DOCSLIB.ORG

Seawater-Buffered Diagenesis, Destruction of Carbon Isotope Excursions, and the Composition of DIC in Neoproterozoic Oceans

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Seawater-Buffered Diagenesis, Destruction of Carbon Isotope Excursions, and the Composition of DIC in Neoproterozoic Oceans Seawater-buffered diagenesis, destruction of carbon isotope excursions, and the composition of DIC in Neoproterozoic oceans Paul F. Hoffmana,b,1 and Kelsey G. Lamothec aSchool of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8P 5C2, Canada; bDepartment of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138; and cDepartment of Earth and Planetary Sciences, McGill University, Montreal, QC H3A 0E8, Canada Edited by Mark H. Thiemens, University of California San Diego, La Jolla, CA, and approved August 16, 2019 (received for review June 4, 2019) Carbonate sediments of nonglacial Cryogenian (659 to 649 Ma) permeable lithologies on the foreslopes of carbonate platforms and early Ediacaran (635 to 590 Ma) age exhibit large positive and (Fig. 2 B and C), where seawater invasion is a response to geo- δ13 negative Ccarb excursions in a shallow-water marine platform in thermally driven porewater convection (17–21). In platform in- 13 northern Namibia. The same excursions are recorded in fringing teriors, where most Neoproterozoic δ Ccarb records have been deep-sea fans and in carbonate platforms on other paleoconti- obtained, diagenesis becomes increasingly sediment buffered with nents. However, coeval carbonates in the upper foreslope of the 13 distance along pore-fluid pathways (12). In these areas, δ Ccarb Namibian platform, and to a lesser extent in the outermost plat- values of the sediment tend to be preserved. δ13 form, have relatively uniform Ccarb compositions compatible Although C is more abundant in carbonate sediment, relative with dissolved inorganic carbon (DIC) in the modern ocean. We to seawater, than is Ca or Mg, seawater-buffered diagenesis may attribute the uniform values to fluid-buffered diagenesis that oc- 13 be capable of altering δ Ccarb toward the range of open-ocean curred where seawater invaded the sediment in response to geo- 13 13 δ CDIC. If complete reequilibration occurred, the altered δ Ccarb thermal porewater convection. This attribution, which is testable δ13 δ13 would be a record of open-ocean CDIC. Our strategy, therefore, with paired Ca and Mg isotopes, implies that large Ccarb excur- was to compare δ13C records from the interior of the Otavi/ sions observed in Neoproterozoic platforms, while sedimentary in carb Swakop platform, where diagenesis is expected to have been origin, do not reflect the composition of ancient open-ocean DIC. sediment buffered, with those from the correlative upper foreslope (IPz and UFz, respectively; see Fig. 2A for definitions), where carbon isotope excursions | carbonate diagenesis | Neoproterozoic seawater | carbonate platform seawater-buffered diagenesis could have prevailed. As a test of the fidelity of the IPz records, we obtained correlative ones from turbidite fans fringing the platform (LFz and BMz; Fig. 2A), on arbon-isotope records from marine carbonate successions the assumption that they represent epi-platform sediment that aged 870 to 485 Ma (Fig. 1) exhibit large excursions outside C was advected to the foot of the foreslope, potentially beyond the the compositional range of modern seawater DIC (δ13C = 0.8 ± reach of seawater-buffered diagenesis (Fig. 2 B and C). Where the 1.5‰ Pee Dee Belemnite (PDB); ref. 1) or Cenozoic benthic δ13 = ± ‰ foreslope record was truncated by end-Cryogenian (Marinoan) foraminifera ( C 0.9 1.7 VPDB; ref. 2). Neoproterozoic δ13 δ13 − + ‰ glacial erosion, we investigated lateral Ccarb change going sea- Ccarb ranges from 12 to 9 (Vienna Pee Dee Belemnite A (VPDB)), and values of +6.0 ± 2.5‰ are sustained for as long ward across the outer platform (OPz; Fig. 2 ). as ≥50 My (3). It is often assumed that such excursions reflect secular