Evaluating the role of coastal hypoxia on the transient expansion of microencruster intervals during the early Aptian

Worldwide, a growing number of modern coastal marine ecosystems are increasingly exposed to suboxic- or even anoxic conditions. Low seawater oxygen levels trigger significant ecosystem changes and may result in mass mortality oxygen-sensitive biota. The applicability observations from recent (anthropogenically influenced) suboxic settings fossil shallow-marine environments is, however, as yet poorly explored. test case documented here upper Barremian lower Aptian strata the Lusitanian Basin (Ericeira section, Portugal). These characterized by transient demise rudist–coral communities rapid establishment microencruster facies vacant ecological niches. hypothesis is tested that temporal expansion microencrusting organism Lithocodium aggregatum took place response platform-top depletion. We critically discuss outcome multi-proxy palaeoseawater redox approach (e.g. Rare Earth Elements (REEs), U isotopes palaeoecology) put robustness proxies applied test. This done considering issues with these methods general but also emphasizing significance terrigenous contamination fractionation effects. Data shown document evidence for depletion prelude Oceanic Anoxic Event (OAE) 1a lacking, hence, anoxia was not driving mechanism proto-North Atlantic platform setting studied here. In contrast, well-oxygenated early water masses proposed this site. Geologically short (decades millennia) fluctuations cannot be excluded, however. But if place, they offer no explanation Kyr Myr-scale patterns discussed present paper relevant it sheds light on complexity mechanisms drive punctuated Early Cretaceous coral–rudist turnover, assess strengths weaknesses ancient carbonates.