An optical luminescence chronology for late Pleistocene aeolian activity in the Colombian and Venezuelan Llanos Quaternary Research

The lowland savannas (Llanos) of Colombia and Venezuela are covered by extensive aeolian landforms for which little chronological information exists. We present the first optically stimulated luminescence (OSL) age constraints for dunes in the Llanos Orientales of lowland Colombia and new ages for dunes in the Venezuelan Llanos. The dunes are fully vegetated and show evidence of post-depositional erosion. Ages range from 4.5 ± 0.4 to 66 ± 4 ka, with the majority dating to 10-27 ka (Marine Isotope Stage 2). Some dunes accumulated quickly during the last glacial maximum, although most were active 16-10 ka. Accretion largely ceased after 10 ka. All dunes are elongated downwind from rivers, parallel with dry season winds, and are interpreted as source-bordering features. As they are presently isolated from fluvial sediments by gallery forest it is proposed that activity was associated with a more prolonged dry season, which restricted gallery forest, leading to greater sediment availability on river shorelines. Such variability in dry season duration was potentially mediated by the mean latitude of the ITCZ. The cessation of most dune accretion after ca. 10 ka suggests reduced seasonality and a more northerly ITCZ position, consistent with evidence from the Cariaco Basi

New Evidence for the Age and Palaeoecology of the Knysna Formation, South Africa

The existence of lignitic deposits (Knysna Formation) on the South African south coast, near to the town of Knysna has been recognised for more than a century. However, a combination of limited study and few natural exposures has meant that the age and stratigraphic position of the Knysna Formation are unclear, despite its potential as a palaeoenvironmental archive. We present a new suite of chronological, geochemical and palynological data obtained from a recently identified lignite exposure in this area. The lignite pollen assemblage is dominated by palms (Arecaceae), which are now locally extinct, and contains additional palynomorphs of tropical affinity, along with (moist-temperate) Podocarpus-type pollen, grasses, and herbaceous pollen types (e.g. Cliffortia-type, Asteraceae). Overall, the assemblage shows some commonalities with the Miocene Elandsfontein Formation in the Western Cape. The lignites are dominated by a diverse range of higher plant biomarkers, including abundant leaf wax lipids, as well as lignin monomers and leaf cuticle-derived macromolecular organic matter. All strongly indicate a terrestrial depositional setting, perhaps akin to contemporary palm swamps. A number of sesquiterpenoids imply the presence of gymnosperms, supporting observations from the pollen data and previously reported macro-fossil finds. The application of isothermal thermoluminescence techniques to coversands overlying the lignite produced a minimum age of ~1.7 Ma. Additional clues as to the likely age of the lignite are provided by compound-specific stable carbon isotope analyses of the leaf wax lipids. These are approximately 8‰ enriched relative to typical C3 vegetation leaf waxes, and imply a potential contribution from C4 vegetation. From this, an age post-dating the Oligocene may be inferred, and in conjunction with the site’s geomorphic setting, an age post dating the middle Miocene is considered plausible. This is markedly younger than previous (Eocene) age estimates for the Knynsa Formation

On the Habitability of Desert Varnish: A Combined Study by Micro-Raman Spectroscopy, X-ray Diffraction, and Methylated Pyrolysis-Gas Chromatography-Mass Spectrometry.

In 2020, the ESA ExoMars and NASA Mars 2020 missions will be launched to Mars to search for evidence of past and present life. In preparation for these missions, terrestrial analog samples of rock formations on Mars are studied in detail in order to optimize the scientific information that the analytical instrumentation will return. Desert varnishes are thin mineral coatings found on rocks in arid and semi-arid environments on Earth that are recognized as analog samples. During the formation of desert varnishes (which takes many hundreds of years), organic matter is incorporated, and microorganisms may also play an active role in the formation process. During this study, four complementary analytical techniques proposed for Mars missions (X-ray diffraction [XRD], Raman spectroscopy, elemental analysis, and pyrolysis-gas chromatography-mass spectrometry [Py-GC-MS]) were used to interrogate samples of desert varnish and describe their capacity to sustain life under extreme scenarios. For the first time, both the geochemistry and the organic compounds associated with desert varnish are described with the use of identical sets of samples. XRD and Raman spectroscopy measurements were used to nondestructively interrogate the mineralogy of the samples. In addition, the use of Raman spectroscopy instruments enabled the detection of β-carotene, a highly Raman-active biomarker. The content and the nature of the organic material in the samples were further investigated with elemental analysis and methylated Py-GC-MS, and a bacterial origin was determined to be likely. In the context of planetary exploration, we describe the habitable nature of desert varnish based on the biogeochemical composition of the samples. Possible interference of the geological substrate on the detectability of pyrolysis products is also suggested

