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New occurrences of Psammichnites gigas are reported from the Mackenzie Mountains, northwest Canada. A locality in the hanging wall of the Plateau Fault, just below the top of the upper member of the Backbone Ranges Formation, demonstrates that the uppermost part of the unit is Tommotian (latter part of Cambrian Age 2) or possibly earliest Atabanian (earliest Cambrian Age 3) in its previously undated proximal manifestation. Localities in the trilobite-bearing Sekwi Formation confirm that Psammichnites gigas can be at least as young as Atdabanian (early to middle parts of Cambrian Age 3) in Laurentia. A review of reported occurrences suggests Psammichnites gigas, and the related ichnotaxa Plagiogmus arcuatus and Taphrelminthopsis circularis, may be valuable for correlations in western Laurentia if their ichnotaxonomic relationships are clarified. [ABSTRACT FROM AUTHOR]

• New carbon-sequestration geosystem paradigm proposed for screening CO 2 repositories. • Deposition, burial history 1st-order controls on repository attributes, traps, etc. • Genetic understanding of geology enables property prediction away from data control. • Case-study application to heavily industrialized region of onshore Canada. In this paper, I propose a new geoscience paradigm for evaluating potential carbon-sequestration targets. I introduce the term carbon-sequestration geosystem to study and describe portions of sedimentary basins where all the geologic components necessary for the safe and long-term storage of CO 2 are present. The purpose of this type of analysis, most appropriately applied at a basin-screening stage, is to derive a holistic, genetic, and predictive understanding of the geology – the depositional systems, structural setting and other factors that are direct controls on storage, injectivity, potential for induced seismicity, and other critical factors. To illustrate the concepts, I present a re-evaluation of the geologic carbon-sequestration options in Southern Ontario (Canada) where business and environmental needs, mostly associated with hard-to-abate industries, require urgent action. Legacy wireline-logs, core, and outcrop data are the main data sources available in this onshore setting. The results of this new, independent study are broadly similar to those of previous studies: the Cambrian section, a saline aquifer, is the most likely candidate to be a CO 2 repository. However, the methodology used identified several issues (e.g., stratigraphic heterogeneity, proximity to basement) that will need addressing by targeted data collection and/or analysis before site-selection for a test should be undertaken. [ABSTRACT FROM AUTHOR]

Paleokarst is most commonly expressed as subtle stratigraphic surfaces rather than large void systems penetrating deeply into the paleo-subsurface. In contrast, a regional Precambrian-Cambrian unconformity on Victoria Island (NWT, Canada), is associated with exceptional exposure of large, intact Cambrian paleocaverns (100 m diameter; tens of m high). The paleocaves are distributed along a paleo-horizontal plane, and an associated gryke network is present in the 30–60 m of Neoproterozoic dolostone between cave rooves and the base of overlying Cambrian sandstone; both are filled by Cambrian sandstone. The formation and preservation of such karst features require aggressive dissolution along a stable paleo-water-table shortly before transgression and deposition of shallow-marine sand over the dolostone. During the transgression, the karst network acted as a conduit for flowing groundwater that was discharged through overlying, unconsolidated Cambrian shallow-marine sand, producing water-escape structures (sand volcanoes and their conduits). The conduits are preserved as cylindrical remnants of the sand volcanoes' feeder pipes. Sediment fluidisation was probably caused by variations in the hydraulic-head gradient in a meteoric lens near the Cambrian coastline under a tropical climate with abundant, probably seasonally variable rainfall that caused pulses in subsurface fluid flow. Spatial distribution of the paleocaves and sand volcanoes suggests their formation on the southeast side of a recently faulted horst of Proterozoic carbonate bedrock that formed a nearshore island during early Cambrian sea-level rise. Fluidisation structures such as those reported here have generally been difficult to interpret owing to a lack of data on the fluid hydraulics of the underlying aquifer. This is the first report linking the hydraulics of a well-characterised paleokarst to development of fluid-escape structures. Such structures are widely known from sandstones overlying the sub-Cambrian unconformity around the circumference of Laurentia. [ABSTRACT FROM AUTHOR]

