Untitled

交 林 草 原 或 沼 泽 草 甸 植 被 ,3 ka BP 之
后 为 海 退 时 期 , 气 候 变 凉 变 干 , 植 被 由
沼 泽 草 甸 演 变 为 盐 生 草 甸 。 尽 管 该 孔
是 目 前 沿 海 平 原 深 孔 分 析 孢 粉 样 品 最
密 的 钻 孔 , 但 是 未 能 发 现 连 续 丰 富 的 孢
粉 , 可 能 与 该 孔 位 于 相 对 较 高 部 位 , 多
与 河 流 沉 积 环 境 有 关 ; 故 而 , 平 原 区 内
并 非 每 一 个 钻 孔 皆 足 以 反 映 整 个 第 四
纪 孢 粉 地 层 学 的 全 貌 。
2010010512
阿 拉 斯 加 Fisher 凝 灰 岩 的 喷 发 与 沉
积 : 火 成 碎 屑 流 演 化 的 证 据 = Eruption
and deposition of the Fisher Tuff
(Alaska): Evidence for the evolution of
pyroclastic flows. ( 英 文 ). Gardner J E;
Burgisser A; Stelling P. Journal of Geology,
2007, 115(4): 417-435
Recognition that the Fisher Tuff
(Unimak Island, Alaska) was deposited
on the leeside of an similar to 500-700-
m-high mountain range (Tugamak
Range) more than 10 km away from its
source played a major role in defining
pyroclastic flows as momentum-driven
currents. We reexamined the Fisher Tuff
to evaluate whether deposition from expanded
turbulent clouds can better explain
its depositional features. We studied
the tuff at 89 sites and sieved bulk
samples from 27 of those sites. We find
that the tuff consists of a complex sequence
of deposits that record the evolution
of the eruption from a buoyant
plume (22 km) that deposited similar to
0.2 km(3) of dacite magma as a pyroclastic
fall layer to erupting similar to
10-100 km(3) of andesitic magma as
Scoria-rich pyroclastic falls and flows
that were mainly deposited to the north
and northwest of the caldera, including
those in valleys within the Tugamak
Range. The distribution of the flow deposits
and their welding, internal stratification,
and the occurrence of lithic
breccia all suggest that the pyroclastic
flows were fed from a fountaining column
that vented from an inclined conduit,
the first time such a conduit has
been recognized during a large-volume
caldera eruption. Pyroclastic flow deposits
before and after the mountain range
and thin veneer deposits high in the
range are best explained by a flow that
was stratified into a dense undercurrent
and an overriding dilute turbulent cloud,
from which deposition before the range
was mainly from the undercurrent.
When the flow ran into the mountain
range, however, the undercurrent was
blocked, but the turbulent cloud continued
on. As the flow continued north, it
restratified, forming another undercurrent.
The Fisher Tuff thus records the
passing of a flow that was significantly
higher (800-1100 m thick) than the
mountain range and thus did not require
excessive momentum.
2010010513
过 去 300m.y. 的 温 室 危 机 = Greenhouse
crises of the past 300 million
years. ( 英 文 ). Retallack G J. Geological
Society of America Bulletin, 2009,
121(9-10): 1441-1455
Proxies of past CO 2 and climate over
the past 300 m.y. now reveal multiple
global climate change events in unprecedented
detail. Evidence for past
CO 2 spikes comes from expanded and
refined stomatal index data of fossil
Ginkgo and related leaves. New evidence
for synchronous climatic change
comes from paleosols in Montana, Utah,
and neighboring states. Each CO 2 spike
was coeval with unusually clayey, red,
and decalcified paleosols that can be
traced throughout the Colorado Plateau.
Spikes in atmospheric CO 2 also were
coeval with increases in paleosol alkali
depletion as an indication of high temperature,
and spikes in paleosol base depletion
and depth to calcic horizons as
indications of high precipitation. In the
Colorado Plateau, times of warmer climate
were also more humid, perhaps due
to the greater moisture potential of
warmer air. Seasonality of climate did
not increase during warm-wet spikes.
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