Fossil Shells Research Articles

High temporal resolution paleoclimate reconstruction by the analysis of growth patterns and stable isotopes of fossil shells of the long-lived bivalve Mercenaria stimpsoni from MIS 5e, 7 and 9

High temporal resolution paleoclimate reconstruction by the analysis of growth patterns and stable isotopes of fossil shells of the long-lived bivalve Mercenaria stimpsoni from MIS 5e, 7 and 9

Late Ediacaran to Early Cambrian stratigraphic correlation and its geological implications in the northwestern Sichuan Basin: insights from phosphorus, isotopes, and small shelly fossils

The characteristics of elements, isotopes, and small shelly fossils were investigated for Late Ediacaran to Early Cambrian stratigraphy division and to discuss their geological implications in the northwestern Sichuan Basin. The results reveal that small shelly fossils can be detected in the high-phosphorous section, with the concentration of phosphorus mainly ranging from 2% to 8%, suggesting that this interval belongs to the Early Cambrian, which is also consistent with the carbon isotopic composition results. In addition, the Early Cambrian is denudated in the Sichuan Basin due to tectonic movement, and the characteristics of some isotopes and small shell fossils are different from those in other basins. It can be proposed that P content can support the recognition of lithological boundaries, and the high phosphorus content can be used as a reference to identify the top and bottom boundaries of the Maidiping Formation in the study area. According to the elemental compositions in the Ediacaran Dengying Formation, the variations in Si, Al, Fe, and K contents are similar in the platform area and rift area, suggesting that the third and fourth member of the Dengying Formation are also developed in the Deyang–Anyue Rift. The results suggest that both the Deng-4 member and Maidiping Formation feature contemporaneous deposition of different facies in the northwestern Sichuan Basin. The strata consist of shale intercalated with thin carbonate rock deposits in the Deyang–Anyue Rift, while carbonate rock deposits in the platform. The Deyang–Anyue Rift expanded gradually in the Late Ediacaran and eventually filled in the Early Cambrian. The data in this study illustrate that elemental compositions, isotopes, and small shelly fossils can be combined to correlate the Late Ediacaran to Early Cambrian strata and provide new evidence for Deyang–Anyue Rift evolution. The results offer some new insights for deep oil and gas exploration in the Sichuan Basin and for the tectonic–depositional–environmental–biological synergistic evolution in the Late Ediacaran to Early Cambrian transition.

Resurgence of cloudinomorph fossils with possible cnidarian affinity at the peak of the Cambrian Explosion (Cambrian Series 2, Stage 3) in southern Shaanxi, China

AbstractDuring the Precambrian–Cambrian transition, tubicolous animals were prevalent among small shelly fossils. These include the oldest‐known skeletal fossil Cloudina from the terminal Ediacaran, and anabarites and hyoliths from the early Cambrian; considered to be possible annelids, cnidarians, and molluscs, respectively. Tubular fossils have important bio‐stratigraphic significance during this period, and their diversity and evolutionary radiation trend herald the Cambrian explosion. However, the relative morphological simplicity of these fossils and lack of preserved soft‐body information has resulted in poor taxonomic constraints. Here, numerous tubular fossils exhibiting multi‐stage cylindrical or conical cups were recovered from the middle–upper Guojiaba Formation of Cambrian Series 2, Stage 3, in Mianxian, South China. One new genus (Mianxiantubus) and three new species (M. cyathiformis, M. obconicus, and M. varius) were established to accommodate the morphological diversity of the fossils. However, their affinities remain contentious and undetermined and have been tentatively ascribed to Cnidaria. The possible morphology and growth patterns of Mianxiantubus suggest a close relationship with cloudinomorph fossils, although it is notably distinct from the quintessential cloudinids owing to the presence of transverse septa. Moreover, many other tubular fossils have been recovered from the same level, which may extend to the overlying Xiannvdong Formation (Stage 3), co‐occurring with archaeocyathids. This suggests that tubicolous organisms continued to diversify and occupied specific ecological niches even during the peak phase of the Cambrian explosion, dominated by bilateral epifaunal vagrants.