changes in the composition of seawater DIC, because Significance they are quantitatively reproducible regionally (SI Appendix, Fig. S1)(4–8) and some are demonstrably correlative in what were Carbonate sediments of Neoproterozoic age exhibit large geographically remote successions (9, 10). Here we present age- secular excursions of carbon isotope composition outside 13 correlative δ Ccarb records from different parts of a single the range of modern seawater dissolved inorganic carbon Neoproterozoic carbonate platform, the Otavi/Swakop Group (DIC), but their origins are controversial. We show that in a (Fig. 1) in northern Namibia, which collectively support Neoproterozoic carbonate platform in Namibia, such excursions a sedimentary origin for the excursions but imply that they are disappear on the flanks of the platform, where compositions decoupled from open-ocean DIC. are more compatible with modern seawater. We attribute the Our approach was inspired by recent studies of carbonate dia- observed spatial variation to early fluid-buffered alteration on genesis within active marine carbonate platforms utilizing Ca and the flanks of the platform, where seawater invaded the sedi- Mg isotopes (11, 12). In tandem, Ca and Mg isotopes can dis- ment in response to geothermal porewater convection. Ac- criminate between 2 end-member diagenetic regimes, seawater cordingly, the isotope excursions in the platform interior are buffered and sediment buffered. Dolomites produced during decoupled from open-ocean DIC, which remained close to the seawater-buffered diagenesis have δ44Ca values that approach modern range. Our interpretation is testable and, if confirmed, that of seawater (0‰), and relatively uniform δ26Mg values that has important ramifications for the origins of ancient carbon are ∼2‰ lighter than seawater (13). In contrast, dolomites formed isotope excursions. under sediment-buffered conditions have variably elevated δ26Mg values, due to distillation of Mg in the dolomitizing fluid (11). Author contributions: P.F.H. and K.G.L. designed research; P.F.H. and K.G.L. performed Their δ44Ca values are inherited from the precursor carbonate research; K.G.L. analyzed data; and P.F.H. wrote the paper. sediment, ∼1.0‰ (calcite) to ∼1.5‰ (aragonite) lighter than The authors declare no conflict of interest. seawater (14) due to equilibrium fractionation that occurs during This article is a PNAS Direct Submission. primary carbonate production but not during diagenesis (15, 16). Published under the PNAS license. Thus, seawater-buffered dolomite has lighter Mg and heavier Ca 1To whom correspondence may be addressed. Email: [email protected]. than sediment-buffered dolomite (11). This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. Seawater-buffered diagenesis requires that seawater persis- 1073/pnas.1909570116/-/DCSupplemental. tently invades the sediment. This is most likely to occur in Published online September 4, 2019. 18874–18879 | PNAS | September 17, 2019 | vol. 116 | no. 38 www.pnas.org/cgi/doi/10.1073/pnas.1909570116 Downloaded by guest on September 29, 2021 GA to 2.0 km of cyclic shallow-water carbonate of the Tsumeb Subgroup (22, 23). There are no δ13C data from syn-glacial strata because + BIOTIC SM EB SS C 0.6 10 VSM Keele AA FA’s .. no primary carbonate was produced. The profiles vary appre- Coppercap Huttenberg 0.5 ciably in thickness (SI Appendix,Figs.S3andS4) and were normalized to IPz thickness (Fig. 3) by procedures described +5 SPICE 0.4 below and in SI Appendix. Samples were prepared and isoto- Gaskiers 0.3 pically analyzed according to methods described in refs. 5 (1) (2) and 41. Marinoan (VPDB) 0 0.2 Sturtian Results carb C 0.1 δ13 13 Cryogenian C profiles from the IPz exhibit 3 negative and 2 -5 Rasthof positive carbon isotope excursions (CIEs) (Fig. 3). For brevity, 0 Shuram we number them Cn1 to 5, with negative CIEs being odd num- Garvellach Bitter Springs Bitter bered and positive ones even numbered. Cn1 is named Rasthof Maieberg Russoya org Trezona -10 Taishir o (33), Cn3 Taishir (8, 42), and Cn5 Trezona (6, 43). Positive ex- 13 C(i)=-6 /oo o Ccarb Otavi/Swakop Group =27/oo cursion Cn4, named Keele peak (44), is accompanied by in- 13 T ONIAN CRYOGENIAN EDIACARAN CAMBR’N creased point-to-point δ C variability (Fig. 3 and SI Appendix, Fig. S5). 