Volkheimerites labyrinthus, a new striate angiosperm pollen from the Paleogene of Patagonia, Argentina

PAULA LILIANA NÁRVAEZ; NATALIA MEGO; DIEGO GONZALO SILVA NIETO; MERCEDES BEATRIZ PRÁMPARO; NORA GRACIELA CABALERI

Manizales

Congreso; 54th AASP Meeting; 2022

The Palynological Society

The profile containing the specimens of the new angiosperm pollen grain crops out at Quebrada Barone (43º50’30’’S and 67º54’25’’W), in the Cañadón Carbón area, Chubut Province (Patagonia, Argentina). The sedimentary sequence is approximately 12 m thick, composed of finely laminated shales interbedded with siltstones and fine sandstones. Fourteen samples were collected for palynological analysis but only one had relevant palynological content (good preservation and number of grains). The remaining samples were rich in organic matter (amorphous and opaque phytoclasts) but devoid of palynomorphs. The sample level is located 8.5 m above the upper beds of the underlying Lonco Trapial Formation. The detailed description of this new angiosperm taxon expands the knowledge of the Paleocene palynofloral diversity in Patagonia. Combined light (LM) and high-resolution scanning electron microscopy (SEM) analyses were done to provide a detailed description of the 24 specimens of Volkheimerites labyrinthus gen. et sp. nov. (Fig. 1. A–D). The generic epithet honors Dr. Wolfgang Volkheimer (1928–2018; (Fig. 1. E), a renowned German-Argentinian palynologist who carried out vast research in Mesozoic and Cenozoic basins from Argentina, and who first illustrated specimens of this species from another locality, leaving them with an open assignation. The specific epithet refers to the characteristic labyrinthine pattern of the ornamentation.The grain is oblate with circular–subcircular outline in polar view, semicircular to ellipsoidal in equatorial view; without defined aperture. Medium to large in size (25.5–55 μm). The presumed distal face is striate, with the muri forming a labyrinthine or dichotomous-radiate pattern. The muri are 1–1.8 μm wide in polar view, broad and rounded. The exine is semitectate. Nexine up to 0.8 µm thick. Columellae 0.5–1.5 µm in diameter, irregularly spaced, 0.8–1.8 μm high. Tectum 1–1.8 μm high. The large circular opening on the presumed proximal face corresponds to the thinning of the exine, that is generally torn or absent. Volkheimerites labyrinthus shares the presence of a coarse semitecate tectum supported by columellae with the fossil genera Dichastopollenites (Nymphaeaceae), Trisectoris and Periretisyncolpites (Schisandraceae), and with some Winteraceae and Annonaceae species, but differs in having striate-labyrinthine or dichotomous-radiate as opposed to a reticulate ornamentation. Volkheimerites is also distinctive by the occurrence of solitary grains (monads) instead of the more frequent presence of tetrads in the Winteraceae family or grains separated into two hemispheres as in Dichastopollenites. The large thin area of the exine appears to be morphologically analogous to the proximal thinning of the exine in the monads making up the tetrads as occurs in some Annonaceae species. Despite the morphological traits shared with the described genera and families, Volkheimerites labyrinthus could not be assigned a botanical affinity, probably consisting of an extinct taxon not closely related to any extant family.