The significance of benthic ecospace expansion following the ROECE at the Cambrian Series 2–Miaolingian boundary, western Henan Province, central China

Abstract

The transition period from the Cambrian Series 2 to Miaolingian was a pivotal juncture in Earth's history, marking the onset of significant shifts in biodiversity and biomass dynamics during the Phanerozoic. Concurrently, profound transformations occurred in the alteration of sedimentary deposits by trace makers, reshaping benthic ecological spaces. This study employs ichnological and ecological methodologies to construct a comprehensive three-dimensional spatial model for ecospace occupation and ecosystem engineering within the Mantou Formation in the western Henan Province, focusing on the transition between the Cambrian Series 2 and Miaolingian. A meticulous statistical analysis of 22 ichnogenera and 32 ichnospecies in the Mantou Formation revealed nuanced variations, such as a decrease in the proportion of predatory organisms in the lower part of Member 2 of the Mantou Formation and a corresponding increase in the upper part. Simultaneously, non-selective deposit-feeding animals exhibit an ascending trend in the lower part of Member 2 and a descending trend in the upper part of Member 2.

In terms of sediment bioturbation, the lower part of Member 2 is characterized by the exclusive presence of biodiffusors and conveyors, whereas regenerators make their appearance in the upper part of Member 2. Affected by the Redlichiid–Olenellid Extinction Carbon isotope Excursion (ROECE) event, metazoans experienced a shift in control dynamics, with microbial mats becoming dominant. Biological activities became intricately intertwined with microbial mats. In the upper part of Member 2, metazoans started recovering, concomitant with the emergence of Thalassinoides and Treptichnus substantially boasting ecosystem engineering impact (EEI) values. These trace makers rapidly amplified the depth and extent of sediment disturbance, giving rise to a profusion of novel ecological niches and catalyzing the transformation of builder functional groups.