900 850 800 750 700 650 600 550 500 Cryogenian profiles from LFz turbidites generally track the Millions of years before present (Ma) IPz (Fig. 3). Cn3 is deeper, but less so than the nominal Taishir Fig. 1. Marine carbonate δ13C from 900 to 485 Ma (3, 66) compiled from CIE in Mongolia (8, 42). Cn4 is shallower than IPz with even various carbonate platforms. Gray bands are ranges for modern seawater more scatter. The descent and nadir of Cn5 went unrecorded DIC (1) and Cenozoic benthic foraminiferal CaCO3 (2). Named C-isotope ex- in the LFz because of a laterally persistent shale (Narachaams cursions in magenta italics. Vertical blue bars are glacial epochs and aqua Formation). A falling-stand carbonate wedge (Franni-aus For- box indicates total age range of the Otavi/Swakop Group in northern mation) preceding the Marinoan lowstand records the recovery Namibia. Fractional organic burial flux (forg) assumes a C-influx (C(i)) with leg of Cn5 (Fig. 3 and SI Appendix, Fig. S3) in the LFz. It climbs δ13 = − ‰ δ13 – δ13 = ‰ C 6 (VPDB) and Ccarb Corg 27 in the burial flux. Biotic first 1.5‰ higher than the IPz because accumulation continued after appearances: SM, scale microfossils (67); VSM, vase-shaped microfossils (68); the platform was subaerially exposed (35). GA, algal biomarkers (69); AA, acanthomorphic acritarchs (70); EB, Ediacara EARTH, ATMOSPHERIC, soft-body fossils (71); SS, small shelly fossils (72); C, Cambrian fauna (73). The UFz profile tracks the IPz through Cn1 and 2, but Cn3 AND PLANETARY SCIENCES and 4 are not expressed at all (Fig. 3). After Cn2, δ13C stabilizes near 3‰ in the UFz, declining slowly with stratigraphic height. Geologic Setting The top of the profile veers off toward lighter values, which we The southwestern promontory of Congo craton is blanketed by a tentatively correlate with the Cn5 downturn (Fig. 3).
Load more

Recommended publications
  • Timeline of Natural History
    Timeline of natural history This timeline of natural history summarizes significant geological and Life timeline Ice Ages biological events from the formation of the 0 — Primates Quater nary Flowers ←Earliest apes Earth to the arrival of modern humans. P Birds h Mammals – Plants Dinosaurs Times are listed in millions of years, or Karo o a n ← Andean Tetrapoda megaanni (Ma). -50 0 — e Arthropods Molluscs r ←Cambrian explosion o ← Cryoge nian Ediacara biota – z ←Earliest animals o ←Earliest plants i Multicellular -1000 — c Contents life ←Sexual reproduction Dating of the Geologic record – P r The earliest Solar System -1500 — o t Precambrian Supereon – e r Eukaryotes Hadean Eon o -2000 — z o Archean Eon i Huron ian – c Eoarchean Era ←Oxygen crisis Paleoarchean Era -2500 — ←Atmospheric oxygen Mesoarchean Era – Photosynthesis Neoarchean Era Pong ola Proterozoic Eon -3000 — A r Paleoproterozoic Era c – h Siderian Period e a Rhyacian Period -3500 — n ←Earliest oxygen Orosirian Period Single-celled – life Statherian Period -4000 — ←Earliest life Mesoproterozoic Era H Calymmian Period a water – d e Ectasian Period a ←Earliest water Stenian Period -4500 — n ←Earth (−4540) (million years ago) Clickable Neoproterozoic Era ( Tonian Period Cryogenian Period Ediacaran Period Phanerozoic Eon Paleozoic Era Cambrian Period Ordovician Period Silurian Period Devonian Period Carboniferous Period Permian Period Mesozoic Era Triassic Period Jurassic Period Cretaceous Period Cenozoic Era Paleogene Period Neogene Period Quaternary Period Etymology of period names References See also External links Dating of the Geologic record The Geologic record is the strata (layers) of rock in the planet's crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it.
