Quantitative Reconstruction of Sediment Provenance: A Geochemical Study of the Amazon Fan/Delta

小行星9627908 保存在亚马逊水下三角洲和深海扇中的硅质沉积物来自亚马逊流域盆地，气候条件截然不同。 三角洲代表相对较新的沉积主要是在热带条件下，而风扇代表沉积在各个更新世冰川阶段时，货架被绕过在低海平面的立场。 仅在最近才为ODP第155航次的亚马逊扇提供了地层约束样品。 本建议涉及定量评估安第斯山脉与安第斯山脉的这些沉积物的来源在这些对比鲜明的气候条件下的相对重要性。 初步的岩相学、地球化学和同位素数据表明，安第斯来源占主导地位，但也表明，详细的物源历史是复杂的。 这项研究将使用钕和铅同位素以及各种地球化学和岩相学技术来评估泥和砂的来源。 对于砂，最常用于古层序物源研究的岩性，我们将进一步使用Pb和Nd测量组合评估主要单个组分、石英、长石和重矿物（使用锆石作为替代物）的物源。 这方面的研究有两个目的：（1）确定由全岩Pb和Nd同位素测量推断的物源是否适用于含Nd相对较少的主要矿物（石英和长石）或Pb（石英）;（2）确定从碎屑锆石研究中推断的物源是否与主要矿物的物源相似（石英和长石）、散砂和相关泥浆。 从这些数据中，我们将能够重建砂和泥的来源，具有一定的精度和评估克拉通是否发挥更大的作用，砂泥，如其他人所建议的，以及克拉通是否发挥更大或更小的作用，在对比的气候条件。 这项研究将提供关于各种来源方法的局限性的基本信息（例如，岩石学、地球化学、放射性同位素）。 亚马逊河流域是世界上最大的水系，了解该水系沉积物的起源和历史本身就具有极大的意义。 保存在扇和三角洲上的沉积物之间的任何对比对于该排水系统的古气候研究都具有重要意义。

9627908 McLennan Siliciclastic sediments preserved within the Amazon subaqueous delta and deep-sea fan were derived from the Amazon drainage basin under contrasting climatic conditions. The delta represents relatively recent deposition largely under tropical conditions whereas the fan represents deposition during various Pleistocene glacial stages when the shelf was by-passed during low sea level stands. Stratigraphically constrained samples have only recently been made available for the Amazon Fan from ODP Leg 155. This proposal is concerned with quantitatively evaluating the relative importance of Andean versus cratonic provenance for these sediments during these contrasting climatic conditions. Preliminary petrographic, geochemical and isotopic data suggest a dominance of Andean sources but also suggest that in detail the provenance history is complex. The study will evaluate the sources of both muds and sands using neodymium and lead isotopes and a variety of geochemical and petrographic techniques. For the sands, the lithology most often used in provenance studies of ancient sequences, we will further evaluate the provenance of the major individual components, quartz, feldspar and heavy minerals (using zircon as the proxy) using a combination of Pb and Nd measurements. The purpose of this aspect of the study is twofold: (1) to determine if the provenance inferred from whole rock Pb and Nd isotope measurements can be applied to the major minerals that contain relatively little Nd (quartz and feldspar) or Pb (quartz); (2) to determine if the provenance inferred from detrital zircon studies is similar to that inferred for major minerals (quartz and feldspar), bulk sands and associated muds. From these data, we will be able to reconstruct the provenance of both sands and muds with some precision and evaluate if the craton plays a greater role for sands that muds, as suggested by others, and whether the craton plays a greater or lesser role during contrasting climatic conditions. Th is study will provide fundamental information regarding limitations on how various approaches to provenance (e.g., petrography, geochemistry, radiogenic isotopes) can be interpreted. The Amazon drainage system is the largest in the world and understanding the origin and history of sediment derived from this system is of the great interest in its own right. Any contrasts between sediment preserved on the fan and delta would have significance for paleoclimatological studies of this drainage system.