The Polonez Cove Formation of King George Island, Antarctica: stratigraphy, facies and implications for mid‐Cenozoic cryosphere development
The Polonez Cove Formation of King George Island, Antarctica: stratigraphy, facies and implications for mid‐Cenozoic cryosphere development
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南极洲乔治王岛的波罗涅斯湾地层：地层学、相及其对新生代中期冰冻圈发育的影响
DOI：
10.1046/j.1365-3091.2002.00441.x
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发表时间：
2002
期刊：
影响因子：
3.5
通讯作者：
J. Smellie
中科院分区：
文献类型：
--
作者：
A. Troedson;J. Smellie
在南设得兰群岛的国王乔治岛东南部出露的渐新世中晚期Polonez Cove地层为西南极中新生代冰冻圈演化提供了罕见的证据。本文对该地层进行了岩石地层学和岩相分析，并对该地层的古环境意义进行了评述。以杂岩为主的地层基底段（Krakowiak Glacier Member）记录了浅大陆架上海洋冰的存在和退缩。五个重叠的成员被确认。这些由玄武岩源沉积岩和熔岩组成，代表了活跃火山环境中的各种滨面和浅大陆架环境。这些单元包含不同的改造和冰筏外来碎屑，这些碎屑在地层顶部变得稀疏，表明冰川的影响持续但正在减弱。新的40 Ar/39 Ar年龄从层间熔岩流表明，晚渐新世年龄（25·6-27·2 Ma）的Polonez湾形成，但略低于骨骼碳酸盐锶同位素年龄先前获得（28·5-29·8 Ma）。 有证据表明，在波罗内斯湾地层的底部存在湿基亚冰条件，但没有沉积相表明存在大量融水。这可能反映了亚极地环境，也可能是由于缺乏保存或高能沉积环境造成的。大多数非玄武质碎屑可能来自南极北方半岛/南设得兰群岛，但可能起源于跨南极和埃尔斯沃思山脉的某些岩性也在整个地层中稀疏出现。有证据表明，在地层底部的冰下沉积相中存在这种远距离移动的碎屑，反映了局部冰帽在含有碎屑的海洋沉积物中的前进作为冰筏材料。这些碎屑的存在表明，广泛的海洋冰排入南部威德尔海地区，并且在Polonez Cove地层沉积之前和沉积期间都有强大的威德尔海表面电流。
The middle to late Oligocene Polonez Cove Formation, exposed on south‐eastern King George Island, South Shetland Islands, provides rare evidence of mid‐Cenozoic West Antarctic cryosphere evolution. A revised lithostratigraphy and facies analysis and a review of the palaeoenvironmental significance of the formation are presented here. The diamictite‐dominated basal member of the formation (Krakowiak Glacier Member) records the presence and retreat of marine‐based ice on a shallow continental shelf. Five overlying members are recognized. These consist of basaltic‐sourced sedimentary rocks and lavas and represent a variety of shoreface and shallow continental shelf environments in an active volcanic setting. These units contain diverse reworked and ice‐rafted exotic clasts that become sparse towards the top of the formation, suggesting a continuing but waning glacial influence. New 40Ar/39Ar dates from interbedded lava flows indicate a late Oligocene age (25·6–27·2 Ma) for the Polonez Cove Formation, but are slightly younger than skeletal carbonate Sr‐isotope ages obtained previously (28·5–29·8 Ma). There is evidence for wet‐based subice conditions at the base of the Polonez Cove Formation, but no sedimentary facies to suggest substantial meltwater. This may reflect a subpolar setting or may result from lack of preservation or a high‐energy depositional environment. A northern Antarctic Peninsula/South Shetland Islands provenance is probable for most non‐basaltic clasts, but certain lithologies with possible origins in the Transantarctic and Ellsworth Mountains also occur sparsely throughout the formation. There is evidence to suggest that the presence of such far‐travelled clasts within subglacially deposited facies at the base of the formation reflects the advance of a local ice cap across marine sediments containing the clasts as ice‐rafted material. The presence of these clasts suggests that extensive marine‐based ice drained into the southern Weddell Sea region and that a strong Weddell Sea surface current operated both before and during deposition of the Polonez Cove Formation.