    [Show full text]
  • Mineralised Pegmatites of the Damara Belt, Namibia: Fluid Inclusion and Geochemical Characteristics with Implications for Post- Collisional Mineralisation
    Mineralised Pegmatites of the Damara Belt, Namibia: Fluid inclusion and geochemical characteristics with implications for post- collisional mineralisation Luisa Ashworth A dissertation submitted to the Fa culty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2014 DECLARATION I declare that this thesis is my own, unaided work. It is being submitted for the degree of Doctor of Philosophy at the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other university. _______________________ Luisa Ashworth 20 of March 2014 i ABSTRACT Namibia is renowned for its abundant mineral resources, a large proportion of which are hosted in the metasedimentary lithologies of the Damara Belt, the northeast-trending inland branch of the Neoproterozoic Pan-African Damara Orogen. Deposit types include late- to post-tectonic (~ 523 – 506 Ma) LCT (Li-Be, Sn-, and miarolitic gem-tourmaline- bearing) pegmatites, and uraniferous pegmatitic sheeted leucogranites (SLGs), which have an NYF affinity. Fluid inclusion studies reveal that although mineralization differs between the different types of pegmatites located at different geographic locations, and by extension, different stratigraphic levels, the fluid inclusion assemblages present in these pegmatites are similar; thus different types of pegmatites are indistinguishable from each other based on their fluid inclusion assemblages. Thorough fluid inclusion petrography indicated that although fluid inclusions are abundant in the pegmatites, no primary fluid inclusions could be identified, and rather those studied are pseudosecondary and secondary. Fluid inclusions are aqueo-carbonic (± NaCl), carbonic, and aqueous. It is proposed that all of the pegmatites studied share a similar late-stage evolution, with fluids becoming less carbonic and less saline with the progression of crystallisation.
    [Show full text]
  • A Community Effort Towards an Improved Geological Time Scale
    A community effort towards an improved geological time scale 1 This manuscript is a preprint of a paper that was submitted for publication in Journal 2 of the Geological Society. Please note that the manuscript is now formally accepted 3 for publication in JGS and has the doi number: 4 5 https://doi.org/10.1144/jgs2020-222 6 7 The final version of this manuscript will be available via the ‘Peer reviewed Publication 8 DOI’ link on the right-hand side of this webpage. Please feel free to contact any of the 9 authors. We welcome feedback on this community effort to produce a framework for 10 future rock record-based subdivision of the pre-Cryogenian geological timescale. 11 1 A community effort towards an improved geological time scale 12 Towards a new geological time scale: A template for improved rock-based subdivision of 13 pre-Cryogenian time 14 15 Graham A. Shields1*, Robin A. Strachan2, Susannah M. Porter3, Galen P. Halverson4, Francis A. 16 Macdonald3, Kenneth A. Plumb5, Carlos J. de Alvarenga6, Dhiraj M. Banerjee7, Andrey Bekker8, 17 Wouter Bleeker9, Alexander Brasier10, Partha P. Chakraborty7, Alan S. Collins11, Kent Condie12, 18 Kaushik Das13, Evans, D.A.D.14, Richard Ernst15, Anthony E. Fallick16, Hartwig Frimmel17, Reinhardt 19 Fuck6, Paul F. Hoffman18, Balz S. Kamber19, Anton Kuznetsov20, Ross Mitchell21, Daniel G. Poiré22, 20 Simon W. Poulton23, Robert Riding24, Mukund Sharma25, Craig Storey2, Eva Stueeken26, Rosalie 21 Tostevin27, Elizabeth Turner28, Shuhai Xiao29, Shuanhong Zhang30, Ying Zhou1, Maoyan Zhu31 22 23 1Department
    [Show full text]
  • Geology of the Kranzberg Syncline and Emplacement Controls of the Usakos Pegmatite Field, Damara Belt, Central Namibia
    GEOLOGY OF THE KRANZBERG SYNCLINE AND EMPLACEMENT CONTROLS OF THE USAKOS PEGMATITE FIELD, DAMARA BELT, CENTRAL NAMIBIA by Geoffrey J. Owen Thesis presented in fulfilment of the requirements for the degree Master of Science at the University of Stellenbosch Supervisor: Prof. Alex Kisters Faculty of Science Department of Earth Sciences March 2011 i DECLARATION By submitting this thesis electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitely otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Signature: Date: 15. February 2011 ii ABSTRACT The Central Zone (CZ) of the Damara belt in central Namibia is underlain by voluminous Pan-African granites and is host to numerous pegmatite occurrences, some of which have economic importance and have been mined extensively. This study discusses the occurrence, geometry, relative timing and emplacement mechanisms for the Usakos pegmatite field, located between the towns of Karibib and Usakos and within the core of the regional-scale Kranzberg syncline. Lithological mapping of the Kuiseb Formation in the core of the Kranzberg syncline identified four litho-units that form an up to 800 m thick succession of metaturbidites describing an overall coarsening upward trend. This coarsening upwards trend suggests sedimentation of the formation’s upper parts may have occurred during crustal convergence and basin closure between the Kalahari and Congo Cratons, rather than during continued spreading as previously thought.
