ICDP Workshop: Archean Surface environments: Drilling the Moodies Group, Barberton Greenstone Belt, South Africa

Barberton WorkshopOct. 5-10, 2017


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Proponents

Christoph Heubeck, Jena University, Germany (organizer)

Nic Beukes, Johannesburg/Pretoria, South Africa
Emmanuelle Javaux, Liege University, Belgium
Takeshi Kakegawa, Tohoku University, Japan
Martin van Kranendonk, UNSW, Sydney, Australia
Stefan Lalonde and Martin Homann, Brest, France
Johanna Marin-Carbonne, St. Etienne, France
Paul Mason, Utrecht University, Netherlands
Mike Tice, Texas A&M University, USA


Preface

We conducted a very successful field workshop outside Barberton in late 2017. The workshop participants inspected, discussed and ranked 8 potential drilling sites. We gave short presentations on the "most urgent" Archean problems to be solved, formed  adminsitrative groups, and had many long discussions going deep into the night. The results of the workshop were integrated

Introduction

There are only two places on Earth where Paleoarchean sedimentary and volcanic strata can be studied in context and detail: The Pilbara region of NW Australia and the Barberton Greenstone Belt (BGB) of South Africa and Swaziland. Sedimentary rocks of the Moodies Group in the BGB are about 3.22 Ga old and represent some of the world's oldest, well-preserved, shallow-water strata (Anhaeusser 1976, Eriksson 1979, Heubeck and Lowe 1994a, b, 1999; Heubeck et al., 2013). The superbly exposed units are probably unique worldwide in allowing the detailed analysis and interpretation of micro-scale and high-resolution Archean analytical data in regional and temporal context.

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Reasons to drill

Most outcrops in the Barberton Greenstone Belt, despite appearing fresh, have been affected by oxidative weathering, the effects of surface - or near-surface - organisms (e.g. endolithic bacteria), and/or by near-surface groundwater alteration. Geochemical work on the short (and usually stratigraphically poorly located) drill core provided by the mining industry is commonly compromised by hydrothermal alteration.

The principal objective of the proposed workshop will be to discuss and visit sites where it may be possible to obtain fresh samples of critically important geological units that are otherwise unavailable at the surface. Because strata were laid down under anoxic and reducing Archean conditions, they contain a host of redox-sensitive minerals such as siderite, Fe-rich dolomite, sulfides and carbonaceous matter that are affected by Phanerozoic surface alteration. These are, however, key to making useful estimates of Archean surface processes, including atmosphere and ocean composition, the abundance of oxygen in the atmosphere or in local surface environments ("oxygen oases"), the distribution and nature of early life, preservation pathways, and the response of depositional environments to the surface system. Without knowing the original composition of these Archean sedimentary materials, it is almost impossible to estimate which minerals precipitated from seawater, were consumed or produced by microbial mats, settled from suspension, or were created by diagenesis and alteration. Fresh drill core will make it possible to answer fundamental questions about the nature, abundance, distribution, and ecology of early life so that the oceanic and atmospheric conditions under which they lived that can be better addressed.

A second objective of the workshop will be to identify areas that will allow continuous sampling across key stratigraphic intervals. In most surface sections, in particular those exposing thick sections of fine-grained sediments, those having undergone pedogenic alteration and/or involving rhythmic deposition, subtle contacts are weathered and very poorly exposed if at all.

Moodies strata are largely preserved in the cores of large (up to 15 km long, up to 5 km wide) synclines with steeply dipping or overturned limbs and steeply plunging fold axes. All proposed drill holes will therefore follow highly inclined (ca. 45°) trajectories in order to penetrate maximum stratigraphic thickness. Detailed site mapping prior to drilling is required to identify and take into account effects from ubiquitous minor brittle faulting.

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Three previous scientific drilling programs in the BGB (the "Barberton Drilling Project: Peering into the Cradle of Life" coordinated by Nick Arndt; the Barberton Barite Drilling Project (BBDP) coordinated by Pascal Philippot (IPGP, Paris), and the Barberton Scientific Drilling Project (BSDP) coordinated by Maarten de Wit) demonstrated that the concept of obtaining fresh samples by core drilling in the BGB is valid and that drilling programs in the BGB can be smoothly executed. These previous projects established protocols regarding permits, land clearance, transport, logistics etc.

