Palaeomagnetism of the Lower Ordovician Orthoceras Limestone, St. Petersburg, and a revised drift history for Baltica in the early Palaeozoic
Palaeomagnetism of the Lower Ordovician Orthoceras Limestone, St. Petersburg, and a revised drift history for Baltica in the early Palaeozoic
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圣彼得堡下奥陶世正角石灰岩的古地磁学以及波罗的海早古生代漂移历史的修正
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发表时间：
1998
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通讯作者：
S. Pisarevsky
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作者：
M. Smethurst;A. Khramov;S. Pisarevsky
对彼得堡附近下奥陶统石灰岩的古地磁调查得出一个极位，位于北纬34.7°，东经59.1°（dp/dm=5.7°/6.4°）。一个可能的一次剩磁的起源是支持在场逆转。灰岩携带另一个与中生代重磁化事件相关的重磁化分量。一个明显的极移路径编制波罗的海包括新的结果，年龄范围从文迪安到白垩纪。根据Tucker & McKerrow（1995）的时间尺度，对已发表的早古生代至中古生代古地磁极位置的年龄进行了调整。新的Arenig结果是一系列来自波罗的海地区石灰岩的奥陶纪和志留纪古磁极位置中最古老的。没有数据来约束Tremadoc，寒武纪和最新的Vendian明显的极移。如果芬复杂的结果，以前采取的Vendian在年龄（c。565 Ma），被重新解释为二叠纪重磁化，在波罗的海的极地漂移路径上的早奥陶世-寒武世-文迪尖点被消除。因此，对于科拉半岛（c. 580 Ma）向我们的新Arenig极点（c. 480 Ma）。寒武纪波罗的海运动的这一变化的结果是显著减少了运动的旋转分量。新的Arenig极点扩展了奥陶纪视极移的知识，并确认了一些已发表的古地理中波罗的海的古纬度和方向。排除芬杂岩的结果将波罗的海置于古生代黎明时偏南的中高纬度地区，这与动物群和沉积学证据一致，但与一些早期的古地磁重建不一致。
SUMMARY Palaeomagnetic investigation of Lower Ordovician limestone in the vicinity of St. Petersburg yields a pole position at latitude 34.7°N, longitude 59.1° E( dp/dm=5.7°/6.4°). A probable primary remanence origin is supported by the presence of a field reversal. The limestone carries one other remanent magnetization component associated with a Mesozoic remagnetization event. An apparent polar wander path is compiled for Baltica including the new result, ranging in age from Vendian to Cretaceous. Ages of the published Lower to midPalaeozoic palaeomagnetic pole positions are adjusted in accordance with the timescale of Tucker & McKerrow (1995). The new Arenig result is the oldest of a series of Ordovician and Silurian palaeomagnetic pole positions from limestones in the Baltic region. There are no data to constrain apparent polar wander for the Tremadoc, Cambrian and latest Vendian. If the Fen Complex results, previously taken to be Vendian in age (c. 565 Ma), are reinterpreted as Permian remagnetizations, an Early Ordovician‐Cambrian‐Vendian cusp in the polar wander path for Baltica is eliminated. The apparent polar wander curve might then traverse directly from poles for Vendian dykes on the Kola peninsula (c. 580 Ma) towards our new Arenig pole (c. 480 Ma). The consequence of this change in terms of the motion of Baltica in Cambrian times is to reduce significantly a rotational component of movement. The new Arenig pole extends knowledge of Ordovician apparent polar wander an increment back in time and confirms the palaeolatitude and orientation of Baltica in some published palaeogeographies. Exclusion of the Fen Complex result places Baltica in mid- to high southerly latitudes at the dawn of the Palaeozoic, consistent with faunal and sedimentological evidence but at variance with some earlier palaeomagnetic reconstructions.