ORCID Profile
0000-0002-1330-6864
Current Organisations
University of Wisconsin Madison
,
University of Adelaide
,
Macquarie University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Springer Science and Business Media LLC
Date: 05-2008
DOI: 10.1038/NATURE06961
Abstract: The start of the Ediacaran period is defined by one of the most severe climate change events recorded in Earth history--the recovery from the Marinoan 'snowball' ice age, approximately 635 Myr ago (ref. 1). Marinoan glacial-marine deposits occur at equatorial palaeolatitudes, and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about -5 and +15 parts per thousand, respectively these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise. This abrupt transition records a climate system in profound disequilibrium and contrasts sharply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating Phanerozoic deglaciation. Hypotheses accounting for the abruptness of deglaciation include ice albedo feedback, deep-ocean out-gassing during post-glacial oceanic overturn or methane hydrate destabilization. Here we report the broadest range of oxygen isotope values yet measured in marine sediments (-25 per thousand to +12 per thousand) in methane seeps in Marinoan deglacial sediments underlying the cap carbonate. This range of values is likely to be the result of mixing between ice-sheet-derived meteoric waters and clathrate-derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater. The equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day. A pool of this size could have provided a massive biogeochemical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excursions, abrupt unidirectional warming, cap carbonate deposition, and a marine oxygen crisis. Our findings suggest that methane released from low-latitude permafrost clathrates therefore acted as a trigger and/or strong positive feedback for deglaciation and warming. Methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change that coincides with critical boundaries in the geological record and may represent one particularly important mechanism active during conditions of strong climate forcing.
Publisher: Springer Science and Business Media LLC
Date: 12-2003
DOI: 10.1038/NATURE02201
Publisher: Geological Society of London
Date: 13-08-2007
Publisher: Proceedings of the National Academy of Sciences
Date: 16-05-2011
Abstract: The majority of carbon sequestration at the Earth’s surface occurs in marine continental margin settings within fine-grained sediments whose mineral properties are a function of continental climatic conditions. We report very high mineral surface area (MSA) values of 300 and 570 m 2 g in Late Cretaceous black shales from Ocean Drilling Program site 959 of the Deep Ivorian Basin that vary on subcentennial time scales corresponding with abrupt increases from approximately 3 to approximately 18% total organic carbon (TOC). The observed MSA changes with TOC across multiple scales of variability and on a s le-by-s le basis (centimeter scale), provides a rigorous test of a hypothesized influence on organic carbon burial by detrital clay mineral controlled MSA. Changes in TOC also correspond with geochemical and sedimentological evidence for water column anoxia. Bioturbated intervals show a lower organic carbon loading on mineral surface area of 0.1 mg-OC m -2 when compared to 0.4 mg-OC m -2 for laminated and sulfidic sediments. Although either anoxia or mineral surface protection may be capable of producing TOC of 5%, when brought together they produced the very high TOC (10–18%) apparent in these sediments. This nonlinear response in carbon burial resulted from minor precession-driven changes of continental climate influencing clay mineral properties and runoff from the African continent. This study identifies a previously unrecognized land–sea connection among continental weathering, clay mineral production, and anoxia and a nonlinear effect on marine carbon sequestration during the Coniacian-Santonian Oceanic Anoxic Event 3 in the tropical eastern Atlantic.
Publisher: Cambridge University Press (CUP)
Date: 2014
DOI: 10.1666/12-158
Abstract: Nilpenia rossi new genus new species, described here from the Ediacara Member (Rawnsley Quartzite, South Australia), provides evidence of a Precambrian macroscopic sessile sediment-dweller. Nilpenia , ranging up to 30 cm in diameter, consists of two zones, a complex central area surrounded by radiating, dichotomously branching structures that decrease in diameter from the center to the outer edges. Other elements of the Ediacara Biota are interpreted to have been mat-encrusters but Nilpenia uniquely grew within the upper millimeters of the actual sediment displacing sediment with growth. This sediment surface was rippled and cohesive and may well have included an endobenthic mat. The branching network on the upper surface of the organisms would have been in contact with the water. The phylogenetic relationships of the Ediacara biota are not well constrained and Nilpenia is no exception. However, the morphology and ecology of Nilpenia represent a novel growth strategy present in the Ediacaran and not common today.
