Abstract Gymnosperm foliar compressions belonging to two fossil taxa, Pseudoctenis ornata (Cycadophyta) and Ginkgoites tigrensis (Ginkgophyta), are chemically characterized for the first time by semi-quantitative Fourier Transform Infrared (FTIR) spectroscopy. The specimens collected in the well-known Baquero Group (Lower Cretaceous, Santa Cruz province, Argentina) are compressions with very well-preserved cuticles. The FTIR data are analyzed along with the available paleoenvironmental data of the Baquero Group localities in order to interpret the volcanic activity role in the preservation of these foliar compressions and, consequently, their chemical compositions. For the spectrometric study, foliar remains are analyzed into two sample forms: compressions (including coalified mesophyll and cuticle; Cp) and cuticles (Ct). Semi-quantitative data, derived from Cp and Ct spectra, are evaluated by principal component analysis (PCA) analyzing the functional groups preserved in the mesophyll and cuticle of each fossil taxon. In general, the fossil taxa reflect similar chemical compositions between compression and cuticle sample forms revealing that P. ornata and G. tigrensis compressions underwent, during diagenesis and probably post-diagenesis, a natural oxidation process. Considering the known information on the preservation model of Squamastrobus tigrensis, a podocarp recovered also in Baquero Group, as well as the paleoenvironments and geochemical conditions in the fossiliferous localities along with the FTIR data, two preservation models are here proposed for P. ornata and G. tigrensis. The volcanic activity was most likely involved in the exceptional preservation of the foliar cuticle characters, the transformation of the organic matter, and the oxidation undergone by G. tigrensis and P. ornata foliar remains.

中文翻译：

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火山灰沉积物中白垩纪裸子植物叶子的化学保存。巴克罗集团，巴塔哥尼亚，阿根廷

摘要 属于两种化石类群 Pseudoctenis ornata (Cycadophyta) 和 Ginkgoites tigrensis (Ginkgophyta) 的裸子植物叶面压缩物首次通过半定量傅里叶变换红外 (FTIR) 光谱进行化学表征。在著名的 Baquero 组（下白垩纪，阿根廷圣克鲁斯省）收集的标本是具有保存非常完好的角质层的压缩物。FTIR 数据与 Baquero Group 地区的可用古环境数据一起分析，以解释火山活动在保护这些叶面压缩中的作用，从而解释它们的化学成分。对于光谱研究，叶残留物被分析为两种样品形式：压缩物（包括煤化叶肉和角质层；Cp）和角质层 (Ct)。半定量数据，来自 Cp 和 Ct 光谱，通过主成分分析 (PCA) 分析保留在每个化石分类群的叶肉和角质层中的官能团进行评估。一般来说，化石类群反映了压缩和角质层样本形式之间相似的化学成分，表明 P. ornata 和 G. tigrensis 压缩在成岩作用期间和可能在成岩作用后经历了自然氧化过程。考虑到 Squamastrobus tigrensis 保存模型的已知信息，一种也在 Baquero Group 中发现的罗汉果，以及化石产地的古环境和地球化学条件以及 FTIR 数据，这里提出了 P. ornata 和 G 的两种保存模型. 老虎。