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A numerically small graptolite assemblage from the Long Dai Formation at Lam Thuy village, southwestern Le Thuy district, Quang Binh Province, central Vietnam, includes Oktavites spiralis (Geinitz). The relative abundance [...]

The Soom Shale Member of the Cedarberg Formation (South Africa) is a key early Paleozoic Lagerstatte that directly overlies glacigenic deposits of the Late Ordovician glacial maximum; it was deposited on the Gondwanan craton during deglacial transgression. We show that it contains a substantial coarse silt to fine sand component that occurs in discrete laminae intimately associated with plankton-derived organic material. We interpret this component as loess, sourced from glacially derived debris and blown into the sea either directly or across seasonal sea ice, as happens today on the McMurdo Ice Shelf, Antarctica. Falling through the water column, this material likely stimulated production of phytoplankton, which then sank as sediment-loaded aggregates. In marked sedimentary partitioning, these silt and/or organic laminae alternate with fine, organic-poor mud laminae that likely represent (river-derived?) nepheloid plumes and that sporadically thicken into centimeter-scale mud turbidites. Sustained eolian input directly into the surface water may have been key to maintaining the high productivity of the Soom sea and then, via eutrophication and anoxia, to the exceptional preservation of its biota. doi: 10.1130/G31426.1

A new component of the Early Palaeozoic arthropod fauna is described from a monospecific accumulate of carapaces in a Late Ordovician (Katian) hemipelagic mudstone from the Cardigan district of southwest Wales (UK). Its non-biomineralized carapace is preserved as a carbonaceous residue, as is more labile anatomy (soft-parts) including the inner lamella and sub-ovate structures near its antero-dorsal margin, which we interpret to be putative eyes. The depositional context and associated fauna indicate that the arthropods inhabited an area of deep water and high primary productivity above a pronounced submarine topography. The preserved density of carapaces suggests the arthropods may have congregated into shoals or been transported post-mortem into depressions which acted as detritus traps. The accumulate provides a rare example of soft-part preservation in hemipelagic mudstones and highlights the role of organic material as a locus for authigenic mineralization during metamorphism. Keywords: taphonomy, organic preservation, inner lamella, eyes, zooplankton, arthropod. doi: 10.1017/S0016756809990045

Despite the Burgess Shale's (British Columbia, Canada) paleobiological importance, there is little consensus regarding its taphonomy. Its organic fossils are preserved as compressions associated with phyllosilicate films ('clay templates'). Debate focuses on whether these templates were fundamental in exceptional preservation or if they formed in metamorphism, meaning that it is important to establish the timing of their formation relative to decay. An early diagenetic origin has been proposed based on anatomy-specific variations in their composition, purportedly reflecting contrasts in decay. However, we demonstrate that these films bear a remarkable similarity to those that occur on organic fossils in graptolitic mudrocks and form as a normal product of low-grade metamorphism. Such phyllosilicates may also occur within voids created by volume loss in maturation, a process that may have aided their formation. In bedding-plane assemblages from graptolitic mudrocks, different taxa are associated with distinct phyllosilicates. This likely reflects stepwise maturation of their constituent kerogens in an evolving hydrothermal fluid, with different phyllosilicates forming as each taxon progressively underwent maturation. These observations provide an analogue for the distribution and composition of phyllosilicates on Burgess Shale fossils, which we interpret as reflecting variations in the maturation of their constituent tissues. Thus, their clay templates seem unremarkable, forming too late to account for exceptional preservation.

To help calibrate the emerging Upper Ordovician chitinozoan biozonation with the graptolite biozonation in the Anglo-Welsh, historical type basin, the graptolite-bearing CaradocAshgill successions between Fishguard and Cardigan, and at Whitland, SW Wales, have been collected for chitinozoans. In the Cardigan district, finds of Armoricochitina reticulifera within strata referred to the clingani graptolite Biozone (morrisi Subzone), together with accessory species, indicate the Fungochitina spinifera chitinozoan Biozone, known from several Ordovician sections in northern England that span the base of the Ashgill Series. Tanuchitina ?bergstroemi, eponymous of the succeeding chitinozoan biozone, has tentatively been recovered from strata of Pleurograptus linearis graptolite Biozone age in the Cardigan area. The T. ?bergstroemi Biozone can also be correlated with the type Ashgill Series of northern England. Chitinozoans suggest that the widespread Welsh Basin anoxic--oxic transition at the base of the Nantmel Mudstones Formation in Wales, traditionally equated with the Caradoc--Ashgill boundary, is of Cautleyan (or younger Ashgill) age in the Cardigan area. In the broadly time-equivalent, graptolite-rich Whitland section, also in SW Wales, two Baltoscandian chitinozoan biozones and a subzone have been recognized (again using accessory species), namely the Spinachitina cervicornis Biozone?, the Fungochitina spinifera Biozone and the Armoricochitina reticulifera Subzone. The new chitinozoan data provide a more precise means of correlation between the Whitland and Cardigan successions and suggest that the Normalograptus proliferation interval of the Whitland section is at least partly attributable to the Dicellograptus morrisi Subzone of the Dicranograptus clingani Biozone, rather than equating with the overlying Pleurograptus linearis Biozone. Keywords: chitinozoans, graptolites, Ordovician, biostratigraphy, Wales.

