Preserved chemistry of Cretaceous gymnosperm leaves in volcanic- ash deposits. Baquer  o Group, Patagonia, Argentina Maiten A. Lafuente Diaz a, * , Georgina M. Del Fueyo a , Jos  e A. D'Angelo b, c , Martín A. Carrizo a a Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”-CONICET, Avda.  Angel Gallardo 470, C1405DJR, Ciudad Aut onoma de Buenos Aires, Argentina b IANIGLA-CCT-CONICET-MENDOZA,  Area de Química, FCEN, Universidad Nacional de Cuyo, M5502JMA, Mendoza, Argentina c Palaeobotanical Laboratory, Cape Breton University,1250 Grand Lake Road, Sydney, Nova Scotia, B1P 6L2, Canada article info Article history: Received 9 April 2020 Received in revised form 11 August 2020 Accepted in revised form 13 September 2020 Available online 19 September 2020 Keywords: Compression Cuticle FTIR spectroscopy Gymnosperms Baquer o Group Lower Cretaceous 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 Baquer o 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 Baquer o Group localities in order to interpret the volcanic activity role in the preservation of these foliar com- pressions 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 cu- ticles (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 Baquer o 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. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction The Baquer o Group (Cladera et al., 2002) is a predominantly volcaniclastic sequence that outcrops in the central region of the Santa Cruz province in Patagonia, Argentina. This Cretaceous unit is world-known by having abundant plant remains that include im- pressions and mainly coalified compressions with exceptionally well-preserved cuticles (Archangelsky, 2003; Del Fueyo et al., 2007; Llorens et al., 2020). Several pieces of evidence revealed that during the Aptian sedimentation of the Baquer o Group the plant assemblages were inhabiting under stressful conditions caused by the recurrent volcanic ash fall which was of varied intensity (Archangelsky, 2001a, 2001b; Cladera et al., 2002; Carrizo et al., 2011). This scenario led to the occurrence of different paleoeco- logical conditions among the lithostratigraphic units that compose the Baquer o Group (Cladera et al., 2002). The plant communities recovered from the Anfiteatro de Tic o Formation (lower unit) are taxonomically richer than those from the Punta del Barco Forma- tion (upper unit). Based on this, Archangelsky (2001a) defined two distinctive biozones: the lower Ptilophyllum biozone (Anfiteatro de Tic o Formation) and the upper Gleichenites biozone (Punta del Barco Formation). The main difference between these two biozones is the absence of Bennettitales and Ginkgoales in the upper plant assemblages. This fact may indicate an important ecological change * Corresponding author. E-mail addresses: maitenlafuentediaz@gmail.com (M.A. Lafuente Diaz), georgidf@yahoo.com.ar (G.M. Del Fueyo), joseadangelo@yahoo.com (J.A. D'Angelo), blackdisck@gmail.com (M.A. Carrizo). Contents lists available at ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes https://doi.org/10.1016/j.cretres.2020.104646 0195-6671/© 2020 Elsevier Ltd. All rights reserved. Cretaceous Research 118 (2021) 104646