Publisher: Wiley
Date: 08-10-2017
DOI: 10.1111/GBI.12217
Abstract: Large magnitude (>10‰) carbon-isotope (δ
Publisher: Society for Sedimentary Geology
Date: 11-1996
DOI: 10.2110/JSR.66.1050
Publisher: Elsevier BV
Date: 03-2017
Publisher: Elsevier BV
Date: 04-2013
Publisher: Society for Sedimentary Geology
Date: 07-2006
DOI: 10.2110/JSR.2006.086
Publisher: American Association for the Advancement of Science (AAAS)
Date: 14-05-1999
Publisher: Elsevier BV
Date: 10-2015
Publisher: Springer Science and Business Media LLC
Date: 05-11-1999
Abstract: We used isotopes of Sr to quantify weathering versus atmospheric sources of foliar Sr in 34 Hawaiian forests on young volcanic soils. The forests varied widely in climate, and in lava flow age and texture. Weathering supplied most of the Sr in most of the sites, but atmospheric deposition contributed 30-50% of foliar Sr in the wettest rainforests. A stepwise multiple regression using annual precipitation, distance from the ocean, and texture of the underlying lava explained 76% of the variation in Sr isotope ratios across the sites. Substrate age did not contribute significantly to variation in Sr isotope ratios in the range of ages evaluated here (11-3000 years), although atmospheric sources eventually dominate pools of biologically available Sr in Hawaiian rainforests in older substrates (≥150,000 years).
Publisher: Geological Society of America
Date: 2012
DOI: 10.1130/G32538.1
Publisher: American Geophysical Union
Date: 22-03-2004
DOI: 10.1029/146GM06
Publisher: Elsevier BV
Date: 03-2018
Publisher: Springer Science and Business Media LLC
Date: 08-2019
DOI: 10.1038/S41467-019-11421-4
Abstract: Today the terrestrial surface drives biogeochemical cycles on Earth through chemical weathering reactions mediated by the biological influence of soils. Prior to the expansion of life on to land, abiotic weathering may have resulted in different boundary conditions affecting the composition of the biosphere. Here we show a striking difference in weathering produced minerals preserved in the Mesoproterozoic Velkerri Formation. While the bulk chemistry and mineralogy is dominated by illite similar to many modern mudstones, application of a novel microbeam technology reveals that the initial detrital minerals were composed of mica (28%) and feldspar (45%) with only a trace amount ( %) of typical soil formed clay minerals. The majority of illite and the high Al 2 O 3 fraction previously interpreted as a weathering signal, is present as a replacement of feldspar and mica. These sediments record physical erosion with limited pedogenic clay mineral formation implying fundamentally different weathering pathways.
Publisher: Informa UK Limited
Date: 06-1993
Publisher: Proceedings of the National Academy of Sciences
Date: 15-07-2002
Abstract: An experimental tracer addition of 84 Sr to an unpolluted temperate forest site in southern Chile, as well as the natural variation of 87 Sr/ 86 Sr within plants and soils, indicates that mechanisms in shallow soil organic horizons are of key importance for retaining and recycling atmospheric cation inputs at scales of decades or less. The dominant tree species Nothofagus nitida feeds nearly exclusively ( %) on cations of atmospheric origin, despite strong variations in tree size and location in the forest landscape. Our results illustrate that ( i ) unpolluted temperate forests can become nutritionally decoupled from deeper weathering processes, virtually functioning as atmospherically fed ecosystems, and ( ii ) base cation turnover times are considerably more rapid than previously recognized in the plant available pool of soil. These results challenge the prevalent paradigm that plants largely feed on rock-derived cations and have important implications for understanding sensitivity of forests to air pollution.
