Uppermost Permian to Middle Triassic palynology of the Salt Range and Surghar Range, Pakistan

Abstract

Independently dated palynostratigraphic zonations of Early Triassic age are rare. One of the best places to study Late Permian to Middle Triassic palynology together with contemporaneous marine faunas is the sedimentary successions of the Salt Range and Surghar Range in Pakistan.

Here, we present a new palynostratigraphic zonation of the Lower Triassic succession of North Gondwana, based on the spore pollen records of the Chhidru Formation, the Mianwali Formation, and the Tredian Formation from sections of the Nammal, Chhidru, Chitta-Landu and Narmia gorges in Pakistan. Within the Lower Triassic succession five palynological biozones are recognised, formally described, and calibrated by ammonoid biostratigraphy and C-isotope chemostratigraphy. Three further palynological associations, two from the uppermost Permian Chhidru Formation, and one from the Middle Triassic Tredian Formation, are informally described. The two basal assemblages (Chhidru 1 and Chhidru 2) are present in the uppermost Chhidru Formation. Chhidru 1 is dominated by gymnosperm pollen, whereas Chhidru 2 is characterised by abundant cavate trilete spores associated with conifer and pteridosperm pollen of Permian affinity. The assemblages of Dienerian to early Smithian age, the Densoisporites spp.–Lundbladispora spp. Assemblage Zone (PTr 1) and the Lundbladispora spp.–Densoisporites spp. Assemblage Zone (PTr 2) are dominated by cavate trilete spores. Compared to PTr 1, ornamented spores are more diverse in PTr 2, and taeniate bisaccate pollen are more abundant. The middle Smithian assemblages of the Densoisporites spp. Abundance Zone (PTr 3) are marked by an acme of Densoisporites spp. The following assemblages of the upper Smithian to lower Spathian Lunatisporites spp.–Densoisporites spp. Assemblage Zone (PTr 4) are characterised by abundant taeniate bisaccate pollen. The Spathian and Anisian assemblages (PTr 5 and Tredian 1) are characterised by abundant non-taeniate bisaccate pollen, and the common occurrence of Aratrisporites spp., and by generally diverse spore assemblages. The new palynostratigraphic zonation can be correlated with several other Gondwanan records (Australia, India, and Madagascar), and allows for reassessment of the floral recovery patterns in the aftermath of the end-Permian event. During periods with relatively stable carbon isotope values (early Smithian, Spathian and Anisian) pulses of diversification have been observed. During episodes of rapid fluctuations of the carbon cycle reduced palynofloral diversity is combined with rapid changes in the quantitative distribution pattern within the palynological assemblages.