Oxidative weathering on the continent and seawater upwelling along the passive continental margin promoted widespread phosphorite formation at the Neoproterozoic-Cambrian boundary in South China

The latest Proterozoic to early Cambrian is characterized by major global phosphogenic events and the diversification of complex multicellular life. However, the feedback mechanism of atmospheric oxidation and upwelling processes to form voluminous phosphorite deposits is unclear. South China is a key example of the sedimentary spectrum related to the Neoproterozoic to Early Cambrian bloom of oxygenic photosynthesis, with alginite deposits (sapropelite; “stone coal”), barite, polymetallic black shales and phosphorites along the passive continental paleo-margin of the Yangtze craton. Here, we present a comprehensive geochemical analysis of drill core samples from the Zhijin phosphorite deposit, including Cr isotope, Fe speciation, and bulk elemental composition of dolostone, phosphorite and black shale from the Ediacaran to Early Cambrian sequence. The positively fractionated δ53Cr values of 0.11 to 1.81 ‰ of leachates from Ediacaran dolostone and Terreneuvian phosphorite indicate intensive oxidative terrestrial weathering. The phosphorite samples exhibit REE distribution patterns similar to modern seawater and strongly negative Ce anomalies (0.47–0.61), suggesting an oxic, open ocean environment. In contrast, the absence of Ce anomaly, high FeHR/FeT, and Fepy/FeHR ratios, enhanced redox-sensitive element concentrations, high Mo/TOC and TS/TOC, and high molar Corg:P ratios suggest euxinic to anoxic conditions for the overlying black shale sedimentation in a restricted sedimentary marine environment. Bulk-rock shale samples retain the positively fractionated Cr isotope pattern. The dramatic change from oxic to anoxic conditions aligns with the fossil record, which shows a proliferation of small shelly fossils in the phosphorite and their extinction in the overlying black shales, likely by hydrogen sulfide poisoning. We infer that nutrient-rich, oxidized upwelling seawater transported phosphorus and other nutrients to the photic zone, from where organic matter settled down to the seafloor and formed thick phosphorite beds at the oxic-anoxic boundary at and below the seafloor. Our study highlights that atmospheric and seawater oxygenation accelerated the Early Cambrian bio-diversification, and the subsequent restricted basin situation is responsible for the extinction at the Neoproterozoic-Cambrian boundary.

Correlation and stratigraphic implications of the lowermost Cambrian small shelly fossils from new sites of South China

Early Cambrian small shelly fossils (SSFs) represent some of the earliest biomineralized examples of metazoans and are often extremely abundant and diverse, so can be useful for regional and intercontinental correlation in pre-trilobitic carbonate or phosphorite deposits. New SSF assemblages chemically extracted from the Cambrian Yangjiagou Member carbonates in the Fucheng area, southern Shaanxi Province, China. The SSFs include anabaritids, protoconodonts, hyolitheminths, maikhanellids, Quadrapyrgites , Archaeooides , Olivooides and Siphogonuchites . The recovered SSFs represent two previously identified SSF assemblage zones: the Anabarites trisulcatus – Protohertzina anabarica assemblage zone and the succeeding Paragloborilus subglobosa – Purella squamulosa assemblage zone. The early Cambrian fossil assemblage zones described from this locality are correlated on a regional scale across the Yangtze Platform from eastern Yunnan, the Three Gorge region of western Hubei, northern Sichuan, the Ningqiang and Xixiang regions of southern Shaanxi and the Nemakit–Daldynian Stages of Siberia. The results reveal that the Yangjiagou Member is provisionally equivalent to the Zhongyicun Member of Yunnan, the Yanjiahe Formation of Hubei, the Maidiping Formation of Sichuan and the Kuanchuanpu Formation of Shaanxi. This paper offers new evidence and fossil data for the location of the Precambrian–Cambrian boundary in the Micangshan area of South China.

