Abstract

Palynology is one of the most useful tools for constructing biostratigraphic charts in the late Paleozoic basins of South America, but the lack of radiometric ages often makes it difficult to establish the precise age of the biozones. This paper focuses on two points: (i) the description of new Argentinian palynological assemblages referred to the Lueckisporites/Weylandites (LW) Biozone and (ii) the application of a new isotopic age that enables more confident large-scale correlations with the neighboring Paraná Basin of Brazil. The palynofloras were recovered from the upper part of the De La Cuesta Formation that crops out in the retroarc basin of the Paganzo Basin, more specifically obtained from mudstones intercalated with limestones, cherts, and tuffs interpreted as being deposited in a shallow water body. The assemblages are characterized by an abundance of bi-taeniate pollen grains of the Lueckisporites complex and multitaeniate pollen grains such as Lunatisporites, Protohaploxypinus, Striatopodocarpidites, Tornopollenites, and Vittatina. Colpate pollen grains are also represented by Marsupipollenites and Pakhapites. A U-Pb CA-ID-TIMS age of 278.84 ± 0.22 Ma, obtained from a tuff level interstratified with the fossiliferous strata, allows the age of the LW Biozone in the Paganzo Basin to be constrained for the first time and the adjustment of the record Lueckisporites virkkiae in Gondwana. Moreover, this date enables precise correlations with other basins, such as the San Rafael Basin (Yacimiento Los Reyunos Formation) in Argentina and the Brazilian Paraná Basin (Iratí Formation).

摘要

孢粉学是构建南美洲晚古生代盆地生物地层图的最有用的工具之一，但由于缺乏辐射年龄，往往难以确定生物带的精确年龄。本文重点关注两点：(i) 新的阿根廷孢粉组合的描述，称为Lueckisporites/Weylandites(LW) 生物带和 (ii) 新同位素年龄的应用，使与邻近的巴西巴拉那盆地的大尺度相关性更加可信。孢粉菌群是从在 Paganzo 盆地的弧后盆地中出露的 De La Cuesta 组的上部发现的，更具体地说，是从夹有石灰岩、燧石和凝灰岩的泥岩中获得的，这些石灰岩和凝灰岩被解释为沉积在浅水体中。这些组合的特点是富含 Lueckisporites复合体的双绦虫花粉粒和多绦虫花粉粒，例如Lunatisporites、Protohaploxypinus、Striatopodocarpidites、Tornopollenites和Vittatina 。Colpate 花粉粒也以Marsupipollenites和Pakhapites为代表。278.84 ± 0.22 Ma 的 U-Pb CA-ID-TIMS 年龄，从与化石地层夹层的凝灰岩水平获得，首次限制了 Paganzo 盆地 LW 生物带的年龄，并调整了在冈瓦纳记录Lueckisporites virkkiae。此外，这一日期可以与其他盆地进行精确关联，例如阿根廷的圣拉斐尔盆地（Yacimiento Los Reyunos 组）和巴西巴拉那盆地（Iratí 组）。