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Volume 145 Issue 02

Sat, 01 Mar 2008 00:00:00 GMT

Geological Magazine, Volume 145 Issue 02

Geological Magazine , established in 1864, is one of the oldest and best-known periodicals in earth sciences. It publishes original scientific papers covering the complete spectrum of geological topics, with high quality illustrations. Its worldwide circulation, attractive layout, Rapid Communications section and extensive Book Review section keep the journal at the forefront of important publications in the field. This journal is included in the Cambridge Journals open access initiative, Cambridge Open Option. Offer readers unrestricted online access to your work, click here for more details.

The Shuram–Wonoka event recorded in a high-grade metamorphic terrane: insight from the Scandinavian Caledonides

Research Articles
V. A. MELEZHIK, D. ROBERTS, A. E. FALLICK, I. M. GOROKHOV,
Geological Magazine, Volume 145 Issue 02 , pp 161-172

Abstract
An approximately 250 m thick polydeformed and polymetamorphosed, isotopically unusual, variegated marble (locally termed the ) shows a great lateral extent in the Scandinavian Caledonides. Its extremely 13C-depleted primary nature ( 1.2 Wonoka isotopic event occurring within the 600 13Ccarb can potentially be used for stratigraphic correlations in high-grade, non-fossiliferous, marble-dominated terranes across the Caledonian orogenic belt in Baltica and Laurentia. Isotope chemostratigraphy has identified a prominent cryptic stratigraphic discontinuity and suggests that the Ediacaran Leivset marble was tectonically juxtaposed above low-grade, Llandovery-age, fossiliferous marbles during the Scandian orogeny.

The Waipounamu Erosion Surface: questioning the antiquity of the New Zealand land surface and terrestrial fauna and flora

Research Articles
C. A. LANDIS, H. J. CAMPBELL, J. G. BEGG, D. C. MILDENHALL, A. M. PATERSON, S. A. TREWICK,
Geological Magazine, Volume 145 Issue 02 , pp 173-197

Abstract
The Waipounamu Erosion Surface is a time-transgressive, nearly planar, wave-cut surface. It is not a peneplain. Formation of the Waipounamu Erosion Surface began in Late Cretaceous time following break-up of Gondwanaland, and continued until earliest Miocene time, during a 60 million year period of widespread tectonic quiescence, thermal subsidence and marine transgression. Sedimentary facies and geomorphological evidence suggest that the erosion surface may have eventually covered the New Zealand subcontinent (Zealandia). We can find no geological evidence to indicate that land areas were continuously present throughout the middle Cenozoic. Important implications of this conclusion are: (1) the New Zealand subcontinent was largely, or entirely, submerged and (2) New Zealand's present terrestrial fauna and flora evolved largely from fortuitous arrivals during the past 22 million years. Thus the modern terrestrial biota may not be descended from archaic ancestors residing on Zealandia when it broke away from Gondwanaland in the Cretaceous, since the terrestrial biota would have been extinguished if this landmass was submerged in Oligocene Early Miocene time. We conclude that there is insufficient geological basis for assuming that land was continuously present in the New Zealand region through Oligocene to Early Miocene time, and we therefore contemplate the alternative possibility, complete submergence of Zealandia.

Integrated Upper Ordovician graptolite–chitinozoan biostratigraphy of the Cardigan and Whitland areas, southwest Wales

Research Articles
THIJS R. A. VANDENBROUCKE, MARK WILLIAMS, JAN A. ZALASIEWICZ, JEREMY R. DAVIES, RICHARD A. WATERS,
Geological Magazine, Volume 145 Issue 02 , pp 199-214

Abstract
To help calibrate the emerging Upper Ordovician chitinozoan biozonation with the graptolite biozonation in the Anglo-Welsh, historical type basin, the graptolite-bearing Caradoc oxic transition at the base of the Nantmel Mudstones Formation in Wales, traditionally equated with the Caradoc Ashgill boundary, is of Cautleyan (or younger Ashgill) age in the Cardigan area. In the broadly time-equivalent, graptolite-rich Whitland section, also in SW Wales, two Baltoscandian chitinozoan biozones and a subzone have been recognized (again using accessory species), namely the Spinachitina cervicornis Biozone?, the Fungochitina spinifera Biozone and the Armoricochitina reticulifera Subzone. The new chitinozoan data provide a more precise means of correlation between the Whitland and Cardigan successions and suggest that the Normalograptus proliferation interval of the Whitland section is at least partly attributable to the Dicellograptus morrisi Subzone of the Dicranograptus clingani Biozone, rather than equating with the overlying Pleurograptus linearis Biozone.

