Paleomagnetism of Late Mesozoic to Holocene Sediments from the Bay of Biscay and Rockall Plateau, Drilled on IPOD Leg 48
Paleomagnetism of Late Mesozoic to Holocene Sediments from the Bay of Biscay and Rockall Plateau, Drilled on IPOD Leg 48
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DOI：
10.2973/dsdp.proc.48.111.1979
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发表时间：
1979-08
期刊：
影响因子：
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通讯作者：
E. Hailwood
中科院分区：
文献类型：
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作者：
E. Hailwood
比斯开湾东北部的 IPOD 孔 400/400A、401 和 402A 以及罗卡尔高原西南端的 403,404 和 405 号地点描述了古地磁结果。 400A孔已经建立了详细的更新世-晚中新世极性反转记录，与已建立的更新世和晚新近极性时间尺度进行比较，可以确定该地点过去1000万年的精确沉积物积累速率。 400A 和 402A 孔中的早白垩世（Aptian-Albian）“黑页岩”层序也得出了相当完整的磁极性记录；该记录表明，恢复的整个部分是在以正常磁极性为主的漫长的早白垩世时期沉积的。在两个洞的阿尔布阶晚期沉积物中都发现了一系列快速反转，并且与 DSDP 263 号站点类似年龄的“混合极性区”相关（Green 和 Brecher，1974 年）。目前还没有发现证据表明阿普第最上面的沉积物存在一段较长的反极性间隔，这可能与 Pechersky 和 Khramov (1973) 确定的阿普第晚期“加坦带”相对应，并被一些作者与海洋磁异常 MO 相关联。 402A 孔 150 个“黑色页岩”样本的平均稳定磁倾角已被用来推导该地点早白垩世的古纬度，所得值与 van der Voo 和 French (1974) 根据海洋磁异常数据和环大西洋大陆古地磁测定综合得出的西欧早白垩世磁极位置非常吻合。从 400A 孔和 401 号站点回收的古新世到中始新世沉积物中得出了不连续的磁极性记录，并在 400A 孔的地下深度约 560 米和 585 米以及 401 号站点的 172 米和 183 米处初步确定了与磁异常 22 和 23 相对应的正常极性区间。在罗卡尔高原西南缘的 404 号站点，古新世晚期至始新世早期的火山凝灰岩、粉砂岩和海绿石泥的厚层序列被穿透，403 号站点的整个 130 米部分和 404 号站点最低 90 米的区域全部被反向磁化，并且被认为是在异常之前的长期反极性间隔期间沉积的。 24. 对这些沉积物的生物地层学研究为异常 24 的年龄提供了重要的新控制，该异常 24 已在 NP 12 超微化石区底部附近的 404 号站点深度 280 米处以及 Costa 和 Downie 的恐龙囊区 II 内（本卷）发现，由于这是东北大西洋发现的最古老的磁异常，这些结果提供了东北大西洋开口年龄的精确生物地层测定。最后，磁化率和强度值为地点之间的相关性提供了有用的基础。例如，在 400A 孔和 401 号地点靠近早/中始新世边界的 NP 14 纳米化石带内，磁化率和强度急剧下降。这被认为代表了早始新世末期陆源物质供应速率的突然下降，这是由于环流模式或沉积物来源的变化所致。同样，403 和 404 号地点的火山沉积物中某些深度的高磁化率和强度的狭窄区域似乎代表了特定的凝灰质层位，可以从一个地点到另一地点进行关联。
Paleomagnetic results are described from IPOD Holes 400/400A, 401, and 402A in the northeast Bay of Biscay, and Sites 403,404, and 405 at the southwest extremity of the Rockall Plateau. A detailed Pleistocene-late Miocene polarity reversal record has been established for Hole 400A, and comparison with the established Pleistocene and late Neogene polarity time scale allows the determination of precise sediment accumulation rates at this site for the past 10 million years. A fairly complete magnetic polarity record also has been derived for the sequence of Early Cretaceous (Aptian-Albian) "black-shales" in Holes 400A and 402A; this record indicates that the entire section recovered was deposited during the long Early Cretaceous interval of dominantly normal magnetic polarity. A sequence of rapid reversals has been identified in late Albian sediments in both holes, and is correlated with the "mixed polarity zone" of similar age at DSDP Site 263 (Green and Brecher, 1974). No evidence has been found for a prolonged interval of reverse polarity in the uppermost Aptian sediments that might correspond with the late Aptian "Gatan zone" identified by Pechersky and Khramov (1973), and correlated by some authors with marine magnetic anomaly MO. The mean inclination of stable magnetism from the 150 samples of "black shale'' from Hole 402A has been used to derive the paleolatitude of this site in Early Cretaceous times, and the resultant value is in good agreement with the Early Cretaceous pole position for western Europe, derived by van der Voo and French (1974), from a synthesis of marine magnetic anomaly data and paleomagnetic determinations from the circum-Atlantic continents. Discontinuous magnetic polarity records have been derived from the Paleocene to middle Eocene sediments recovered from Hole 400A and Site 401, and normal polarity intervals, corresponding with magnetic anomalies 22 and 23 are tentatively identified at sub-bottom depths of approximately 560 and 585 meters in Hole 400A, and 172 and 183 meters at Site 401. At Sites 403 and 404 on the southwest margin of the Rockall Plateau, a thick sequence of volcanic tuffs, siltstones, and glauconitic muds of late Paleocene-early Eocene age was penetrated. The entire 130-meter section at Site 403 and the lowermost 90 meters at Site 404 is reversely magnetized throughout, and is thought to have been deposited during the long reverse polarity interval which preceded anomaly 24. Biostratigraphic studies of these sediments provides important new control on the age of anomaly 24, which has been identified at a depth of 280 meters at Site 404, near the base of nannofossil Zone NP 12, and within dinocyst Zone II of Costa and Downie (this volume). Since this is the oldest magnetic anomaly identified in the northeast Atlantic, these results provide a precise biostratigraphic determination of the age of opening of the northeast Atlantic. Finally, magnetic susceptibility and intensity values are shown to provide a useful basis for correlation between sites. For example, a sharp decrease in susceptibility and intensity occurs within the NP 14 nannofossil zone, close to the early/middle Eocene boundary at both Hole 400A and Site 401. This is considered to represent an abrupt reduction in the rate of supply of terrigenous material at the end of the early Eocene, due to a change in circulation pattern or sediment source area. Similarly, narrow zones of high susceptibility and intensity at certain depths in the volcanogenic sediments of Sites 403 and 404 appear to represent specific tuffaceous horizons, which can be correlated from one site to the other.