SIMS dating of detrital zircons from the stratigraphically enigmatic Radzimowice Slates of the Kaczawa Mountains (Sudetes, SW Poland), near the eastern termination of the European Variscides, has yielded age populations of: (1) 493-512 Ma, corresponding to late Cambrian to early Ordovician magmatism and constraining a maximum depositional age; (2) between 550 and 650 Ma, reflecting input from diverse Cadomian sources; and (3) older inherited components ranging to c. 3.3 Ga, with age spectra similar to those from Gondwanan North Africa. The new data show that the Radzimowice Slates cannot form a Proterozoic base to the Kaczawa Mountains succession, as suggested by earlier models, but was deposited, at the earliest, as an extensional basin-fill, during a relatively late stage of the break-up of this part of northern Gondwana. Keywords: SIMS zircon dating, slates, Kaczawa Complex, Sudetes, Variscides, Gondwana.

We propose ending the distinction between the dual stratigraphic terminology of time-rock units (of chronostratigraphy) and geologic time units (of geochronology). The long-held, but widely misunderstood, distinction between these two essentially parallel time scales in stratigraphy has been rendered unnecessary by the widespread adoption of the global stratotype sections and points (GSSP--golden spike) principle in defining intervals of geologic time within rock strata. We consider that the most appropriate name for this stratigraphic discipline is 'chronostratigraphy,' which would allow 'geochronology' to revert to its mainstream and original meaning of numerical age dating. This in turn makes the little-used formal term 'geochronometry' redundant. The terms 'eonothem,' 'erathem,' 'system,' 'series,' and 'stage' would become redundant, in favor of 'eon,' 'era,' 'period,' 'ep-och' and (disputably) 'age.' Our favored geologic time units may be qualified by 'early' and 'late,' but not by 'lower' and 'upper.' These suggested changes should simplify stratigraphic practice, encompass both stratified and nonstratified rocks, and help geologic understanding, while retaining precision of meaning. Keywords: stratigraphy, chronostratigraphy, geochronology.

Pyritized graptolites from the Welsh Basin (United Kingdom) slate belt acted as rigid bodies during cleavage formation, and epizonal white micas formed within the resulting strain shadows, orthogonal to the principal stress orientation. Although the quantities of mica are small, they are a pure synkinematic mineral and have been dated by [sup.40]Ar-[sup.39]Ar infrared laser microprobe as a means to dating cleavage. Four samples of strain-fringe mica from different hand samples yielded ages ranging from 394.4 [+ or -] 3.1 to 397.8 [+ or -] 1.8 Ma (2[sigma]), with a mean age of 396.1 [+ or -] 1.4 Ma (2[sigma]). By focusing on minerals that are unequivocally synkinematic, this technique provides a novel solution to the problems of isotopically dating slaty cleavage. Previous studies have predominantly relied on dating whole-rock slate samples or separated illite grains by [sup.40]Ar-[sup.39]Ar techniques; problems encountered included (1) separating the effects of isotopic contamination by detrital phases, (2)[sup.39]Ar loss during the irradiation of illite mineral separates, and (3) thermally induced [sup.40]Ar loss in nature from fine-grained minerals. By circumventing these problems, this new method provides the first unequivocal and high-precision age data for Acadian deformation in the well-characterized Welsh Basin slate belt. With such precision, the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent-continent collision. Keywords: [sup.40]Ar-[sup.39]Ar laserprobe, low temperature, slate, deformation, geochronology, Acadian.