Geochronology and geochemistry of Neoproterozoic mafic rocks from western Hunan, South China: implications for petrogenesis and post-orogenic extension

Research Articles
XIAO-LEI WANG, JIN-CHENG ZHOU, JIAN-SHENG QIU, SHAO-YONG JIANG, YU-RUO SHI,
Geological Magazine, Volume 145 Issue 02 , pp 215-233

Abstract
The Neoproterozoic mafic rocks in western Hunan, South China, form a NNE-striking mafic rock belt for which outcrops are found predominantly in Guzhang, Qianyang and Tongdao. Samples from Qianyang and Tongdao yielded ion microprobe U 18 Ma and 772 Hf isotopes, and geochemical features similar to the c. 761 Ma mafic Nd(t) value is Hf isotopes. They are geochemically similar to ocean island basalts and show fractional crystallization of Fe Ti oxides, olivine and pyroxene in the mafic magma. The c. 760 Ma mafic rocks in western Hunan may be the products of post-orogenic magmatism. After the Jinningian (Sibao) orogenic process, the upwelling of the deep asthenospheric mantle caused by the break-off and detachment of the subducted oceanic slab led to extension in the area. The extension might have taken place earlier in the Tongdao and Longsheng areas, which led to the partial melting of the lithospheric mantle that had been metasomatized during early oceanic subduction to generate a relatively large amount of sub-alkaline rocks. However, the less alkaline mafic rocks in Qianyang and Guzhang might have been generated in the relatively later stage of the extension, and may have resulted from a small degree of partial melting of the asthenospheric mantle.

The Newer Granite problem revisited: a transtensional origin for the Early Devonian Trans-Suture Suite

Research Articles
P. E. BROWN, P. D. RYAN, N. J. SOPER, N. H. WOODCOCK,
Geological Magazine, Volume 145 Issue 02 , pp 235-256

Abstract
The origin of the Newer Granites is long-standing problem. In the Caledonian orthotectonic zone the intrusions span the period of late orogenic convergence and uplift, but attempts to relate them as a group to late Iapetan subduction have been unsuccessful. A range of rock types is represented, mainly with I-type affinities, and granodiorite is the most voluminous. In contrast, granitic intrusions south of the Moniaive shear zone in Scotland and also in the north of England have significant S-type characteristics, span the trace of the Iapetus suture and have ages in the range 400 soft collision under the Trans-Suture Suite zone; thermal relaxation to remove any subduction refrigeration; crust composed of juvenile volcanogenic material; and Devonian transtension. Our models suggest that if hydration pre-dated transtension then only small granitic bodies could be produced, unless the zone of lamprophyre generation extends beyond the rift zone. The emplacement of the Trans-Suture Suite intrusions overlapped the Acadian deformation period that succeeded the transtensional episode during which the granite magmas were generated.

The earliest phyllolepid (Placodermi, Arthrodira) from the Late Lochkovian (Early Devonian) of Yunnan (South China)

Research Articles
V. DUPRET, M. ZHU,
Geological Magazine, Volume 145 Issue 02 , pp 257-278

Abstract
Gavinaspis convergens, a new genus and species of the Phyllolepida (Placodermi: Arthrodira), is described on the basis of skull remains from the Late Lochkovian (Xitun Formation, Early Devonian) of Qujing (Yunnan, South China). This new form displays a mosaic of characters of basal actinolepidoid arthrodires and more derived phyllolepids. A new hypothesis is proposed concerning the origin of the unpaired centronuchal plate of the Phyllolepida by a fusion of the paired central plates into one single dermal element and the loss of the nuchal plate. A phylogenetic analysis suggests the position of Gavinaspis gen. nov. as the sister group of the Phyllolepididae, in a distinct new family (Gavinaspididae fam. nov.). This new form suggests a possible Chinese origin for the Phyllolepida or that the common ancestor to Phyllolepida lived in an area including both South China and Gondwana, and in any case corroborates the palaeogeographic proximity between Australia and South China during the Devonian Period.

