Sprecher
Beschreibung
The Early Triassic of the Sydney Basin (southeastern Australia) records successive floral communities dominated by arborescent seed ferns (Peltaspermales, Umkomasiales) and conifers (Voltziales), and shrubby isoëtaleans (Pleuromeiaceae, Isoëtaceae). These changes track the climatic instability following the end-Permian event (ca. 252.3−251.9 Ma), likely driven by recurrent outgassing pulses from the Siberian Traps Large Igneous Province after its main eruptive phase. Stable carbon isotope stratigraphy links the floristic turnovers to extreme warming during the late Smithian thermal maximum (ca. 249.9−249.4 Ma), followed by two cooling phases: the Smithian-Spathian event (SSE; ca. 249.4−249.1 Ma), and the end-Early Triassic event (EETE; ca. 248.1−247.4 Ma).
Between the SSE and EETE lies a distinctive interval of kaolinitic mudrocks with high hematite content, characterised by pervasive oxidation that imparted in them a red colouration (i.e., red bed). X-ray fluorescence (XRF) data indicate intense chemical weathering, reflected by sodium- and potassium-oxide depletion and chemical index of alteration values averaging ~92. Despite this weathering signature, recovered palynomorphs exhibit unexpectedly remarkable preservation. Sedimentological evidence indicates a major palaeocurrent shift during the upper Early Triassic, coinciding with a geochemical trend revealing a change in sedimentary provenance from plutonic to volcanic sources. Biostratigraphy demonstrates that palynomorphs were contemporaneous with red bed deposition, suggesting that sediment likely underwent an initial phase of weathering prior to being transported and deposited, followed by additional alteration under a warm, humid Spathian climate.
These findings highlight that continental red bed deposits can remain viable targets for palynological sampling despite superficial sedimentary and geochemical evidence for intense weathering.