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首页> 外文期刊>Geosphere >A physical and chemical sedimentary record of Laramide tectonic shifts in the Cretaceous-Paleogene San Juan Basin, New Mexico, USA
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A physical and chemical sedimentary record of Laramide tectonic shifts in the Cretaceous-Paleogene San Juan Basin, New Mexico, USA

机译：美国新墨西哥新古代圣胡安盆地LARAMIDE构造换切的物理和化学沉积记录

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摘要

Fluvial siliciclastic rocks bracketing the Cretaceous- Paleogene (K-Pg) boundary in the San Juan Basin, New Mexico (USA), provide records of regional fluvial and tectonic evolution during the Laramide orogeny. Petrographic analyses of sandstones from the Upper Cretaceous Fruitland Formation and Kirtland Formation and the Paleocene Ojo Alamo Sandstone and Nacimiento Formation show that the rivers depositing these sediments were sourced in areas where unroofing of crystalline basement rocks took place, introducing an increasing proportion of immature detrital grains into the fluvial system through time. After the Cretaceous-Paleogene boundary, rivers deposited an increasing amount of microcline and orthoclase feldspar relative to plagioclase feldspar, suggesting a growing source in unique crystalline basement rocks. Geochemical analyses show significant differences between Al- and K-poor Upper Cretaceous sandstones and Al- and K-rich lower Paleocene sandstones in the San Juan Basin. The high proportion of sand-sized material in the Ojo Alamo Sandstone suggests that it was deposited in a basin with a low ratio of sediment supply to accommodation. However, magnetostrati-graphic age constraints suggest it had a relatively high sedimentation and/or subsidence rate of as much as 0.38 m/k.y. The sediment supply must have been high in order to deposit a basin-wide coarse sand-dominated package, suggesting rapid creation of topographic relief in the San Juan uplift, the proposed source area of the Ojo Alamo fluvial system. The observed sedimentary architecture and age constraints of the Ojo Alamo Sandstone, including kilometers-wide sand bodies and limited overbank mudstones throughout most of the outcrop area, are difficult to reconcile with accepted models of aggradation and avulsion in large fluvial systems, but available age and lithologic data make difficult a complete understanding of Paleocene San Juan Basin fluvial systems and basin evolution. Here, we present new lithologic, petrographic, and thickness data from San Juan Basin K-Pg fluvial siliciclastic units and interpretations of their origins.
机译：氟硅硅岩包围新墨西哥州（美国）圣胡安盆地的白垩纪 - 古代（K-PG）边界，在Laramide Orogeny期间提供区域河流和构造演进的记录。来自上白垩纪的外壳形成和Kirtland形成和古典ojo阿拉莫砂岩和Nacimiento形成的岩石分析表明，沉积这些沉积物的河流在发生了结晶地下岩石的区域，引入了不成熟的碎屑颗粒的增加比例通过时间进入河流系统。在白垩纪古缩略边界之后，河流相对于Plagioclase长石相对于Plagioclase Feldspar沉积了越来越多的微管和正阳裂式长石，表明独特的晶体基底岩石中的生长源。地球化学分析显示了San Juan盆地的Al-k-Pop Unduper Cretape Sandstones和Al-o和K富古古岛砂岩之间的显着差异。 OJO Alamo砂岩中的砂尺寸高比例的砂尺寸暗示它表明它在盆地中沉积在盆地中的沉积物供应量低。然而，磁体 - 图形年龄约束表明它具有相对高的沉降和/或沉降率，高达0.38米/克。沉积物供应必须很高，以便沉积盆地粗砂主导的包装，表明在圣胡安隆起的地形救济中迅速创造了ojo Alamo河流系统的建议源区。观察到的Ojo Alamo砂岩的沉积建筑和年龄限制，包括在大部分露头区域的公里范围内的砂体和有限的过银泥岩，很难与大型河流系统中的可接受的繁殖和禽流血模型进行调和，但可用的年龄和岩性数据使古典圣胡安河流域河流系统和盆地演化完全了解。在这里，我们提出了来自San Juan Basin K-PG河丝状单位的新型岩性，岩化和厚度数据，并对其起源的解释。

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