Depositional origin of tuffaceous units in the Pliocene Upper Siwalik Subgroup, Jammu (India), NW Himalaya

Research Articles
G. M. Bhat, S. N. Kundal, S. K. Pandita, G. V. R. Prasad,
Geological Magazine, Volume 145 Issue 02 , pp 279-294

Abstract
During late Pliocene times, extrabasinally derived acidic volcanic ashes were deposited as distal pyroclastic fallout in upland interfluvial Matuyama boundary at 2.48 Ma. This bentonitized tuff band and tuffaceous mudstone association represents a stratigraphic marker horizon in the diachronous and sporadic vertebrate fauna-yielding Siwalik strata. The claystone, siltstone, and sandstone units and embedded bentonitized tuff band and tuffaceous mudstone beds represent a coarsening-upward sequence reflecting deposition in lacustrine proximal and distal bottomsets, pro-delta foresets, and mouth-bar facies capped by fluvial topsets. This study reports a chain of four contemporaneous, palaeo-lake basins at this stratigraphic level, which ranged in length from 2 to 7 km.

The palaeogeographical significance of specimens attributed to Protolepidodendron scharyanum Krejči (Lycopsida) from the Middle Devonian of North Xinjiang, China

Rapid Communication
HONG-HE XU, YI WANG,
Geological Magazine, Volume 145 Issue 02 , pp 295-299

Abstract
Morphology of the leaves of stem compressions originally attributed to Protolepidodendron scharyanum from the Middle Devonian of North Xinjiang, China is reinvestigated. The leaf is three-dimensional, consisting of one central abaxial segment and four lateral adaxial segments, and does not conform to the once bifurcate leaf of Protolepidodendron. Specimens are therefore transferred to Leclercqia cf. L. complexa. This is the first unequivocal report of the genus Leclercqia in China based on complete leaf morphology. The distribution of Leclercqia is discussed, demonstrating a more or less cosmopolitan genus in the Middle Devonian. The Middle Devonian flora of North Xinjiang shows great similarity to that of Venezuela and North America, and almost no relationship with that of Yunnan, South China.

A. Seilacher 2007. Trace Fossil Analysis . xiii + 226 pp. Berlin, Heidelberg, New York: Springer-Verlag. Price Euros 53.45, SFr 87.00, US $69.95, £38.50 (hard covers). ISBN 9783 540 47225 4.

Book Reviews
Richard G. Bromley, Jesper Milàn,
Geological Magazine, Volume 145 Issue 02 , pp 301-301

Abstract

O. Oncken, G. Chong, G. Franz, P. Giese, H.-J. Götze, V. A. Ramos, M. R. Strecker & P. Wigger (eds) 2006. The Andes. Active Subduction Orogeny . Frontiers in Earth Sciences Series. xxii + 569 pp. + CD-ROM. Berlin, Heidelberg, Dordrecht: Springer-Verlag. Price Euros 149.95, US $189.00, £115.50 (hard covers). ISBN 9783 540 24329 8.

Book Reviews
R. J. Pankhurst,
Geological Magazine, Volume 145 Issue 02 , pp 301-302

Abstract

P. C. H. Veeken 2007. Seismic Stratigraphy, Basin Analysis and Reservoir Characterisation . Handbook of Geophysical Exploration, Volume 37. xi + 509 pp. Amsterdam, Boston, Heidelberg, London: Elsevier. Price £85.00, US $145.00, Euros 125 (hard covers). ISBN 9780 0804 5311 8.

Book Reviews
David James,
Geological Magazine, Volume 145 Issue 02 , pp 302-302

Abstract

PUBLICATIONS RECEIVED

Books Received

Geological Magazine, Volume 145 Issue 02 , pp 303-303

Abstract