Reactivation of a Cretaceous Thrust Surface by Basin-and-Range Extension, Southwestern Gunnison Plateau, Central Utah

S. Mattox, M. Weiss
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引用次数: 2

Abstract

Recent work in central Utah has outlined the broader features of the area's thrust geometry. Although individual interpretations differ, most models indicate the region is similar to better understood segments of the Cordilleran thrust belt. Poor and limited seismic data and the paucity of drill-hole information has hindered the investigation of the south- west quadrant of the Gunnison Plateau. Detailed surface mapping of a centrally located quadrangle has provided strati- graphic evidence for a previously unrecognized Cretaceous-Paleocene thrust fault. The present expression of the thrust surface requires reactivation with a reverse sense of motion during Tertiary extension. Drastic facies changes in the Late Cretaceous-Early Paleocene North Horn Formation occur over a short distance - essentially across a fault. The gray, eastern lithofacies is dominated by massive conglomerate, sandstone, and oncolitic limestone. Maximum thickness is 253 m (830 ft). Clast composition indicates a local source/positive area of Cretaceous lndianola Group. The thinner 38 m (126 ft), red, western lithofacies consists of pebbly sandstone, sandstone, and mudstone. Reddish brown mudstones and intrac lasts suggest red beds, possibly the Cretaceous Cedar Mountain Formation and/or the Jurassic Twist Gulch Formation and Arapien Shale, as a primary source. After careful consideration of several hypotheses, the only valid conclusion seems to be the presence of thrusted Indianola, creating a topo- graphic barrier between the two separate and unique basins. Two major structural features can be traced to the north, an area of better seismic and drill-hole data. The southern terminus of the Wasatch fault zone, has been interpreted by numerous investigators as eithera reactivated Cretaceous thrust (with a reverse sense of motion) or a high-angle planar Tertiary normal fault. The Escarpment fault, the eastern boundary of a Basin and Range graben, has also been presented in both configurations (listric or high-angle planar). No observations were made to support a listric geometry for the Fayette fault. The Escarpment fault, however, appears to have been active during North Horn time, thrusting lndianola conglomerate into a topographic/structural high. The upper plate underwent a reversed sense of motion in the Tertiary to create the present Chriss/Mellor graben.
美国犹他州中部甘尼森高原西南部盆地-山脉伸展对白垩纪逆冲面的激活作用
最近在犹他州中部的工作概述了该地区推力几何形状的更广泛特征。尽管个人的解释不同,但大多数模型表明该地区与科迪勒拉冲断带的较好理解部分相似。有限的地震资料和钻孔资料的缺乏阻碍了甘尼森高原西南象限的勘探工作。一个位于中心的四合院的详细地表测绘为以前未被识别的白垩纪-古新世逆冲断层提供了地层学证据。冲断面目前的表现需要在第三纪伸展期间以一种反向的运动感觉重新激活。晚白垩世-早古新世北角组的剧烈相变化发生在很短的距离上-基本上是穿过断层。灰色东部岩相以块状砾岩、砂岩和溶瘤灰岩为主。最大厚度253米(830英尺)。碎屑组成指示白垩系印地诺拉组为局部源/阳性区。较薄的38米(126英尺)的红色西部岩相由含砾砂岩、砂岩和泥岩组成。红棕色泥岩和内储层表明,主要烃源岩可能为白垩纪雪松山组和/或侏罗纪扭湾组和阿拉皮恩页岩。在仔细考虑了几个假设之后,唯一有效的结论似乎是逆冲印地安纳诺拉的存在,在两个独立而独特的盆地之间形成了地形屏障。两个主要的构造特征可以追溯到北部,这是一个地震和钻孔资料较好的地区。瓦萨奇断裂带的南端被许多研究者解释为白垩纪逆冲断层(具有反向运动感)或高角度平面第三纪正断层。断裂带是盆地和岭地堑的东部边界,也呈现出两种构型(盘状或高角度平面)。没有观测结果支持法耶特断层的列状几何形状。然而,陡崖断层在北角时期似乎很活跃,将印第安纳拉砾岩推入地形/构造高点。上板块在第三纪经历了反向运动,形成了现在的克里斯/梅勒地堑。
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