    [Show full text]
  • A Template for an Improved Rock-Based Subdivision of the Pre-Cryogenian Timescale
    Downloaded from http://jgs.lyellcollection.org/ by guest on September 28, 2021 Perspective Journal of the Geological Society Published Online First https://doi.org/10.1144/jgs2020-222 A template for an improved rock-based subdivision of the pre-Cryogenian timescale Graham A. Shields1*, Robin A. Strachan2, Susannah M. Porter3, Galen P. Halverson4, Francis A. Macdonald3, Kenneth A. Plumb5, Carlos J. de Alvarenga6, Dhiraj M. Banerjee7, Andrey Bekker8, Wouter Bleeker9, Alexander Brasier10, Partha P. Chakraborty7, Alan S. Collins11, Kent Condie12, Kaushik Das13, David A. D. Evans14, Richard Ernst15,16, Anthony E. Fallick17, Hartwig Frimmel18, Reinhardt Fuck6, Paul F. Hoffman19,20, Balz S. Kamber21, Anton B. Kuznetsov22, Ross N. Mitchell23, Daniel G. Poiré24, Simon W. Poulton25, Robert Riding26, Mukund Sharma27, Craig Storey2, Eva Stueeken28, Rosalie Tostevin29, Elizabeth Turner30, Shuhai Xiao31, Shuanhong Zhang32, Ying Zhou1 and Maoyan Zhu33 1 Department of Earth Sciences, University College London, London, UK 2 School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, UK 3 Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA, USA 4 Department of Earth and Planetary Sciences, McGill University, Montreal, Canada 5 Geoscience Australia (retired), Canberra, Australia 6 Instituto de Geociências, Universidade de Brasília, Brasilia, Brazil 7 Department of Geology, University of Delhi, Delhi, India 8 Department of Earth and Planetary Sciences, University of California, Riverside,
    [Show full text]
  • GEOLOGIC TIME SCALE V
    GSA GEOLOGIC TIME SCALE v. 4.0 CENOZOIC MESOZOIC PALEOZOIC PRECAMBRIAN MAGNETIC MAGNETIC BDY. AGE POLARITY PICKS AGE POLARITY PICKS AGE PICKS AGE . N PERIOD EPOCH AGE PERIOD EPOCH AGE PERIOD EPOCH AGE EON ERA PERIOD AGES (Ma) (Ma) (Ma) (Ma) (Ma) (Ma) (Ma) HIST HIST. ANOM. (Ma) ANOM. CHRON. CHRO HOLOCENE 1 C1 QUATER- 0.01 30 C30 66.0 541 CALABRIAN NARY PLEISTOCENE* 1.8 31 C31 MAASTRICHTIAN 252 2 C2 GELASIAN 70 CHANGHSINGIAN EDIACARAN 2.6 Lopin- 254 32 C32 72.1 635 2A C2A PIACENZIAN WUCHIAPINGIAN PLIOCENE 3.6 gian 33 260 260 3 ZANCLEAN CAPITANIAN NEOPRO- 5 C3 CAMPANIAN Guada- 265 750 CRYOGENIAN 5.3 80 C33 WORDIAN TEROZOIC 3A MESSINIAN LATE lupian 269 C3A 83.6 ROADIAN 272 850 7.2 SANTONIAN 4 KUNGURIAN C4 86.3 279 TONIAN CONIACIAN 280 4A Cisura- C4A TORTONIAN 90 89.8 1000 1000 PERMIAN ARTINSKIAN 10 5 TURONIAN lian C5 93.9 290 SAKMARIAN STENIAN 11.6 CENOMANIAN 296 SERRAVALLIAN 34 C34 ASSELIAN 299 5A 100 100 300 GZHELIAN 1200 C5A 13.8 LATE 304 KASIMOVIAN 307 1250 MESOPRO- 15 LANGHIAN ECTASIAN 5B C5B ALBIAN MIDDLE MOSCOVIAN 16.0 TEROZOIC 5C C5C 110 VANIAN 315 PENNSYL- 1400 EARLY 5D C5D MIOCENE 113 320 BASHKIRIAN 323 5E C5E NEOGENE BURDIGALIAN SERPUKHOVIAN 1500 CALYMMIAN 6 C6 APTIAN LATE 20 120 331 6A C6A 20.4 EARLY 1600 M0r 126 6B C6B AQUITANIAN M1 340 MIDDLE VISEAN MISSIS- M3 BARREMIAN SIPPIAN STATHERIAN C6C 23.0 6C 130 M5 CRETACEOUS 131 347 1750 HAUTERIVIAN 7 C7 CARBONIFEROUS EARLY TOURNAISIAN 1800 M10 134 25 7A C7A 359 8 C8 CHATTIAN VALANGINIAN M12 360 140 M14 139 FAMENNIAN OROSIRIAN 9 C9 M16 28.1 M18 BERRIASIAN 2000 PROTEROZOIC 10 C10 LATE
    [Show full text]
  • U-Pb and Sm-Nd Data of the Rhyacian and Statherian Orthogneisses From
