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The Steptoean Positive Carbon Isotope Excursion (SPICE) of earliest late Cambrian (Furongian) age is identified in England. The excursion is found within a c . 145 m thick siliciclastic succession within the middle and higher part of the Outwoods Shale Formation of Warwickshire, and reaches a maximum δ 13 C org amplitude of 4.1‰ at values of −25.6‰. Biostratigraphical data show that the excursion occupies the greater part of the Olenus Biozone, an equivalent of the Glyptagnostus reticulatus Biozone that marks the base of the Furongian and coeval base of the Steptoean in North America. The amplitude of the excursion approaches that recorded in limestone-dominated Laurentian successions, and is greater than that recently documented for organic-rich mudstones of palaeocontinental Baltica in southern Sweden. A minor positive excursion above the SPICE may equate with a similar excursion recognized in Siberia. The SPICE in the Outwoods Shale Formation seems closely linked to the widely recognized early Furongian eustatic sea-level rise. There is no evidence in the English succession for slightly later regression, elsewhere considered coincident with the peak of the excursion and pivotal to some previous models explaining the SPICE. Supplementary material: Analytical results, including total organic carbon (TOC) values for each sample, are available at www.geolsoc.org.uk/SUP18455.

Three dated (U–Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire (England) and Pembrokeshire (Wales) delimit the traditional ‘Lower9–‘Middle9 Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.45 ± 0.36 [0.81 including tracer calibration and 238 U decay constant errors] Ma from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, and a date of 509.10 ± 0.22 [0.77 including tracer calibration and 238 U decay constant errors] Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates offer a calibration of early metazoan evolution by directly constraining the age of the intervening Comley Limestones, which contain diverse small shelly fossils in addition to trilobites, and also a key early occurrence of exceptional, three-dimensionally preserved arthropods. In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.30 ± 0.23 [0.77 including tracer calibration and 238 U decay constant errors] Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level at which trilobites make their first local appearance. Supplementary material: Appendix 1, a table of isotope data, is available at http://www.geolsoc.org.uk/SUP18444.

A new U–Pb date of 615.2 ± 1.3 (2σ) Ma for the Twt Hill Granite, North Wales, contrasts with an Rb–Sr isochron age of 491 ± 12 (2σ) Ma from the same body. The latter age is thought to result from isotope resetting during regional low-grade metamorphism or fault reactivation. The Rb–Sr age also coincides with the onset of latest Cambrian to Early Tremadoc regression and is taken to reflect tectonic uplift prior to the Arenig overstep at around 478 Ma. It is proposed that this in turn reflects plate-scale processes along the contemporary peri-Gondwanan continental margin.

Monazite paragenesis during low-grade metamorphism is poorly understood. The first unequivocal instance of the mineral having crystallized synchronously with compressional cleavage formation is reported. Compositionally, these monazites resemble diagenetic forms but differ texturally by displaying syntectonic microfabrics. Their predominant association with organic-walled fossils implies that organic material may play an important role in controlling the behaviour of light rare earth elements (LREE) during low-grade metamorphism, probably by releasing diagenetically sequestered LREE and organically bound phosphorus during thermal maturation (devolatilization), and/or by promoting a favourable environment for monazite precipitation. Potentially, such monazites could provide a powerful geochronometer for cleavage formation.

Authigenic minerals play an important role in the preservation of most soft-bodied fossils. The greatest detail is preserved in apatite (calcium phosphate) but its precipitation is usually inhibited by the high concentrations of HCO 3 - in aqueous settings. Nonetheless, investigations of soft-bodied biotas have revealed very early authigenic calcite crystal bundles in close association with phosphatized soft-tissues. This demonstrates that the geochemical controls on soft-tissue mineralization are dynamic and act on a very local scale. Direct comparisons with experimental results permit the conditions of fossilization to be inferred.

Soft-tissues phosphatized in laboratory experiments closely resemble fossil phosphatized soft-tissues, indicating that similar processes were involved. The smaller the aggregations of calcium phosphate particles precipitated the greater the fidelity of morphological preservation. The highest fidelity occurs where the bacteria themselves are not replicated even though precipitation is bacterially induced. While extensive phosphatization of larger carcasses, however, may necessitate the build-up of concentrations in the sediment beforehand, this is not the case for phosphatization of small quantities of soft-tissue. Mineralization of soft-tissue in the laboratory is not ‘instant’ but may take several weeks, or even months if decay is inhibited. The precipitation of associated calcium carbonate is controlled by shifts in pH in response to the decay process.

Exceptionally well-preserved specimens of a new cypridid ostracode (Crustacea), Raepula ira sp. nov., are described from palaeolake sediments of the Middle Miocene Barstow Formation of the Mud Hills, southern California. This is only the second occurrence of exceptionally preserved ostracodes from the Miocene. Based on ages obtained from associated volcanic tuffs the palaeolake sediments were deposited between 16.3 and 15.8 Ma. The ostracodes form one element of a diverse lake community dominated by fairy shrimps, copepods, diatoms, larvae of diving beetles, flies and mosquitoes, and body fossils and ephippia of branchiopods and anomopods. The ostracodes are preserved three dimensionally with their soft anatomy replicated in microcrystalline silica. Submicron-scale details such as sensory setae are preserved, surpassing the resolution of most other ostracode-bearing lagerstatten and allowing their biology to be compared with extant taxa. Supplementary material: Red–blue anaglyphs of the exceptionally preserved ostracodes are available at http://www.geolsoc.org.uk/SUP18407.

The mineralized soft tissue of a dinosaur, only the second discovery of its kind is reported from the Lower Cretaceous of Las Hoyas, Spam. Cellular details of mineralized skin and muscle of Pelecanimimus are replicated in an iron carbonate. The outline of this ornithomimosaur is preserved by a phosphatized microbial mat that enshrouded the carcass. It confirms the existence of either a throat pouch or dewlap, and soft occipital crest. This study confirms the importance of microbial mats hi the fossilization of soft tissues and emphasises the need for careful monitoring of vertebrate remains for mineralized soft tissues prior to acid preparation. The multitoothed ornithomimosaur dinosaur Pelecanimimus polyodon was recently described from the Lower Cretaceous lacustrine lithographic limestones of Las Hoyas (Cuenca, Spain) (Perez-Moreno et al. 1994). The only known specimen of this, the first ornithomimosaur theropod found in Europe, preserves what were originally described as 9integumentary impressions9. These occur in the throat region, flanking the more proximal neck vertebrae, in the vicinity of the ribs, and behind the elbow. In addition a small triangular area at the rear of the skull was interpreted as a possible occipital crest (Perez-Moreno et al. 1994). Analyses confirm that these features represent mineralized traces of soft tissues. They are preserved both as replicas of the original skin and muscle tissue, and as impressions on microbial mats or veils that grew over them. In addition to Pelecanimimus, the lacustrine limestones of Las Hoyas (Melendez 1995) have yielded a well preserved diverse biota of plants