Publisher: Wiley
Date: 05-03-2020
DOI: 10.1111/AAB.12585
Publisher: Wiley
Date: 28-08-2019
DOI: 10.1111/AAB.12540
Publisher: Geological Society of America
Date: 08-03-2011
DOI: 10.1130/G31348.1
Publisher: Geological Society of London
Date: 2011
DOI: 10.1144/M36.40
Publisher: Geological Society of America
Date: 2002
Publisher: American Association for the Advancement of Science (AAAS)
Date: 10-03-2006
Abstract: An enigmatic stepwise increase in oxygen in the late Precambrian is widely considered a prerequisite for the expansion of animal life. Accumulation of oxygen requires organic matter burial in sediments, which is largely controlled by the sheltering or preservational effects of detrital clay minerals in modern marine continental margin depocenters. Here, we show mineralogical and geochemical evidence for an increase in clay mineral deposition in the Neoproterozoic that immediately predated the first metazoans. Today most clay minerals originate in biologically active soils, so initial expansion of a primitive land biota would greatly enhance production of pedogenic clay minerals (the “clay mineral factory”), leading to increased marine burial of organic carbon via mineral surface preservation.
Publisher: National Academies Press
Date: 02-08-2011
DOI: 10.17226/13111
Publisher: Informa UK Limited
Date: 24-05-2018
Publisher: Elsevier BV
Date: 05-2005
Publisher: Wiley
Date: 02-2019
DOI: 10.1002/DEP2.60
Publisher: Geological Society of America
Date: 1998
Publisher: Geological Society of America
Date: 04-2012
DOI: 10.1130/G33214Y.1
Publisher: Geological Society of America
Date: 06-2012
DOI: 10.1130/G33346Y.1
Publisher: Geological Society of America
Date: 06-2011
DOI: 10.1130/G32002.1
Publisher: Proceedings of the National Academy of Sciences
Date: 11-08-2009
Abstract: Assemblages of clay minerals are routinely used as proxies for paleoclimatic change and paleoenvironmental conditions in Phanerozoic rocks. However, this tool is rarely applied in older sedimentary units. In this paper, the clay mineralogy of the Doushantuo Formation in South China is documented, providing constraints on depositional conditions of the Ediacaran Yangtze platform that host the earliest animal fossils in the geological record. In multiple sections from the Yangtze Gorges area, trioctahedral smectite (saponite) and its diagenetic products (mixed-layer chlorite/smectite, corrensite, and chlorite) are the dominant clays through the lower 80 m of the formation and constitute up to 30 wt% of the bulk rock. Saponite is interpreted as an in situ early diagenetic phase that formed in alkaline conditions (pH ≥ 9). The absence of saponite in stratigraphically equivalent basin sections, 200–400 km to the south, indicates that alkaline conditions were localized in a nonmarine basin near the Yangtze Gorges region. This interpretation is consistent with crustal abundances of redox-sensitive trace elements in saponitic mudstones deposited under anoxic conditions, as well as a 10‰ difference in the carbon isotope record between Yangtze Gorges and basin sections. Our findings suggest that nonmarine environments may have been hospitable for the fauna preserved in the Yangtze Gorges, which includes the oldest ex les of animal embryo fossils and acanthomorphic acritarchs.
Publisher: Geological Society of America
Date: 1998
Publisher: Elsevier BV
Date: 12-2018
Publisher: University of Chicago Press
Date: 05-2013
DOI: 10.1086/670023
Abstract: The biomass of living organisms hosts only a small portion of the elemental abundance at the surface of the Earth, yet biology plays a defining role in the composition and stability of the biosphere by acting on sensitive geochemical feedbacks controlling global element cycles. This type of influence is evident in a class of evolutionary innovations that have a profoundly disproportionate effect on the biosphere, referred to here as evolutionary innovation biospheric feedbacks (EIBFs). A particular biological innovation need not be complex, rather its influence is lified by its effect on geochemical feedbacks controlling elemental cycling. The lead-up to the metazoan radiation (~585 million years ago) provides an ex le of such an EIBF. While commonly attributed to an increase in free oxygen concentration, the reason for this step increase in O2 almost 2 billion years after the advent of oxygenic photosynthesis is traced to a seemingly unrelated evolutionary innovation resulting in a critical by-product of the first soils: secondary clay minerals. Detrital clay minerals deposited in continental margin sediments sequester organic carbon compounds and thus prevent consumption of atmospheric oxygen produced during photosynthesis. The transition from the abiotic to biotic land surface at the end of the Precambrian shifted biogeochemical cycling to this terrestrial-dominated modern mode that enabled sufficient oxygenation of the biosphere to trigger the metazoan radiation.
