Global perturbation of the marine Ca isotopic composition in the aftermath of the Marinoan global glaciation

Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada were measured Both basal dolostones display delta(44/40)Ca values between 1 and 0 7 parts per thousand overlying limestones show a negative Ca isotope excursion to values around 0 1 parts per thousand and delta(44/40)Ca values rapidly increase up-section to near 2 0 parts per thousand In the Brazilian successions those high delta(44/40)Ca values rapidly decrease and stabilize to values between 0 6 and 0 9 parts per thousand These Ca isotope secular variation trends are unlike those of Sturtian post-glacial carbonate successions but similar to those of Marinoan post-glacial carbonate successions in Namibia suggesting that the perturbation of the marine Ca cycle was global This recommends Ca isotope stratigraphy as a tool to correlate Neoproterozoic post-glacial carbonate successions worldwide While the lowermost and uppermost strata have delta(44/40)Ca values typical of Phanerozoic carbonates the extremes 0 1 and 2 0 parts per thousand have not been thus far reported for other marine carbonates These extreme values suggest a short-lived non-actualistic perturbation in the marine Ca cycle Simple box modelling of the Marinoan post-glacial marine Ca cycle can reproduce the extreme values only by postulating a two-step process with Ca input initially exceeding Ca removal trough carbonate precipitation followed by precipitation overtaking a decreased Ca Input (C) 2010 Elsevier B V All rights reservedSwiss National Science Foundation (SNSF)[200021-107465]Swiss National Science Foundation (SNSF)Swiss National Science Foundation (SNSF)[200020-115911]Swiss National Science Foundation (SNSF)Swiss National Science Foundation (SNSF)Swiss National Science Foundation (SNSF)[200021-116486

The Ediacaran Aspidella-type impressions in the Jinxian successions of Liaoning Province, northeastern China

We identify the macroscopic impression fossils from the Xingmincun Formation of the Jinxian Group, Liaoning Province of northeastern China as members of the Aspidella plexus of the Ediacaran age. This is the first recognition of the taxon in the Liaoning Province, although such fossils have been previously recorded in the succession but were referred to as new species and relegated to an earlier Neoproterozoic age. A revision of the taxonomic interpretation and relative age estimation of the previous record is provided as well as an evaluation of abiotic vs biotic processes that could produce similar structures to studied impressions. We consider the mode of preservation of the fossils from a biochemical point of view and the properties of organic matter in the integument of soft-bodied metazoans. The selective preservation of the Ediacaran organisms, including metazoans, as impressions (moulds and casts) against the organically preserved contemporaneous cyanobacterial and algal microfossils and an exceptionally small number of terminal Ediacaran metazoan fossils (Sabellidites, Conotubus and Shaanxilites), demonstrates the non-resistant characteristics and the very different biochemical constitution of the Ediacaran metazoans compared with those that evolved in the Cambrian and after. The refractory biomacromolecules in cell walls of photosynthesizing microbiota (bacterans, cutans, algaenan and sporopollenin groups) and in the chitinous body walls of Sabellidites sharply contrast to the labile biopolymers in Ediacaran metazoans known only from impressions. The newly emerging biosynthesis of resistant biopolymers in metazoans (chitin and collagen groups) initiated by the annelids at the end of Ediacaran and fully evolved in Cambrian metazoans, considered with the ability to biomineralize, made their body preservation possible. The Chengjiang and Burgess Shale metazoans show evidence of this new biochemistry in body walls and cuticles, and not only because of the specific taphonomic window that enhanced their preservation.Divergence of Proterozoic-Cambrian phytoplankton and timing of the symbiotic origins of chlorophyte alga