Abstract In this chapter we summarize the depositional setting and occurrences of life traces wit... more Abstract In this chapter we summarize the depositional setting and occurrences of life traces within the 3.48 Ga Dresser Formation of the Pilbara Craton, Western Australia. All fossiliferous and chemical traces of life occur with the lowermost of two chert units within the Dresser Formation, known as the North Pole chert. This is separated from an overlying, nonfossiliferous chert unit of the formation by a unit of pillowed and massive basalt. Highly morphologically varied stromatolites of assemblage 2 occur in shallow water conditions, including lacustrine, fluvial, and terrestrial hot spring settings. The recent discovery of geyserite and other sinter deposits containing biosignatures shows that life inhabited a terrestrial setting much earlier than previously thought. A range of evidence points to diverse life at this time that occupied several distinct niches using, probably, a variety of metabolisms.
Gas chromatography-mass spectrometry was applied to samples collected from an exceptionally well-... more Gas chromatography-mass spectrometry was applied to samples collected from an exceptionally well-preserved Late Jurassic (~150 Ma) sinter complex of the Claudia palaeo-geothermal field, Deseado Massif geological province, Argentinean Patagonia, which, despite its age, has never been deeply buried. Results indicate that the distal sinter apron has a much higher preservation potential for indigenous organic matter (OM) than the more proximal (vent area) facies of this palaeo-geothermal field. Specifically, homohopane ratios show that the OM of the proximal apron is of mixed thermal maturities and is in low abundance. In contrast, the OM extracted from the distal apron contains highly abundant, thermally immature biomarkers, the presence of which are consistent with the lower original fluid temperatures of the distal spring facies. Moreover, despite indications of the presence of some thermally mature aromatic compounds, hopane and sterane ratios confirm that the distal apron samples are extremely thermally immature and thereby constitute an area of exceptional molecular preservation. From an astrobiological viewpoint, these results suggest that silica sinter can preserve abundant organics over millions of years in palaeoenvironmentally conducive settings, and that sample-site selection within a hot spring facies-model framework may be critical in the successful search for ancient extra-terrestrial life.
Highly promising locales for biosignature prospecting on Mars are ancient hydrothermal deposits, ... more Highly promising locales for biosignature prospecting on Mars are ancient hydrothermal deposits, formed by the interaction of surface water with heat from volcanism or impacts [1-3]. On Earth, they occur throughout the geological record (to at least ~3.5 Ga), preserving robust mineralogical, textural and compositional evidence of thermophilic microbial activity [e.g., 3-5]. Hydrothermal systems were likely present early in Mars’ history [6], including at two of the three finalist candidate landing sites for M2020, Columbia Hills [7-9] and NE Syrtis Major [10 & refs. therein]. Hydrothermal environments on Earth’s surface are varied, constituting subaerial hot spring aprons, mounds and fumaroles; shallow to deep-sea hydrothermal vents (black and white smokers); and vent mounds and hot-spring discharges in lacustrine and fluvial settings. Biological information can be preserved by rapid, spring-sourced mineral precipitation [1,2,9], but also could be altered or destroyed by postdeposit...
Recent discoveries of geyserite and siliceous sinter with textural biosignatures in the ∼3.5 Ga D... more Recent discoveries of geyserite and siliceous sinter with textural biosignatures in the ∼3.5 Ga Dresser Formation of the Pilbara Craton, Western Australia, extended the record of inhabited subaerial hot springs on Earth by ∼3 billion years, back to the time when siliceous sinter deposits are known to have formed on Mars (e.g., at Columbia Hills, Gusev Crater). Here, we present more detailed lithostratigraphic, petrographic and geochemical data collected from 100 measured sections across a ∼14 km strike length in the Dresser Formation. The data indicate deposition of a wide range of hot spring and associated deposits in a restricted interval that directly overlies a hydrothermally influenced volcanic caldera lake facies, with shoreline stromatolites. Hot spring deposits show abrupt lateral facies changes and include associated channelized clastic deposits that support fluvial, subaerial hot spring deposition. All Dresser hot spring and associated lithofacies have direct analogs with proximal, middle, and distal apron hot spring facies that are characteristic of those from New Zealand, Yellowstone National Park, USA, and Argentina. Rare earth element and yttrium geochemistry shows that the Dresser geyserite shares identical patterns with Phanerozoic hot spring sinters. This geochemical data further supports textural and contextual evidence that indicate the Dresser geyserite formed as a subaerial hot spring sinter. Further, the Dresser hot spring deposits are temporally associated with a diverse suite of textural biosignatures that indicate a thriving microbial community existed within in a Paleoarchean hot spring field. The results presented here underscore the importance of continued study of the early geological record for astrobiological research. In particular these findings reinforce the long-standing hypothesis that hydrothermal systems are optimal places to search for past life on Mars.