The upper lower Cambrian Gog Group in the southern Rocky Mountains of Canada displays a high diversity and abundance of arthropod traces. Four ichnogenera,Cruziana, Diplichnites, Monomorphichnus, Rusophycus, and “Indeterminate Arthropod Scratches” are discussed, with a total of 17 different ichnospecies, as follows:Cruziana billingsiFillion and Pickerill, 1990,Cruziana irregularisFenton and Fenton, 1937,Cruziana jenningsiFenton and Fenton, 1937,Cruziana navicellaFenton and Fenton, 1937,Cruziana omanicaSeilacher, 1970,Cruziana pectinataSeilacher, 1994,Cruziana penicillataGibb, Chatterton, and Pemberton, 2009,Cruziana plicataCrimes, Legg, Marcos, and Arboleya, 1977,Cruziana tenellaLinnarsson, 1871,Diplichnites twelvetreesi(Chapman, 1928),Monomorphichnus bilinearisCrimes, 1970b,Monomorphichnus lineatusCrimes, Legg, Marcos, and Arboleya, 1977,Rusophycus eutendorfensis(Linck, 1942), andRusophycus unilobus(Seilacher, 1970). Three new ichnospecies, i.e.,Cruziana caputinclinataisp. nov.,Rusophycus subnotousisp. nov., andDiplichnites obliquusisp. nov., are proposed, described, and illustrated. The ichnofauna collected from three localities (Lake O'Hara, Mount Babel, and Redoubt Mountain) are predominantlyCruziana. Evidence of nutrient-rich substrates containing microbially induced sedimentary structures and the ichnospecies present confirm that the trace fossil bearing strata are part of theCruzianaichnofacies and were deposited in a fully marine basin between fair weather wave base and storm wave base. [ABSTRACT FROM PUBLISHER]

Abstract: Upper Cambrian to Lower Ordovician pelagic carbonate rocks of the Cow Head Group in western Newfoundland (Canada) were sampled for the study of their radiolarian fauna. Well-preserved and diverse faunal assemblages were obtained from a number of levels of the Shallow Bay and Green Point formations. Three different assemblages, including a total of five families, eight genera and 20 species, are recognized in three different sections situated on a palaeobathymetric profile. The various recognized assemblages are compared with previous studies conducted on the Cow Head Group; they improve considerably our understanding of the pattern of changes in radiolarian diversity during the Cambrian–Ordovician transition. The Radiolarian biotic record of western Newfoundland unveils a two step faunal change across the Cambrian–Ordovician transitional interval: one situated at the base of the uppermost Cambrian Stage 10 and the second at a poorly constrained interval situated towards the top of the same Stage 10. These biotic changes consist of genus-level selective extinctions, as well as within-clade species faunal turnover (i.e. Echidnina, Paleospiculum), decrease of species abundance, species extinction and within-clade episodes of species diversification (i.e. Protoentactinia, Parechidnina). [Copyright &y& Elsevier]

The complex history of description of the anomalocaridids has partly been caused by the fragmentary nature of these fossils. Frontal appendages and mouth parts are more readily preserved than whole-body assemblages, so the earliest work on these animals examined these structures in isolation. After several decades of research, these disarticulated elements were assembled together to reconstruct the anomalocaridid body plan, and a total of three Burgess Shale genera, Anomalocaris, Laggania and Hurdia, were described in full. Here we present new frontal appendage material of additional anomalocaridid taxa from the ‘Middle’ Cambrian (Series 3) Burgess Shale Formation in Canada, showing that the diversity of anomalocaridids in this locality is even higher than previously thought. Material includes Amplectobelua stephenensis sp. nov. , the first known occurrence of this genus outside of China; Caryosyntrips serratus gen. et sp. nov., which is similar to the Anomalocaris appendage but has a straighter outline and a different arrangement of spines; and an appendage that may be either the Laggania appendage or a third morph of the Hurdia appendage. The new anomalocaridid material is contemporaneous with the previously described taxa Anomalocaris, Laggania, and Hurdia, and the differences in morphology between the frontal appendages may reflect different feeding strategies. The stratigraphically lowest locality, S7 on Mount Stephen, yields material from all anomalocaridid taxa, but the assemblages in the younger quarries on Fossil Ridge are dominated by Anomalocaris and Hurdia only. [ABSTRACT FROM AUTHOR]

Abstract: Until recently, research on the renowned fossil animals of the Burgess Shale has advanced to a greater degree than an understanding of the rocks in which they are found. Studies addressing lithostratigraphy and hydrothermal petrography of the so-called ‘inner carbonate belt’ and adjacent Chancellor Group, however, have begun to re-evaluate long-standing hypotheses on the Middle Cambrian of Western Canada. Tectonic activity along the Kicking Horse Rim (buried remnants of Neoproterozoic rifting) during the Cambrian Period had more influence on local sedimentation than previously thought. Notably, large-scale collapse of the Cathedral carbonate platform margin at ∼509 Ma BP is evidence of reactivated basement faults. These failures produced listric Megatruncation Surfaces, having near vertical escarpments (>150 m in height) where they terminate against the platform. The majority of what have been interpreted as shed olistoliths from the Cathedral platform margin is herein shown instead to be carbonate mud mounds. These grew in situ along the face of the Cathedral Escarpment, and are associated with fossiliferous intervals in overlying basinal mudstones at three distinct stratigraphic horizons (two within the Burgess Shale) during the Delamaran and Marjuman stages. The mounds nucleated where deep-seated normal faults intersected the seafloor, building primarily during periods of relative sea level transgression. Mound growth is associated with syndepositional exhalative activity, inferred from stratigraphic relations, sedimentology, and geochemistry. The new name Monarch Formation is proposed for the initial post-collapse beds and mounds deposited against the Cathedral Escarpment (early Glossopleura Zone); the variably-defined term ‘Takakkaw Tongue’ is thereby confined to pre-collapse slope deposits coeval to and correlative with the Cathedral Formation. [Copyright &y& Elsevier]

