Early Mississippian sandy siltstones preserve rare vertebrate fossils in seasonal flooding episodes

Abstract

across the floodplain in seasonal rainfall episodes. These deposits are significant new sites that can be explored for the preservation of rare non-marine fossil material and provide unique insights into the evolution of early terrestrial ecosystems.

A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits

“…The Ballagan Formation comprises 10 facies and three facies associations, each of which occur throughout the formation: (1) fluvial facies association; (2) overbank facies association; and (3) saline‐hypersaline lake facies association (Bennett et al . ). The sandy siltstone facies occurs within the overbank facies association, and is characterized as matrix‐supported, ungraded siltstones, with millimetre‐sized siltstone and very fine sandstone lithic clasts.…”

“…Beds are randomly distributed through the succession, laterally variable, and range in thickness from 0.2 to 140 cm (Bennett et al . ). 71% of beds overlie palaeosols or desiccation cracks and often occur in stacked sequences with palaeosols.…”

“…The sandy siltstone beds are interpreted as having formed as a cohesive flow resulting from monsoonal‐type flood events, picking up sediment clasts and fossil material from desiccated floodplain lakes and vegetated ground as the flood travelled (Bennett et al . ). The beds either deposited material in depressions on a dry vegetated floodplain, or into existing floodplain lakes or pools.…”

“…The high degree of vertebrate and invertebrate fossil articulation within these units indicates a local origin and minimal transport of the fossil components (Bennett et al . ).…”

“…The last of these have been identified as an important facies for preserving fossils both in the Ballagan and elsewhere in the Carboniferous (Bennett et al . ; Kearsey et al . ).…”