Origin of red beds and paleosols in the Palaeoproterozoic Transvaal and Olifansthoek Supergroups of South Africa: provenance versus metasomatic controls

The Palaeoproterozoic Transvaal and Olifantshoek Supergroups of South Africa contain some of the earliest hematite‐rich sedimentary rocks (red‐beds) and paleosols on record. The origin of these rocks has been variously attributed to surface processes under an oxygenated atmosphere that post‐dated the ca. 2.3 Ga Great Oxidation Event (GOE). Interpretations of their geochemical signatures, however, have been inconclusive with respect to the causes of the apparent K‐enrichment that these rocks record. Here, we re‐visit the basal Mapedi Formation of the Olifantshoek Supergroup and the unconformably underlying Drakenstein palaeo‐weathering profile that develops against the Ongeluk Formation of the upper Transvaal Supergroup, and present new petrographic and geochemical data in an attempt to constrain the burial metasomatic history of these rocks. Apart from the strong hematitic nature and K‐metasomatic overprint seen in both the Mapedi Formation and Ongeluk paleosol, a curious and hitherto unexplored enrichment in high‐field strength elements (HFSEs: Ti, Nb, Y, Zr, REE, etc.) by several orders of magnitude higher than average shale characterizes the lower part of the Mapedi Formation as examined here. We show that such enrichments cannot be explained by normal source‐to sink weathering processes, unless an unlikely provenance of special geochemical composition (i.e. alkali igneous rocks) is to be invoked. We conclude that the HFSE enrichment, K‐metasomatism and evidently transgressive Fe‐oxidation effects in the Mapedi shales can only be accounted for via post‐depositional fluid‐rock interaction, possibly involving F‐bearing diagenetic brines. This opens the distinct possibility that such fluids may have also been implicated in alteration processes, enhanced Fe mobility and development of epigenetic hematitic iron‐ores as seen at the Transvaal‐Olifantshoek unconformity on regional scales. Copyright © 2017 John Wiley & Sons, Ltd.

Sedimentary environment and geomorphic development of the uppermost Siwalik molasse in Kumaun Himalayan Foreland Basin, North India

An area of about 250 sq. km. around Ramnagar and Garjiya within the Siwalik molasse in the Kumaun foothills was mapped for geomorphic evolution and sedimentation pattern. The area, bounded by Himalayan Frontal Thrust (HFT) in the south and Main Boundary Thrust (MBT) in the north, consists of the sediments of uppermost part of the Pinjor and overlying Boulder Conglomerate Formations. Sedimentologically, three facies associations (FAA–FAC) were recognized with their order of superposition as FAA → FAB, FAA → FAC, FAB → FAC and FAC → FAB with variability in depositional setting. Lithofacies FAA–FAC were seemingly deposited in sand‐dominated fluvial channel belt, gravelly braided channel belt and cut‐off channel settings, respectively. The sediment dispersal in the basin was influenced by active basinal tectonics that caused frequent avulsions during the Bounder Bed times. The compositions of the clasts of these lithofacies reveal a shift in the primary provenance from pre‐Tertiary Himalayan hinterlands during the emplacement of FAA (of the Pinjor Formation) to evolving frontal Siwalik highlands during the emplacement of FAB and FAC (of the Bouldder Conglomerate Formation). This temporal shift in the provenance indicates exhumation of the older Siwalik sequences during the later phases of Himalayan orogeny. A number of subordinate faults, oblique to above mentioned intracrustal boundary thrusts and formed after the sedimentation was seized, were likely responsible for displacement between the sediments of different associations. The neotectonic rejuvenation is also reflected by the upliftment of two sister basins in opposite direction, rapid uplift in V‐shaped valleys, fault escarpments, three levels of terrace development and displacement of rock types along the subordinate faults as well as deflection and entrenchment in the course of lower order streams. Copyright © 2017 John Wiley & Sons, Ltd.

Palaeo‐Mesoproterozoic magmatic and metamorphic events from the Kuluketage block, northeast Tarim Craton: geochronology, geochemistry and implications for evolution of Columbia

