Lycopodiopsis derbyi Renault from the Corumbataí Formation in the state of São Paulo (Guadalupian of Paraná Basin, Southern Brazil): New data from compressed silicified stems

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• 作者：Rafael Souza de Faria ; Fresia Ricardi-Branco ; Paulo C&#xe9 ; sar F. Giannini ; Andr&#xe9 ; O. Sawakuchi ; Luiz Eduardo Vieira Del Bem
• 关键词：Lycopsids ; Lycopodiopsis derbyi ; Guadalupian ; Paran&#xe1 ; Basin
• 刊名：Review of Palaeobotany and Palynology
• 出版年：2009
• 出版时间：December 2009
• 年：2009
• 卷：158
• 期：1-2
• 页码：180-192
• 全文大小：1663 K

文摘

Lycopodiopsis derbyi Renault was analyzed on the basis of compressed silicified stems from four Guadalupian outcrops of the Paraná Basin (Corumbataí Formation) in the State of São Paulo, Southern Brazil. Dichotomous stems have been recorded, and three different branch regions related to apoxogenesis are described. The most proximal region has larger, clearly rhomboidal leaf cushions, with protruding upper edges; the intermediate transitional region also has rhombic leaf cushions, but they are smaller and less elongated than the lower in the same axis; finally, the most distal region reveals only incipient cushions, with inconspicuous infrafoliar bladders; interspersed microphylls were still attached. A well preserved branch representative of this most distal region was sectioned; it has a siphonostelic cylinder similar to that previously described for L. derbyi. The cortex, however, shows new traits, such as a short portion of elongated cells between the periderm and the external cortex (or leaf cushion tissue). The stems were apparently silicified prior to their final burial but were probably not transported for long distances. Their final burial may have taken place during storm events, which were common during the deposition of the Corumbataí Formation. These stems are commonly deformed due to compression, mainly because the internal cortical portions rapidly decayed prior to silicification due to their thin-walled tissue, and are therefore not preserved. The common alkalinity of a shallow marine environment such as that in which the Corumbataí Formation was deposited, should mobilize the silica and favors petrifaction. Based on the new data, an emended diagnosis is proposed and a modification of the identification key published by Thomas and Meyen in 1984 for Upper Paleozoic Lycopsida is suggested.