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由 Kaczawa 复 合 体 ( 欧 洲 中 部 华 力 西 构 造
带 )Radzimowice 板 岩 中 碎 屑 锆 石 所 推 断
的 冈 瓦 那 大 陆 北 部 边 缘 太 古 代 至 古 早 生 代
多 期 次 事 件 = Multiple Archaean to Early
Palaeozoic events of the northern Gondwana
margin witnessed by detrital zircons from the
Radzimowice Slates, Kaczawa Complex (Central
European Variscides). ( 英 文 ). Tyszka R;
Kryza R; Zalasiewicz J A; Larionov A N.
Geological Magazine, 2008, 145(1): 85-93
SIMS dating of detrital zircons from the
stratigraphically enigmatic Radzimowice
Slates of the Kaczawa Mountains (Sudetes,
SW Poland), near the eastern termination of
the European Variscides, has yielded age
populations of. (1) 493-512 Ma, corresponding
to late Cambrian to early Ordovician
magmatism and constraining a maximum depositional
age; (2) between 550 and 650 Ma,
reflecting input from diverse Cadomian
sources; and (3) older inherited components
ranging to c. 3.3 Ga, with age spectra similar
to those from Gondwanan North Africa. The
new data show that the Radzimowice Slates
cannot form a Proterozoic base to the Kaczawa
Mountains succession, as suggested by
earlier models, but was deposited, at the earliest,
as an extensional basin-fill, during a relatively
late stage of the break-Lip of this part of
northern Gondwana.
2010040499
雪 球 假 说 的 起 源 和 评 价 = Origins and assessment
of snowball Earth hypotheses. ( 英
文 ). Harland W B. Geological Magazine,
2007, 144(4): 633-642
Records of Precambrian glaciation onwards
from the late nineteenth century led to the
concept of one or more major ice ages. This
concept was becoming well advanced by the
mid 1930s, particularly through the compilation
of Kulling in 1934. Even so tillite stratigraphy
shows that glaciation was exceptional
rather than typical of Earth history. Some Proterozoic
tillites, sandwiched between warm
marine facies, indicate low, even equatorial
palaeolatitudes as determined magnetically,
and more recently led to ideas of a snow- and
ice-covered 'snowball Earth'. However, interbedded
non-glacial facies as well as thick tillite
successions requiring abundant snowfall
both militate against the hypothesis of extreme
prolonged freezing temperatures referred to
here as an 'iceball Earth' in which all oceans
and seas were sealed in continuous ice cover.
On the other hand tropical environments were
interrupted by glaciation several times in the
Proterozoic, something that did not recur in
the Phanerozoic. The term 'snowball Earth' is
consistent with the established view of extremely
widespread Proterozoic glaciation, but
the 'iceball Earth' version of this is not compatible
with the geological record.
2010040500
西 伯 利 亚 地 台 西 北 部 前 寒 武 纪 - 寒 武 纪
Sukharikha 河 剖 面 碳 同 位 素 地 层 学 = Carbon
isotope stratigraphy of the Precambrian-
Cambrian Sukharikha River section, northwestern
Siberian platform. ( 英 文 ). Kouchinsky
A; Bengtson S; Pavlov V; Runnegar B;
Torssander P; Young E; Ziegler K. Geological
Magazine, 2007, 144(4): 609-618
A high-resolution carbon isotope profile
through the uppermost Neoproterozoic-Lower
Cambrian part of the Sukharikha section at the
northwestern margin of the Siberian platform
shows prominent secular oscillations of delta
C-13 with peak-to-peak range of 6-10 parts
per thousand. There are six minima, In-6n,
and seven maxima 1p-7p, in the Sukharikha
Formation and a rising trend of VC from the
minimum In of - 8.6 parts per thousand to
maximum 6p of + 6.4 parts per thousand. The
trough In probably coincides with the isotopic
minimum at the Precambrian-Cambrian
boundary worldwide. Highly positive delta C-
13 values of peaks 5p and 6p are typical of the
upper portion of the Precambrian-Cambrian
transitional beds just beneath the Tommotian
Stage in Siberia. A second rising trend of VC
is observed through the Kxasnoporog and
lower Shumny formations. It consists of four
excursions with four major maxima that can
be correlated with Tommotian-Botomian
peaks II, IV, V, and VII of the reference profile
from the southeastern Siberian platform.
According to the chemostratigraphic correlation,
the first appearances of the index forms
of archaeocyaths are earlier in the Sukharikha
section than in the Lena-Aldan reuion.
2010040501
条 带 状 含 铁 建 造 (Gua 矿 山 , 印 度 ) 的 显
微 结 构 = Microstructures in a banded iron
formation (Gua mine, India). ( 英 文 ). Mamtani
M A; Mukherji A; Chaudhuri A K. Geological
Magazine, 2007, 144(2): 271-287
This paper provides a detailed documentation
of microstructures developed in the
banded iron formation (13117) of Gua mine,
located in the Bonai Synclinorium (eastern
India), where the rocks have been subjected to
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