Depositional cyclicity and paleoecological variability in an outcrop of Rio Bonito formation, Early Permian, Paraná Basin, Rio Grande do Sul, Brazil
Depositional cyclicity and paleoecological variability in an outcrop of Rio Bonito formation, Early Permian, Paraná Basin, Rio Grande do Sul, Brazil
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DOI：
10.1016/j.jsames.2006.05.002
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发表时间：
2006-07
影响因子：
1.8
通讯作者：
A. Jasper;R. Menegat;M. Guerra-Sommer;M. Cazzulo-Klepzig;Paulo A. Souza
中科院分区：
文献类型：
--
作者：
A. Jasper;R. Menegat;M. Guerra-Sommer;M. Cazzulo-Klepzig;Paulo A. Souza
本文综合了岩相学、古植物学和孢粉学分析，建立了南里奥格兰德州巴拉那盆地南部Rio Bonito组（早二叠世）Quitéria露头的沉积旋回性与古生态模式之间的关系。该露头的基底部分代表了在微潮条件下受屏障保护的沿海泻湖沉积体系，其中泥炭形成条件在低地发育，并伴随着远端冲积扇沉积物的侵入。上部碎屑岩段代表了不同的环境条件，其成因是由冲刷扇带来的障壁切割作用。在基底部鉴定的孢粉植物区系中，以乔木和草本石松植物产生的孢子为主，也有裸子植物花粉粒的互补形式--蝶形植物和丝状植物。藻类或藻类元素，指示淡水，半咸水或海水，与陆生孢子和花粉粒一起记录。支持砾岩的基质的孢粉学内容表明与煤相的密切，定性的相似性，然而，裸子植物花粉粒的增加伴随着减少孢子产生的蕨类植物植被是显着的。与碎屑岩上部有关的原地屋顶页岩植物群由乔木状石松（Brasilodendron pedroanum）的基部树桩、林下植被（Botrychiopsis valida，Lycopodites sp.）小乔木（Coricladus quiteriensis），未定丝状的棒羊齿类复叶，和准原地成分（Rubidgea sp.，Cordaites sp.）。孢粉植物区系表明了屋顶页岩植物区系与下地壳成煤的准原地植物区系之间的相似性。植物区系数据和高分辨率层序地层学方法之间的相关性表明，这段时间与Rio Bonito组海侵道的最后准层序有关，那里的煤层很薄。在巴拉那盆地的孢粉地层框架中定义的Hamiapollenites karrooensis亚带的组成部分Striadopodocarpites fusus的一些煤孢粉植物群中的记录表明了孢粉植物群的Kungurian时代。
This article integrates faciological, paleobotanical, and palynological analyses to establish the relationship between depositional cyclicity and paleoecological patterns for the (Early Permian) Quitéria outcrop, Rio Bonito Formation, southern Paraná Basin, Rio Grande do Sul state. The basal section of this outcrop represents a coastal lagoon depositional system protected by barriers in microtide conditions, where peat-forming conditions developed in lowlands with ingression of distal alluvial fan deposits. The upper clastic section represents different environmental conditions, originated by the barrier sectioning brought by washover fans. The palynoflora identified in the basal section present a dominance of spores produced by arborescent and herbaceous lycophytes, as well as by sphenophytes and filicophytes, complementary forms of gymnosperm pollen grains. Algae or algae-elements, indicative of fresh, brackish, or marine water, are recorded together with terrestrial spores and pollen grains. The palynological content of matrix-supported conglomerates suggests a close, qualitative similarity with the coaly facies; however, the increase in gymnosperm pollen grains accompanied by a decrease in spores produced by pteridophyte vegetation is remarkable. The autochthonous roof-shale flora related to the clastic upper section is composed of basal stumps of arborescent cormose lycophytes (Brasilodendron pedroanum), understory vegetation (Botrychiopsis valida, Lycopodites sp.), small trees (Coricladus quiteriensis), undetermined filicoid rodheopterid fronds, and parautochthonous elements (Rubidgea sp., Cordaites sp.). Palynofloras point to floristic similarity between the roof-shale floras and the subjacent coal-forming parautochthonous floras. Correlations between the floristic data and those from high-resolution sequence stratigraphic methods indicate that this interval is associated with the final parasequences of the transgressive tract of Rio Bonito Formation, where coal levels are thin. The record in some coal palynofloras of Striadopodocarpites fusus, a component of the Hamiapollenites karrooensis subzone, as defined in the palynostratigraphic framework for the Paraná Basin, indicates a Kungurian age for the palynoflora.