Stable carbon and oxygen isotope-based sclerochronology of bivalve mollusk shells from the Upper Cretaceous (upper Campanian) Coon Creek Formation in Tennessee, USA: Implications for paleoecology and paleoenvironment

Stable carbon and oxygen isotope-based sclerochronology was carried out on well-preserved fossil shells of bivalve mollusks Crassatella vadosa and Cucullaea vulgaris from the Upper Cretaceous (upper Campanian) Coon Creek Formation in Tennessee, USA, to reconstruct their life-history traits and sedimentary settings on an intra-annual time scale. The δ13CShell values along with the shell growth showed the cyclic variation with downward convex to lower value, likely reflecting the seasonal cycle of ambient seawater dissolved inorganic carbon (DIC) or metabolism of the bivalve or both. The δ13CShell cycles were largely associated with the strong growth disturbance lines, supporting hypothesis that the growth lines were formed annually. We estimated the ages of the shells based on both δ13C cycle or the growth cessation line. The modeled relationship between age and shell growth showed that Cr. vadosa and Cu. vulgaris grew up to about 40 mm at 7 years old and about 65 mm at 10 years old, respectively. The paleotemperatures estimated from the δ18OShell profiles of the examined specimens ranged from 16.2 °C to 24.2 °C and from 18.8 °C to 27.0 °C when assuming the bottom seawater δ18O to be −1.00‰ and −0.46‰ (VSMOW), respectively, and showed no clear seasonal cycle. The bottom seawater temperatures reconstructed from the specimens of the two bivalve species were lower than the near-surface seawater temperatures (29.0–30.6 °C) estimated from the planktic foraminiferal δ18O. We inferred that the benthic bivalve habitat of the Coon Creek Formation was at least 10 m or deeper below the thermocline.

Dawn of diverse shelled and carbonaceous animal microfossils at ~ 571 Ma

The Ediacaran-Cambrian transition documents a critical stage in the diversification of animals. The global fossil record documents the appearance of cloudinomorphs and other shelled tubular organisms followed by non-biomineralized small carbonaceous fossils and by the highly diversified small shelly fossils between ~ 550 and 530 Ma. Here, we report diverse microfossils in thin sections and hand samples from the Ediacaran Bocaina Formation, Brazil, separated into five descriptive categories: elongate solid structures (ES); elongate filled structures (EF); two types of equidimensional structures (EQ 1 and 2) and elongate hollow structures with coiled ends (CE). These specimens, interpreted as diversified candidate metazoans, predate the latest Ediacaran biomineralized index macrofossils of the Cloudina-Corumbella-Namacalathus biozone in the overlying Tamengo Formation. Our new carbonate U–Pb ages for the Bocaina Formation, position this novel fossil record at 571 ± 9 Ma (weighted mean age). Thus, our data point to diversification of metazoans, including biomineralized specimens reminiscent of sections of cloudinids, protoconodonts, anabaritids, and hyolithids, in addition to organo-phosphatic surficial coverings of animals, demonstrably earlier than the record of the earliest known skeletonized metazoan fossils.

Geochemical relationships between shells of the gastropod Gyraulus convexiusculus and modern water bodies on the Tibetan Plateau, and their paleoenvironmental significance

Fossil shells of the gastropod Gyraulus sp. are widespread in the sediments of wetlands and lakes, and in fluvial and lacustrine depositional sequences on the Tibetan Plateau (TP). Although aragonite shells of Gyraulus sp. are a potentially valuable archive of information on environmental changes, the living environment of Gyraulus sp. and the significance of its shell geochemistry (e.g., Sr/Cas, Mg/Cas, δ13Cs, δ18Os) are unknown or disputed. In this study we investigated living specimens of the dominant species of Gyraulus sp. (Gyraulus convexiusculus) in rivers, wetlands, and lakes on the TP, together with its fossil shells in the Holocene lacustrine sediments of Nam Co (NC) on the TP. Specifically, we measured the values of Sr/Cas, Mg/Cas, δ13Cs, and δ18Os of the modern and fossil shells. Our results indicate that the hydrochemical composition and electrical conductivity of the ambient water significantly affect the survival and abundance of G. convexiusculus. The environmental tolerance of G. convexiusculus can be ordered as: carbonate-type > sulfate-type > chloride-type. Additionally, we speculate that the upper threshold of electrical conductivity for the survival of G. convexiusculus does not exceed ∼4544 μS/cm. Furthermore, we established the relationship between modern G. convexiusculus shells and its host water and developed Gyraulus-based transfer functions (TFs). To assess their potential for paleoenvironment reconstruction, the TFs were then applied to fossil shells of G. convexiusculus collected from a Holocene lake sediment profile from a terrace around NC. We show that Sr/Cas in G. convexiusculus is a potentially reliable proxy for reconstructing the Sr/Ca of the paleo-water (Sr/CaPaleo-w) and the paleoconductivity. By contrast, Mg/Cas in G. convexiusculus cannot be used for environmental reconstruction. δ13Cs in G. convexiusculus primarily reflects the δ13CDIC of the host water. When the host water is deficient in HCO3− + CO32− (<280 mg/L) there is an increased supply of dissolved carbon derived from organic sources to the shells of G. convexiusculus. Overall, δ18Os in G. convexiusculus is likely one of the most reliable indicators for the δ18Ow of the host water of the lakes on the TP.

