The first record of Permo-Triassic palynomorphs and palynological change across the Triassic-Jurassic transition in the onshore Ruvu Basin, Tanzania

Abstract

The Ruvu Basin in northeastern coastal Tanzania is one of the least studied basins in the country. It likely contains a record of the pre-and post-breakup sequences of the Gondwana supercontinent. In this study, the first comprehensive palynological investigation on drill-cuttings samples from the Makarawe-1 well in the Ruvu Basin was conducted. In the lower section of this well, four distinct palynologic intervals are recorded: Aratrisporites spp.-Klausipollenites schaubergeri interval (Upper Permian); Reduviasporonites spp. interval (Permo-Triassic transition); Extinction Interval (Permo-Triassic extinction) and Alisporites-Falcisporites Interval (Upper Triassic). This implies that the Ruvu Basin heralds a succession across the Permian-Triassic boundary and its associated extinction. We also record substantial palynological change occurs across the transition to the upper portion of the Makarawe-1 well, where marine dinoflagellate cysts and abundant Classopollis pollen dominate the assemblage. Based on the ranges of dinoflagellate cysts supplemented by pollen-spore ranges, two main palynological intervals (the Classopollis-Nannoceratopsis interval and the Wanaea clathrata interval) are here established. These intervals are of late Middle Jurassic and Late Jurassic (Bajocian - Kimmeridgian) age. This suggests possible correlations with the Lugoba, Msata, Msolwa, Magindu and Malivundo formations of the Ruvu Basin. The findings presented herein suggest a downhole extension of the Wanaea clathrata interval (Oxfordian-Kimmeridgian) sensu [Msaky 2007] to 1215–1235 m. In addition, the Nannoceratopsis-dominated assemblage is indicative of an Early Jurassic association that developed during immediate post-break-up phase, with low-salinities and basinal restriction. With similarity to the Ngerengere dinocyst assemblage reported in previous studies, these results further suggest that the Ngerengere beds are not a so-called Karoo equivalent, but rather a syn- or post-breakup sequence. The recorded intervals are highly similar to other palynostratigraphic units of Africa, Australia, Europe and South America. The data collected in this study add important insights for the general stratigraphic framework within this poorly constrained coastal basin, while also providing a perspective on more distant correlations using palynology.