Moodies Group strata reach up to 3.5 km in stratigraphic thickness, are lithologically variable and were probably deposited within a short time frame (ca. 1-14 Ma; Heubeck et al. 2013). Their metamorphic grade is lower greenschist facies; widespread early diagenetic silicification preserved micro- and macrotextures virtually without strain despite tight regional folding. Moodies strata thus represent a very clear window of Archean surface conditions and processes. Their coastal and fluvial-alluvial facies (sensu lato) is ideal to investigate and combine information from adjacent terrestrial and marine settings.

Analytical work in Moodies strata, based on detailed field studies, has identified several features related to Archean surface processes and the interactions of the bio-, geo-, atmo- and hydrosphere. These include extensive microbial mats in tidal and fluvial facies, pedogenic concretions and biogenic diagenetic reactions in paleosols, weathering rinds, eolian strata, shallow-water banded-iron formations, exquisitely preserved microfossils and detailed reconstructions of shoreline processes (Hessler and Lowe 2006, Noffke et al. 2006, Javaux et al. 2010, Simpson et al. 2012, Heubeck et al. 2016, Homann et al. 2015, 2016, Köhler and Heubeck 2016, Nabhan et al. 2016a, 2016b, Nakajima et al. 2016).

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Scientific Objectives of Wells to be Drilled

The overall target of this endeavour is to learn about the nature of Archean surface environments, in particular those related to the origin and evolution of life, and to constrain Archean basin dynamics by conducting high-resolution research on Archean shallow-water siliciclastic (and subordinate volcanic and subvolcanic) strata. Questions to be addressed can be grouped in five broad groups:

(1) What is the paleoenvironmental record preserved in the laminated siltstones, fine-grained sandstones and shales of the pro-delta facies? (Rhythmicity of the stratigraphic sequence,  origin of the shales, linkage of ferruginous sediments including BIFs, magnetic shales, ferruginous siltstones, jaspilites and cherts in the prodelta facies to (likely oxygenic) microbial mats in the adjacent tidal facies; potential to discover one or several spherule bed(s)).

(2) What is the paleoecology of the abundant microbial mats in the shallow-water high-energy sandstone sections? (Origin, types of microbes, metabolism, microbial ecology, unexplained paucity of preserved filamentous microstructures, origin of thin chert bands associated with the microbial mats, degree of regional thermal overprint; in-situ isotope composition of C, S and Fe; enigmatic preservation pathways; 3-D morphology; relationship to the organic-walled macrospheres from shallow-water shales and siltstones (Javaux et al. 2013); early evolution of the Nitrogen cycle and signals of N2-fixation followed by nitrification/denitrification driven by oxygenic photosynthesis.)


(3) What information is related to the global surface environment? (Isotopes of Fe: tracers of biological oxidation/reduction; of O2: seawater composition and ocean temperature; of Si: origin of chert, seawater composition and temperature; redox balance, chemical composition of the 3.2 Ga ocean water, importance of weathering and early diagenesis as derived from coastal and fluvial facies; relevance and significance of coastal paleosols in the Paleoarchean?)


(4) Which constraints can be derived from the synsedimentary volcanics, including the Moodies basaltic lava: Paleomagnetic studies, variation of vacuole size with stratigraphic height; stratigraphic detail, lack of strain despite tight folding, and tectonic association with the syn-Moodies sill and stockwork intrusion; mineralogy and chemistry of the sill and its contact relationships.


(5) Can geochronology constrain estimates of Moodies sedimentation rates and basin subsidence based on interbedded tuffs? These would serve as calibration points for any cyclostratigraphic data sets.


Sites and strata will be discussed and selected according the following main criteria:

(1) Provide information that cannot be obtained from surface outcrops (such as essential but unobserved contacts and fresh material);

(2) Address specific scientific questions relating to conditions or processes at the surface or in the shallow subsurface of the Archean Earth;

(3) Based on significant prior field studies and laboratory work, and

(4) Drillable at a reasonable cost and effort.



Selected Literature

Anhaeusser, C.R.A., 2014, Archaean greenstone belts and associated granitic rocks - A review. Journal of African Earth Sciences 100, 684-732.

Claire, M.W., Sheets, J., Cohen, M., Ribas, I., Meadows, V.S., and Catling, D.C. (2012) The evolution of solar flux from 0.1 nm to 160 lm: quantative estimates for planetary studies. Astrophys J. 757-

Eriksson, K.A. (1979): Marginal marine depositional processes from the Archaean Moodies Group, Barbteron Mountain Land, South Africa: Evidence and Significance, Precambrian Research 8, 153-182 pp.

