Conodont biostratigraphy and correlation of the San Juan Formation at the Cerro La Silla section, middle Tremadocian-lower Dapingian, Central Precordillera, Argentina

IF 0.9 4区 地球科学 Q3 GEOLOGY
M. Mango, G. Albanesi
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引用次数: 14

Abstract

This study deals with the conodont biostratigraphy from the uppermost part of La Silla Formation (9.6 m) and the overlying San Juan Formation (264.7 m), at the Cerro La Silla section, Central Precordillera of San Juan, Argentina. The 41 samples of carbonate rocks that were digested for microfossils yielded 11,388 conodont elements corresponding to 78 species. The Paltodus deltifer deltifer Subzone of the Paltodus deltifer Zone from the Baltic biostratigraphic scheme is represented at the top stratum of the La Silla Formation and the basal part of the San Juan Formation (28.4 m), which correlates with the Macerodus dianae Zone (middle Tremadocian) of the Precordilleran and North American schemes. Following upwards, the Paroistodus proteus, Prioniodus elegans, Oepikodus evae, Oepikodus intermedius and Baltoniodus triangularis-Tripodus laevis zones (middle Tremadocian-lower Dapingian) are recorded in the San Juan Formation. The Baltoniodus triangularis-Tripodus laevis Zone is recognized from the second reef level (177.3 m from the base of the San Juan Formation) up to the top stratum in the section, in contrast to previous interpretations that assigned the referred interval to the Baltoniodus navis, Paroistodus originalis and Microzarkodina parva zones of the Baltic biostratigraphic scheme. The division of the Oepikodus evae Zone in subzones, according to its original definition for the Precordillera, is not applicable at the Cerro La Silla section due to the particular species distribution. The conodont elements show a brown alteration color (CAI 2-2.5), which indicates a burial paleotemperature of 60-155°C for the bearer strata.
阿根廷中前寒武纪中-下大坪阶Cerro La Silla剖面San Juan组牙形石生物地层学及对比
本文研究了阿根廷圣胡安中部Precordillera地区Cerro La Silla剖面的La Silla组最上部(9.6 m)和上覆的San Juan组(264.7 m)的牙形石生物地层学。41个碳酸盐岩微化石样品中牙形石元素78种,共11388个。波罗的海生物地层体系Paltodus deltifer带的Paltodus deltifer亚带位于La Silla组顶部和San Juan组底部(28.4 m),与前cordilleran和北美体系的Macerodus dianae带(中Tremadocian)相对应。其后,圣胡安组分别记录有paristodus proteus、Prioniodus elegans、Oepikodus evae、Oepikodus intermedius和Baltoniodus triangularis-Tripodus laevis带(特雷马多纪中—大平纪下)。Baltoniodus triangularis-Tripodus laevis带在剖面中从第2礁层(距离圣胡安组底部177.3米)到顶部地层被识别出来,这与之前将参考区间分配给波罗的海生物地层方案中的Baltoniodus navis, Paroistodus originalis和Microzarkodina parva带的解释形成了对比。根据其对Precordillera的原始定义,将Oepikodus evae带划分为亚带,但由于其特定的物种分布,因此不适用于Cerro La Silla剖面。牙形石元素呈棕褐色蚀变(CAI 2 ~ 2.5),表明承载层的埋藏古温度为60 ~ 155℃。
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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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