The Neoproterozoic Uinta Mountain Group Revisited: A Synthesis of Recent Work on the Red Pine Shale and Related Undivided Clastic Strata, Northeastern Utah, U.S.A.
The Neoproterozoic Uinta Mountain Group Revisited: A Synthesis of Recent Work on the Red Pine Shale and Related Undivided Clastic Strata, Northeastern Utah, U.S.A.
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重新审视新元古代尤因塔山群：美国犹他州东北部红松页岩和相关未分割碎屑岩地层的最新研究综述
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发表时间：
2007
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通讯作者：
A. Brehm
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作者：
C. Dehler;S. Porter;Laura D. De Grey;D. Sprinkel;A. Brehm
我们对新元古代云塔山群的研究主要集中在西部云塔山的红松页岩和东部云塔山的未分割碎屑地层，分别记录了三角洲-海相沉积和辫状河-海岸沉积。红松页岩沉积时间晚于< 770 Ma的东部碎屑地层，温塔山群沉积时间早于劳伦西亚西部~ 700 Ma的裂谷期。实测剖面和地层填图显示，红松页岩在山脉西部厚~ 550 ~ 1200 m，中东部薄至< 300 m，东部缺失。实测剖面显示富有机质页岩与中粗粒砂岩互层。沉积构造包括级配层理、丘状交叉层理、平行纹层理、板状交叉层理、纹痕、滑塌褶皱等。化石包括浅纹线虫，丝状线虫，鳞状线虫，以及更罕见的花瓶状微化石和装饰线虫。初步全岩！对富有机质页岩的长期分析显示，其PDB值为13.9‰（PDB值范围为-16.9 ~ -30.8‰），TOC值范围为0.07 ~ 5.9%。综合资料表明，在一个海相三角洲体系中，公平天气波基下方和附近有沉积，并与大峡谷~ 770 ~ bbb742马chuar群有相关性。温塔山东部温塔山群未划分的碎屑地层以槽状、板状交错层状块状砂岩为主，古水流方向为南-西南方向。在这些砂岩层段中，至少发现了3个横向连续（千米尺度）~ 50米厚的灰绿色含有机质页岩层段，包括波纹痕、泥裂铸型、波纹交叉纹层、石膏铸型和模具。最下面的页岩层段允许将碎屑地层细分为三个非正式单元。碎屑地层中-上段页岩化石主要包括枝状微化石和可能的花瓶状微化石。在剖面底部附近的黑色至绿色页岩中也发现了简单的球形和碳质细丝。碎屑地层为砂质辫状体系，可能有来自西部的海相淹没事件。除了冲积扇环境外，杰西尤因峡谷组是碎屑地层下UMG的基本单元，代表了高能海岸线和扇三角洲沉积。北美西部和西伯利亚元古代地质学SEPM特刊86，版权所有©2007 SEPM（美国沉积地质学会），ISBN 1-56576-126-X, p. 151-166。地球上保存完好、暴露良好、未变形的元古代沉积序列很少。尽管它们的厚度很大，但由于它们看似均匀的、非化石的和难以接近的性质，一些幸存的硅碎屑地层仍然知之甚少（“元古宙砂岩的诅咒”，Link et al., 1993）。温塔山脉群（UMG）通常被认为是这样一个序列，由4-7公里的胶结砂岩组成（Hansen, 1965； Wallace和Crittenden， 1969），坐落在温塔山脉的高海拔地区（图1）。本文综合了最近和正在进行的研究，旨在通过详细的地层和相分析、岩石学、地球化学、野外测绘和微古生物学对UMG未勘探单元进行分析，以消除“诅咒”。另一个目标是开始解开UMG的沉积环境，年龄，构造背景和古地理。这项工作还提供了在构造发展的关键时期对西劳伦西亚演化的见解（Karlstrom et al., 2001; Colpron et al., 2002）。我们的碳同位素数据与重建早期新元古代真核生物多样化有关（Knoll, 2003; Porter, CAROL M. DEHLER, SUSANNAH M. Porter, LAURA D. DE GREY, DOUGLAS A. SPRINKEL, AND ANDY BREHM）。1。- G eo瞧gi c m ap m o f t他U在助教或者nt ai ns s w ho在G ou tc p ro迪圣国际扶轮bu tio n p再保险ca m br ia n ro ck s, G在cl ud th os e di再保险ct ly w es tw ar d i n th e w作为通用电气在ch R。M - a - B（1997）和R - a - B（1997）等人的研究表明，M - a - c是一种有效的方法。（19 85），和Sp . k . el（2 2002）。年代是pl l e oc io ns: (1) T yp e S ec tio的th e R ed P n e S哈勒;(2) H广告es C re艾克米苏ea再保险d se ct io的th e R ed P n e S哈勒;(3) H × × × × × × × × × × × × × × × × × × × × × × × ×。(4) W嗨te R oc ks sa m e pl l oc al密度o f t他在e R ed P S哈勒;(5) sh le y C re ek m ea苏再保险d se ct io n th e R ed P e sh al e;(6) L - 1 - 2 - 1 - 2 - 1 - 2 - 2 - 1 - 2 - 2 - 1 - 2 - 2 - 2 - 2 - 3 - 2 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 2 - 3 - 22);(7)耶稣看见耶稣在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上，在天上。(8) B P ro w ns ar k ar ea - ge ol og ic 7。5 '问ua gl e m apπng博士在th e di联合国六世德d cl抽搐圣ra ta o f t他圣er n U ea ta m或者nt ai n G ro;(9) H oo p拉柯s是pl e lo ca点燃y th e R p e Sh阿尔·e。M od ifi ed fr om D呃le R一个D Sp ri nk el(2 00 5)。153新元古代的乌塔山脉群（2004）和前斯图亚特时代的气候变化（Hoffman and Schrag, 2002; Dehler et, 2005）。在接下来的章节中，我们将介绍沉积学、地层学、碳同位素和古生物学数据，首先是山脉西部的红松页岩，其次是乌塔山脉东部的未划分碎屑地层。在初步解释的基础上，讨论了东西部构造单元之间的相互关系、UMG的年龄和区域对比以及构造和古地理意义。推测红松页岩为海相三角洲沉积，东部未划分碎屑地层主要为辫状河系，整个盆地为中新元古代沉积（~ 770 ~ 742 Ma），盆地南部原始边缘延伸至现代南缘以外。
