Stratigraphical, sedimentological and palaeofloristic characterization of the Sorocayense Group (Triassic) in Barreal depocenter, San Juan Province, Argentina

IF 0.9 4区 地球科学 Q3 GEOLOGY
J. Bodnar, A. Iglesias, C. Colombi, J. Drovandi
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引用次数: 11

Abstract

The northern area of Cuyo Basin (west‐central Argentina) corresponds to the Rincón Blanco half-graben, whose filling is arranged into the Rincón Blanco and Sorocayense groups. In the present study, we propose a new stratigraphic scheme for the Sorocayense Group in the Barreal depocenter (San Juan Province), revise the palaeoenvironmental interpretations, and organize and analyse the plant assemblages of previous and new fossiliferous levels. We defined three tectosedimentary sequences. The basal sequence represents the initial graben filling with pyroclastic flows, alluvial fan, and ephemeral fluvial systems, and is arranged in a new unit, the Cerro Colorado del Cementerio Formation. The middle sequence, including Barreal and Cortaderita formations, is characterized by sediment gravity flow deposits and different fluvial systems, with development of floodplains with vertisols and calcisols, and temporal ponds/lakes. In turn, the Cortaderita Formation was divided into the following lithostratigraphic members: Don Raúl and La Emilia. The upper sequence, represented by Cepeda Formation, was deposited by distributary fluvial and ephemeral fluvial systems. Twelve fossiliferous strata (EF) were recognized, which were all identified in the middle sequence: EF1 to EF3 in the Barreal Formation, EF4 to EF8 in the Don Raúl Member, and EF9 to EF12 in the La Emilia Member, both of Cortaderita Formation. The taphocoenosis found in the Barreal and Cortaderita formations were dominated by corystosperms, with conifers, cycadales, and peltasperms as subordinate forms. The available evidence from the taphofloras, palaeosols and palaeonvironments indicate the development of seasonal subtropical climates, which vary from arid or semi-arid in the basal sequence, sub-humid to semi-arid in the middle sequence, and arid or semi-arid in the upper sequence. On the basis of the new information, geological correlation and age of the lithostratigraphic units were accurately re-evaluated. Based on the palaeofloristic content and the correlation with the Rincón Blanco Group, it is possible to infer that the basal sequence was accumulated during late Early Triassic-early Middle Triassic, the middle sequence during the Middle Triassic, while the upper sequence was deposited in the early Late Triassic.
阿根廷圣胡安省Barreal沉积中心三叠系Sorocayense群地层、沉积学及古植物区系特征
Cuyo盆地北部(阿根廷中西部)对应于Rincón Blanco半地堑,其填充物被排列成Rincón Blanco和Sorocayense群。在本研究中,我们为Barreal沉积中心(圣胡安省)的Sorocayense群提出了一个新的地层方案,修改了古环境解释,并组织和分析了以前和新的含化石水平的植物组合。我们定义了三个顶盖沉积序列。基底序列代表了充满火山碎屑流、冲积扇和短暂河流系统的初始地堑,并被布置在一个新的单元中,即Cerro Colorado del Cementerio组。中间序列,包括Barreal和Cortaderita地层,以沉积物重力流沉积和不同的河流系统为特征,发育有含有垂直土和钙质土的泛滥平原,以及临时池塘/湖泊。反过来,Cortaderita组又分为以下岩石地层成员:Don Raúl和La Emilia。以Cepeda组为代表的上部层序由分流河流和短暂河流系统沉积。识别出12个含化石地层(EF),它们都位于中间序列:Barreal组的EF1至EF3,Don Raúl段的EF4至EF8,La Emilia段的EF9至EF12,均为Cortaderita组。在Barreal和Cortaderita地层中发现的taphocoenosis主要由球茎植物组成,针叶树、苏铁目和盾形目是次要形式。来自Taphoflora、古土壤和古环境的现有证据表明季节性亚热带气候的发展,这些气候从底部序列的干旱或半干旱,中间序列的亚湿润到半干旱,以及上部序列的干旱和半干旱不等。在此基础上,对岩石地层单元的地质对比和年代进行了准确的重新评价。根据古区系含量和与Rincón Blanco群的对比,可以推断出基底层序沉积于早三叠世晚期-中三叠世早期,中间层序沉积于中三叠统,而上部层序沉积于晚三叠世前期。
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来源期刊
Andean Geology
Andean Geology 地学-地质学
CiteScore
3.90
自引率
0.00%
发文量
17
审稿时长
>12 weeks
期刊介绍: This journal publishes original and review articles on geology and related sciences, in Spanish or English, in three issues a year (January, May and September). Articles or notes on major topics of broad interest in Earth Sciences dealing with the geology of South and Central America and Antarctica, and particularly of the Andes, are welcomed. The journal is interested in publishing thematic sets of papers and accepts articles dealing with systematic Paleontology only if their main focus is the chronostratigraphical, paleoecological and/or paleogeographical importance of the taxa described therein.
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