Episodic events in long-term geological processes: A new classification and its applications

Abstract

Long-term geological processes are usually described with curves reflecting continuous changes in the characteristic parameters through the geological history, and such curves can be employed directly for recognition of episodic (relatively long-term) events linked to these changes. The episodic events can be classified into several categories according to their scale (ordinary and anomalous events), “shape” (positive, negative, and neutral events), and relation to long-term trend change (successive, interruptive, facilitative, stabilizing, transformative, increasing, and decreasing). Many types of these events can be defined depending on the combination of the above-mentioned patterns. Of course, spatial rank, duration, and origin can be also considered in description of these events. The proposed classification can be applied to events in some real long-term geological processes, which include global sea-level changes, biodiversity dynamics, lithospheric plate number changes, and palaeoclimate changes. Several case examples prove the usefulness of the classification. It is established that the Early Valanginian (Early Cretaceous) eustatic lowstand (the lowest position of the sea level in the entire Cretaceous) was negative, but ordinary and only interruptive event. In the other case, it becomes clear that the only end-Ordovician and the Permian/Triassic mass extinctions transformed the trends of the biodiversity dynamics (from increase to decrease and from decrease to increase respectively), and the only Cretaceous/Paleogene mass extinction was really anomalous event on the Phanerozoic biodiversity curve. The new palaeontological data are employed to reconstruct the diversity dynamics of brachiopods in Germany (without the Alps) and the Swiss Jura Mountains. The further interpretation of the both diversity curves implies that the Early Toarcian mass extinction affected the regional brachiopod faunas strongly, but this event was only decreasing (biotic radiation continued after it, although “restarted” from the lower point) similarly to the end-Triassic and Cretaceous/Paleogene mass extinctions. The number of lithospheric plates decreased in the Early Cretaceous; however, the previous trend to increase in this number re-established after the noted event. The Oi-1 glaciation in the very beginning of the Oligocene was anomalous event, but it only stabilized the earlier trend of temperature decline and did not transform it. Further development of the comprehensive classification of geological events is necessary. For instance, it has become clear that the Silurian environmental perturbations and the Cretaceous oceanic anoxic events should be classified as discrete events that differ essentially from episodic events, the latter of which are relevant to continuous changes in geological processes.