Stratigraphy, sediment dispersal and paleogeography of the lower Eocene San Jose Formation, San Juan Basin, New Mexico

L. Smith
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引用次数: 10

Abstract

The fluvial lower Eocene San Jose Formation represents the last preserved period of deposition in the Laramide San Juan Basin. The basal Cuba Mesa Member of the formation is a nearly basinwide, coarsegrained sheet sandstone composed of mult ilateral and multistoried low-sinuosity tluvial channels. The Cuba Mesa is locally thickened where sheet sandstones are vertically amalgamated. The Cuba Mesa thins by intertongu ing with mudrock and pinches out along the basin axis where the San Jose Formation conformably overlies the Paleocene Nacimiento and Animas Formations in northern New Mexico and Colorado. The Cuba Mesa Member unconformably overlies Paleocene and Mesozoic strata toward margins of the basin, with as much as 90° of angular discordance. Floodplain mudrock and di sconnec ted sheet sandstones of the Regi na Member were deposited laterally adjacent to and above the Cuba Mesa Member. Mudrock of the Regina Member also intertongues with the lobate. sandstone-dominated Ditch Canyon Member (named here ) and Llaves Member. The Ditch Canyon Member represents southeast-directed fluvial deposition in the northwestern San Juan Basin from the Four Comers pla tform and southwestern San Juan upli ft . The Llaves Member was deposited on the eastern side of the bas in by west-southwest-flowing streams and is sedimentologically and stratigraphically similar to, but not continuous with. the Ditch Canyon Member. The Llaves Member is overlain by the siltstonedominated Tapicitos Member. The Tapicitos was derived from uplifts east of the basin. Grain size in the Regina Member decreases toward the San Juan and Nacimiento uplifts, due to minimal erosion of coarse-grained sediment from these active, reverse-fau lted monoclines . Small drainage basins along these active mountain fronts eroded most ly fine-grained sediment from Phanerozoic strata. Coarse-grained sediment of the Di tch Canyon and Llaves Members was deposited by fluvial systems that emanated from different paleo-drainage basins within structural reentrants between basin-marginal uplifts. The Cuba Mesa Member was deposited during late Paleocene through early Eocene subsidence in the center of the San Juan Basin with concurrent erosion and possibly slow sedimentation nearer basin margins . Synsedimentary angu lar unconformities within the Regina Member show that the Regina, Llaves and Ditch Canyon Members were deposited during episodic monoclinal fo lding near the Nacimiento fault.
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新墨西哥州圣胡安盆地始新统圣何塞组地层、沉积扩散及古地理
始新世下游河流圣何塞组代表了Laramide圣胡安盆地最后保存下来的沉积时期。该组的古巴台地基段是一个近盆地宽度的粗粒片状砂岩,由多层、多层低弯度的河流河道组成。古巴台地局部增厚,片状砂岩垂直混合。古巴台地通过与泥岩相交而变薄,并沿着盆地轴线向外挤压,在新墨西哥州和科罗拉多州北部,圣何塞组整合地覆盖在古新世的Nacimiento和Animas组上。古巴台地段向盆地边缘不整合覆于古新世和中生代地层之上,角度不一致度达90°。雷吉那段的漫滩泥岩和非连通片状砂岩侧向沉积于古巴台地段相邻和上方。里贾纳成员的泥岩也与裂片交错。砂岩为主的沟峡谷段(此处命名)和拉维斯段。沟峡谷段代表圣胡安盆地西北部的四角构造和圣胡安隆起西南部的东南向河流沉积。拉维斯段沉积于盆地东侧,受西南向流流作用,其沉积地层学特征与盆地东侧相似,但不连续。迪奇峡谷会员。laves成员被粉砂岩主导的Tapicitos成员覆盖。塔皮西托山脉起源于盆地东部的隆起。里贾纳地区的颗粒尺寸向圣胡安和纳西米恩托隆起方向减小,这是由于这些活动的、反向断裂的单斜岩对粗颗粒沉积物的侵蚀最小。沿着这些活山锋面的小流域主要侵蚀显生宙地层的细粒沉积物。迪契峡谷和拉叶段的粗粒沉积物是由不同古流域的河流系统沉积的,这些河流系统来自盆地边缘隆起之间的构造回入体。古巴台地段沉积于圣胡安盆地中心的古新世晚期至始新世早期的沉降期间,盆地边缘附近可能存在侵蚀和缓慢沉积。里贾纳段同沉积角状不整合表明,里贾纳段、拉维斯段和迪奇峡谷段是在Nacimiento断裂附近的幕式单斜构造时期沉积的。
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