Mineralogical, Petrographical and Geochemical Properties of the Late Oligocene Coal Seam (Seam-VI): Insights into Elemental Enrichments and Palaeodepositional Environment (İbrice field, Thrace Basin)

The Thrace Basin hosts several mineable coal seams (upwards numbered I to VII) within the coal-bearing Late Oligocene-age Danişmen Formation. For the first time, the properties of the Seam-VI in the İbrice (Malkara) area have been investigated in order to evaluate elemental enrichments and palaeoenvironmental conditions. The xylite-rich and mineral-rich lithotypes were identified from the studied coal samples representing the whole-coal thickness. The coal samples, on a dry basis, display variable ash yields (13.2–63.0%), total C (21.2–57.8%), and total S (0.9–4.1%) contents. The minerals identified using XRD-whole rock analysis include clay minerals, quartz, pyrite, calcite, dolomite, and feldspars. Siderite is only identified in a single sample. Aragonite is detected in two samples, which contain fossil shell remains. The SEM observations agree with XRD data, and apatite, barite, biotite, pentlandite, sphalerite, Ti-oxide, and zircon were also identified as accessory phases. Huminite is the predominant maceral group in the studied samples, while liptinite and inertinite group macerals display variable proportions. The mean %Rr values of ulminite macerals are around 0.40-0.41±0.01-0.02%, indicating relatively low-rank coal. This study implies that the precursor peat-mires of the Seam-VI were mainly developed under forested mire conditions, where woody peat-forming plants were abundant, and occasionally the contributions of herbaceous plants were important. The coexistence of syngenetic pyrite and carbonate minerals (e.g., siderite and carbonate mineral bands) could be related to the development of weakly acidic to neutral conditions within palaeomires. Furthermore, the predominance of clay minerals and the presence of detrital accessory minerals (e.g., apatite, pentlandite, and Ti-oxides) can also be indicators of clastic influx into palaeomires. Although aluminosilicate minerals (e.g., clay minerals) are abundant in dominant phases, SEM-EDX data shows that accessory minerals mainly control the elemental enrichments in the Seam-VI. The Mn enrichments in the samples seem to be controlled by Mn-bearing siderite micronodules. Considering the presence of sulphide mineralization and metallic ore deposits in the Strandja and Rhodope massifs, enrichments of Cr, Co, Ni, Ge, and Mo are related to As-bearing pyrite grains and accessory sphalerite and pentlandite grains within clay mineral aggregates in the samples. In addition, the Sr-bearing barite overgrowths around feldspar grains and syngenetic carbonate mineral bands could also cause Sr enrichments. Overall, clastic influx ratios into palaeomires and pH conditions during peat accumulation controlled the elemental enrichments in the Seam-VI.

