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首页> 外文期刊>Brazilian Journal of Geology >Famennian glaciation in the eastern side of Parnaíba Basin, Brazil: evidence of advance and retreat of glacier in Cabe?as Formation
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Famennian glaciation in the eastern side of Parnaíba Basin, Brazil: evidence of advance and retreat of glacier in Cabe?as Formation

机译：巴西Parnaíba盆地东侧的法门尼河冰川化：Cabe？as地层冰川进退的证据

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ABSTRACTGlaciotectonic features studied in the siliciclastic deposits of Cabe?as Formation, Upper Devonian, represent the first evidence of Famennian glaciation in Southeastern Parnaíba Basin, Brazil. Outcrop-based stratigraphic and facies analyses combined with geometric-structural studies of these deposits allowed defining three facies association (FA). They represent the advance-retreat cycle of a glacier. There are: delta front facies association (FA1) composed of massive mudstone, sigmoidal, medium-grained sandstone with cross-bedding and massive conglomerate organized in coarsening- and thickening-upward cycles; subglacial facies association (FA2) with massive, pebbly diamictite (sandstone, mudstone and volcanic pebbles) and deformational features, such as intraformational breccia, clastic dikes and sills of diamictite, folds, thrust and normal faults, sandstone pods and detachment surface; and melt-out delta front facies associations (FA3), which include massive or bedded (sigmoidal cross-bedding or parallel bedding) sandstones. Three depositional phases can be indicated to Cabe?as Formation: installation of a delta system (FA1) supplied by uplifted areas in the Southeastern border of the basin; coastal glacier advance causing tangential substrate shearing and erosion (FA1) in the subglacial zone (FA2), thus developing detachment surface, disruption and rotation of sand beds or pods immersed in a diamicton; and retreat of glaciers accompanied by relative sea level-rise, installation of a high-energy melt-out delta (FA3) and unloading due to ice retreat that generates normal faults, mass landslide, folding and injection dykes and sills. The continuous sea-level rise led to the deposition of fine-grained strata of Longá Formation in the offshore/shoreface transition in the Early Carboniferous.
机译：在上泥盆统Cabe？as组的硅质碎屑沉积中研究的ABSTRACTG冰期构造特征是巴西东南部帕纳伊巴盆地法门尼河冰川化的第一个证据。基于露头的地层和相分析与这些矿床的几何结构研究相结合，可以定义三个相联系（FA）。它们代表了冰川的进退循环。有：三角洲前相组合（FA1），由块状泥质，S形，中粒砂岩，交叉层理和块状砾岩组成，沿粗化-增厚-向上循环组织;冰川下相（FA2）具有大量卵石状的铁矾土（砂岩，泥岩和火山卵石）和变形特征，例如构造内角砾岩，碎屑岩和硅藻土，褶皱，逆冲和正断层，砂岩荚和脱离表面;以及融化的三角洲前相组合（FA3），其中包括块状或层状（S型交叉层理或平行层理）砂岩。卡贝斯形成可以指示三个沉积阶段：在盆地东南边界的隆起地区安装三角洲系统（FA1）;在盆地内形成一个沉积系统。沿海冰川的发展导致在冰川下带（FA2）上切向的基底剪切和侵蚀（FA1），从而形成了分离表面，破坏了浸入敌对角的沙床或豆荚的旋转;冰川退缩，伴随着相对海平面上升，安装了高能融化三角洲（FA3），以及由于退缩而产生的冰消退导致了正常的断层，大规模滑坡，褶皱和注入堤坝和基石。持续的海平面上升导致早期石炭纪近海/岸面过渡带中长隆组细颗粒地层的沉积。

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