Carboniferous Events : The Interplay of Life, Climate and Geodynamics

Global events and event stratigraphy have received little attention within the Carboniferous community, in contrast to most other Paleozoic systems. This is surprising given the complex geological, biological, and climatic history of the Carboniferous, which provides numerous opportunities to identify significant events and turning points in Earth history. Our selection is necessarily incomplete and intends to highlight the diversity of event types rather than provide an exhaustive inventory. The post-extinction diversification following the Hangenberg event at the Devonian-Carboniferous Boundary has long been noticed in many fossil groups and several biotic events were documented, although rarely named or recognized as global events. At a super-regional scale, the Alum Shale Event of the early Tournaisian represents a major transgressive phase and shares characteristics with anoxic (black shale) events documented in other systems. Its potential relationship to isotope perturbations called TICE remains so far unresolved. Moreover, only minor extinctions are associated with this episode, hence regarded as geochemical or sedimentological event. A key global event is the latest Tournaisian transgression (“Avins Event”), which corresponds to one of the highest relative sea levels of the Carboniferous. This episode facilitated the breakdown of marine biogeographic barriers and promoted extensive faunal exchange and subsequent faunal cosmopolitanism. It was followed by a major regression associated with the first major glaciation of the LPIA, leading to basin isolation and setting the stage for the following Visean biodiversification. Sea-level fluctuations, notably maxima of transgressive phases also caused numerous regional events. Examples include the late Visean crenistria transgression in the Rhenohercynian Realm and Early and Middle Pennsylvanian marine bands/horizons (e.g., the Aegir Event) in central European foreland basins. Not all events were catastrophic. The Carboniferous also records key evolutionary innovations and ecological expansions. The earliest evidence of powered flight marks a major milestone in the colonization of aerial environments during the (late) Visean, although its precise timing remains uncertain. At regional scales, evolutionary novelties often follow colonization of new ecospaces; for instance, the development of colonial (modular) growth forms in the late early Visean corals, the rapid evolution of complex foraminifers, and of course, the development of the amniotic egg in tetrapods during the late Visean. The most severe biotic crisis of the Carboniferous is the so-called mid-Carboniferous mass extinction near the Mississippian–Pennsylvanian boundary, commonly linked to the onset of the Late Paleozoic Ice Age and/or the Variscan Orogeny, including associated seaway closures. Regarded as a second-order mass extinction, its ecological impact is comparable to the Big Five events. However, its nature and timing remain poorly resolved. Apparent diversity loss is pronounced when comparing Mississippian and Pennsylvanian faunas on the stage-level, yet precise extinction and origination timings are rarely constrained. This raises the question of whether the pattern reflects a discrete mass extinction event or a prolonged faunal turnover, the latter being more consistent with long-term environmental drivers and major possible causes mentioned above. These examples illustrate that the Carboniferous contains a rich spectrum of events, which offer significant potential for improved global correlation of the Carboniferous timescale.