Eriksson, P.G., Altermann, W., Nelson, D.R., Mueller, W.U., Catuneanu, O., 2004, The Precambrian Earth: Tempos and Events, Developments in Precambrian Geology 12: Amsterdam, The Netherlands, Elsevier, 966 p.

Fugmann, 2017, Field geology, petrography, age and geochemistry of the Lomati River Complex: A unique late-phase igneous contribution to the interior of the Archean Barberton Greenstone Belt, South Africa. MSc-thesis (unpublished), Friedrich-Schiller-Universität Jena, 101 p.

Galić, A. Mason, P.R.D., Mogollón, J.M., Wolthers, M., Vroon, P.Z., Whitehouse, M.J. 2017. Pyrite in a sulfate-poor Paleoarchean basin was derived predominantly from elemental sulfur: Evidence from 3.2 Ga sediments in the Barberton Greenstone Belt, Kaapvaal Craton. Chemical Geology

Heubeck, C. and Lowe, D.R., 1994a, Depositional and tectonic setting of the Archaean Moodies Group, Barberton Greenstone Belt, South Africa: Precambrian Res., 68, p. 257-290.

Heubeck, C., and Lowe, D.R., 1994b, Late Syndepositional Deformation and Detachment Tectonics in the Barberton Greenstone Belt, South Africa: Tectonics, 13, p.1514-1536.

Heubeck, C., and D.R. Lowe, 1999, Sedimentary petrology and provenance of the Archaean Moodies Group, Barberton Greenstone Belt, South Africa; in: Lowe, D.R., and Byerly, G.R., eds., Geology of the Barberton Greenstone Belt, South Africa: Geol. Soc. America Special Paper 329, pp. 259-287.

Heubeck, C., Engelhardt, J., Byerly, G.R., Zeh, A., Sell, B., Luber, T, Lowe, D.R., 2013. Timing of deposition and deformation of the Moodies Group (Barberton Greenstone Belt, South Africa): Very-high-resolution of Archaean surface processes. Precambrian Research 231, 236-262.

Heubeck, C., S. Bläsing, N. Drabon, M. Grund, M. Homann and S. Nabhan, 2016, Geological constraints on Archean (3.22 Ga) coastal-zone processes from the Dycedale Syncline, Barberton Greenstone Belt: South African Journal of Geology, 119, 495-518.

Homann, M, C. Heubeck, T.R.R. Bontognali, A.-S. Bouvier, L.P. Baumgartner, A. Airo, 2016, Evidence for cavity-dwelling microbial life in 3.22 Ga tidal deposits: Geology, 44, 51-54.

Homann, M., C. Heubeck, A. Airo, M.M. Tice, 2015, Morphological adaptations of 3.22 Ga-old microbial communities to Archean coastal habitats (Moodies Group, Barberton Greenstone Belt, South Africa): Precambrian Research, 266, 47-64.

Jackson, M.P.A., K.A. Eriksson, C.W. Harris, 1987, Early Archean foredeep sedimentation related to crustal shortening: a reinterpretation of the Barberton Sequence, southern Africa. Tectonophysics, 136, 197-221.

Javaux EJ, 2011. Microfossils from early Earth. Nature Geosciences, 4, 663-665.

Javaux EJ, Marshall CP, Bekker A, 2010. Organic-walled microfossils in 3.2-billion-year-old shallow-marine siliciclastic deposits. Nature, 463, 934-938.

Kakegawa T. and H. Ohmoto (1999) Sulfur isotope evidence for the origin of 3.4 and 3.1 Ga pyrite at the Princeton gold mine, Barberton greenstone belt, South Africa. Precam. Res. 96. 209-224.

Kasting, J.F., 2005, Methane and climate during the Precambrian era. Precambrian Res. 137, 119-129.

Kisters, A.F.M., Stevens, G., Dziggel, A., and Armstrong, R.A., 2003, Extensional detachment faulting and core complex formation in the southern Barberton granite-greenstone terrain, South Africa: evidence for a 3.2 Ga orogenic collapse. Precambrian Research 127, 355-378.

Kisters, A.F.M., Belcher, R.W., Poujol, M., Dziggel, A., 2010. Continental growth and convergence-related arc plutonism in the Mesoarchaean: Evidence from the Barberton granitoid-greenstone terrain, South Africa. Precambrian Research 178, 15-26.