Reconstructed seasonality during the Mid Piacenzian Warm Interval and early Pleistocene cooling as recorded by growth temperatures from Mercenaria shells

The Mid Piacenzian Warm Interval (MPWI) has been identified as an analogue for future global warming because it had warmer temperatures and higher atmospheric CO2 levels than today, while subsequent early Pleistocene cooling is more similar to modern climate. However, reconstructions of these intervals lack seasonal-scale temperature reconstructions. Seasonal sea surface temperature (SST) reconstructions from deep-time archives can potentially provide insight into the nature of the climate system on sub-annual scales during critical climate states. Here we compared seasonal variability in growth temperatures during the MPWI and subsequent early Pleistocene cooling to modern climate reconstructed from oxygen isotope ratios recorded by the bivalve Mercenaria. Modern shells were collected from the University of North Carolina's Marine Sanctuary. Fossil shells from the Mid-Atlantic Coastal Plain (North Carolina) were collected from the Duplin Formation (MPWI) and the Waccamaw Formation (early Pleistocene). Oxygen isotope ratios range from −1 to 2.4 ‰ during the MPWI, −1–2.4 ‰ during the early Pleistocene, and −2.2 to 2.3 ‰ in modern shells. Stable carbon isotope ratios ranged from −0.91 to 1.67 ‰ during the MPWI, 0.19–1.87 ‰ during the early Pleistocene, and −2.46 to 0.60 ‰ in modern shells. Average seasonal growth temperature variations for the MPWI (∼11 ± 3 °C) are reduced compared to modern instrument records (∼16 ± 3 °C), while the early Pleistocene (∼14 ± 2 °C) was more similar to today. Modern Mercenaria record dark increment formation during the summer while fossil Mercenaria record dark increment formation during the winter. We hypothesize that this difference is timing of dark increment formation may be due in part to differences in water depth (∼1m for modern shells and ∼20m for fossil shells) or a shift in the location of the boundary between biogeographic zones. A −1.6 ‰ shift in mean stable carbon isotope ratios between fossil (0.92 ± 0.66 ‰) and modern (−0.65 ± 0.44 ‰) shells has been observed and may be a result of the “Suess Effect” and/or influences of estuarine/freshwater relative to marine settings.

Knowledge Gaps on the Utilization of Fossil Shell Flour in Beef Production: A Review.

Population growth in many countries results in increased demand for livestock production and quality products. However, beef production represents a complex global sustainability challenge, including meeting the increasing demand and the need to respond to climate change and/or greenhouse gas emissions. Several feed resources and techniques have been used but have some constraints that limit their efficient utilization which include being product-specific, not universally applicable, and sometimes compromising the quality of meat. This evokes a need for novel techniques that will provide sustainable beef production and mitigate the carbon footprint of beef while not compromising beef quality. Fossil shell flour (FSF) is a natural additive with the potential to supplement traditional crops in beef cattle rations in response to this complex global challenge as it is cheap, readily available, and eco-friendly. However, it has not gained much attention from scientists, researchers, and farmers, and its use has not yet been adopted in most countries. This review seeks to identify knowledge or research gaps on the utilization of fossil shell flour in beef cattle production, with respect to climate change, carcass, and meat quality. Addressing these research gaps would be a step forward in developing sustainable and eco-friendly beef production.

Detection of intact polyene pigments in Miocene gastropod shells

AbstractPolyene pigments represent a major class of pigments in present‐day organisms. Their occurrence in fossils has been frequently discussed, but to date no spectroscopic evidence has been found. Here, we use in situ Raman spectroscopy to examine the chemistry of exceptionally well‐preserved gastropod shells with colour preservation from the Middle Miocene of the Vienna Basin (Austria, Hungary). Raman signals indicative of the presence of intact (i.e. non‐hydrogenated) polyene pigments were obtained from fossil shells with reddish colour patterns, thus revealing the first record of intact polyenes in fossils. The observed Raman values are in good agreement with those of unmethylated (non‐carotenoid) polyenes. Fossil polyene pigments were detected in representatives of the superfamily Cerithioidea, but not in representatives of other gastropod families with colour preservation found at the same localities, demonstrating that the occurrence of polyene pigments is taxon‐specific. Our results show that Raman spectroscopy represents a valuable tool for the non‐destructive screening of rare fossils with colour preservation for the occurrence of polyene pigments.

