Although an early Cambrian origin of cephalopods has been suggested by molecular studies, no unequivocal fossil evidence has yet been presented. Septate shells collected from shallow-marine limestone of the lower Cambrian (upper Terreneuvian, c. 522 Ma) Bonavista Formation of southeastern Newfoundland, Canada, are here interpreted as straight, elongate conical cephalopod phragmocones. The material documented here may push the origin of cephalopods back in time by about 30 Ma to an unexpected early stage of the Cambrian biotic radiation of metazoans, i.e. before the first occurrence of euarthropods.

Abstract. Cold-water corals (CWCs) constitute important deep-water ecosystems that are under increasing environmental pressure due to ocean acidification and global warming. The sensitivity of these deep-water ecosystems to environmental change is demonstrated by abundant paleorecords drilled through CWC mounds that reveal characteristic alterations between rapid formation and dormant or erosive phases. Previous studies have identified several central parameters for driving or inhibiting CWC growth such as food supply, oxygenation, and the carbon saturation state of bottom water, yet there are still large uncertainties about the relative importance of the different environmental parameters. To advance this debate we have performed a multiproxy study on a sediment core retrieved from the 25 m high Bowie Mound, located at 866 m water depth on the continental slope off southeastern Brazil, a structure built up mainly by the CWC Solenosmilia variabilis. Our results indicate a multifactorial control on CWC growth at Bowie Mound during the past ∼ 160 kyr, which reveals distinct formation pulses during northern high-latitude glacial cold events (Heinrich stadials, HSs) largely associated with anomalously strong monsoonal rainfall over the continent. The ensuing enhanced runoff elevated the terrigenous nutrient and organic-matter supply to the continental margin and likely boosted marine productivity. The dispersal of food particles towards the CWC colonies during HSs was facilitated by the highly dynamic hydraulic conditions along the continental slope that prevailed throughout glacial periods. These conditions caused the emplacement of a pronounced nepheloid layer above Bowie Mound, thereby aiding the concentration and along-slope dispersal of organic matter. Our study thus emphasizes the impact of continental climate variability on a highly vulnerable deep-marine ecosystem.

Abstract. Baddeleyite (ZrO2) is widely used in U-Pb geochronology, but different patterns of discordance often hamper accurate age interpretations. This is also the case for baddeleyite from the Spread Eagle Intrusive Complex (SEIC) and Cape St. Mary’s sills (CSMS) from Newfoundland, which we investigated combining high precision and high spatial resolution methods. Literature data and our own observations suggest that at least seven different types of baddeleyite–zircon intergrowths can be distinguished in nature, among which we describe xenocrystic zircon inclusions in baddeleyite for the first time. Baddeleyite 207Pb/206Pb dates from secondary ionization mass spectrometry (SIMS) and isotope dilution thermal ionization mass spectrometry (ID-TIMS) are in good agreement with each other and with stratigraphic data, but some SIMS sessions of grain mounts show reverse discordance. This suggests that matrix differences between references and unknowns biased the U-Pb relative sensitivity calibration, possibly due to crystal orientation effects, or due to alteration of the baddeleyite crystals, which is indicated by unusually high common Pb contents. ID-TIMS data for SEIC and CSMS single baddeleyite crystals reveal normal discordance as linear arrays with decreasing 206Pb/238U dates, indicating that their discordance is dominated by recent Pb loss due to fast pathway or volume diffusion. Hence, 207Pb/206Pb dates are more reliable than 206Pb/238U dates even for Phanerozoic baddeleyite. Negative lower intercepts of baddeleyite discordias and direct correlations between ID-TIMS 207Pb/206Pb dates and degree of discordance indicate preferential 206Pb loss, possibly due to 222Rn mobilization. In such cases, the most reliable crystallization ages are concordia upper intercept dates or weighted means of the least discordant 207Pb/206Pb dates. We regard the best estimates of the intrusion ages to be 498.7 ± 4.5 Ma (2σ; ID-TIMS upper intercept date for one SEIC dike) and 439.4 ± 0.8 Ma (ID-TIMS weighted mean 207Pb/206Pb date for one sill of CSMS). Sample SL18 of the Freetown Layered Complex, Sierra Leone (associated with the Central Atlantic Magmatic Province) was investigated as an additional reference. For SL18, we report a revised 201.07 ± 0.64 Ma intrusion age, based on a weighted mean 207Pb/206Pb date of previous and new baddeleyite ID-TIMS data, agreeing well with corresponding SIMS data. Increasing discordance with decreasing crystal size in SL18 indicates that Pb loss affected baddeleyite rims more strongly than cores. Employment of SIMS or mechanical abrasion prior to ID-TIMS analysis may therefore produce more concordant baddeleyite data. We emphasize that the combination of high precision and high spatial resolution dating, along with detailed microscale imaging of baddeleyite, is powerful for extracting reliable age information from baddeleyite from rocks with a complex post-magmatic evolution.