Lalonde SV and Konhauser KO (2015) Benthic perspective on Earth's oldest evidence for oxygenic photosynthesis. Proceedings of the National Academy of Sciences 112, 995-1000.

Lowe, D.R., 1994. Accretionary history of the Archean Barberton Greenstone Belt (3.55-3.22 Ga), southern Africa. Geology 22, 1099-1102.

Lowe, D.R., Byerly, G.R., 2007. An overview of the geology of the Barberton Greenstone Belt and vicinity: Implications for early crustal development, in: M.J. Van Kranendonk, R.H. Smithies, V. Bennett (Eds.), Earth's Oldest Rocks, Developments in Precambrian Geology, Vol. 15, Elsevier, Amsterdam, pp. 481-526.

Lowe, D.R., G. Byerly and C. Heubeck, 2012, Geologic Map of the west-central Barberton Greenstone Belt, South Africa, scale 1:25,000: Geol. Soc. Am. Map and Chart Series No. 103.

Luber, T., 2014, Archaean Geology of the east-central Stolzburg Syncline, Barberton Greenstone Belt, South Africa. MSc-thesis (unpublished), Freie Universität Berlin.

Lyons, T.W., C.T. Reinhard, N.J. Planavsky, 2014, The rise of oxygen in Earth's early ocean and atmosphere.  Nature, 506 (2014), 307-315.

Marin-Carbonne, J., Chaussidon, M. and Robert, F. (2012) Micrometer-scale chemical and isotopic criteria (O and Si) on the origin and history of Precambrian cherts: Implications for paleo-temperature reconstructions. Geochimica et Cosmochimica Acta 92, 129-147.

Marin-Carbonne, J., Robert, F. and Chaussidon, M. (2014) The silicon and oxygen isotope compositions of Precambrian cherts: A record of oceanic paleo-temperatures? Precambrian Research 247, 223-234.

Marin-Carbonne, J., Rollion-Bard, C., Bekker, A., Rouxel, O., Agangi, A., Cavalazzi, B., Wohlgemuth-Ueberwasser, C.C., Hofmann, A. and McKeegan, K.D. (2014) Coupled Fe and S isotope variations in pyrite nodules from Archean shale. Earth and Planetary Science Letters 392, 67-79.

Nabhan, S., M.Wiedenbeck, R. Milke, C. Heubeck, 2016, Biogenic overgrowth on detrital pyrite in 3.2 Ga Archean paleosols: Geology, 44, 763-766.

Nabhan, S., T. Luber, F. Scheffler, C. Heubeck, 2016, Climatic and geochemical implications of Archean pedogenic gypsum in the Moodies Group (3.2 Ga), Barberton Greenstone Belt, South Africa: Precambrian Research, 275, 119-134.

Noffke, N., 2010, Geobiology: microbial mats in sandy deposits from the Archean era to today: Springer-Verlag, Berlin, 194 p.

Ohmoto H., T.Kakegawa and D. Lowe (1993) 3.4-billion-year-old biogenic   pyrites from Barberton, South Africa: Sulfur isotope evidence, Science,   vol.262, 555-557

Roerdink, D.L., Mason, P.R.D., Farquhar, J., Reimer, T.  2012. Multiple sulfur isotopes in Paleoarchean barites identify an important role for microbial sulfate reduction in the early marine environment. Earth and Planetary Science Letters, 331, 177-186.

Retallack, G.J., D.H. Krinsley, R. Fischer, J.J. Razink, K.A. Langworthy, 2016, Archean coastal-plain paleosols and life on land: Gondwana Res., 40, 1-20.

Sheldon, N., 2006, Precambrian paleosols and atmospheric CO2 levels; Precambrian Research 147, 148-155.

Scheffler, F., Oberhänsli, R., Pourteau, A., Immenhauser, A., Candon, O., 2016, Sedimentologic to metamorphic processes recorded in the high-pressure/low-temperature Mesozoic Rosetta Marble of Anatolia. International Journal of Earth Sciences, 105, 225-246.

Schieber, J., Bose, P.K., Eriksson, P.G., Banerjee, S., Sarkar, S., Altermann, W., Catuneau, O. (Eds.), 2007, Atlas of Microbial Mat Features Preserved within the Clastic Rock Record: Amsterdam, The Netherlands, Elsevier, 324 p.

Schopf, J.W., 1983, Earth's Earliest Biosphere: Its Origin and Evolution: Princeton, New Jersey, USA, Princeton University Press, Princeton, 610 p.