    View9797 metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Cadernos Espinosanos (E-Journal) DOI: 10.5327/Z1519-874X201400030007 Revista do Instituto de Geociências - USP Geol. USP, Sér. cient., São Paulo, v. 14, n. 3, p. 9-110, Setembro 2014 U-Pb and Sm-Nd data of the Rhyacian and Statherian Orthogneisses from Rio Piranhas-Seridó and Jaguaribeano Terranes, Borborema Province, Northeast of Brazil U-Pb e Sm-Nd em Ortognaisses Riacianos e Estaterianos nos Terrenos Rio Piranhas-Seridó e Jaguaribeano, Província Borborema, Brasil Jaziel Martins Sá1, Laécio Cunha de Sousa1, Jean Michel Legrand1, Antonio Carlos Galindo1,2, Heitor Neves Maia1, Rafael Rabelo Fillippi2 1Departamento de Geologia, Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte - UFRN, Avenida Senador Salgado Filho s/n, Caixa Postal 156, Campus Universitário, CEP 5098-90, Natal, RN, BR ([email protected]; [email protected]; [email protected]; [email protected]; [email protected]) 2Pós-graduação em Geodinâmica e Geofísica, Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte - UFRN, Natal, RN, BR ([email protected]) Received on January 20th, 2014; accepted on August 4th, 2014 Abstract The Portalegre shear zone separates the Rio Piranhas-Seridó and the Jaguaribeano geological terranes in the Northern Domain of the Borborema Province. Banded gneisses of the Caicó and the Jaguaretama Complexes represent the basements of these terranes. U-Pb analyses yielded ages of 2,193 ± 16 Ma for the Jaguaretama Complex, which is similar to those obtained for the Caicó Complex.
    [Show full text]
  • Formation and Collapse of the Kalahari Duricrust ['African Surface
    Formation and Collapse of the Kalahari Duricrust [‘African Surface’] Across the Congo Basin, 10 with Implications for Changes in Rates of Cenozoic Off-Shore Sedimentation Bastien Linol, Maarten J. de Wit, Francois Guillocheau, Michiel C.J. de Wit, Zahie Anka, and Jean-Paul Colin{ 10.1 Introduction margins, and to the east by the East African Rift System (EARS). Their relatively flat interior is covered by an exten- The Congo Basin (CB) of central Africa lies at about 400 m sive Upper Cretaceous-Cenozoic succession of sand dunes, above mean sea level (amsl), and is linked to the south, pan-lacustrine sediments and alluviums with hard-caps across a central African drainage divide, to the high interior (duricrusts) of calcrete, silcrete and ferricrete, collectively Kalahari Plateau (KP) at ca. 1,100 m amsl (Fig. 10.1). The named the Kalahari Group (SACS, 1980). This succession CB and KP are flanked by distinct marginal escarpments reaches a maximum thickness of about 500 m, but across along the South Atlantic and southwest Indian Ocean southern and central Africa is generally less than 100 m thick, representing one of the world’s most extensive, long- lived condensed stratigraphic sequences. The Kalahari Group directly overlies Precambrian base- ment of the Kalahari and Central African Shields (Fig. 10.1b), late Paleozoic to mid-Mesozoic sequences of {Author was deceased at the time of publication. the Karoo Supergroup including Lower Jurassic flood basalts in southern Africa, dated at 178–183 Ma (the B. Linol (*) AEON-ESSRI (African Earth Observatory Network – Earth Stormberg Group; Jourdan et al.