30th International Meeting on Organic Geochemistry (IMOG 2021), 2021
Summary The study of kerogen can aid in understanding the evolution of life on Earth by yielding ... more Summary The study of kerogen can aid in understanding the evolution of life on Earth by yielding geochemical information on ancient organisms. However, the study of kerogen in Precambrian overmature rocks is problematic due to uncertainty regarding biogenicity. Ancient kerogens are commonly simplified, having lost most of their structural information during catagenesis and metagenesis. Therefore, careful study of candidate Precambrian-age kerogen is required to find primary structural information. Here we examine organic matter in a well-preserved (metamorphic temperature ∼230°C) dolomite microbialite reef complex of the ∼2.4 Ga Turee Creek Group, Western Australia. This group contains diverse stromatolites, thrombolites, and shallow and deep-water microfossil assemblages preserved in black chert, and enigmatic branched organic structures (Fig. 1; Barlow and Van Kranendonk, 2016; Barlow et al., 2018). Total organic carbon values are low (0.02–0.5 wt%), but kerogen bands in Raman spectroscopy are abundant, and consistent with regional thermal maturity estimates. In addition, FTIR and micro-FTIR studies showed significant chemical differences between the fossil organisms. The different characteristics support biogenicity of the kerogen and derivation from different living sources. This work demonstrates that information gained from in situ measurements of Precambrian overmature kerogen retains more information than from analysis of homogenised overmature kerogens.
Abstract The ancient rocks of the Pilbara region of Western Australia have been an important anal... more Abstract The ancient rocks of the Pilbara region of Western Australia have been an important analog site for the study of possible inhabited environments in the search for life on early Mars for over four decades. Here, we review the evidence for Paleo- to Neoarchean life and the habitats that it occupied in the Pilbara Craton and unconformably overlying Fortescue Group of the Mount Bruce Supergroup. Nine major inhabited environments are described, which range from land to sea, and into the subsurface, showing that life had diversified into, and flourished within, a range of different environments early in Earth history. An important additional component in the search for life on Mars involves the manner in which evidence for early life is preserved. From the examples studied here, early mineralization of organic matter is key to the preservation of reliable biosignatures, in either silica, carbonate, or pyrite, but burial by volcanic ash can also provide excellent preservation.
The 3.4-Ga Strelley Pool Formation (SPF) at the informally named 'Waterfall Locality' in ... more The 3.4-Ga Strelley Pool Formation (SPF) at the informally named 'Waterfall Locality' in the Goldsworthy greenstone belt of the Pilbara Craton, Western Australia, provides deeper insights into ancient, shallow subaqueous to possibly subaerial ecosystems. Outcrops at this locality contain a thin (<3 m) unit of carbonaceous and non-carbonaceous cherts and silicified sandstones that were deposited in a shallow-water coastal environment, with hydrothermal activities, consistent with the previous studies. Carbonaceous, sulfide-rich massive black cherts with coniform structures up to 3 cm high are characterized by diverse rare earth elements (REE) signatures including enrichment of light [light rare earth elements (LREE)] or middle rare earth elements and by enrichment of heavy metals represented by Zn. The massive black cherts were likely deposited by mixing of hydrothermal and non-hydrothermal fluids. Coniform structures in the cherts are characterized by diffuse laminae comp...
