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The Pelagonian Zone in Greece represents
the westermost belt of the Hellenide hinted
and (Internal Hellenides). Previous geochronological
studies of basement rocks from the
Pelagonian Zone have systematically yielded
Pernio-Carboniferous ages. In this study we
demonstrate, for the first time, the existence of
a Precambrian crustal unit within the crystalline
basement of the Pelagonian Zone. The U-
Pb single-zircon and SHRIMP ages of these
orthogneisses vary from 699 +/- 7 Ma to 713
+/- 18 Ma, which identify them as the oldest
rocks in Greece. These Late Proterozoic rocks,
which today occupy an area of c. 20 x 100 km,
are significantly different from the neighbouring
rocks of the Pelagonian Zone. They are
therefore interpreted as delineating a terrane,
named here the Florina Terrane. During the
Permo-Carboniferous, Florina was incorporated
into all active continental margin, where
it formed part of the basement for the Pelagonian
magmatic arc. The activity of this arc was
dated in this study by single-zircon Pb/Pb ages
as having taken place at 292 +/- 5 Ma and 298
+/- 7 Ma. During the Alpine orogeny, Florina,
together with the Pelagonian Zone, eventually
became a constituent of the Hellenides. Geochemically,
the Florina orthogneisses represent
granites formed at an active continental
margin. Because of the Late Proterozoic ages,
this Late Proterozoic active continental margin
can be correlated to a Pan-African or
Cadomian arc. As the gneisses contain inherited
zircons of Late to Middle Proterozoic age,
the original location of Florina was probably
at the northwestern margin of Gondwana.
Similar to other Gondwana-derived terranes,
such as East Avalonia, Florina approached the
Southern margin of Eurasia during Palaeozoic
times, where it became part of an active continental
margin above the subducting Palaeotethys.
These interpretations further indicate
that terrane accretion was already playing all
important role in the early pre-alpine evolution
of the Hellenides.
2010040504
纳 米 比 亚 Nama 群 受 到 风 暴 控 制 的 碳 酸 岩
斜 坡 ( 约 549 百 万 年 ) 的 地 貌 演 化 = Geomorphic
evolution of a storm-dominated carbonate
ramp (c. 549 Ma), Nama Group, Namibia.
( 英 文 ). Dibenedetto S; Grotzinger J.
Geological Magazine, 2005, 142(5): 583-604
The well-exposed Hoogland Member (c.
549 Ma) of the northern Nama Group (Kuibis
Subgroup), Namibia, represents a stormdominated
carbonate ramp developed in a
foreland basin of terminal Proterozoic age.
The ramp displays facies gradients involving
updip grainstones which pass downdip into
broad, spatially extensive tracts of microbial
laminites and finely laminated mudstones deposited
above and below storm wave base.
Trough cross-bedded, coarse grainstones are
shown to transit downdip into finer-grained
calcarenites, irregular microbial laminites and
mottled laminites. Siliciclastic siltstones and
shales were deposited further downdip. Platform
growth was terminated through smothering
by orogen-derived siliciclastic deposits.
Ramp morphology was controlled by several
different processes which acted across many
orders of magnitude (millimetres to kilometres),
including in situ growth of mats and
reefs, scouring by wave-produced currents,
and transport and infilling of coarse-grained
carbonates and fine-grained carbonates and
clastics. At the smallest scale,,roughening' of
the sea-floor through heterogeneous trapping
and binding by microbial mats was balanced
by smoothing of the sea-floor through accumulation
of loose sediment to fill the topographic
lows within the upward-propagating
mat. At the next scale up, parasequence development
involved roughening of the sea-floor
through shoal growth and grainstone progradation,
balanced by sea-floor smoothing
through shale infilling of resulting downdip
accommodation, as well as the metre-scale
topographic depressions within the mosaic of
shoal-water facies. At even larger (sequence/platform)
scales, roughening of the
sea-floor occurred through aggradation and
progradation of thick carbonates, balanced by
infilling of the foreland basin with orogenderived
siliciclastic sediments. At all scales a
net balance was achieved between sea-floor
roughening and sea-floor smoothing to maintain
a more or less constant ramp profile.
2010040505
Port Nolloth 组 ( 纳 米 比 亚 ) 上 部 的 有 机 质
壁 微 体 化 石 和 生 物 地 层 学 研 究 : 对 新 元 古
代 最 后 一 个 冰 期 的 启 示 = Organic-walled
microfossils and biostratigraphy of the upper
Port Nolloth Group (Namibia): implications
for latest Neoproterozoic glaciations. ( 英 文 ).
Gaucher C; Frimmel H E; Germs GJB. Geological
Magazine, 2005, 142(5): 539-559
The occurrence of organic-walled microfossils
is reported for the first time from the Neoproterozoic
Port Nolloth Group, Gariep Belt
(southern Namibia). Acritarchs assigned to
Bavlinella faveolata occur in the Hilda Sub-
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