Compaction-corrected paleomagnetic paleolatitudes for Late Cretaceous rudists along the Cretaceous California margin: Evidence for less than 1500 km of post–Late Cretaceous offset for Baja British Columbia
Compaction-corrected paleomagnetic paleolatitudes for Late Cretaceous rudists along the Cretaceous California margin: Evidence for less than 1500 km of post–Late Cretaceous offset for Baja British Columbia
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DOI：
10.1130/0016-7606(2001)113
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发表时间：
2001-09
影响因子：
4.9
通讯作者：
K. Kodama;P. Ward
中科院分区：
文献类型：
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作者：
K. Kodama;P. Ward
双壳类红壳类的古纬度分布对于巴哈不列颠哥伦比亚省 (Baja BC) 假说具有重要意义，该假说认为，自白垩纪以来，加拿大西部不列颠哥伦比亚省的超级地体已移动了 3000 公里。在 Baja BC 沉积岩中未观察到赤色岩，但它们在加利福尼亚州和下加利福尼亚州的晚白垩世地层中很常见，这些地层与晚白垩世的 Baja BC 岩石具有相同的古地磁确定的古纬度（约 25°N）。为了解决这一矛盾并更准确地划定公元前巴哈南部的古纬度，利用根据埋藏压实影响进行校正的古地磁倾角来确定沿加利福尼亚州边缘的粗地岩的古纬度分布。来自半岛山脉和萨利尼亚地体的压实校正古地磁数据表明，裸岩仅限于北纬 34° 至 40° 之间的古纬度。白垩纪晚期马卡页岩中沿海上升流的证据可以解释红岩分布的北部界限。这些数据表明，Baja BC在晚白垩世的位置不超过北纬40°，从而将其白垩纪后的位移限制在1500公里以内，并且埋藏压实也影响了温哥华岛纳奈莫群沉积岩的古地磁作用。这一结果还有助于解决古地磁结果与地质观测结果之间的冲突，古地磁结果显示晚白垩世后岛岸深成杂岩体与山间超地体之间存在 1500 公里的偏移，而地质观测仅允许 Methow-Tyaughton 盆地这些地体之间存在数十公里的偏移。
The paleolatitudinal distribution of bivalve rudists has important significance for the Baja British Columbia (Baja BC) hypothesis that western Canadian superterranes from British Columbia have been displaced 3000 km since Cretaceous time. Rudists are not observed in Baja BC sedimentary rocks, yet they are common in Late Cretaceous strata in California and Baja California, which have the same paleomagnetically determined paleolatitudes (approximately 25°N) as Baja BC rocks of Late Cretaceous age. In order to resolve this contradiction and to delimit more exactly the southern paleolatitudes of Baja BC, paleomagnetic inclinations corrected for the effects of burial compaction were used to determine the paleolatitudinal distribution of rudists along the California margin. Compaction-corrected paleomagnetic data from the Peninsular Ranges and Salinia terranes indicate that rudists were restricted to paleolatitudes between 34° and 40°N. Evidence of coastal upwelling in the latest Cretaceous Marca Shale may explain the northern limit of the rudist distribution. These data suggest that Baja BC was no farther south than 40°N in the Late Cretaceous, thus limiting its post-Cretaceous displacement to less than 1500 km, and that burial compaction has also affected the paleomagnetism of Nanaimo Group sedimentary rocks from Vancouver Island. This result also helps resolve the conflict between paleomagnetic results, which show 1500 km of post–Late Cretaceous offset between the Insular–Coast Plutonic Complex superterrane and the Intermontane superterrane and geologic observations, which can allow only tens of kilometers of offset between these terranes in the Methow- Tyaughton basin.