    [Show full text]
  • Paleogeographic Maps Earth History
    History of the Earth Age AGE Eon Era Period Period Epoch Stage Paleogeographic Maps Earth History (Ma) Era (Ma) Holocene Neogene Quaternary* Pleistocene Calabrian/Gelasian Piacenzian 2.6 Cenozoic Pliocene Zanclean Paleogene Messinian 5.3 L Tortonian 100 Cretaceous Serravallian Miocene M Langhian E Burdigalian Jurassic Neogene Aquitanian 200 23 L Chattian Triassic Oligocene E Rupelian Permian 34 Early Neogene 300 L Priabonian Bartonian Carboniferous Cenozoic M Eocene Lutetian 400 Phanerozoic Devonian E Ypresian Silurian Paleogene L Thanetian 56 PaleozoicOrdovician Mesozoic Paleocene M Selandian 500 E Danian Cambrian 66 Maastrichtian Ediacaran 600 Campanian Late Santonian 700 Coniacian Turonian Cenomanian Late Cretaceous 100 800 Cryogenian Albian 900 Neoproterozoic Tonian Cretaceous Aptian Early 1000 Barremian Hauterivian Valanginian 1100 Stenian Berriasian 146 Tithonian Early Cretaceous 1200 Late Kimmeridgian Oxfordian 161 Callovian Mesozoic 1300 Ectasian Bathonian Middle Bajocian Aalenian 176 1400 Toarcian Jurassic Mesoproterozoic Early Pliensbachian 1500 Sinemurian Hettangian Calymmian 200 Rhaetian 1600 Proterozoic Norian Late 1700 Statherian Carnian 228 1800 Ladinian Late Triassic Triassic Middle Anisian 1900 245 Olenekian Orosirian Early Induan Changhsingian 251 2000 Lopingian Wuchiapingian 260 Capitanian Guadalupian Wordian/Roadian 2100 271 Kungurian Paleoproterozoic Rhyacian Artinskian 2200 Permian Cisuralian Sakmarian Middle Permian 2300 Asselian 299 Late Gzhelian Kasimovian 2400 Siderian Middle Moscovian Penn- sylvanian Early Bashkirian
    [Show full text]
  • 2009 Geologic Time Scale Cenozoic Mesozoic Paleozoic Precambrian Magnetic Magnetic Bdy
    2009 GEOLOGIC TIME SCALE CENOZOIC MESOZOIC PALEOZOIC PRECAMBRIAN MAGNETIC MAGNETIC BDY. AGE POLARITY PICKS AGE POLARITY PICKS AGE PICKS AGE . N PERIOD EPOCH AGE PERIOD EPOCH AGE PERIOD EPOCH AGE EON ERA PERIOD AGES (Ma) (Ma) (Ma) (Ma) (Ma) (Ma) (Ma) HIST. HIST. ANOM. ANOM. (Ma) CHRON. CHRO HOLOCENE 65.5 1 C1 QUATER- 0.01 30 C30 542 CALABRIAN MAASTRICHTIAN NARY PLEISTOCENE 1.8 31 C31 251 2 C2 GELASIAN 70 CHANGHSINGIAN EDIACARAN 2.6 70.6 254 2A PIACENZIAN 32 C32 L 630 C2A 3.6 WUCHIAPINGIAN PLIOCENE 260 260 3 ZANCLEAN 33 CAMPANIAN CAPITANIAN 5 C3 5.3 266 750 NEOPRO- CRYOGENIAN 80 C33 M WORDIAN MESSINIAN LATE 268 TEROZOIC 3A C3A 83.5 ROADIAN 7.2 SANTONIAN 271 85.8 KUNGURIAN 850 4 276 C4 CONIACIAN 280 4A 89.3 ARTINSKIAN TONIAN C4A L TORTONIAN 90 284 TURONIAN PERMIAN 10 5 93.5 E 1000 1000 C5 SAKMARIAN 11.6 CENOMANIAN 297 99.6 ASSELIAN STENIAN SERRAVALLIAN 34 C34 299.0 5A 100 300 GZELIAN C5A 13.8 M KASIMOVIAN 304 1200 PENNSYL- 306 1250 15 5B LANGHIAN ALBIAN MOSCOVIAN MESOPRO- C5B VANIAN 312 ECTASIAN 5C 16.0 110 BASHKIRIAN TEROZOIC C5C 112 5D C5D MIOCENE 320 318 1400 5E C5E NEOGENE BURDIGALIAN SERPUKHOVIAN 326 6 C6 APTIAN 20 120 1500 CALYMMIAN E 20.4 6A C6A EARLY MISSIS- M0r 125 VISEAN 1600 6B C6B AQUITANIAN M1 340 SIPPIAN M3 BARREMIAN C6C 23.0 345 6C CRETACEOUS 130 M5 130 STATHERIAN CARBONIFEROUS TOURNAISIAN 7 C7 HAUTERIVIAN 1750 25 7A M10 C7A 136 359 8 C8 L CHATTIAN M12 VALANGINIAN 360 L 1800 140 M14 140 9 C9 M16 FAMENNIAN BERRIASIAN M18 PROTEROZOIC OROSIRIAN 10 C10 28.4 145.5 M20 2000 30 11 C11 TITHONIAN 374 PALEOPRO- 150 M22 2050 12 E RUPELIAN
    [Show full text]
  • Chapter 11. Glacial Lithofacies and Stratigraphy