Publisher: National Academies Press
Date: 02-08-2011
DOI: 10.17226/13111
Publisher: Geological Society of America
Date: 2001
Publisher: American Association of Petroleum Geologists AAPG/Datapages
Date: 09-2015
DOI: 10.1306/04061514181
Publisher: Springer Science and Business Media LLC
Date: 08-07-2009
DOI: 10.1038/NATURE08213
Abstract: Many aspects of the carbon cycle can be assessed from temporal changes in the (13)C/(12)C ratio of oceanic bicarbonate. (13)C/(12)C can temporarily rise when large amounts of (13)C-depleted photosynthetic organic matter are buried at enhanced rates, and can decrease if phytomass is rapidly oxidized or if low (13)C is rapidly released from methane clathrates. Assuming that variations of the marine (13)C/(12)C ratio are directly recorded in carbonate rocks, thousands of carbon isotope analyses of late Precambrian ex les have been published to correlate these otherwise undatable strata and to document perturbations to the carbon cycle just before the great expansion of metazoan life. Low (13)C/(12)C in some Neoproterozoic carbonates is considered evidence of carbon cycle perturbations unique to the Precambrian. These include complete oxidation of all organic matter in the ocean and complete productivity collapse such that low-(13)C/(12)C hydrothermal CO(2) becomes the main input of carbon. Here we compile all published oxygen and carbon isotope data for Neoproterozoic marine carbonates, and consider them in terms of processes known to alter the isotopic composition during transformation of the initial precipitate into limestone/dolostone. We show that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic ex les that lithified in coastal pore fluids, receiving a large groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturbations to the carbon cycle, widely reported decreases in (13)C/(12)C in Neoproterozoic carbonates are more easily interpreted in the same way as is done for Phanerozoic ex les. This influx of terrestrial carbon is not apparent in carbonates older than approximately 850 Myr, so we infer an explosion of photosynthesizing communities on late Precambrian land surfaces. As a result, biotically enhanced weathering generated carbon-bearing soils on a large scale and their detrital sedimentation sequestered carbon. This facilitated a rise in O(2) necessary for the expansion of multicellular life.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 31-10-2003
Abstract: The evolutionary success of planktic calcifiers during the Phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate-ion concentration: the saturation-dependent preservation of carbonate in sea-floor sediments. Before this, buffering was primarily accomplished by adjustment of shallow-water carbonate deposition to balance oceanic inputs from weathering on land. Neoproterozoic ice ages of near-global extent and multimillion-year duration and the formation of distinctive sedimentary (cap) carbonates can thus be understood in terms of the greater sensitivity of the Precambrian carbon cycle to the loss of shallow-water environments and CO 2 -climate feedback on ice-sheet growth.