Banded iron formations (BIFs), granites and diabases are extensively distributed in the Kuluketage block of the northeast Tarim Craton. Here we report laser ablation–inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) zircon U–Pb ages and whole‐rock elemental data for these rocks. The detrital zircons from the BIFs show a peak age of 2.0–1.8 Ga with a weighted mean age of 1945 ± 10 Ma (MSWD = 0.77), and the zircons from the granite give an upper intercept age of 1974 ± 27 Ma (MSWD = 1.05). The trace element features suggest that the Asitingbulake granite, which belongs to the I‐type granite, may originate from the re‐melting of continental crust in a ~1.95 Ga collisional orogenic setting. Recently, the 2.0–1.8 Ga continuous magmatic and metamorphic events which are contemporaneous with the global orogenic event have been reported in the Kuluketage block and other massifs around the Tarim Craton (e.g. Central Tianshan, Dunhuang, Quanji, Altyn Tagh, West Kunlun). Based on the previous geochronological data, two 2.0–1.8 Ga orogens associated with the assembly of the Columbia supercontinent can be identified along the north and south margins of Tarim Craton: (1) the north Tarim Orogen, Central Tianshan–Kuluketage–Dunhuang orogenic belt and (2) the south Tarim Orogen, West Kunlun–Altyn Tagh–Aketashtage–Quanji orogenic belt. Additionally, this paper reports a new zircon U–Pb age of 1497 ± 21 Ma (MSWD = 0.96) from the Baowenbulake diabase dykes where the trace element features suggest that the parental magma of Baowenbulake diabases is derived from the mantle in an intra‐plate rifting or extensional setting. The ~1.5 Ga diabases from northwest Tarim corresponded to a major episode of mafic magmatism during the early Mesoproterozoic period identified in other crustal fragments of Laurentia, Siberia, Greater Congo, South China and North China Craton and probably belong to one of the three major large igneous provinces associated with the breakup of the Mesoproterozoic Columbia supercontinent. The data from this paper provide important constraints on the configuration of the Tarim Craton during the assembly and breakup of the Columbia supercontinent. Copyright © 2017 John Wiley & Sons, Ltd.

Mountain: Nature and Culture by Veronica della Dora. Reaktion Books, London, 2016. No. of pages: 264. Price: £14–95. ISBN 978‐1‐78023‐647‐6 (paperback).

Book Review Authors Stephen K. Donovan Corresponding author E-mail address: Steve.Donovan@naturalis.nl Naturalis Biodiversity Center, Leiden, The Netherlands Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2894 View/save citation Format Available Full text: HTML | PDF Copyright © 2017 John Wiley …

A Monograph of the Fauna of the Cornbrash by John Frederick Blake. Cambridge University Press, Cambridge, 2015. No. of pages: viii + 106. Price: UK£18–99. ISBN 978–1–108‐08434‐5 (softback).

Book Review Authors Simon R. A. Kelly Corresponding author E-mail address: simon.kelly@casp.cam.ac.uk CASP, Cambridge, UK Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2898 View/save citation Format Available Full text: HTML | PDF Copyright © 2017 John Wiley & Sons, …

Monograph on the Fossil Reptilia of the Wealden and Purbeck Formations by Richard Owen. Cambridge University Press, Cambridge, 2015. No. of pages: 492. Price: UK £29.99. ISBN 978-1-108-08113-9 (paperback).

Book Review Authors Paul Ensom Falmouth, Cornwall, UK Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2889 View/save citation Format Available Full text: HTML | PDF Copyright © 2017 John Wiley & Sons, Ltd. Request Permissions Publication History Issue online: …

Tools of the Trade: the Sedgwick Museum’s Historical Collection of Geological Hammers by Douglas Palmer. Sedgwick Museum, Cambridge, 2016. No. of pages: 48. Price: UK£7–50. ISBN 978–0–9927270‐1‐7 (paperback).

Book Review Authors Stephen K. Donovan Corresponding author E-mail address: steve.donovan@naturalis.nl Naturalis Biodiversity Center, Leiden, The Netherlands Search for more papers by this author No abstract is available for this article. Ancillary Article Information DOI 10.1002/gj.2896 View/save citation Format Available Full text: HTML | PDF Copyright © 2017 John Wiley …

Serpukhovian (Mississippian) foraminiferal zones from the Fenghuangshan section, Anhui Province, South China: implications for biostratigraphic correlations

In traditional Chinese Carboniferous zonal schemes, Serpukhovian foraminiferal zones were broadly defined by genera, long‐ranging species or local species, making it difficult to correlate to equivalent foraminiferal zones worldwide. The Serpukhovian Hezhou Formation at the Fenghuangshan section on the Lower Yangtze Platform was deposited in an open to restricted shallow‐water environment, in which foraminifers flourished. Four foraminiferal zones named for cosmopolitan species found in this formation are established. In ascending order, they are the Plectomillerella tortula Zone, Eostaffellina paraprotvae Zone, Bradyina cribrostomata Zone and Monotaxinoides transitorius Zone. These zones permit reasonable correlation of the regional Chinese Dewuan (Serpukhovian) Stage to regional Russian substages (Tarussian, Steshevian, Protvian and Zapaltjubian). Preliminary correlations are also proposed between the Dewuan Stage and western European regional Mississippian substages (late Brigantian, Pendleian and Arnsbergian) and Chesterian formations of the type Mississippian region in North America. Copyright © 2017 John Wiley & Sons, Ltd.