On the Habitability of Desert Varnish: a Combined Study by Micro-Raman Spectroscopy, X-Ray Diffraction and Methylated Pyrolysis-Gas Chromatography-Mass Spectrometry

In 2020, the ESA ExoMars and NASA Mars 2020 missions will be launched to Mars, searching for evidence of past and present life. In preparation for these missions, terrestrial analogue samples of rock formations on Mars are studied in detail in order to optimize the scientific information that the analytical instrumentation will return. Desert varnishes are thin mineral coatings found on rocks in arid and semi-arid environments on Earth that are recognized as analogue samples. During the formation of desert varnishes (which takes many hundreds of years) organic matter is incorporated and microorganisms may also play an active role in the formation process. During this study, four complementary analytical techniques proposed for Mars missions (X-rays diffraction, Raman spectroscopy, elemental analysis and pyrolysis-gas chromatography-mass spectrometry) were used to interrogate samples of desert varnish and to describe their capacity to sustain life under extreme scenario. For the first time, both the geochemistry and the organic compounds associated with desert varnish are described using an identical set of samples. XRD and Raman spectroscopy measurements were used to non-destructively interrogate the mineralogy of the samples. In addition, the use of Raman spectroscopy instruments enabled the detection of β-carotene, a highly Raman active biomarker. The content and the nature of the organic material in the samples was further investigated using elemental analysis and methylated Py-GC-MS and a bacterial origin was determined to be likely. In the context of planetary exploration, we describe the habitable nature of desert varnish based on the bio-geochemical composition of the samples. Possible interference of the geological substrate on the detectability of pyrolysis products is also suggested

Improving estimates of carbon storage and flux in tropical peatlands

Our limited knowledge of the size of the carbon pool and exchange fluxes in forested lowland tropical peatlands represents a major gap in our understanding of the global carbon cycle. Peat deposits in several regions (e.g. the Congo Basin, much of Amazonia) are only just beginning to be mapped and characterised. Here we consider the extent to which methodological improvements and improved coordination between researchers could help to fill this gap. We review the literature on measurement of the key parameters required to calculate carbon pools and fluxes, including peatland area, peat bulk density, carbon concentration, above-ground carbon stocks, litter inputs to the peat, gaseous carbon exchange, and waterborne carbon fluxes. We identify areas where further research and better coordination are particularly needed in order to reduce the uncertainties in estimates of tropical peatland carbon pools and fluxes, thereby facilitating better-informed management of these exceptionally carbon-rich ecosystems

Improving estimates of tropical peatland area, carbon storage, and greenhouse gas fluxes

Our limited knowledge of the size of the carbon pool and exchange fluxes in forested lowland tropical peatlands represents a major gap in our understanding of the global carbon cycle. Peat deposits in several regions (e.g. the Congo Basin, much of Amazonia) are only just beginning to be mapped and characterised. Here we consider the extent to which methodological improvements and improved coordination between researchers could help to fill this gap. We review the literature on measurement of the key parameters required to calculate carbon pools and fluxes, including peatland area, peat bulk density, carbon concentration, above-ground carbon stocks, litter inputs to the peat, gaseous carbon exchange, and waterborne carbon fluxes. We identify areas where further research and better coordination are particularly needed in order to reduce the uncertainties in estimates of tropical peatland carbon pools and fluxes, thereby facilitating better-informed management of these exceptionally carbon-rich ecosystems