The Early Silurian graptolites Spirograptus turriculatus and Sp. guerichi are typically preserved in condensed graptolite shale lithologies as entirely flattened outlines; all whorls are visible and little or no sediment infills the originally cone-shaped rhabdosomes, as though the graptolites had been sealed in clingfilm, or plastic wrap, prior to burial and compaction. By contrast, the rhabdosomes of graptolites transported in turbidity currents typically are filled with sediment. The most likely reason for the clingfilm mode of preservation is encasement or covering of the graptolite rhabdosomes by marine snow and/or microbial mats prior to burial by clastic sediment and compaction on an anoxic seafloor. Experimental evidence reported herein supports this suggestion. The organic material that mediated the preservation of such graptolites was likely akin to, but probably physically stronger than, the delicate benthic flocculation layer of the current Black Sea floor. Like the latter, it probably formed significant microtopography at and just below the sediment-water interface and mediated geologic processes such as early diagenesis in graptolite shale lithologies. Keywords: graptolites, black shales, marine snow, microbial mats.

We describe a remarkably preserved assemblage of sedimentary and tectonic fabrics in cores from the Kaczawa complex, Sudetes, SW Poland. These fabrics indicate a continuum of process from repeated remobilization of Upper Devonian--Lower Carboniferous muddy flysch and volcaniclastic sediments as debris flows and olistostromes, to fracturing, fluid-streaming and soft-sediment injection triggered by high pore-water pressures during the initial stages of tectonic deformation, to contractional cleavage formation and local cataclasis while the sediment was still only partially consolidated. These structures are similar to those described from ODP cores through the toes of active accretionary prisms. They indicate active subduction of oceanic crust during the Late Devonian, suggesting that ophiolite obduction and significant overthrusting in the Sudetes occurred as an integral part of the Variscan orogeny. Keywords: Sudetes, Kaczawa complex, melange, soft-sediment deformation.

We analyse the 'three flaws' to potentially defining a formal Anthropocene geological time unit as advanced by Ruddiman (2018). (1) We recognize a long record of pre-industrial human impacts, but note that these increased in relative magnitude slowly and were strongly time-transgressive by comparison with the extraordinarily rapid, novel and near-globally synchronous changes of post-industrial time. (2) The rules of stratigraphic nomenclature do not 'reject' pre-industrial anthropogenic signals – these have long been a key characteristic and distinguishing feature of the Holocene. (3) In contrast to the contention that classical chronostratigraphy is now widely ignored by scientists, it remains vital and widely used in unambiguously defining geological time units and is an indispensable part of the Earth sciences. A mounting body of evidence indicates that the Anthropocene, considered as a precisely defined geological time unit that begins in the mid-20th century, is sharply distinct from the Holocene. [ABSTRACT FROM AUTHOR]

What is the reach of geology, today? The word evokes strata, minerals and fossils. But how about metro systems, farmyard animals, factory smoke, ballpoint pens, tree‐rings and the fluff that comes off our clothes? These kinds of objects are just part of the evidence that is now being assembled to build a picture of the Anthropocene—the idea that human activities are now sufficiently powerful and pervasive to build the geology of the present—and to influence the course of the geology of our planet's future, too. [ABSTRACT FROM AUTHOR]

The graptolite biozonation of the Wenlock Series in the Builth Wells district is reassessed. The graptolite fauna is dominated by relatively few, but variable, species of Monograptus s.s., Pristiograptus and Monoclimacis. These species are mostly long-ranging and are of limited biostratigraphical use. Biozonation is based largely on the relatively rare cyrtograptids. The lower Wenlock Series of the district comprises the widely recognized centrifugus, murchisoni and riccartonensis biozones. The middle to upper Wenlock biostratigraphy differs from that previously recognized in the UK. Above the riccartonensis Biozone, dubius, rigidus and lundgreni biozones are distinguished. Separate flexilis and ellesae biozones are not recognized: Monograptus flexilis appears earlier than, then largely co-exists with, Cyrtograptus rigidus s.l.; while Cyrtograptus ellesae appears later than Cyrtograptus lundgreni. The uppermost Wenlock nassa-ludensis Biozone is sparsely fossiliferous; its subdivision has not proved possible. This revised biostratigraphical scheme for the Wenlock Series of the Builth Wells district suggests that the Sheinwoodian-Homerian boundary, as defined in the Welsh Borderland, might occur within, rather than at the base of, the lundgreni Biozone. However, difficulties in correlation with other Wenlock sequences, particularly overseas, suggest significant biofacies control, with the Wenlock seas of the Builth Wells district appearing to have been periodically inhospitable to graptolites.