Volcanics of the Skinner Cove Formation of western Newfoundland carry a primary remanence acquired at 550 Ma at a paleolatitude of 19°S. There has been doubt that this represents the latitude of the Laurentian margin at 550 Ma, because the Skinner Cove Formation is allochthonous. We present new evidence from inherited zircons in the volcanics that should remove this doubt. Zircon crystals extracted from an ankaramite flow and a trachyte flow were dated individually by measuring U–Th–Pb isotopes for ∼30 μm×30 μm areas using a laser ablation microprobe (LAM) linked to an inductively coupled plasma mass spectrometer (ICP-MS). Most of the zircons from the ankaramite are concordant and yield a 550±5 Ma date indistinguishable from the 550+3/−2 Ma date previously reported using multi-grain thermal ionisation mass spectrometry. About half of the zircons from the trachyte are also concordant yielding an overlapping date of 556±5 Ma. The other half clustered at ∼1000 and 1500–1600 Ma, which are characteristic ages of the Grenvillian basement exposed nearby in the Long Range Inlier. These zircon xenocrysts were very likely picked up as the Skinner Cove magma ascended through Grenvillian basement of the Laurentian margin. There can now be little doubt that the ∼19°S Skinner Cove paleolatitude represents Laurentia’s southern margin at 550 Ma. This makes it unlikely that Laurentia changed from south polar at ∼523 Ma to equatorial at ∼508 Ma due to a rapid ∼90° change in the Earth’s rotation axis. Such an inertial interchange true polar wander (IITPW) event has been proposed as a trigger for the Cambrian faunal explosion. An IITPW event may have occurred in the Vendian, mostly between 577 and 565 Ma, judging by paleomagnetic results from Laurentia. However, it is more likely that the paleomagnetic results suggesting high latitude for Laurentia at 577 Ma or low latitude at 565 Ma are flawed. We suggest that Laurentia remained at low latitude throughout the Vendian (from the ∼600 Ma start of near-equatorial glaciations). This is supported by magmatic evidence suggesting that Laurentia’s incipient Iapetus margin was stationary over a mantle plume throughout the Vendian. Laurentia at low latitude throughout the Vendian also helps provide the predominance of low latitude continents needed to account for the Vendian’s near-equatorial glaciations, according to the snowball Earth hypothesis. [Copyright &y& Elsevier]

Tepee structures are common in many ancient carbonate tidal flat successions, and because analogues are known from tropical coastal areas, they are well established as evidence for synsedimentary lithification of subaerially exposed carbonate sediment. Existing explanations involving desiccation, thermal expansion and contraction, fluctuating groundwater pore pressure or diagenetic force of crystallization do not adequately account for the style and degree of deformation seen in some examples, such as those in the Middle Cambrian Cathedral Formation of the southern Rocky Mountains, western Canada. These tepees provide evidence for essentially instantaneous events causing brittle failure of decimetre-thick crusts of ooidal and pisoidal grainstone, followed by their dilation, rupturing, separation, tilting and shingling. They can be explained as breccias generated by sporadic episodes of strong ground motion from earthquakes that emanated from a syndepositionally active fault system nearby. Variably directed tensile and compressive stresses broke crusts, shifted them upwards and shuffled them laterally. Subsequent microbial encrustation and vigorous flushing by seawater in the resulting shelter cavities led to rapid stabilization by cementation. Recognition of the role of seismically induced deformation in explaining some tepee structures furnishes a proxy for synsedimentary tectonism and adds another member to the family of ‘seismites’ which reflect a range of rheological properties of unlithified and lithifying sediments. [Copyright &y& Elsevier]

A slab of Burgess Shale (Middle Cambrian), displaying an incomplete exoskeleton of the large arthropod Sidneyia inexpectans and encompassed by nine specimens of the priapulid worm Ottoia prolifica, is interpreted as a death assemblage, with the worms once living off or feeding around a carcass or freshly moulted instar of Sidneyia. Death is thought to have been caused by an obrution event that preserved the organisms in situ. [ABSTRACT FROM AUTHOR]