Atmospheric CO2 Estimates for the Late Oligocene and Early Miocene Using Multi‐Species Cross‐Calibrations of Boron Isotopes

AbstractThe boron isotope (δ11B) proxy for seawater pH is a tried and tested means to reconstruct atmospheric CO2 in the geologic past, but uncertainty remains over how to treat species‐specific calibrations that link foraminiferal δ11B to pH estimates prior to 22 My. In addition, no δ11B‐based reconstructions of atmospheric CO2 exist for wide swaths of the Oligocene (33–23 Ma), and large variability in CO2 reconstructions during this epoch based on other proxy evidence leaves climate evolution during this period relatively unconstrained. To add to our understanding of Oligocene and early Miocene climate, we generated new atmospheric CO2 estimates from new δ11B data from fossil shells of surface‐dwelling planktic foraminifera from the mid‐Oligocene to early Miocene (∼28–18 Ma). We estimate atmospheric CO2 of ∼680 ppm for the mid‐Oligocene, which then evolves to fluctuate between ∼500–570 ppm during the late Oligocene and between ∼420–700 ppm in the early Miocene. These estimates tend to trend higher than Oligo‐Miocene CO2 estimates from other proxies, although we observe good proxy agreement in the late Oligocene. Reconstructions of CO2 fall lower than estimates from paleoclimate model simulations in the early Miocene and mid Oligocene, which indicates that more proxy and/or model refinement is needed for these periods. Our species cross‐calibrations, assessing δ11B, Mg/Ca, δ18O, and δ13C, are able to pinpoint and evaluate small differences in the geochemistry of surface‐dwelling planktic foraminifera, lending confidence to paleoceanographers applying this approach even further back in time.

Taphonomic significance of Aristotle's 'Wheel Paradox': an example with the cerithid gastropod Cerithium atratum (Born, 1778) from Conceição Lagoon, Santa Catarina State, Southern Brazil

In the book Mechanical Problems, attributed to Aristotle, the author relates the differential degrees of wearing and rounding of pebbles and shells moved by waves on the seashore to the variable radii and diameters of these particles. This phenomenon, which became known as Aristotle’s ‘Wheel Paradox,’ seems to explain the pattern of abrasion observed in shells of gastropods Cerithium atratum (Born) found in Conceição Lagoon, on the Island of Santa Catarina, Brazil. In situ observations show that the elongated turriform shells of C. atratum deposited at shallow (&lt; 30 cm) depths on a sandy bottom with pavements of disarticulated valves of Anomalocardia flexuosa Gmelin are subject to bidirectional wave-generated currents under fairweather conditions. The 47 specimens analyzed exhibit a pattern of abrasion characterized by the loss of the shell wall, apparently proceeding from the wider last whorl toward the narrow apex, culminating in the exposure of the columella. Experiments designed to test whether this pattern could be related to the ‘Wheel Paradox’ principle show that under bidirectional flow, the shells describe circles on the vertical plane around the longitudinal axis (rolling) and a pendulum movement (revolution) on the horizontal plane centered on the apex. The whorls located farther from the apex have larger diameters and describe broader arc segments. Thus, they have higher tangential velocities and travel longer paths, which could explain why they are abraded earlier than the narrower whorls. Recognizing similar abrasion features in fossil shells can provide information on the local paleo-currents, hydrodynamics, and relative time-averaging of death assemblages and allow distinguishing between natural or anthropogenic modification in archaeological specimens. Although the effects vary between shells with different shapes, Aristotle’s ‘Wheel Paradox’ principle explains the general abrasion pattern among gastropods under certain hydrodynamic conditions. Keywords: Actualistic Taphonomy, Aktuopaläontologie, shell abrasion, shell orientation, biostratinomy, hydrodynamics

Comparison of δ13 C analyses of individual foraminifer (Orbulina universa) shells by secondary ion mass spectrometry and gas source mass spectrometry.

