Untitled

2010010221
白 垩 纪 海 洋 营 养 物 质 、 温 室 碳 酸 盐 和
锥 螺 类 腹 足 动 物 的 丰 度 = Cretaceous
marine nutrients, greenhouse carbonates,
and the abundance of turritelline gastropods.
( 英 文 ). Allmon W D. Journal of
Geology, 2007, 115(5): 509-523
Modern marine carbonate sediments
accumulate where carbonate-producing
organisms are abundant and siliciclastic
input is low. Such accumulations occur
today in two main environments and
may be characterized as warm, lownutrient
(WLN; also known as tropical or
chlorozoan) carbonates or cool, highnutrient
(CHN; also known as coolwater,
temperate, nontropical, foramol, or heterozoan)
carbonates. Few carbonates
form today in warm, high-nutrient
(WHN) conditions because such environments
are very rare. Modern WLN
environments occur mainly in low latitudes,
where nutrients from upwelling or
terrestrial runoff are low. Modern CHN
environments occur mainly in middle to
high latitudes, where nutrients, mostly
from upwelling, are abundant. However,
WHN depositional environments may
have been widespread during the Cretaceous
and Paleogene. During these times,
upwelled nutrientrich waters would, in
general, have been warmer than they are
today. Nutrients in these waters supported
diverse carbonate-producing biotas
that are not equivalent to either modern
chlorozoan or heterozoan biotas.
These conclusions derive from analysis
of a growing data set of more than 40
turritelline gastropod-dominated fossil
assemblages (TDAs), a term herein redefined,
ranging in age from Lower Cretaceous
to Pleistocene. Today TDAs occur
mainly in CHN conditions. They
were widespread in both carbonate and
siliciclastic facies in the Cretaceous and
Paleogene but (with only a single known
exception in the Pliocene of Chile) occur
in the Neogene only in siliciclastic
sediments. This change in environmental
distribution can be explained by positing
changes in (1) modal environmental
preferences of turritellines, from WHN
to CHN, and (2) carbonate depositional
environments, from to WLN + WHN
WLN +. Both changes were roughly coincident
with the global change from "
greenhouse" to " icehouse" conditions in
CHN the Oligocene.
2010010222
浅 水 海 洋 环 境 的 碳 酸 盐 保 存 : 热 带 硅
质 碎 屑 的 意 外 作 用 = Carbonate preservation
in shallow marine environments:
Unexpected role of tropical siliciclastics.
( 英 文 ). Best M M R; Ku T C W;
Kidwell S M; Walter L M. Journal of
Geology, 2007, 115(4): 437-456
Coordinated taphonomic, geochronologic,
and geochemical studies of bivalve
death assemblages and their sedimentary
environments of San Blas, Caribbean
Panama, permit us to identify the
major factors controlling skeletal degradation
in mixed carbonate-siliciclastic
tropical shelf sediments. Ten sites were
studied along environmental gradients
including water nutrients, grain size, and
sediment chemistry (carbonate, organic
carbon, and reactive iron contents). Taphonomic
data were derived from naturally
occurring bivalve death assemblages
and experimentally deployed
specimens of Mytilus edulis and Mercenaria
mercenaria to determine environmental
controls on types and intensities
of postmortem damage to skeletal hardparts
and to quantify short-term rates of
damage accrual. Death assemblage
shells were dated using C-14 and amino
acid racemization techniques to examine
shell persistence, scales of time averaging,
and long-term rates of damage accrual,
including correlations between
shell damage and shell age. Pore water
and sediment geochemical analyses
were used to determine the pathways
and extent of early diagenetic change in
the different sediment-pore water environments.
We found that carbonate shell
preservation is enhanced in dominantly
71