Seismic stratigraphy and history of deep circulation and sediment drift development in Baffin Bay and the Labrador Sea
Seismic stratigraphy and history of deep circulation and sediment drift development in Baffin Bay and the Labrador Sea
复制标题
巴芬湾和拉布拉多海的地震地层学以及深部环流和沉积物漂移发展的历史
DOI：
10.2973/odp.proc.sr.105.118.1989
复制
发表时间：
1989
影响因子：
5.3
通讯作者：
J. Osler
中科院分区：
文献类型：
--
作者：
Arthur;S. P. Srivastava;M. Kaminski;R. Jarrard;J. Osler
在大洋钻探计划（ODP）645号（巴芬湾西部）、646号和647号（拉布拉多海）的钻探结果和地震反射记录提供了对新生代气候变化的深水环流和沉积历史以及该地区构造演化的重要制约。第646和647号地点分别在两个沉积物漂移沉积物--Eirik岭和格洛丽亚漂移物--的侧翼钻探。645号现场的年龄控制很差，因为那里的生物化石有限，但钻探现场提供了一个从中新世早期到现在的连续序列。646号站点的沉积物以高速率沉积，提供了过去8.5 Ma的高分辨率记录。在647号站点，沉积作用是可变的和不连续的，但完整的上-下始新统到下渐新统序列被恢复，而上渐新统到全新世序列被几个间断中断。
646号站的漂移序列是在上新世中期至早期（约1000年）之后建造的。4.5 Ma）。在此之前，有证据表明底流活动是可变的，事件发生在大约7.5 Ma（水团特征的变化和速度的降低）和5.6 Ma（在主要的4.5 Ma事件之前流速的增加; R2区域反射层）。7.5Ma的地震产生了一个主要的区域反射层（R3/R4），最初认为其时代为始新世/渐新世。一个主要的水团的变化也发生在约2.5马在上新世晚期的冰漂流的发病。在地震记录中，没有证据表明上新世早期之前存在漂移建造，但在Eirik岭南翼和西格陵兰边缘沿着可能发生了中新世中晚期的侵蚀事件。沉积物供应从Imarssuak大洋中峡谷（IMOC）的同时增加了漂移建设的到来。
格洛丽亚漂流也主要是在中新世晚期之后建造的。沉积物供给的主要增加发生在上新世早期，之后出现了一个主要的间断（5.6 ~ 2.5 Ma;相当于格洛丽亚漂移下的R2反射层可能的最年轻年龄），大多数地震记录显示沉积物波在该层位以上。沉积物供应的增加是北大西洋中洋峡谷侵蚀沉积物的半远洋沉积以及上新世晚期冰筏碎屑供应的结果。一个裂孔包含了大约17.5 ~ 8.2 Ma的时间间隔，两个主要裂孔之间的时间间隔非常紧凑。一个更深的反射层（R3）对应于从石灰质（下）到富含蛋白石的半远洋地层在渐新世下部的变化，而不是区域不整合，反映了增加的底层水活动，如以前所认为的。然而，存在一些证据支持最新始新世-最早渐新世底流活动增加格洛丽亚漂移。
在巴芬湾，从岩心的结构研究和沿着西缘的多通道测线所显示的明显漂流特征中，可以找到底层水活动的证据。可能的等深流至少从中新世晚期开始就一直活跃，在中新世晚期和第四纪明显出现强度下降的事件。从站点645和地震测线的记录可能表明，底层水的形成发生在晚第三纪在巴芬湾与气候恶化，但巴芬湾不是一个重要的来源，深水质量的拉布拉多海上新世晚期后。
毫不奇怪，许多拉布拉多海深环流事件密切对应于北大西洋重大事件和重要的全球气候和古海洋学事件，但一个主要的漂移建设事件可能发生在拉布拉多海晚于它在北大西洋东部或西北大西洋。
Drilling results and seismic-reflection records at and across Ocean Drilling Program (ODP) Sites 645 (western Baffin Bay), 646, and 647 (Labrador Sea) provide important constraints on the history of deep-water circulation and sedimentation in response to Cenozoic climatic change, as well as the tectonic evolution of the region. Sites 646 and 647 were drilled on the flanks of two sediment drift deposits—the Eirik Ridge and Gloria Drift, respectively. Age control at Site 645 was poor because of the restricted biotas there, but the drill site provides a continuous sequence from the lower Miocene to the present. Sediment at Site 646 was deposited at high rates, providing a high resolution record of the last 8.5 Ma. At Site 647 sedimentation was variable and discontinuous, but a complete upper-lower Eocene through lower Oligocene sequence was recovered, whereas the upper Oligocene to Holocene sequence was interrupted by several hiatuses.
The drift sequence at Site 646 was constructed after the middle to early Pliocene (ca. 4.5 Ma). Before that time, evidence exists for variable bottom-current activity, with events at about 7.5 Ma (a change in water-mass characteristics and decreasing velocities) and 5.6 Ma (an increase in current velocity preceding the major 4.5-Ma event; R2 regional reflector). The 7.5-Ma event produced a major regional reflector (R3/R4), which was originally thought to be Eocene/ Oligocene in age. A major water-mass change also occurred at the onset of ice-rafting at about 2.5 Ma in the late Pliocene. In seismic records no evidence exists of drift building before the early Pliocene, but a probable late-middle Miocene erosional event occurred on the south flank of Eirik Ridge and along the West Greenland margin. Sediment supply from the Imarssuak mid-ocean canyon (IMOC) increased concurrently with the advent of drift construction.
Gloria Drift also was built largely after the late Miocene. A major increase in sediment supply occurred in the early Pliocene, following a major hiatus (5.6 to 2.5 Ma; equivalent to the youngest possible age for the R2 reflector underlying Gloria Drift), and most seismic records exhibit sediment waves above this horizon. This increased sediment supply is the result of hemipelagic deposition from encroaching deposits of the North Atlantic mid-ocean canyon, as well as to supply of ice-rafted detritus in the late Pliocene. A hiatus encompasses the interval from approximately 17.5 to 8,2 Ma, and the interval between the two major hiatuses is extremely condensed. A deeper reflector (R3) corresponds to a change from calcareous (below) to opal-rich hemipelagic strata in the lower Oligocene, not to a regional unconformity reflecting increased bottom-water activity, as previously thought. However, some evidence exists to support a latest Eocene-earliest Oligocene increase in bottom-current activity on Gloria Drift.
In Baffin Bay, there is evidence for bottom-water activity from textural studies of cores and from apparent drift features exhibited in multichannel lines along the western margin. Probable contour-currents have been active since at least the late middle Miocene, with episodes of decreasing intensity that apparently occurred in the late Miocene and Quaternary. The record from Site 645 and in seismic lines may indicate that formation of bottom water occurred in the late Neogene in Baffin Bay in conjunction with climatic deterioration, but Baffin Bay was not an important source of deep-water masses to the Labrador Sea after the late Pliocene.
Not surprisingly, many of the Labrador Sea deep-circulation events correspond closely to major North Atlantic events and to important global climatic and paleoceanographic events, but a major drift-building episode may have occurred later in the Labrador Sea than it did in either the eastern North Atlantic or the western North Atlantic.