information about fire dynamics. In this study, we used an approximately 850‐year sedimentary charcoal record extracted from Lake Atezca in east‐central Mexico to reconstruct the history of fire activity, including frequency and intensity. We present innovative information on charcoal morphotypes to interpret fire regimes, identify the types of vegetation burned and analyze human impact. The results reveal a shift in fire regimes during the Spanish Conquest, transitioning from local‐scale burning associated with intensive wood burning for indigenous agriculture to regional‐scale burning characterized by the burning of herbs and grasses linked to the expansion of extensive livestock grazing. This transition is reflected in the decrease of wood charcoal and the increase of smaller particles, as well as in the rise in titanium in the sediments, indicating greater landscape alteration. The evolution of fire regimes in Lake Atezca was driven primarily by human activities since pre‐Hispanic times, although climatic factors, such as severe droughts, may have also influenced fire activity.

Detailed Investigation of Dolomites in the Middle Jurassic Samana Suk Formation, Kahi Section, Nizampur Basin, North-Western Himalayas (Pakistan)

Abstract —Diagenetically modified carbonate rocks are more common in the rock record. Among these modifications, multiphase dolomitization is the most common process. The Middle Jurassic carbonates of the Samana Suk Formation are extensively altered by the dolomitization process in the Kahi section, Nizampur Basin. The primary objective of this study is to investigate this multiphase dolomitization and to elucidate its possible mechanism. Field investigation shows both host limestone (oolitic, fossiliferous, and massive) and dolomites. Dolomite bodies are of both beddings: parallel to and crosscutting the bedding planes. Different types of dolomites were recognized on the basis of color contrast as dark gray replacive dolomite, light gray dolomite, brownish dolomite, and yellowish dolomite. Along with the replacive phase, void- and fracture-filling cementing saddle dolomite and cementing calcites are recognized in the field. Petrographic studies show the complex diagenetic history of the Samana Suk Formation from near-surface diagenesis, including micritization, neomorphism, and several varieties of dolomites. These varieties are as follows: RD1 is very fine- to fine-grained dolomite; RD2 is medium- to coarse-grained and anhedral to subhedral dolomite; RD3 is coarse- to very coarse-grained and planar euhedral zoned dolomite; and RD4 is coarse-grained euhedral to subhedral ferroan dolomite. In addition, cementing saddle dolomite SD consists of large crystals with curved faces showing sweeping extinction. Cementing calcite phases are as follows: CC1 is granular mosaic; CC2 is twin; CC3 is fracture-filling; and CC4 is ferroan calcite. The stable isotope values of limestone (δ18O is –7.13 to –0.73‰ V-PDB, and δ13C is –0.05 to 1.32‰ V-PDB) show depletion with respect to the Jurassic marine signature. The values of multiphase dolomites RD1–RD4 and SD (δ18O is –8.65 to –3.16‰, and δ13C is –3.56 to 2.09‰) indicate multiphase dolomitization. The CC1–CC3 values (δ18O is –11.07 to –8.97‰, and δ13C is –2.14 to 0.76‰) indicate highly depleted values of δ18O, showing hydrothermal origin. From field, petrography, and geochemistry data, it is deduced that a possible source of Mg for hydrothermal dolomites is activation of faults and fractures during active tectonic regime in the area and might be related to activation and reactivation of the Kahi Thrust system.

A Northgrippian sedimentary magnetic enhancement along the western margin of India

Sedimentary magnetic records of shelf region contains complex environmental evolution information, necessitating records from various global regions to accurately interpret its significance. A sediment core (SSD-39/GC-01) retrieved from the eastern Arabian Sea was analyzed to elucidate the geologic and climatic controls on the sediment rock magnetic and grain size properties. We report the first record of high energy sediment deposits linked with intense monsoon phases, sea level variations, and extreme natural events during the Northgrippian period (8.27 ka to 4.20 ka). The compilation of magnetic susceptibility profiles of six sediment cores from the western margin of India revealed the presence of multiple sedimentary intervals of enhanced magnetic susceptibility and most likely reflect periods of high sedimentation events controlled by the regional geologic and climatic processes. We identified two anomalous sedimentary magnetic zones (Z-II, Z-IV) marked by an elevated magnetite content and sediment grain size, which reflect the periods of high-sedimentation events on the shelf off Goa. A shift in the magnetic mineral composition, clastic grain size, calcium carbonate, and organic carbon content at ~1.8 ka (Z-I) indicate a abrupt change in monsoon intensity. The elevated organic content within Z-I indicate efficient preservation of labile organic matter which survived oxidation due to rapid sediment deposition. End-member modeling of rock magnetic and grain size properties enabled us to discriminate and quantify the contributions of terrigenous fluxes and post-depositional mineral phases to the bulk magnetic mineral assemblage. We demonstrate that rapid scanning of magnetic susceptibility of sediment cores has the potential to precisely detect the periods of increased continental (magnetic flux) inputs into the marine shelf system. The proposed magnetic mineralogical approach has wider scope to constrain the understanding of how shelf sedimentation responded to past geological and climatic conditions globally.