    CHAPTER GLACIAL LITHOFACIES AND STRATIGRAPHY 11 J. Lee British Geological Survey, Nottingham, United Kingdom 11.1 INTRODUCTION Reconstructing the environments, dynamics, and record of past glaciation requires a detailed knowl- edge of both the products of glaciation—effectively the sediments, landforms, and glacitectonic structures that we see in the geological record, and the genetic processes that formed them (Fig. 11.1). Such an understanding of glacial deposits, landforms, and processes underpins our understanding of glacier behaviour, the links between ice masses, climate change, and other feed- back mechanisms, and the applied significance of glaciated terrains from the perspective of resources and geohazards (Fig. 11.1). Building all of this knowledge into a robust geological model requires the employment of a systematic methodology for describing, recording, and interpreting geological evidence. For glacial sediments the principal method, and one routinely employed elsewhere in sedimentology, is the hierarchical lithofacies approach. In turn, understanding how these lithofacies and other glacial features (e.g., landforms and glacitectonic structures) fit together and correlate in both time and space is called stratigraphy. Stratigraphy is a key concept within geology. It enables the development of a framework of events and features that describe both the evolution of a geological succession and how that succession fits into the wider palaeoenvironmental picture or Earth system. Within the context of glacial geology, e.g., a succession of glacigenic sediments and landforms in the Great Lakes region of Canada might document the repeated glaciation of the area. Studying the sediments (lithofacies) and landforms plus their temporal and spatial relationships (stratigraphy), would enable the number of ice advances, their flow directions, and associated geological processes to be reconstructed.
    [Show full text]
  • To Neoproterozoic Ghanzi Basin in Botswana and Namibia, and Implications for Copper-Silver Mineralization in the Kalahari Copperbelt
    GEOCHRONOLOGY, MAGNETIC LITHOSTRATIGRAPHY, AND THE TECTONOSTRATIGRAPHIC EVOLUTION OF THE LATE MESO- TO NEOPROTEROZOIC GHANZI BASIN IN BOTSWANA AND NAMIBIA, AND IMPLICATIONS FOR COPPER-SILVER MINERALIZATION IN THE KALAHARI COPPERBELT By Wesley Scott Hall Copyright by Wesley S. Hall 2017 All Rights Reserved A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Geology). Golden, Colorado Date ____________________________ Signed: ________________________________ Wesley S. Hall Signed: ________________________________ Dr. Murray H. Hitzman Thesis Advisor Signed: ________________________________ Dr. Yvette Kuiper Thesis Advisor Golden, Colorado Date ____________________________ Signed: ________________________________ Dr. Merritt Stephen Enders Professor and Department Head of Geology and Geological Engineering ii ABSTRACT Despite a wealth of research on the Kalahari Copperbelt over the past 30 years, two crucial aspects of the mineralizing systems have remained elusive. First, the age of the rift sequence hosting the deposits and, second, the nature of the fluid pathways for the mineralizing fluids. Laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb isotopic analysis on one igneous sample of the Makgabana Hills rhyolite (Kgwebe Formation) within the central Kalahari Copperbelt in Botswana constrains the depositional age of the unconformably overlying Ghanzi Group to after 1085.5 ± 4.5 Ma. The statistically youngest detrital zircon age populations obtained from the uppermost unit of the Ngwako Pan Formation (1066 ± 9.4 Ma, MSWD = 0.88, n = 3), the overlying D’Kar Formation (1063 ± 11, MSWD = 0.056, n = 3), and the lower Mamuno Formation (1056.0 ± 9.9 Ma, MSWD = 0.68, n = 4) indicate that the middle and upper Ghanzi Groups were deposited after ~1060 to ~1050 Ma.
    [Show full text]