Publisher: Copernicus GmbH
Date: 18-09-2014
Abstract: Abstract. Organic carbon (OC) enrichment in sediments deposited during Oceanic Anoxic Events (OAEs) is commonly attributed to elevated productivity and marine anoxia. We find that OC enrichment in the late Cenomanian aged OAE 2 at the Demerara Rise was controlled by the co-occurrence of anoxic bottom water, sufficient productivity to saturate available mineral surfaces, and variable deposition of high surface area detrital smectite clay. Redox indicators show consistently oxygen-depleted conditions, while a strong correlation between OC concentration and sediment mineral surface area (R2 = 0.92) occurs across a range of total organic carbon (TOC) values from 9 to 33%. X-ray diffraction data indicate the intercalation of OC in smectite interlayers, while electron, synchrotron infrared and X-ray microscopy show an intimate association between clay minerals and OC, consistent with preservation of OC as organomineral nanocomposites and aggregates rather than discrete, μm-scale pelagic detritus. Since the consistent ratio between TOC and mineral surface area suggests that excess OC relative to surface area is lost, we propose that it is the varying supply of smectite that best explains variable organic enrichment against a backdrop of continuous anoxia, which is conducive to generally high TOC during OAE 2 at the Demerara Rise. Smectitic clays are unique in their ability to form stable organomineral nanocomposites and aggregates that preserve organic matter, and are common weathering products of continental volcanic deposits. An increased flux of smectite coinciding with high carbon burial is consistent with evidence for widespread volcanism during OAE 2, so that organomineral carbon burial may represent a potential feedback to volcanic degassing of CO2.
Publisher: Geological Society of America
Date: 2008
DOI: 10.1130/G24968A.1
Publisher: Elsevier BV
Date: 08-2012
Publisher: Springer Science and Business Media LLC
Date: 12-03-2015
DOI: 10.1038/NCOMMS7589
Abstract: Animal burrowers leave an indelible signature on the sedimentary record in most marine environments, with the seeming exception of low-oxygen environments. In modern sedimentary settings, however, sub-millimetre-sized benthic animals (meiofauna) are adapted to low oxygen and even sulfidic conditions. Almost nothing is known about their impact on ancient marine sediments because they leave few recognizable traces. Here we show, in classic Pliocene-aged anoxic facies from the Mediterranean, the first reported trace fossil evidence of meiofaunal activity and its relation to changing oxygenation. A novel approach utilizing electron imaging of ion-polished s les shows that meiofauna pervasively reworked sediment under oxygen-depleted conditions that excluded macrofauna, fragmenting organic laminae and emplacing 15- to 70-μm-diameter faecal pellets without macroscopically influencing the fabric. The extent of reworking raises the question: how pervasively altered are other sediments presently assumed to lack animal influence and how far into the geological record does this influence extend?
Publisher: Cambridge University Press (CUP)
Date: 12-06-2012
DOI: 10.1017/S0016756812000313
Abstract: Zoophycos -group burrows are prevalent elements of the post-Cambrian trace fossil record. Here we report the oldest specimens of Zoophycos from Lower Cambrian strata of the Lower Member Wood Canyon Formation in southeastern California. In addition to these being the oldest ex les of this well-known trace fossil, the discovery of these specimens also reveals the presence of deposit feeding considerably earlier than has been suggested for the advent of this feeding style. This type of activity may have had a significant impact on sediment mixing during the Precambrian–Cambrian transition, though the rarity and shallow tier position of these specimens suggests otherwise.
Publisher: Elsevier BV
Date: 02-2014
Publisher: Elsevier BV
Date: 2018
Publisher: Elsevier
Date: 2012
Publisher: Geological Society of America
Date: 2002
Publisher: Springer Science and Business Media LLC
Date: 05-06-2020
DOI: 10.1038/S41467-020-16614-W
Abstract: An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-01-2002
Abstract: We show that 85% of variation in total organic carbon can be explained by mineral surface area in a black shale deposit from two locations in the late Cretaceous Western Interior Seaway, United States. This relation suggests that, as in modern marine sediments, adsorption of carbon compounds onto clay mineral surfaces played a fundamental role in the burial and preservation of organic carbon. Our data also provide evidence for organic matter within the smectite interlayer. This association implies that organic carbon sequestration in a representative oil-prone black shale facies may be more closely related to patterns of continental weathering and clay mineralogy than to ocean water chemistry or marine productivity.
Publisher: Geological Society of America
Date: 2005
DOI: 10.1130/G21418.1
Publisher: Geological Society of America
Date: 2001
No related grants have been discovered for Martin Kennedy.