Abstract In this chapter we summarize the depositional setting and occurrences of life traces wit... more Abstract In this chapter we summarize the depositional setting and occurrences of life traces within the 3.48 Ga Dresser Formation of the Pilbara Craton, Western Australia. All fossiliferous and chemical traces of life occur with the lowermost of two chert units within the Dresser Formation, known as the North Pole chert. This is separated from an overlying, nonfossiliferous chert unit of the formation by a unit of pillowed and massive basalt. Highly morphologically varied stromatolites of assemblage 2 occur in shallow water conditions, including lacustrine, fluvial, and terrestrial hot spring settings. The recent discovery of geyserite and other sinter deposits containing biosignatures shows that life inhabited a terrestrial setting much earlier than previously thought. A range of evidence points to diverse life at this time that occupied several distinct niches using, probably, a variety of metabolisms.
Gas chromatography-mass spectrometry was applied to samples collected from an exceptionally well-... more Gas chromatography-mass spectrometry was applied to samples collected from an exceptionally well-preserved Late Jurassic (~150 Ma) sinter complex of the Claudia palaeo-geothermal field, Deseado Massif geological province, Argentinean Patagonia, which, despite its age, has never been deeply buried. Results indicate that the distal sinter apron has a much higher preservation potential for indigenous organic matter (OM) than the more proximal (vent area) facies of this palaeo-geothermal field. Specifically, homohopane ratios show that the OM of the proximal apron is of mixed thermal maturities and is in low abundance. In contrast, the OM extracted from the distal apron contains highly abundant, thermally immature biomarkers, the presence of which are consistent with the lower original fluid temperatures of the distal spring facies. Moreover, despite indications of the presence of some thermally mature aromatic compounds, hopane and sterane ratios confirm that the distal apron samples are extremely thermally immature and thereby constitute an area of exceptional molecular preservation. From an astrobiological viewpoint, these results suggest that silica sinter can preserve abundant organics over millions of years in palaeoenvironmentally conducive settings, and that sample-site selection within a hot spring facies-model framework may be critical in the successful search for ancient extra-terrestrial life.
Highly promising locales for biosignature prospecting on Mars are ancient hydrothermal deposits, ... more Highly promising locales for biosignature prospecting on Mars are ancient hydrothermal deposits, formed by the interaction of surface water with heat from volcanism or impacts [1-3]. On Earth, they occur throughout the geological record (to at least ~3.5 Ga), preserving robust mineralogical, textural and compositional evidence of thermophilic microbial activity [e.g., 3-5]. Hydrothermal systems were likely present early in Mars’ history [6], including at two of the three finalist candidate landing sites for M2020, Columbia Hills [7-9] and NE Syrtis Major [10 & refs. therein]. Hydrothermal environments on Earth’s surface are varied, constituting subaerial hot spring aprons, mounds and fumaroles; shallow to deep-sea hydrothermal vents (black and white smokers); and vent mounds and hot-spring discharges in lacustrine and fluvial settings. Biological information can be preserved by rapid, spring-sourced mineral precipitation [1,2,9], but also could be altered or destroyed by postdeposit...
Recent discoveries of geyserite and siliceous sinter with textural biosignatures in the ∼3.5 Ga D... more Recent discoveries of geyserite and siliceous sinter with textural biosignatures in the ∼3.5 Ga Dresser Formation of the Pilbara Craton, Western Australia, extended the record of inhabited subaerial hot springs on Earth by ∼3 billion years, back to the time when siliceous sinter deposits are known to have formed on Mars (e.g., at Columbia Hills, Gusev Crater). Here, we present more detailed lithostratigraphic, petrographic and geochemical data collected from 100 measured sections across a ∼14 km strike length in the Dresser Formation. The data indicate deposition of a wide range of hot spring and associated deposits in a restricted interval that directly overlies a hydrothermally influenced volcanic caldera lake facies, with shoreline stromatolites. Hot spring deposits show abrupt lateral facies changes and include associated channelized clastic deposits that support fluvial, subaerial hot spring deposition. All Dresser hot spring and associated lithofacies have direct analogs with proximal, middle, and distal apron hot spring facies that are characteristic of those from New Zealand, Yellowstone National Park, USA, and Argentina. Rare earth element and yttrium geochemistry shows that the Dresser geyserite shares identical patterns with Phanerozoic hot spring sinters. This geochemical data further supports textural and contextual evidence that indicate the Dresser geyserite formed as a subaerial hot spring sinter. Further, the Dresser hot spring deposits are temporally associated with a diverse suite of textural biosignatures that indicate a thriving microbial community existed within in a Paleoarchean hot spring field. The results presented here underscore the importance of continued study of the early geological record for astrobiological research. In particular these findings reinforce the long-standing hypothesis that hydrothermal systems are optimal places to search for past life on Mars.