Simpson, E.L., Eriksson, K.A., Mueller, W.U., 2012, 3.2 Ga eolian deposits from the Moodies Group, Barberton Greenstone Belt, South Africa: Implications for the origin of first-cycle quartz sandstones. Precambrian Research 214, 185-191.

Stüeken, E.E., E.J. Bellefroid, A. Prave, D. Asael, N.J. Planavsky, T.W. Lyons, 2017, Not so non-marine? Revisiting the Stoer Group and the Mesoproterozoic biosphere: Geochemical Van Kranendonk, M.J., 2011. Cool greenstone drips, hot rising domes, and the role of partial convective overturn in Barberton greenstone belt evolution. Journal of African Earth Sciences 60, 346-352.

Tice, M. M., Bostick, B. C. & Lowe, D. R., 2004, Thermal history of the 3.5-3.2 Ga Onverwacht and Fig Tree Groups, Barberton greenstone belt, South Africa, inferred by Raman microspectroscopy of carbonaceous material. Geology  32, 37-40.

Van Kranendonk, M.J., Kröner, A., Hoffman, J.E., Nagel, T., Anhaeusser, C.R., 2014a. Just another drip: Re-analysis of a proposed Mesoarchean suture from the Barberton Mountain Land. Precambrian Research 54, 19-35.

Van Kranendonk, M.J., Smithies, R.H., Griffin, W.L., Huston, D.L., Hickman, A.H., Champion, D.C., Anhaeusser, C.R., Pirajno, F., 2014b. Making it thick: A volcanic plateau model for Paleoarchean continental lithosphere of the Pilbara and Kaapvaal cratons. In: Roberts, N.M.W., Van Kranendonk, M., Parman, S., Shirey, S. & Clift, P.D. (eds), Continent Formation Through Time. Geological Society, London, Special Publications, 389.



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The Workshop

Preliminary Program

Oct. 5: Pick-up from Nelspruit (Lime and City Bug airport shuttles) and from the airport; transfer to accommodation. Evening Program: Introduction of participants, Introduction to the BGB, Moodies Basics, Objectives of the Workshop. Welcome braai.

Oct. 6: Site visits in close vicinity of Barberton: Site 1 - Eureka Syncline (Elephant's Kloof); Site 2 - Dycedale Syncline; Site 7 - Saddleback Pass. Dinner at Lodge; Evening discussion

Oct. 7: Site visits in the central BGB: Site 3 - Oosterbeek (Saddleback Syncline); Site 5 - Lomati River Intrusive. Dinner in town. Evening visit to the Shellhole; Barberton history presentation there

Oct. 8: Half-day break: Time on your own and for discussions. Afternoon: Site 4 - Striped Hill (central BGB, near the road to Shiyalongubo Dam)

Oct. 9: Site vist to the western BGB: Site 6 - Stolzburg Syncline (Nkomazi Wilderness)

Oct. 10: Stay at lodge. Discussion - proposal writing - Discussion.

Oct. 11: Morning Departure. Shuttle service to Nelspruit

 

Getting there

Workshop participants are requested to arrive in Nelspruit during daytime on October 5, 2017. Arrivals by air will be at Nelspruit-Kruger International Airport about 20 km nw of Nelspruit. Arrivals by bus (e.g., Citybug offers four daily, about 3-hr nonstop connections between the OR Tambo airport in Johannesburg and downtown Nelspruit; book at http://www.citybug.co.za/) can be picked up in Nelspruit.

Upon receiving the registration lists, field trip organizers will contact the registered participants by e-mail, query them for their detailed arrival information and organize pickup and transport from Nelspruit to Barberton. Ideal arrival times in Nelspruit would be October 5 around midday.

The workshop will then begin around 5:30 p.m. with a welcoming reception for participants.

We will also provide return shuttle transport to depart Nelspruit mid-morning Oct. 11 so that you can catch evening flights to Europe.

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Accommodation

has not been finalized yet but will be in a spacious resort-like venue (meeting facilities, refreshments, pool, security, comfortable rooms) near Barberton. Breakfast buffet-style, lunch in the field, dinners either at the lodge or in town. Please let us know about meal restrictions.

 

Transportation in the field

Some days, we will use minibuses. On at least two days, we will use 4-WD.


Other

The weather will be warm, mostly dry. Please make sure your passport will have at least one free page after entering the country. If you come in from a yellow-fever country, make sure you have the vaccination.

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