The environmental consequences of rapid urbanization in central Florida reconstructed with high resolution 241Am and 210Pb dating in lake sediments

Throughout the 20th century, Florida was one of the fastest growing states in the US, putting unique environmental stress on the region. Accurately dated lake sediments can provide invaluable records of environmental change that extend beyond monitoring records. Here, we analyze profiles of americium-241 (241Am), cesium-137 (137Cs), lead (Pb), zinc (Zn), and uranium-series radionuclides in Lake Bonny in Lakeland, Florida. The 241Am peak is sharp in the sediment profile, while the 137Cs peak is broader and spread evenly across two layers. The measured 137Cs inventory of ~448Bq/m2 is less than half of the expected inventory from atmospheric deposition (accounting for decay since deposition), indicating significant losses. The reliability of 137Cs as a chronological tool can be complicated in environments with low quantities of 2:1 clays and low available potassium (K), characteristic of Florida and the U.S. southeast. Using a piecewise constant rate of supply 210Pb model verified by 241Am, we reconstruct sedimentation and chemical change in this lake. Highest sedimentation rates in the lake occur during decades of peak population growth in the mid-20th century. Uranium (U) and radium-226 (226Ra) inputs to the lake reach a maximum in the 1960s, consistent with expansion of local phosphate mines and elevated groundwater pumping during that time in response to drought conditions. Total Pb in the sedimentary record captures the rise and fall of the use of leaded gasoline, but Zn inputs to the lake remain nearly two orders of magnitude above background levels in the last decade. Our high-resolution chronology of the lake reveals regional impacts on water and lake quality in central Florida during a period of rapid population growth.

Mesoarchean Microbial Cd, Ba, and Ni Cycling: Evidence for Photosynthesis in Pongola Group Stromatolites through Novel Stable Isotopes and High-Resolution Trace Element Maps.

Nontraditional stable isotopes of bioactive metals emerged as novel proxies for reconstructing the biogeochemical cycling of metals, which serve as cofactors in major metabolic pathways. The fractionation of metal isotopes between ambient fluid and microorganisms is ultimately recorded in authigenic minerals, such as carbonates, which makes them potentially more reliable than standard biomarkers in organic matter. Stromatolitic carbonates are geochemical archives that allow for the study of the long-term interplay of the biosphere, atmosphere, and hydrosphere through deep time, with the unique potential to investigate early life environments and the evolution of the metallome. The present study uses stromatolites from the ∼2.95-billion-year-old Pongola Supergroup (S. Africa) as a field laboratory for combined in situ trace metal mapping and layer-specific, novel stable metal isotope compositions to infer early Earth microbial metal cycling via phototrophic and chemo-litho-autotrophic metabolisms. Quantitative in situ trace element maps reveal intrinsic biosedimentary enrichments of nickel (Ni), cadmium (Cd), phosphorus (P), iron (Fe), and manganese (Mn) in stromatolitic laminae. In contrast, barium (Ba) shows a more homogeneous distribution. Authigenic carbonates from pristine stromatolite laminae show distinct δ138Ba and δ112Cd fractionation above detrital background and bulk silicate Earth values, but opposing correlation with trace metal concentrations. Authigenic δ60Ni values overlap with Mesoarchean diamictite compositions. Nickel isotopic compositions in authigenic stromatolitic carbonates, potentially a new proxy for methanogenic metal uptake, do not show any proof of the presence of this metabolism in the samples of this study. Meanwhile, Cd isotopic compositions in authigenic carbonates follow typical Rayleigh-type isotope fractionation; that is, the isotopic composition of Cd evolves to heavy values close to modern surface compositions. Correlations of δ112Cd with the micronutrients copper (Cu), molybdenum (Mo), and P, at positively fractionated carbon (C) isotopes (δ13C ∼+2‰), argue for active photosynthesis in the Pongola microbial habitat. We show that Ba isotopes can be used to infer carbonate precipitation rates similar to modern microbial carbonates. Thus, the combination of Cd and Ni isotopes has the unique potential as novel isotope biomarkers for the biochemical sedimentary record of early Earth where traditional lipid biomarkers are not applicable due to the incomplete preservation of organic matter. Key Words: Early life-Stromatolites-Novel stable isotopes-Cadmium isotopes-Nickel isotopes-Barium isotopes-Trace element mapping.