30th International Meeting on Organic Geochemistry (IMOG 2021), 2021
Summary The study of kerogen can aid in understanding the evolution of life on Earth by yielding ... more Summary The study of kerogen can aid in understanding the evolution of life on Earth by yielding geochemical information on ancient organisms. However, the study of kerogen in Precambrian overmature rocks is problematic due to uncertainty regarding biogenicity. Ancient kerogens are commonly simplified, having lost most of their structural information during catagenesis and metagenesis. Therefore, careful study of candidate Precambrian-age kerogen is required to find primary structural information. Here we examine organic matter in a well-preserved (metamorphic temperature ∼230°C) dolomite microbialite reef complex of the ∼2.4 Ga Turee Creek Group, Western Australia. This group contains diverse stromatolites, thrombolites, and shallow and deep-water microfossil assemblages preserved in black chert, and enigmatic branched organic structures (Fig. 1; Barlow and Van Kranendonk, 2016; Barlow et al., 2018). Total organic carbon values are low (0.02–0.5 wt%), but kerogen bands in Raman spectroscopy are abundant, and consistent with regional thermal maturity estimates. In addition, FTIR and micro-FTIR studies showed significant chemical differences between the fossil organisms. The different characteristics support biogenicity of the kerogen and derivation from different living sources. This work demonstrates that information gained from in situ measurements of Precambrian overmature kerogen retains more information than from analysis of homogenised overmature kerogens.
Abstract The ancient rocks of the Pilbara region of Western Australia have been an important anal... more Abstract The ancient rocks of the Pilbara region of Western Australia have been an important analog site for the study of possible inhabited environments in the search for life on early Mars for over four decades. Here, we review the evidence for Paleo- to Neoarchean life and the habitats that it occupied in the Pilbara Craton and unconformably overlying Fortescue Group of the Mount Bruce Supergroup. Nine major inhabited environments are described, which range from land to sea, and into the subsurface, showing that life had diversified into, and flourished within, a range of different environments early in Earth history. An important additional component in the search for life on Mars involves the manner in which evidence for early life is preserved. From the examples studied here, early mineralization of organic matter is key to the preservation of reliable biosignatures, in either silica, carbonate, or pyrite, but burial by volcanic ash can also provide excellent preservation.
The 3.4-Ga Strelley Pool Formation (SPF) at the informally named 'Waterfall Locality' in ... more The 3.4-Ga Strelley Pool Formation (SPF) at the informally named 'Waterfall Locality' in the Goldsworthy greenstone belt of the Pilbara Craton, Western Australia, provides deeper insights into ancient, shallow subaqueous to possibly subaerial ecosystems. Outcrops at this locality contain a thin (<3 m) unit of carbonaceous and non-carbonaceous cherts and silicified sandstones that were deposited in a shallow-water coastal environment, with hydrothermal activities, consistent with the previous studies. Carbonaceous, sulfide-rich massive black cherts with coniform structures up to 3 cm high are characterized by diverse rare earth elements (REE) signatures including enrichment of light [light rare earth elements (LREE)] or middle rare earth elements and by enrichment of heavy metals represented by Zn. The massive black cherts were likely deposited by mixing of hydrothermal and non-hydrothermal fluids. Coniform structures in the cherts are characterized by diffuse laminae comp...
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