Ideal Seismic Reflection Site Survey of Lake Edward, Uganda and Zaire, East African Rift

9710146 Scholz本项目是“东非湖泊国际十年”的核心项目。该项目将对位于东非裂谷西部分支北部的爱德华湖进行中分辨率地震反射现场调查，为后续钻探做好准备。钻探计划的主要目标是记录东非高原南纬100 - 10度盆地及周边地区的定量高分辨率古气候和古湖泊学历史，至少可以追溯到两个冰期-间冰期旋回。辅助目标包括回答伸展构造学领域的基本问题，以及大陆裂谷的进化生物学和宏观生态学。本次地震反射钻孔前现场调查的主要目标是：1)为该半地堑盆地上1000公里的沉积剖面建立一个可靠的层序和年代地层格架；2)获取高质量、中等分辨率的多通道和单通道地震反射数据网格，用于在盆地中定位一个或多个钻孔；3)表征上地壳的变形结构；4)确定了盆地同裂谷基底的总沉积厚度和深度。通过解释地震数据集需要考虑的重要问题包括：建立盆地的相对湖平面曲线；确定湖泊的哪些区域可能包含连续的地层记录；并评估基底内的变形结构，以帮助确定东非裂谷的延伸方向。将地震数据与钻孔数据集相结合，可以建立定量的、高分辨率的湖泊裂谷盆地演化模型。由于主要钻探目标集中于古气候研究，并且仅限于100-500米，并且必须将船只运送到湖泊进行调查，因此将使用小型气枪震源和短（300-600米）地震拖缆进行中分辨率调查，以获得~ 1500公里的数据和图像，深度为~ 1000米

9710146 Scholz This program is a core project of IDEAL, the International Decade for the East African Lakes. The project will conduct an intermediate-resolution seismic reflection site survey of Lake Edward, in the northern part of the western branch of the East African Rift, in anticipation of subsequent drilling. The primary goal of the drilling program is to chronicle a quantitative high- resolution paleoclimate and paleolimnological history of the basin and surrounding region at 0o-1o S latitude on the East African plateau, extending back through at least two glacial-interglacial cycles. Ancillary goals include answering fundamental questions in the ares of extensional tectonics, and evolutionary biology and macroecology in continental rifts. The principal objectives of this seismic-reflection pre- drilling site survey are to 1) develop a robust sequence- and chron-stratigraphic framework for the upper 1000, of sedimentary section in this half-graben basin, 2) acquire a grid of high- quality, intermediate-resolution multichannel and single-channel seismic reflection data for siting one or more drill holes in the basin, 3) characterize the deformational fabric of the uppermost crust, and 4) determine the total sediment thickness and depth to syn-rift basement in the basin. Important issues to be considered through interpretation of the seismic data set include developing a relative lake level curve for the basin; determining which areas of the lake are likely to contain continuous stratigraphic records; and assessing the intrabasinal deformational fabric for helping determine extension direction in the East African Rift. Integrating the seismic data with the drill hole data sets will permit the development of quantitative, high-resolution models of lacustrine rift basin evolution. Since the primary drilling objectives are focused toward paleoclimate studies and limited to 100-500 m, and a vessel must be transported to the lake for the survey, an intermediate-resolution survey will be carried out using a small air gun seismic source and a short (300-600 m) seismic streamer, to acquire ~ 1500 km of data and image to a depth of ~ 1000 m. ***