The Avalon Peninsula, Newfoundland, Canada, defined as the type zone of Avalonia is believed to have been impacted by several orogenetic and deformation events since the Neoproterozoic. Previous studies determined the lowest degree of metamorphism reached in the successions was of the prehnite-pumpellyite or greenschist facies. We sampled and measured thirteen clastic sedimentary sections ranging from the late Ediacaran to the Early Ordovician and analysed the illite “crystallinity” of 331 samples using the Kübler index. Our results show diagenetic zones occur related to lithology, age and burial depth, respectively, and regional setting. Samples adjacent to the fault zones bounding the Holyrood Horst experienced among the highest degree of metamorphism (anchizone) in the study area. The lowest degree of thermal alteration occurs in the high stratigraphic sections at the centre of the horst structure where shallow diagenetic conditions are preserved. Fault zones, most probably active during the Acadian Orogeny, may have served as potential paths for hot fluids in bounding areas of the horst, whereas the centre of the horst remained almost unaffected by any metamorphic overprint. The thermal impact decreases from the Bonavista Peninsula to the study area from greenschist facies to anchizonal and diagenetic. The study area experienced lower metamorphic conditions than major regions of Avalonia south of the study area on the mainland of New Brunswick and Maine and eastwards in Europe. The thermal impact is in part consistent with a few other areas of Avalonia, such as the Mira terrane and the Antigonish Highlands in Nova Scotia.

Abstract. Cold-water corals (CWC) constitute important deep-water ecosystems that are increasingly under environmental pressure due to ocean acidification and global warming. The sensitivity of these deep-water ecosystems to environmental change is demonstrated by abundant paleo-records drilled through CWC mounds that reveal a characteristic alteration between rapid formation and dormant or erosive phases. Previous studies have identified several parameters such as food supply, oxygenation, and carbon saturation state of bottom water as central for driving or inhibiting CWC growth, yet there is still a large uncertainty about the relative importance of the different environmental parameters. To advance this debate we have performed a multi-proxy study on a sediment core retrieved from the 25 m high Bowie Mound, located in 866 m water depth on the continental slope off south-eastern Brazil, a structure built up mainly by the CWC Solenosmilia variabilis. Our results indicate a multi-factorial control on CWC growth and mound formation at Bowie Mound during the past ~160 kyrs, which reveals distinct formation pulses during glacial high northern latitude cold events (Heinrich Stadials, HS) largely associated with anomalous continental wet periods. The ensuing enhanced run-off elevated the terrigenous nutrient and organic matter supply to the continental margin, and might have boosted marine productivity. The dispersal of food particles towards the CWC colonies during HS was facilitated by the highly dynamic hydraulic conditions along the continental slope that prevailed throughout glacial periods. These conditions caused the emplacement of a pronounced nepheloid layer above Bowie Mound aiding the concentration and along-slope dispersal of organic matter. Our study thus demonstrates a yet unrecognized impact of continental climate variability on a highly vulnerable deep-marine ecosystem.