Chemostratigraphy of Neoproterozoic carbonates: implications for 'blind dating'

The delta C-13(carb) and Sr-87/Sr-86 secular variations in Neoproteozoic seawater have been used for the purpose of 'isotope stratigraphy' but there are a number of problems that can preclude its routine use. In particular, it cannot be used with confidence for 'blind dating'. The compilation of isotopic data on carbonate rocks reveals a high level of inconsistency between various carbon isotope age curves constructed for Neoproteozoic seawater, caused by a relatively high frequency of both global and local delta C-13(carb) fluctuations combined with few reliable age determinations. Further complication is caused by the unresolved problem as to whether two or four glaciations, and associated negative delta C-13(carb) excursions, can be reliably documented. Carbon isotope stratigraphy cannot be used alone for geological correlation and 'blind dating'. Strontium isotope stratigraphy is a more reliable and precise tool for stratigraphic correlations and indirect age determinations. Combining strontium and carbon isotope stratigraphy, several discrete ages within the 590-544 Myr interval, and two age-groups at 660-610 and 740-690 Myr can be resolved

A possible billion-year-old holozoan with differentiated multicellularity.

Sediments of the Torridonian sequence of the Northwest Scottish Highlands contain a wide array of microfossils, documenting life in a non-marine setting a billion years ago (1 Ga).1, 2, 3, 4 Phosphate nodules from the Diabaig Formation at Loch Torridon preserve microorganisms with cellular-level fidelity,5,6 allowing for partial reconstruction of the developmental stages of a new organism, Bicellum brasieri gen. et sp. nov. The mature form of Bicellum consists of a solid, spherical ball of tightly packed cells (a stereoblast) of isodiametric cells enclosed in a monolayer of elongated, sausage-shaped cells. However, two populations of naked stereoblasts show mixed cell shapes, which we infer to indicate incipient development of elongated cells that were migrating to the periphery of the cell mass. These simple morphogenetic movements could be explained by differential cell-cell adhesion.7,8 In fact, the basic morphology of Bicellum is topologically similar to that of experimentally produced cell masses that were shown to spontaneously segregate into two distinct domains based on differential cadherin-based cell adhesion.9 The lack of rigid cell walls in the stereoblast renders an algal affinity for Bicellum unlikely: its overall morphology is more consistent with a holozoan origin. Unicellular holozoans are known today to form multicellular stages within complex life cycles,10, 11, 12, 13 so the occurrence of such simple levels of transient multicellularity seen here is consistent with a holozoan affinity. Regardless of precise phylogenetic placement, these fossils demonstrate simple cell differentiation and morphogenic processes that are similar to those seen in some metazoans today

True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces

Abstract: Rock outcrops of the sedimentary–stratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sediment–water or sediment–air interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. Some true substrates are notable for their sedimentary, palaeontological and ichnological signatures that provide windows into key intervals of Earth history, but countless others occur routinely throughout the sedimentary–stratigraphic record. They frequently reveal patterns that are strikingly familiar from modern sedimentary environments, such as ripple marks, animal trackways, raindrop impressions or mudcracks: all phenomena that are apparently ephemeral in modern settings, and which form on recognizably human timescales. This paper sets out to explain why these short‐term, transient, small‐scale features are counter‐intuitively abundant within a 3.8 billion year‐long sedimentary–stratigraphic record that is known to be inherently time‐incomplete. True substrates are fundamentally related to a state of stasis in ancient sedimentation systems, and distinguishable from other types of bedding surfaces that formed from a dominance of states of deposition or erosion. Stasis is shown to play a key role in both their formation and preservation, rendering them faithful and valuable archives of palaeoenvironmental and temporal information. Further, the intersection between the time–length scale of their formative processes and outcrop expressions can be used to explain why they are so frequently encountered in outcrop investigations. Explaining true substrates as inevitable and unexceptional by‐products of the accrual of the sedimentary–stratigraphic record should shift perspectives on what can be understood about Earth history from field studies of the sedimentary–stratigraphic record. They should be recognized as providing high‐definition information about the mundane day to day operation of ancient environments, and critically assuage the argument that the incomplete sedimentary–stratigraphic record is unrepresentative of the geological past

The lower cambrian transgression and glauconite-phosphate facies in western Europe

