VOLCANIC ACTIVITY AND ENVIRONMENTAL STRESS EVIDENCED BY TERATOLOGY AND MUTAGENESIS IN PALYNOLOGICAL ASSEMBLAGES FROM THE LADINIAN QUEBRADA DE LOS FOSILES FORMATION, SAN RAFAEL BASIN, CENTRAL WESTERN ARGENTINA

ZAVATTIERI, A.M.; GUTIÉRREZ, P.R.

Buenos Aires - Virtual

Congreso; XII Congreso de la Asociacion Paleontologica Argentina; 2021

Asociación Paleontologica Argetina

Phytotoxic substances (e.g., chemical compounds, UV-B radiation) can induce stress reactions and cause morphological abnormalities in the plants and their reproductive cells. Records of abnormal spores and pollen morphology (teratogenesis) and mutagenesis provide independent evidence of deteriorating atmospheric conditions caused by extensive volcanic activity. In central western Argentina, the Middle Triassic was characterized by intense explosive volcanic activity. Rhyolitic pyroclastic flow deposits, andesitic lavas, basaltic intrusives and volcaniclastic facies reveal intense volcanism coeval with the deposition of the Quebrada de los Fósiles Formation (QdlFF), lower unit of the Puesto Viejo Group, San Rafael Block, Mendoza Province. Sedimentological data suggest that the vegetation recorded from this unit grew in fluvial systems while profuse volcanic activity introduced large volumes of ash and the emission of large amounts of greenhouse (thermogenic) gases into the atmosphere. The extensive events of explosive acid volcanism during the deposition of the Puesto Viejo Group and its consequent effects on climate (resulting in generalized regional aridity) and the paleoenvironment, created stressful and adverse conditions that directly influenced the development of plant communities. To assess the degree of teratology and mutagenesis on the aberrant palynomorphs recorded at the QdlFF, we characterized anomalous variations in overall shape, size and wall thickness, disorganized wall structure and the presence of permanent tetrads or dyads that failed to separate from one another during sporogenesis. Such unusual morphological variants or imperfections are evident among spores and pollen grains, and also in some aquatic zygospores of algae recorded in the different QdlFF assemblages. Common dispersed tetrads of the sphenophyte Calamospora showing aborted spores may indicate genetic disturbance and unbalanced or incomplete cell division; malformations such as thickened labra and growths/crassitudes on the proximal face in lycophyte spores (Retusotriletes) and ferns (Deltoidospora, Dictyophyllidites) are also observed in low frequencies within the QdlFF assemblages. Pollen abnormalities include aberrant/aborted sacs in Goubinispora, thickenings around tetrad mark in conifers/voltziales pollen (Triadispora), aberrant sacci in Bascanisporites, aborted sacci (protosacci) and protuberances or thickenings in the central bodies of conifer striate pollen (Crustaesporites, Striomonosaccites, Variapollenites, Protohaploxypinus, Striatoabieites, Hamiapollenites) are the most mutagenetic teratological evidence in gymnosperm grains. Otherwise, common occurrence of dwarfed spores and pollen (immature or aberrant small size) suggests premature shedding as additional traits of teratology. Within freshwater aquatic algae, the massive occurrence of Ovoidites, interpreted as blooms of zygnematacean algae, also show aberrant zygospores or aplanospores morphologies. Additionally, the palynological preparations also contain dispersed pteridosperm (leaf) cuticle fragments showing xeromorphic features such as clogged stomata, sunken guard cells, thickening of the ostiole margins and dorsal sectors in the guard cells, abundant small hollow papillae, and short single-celled hairs, that reveal mutagenetic responses to a stressful environment at the time of deposition of the QdlFF. This is the first case study of teratology and mutagenesis used as bioindicators of environmental stress, an especially useful proxy for phytotoxicity in the Triassic fossil record in Argentina.