Field Test of Models of Sedimentation in Continental Half Grabens

麦克9627468 一个有影响力的构造-地层模型表明，半地堑中冲积扇和湖泊或轴流-河流相的不对称分布主要受构造倾斜和该倾斜所施加的集水区大小的控制。 此外，该模型指出，在活动期间的盆地边界的正断层，相带转移到下盘块体，作为结果的切割上盘派生的排水沟，下盘派生的排水沟，和下盘的盆地轴向沉积体系的侵入。 后一种观点通常被认为是事实，但在很大程度上没有经过岩石记录的检验，许多问题仍然存在，涉及规模，机制和相变速率，以及构造特征是否与其他外在变量区分开来。 新墨西哥州格兰德河裂谷南部现存的Palomas半地堑是一个很好的现场验证构造诱发相位移假说的地方，因为（1）早更新世后的格兰德河及其支流的海沟暴露了长达100 m的上新世-早更新世冲积扇和轴向河流地层，（2）出露地层具有高分辨率反转磁性地层学的年代地层格架;（3）成壤碳酸盐的稳定氧、碳同位素组成提供了上新世和更新世时期的古气候记录。而海平面上升不是有关地层沉积过程中的一个因素。 在Palomas盆地的三维结构和跨盆地的相的相关性的描绘不仅提供了一个测试的构造引起的相变的假设的biability，但将解决许多问题的过程和速率的沉积体系转移到整个盆地。 数据收集将包括：（1）沿峡谷壁的沿着5个切割上盘水系和6个切割下盘水系的25个测量剖面;（2）以1：12，000比例尺和照片镶嵌法绘制裸露荒地区域的岩相图;（3）21个地层剖面的反向磁性地层学，补充P.I.已经分析的11个磁性地层剖面。 古地磁取样将在0.5-2米的垂直尺度上进行，并将涉及沉积岩的标准钻探和软沉积物取样技术。 私家侦探Stephen Salyards博士（加州大学洛杉矶分校）将陪同进行古地磁采样，他将进行随后的实验室分析，其现场和实验室费用已包括在本提案中。 此外，PI。Michael利德博士（英国利兹大学）将陪同进行一些实地工作，由NERC独立资助

Mack 9627468 An influential tectono-stratigraphic model suggests that asymmetrical distribution of alluvial-fan and lacustrine or axial-fluvial facies in half grabens is primarily controlled by tectonic tilting and the size of catchment areas imposed by that tilting. Moreover, the model states that during periods of activity on the basin-bounding normal fault, the facies belts shift towards the footwall block, as a result of incision of hanging wall-derived drainages, backfilling of footwall-derived drainages, and footwall-directed incursion of the basin-axis depositional system. This latter idea is often accepted as fact, but is largely untested against the rock record, and many questions remain concerning the scale, mechanism and rate of facies shift, as well as whether the tectonic signature is distinguishable from that of other extrinsic variables. The extant Palomas half graben in the southern Rio Grande rift, New Mexico, is an excellent place to field test the hypothesis of tectonically induced facies shift, because (1) up to 100m of Pliocene-early Pleistocene alluvial-fan and axial-fluvial strata have been exposed by post-early Pleistocene entrenchment of the Rio Grande and its tributaries, (2) a chronostratigraphic framework exists for the exposed strata in the form of high-resolution reversal magnetostratigraphy, and (3) the stable oxygen and carbon isotopic composition of pedogenci carbonate provides a paleoclimatic record of the region in Pliocene and Pleistocene time, and eustacy was not a factor during deposition of the strata in question. Delineation of three-dimensional architecture and across-basin correlation of facies in the Palomas basin will not only provide a test of the biability of the hypothesis of tectonically induced facies shift, but will address many of the questions concerning the processes and rates at which the depositional systems shifted across the basin. Data collection will include (1) 25 measured sections along the canyon walls of 5 incised hanging wal l drainages and 6 incised footwall drainages, (2) facies mapping of regions of well exposed badlands at the scale of 1:12,000 and on photo mosaics, and (3) reversal magnetostratigraphy of 21 stratigraphic sections, supplementing the11 magnetostratigraphic sections already analyzed by the P.I. Paleomagnetic sampling will be on the vertical scale of 0.5-2 m and will involve standard drilling of sedimentary rock and a soft-sediment sampling technique. The P.I. will be accompanied during paleomagnetic sampling by Dr. Stephen Salyards (UCLA), who will perform the subsequent laboratory analyses and whose field and lab expenses are included in this proposal. In addition, the P.I. will be accompanied during some of the field work by Dr. Michael Leeder (University of Leeds, U.K.), who will be independently funded by NERC.