Foraminifera and their habitats within a cool-water carbonate succession following glaciation, early Permian (Sakmarian), Western Australia
Foraminifera and their habitats within a cool-water carbonate succession following glaciation, early Permian (Sakmarian), Western Australia
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DOI：
10.2113/34.4.308
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发表时间：
2004-10
影响因子：
1.1
通讯作者：
M. Dixon;D. Haig
中科院分区：
文献类型：
--
作者：
M. Dixon;D. Haig
Gondwana东部下二叠世最发育的碳酸盐岩序列之一是Callytharra组，它沉积在远离开阔海洋的狭长裂谷盆地中受冰川影响的沉积物之上。这个地层和下面的卡兰迪比地层为Sakmarian Gondwanan冰原融化时的动物变化提供了证据。各种较小的底栖有孔虫，包括有机胶结凝集、透明和瓷状钙化形式，伴随着异种动物的大型动物（主要是苔藓虫、海百合和腕足动物）。没有镰刀虫类有孔虫和钙质藻类。七个有孔虫组合带细分了相关大型动物群和岩相的演替和平行变化。由演替确定的环境变化包括：(1)从近岸、低能量、低盐度、凉爽的水域向支持苔藓虫、海珊瑚和非骨藻草甸的高能量、正常的海水过渡；(2)由富氧、浅水、沙质基质向深水、低氧、泥泞基质过渡。动物区系比较表明，在古纬度高于45°S的冈瓦纳盆地东部，在广泛分离的内陆盆地中，Sakmarian发生了从低多样性、硅质凝集到高多样性、富含Calcitornella的有孔虫组合的变化。这一变化可能与冈瓦纳冰盖退缩导致流入内陆盆地的融水减少有关。气候变暖不足以让褐藻和钙质藻类在浅海定居，它们的活动范围只在南纬45度的古纬度。
One of the best-developed carbonate successions of the Lower Permian in eastern Gondwana is the Callytharra Formation, deposited above glacially influenced sediments in a narrow elongate rift basin far from the open ocean. This formation and the underlying Carrandibby Formation provide evidence for faunal changes that accompanied the melting of the Sakmarian Gondwanan ice sheets. Diverse smaller benthic foraminifera including organic-cemented agglutinated, hyaline, and porcelaneous calcitic forms, accompany a heterozoan macrofauna (mainly bryozoans, crinoids and brachiopods). Fusulinid foraminifera and calcareous algae are absent. Seven foraminiferal assemblage zones subdivide the succession and parallel changes in associated macrofauna and lithofacies. Environmental changes determined from the succession include (1) a transition from nearshore, low-energy, low-salinity, cool waters to higher-energy, normal-marine waters supporting bryozoan, crinoidal and non-skeletal-macroalgal meadows; and (2) a transition from well-oxygenated, shallow-water, sandy substrates to deeper-water, less-oxygenated, muddy substrates. Faunal comparisons suggest that at paleolatitudes higher than 45°S, in widely separated interior basins in eastern Gondwana, a change from low-diversity, siliceous-agglutinated to high-diversity, Calcitornella -rich, foraminiferal assemblages took place during the Sakmarian. This change may have been associated with a reduction in melt-water influx into the interior basins from retreating Gondwanan ice sheets. The warming was insufficient to allow colonization of the shallow seas by fusulinids and calcareous algae, which only ranged as far south as 45°S paleolatitude.