Field Test of Models of Sedimentation in Continental Half Grabens

大陆半地堑沉积模型的现场试验

• 批准号: 9627468
• 负责人: Greg Mack
• 金额: $ 4.91万
• 依托单位: New Mexico State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-07-15 至 1998-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9627468&HistoricalAwards=false
• 关键词: Field; Test; Models; Sedimentation; Continental

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.

MACK 9627468是一个有影响力的构造-地层学模型，该模型认为冲积扇、湖泊或轴向河流相在半地堑中的不对称分布主要受构造倾斜及其所造成的集水区大小的控制。此外，该模型指出，在盆地边界正断层的活动期间，由于上盘派生的排水系统的切割、底盘派生的排水系统的回填以及盆地-轴线沉积体系的底部定向侵入，相带向下盘块移动。后一种观点通常被认为是事实，但在很大程度上没有得到岩石记录的检验，许多问题仍然存在，涉及相移的规模、机制和速率，以及构造特征是否与其他外部变量的特征相区别。新墨西哥州里奥格兰德裂谷南部现存的Paloma半地堑是野外检验构造引起相变假说的绝佳地点，因为(1)早更新世-早更新世-里奥格兰德及其支流的后更新世挖坑暴露了长达100米的上新世-早更新世冲积扇和轴向河流地层，(2)出露地层存在高分辨率反转磁性地层学的年代地层格架，以及(3)泥炭碳酸盐稳定的氧和碳同位素组成提供了该地区上新世和更新世的古气候记录，而隆起作用不是该地层沉积的一个因素。帕尔马斯盆地三维结构和跨盆地相对比的描述不仅将检验构造引起的相转移假说的双向性，而且将解决许多与沉积体系在盆地中转移的过程和速率有关的问题。收集的数据将包括(1)沿峡谷壁切割的5条L水系和6条下壁水系的25个测量断面；(2)1：12,000比例尺的裸露荒地区域相图和照片马赛克；(3)21个地层剖面的反转磁性地层，补充P.I.已经分析的11个磁性地层剖面。在古地磁采样期间，P.I.将由加州大学洛杉矶分校(UCLA)的Stephen Salyards博士陪同，他将执行随后的实验室分析，其现场和实验室费用包括在本提案中。此外，P.I.在一些实地工作期间将由Michael Leeder博士(英国利兹大学)陪同，他将由NERC独立资助。