International audienc

Phytophthora cinnamomi

Phytophthora cinnamomi is a soil-borne pathogen that causes crown and root rot of many horticultural, ornamental and forestry crops. It preferentially attacks 'feeder' roots. The geographical origin of P. cinnamomi is not clearly established. It was first described on Cinnamonum burmannii (Lauraceae) in Sumatra (ID) in 1922, but now has a nearly worldwide distribution, including most of Europe (CABI. 1991). The pathogen is found in tropical and subtropical countries and in the Mediterranean and some mild, temperate regions where it has almost certainly been introduced (EPPO/CABI, l998). P. cinnamomi is the most widely distributed Phytophthora species, with over 1000 host species (Zentmeyer, 1983). The most significant food-crop losses due to P. cinnamomi root rot occur in avocado but the pathogen also attacks Ananas comosus, Castanea dentata and C. sativa, Cinchona spp., Chamaecyparis lawsoniana, Cinnamomum spp., conifers, Ericaceae (including Rhododendron spp.), Eucalyptus spp., especially E. marginata. Fagus spp., Juglans spp., Pinus spp., Prunus spp., Quercus spp. and many ornamental trees and shrubs, including Vaccinium macrocarpon. It has caused extensive damage to natural Eucalyptus Forest in Western Australia. The recorded host range includes most of the temperate fruit trees, but these are not relevant hosts in practice. In the EPPO region, the most significant hosts are nursery stock of ornamental and amenity trees and avocados, in the limited areas where they are grown. It has been reported to be the main causal agent of ink disease of C. sativa in southern France and has been indicated as a possible causal agent of oak decline in the Iberian Peninsula. Propagules are spread by soil movement, including wind-blow or debris, or by water flow and run-off in drainage/irrigation ditches. Control is complicated by the very wide host range as well as by the longevity (often many years) of propagules (mainly sporangia and encysted zoospores) in nonsterile moist soil and root debris at depths at which soil fumigation is not always effective (Munnecke, 1984). Symptomless plants are a major means of spreading the pathogen to disease-free areas and this is the main problem for intensive production systems in the nursery industry. The first line of control is therefore planting disease-free stock. Imported plants for planting should be kept well separated in nurseries and preferably grown in containers for several months until their phytosanitary status has been checked. Strict hygiene should be observed at all times

Evaluating evidence from the Torridonian Supergroup (Scotland, UK) for eukaryotic life on land in the Proterozoic

Taxonomy of Torridon Group microfossils from thin sections of phosphatic material (adapted from Battison 2012)

Effaced preservation in the Ediacara biota and its implications for the early macrofossil record

Abstract: Ediacaran structures known as 'pizza discs' or Ivesheadia have long been considered enigmatic. They are amongst the oldest known members of the Ediacara biota, apparently restricted to the Avalonian successions of Newfoundland and the UK, c. 579-560Ma. Here, we suggest that these impressions are taphomorphs, resulting from the post-mortem decay of the frondose Ediacaran biota. Ediacaran fossils range from well-preserved, high-fidelity variants to almost completely effaced specimens. The effaced specimens are inferred to have undergone modification of their original morphology by post-mortem microbial decay on the sea floor, combined with sediment trapping and binding. In this style of preservation, morphological details within the organism became variously subdued as a function of the extent of organic decay prior to casting by overlying sediments. Decay and effacement were progressive in nature, producing a continuum of grades of preservation on Ediacaran bedding planes. Fossils preserved by such 'effaced preservation' are those that have suffered these processes to the extent that only their gross form can be determined. We suggest that the lack of detailed morphology in effaced specimens renders such fossils unsuitable for use as type material, as it is possible that several taxa may, upon degradation and burial, generate similar morphological taphomorphs. We here reinterpret the genus Ivesheadia as a taphomorph resulting from extensive post-mortem decay of frondose organisms. Blackbrookia, Pseudovendia and Shepshedia from beds of comparable age in England are likewise regarded as taphomorphs broadly related to Charnia or Charniodiscus spp. To reflect the suggestion that such impressions are likely to be taphomorphs, and not taxonomically discrete, we propose the term ivesheadiomorphs to incorporate all such effaced taphonomic expressions of Ediacaran macrofossil taxa in Avalonian assemblages. Our recognition of effaced preservation has significant implications for Ediacaran taxonomy, and consequently for measures of Ediacaran diversity and disparity. It is implied that Avalonian assemblages preserve both organisms that were alive and organisms that were already dead at the time of burial. As such, the fossil assemblages cannot be taken to represent census populations of living organisms, as in prior interpretations. © The Palaeontological Association