Our studies of the Neoproterozoic Uinta Mountain Group focus on the Red Pine Shale in the western Uinta Mountains and the undivided clastic strata in the eastern Uinta Mountains, which record deltaic–marine and braided-fluvial to shoreline deposition, respectively. We conclude that the Red Pine Shale postdates the < 770 Ma eastern clastic strata, and the Uinta Mountain Group represents deposition in a rift basin predating the rift episode recorded at ~ 700 Ma in western Laurentia. Measured sections and stratigraphic mapping of the Red Pine Shale show that it is ~ 550–1200 m thick in the western part of the range, thins to < 300 m in the east-central range, and is missing in the eastern range. Measured sections show organic-rich shale interbedded with mediumto coarse-grained sandstone. Sedimentary structures include graded bedding, hummocky cross stratification, parallel to ripple lamination, tabular crossbeds, ripple marks, and slump folds. Fossils include Bavlinella faveolata, filaments, leiosphaerid acritarchs, and, more rarely, vase-shaped microfossils and ornamented acritarchs. Preliminary whole-rock !Corg analysis of organic-rich shales reveal 13.9‰ (PDB) variability (values range from –16.9 to –30.8‰ PDB) and TOC values range from 0.07 to 5.9%. Combined data suggest deposition below and near fair-weather wave base in a marine deltaic system, and correlation with the ~ 770 to > 742 Ma Chuar Group, Grand Canyon. The undivided clastic strata of the Uinta Mountain Group, eastern Uinta Mountains, are dominated by troughand tabular-cross-bedded and massive sandstones showing south-southwesterly paleocurrent flow. At least three laterally continuous (kilometer-scale) ~ 50-m-thick intervals of gray-green, organic-bearing shale have been mapped amongst these sandstone intervals and contain ripple marks, mud-crack casts, ripple cross laminae, and gypsum casts and molds. The lowermost shale interval allows subdivision of the clastic strata into three informal units. Fossils from shale in the middle–upper (?) interval of the clastic strata include acritarchs and possible vase-shaped microfossils. Simple sphaeromorphs and carbonaceous filaments have also been found in black to green shale near the base of the section. The clastic strata represent a sandy braid system with possible marine drowning events from the west. In addition to an alluvial-fan setting, the Jesse Ewing Canyon Formation, the basal unit of the UMG below the clastic strata, represents high-energy shoreline and fan-delta deposition. Proterozoic Geology of Western North America and Siberia SEPM Special Publication 86, Copyright © 2007 SEPM (Society for Sedimentary Geology), ISBN 1-56576-126-X, p. 151–166. INTRODUCTION There are few well preserved, well exposed, and undeformed Proterozoic sedimentary successions on Earth. Despite their vast thicknesses, some of these surviving siliciclastic strata remain poorly understood due to their seemingly homogeneous, unfossiliferous, and inaccessible nature (“Curse of the Proterozoic Sandstone”, Link et al., 1993). The Uinta Mountain Group (UMG) is