Record of two Late-Holocene tsunamis along the north Peruvian coast and their relation to archaeological sites of the Chicama River valley

South America’s Pacific margin is subject to recurring subduction-zone earthquakes that have generated devastating historical tsunamis, as well as earlier events impacting indigenous populations that have lived along the region’s rich upwelling coastlines throughout the Holocene. Despite recurring events, the geologic record of paleo-tsunamis is relatively sparse. Here we report evidence for two paleo-tsunamis striking the Chicama River coastline (8°S) around 2.8 and 2.0 ka. The two sedimentary deposits are amalgamated in many locations and can be difficult to distinguish, but floodplain or shoreface deposits separate the two units when traced landward and seaward, respectively. The magnitude of each event was sufficient to erode coarse cobbles (13–25 cm) from the shoreface and transport them ~100 m before being deposited as rapidly thinning and fining gravel units. Based on the distribution of mobilized cobbles, we consider plausible flow characteristics for the two tsunamis suggesting that each was on the order of at least a few meters in height with most of the cobble transport occurring only under critical to supercritical flow at the wave front. Previous archaeological reports from the area correctly recognized the older tsunami event but did not describe the younger, better-preserved second event. Further, we revisit the archaeological evidence for the tsunami and recast the older event as likely being more moderate than previously suggested. Broader archaeological evidence from this 30-km reach of the Chicama valley shoreline also suggests that the late Cupisnique to Salinar and Gallinazo cultures were not severely disrupted by the tsunamis, even with these events undoubtedly impacting nearshore inhabitants at the time.

Multiple late Holocene glacier advances on the sub-Antarctic Kerguelen (49°S) islands: Evidence from a 1200 yr sediment core from a glacial threshold basin

Southern Ocean (SO) climate is rapidly changing because of global warming and regional climate feedback loops like shifts of the Southern Hemisphere (SH) westerly winds (SHW) and related Southern Annular Mode (SAM). Over the past decades, the former has been persistently positive, shifting the latter southwards: the ensuing changes in temperature and precipitation are linked to the rapid retreat of mid-latitude mountain glaciers. Beyond the short instrumental period, the long-term impact of this coupled SHW-SAM system on regional glaciers remains poorly constrained. To help close this gap, we reconstruct glacier advances from an outlet glacier on the sub-Antarctic Kerguelen (49°S, 69°E), an archipelago that is strategically located in an under-investigated region of the SHW core belt. Based on alternations between relatively organic and minerogenic mud detected using a multiproxy approach on a 1200-year-long sediment record from a glacial threshold basin, we document glacier advances between 1150 and 850, 820–620, 500–250 and 160–90 cal yr BP. Coincident glacier advances in adjacent regions like sub-Antarctic South Georgia and southern Patagonia, suggest that SO glaciers responded symmetrically to climate forcings during the past 1200 years. We attribute this synchronicity to shifting SAM-like conditions and associated temperature changes. We suggest that cold and negative SAM-like conditions, favourable for glacier growth on the Kerguelen and other SO land masses, dominated during much of this period. Furthermore, the findings presented here support the growing consensus for a two-phased regional expression of the Little Ice Age (LIA).

Recent depositional history of noble and critical elements in sediments from a wastewater-impacted bay (Vidy Bay, Lake Geneva, Switzerland)

Opposing trends in environmental pollution have been observed in recent years, with a growing awareness of the need to reduce emissions to the environment being accompanied by a concomitant increase in the use of polluting substances, which can potentially end up in the environment and harm humans and ecosystems. In order to assess the temporal evolution of loadings of seldom monitored trace elements, including noble metals and some technology critical elements, we analyzed a sediment core taken from the Bay of Vidy (Lake Geneva), impacted by the effluent of an urban wastewater treatment plant (WWTP). The temporal profiles of the chemical elements show essentially two patterns linked to the implementation of the WWTP, with some elements increasing sharply (e.g. Au, In, Ba, Sb, Sn, platinum group elements), while others (e.g. Ga, Ge, rare earth elements) show decreasing concentrations due to dilution by additional effluent particle loads. The origin of the elements showing a marked increase is attributed to local sources (photographic industry and municipal incinerator). There is (still?) no evidence in the sedimentary record of concentration increases linked to the growing use of technologically critical elements by industry.

