Palynofacies in Lower Jurassic epicontinental deposits of Poland: Tool to interpret sedimentary environments

Abstract

Diversified continental, marginal-marine and marine epicontinental deposits in Poland of Early Jurassic age yielded unusually rich palynomacerals. Numerous parameters, such as the presence of acritarchs and dinoflagellate cysts, spore/bisaccate pollen grain ratio, content of terrestrial phytoclasts, degree of oxidation, presence of tetrads and sporangia, degree ofpalynomorph alteration, presence and character of amorphous organic matter, presence of epibionts on palynomorphs, were collectively found as indicative of certain palynofacies. The ratio of spores and bisaccate pollen grains significantly depends on the climatic conditions where also seasonal changes may influence the local characteristics of palynofacies. However, the ratio also strongly reflects the local depositional environment which may vary regionally and spore/bisaccate pollen grain ratio can be taken as a general indicator of distance from the shore. Early Jurassic palynomacerals from the Polish Basin are strongly dominated by terrestrial elements, marine palynomacerals occur in significant quantities only in Pliensbachian deposits in Pomerania Western Poland. Charcoal is an important component of palynomacerals. Due to its resistance to biogenic degradation and buoyancy, charcoal produced by extensive wildfires was widely re-deposited and concentrated particularly in foreshore to shallow shoreface and delta plain environments. Three types of palynofacies inversions (abnormal palynofacies composition) are discussed. Six main palynofacies types linked to depositional systems previously determined by sedimentological studies have been distinguished providing a robust paleoenvironmental tool for recognition of palynofacies attributed to certain palaeoenvironments.