The use of secondary ion mass spectrometry (SIMS) to perform micrometer-scale in situ carbon isotope (δ13 C) analyses of shells of marine microfossils called planktic foraminifers holds promise to explore calcification and ecological processes. The potential of this technique, however, cannot be realized without comparison to traditional whole-shell δ13 C values measured by gas source mass spectrometry (GSMS). Paired SIMS and GSMS δ13 C values measured from final chamber fragments of the same shell of the planktic foraminifer Orbulina universa are compared. The SIMS-GSMS δ13 C differences (Δ13 CSIMS-GSMS ) were determined via paired analysis of hydrogen peroxide-cleaned fragments of modern cultured specimens and of fossil specimens from deep-sea sediments that were either untreated, sonicated, and cleaned with hydrogen peroxide or vacuum roasted. After treatment, fragments were analyzed by a CAMECA IMS 1280 SIMS instrument and either a ThermoScientific MAT-253 or a Fisons Optima isotope ratio mass spectrometer (GSMS). Paired analyses of cleaned fragments of cultured specimens (n = 7) yield no SIMS-GSMS δ13 C difference. However, paired analyses of untreated (n = 18) and cleaned (n = 12) fragments of fossil shells yield average Δ13 CSIMS-GSMS values of 0.8‰ and 0.6‰ (±0.2‰, 2 SE), respectively, while vacuum roasting of fossil shell fragments (n = 11) removes the SIMS-GSMS δ13 C difference. The noted Δ13 CSIMS-GSMS values are most likely due to matrix effects causing sample-standard mismatch for SIMS analyses but may also be a combination of other factors such as SIMS measurement of chemically bound water. The volume of material analyzed via SIMS is ~105 times smaller than that analyzed by GSMS; hence, the extent to which these Δ13 CSIMS-GSMS values represent differences in analyte or instrument factors remains unclear.

Growth patterns and affinities of Huizenodus oligaspinosus (?Cnidaria) from the lower Cambrian of South China

Helmet-like small shelly fossils from the Cambrian Fortunian Stage of South China are a class of morphological taxa with uncertain affinities. Here, we redefine the genera Amoebinella and Huizenodus and consider Huizenodus oligaspinosus to be a senior synonym of Amoebinella echinata. In addition, we report two compound fossils of H. oligaspinosus for the first time from the Fortunian Zhangjiagou Lagerstätte in southern Shaanxi. Their multi-branched, dendritic, rigid structure is similar to the skeletons in several groups of colonial anthozoans, and thus, H. oligaspinosus may represent the skeletal structure of an ancestral anthozoan. H. oligaspinosus could have further constructed its skeleton by producing secondary individuals from the main branches or the sub-branches of the primary individuals to accommodate more polyps.

The signature of accumulated permanent uplift, northern Cascadia subduction zone

AbstractUplift of the overriding plate at a subduction zone denotes interseismic strain accumulation, which is subsequently released during a megathrust earthquake. Although most interseismic strain is thought to be released elastically, observations of uplifted coastal regions at subduction zones worldwide indicate that some strain may result in permanent uplift. The Grays Harbor and Willapa Bay (Washington, USA) coastal region of the Cascadia subduction zone hosts flights of marine terraces testifying to late Pleistocene rock uplift. Our new detailed mapping of the marine terraces recognizes nine new units, including estuarine and fluvial sediments. Luminescence dating, relative age based on soil maturity and terrace elevation, and an evaluation of previous ages from fossil shells collectively constrain the probable ages of three estuarine units to sea-level high stands during Marine Isotope Stages 5a, 5c, and 5e. We estimate an average uplift rate of 0.4 ± 0.1 mm/yr for the terraced estuarine units, consistent with other Pleistocene uplift and incision rates in Cascadia. When compared with observed interseismic vertical deformation, these rates suggest that about one-tenth of interseismic strain may become permanent. The values are permissible within the uncertainties of uplift based on regional estimates of interseismic vertical strain rates and of coseismic subsidence.

U–Pb zircon ages from tuffaceous beds in the Terreneuvian to Cambrian Series 2 sections of Avalonian southern New Brunswick, Canada: new constraints on chronostratigraphic correlations and the Cambrian time scale

