Collaborative Research: Antarctic Cretaceous-Cenozoic Climate, Glaciation, and Tectonics: Site Surveys for Drilling from the edge of the Ross Sea Shelf

Luyendyk等人：OPP 0088143 Bartek：OPP 0087392 Dieold：OPP 0087983该奖项由极地计划办公室南极地质和地球物理计划提供，支持罗斯海中南部和东部的海洋地质和地球物理合作研究计划。该项目将进行现场勘测，从罗斯冰架钻探到其下方的海底。通过钻探罗斯海的海底，可以解决许多悬而未决的问题，如南极东西冰盖的演化、南极气候、全球海平面以及西南极裂谷系统的构造历史。南极洲这一地区白垩纪和早新生代的气候数据是缺乏的。气候问题包括：白垩纪晚期有冰吗？古新世-始新世全球变暖时期的南极气候是什么？新生代南极冰川是什么时候开始的，冰川什么时候到达海岸，什么时候向边缘挺进？罗斯海陆架在白垩纪晚期是否是非海相的；它是什么时候变成海相的？构造问题包括：罗斯海裂谷白垩纪伸展的时间是什么时候；它位于哪里？基底的组成和结构是什么？阿达尔海槽扩散效应的时间和空间限制在哪里？另一个钻探目标是对东部盆地和中央海槽绘制的RSU6不整合面上的沉积剖面进行采样和年代测定，以解决其年龄和区域范围的问题。20世纪70年代初，深海钻探项目第28标段在4个钻探点完成了采样，但S的采收率较低，没有对早新生代进行采样。其他钻探仅限于罗斯海西部的麦克默多海湾地区，结果可以与维多利亚陆盆相关联，但不能向东穿过地下室隆起。此外，早新生代和白垩纪的岩石还没有取样。在罗斯冰架进行钻探的新机会正在形成。这是罗伯茨角钻井项目的后续项目。最大的困难之一是需要在冰架下的钻探地点进行现场勘测。该项目将通过在中央海槽和东部盆地的罗斯冰架前部进行海洋地球物理钻探现场勘测来克服这一障碍。调查将在冰架前缘以北一至两公里处进行，最近的崩解事件导致冰架边缘向南移动。几年后，冰架向北的推进将覆盖所调查的地点，钻探工作可能会完成。将使用的系统包括条带测深、重力、磁学、线性调频声纳、高分辨率地震剖面和48倍地震。将采集岩心以获取岩土性质的样本，研究冰架下现代沉积过程，以及在更深层次暴露的位置。这项调查将包括潜在钻探地点的长剖面和详细网格。测量线将绑定到现有的地球物理剖面和DSDP 270。最近的一个事件使这一计划变得及时，那就是巨型冰山B-15(2000年3月)和其他冰山在罗斯海东部冰锋的崩解。这次新的冰解事件和1987年的一次冰川崩解事件暴露了16,000平方公里的海底，这些海底几十年来一直被冰架覆盖，没有得到勘探。新暴露的领土现在可以用现代地球物理方法绘制地图。该项目将进一步向南和向东绘制RSU6不整合下方的地质构造和地层图，研究罗斯福岛在罗斯海裂谷历史中的位置，并确定最南端和最东部的晚新生代时期(后RSU6)的沉降史。最后，该项目将观察新暴露地区冰架下现今的沉积过程。

Luyendyk et al.: OPP 0088143Bartek: OPP 0087392Diebold: OPP 0087983This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a collaborative research program in marine geology and geophysics in the southern central and eastern Ross Sea. The project will conduct sites surveys for drilling from the Ross Ice Shelf into the seafloor beneath it. Many of the outstanding problems concerning the evolution of the East and West Antarctic Ice Sheets, Antarctic climate, global sea level, and the tectonic history of the West Antarctic Rift System can be addressed by drilling into the seafloor of the Ross Sea. Climate data for Cretaceous and Early Cenozoic time are lacking for this sector of Antarctica. Climate questions include: Was there any ice in Late Cretaceous time? What was the Antarctic climate during the Paleocene-Eocene global warming? When was the Cenozoic onset of Antarctic glaciation, when did glaciers reach the coast and when did they advance out onto the margin? Was the Ross Sea shelf non-marine in Late Cretaceous time; when did it become marine? Tectonic questions include: What was the timing of the Cretaceous extension in the Ross Sea rift; where was it located? What is the basement composition and structure? Where are the time and space limits of the effects of Adare Trough spreading? Another drilling objective is to sample and date the sedimentary section bounding the mapped RSU6 unconformity in the Eastern Basin and Central Trough to resolve questions about its age and regional extent. Deep Sea Drilling Project (DSDP) Leg 28 completed sampling at four drill sites in the early 1970's but had low recovery and did not sample the Early Cenozoic. Other drilling has been restricted to the McMurdo Sound area of the western Ross Sea and results can be correlated into the Victoria Land Basin but not eastward across basement highs. Further, Early Cenozoic and Cretaceous rocks have not been sampled. A new opportunity is developing to drill from the Ross Ice Shelf. This is a successor program to the Cape Roberts Drilling Project. One overriding difficulty is the need for site surveys at drilling locations under the ice shelf. This project will overcome this impediment by conducting marine geophysical drill site surveys at the front of the Ross Ice Shelf in the Central Trough and Eastern Basin. The surveys will be conducted a kilometer or two north of the ice shelf front where recent calving events have resulted in a southerly position of the ice shelf edge. In several years the northward advance of the ice shelf will override the surveyed locations and drilling could be accomplished. Systems to be used include swath bathymetry, gravity, magnetics, chirp sonar, high resolution seismic profiling, and 48 fold seismics. Cores will be collected to obtain samples for geotechnical properties, to study sub-ice shelf modern sedimentary processes, and at locations where deeper section is exposed.This survey will include long profiles and detailed grids over potential drill sites. Survey lines will be tied to existing geophysical profiles and DSDP 270. A recent event that makes this plan timely is the calving of giant iceberg B-15 (in March, 2000) and others from the ice front in the eastern Ross Sea. This new calving event and one in 1987 have exposed 16,000 square kilometers of seafloor that had been covered by ice shelf for decades and is not explored. Newly exposed territory can now be mapped by modern geophysical methods. This project will map geological structure and stratigraphy below unconformity RSU6 farther south and east, study the place of Roosevelt Island in the Ross Sea rifting history, and determine subsidence history during Late Cenozoic time (post RSU6) in the far south and east. Finally the project will observe present day sedimentary processes beneath the ice shelf in the newly exposed areas.