often thought of as such a succession, composed of 4–7 km of dominantly well cemented sandstone (Hansen, 1965; Wallace and Crittenden, 1969) and nestled in the high elevations of the Uinta Mountains (Fig. 1). This paper is a synthesis of recent and ongoing research aimed at removing the “curse” through detailed stratigraphic and facies analyses, petrography, geochemistry, field mapping, and micropaleontology on the unexplored units of the UMG. Another goal is to begin to unravel the depositional environments, age, tectonic setting, and paleogeography of the UMG. This work also provides insight on the evolution of western Laurentia at a key time in its tectonic development (Karlstrom et al., 2001; Colpron et al., 2002). Our carbon-isotope data are relevant to reconstructing early Neoproterozoic eukaryotic diversification (Knoll, 2003; Porter, CAROL M. DEHLER, SUSANNAH M. PORTER, LAURA D. DE GREY, DOUGLAS A. SPRINKEL, AND ANDY BREHM 152 F G . 1 .— G eo lo gi c m ap o f t he U in ta M ou nt ai ns s ho w in g ou tc ro p di st ri bu tio n of P re ca m br ia n ro ck s, in cl ud in g th os e di re ct ly w es tw ar d i n th e W as at ch R an ge . M ap w as co ns tr uc te d us in g m ap s f ro m B ry an t ( 19 97 ), R ow le y et al . ( 19 85 ), an d Sp ri nk el (2 00 2) . S am pl e l oc at io ns : ( 1) T yp e s ec tio n of th e R ed P in e S ha le ; ( 2) H ad es C re ek m ea su re d se ct io n of th e R ed P in e S ha le ; ( 3) H en ry ’s F or k m ea su re d se ct io n of th e R ed P in e S ha le ; ( 4) W hi te R oc ks sa m pl e l oc al ity o f t he R ed P in e S ha le ; ( 5) A sh le y C re ek m ea su re d se ct io n of th e R ed P in e Sh al e; (6 ) L ei dy P ea k sa m pl e lo ca lit y in st ra ta p ro je ct ed to b e be lo w th e R ed P in e Sh al e (s ee F ig . 2 ); (7 ) J es se E w in g C an yo n Fo rm at io n sa m pl e lo ca lit y in b as al sh al e an d ar ea o f n ew 1 :1 2, 00 0 sc al e ge ol og ic m ap pi ng ; ( 8) B ro w ns P ar k ar ea — ge ol og ic 7 .5 ' q ua dr an gl e m ap pi ng in th e un di vi de d cl as tic st ra ta o f t he ea st er n U in ta M ou nt ai n G ro up ; ( 9) H oo p La ke s am pl e lo ca lit y of th e R ed P in e Sh al e. M od ifi ed fr om D eh le r an d Sp ri nk el (2 00 5) . 153 THE NEOPROTEROZOIC UINTA MOUNTAIN GROUP REVISITED 2004) and pre-Sturtian climate change (Hoffman and Schrag, 2002; Dehler et al., 2005a). In the following sections we present sedimentologic, stratigraphic, carbon-isotope, and paleontologic data, first for the Red Pine Shale in the western part of the range, and second for the undivided clastic strata in the eastern Uinta Mountains. We discuss the relationship between these western and eastern units, age and regional correlation of the UMG, and tectonic and paleogeographic implications based on our preliminary interpretations. We hypothesize that the Red Pine Shale represents marine– deltaic deposition, the eastern undivided clastic strata represent dominantly a braided fluvial system, the entire UMG is genetically related and mid-Neoproterozoic in age (~ 770–742 Ma), and the original southern basin edge reached beyond the modern southern edge of the range.