Abstract Avalonian sections in the Saint John area, southern New Brunswick, have long contributed to global understanding of Cambrian chronostratigraphy. A tuffaceous bed in the Ratcliffe Brook Formation (RBF) in the Somerset Street section dated at c. 531 Ma has traditionally been considered to post-date small shelly fossils attributed to the Watsonella crosbyi Zone in the Hanford Brook section. A fine-grained tuffaceous bed approximately 8 m stratigraphically lower in the Somerset Street section yields a chemical abrasion isotope dilution–thermal ionization mass spectrometry zircon age of 532.3 ± 0.3 Ma; a tuffaceous carbonate unit in the lower RBF in Hanford Brook gives an age of 531.5 ± 0.3 Ma. Crystal and crystal-lithic tuff beds near the top of the RBF yield ages of 520.3 ± 0.3 Ma (in Hanford Brook) and 519.1 ± 0.3 Ma (in Ratcliffe Brook). The new ages confirm the correlation between the Somerset Street and Hanford Brook sections based on acritarchs and make the association of small shelly fossils in the Hanford Brook section younger than 531 Ma. This result is relevant to ongoing discussions on the age of the base of undefined Cambrian Stage 2. The radiometric ages also support a young age for the upper part of the RBF, perhaps extending into Epoch 2.

U–Pb zircon ages from tuffaceous beds in the Terreneuvian to Cambrian Series 2 sections of Avalonian southern New Brunswick, Canada: new constraints on chronostratigraphic correlations and the Cambrian time scale

Abstract Avalonian sections in the Saint John area, southern New Brunswick, have long contributed to global understanding of Cambrian chronostratigraphy. A tuffaceous bed in the Ratcliffe Brook Formation (RBF) in the Somerset Street section dated at c. 531 Ma has traditionally been considered to post-date small shelly fossils attributed to the Watsonella crosbyi Zone in the Hanford Brook section. A fine-grained tuffaceous bed approximately 8 m stratigraphically lower in the Somerset Street section yields a chemical abrasion isotope dilution–thermal ionization mass spectrometry zircon age of 532.3 ± 0.3 Ma; a tuffaceous carbonate unit in the lower RBF in Hanford Brook gives an age of 531.5 ± 0.3 Ma. Crystal and crystal-lithic tuff beds near the top of the RBF yield ages of 520.3 ± 0.3 Ma (in Hanford Brook) and 519.1 ± 0.3 Ma (in Ratcliffe Brook). The new ages confirm the correlation between the Somerset Street and Hanford Brook sections based on acritarchs and make the association of small shelly fossils in the Hanford Brook section younger than 531 Ma. This result is relevant to ongoing discussions on the age of the base of undefined Cambrian Stage 2. The radiometric ages also support a young age for the upper part of the RBF, perhaps extending into Epoch 2.

Organic Phases in Bivalve (Arctica Islandica) Shells: Their Bulk and Amino Acid Nitrogen Stable Isotope Compositions

AbstractThe stable nitrogen isotope composition of bivalve shell organics serves as a proxy for nitrogen fluxes in modern and past ecosystems. An essential prerequisite to reconstruct environmental variables from δ15N values of bivalve shells is to understand if pristine isotope signals can be retrieved from shell organics after sample pretreatment. δ15N analyses of fossil shells should be limited to the intra‐crystalline organic matrix (intra‐OM), which is trapped within biomineral units and less likely contaminated or diagenetically overprinted than inter‐crystalline organics (inter‐OM). However, it remains unclear whether the different shell organic phases (insoluble/soluble inter‐OM, intra‐OM) are isotopically distinct and whether δ15N values of intra‐OM agree with those of bulk organic matter. These questions were tackled by applying different solvents (H2O, HCl, H2O2, NaOCl) to homogenized shell powder of a modern Arctica islandica. Milli‐Q water did not alter bulk δ15N values indicating the dissolution of the inter‐OM was negligible. Acid‐extracted intra‐OM exhibited a larger isotope variation within replicates and showed a minor but significant fractionation in bulk δ15N values related to the loss of acid‐soluble components. Compared to H2O2, NaOCl oxidative treatment was more effective in cleaning inter‐OM and produced reliable bulk and amino acid (AA)‐specific δ15N data of intra‐OM. Furthermore, differences in the relative abundance and δ15N values of individual AAs suggested that the N isotope composition is not uniform within shells, and the N‐bearing content and AA composition differ between organic phases. Future studies should test the capability of bulk and CSIA‐AA δ15N proxies in fossil shells as paleoenvironmental archives.