Microbe-forced Mn‑carbonate direct precipitation in Ediacaran micro-stromatolites of South China

The direct precipitation model of Mn‑carbonate formation, based on investigation of the modern sedimentary record and simulation experiments, is commonly used to explain the genesis of both modern and ancient Mn‑carbonate deposits. This process is considered to be primarily influenced by physicochemical conditions and lacks microbial mediation. Despite the established role of microbes in global Mn cycling and biomineralization, the specific contribution of microbial processes to Mn‑carbonate formation remains understudied. In this study, Ediacaran Mn‑carbonates from South China with well-preserved micro-stromatolites offer a novel insight into understanding the microbes involved in the formation of Mn-deposits. Petrological observations reveal that the laminated Mn-ores mainly consist of alternating layers of dark Mn‑carbonate and light-colored dolomite laminae. Mn‑carbonate minerals, dominantly rod-like rhodochrosite crystals, exhibit a close spatial relationship with micro-stromatolites, suggesting a possible link to microbial activity. Geochemical results display that these Mn‑carbonates document high δ13C values (average = −1.65 ‰) compared to typical diagenetic Mn‑carbonate indicating the seawater likely contributed to the carbon source. Combined with alabandite deposition, small-sized pyrite framboids, and positive Eu anomalies, the Ediacaran Mn‑carbonates may have formed by microbially-mediated direct precipitation in Mn-rich anoxic seawater. The Mn‑carbonate and micro-stromatolite laminae accumulated during a period of enhanced bacterial activity, driven by episodic inputs of hydrothermal Mn2+ and bioessential elements. The present study highlights the microbially-mediated significant role in the primary precipitation pathway of Mn‑carbonate. Direct precipitation of Mn‑carbonate deposits, controlled by ocean conditions as well as enhanced by microbial processes, may account for the formation of other ancient economic manganiferous sedimentary deposits.

Tectonic Evolution of Tuvinian Trough (Northern Part of Central Asian Orogenic Belt): Synthesis of Geological Data and Results of Feldspar Ar‒Ar Dating

The Tuvinian rift trough, located in the northern part of the Central Asian orogenic belt (CAOB), was formed in the Early Devonian on late Proterozoic (?)‒Early Paleozoic terranes as a result of the activity of the Altai-Sayan mantle plume. The sedimentary record from the middle Paleozoic to the middle Mesozoic, preserved in the Tuvinian trough, and the middle Paleozoic igneous complexes confined to the structures of the trough, reflect the stages of evolution of the Earth’s crust in the Tuva segment, that necessary for understanding the history of the geological development of the CAOB as a whole. Dating of accessory and rock-forming minerals from igneous rocks using low-temperature geochronology methods allows us to obtain additional information about post-magmatic processes and thereby update the model of tectonic evolution of the region. In this study, we have reconstructed the stages of tectonic development of the Tuvinian trough in the northern part of the CAOB based on the analysis of geological data and new Ar‒Ar dating data on feldspars from mafic intrusions. As a result of this study, the chronology of the previously known stages of post-magmatic processes manifested in the Tuvinian trough was clarified, and new stages were identified according to the tectonic evolution of the CAOB. Ar‒Ar dating of feldspars carried out on eight samples showed four age groups: (i) Late Devonian, (ii) middle Carboniferous, (iii) early Permian and (iv) Early Jurassic. Late Devonian (~377 and 375 Ma) ages record an impulse of mafic magmatism, widely manifested in the northern segments of the CAOB (~380‒365 Ma). Middle Carboniferous (~320 and 319 Ma) dates may be associated with the closure of the Ob-Zaisan branch of the Paleo-Asian ocean as a result of the Kazakhstan-Siberian collision. Early Permian (~290–279 Ma) ages are consistent with the formation of late Carboniferous–Early Permian (~305–275 Ma) large igneous provinces in connection with rifting processes in the northern segments of the CAOB. Finally, a single Early Jurassic (~188 Ma) age marks tectonic reorganization of the CAOB in Late Triassic‒Early Jurassic in response to (i) closure of the Paleotethys ocean with subsequent collision of the Cimmerian blocks and the southern margin of the Eurasian continent and/or (ii) activity of the Mongolian mantle plume.

