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 0088143Bartek: OPP 0087392Diebold: OPP 0087983该奖项由极地计划办公室的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。该项目将进行现场调查，以便从罗斯冰架钻探到其下方的海底。许多突出的问题，如南极东西冰盖的演变、南极气候、全球海平面和南极西部裂谷系的构造历史，都可以通过在罗斯海的海底钻探来解决。南极洲这一地区缺乏白垩纪和早期新生代的气候资料。气候问题包括：白垩纪晚期有冰吗？在古新世-始新世全球变暖期间，南极的气候是怎样的？新生代南极冰川是什么时候开始的，冰川是什么时候到达海岸的，又是什么时候向边缘移动的？晚白垩世罗斯海陆架是否为非海相；什么时候变成海洋的？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？地下室的组成和结构是什么？Adare槽扩散效应的时间和空间限制在哪里？另一个钻探目标是在东部盆地和中央海槽绘制的RSU6不整合面边界的沉积剖面取样和定年，以解决其年龄和区域范围的问题。深海钻井项目（DSDP） Leg 28在20世纪70年代初完成了四个钻井点的采样，但采收率低，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地盆地相关联，但不能向东穿过基底高地。此外，早新生代和白垩纪岩石尚未采样。从罗斯冰架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。一个最重要的困难是需要在冰架下的钻探地点进行现场调查。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调查来克服这一障碍。这些调查将在冰架前沿以北一到两公里处进行，最近的冰裂事件导致冰架边缘向南移动。几年后，冰架向北移动将覆盖已勘测的地点，钻探就可以完成了。将使用的系统包括带状测深、重力、磁力、啁啾声纳、高分辨率地震剖面和48次地震。将收集岩心以获取岩土力学性质的样本，研究冰架下的现代沉积过程，并在较深的部分暴露的位置。这项调查将包括对潜在钻探地点的长剖面和详细网格。测量线将与现有的地球物理剖面和DSDP 270相关联。最近发生的一件事使这个计划变得及时，那就是巨大的冰山B-15（2000年3月）和其他冰山从罗斯海东部的冰锋处崩解。这次新的冰裂事件和1987年的一次冰裂事件暴露了16000平方公里的海底，这些海底几十年来一直被冰架覆盖着，没有被勘探过。新暴露的地区现在可以用现代地球物理方法绘制地图。本项目将绘制RSU6不整合面更南部和东部的地质构造和地层学图，研究罗斯福岛在罗斯海裂谷史中的位置，确定远南部和东部晚新生代（后RSU6）的沉降史。最后，该项目将在新暴露的地区观察冰架下目前的沉积过程。

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.