Orbital‐scale droughts in central‐northern Mexico during the late Quaternary and comparison with other subtropical and tropical records

Palaeoclimate research in subtropical arid Mexico is mainly focused to infer dynamics and geographic distributions of different precipitation regimes, but droughts have received less attention. We present a new sedimentary core record indicating orbital‐scale dynamics of droughts that occurred in central‐northern Mexico during the late Quaternary. This record is reconstructed from abundances of authigenic carbonate and windblown clastic sediments in a 1026‐cm‐long sediment core from the Santiaguillo ephemeral lake. The Marine Isotope Stage (MIS) 2 lacked drought, and at least two different droughts were centred at c. 13.5 ka and at c. 7 ka during the MIS 1. The drought of c. 13.5 ka in the Santiaguillo ephemeral lake was contemporary to an interval of droughts in the Basin of Mexico (central Mexico) and stronger aeolian activity in the Baja California peninsula (northwestern Mexico). This synchronous arid condition, observed in the subtropical as well as tropical Mexico, occurred during an interval of higher spring insolation, relatively warmer but fluctuating global temperature, and stronger El Niño‐Southern Oscillation. Unsuccessful radiocarbon dating for the lower part of the sediment core led to an assignment of uncertain chronology to droughts that occurred possibly between MIS 5 and MIS 3. Copyright © 2017 John Wiley & Sons, Ltd.

Multistage dolomitization in the Qal’eh Dokhtar Formation (Middle‐Upper Jurassic), Central Iran: petrographic and geochemical evidence

The late Jurassic Qal’eh Dokhtar Formation lithologically comprises three parts, from bottom to top, a lower sandstone unit, middle shale unit and an upper carbonate unit, which extend in a N–S direction over a wide area to the east of the Shotori Range and west of the Lut Block (Central Iran). This succession was deposited on a mixed carbonate–siliciclastic ramp. Carbonate rocks of the Qal’eh Dokhtar Formation vary from undolomitized, to partly dolomitized, to completely dolomitized. Field observations from two measured sections (the type section, 955 m thick, and the Sorond section, 639 m thick), combined with detailed petrographic and geochemical analyses, revealed the diverse types of dolomite in this formation. Five types of replacement dolomite and one type of dolomite cement were distinguished. Replacement dolomites (RD) consist of: (1) fine crystalline planar‐s (RD1); (2) medium crystalline planar‐s (RD2); (3) medium crystalline planar‐e (RD3); (4) coarse crystalline planar‐s (RD4); and (5) coarse crystalline planar‐e (RD5). Coarse crystalline planar dolomite cements (DC) were observed in low abundance and filling dissolution voids and fractures. Variation in dolomite types is mainly related to early to late diagenetic processes leading to changes in composition of the dolomitizing fluids. Replacement dolomites are non‐stoichiometric (Ca43‐56–Mg34‐45) with Sr, Mn and Fe concentrations of 41–138 ppm, 168–919 ppm and 5000–21000 ppm, respectively. These dolomites are characterized by δ18O values ranging from 0.0 to –11.8 ‰ VPDB and δ13C values of +1.1 to +3.2 ‰ VPDB. These values are depleted in δ18O relative to the postulated values for late Jurassic dolomites precipitated in equilibrium with seawater, while δ13C values are within the range of Jurassic seawater dolomite values. Fluid inclusion data of RD4, RD5 and DC yield homogenization temperatures of 72 to 118 °C. Based on petrographic, fluid inclusion microthermometric data and geochemical results, the replacement dolomites in the Qal’eh Dokhtar Formation are interpreted to have formed in the subsurface at shallow to intermediate burial depths. These dolomites were then recrystallized at increased burial depths and temperatures. Seawater was the major source of Mg2+ for early diagenetic dolomite (DR1), while Mg2+ for late diagenetic dolomites was provided from diagenesis of clay minerals in shales and mechanical compaction of mudstone in the Qal’eh Dokhtar Formation. The dolomite cement is postdated by coarsely crystalline mosaic calcite cement indicating that diagenetic fluids eventually became undersaturated with respect to dolomite and oversaturated with respect to calcite. Copyright © 2016 John Wiley & Sons, Ltd.