Localization and Delocalization During Seismic Slip

AbstractThe thickness of a seismic slip layer controls style and rate of rupture propagation, frictional heating, weakening, and energy budget of earthquakes. Slip layer thickness changes dynamically with feedbacks between temperature rise, roughness, damage, and fluid pressurization. Natural faults have complex slip histories, ambiguating which layer thicknesses represent a record of seismic slip. The thickness of proven paleoseismic slip layers in nature are 1 mm–1 cm. Thicker slip layers do not get hot enough to retain coseismic frictional temperature anomalies and thereby prevent the detection of big earthquakes using current methods. We suggest that delocalization—the spontaneous increase in slipping layer thickness during slip—plays a role in coseismic healing and cause biases in the rock record of earthquakes. Recognizing the importance of feedbacks affecting slipping layer thickness is critical to understanding strength and stress variations during earthquakes and to correctly interpreting earthquake source parameters from exhumed faults.

A late Oligocene chiton fauna (Polyplacophora) from a rocky shore ecosystem, Cosy Dell, Southland, New Zealand

ABSTRACT Chiton (Class Polyplacophora) fossils are rare globally, mostly because they are restricted to hard habitats such as rocky shores that are taphonomically under-represented in the geological record. New Zealand is rich in Cenozoic marine molluscan fossils, but chitons are very uncommon. The earliest New Zealand records of fossil chiton species are all from the Late Oligocene (Duntroonian) Chatton Formation in Southland. They include Callochiton chattonensis Ashby 1929 [New Zealand fossil Polyplacophora (Chitons). Transactions and Proceedings of the Royal Society of New Zealand. 60:366–369], Acanthochitona (Notoplax) ashbyi (Laws 1932 [New Tertiary Mollusca from New Zealand. No. 2. Transactions and Proceedings of the New Zealand Institute. 62:183–199]) and Rhyssoplax allanthomsoni Mestayer 1929 [Notes on New Zealand Mollusca. Transactions and Proceedings of the Royal Society of New Zealand. 60(4):247–150]. At Cosy Dell farm, Waimumu, New Zealand, the Chatton Formation contains a diverse chiton fauna representing seven families and seven genera, including Callochiton cf. chattonensis, Acanthochitona cf. ashbyi, Ischnochiton sp., Leptochiton cf. inquinatus, Lorica sp., Plaxiphora sp., and Rhyssoplax sp., the highest recorded fossil chiton diversity in New Zealand. All genera described in the fossil assemblage are associated with extant taxa around modern New Zealand rocky intertidal and shallow near shore environments. The study extends the New Zealand stratigraphic range of four genera (Ischnochiton, Plaxiphora, Lorica and Leptochiton) back to the Duntroonian (Late Oligocene), provides the first taxonomic descriptions of each chiton taxon from the site and discusses the paleoecological and biostratigraphic significance of these rarely preserved components of a rocky shore ecosystem.

Sedimentary record of oceanic plateau accretion: Revisiting the Eocene to Miocene stratigraphy of the northern Olympic Peninsula, Washington (USA)

Sedimentary record of oceanic plateau accretion: Revisiting the Eocene to Miocene stratigraphy of the northern Olympic Peninsula, Washington (USA)

The climatic pattern of East Asia shifted in response to cratonic thinning in the Early Cretaceous

In response to westward subduction of the Paleo-Pacific, the North China Craton experienced the uplift of an eastern coastal plateau followed by subsidence in the Early Cretaceous, which potentially drove a shift in climatic patterns. Here we use the oxygen isotope ratios of garnets from magmatic-hydrothermal ore systems to infer the origins and signatures of mineralization fluids during this tectonic transition. The garnet oxygen isotope values range from approximately –11.4 to +13.5‰, with extremely depleted oxygen isotope ratios exclusively found in the northern margin, indicating extensive involvement of meteoric and lacustrine fluid in the back-arc hinterland. This geological record aligns with climate modeling exhibiting that the coastal plateau amplified northeastward transport of moisture from tropical Tethyan Ocean. The long-distance transport strongly depleted 18O and 2H (D). As the cratonic lithosphere thinned and the plateau subsided, the Pacific influences began to dominate the climatic pattern of East Asia.