Palynostratigraphy of the Upper Jurassic to Lower Cretaceous strata, Upper Indus Basin, Pakistan: implication for Jurassic/Cretaceous boundary and paleoclimate in the Eastern Tethys

Abstract

This paper investigates the much-debated Jurassic/Cretaceous (J/K) boundary as well as the Early Cretaceous climate using palynomorphs of the Chichali Formation, Upper Indus Basin, North Pakistan. Based on the palynostratigraphy, two dinoflagellates and one spore/pollen assemblage are recorded, suggesting a Kimmeridgian to Valanginian age for the sediments of the Chichali Formation. The palynostratigraphic results further suggest that the Tithonian to Berriasian strata are truncated along the J/K boundary. The warm and humid conditions are supported by the consistent dominance of ferns corresponding to the Schizaeaceae and the intermittent appearance of herbs from Gleicheniaceae. Such climatic conditions are further supported by the consistent presence of evergreen trees with a broad leave of Cyatheaceae and Matoniaceae. The warm and humid conditions are also supported by conifers of the Araucariaceae in association with Cycadaceae. Such conditions during the Valanginian are further supported by the switch from the Bajocian–Oxfordian shallow carbonates of the Samana Suk Formation to the Kimmeridgian–Valanginain clastics of the Chichali Formation. Hence, the expansion of warm and humid tropical flora to the middle latitude (∼40°S) during the Valanginain hints strongly for global warming instead of previously suggested global cooling. KEY POINTS: Palynostratigraphic investigation shows Kimmeridgian to Valanginian age for the Chichali Formation, Upper Indus Basin, Pakistan. The J/K boundary is marked by an unconformity along which the Tithonian to Berriasian time record is missing. The reconstruction of paleovegatation indicates warm humid climate during the Valanginian instead of previously reported global cooling.