Emmanuelle Grosjean

Fossil steroids record the appearance of Demospongiae during the Cryogenian period

The Neoproterozoic era (1,000–542u2009Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C30 sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation (∼635u2009Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology, constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635u2009Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635u2009Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100u2009Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, ∼713u2009Myr ago in Oman).

Composition of the lipids of Nanoarchaeum equitans and their origin from its host Ignicoccus sp. strain KIN4/I

The contents and nature of the membrane lipids of Nanoarchaeum equitans and Ignicoccus sp. strain KIN4/I, grown at 90°C, and Ignicoccus sp. strain KIN4/I, cultivated at its lowest and highest growth temperatures (75°C and 95°C) were analyzed. Both organisms contained very simple and qualitatively identical assemblages of glycerol ether lipids, showing only differences in the amounts of certain components. LC–MS analyses of the total lipid extracts revealed that archaeol and caldarchaeol were the main core lipids. The predominant polar headgroups consisted of one or more sugar residues attached either directly to the core lipid or via a phosphate group. GC–MS analyses of hydrolyzed total lipid extracts revealed that the co-culture of N. equitans and Ignicoccus sp. strain KIN4/I, as well as Ignicoccus sp. strain KIN4/I grown at 90°C, contained phytane and biphytane in a ratio of approximately 4:1. Purified N. equitans cells and Ignicoccus sp. strain KIN4/I cultivated at 75°C and 95°C had a phytane to biphytane ratio of 10:1. Sugar residues were mainly mannose and small amounts of glucose. Consistent 13C fractionation patterns of isoprenoid chains of N. equitans and its host indicated that the N. equitans lipids were synthesized in the host cells.

Detecting the source of Heinrich layers: An organic geochemical study

[1]xa0There are controversies regarding the origin of Heinrich layer 3 (H3), the massive ice-rafting and meltwater event in the North Atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr B.P. Some argue in favor of a Laurentide Ice Sheet source similar to other Heinrich layers, while a contending view argues for the European ice sheet source. Existing geochemical proxies such as 40Ar/39Ar, 206Pb/204Pb, or ɛNd, etc., could not be used to distinguish among various sources of ice-rafted debris in H3 because of their low abundances, suggesting a background glacial sediment signal. In order to circumvent this problem a biomarker-based approach is used to characterize the provenance of H layers 2, 3, and 4 and other non-Heinrich layers. The presence of hopanes and steranes and their aromatic counterparts in the H layers is incompatible with Recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks. The most diagnostic and useful signatures of this ancient organic matter in the H layers are the dominance of C34 hopanoids over C33 and the occurrence of isorenieratane along with palaerenieratane. Biomarkers signatures in H layers 2 and 3 of the Labrador Sea suggest no difference in their source. Hydrocarbon distributions suggest that these sediments were derived from the Middle to Late Ordovician and Silurian source rocks of the Hudson Bay of eastern Canada. Biomarker data of the H layer 4 from the northwest Atlantic reveal that the sediments of this layer have a similar source to the H layers in the Labrador Sea.