U-Pb zircon constraints on the age of the Cretaceous Mata Amarilla Formation, Southern Patagonia, Argentina: its relationship with the evolution of the Austral Basin
U-Pb zircon constraints on the age of the Cretaceous Mata Amarilla Formation, Southern Patagonia, Argentina: its relationship with the evolution of the Austral Basin
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DOI：
10.5027/andgeov39n3-a01
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发表时间：
2012-08
期刊：
影响因子：
0.9
通讯作者：
A. Varela;D. Poiré;T. Martin;A. Gerdes;F. Goin;J. Gelfo;S. Hoffmann;S. Hoffmann
中科院分区：
文献类型：
--
作者：
A. Varela;D. Poiré;T. Martin;A. Gerdes;F. Goin;J. Gelfo;S. Hoffmann;S. Hoffmann
尽管Mata Amarilla组（阿根廷圣克鲁斯省南巴塔哥尼亚）的化石含量丰富，但其年龄总是产生相当多的问题和争论。无脊椎动物、恐龙、鱼类、海龟、蛇颈龙和化石植物群提供的年代学数据相互矛盾。本文对玛塔阿马里拉组中段凝灰岩层中环带状锆石晶体的外部进行了20次激光烧蚀U-Pb斑点分析，获得了96.23± 0.71Ma的U-Pb一致年龄，相当于赛诺曼阶中期。Mata Amarilla组下段的沉积标志着Austral盆地（又称马加拉内斯盆地）前陆阶段的开始;这一过渡的特征是沉积体系的西向东转移，这与白垩纪褶皱冲断带的扩张一致。因此，前陆阶段的开始可能发生在上阿尔布阶和下塞诺曼阶之间，因为下面的Piedra Clavada地层的年龄是下阿尔布阶。将获得的数据与智利Ultima Esperanza省的资料进行比较，可以认为Rocas Verdes Marginal盆地的封闭是同时发生的。
Despite the abundant fossil content of the Mata Amarilla Formation (Southern Patagonia, Santa Cruz Province, Argentina), its age has always generated a considerable number of questions and debates. The chronological data provided by invertebrates, dinosaurs, fish, turtles, plesiosaurs and fossil flora are contradictory. In this work, twenty U-Pb spot analyses by laser ablation were carried out on the outer parts of the zoned zircon crystals from a tuff layer of the middle section of the Mata Amarilla Formation, yielding a U-Pb concordia age of 96.23±0.71 Ma, which corresponds to the middle Cenomanian. The deposition of the lower section of the Mata Amarilla Formation marks the onset of the foreland stage of the Austral Basin (also known as Magallanes Basin); this transition is characterized by the west-east shift of the depositional systems, which is consistent with the progradation of the Cretaceous fold-and-thrust belt. Thus, the onset of the foreland stage could have occurred between the upper Albian and lower Cenomanian, as the underlying Piedra Clavada Formation is lower Albian in age. On comparing the data obtained with information from the Ultima Esperanza Province in Chile, it can be suggested that the initiation of the closure of the Rocas Verdes Marginal Basin occurred simultaneously.