Chemometric approach to the foliar cuticle of Ptilophyllum micropapillosum sp. nov. from the Springhill Formation (Lower Cretaceous, Argentina)

Abstract

Ptilophyllum micropapillosum sp. nov. is a new bennettitalean frond recovered from the Lower Cretaceous Springhill Formation, Patagonia, Argentina. The foliar cuticle is herein characterized by means of light and scanning electronic microscopy along with its preserved chemistry. The aim of the chemical study is to reveal mesophyll and cuticle chemical structures (functional groups) preserved in different frond parts (apical, middle, and basal) as well as their relation with kerogen types and coal macerals. Fronds of P. micropapillosum sp. nov. are bipinnate, the abaxial epidermis has different papillae types: (1) abundant, small and simple, (2) scarce compound papillae, and (3) few big simple papillae. For the first time, plant fossil remains from the Springhill Formation are studied by semi-quantitative Fourier transform infrared (FTIR) spectroscopy. Two sample forms are included: compressions (Cp) and cuticles (Ct). Additionally, the host rock is analyzed through concentrate kerogen and entire rock samples. From these, thermal indices (Ro%, TAI, and VRE) and organic and inorganic matter characterization are derived. Semi-quantitative data (area ratios), derived from the Cp and Ct FTIR spectra, are interpreted by principal component analysis. Results indicate differences between Cp and Ct, revealing a high content of aromatic compounds in P. micropapillosum sp. nov. foliar cuticle. This is most likely attributed to the presence of aromatic monomers in cutin/cutan biomacropolymers. The chemical composition is similar among apical, middle, and basal frond parts. This fact probably implies a distinctive frond construction pattern where the energy investment and the metabolic cost are similar throughout the analyzed fronds.