J.W. de Leeuw

High molecular weight organic matter in martian meteorites

We have performed an investigation to detect high molecular weight organic matter in martian meteorites. Solvent-extracted samples of two Antarctic 5nds (ALH 84001, sub-sample 106 and EET A79001, sub-sample 351) and one non-Antarctic fall (Nakhla) were analysed by :ash pyrolysis–gas chromatography–mass spectrometry. Results suggest that our sub-sample of ALH 84001 contains no pyrolysable organic matter. In contrast, our samples of EET A79001 and Nakhla contain organic matter of high molecular weight, which releases aromatic and alkylaromatic hydrocarbons, phenol and benzonitrile as major compounds upon pyrolysis. The detection of similar pyrolysis products from Nakhla and EET A79001 indicates that these martian meteorites may have a common high molecular weight organic phase. Carbon isotopic measurements of individual molecules in the Nakhla pyrolysate, by :ash pyrolysis– gas chromatography–isotope ratio mass spectrometry, reveal that this high molecular weight organic matter has some similarities to that found in carbonaceous chondrites. At this point, an origin by terrestrial contamination cannot be unequivocally ruled out, but the data seem to support proposals that martian samples contain organic matter originating from meteoritic infall on Mars. The results suggest that a wider, pyrolysis-based study of martian meteorites would be a justi5able use of these precious samples. ? 2002 Elsevier Science Ltd. All rights reserved.

The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown

Enormous quantities of the free-floating freshwater fern Azolla grew and reproduced in situ in the Arctic Ocean during the middle Eocene, as was demonstrated by microscopic analysis of microlaminated sediments recovered from the Lomonosov Ridge during Integrated Ocean Drilling Program (IODP) Expedition 302. The timing of the Azolla phase (approximately 48.5 Ma) coincides with the earliest signs of onset of the transition from a greenhouse towards the modern icehouse Earth. The sustained growth of Azolla, currently ranking among the fastest growing plants on Earth, in a major anoxic oceanic basin may have contributed to decreasing atmospheric pCO2 levels via burial of Azolla-derived organic matter. The consequences of these enormous Azolla blooms for regional and global nutrient and carbon cycles are still largely unknown. Cultivation experiments have been set up to investigate the influence of elevated pCO2 on Azolla growth, showing a marked increase in Azolla productivity under elevated (760 and 1910 ppm) pCO2 conditions. The combined results of organic carbon, sulphur, nitrogen content and 15N and 13C measurements of sediments from the Azolla interval illustrate the potential contribution of nitrogen fixation in a euxinic stratified Eocene Arctic. Flux calculations were used to quantitatively reconstruct the potential storage of carbon (0.9-3.5 10(18) gC) in the Arctic during the Azolla interval. It is estimated that storing 0.9 10(18) to 3.5 10(18) g carbon would result in a 55 to 470 ppm drawdown of pCO2 under Eocene conditions, indicating that the Arctic Azolla blooms may have had a significant effect on global atmospheric pCO2 levels through enhanced burial of organic matter.

Cyclic diaryl ethers in a Late Permian sediment

Abstract Abundant cyclic diaryl ethers, such as dibenzofuran and its alkyl derivatives are found in solvent extracts and kerogen pyrolysates of a Late Permian organic-rich marl from northern Italy. These organic compounds are distinguishable from biphenyl and its alkyl derivatives by high resolution GC–MS. Bulk geochemical (Rock-Eval) and transmitted/reflected light microscopic analyses indicate that the dominant source of organic matter in the sediment is from partially decomposed land plant debris which has been transported into the marine depositional setting. A likely origin for the cyclic diaryl ether moieties is dehydrated and condensed polysaccharides. Possible sources for the polysaccharides are the organic constituents of land plants, microbes and fungi.

The Combined Petrographic and Chemical Analysis of end-Permian Kerogens

The end of the Permian was marked by one of the greatest mass extinctions of all time. A valuable record of life and death during this event is contained within sedimentary organic matter. The stable isotopic, molecular and morphological information contained within remains of end-Permian organisms represent an important resource for scientists attempting to produce paleoenvironment reconstructions. Most meaningful data derive from multidisciplinary analyses of the same samples. In these circumstances it is desirable that sample preparation for one approach does not hinder subsequent analysis by another. To ensure compatibility of sample processing procedures the petrographic and chemical consequences of two common kerogen preparation steps, demineralization and screening (sieving), were simultaneously monitored using transmitted light microscopy and flash pyrolysis. Two end-Permian sediments, whose organic content was predominated by land-plant debris, were chosen for this purpose. A limestone was used to assess the problem of fluoride production when dematerializing carbonates and a marl was used to investigate the possibility of introducing a sampling bias following kerogen screening. Flash pyrolysis results of demineralization residues indicate that neoformed fluorides can be effectively removed by repeated treatments with excess concentrated HCl. Flash pyrolysis of screened size fractions ( 250 μm) suggest that, for the end-Permian kerogen used, the various fractions are qualitatively representative of the unscreened kerogen. In a paleoenvironmental context, the homogeneity of the land plant derived kerogen reflects a period of organic accumulation on land followed by rapid deposition and burial in a marine setting. These findings constitute a step forward in the quest for parity between petrographic and chemical analyses of the same kerogen samples.

Lateral Variations in End-Permian Organic Matter in Northern Italy

The end-Permian mass extinction is the most profound biotic disturbance in the Phanerozoic and is accompanied by a dramatic change in the carbon chemistry of the oceans. The cause of these disturbances remains controversial. One valuable source of information for the end-Permian event is that contained within sedimentary organic matter. We have used organic geochemical methods to investigate end-Permian organic matter in the Dolomites of northern Italy. Samples of the same marl, which marks the junction between the Bellerophon Formation and Werfen Formation, from five different sections were analysed to establish lateral variations in organic matter deposited at the end of the Permian. As the basal unit of the Werfen Formation (the Tesero Oolite Horizon) is thought to have been deposited almost synchronously throughout the Southern Alps, the marl that lies immediately beneath it may also show some synchroneity within the area. Organic geochemical data were compared to mineralogical data from the same samples. The amounts of organic matter vary with distance from the palaeocoastline but similar organic molecules are found in each sample. Both the inorganic and organic constituents point to a widespread and rapid introduction of land-derived material into the western Tethys Ocean in the Late Permian. It is possible that the features observed in the marl are the result of environmental changes occurring at the end of the Period. Acidifying emissions from the massive volcanism of the Siberian Traps may have caused a terrestrial ecosystem collapse, a loss of soil deposits and an increase in weathering rates. Future organic geochemical work will benefit from the identification of relatively low maturity organic matter in the sections in the west of the study area.

Keynote Speech - Taking Physical Modelling of Deepwater Depositional Systems Forwards

We show how new scaling considerations, which we term Shields scaling, have opened up new avenues of investigation in the physical modelling of deepwater depositional systems. We demonstrate the added value of the new approach with two examples: A) Channel-levee relief development. B) Depositional patterns in a break-of-slope setting. The flow dynamics results of the experiments are consistent with the extensive body of previously published physical modelling results in both examples. The sediment distribution, however, shows a clear departure from the draping depositional behavior encountered predominantly in previous work. In contrast, the experimental deposits presented here display a subtle spatio-temporal interplay between erosion, transport, and deposition of sediment by turbidity currents, which results in a morphodynamic evolution that is a much better analogue for deepwater system development.