The Permian-Triassic boundary in Jordan: transitional alluvial to marine depositional sequences and palynology, conodont and foraminifera biostratigraphy from the Dead Sea margins, Jordan

The Permian to Triassic transition in Jordan is characterised by a sequence boundary underlain by red-bed alluvial lithofacies deposited in a humid-tropical climate by low-sinuosity rivers, and overlain by shallow marine... [ view full abstract ]

The Permian to Triassic transition in Jordan is characterised by a sequence boundary underlain by red-bed alluvial lithofacies deposited in a humid-tropical climate by low-sinuosity rivers, and overlain by shallow marine siliciclastics with thin carbonates. The low-gradient alluvial floodplain was repeatedly subjected to the development of ferralitic and pisolitic paleosols on the interfluves. In contrast, fluvial channels and abandoned lakes were the sites of wetter, humic conditions that preserved a prolific flora of macro-plants and palynomorphs that indicate a probable range from Mid- to Late Permian age, though the abundant presence of the distinctive pollen Pretricolpipollenites bharadwaji probably indicates the youngest part of that range.
The palynology of the fluvial channels and abandoned lakes is remarkably varied. Samples from argillaceous beds of fluvial origin appear to contain a palynomorph representation of the wider hinterland of the drainage basin of the river including floodplain plants and more distant communities. In restricted water bodies like oxbow lakes or other impermanent stagnant floodplain ponds and peaty mires (immature coals), a higher proportion of purely local palynomorphs appear to be preserved in associated sediments. One of the assemblages representing local plant communities displays a Cathaysian palaeophytographic affinity, while others from similar levels within the Umm Irna Formation present a Gondwanan affinity. This indicates the risk of generalisation from single borehole or limited outcrop studies
Above the sequence boundary, reddened shallow-marine beds characterised by ripple cross-laminated, siltstones/sandstone with desiccation cracks and sparse surface burrows mark the initial Triassic marine transgression in the region (Arabian Plate Tr 10). These are followed by two thin limestone (wackestone) beds with shallow scours and bivalve lags, that have yielded a low diversity assemblage of conodonts and foraminifera that are interpreted as euryhaline recovery taxa characterising the early Induan (Early Triassic). Thus the absence of body fossils and vertical infaunal burrows in the lowest marine beds may reflect low-diversity ecosystems following the Permian-Triassic extinction event, or be a result of stressed shallow marine environments. A gradational upward increase in grey, green and yellow siltstones beds accompanied by a concomitant increase in bioturbation (and infaunal vertical burrows) and thin-shelled bivalves about 15 m above the boundary indicates colonisation of the substrate under more normal shallow marine conditions perhaps indicating recovery phase following the extinction event.