The mid-Cretaceous was marked by emplacement of large igneous provinces (LIPs) that formed gigantic oceanic plateaus, affecting ecosystems on a global scale, with biota forced to face excess CO 2 resulting in climate and ocean perturbations. Volcanic phases of the Ontong Java Plateau (OJP) and the southern Kerguelen Plateau (SKP) are radiometrically dated and correlate with paleoenvironmental changes, suggesting causal links between LIPs and ecosystem responses. Aptian biocalcification crises and recoveries are broadly coeval with C, Pb, and Os isotopic anomalies, trace metal influxes, global anoxia, and climate changes. Early Aptian greenhouse or super-greenhouse conditions were followed by prolonged cooling during the late Aptian, when OJP and SKP developed, respectively. Massive volcanism occurring at equatorial versus high paleolatitudes and submarine versus subaerial settings triggered very different climate responses but similar disruptions in the marine carbonate system. Excess CO 2 arguably induced episodic ocean acidification that was detrimental to marine calcifiers, regardless of hot or cool conditions. Global anoxia was reached only under extreme warming, whereas cold conditions kept the oceans well oxygenated even at times of intensified fertility. The environmental disruptions attributed to the OJP did not trigger a mass extinction: rock-forming nannoconids and benthic communities underwent a significant decline during Oceanic Anoxic Event (OAE) 1a, but recovered when paroxysmal volcanism finished. Extinction of many planktonic foraminiferal and nannoplankton taxa, including most nannoconids, and most aragonitic rudists in latest Aptian time was likely triggered by severe ocean acidification. Upgraded dating of paleoceanographic events, improved radiometric ages of the OJP and SKP, and time-scale revision are needed to substantiate the links between magmatism and paleoenvironmental perturbations.

Among various paleoenvironmental proxy records across the lower Aptian Selli Level (Umbria-Marche basin, Italy) and its equivalents (i.e., sedimentary expressions of oceanic anoxic event [OAE] 1a), one very intriguing feature is a prominent negative δ 13 C excursion at the base of this sedimentary unit, generally by as much as a few per mil in marine carbonates. This early Aptian δ 13 C event has received special attention as an important clue to the genesis of OAE 1a, but the exact amplitude of this relatively short lived δ 13 C variation is not precisely constrained, and this fact has been an obstacle in paleoenvironmental modeling. Particularly enigmatic is the large amplitude, by −7‰, in pelagic limestones at the central Pacific Deep Sea Drilling Project (DSDP) Site 463; it may be a primary δ 13 C signal, considering its deposition in a fully open-ocean setting and a conservative burial diagenetic environment. Nevertheless, new Sr isotope data help identify a peculiar diagenetic overprint on the lower Aptian interval of this site. While the majority of examined samples represent slightly shifted, but acceptable, 87 Sr/ 86 Sr ratios for marine carbonates of this age, markedly unradiogenic 87 Sr/ 86 Sr ratios are recorded within and just below the Selli Level–equivalent interval. In particular, extremely unradiogenic 87 Sr/ 86 Sr ratios (0.70623–0.70642) are detected at exactly the same interval as the most negative δ 13 C values and a smectite-rich lithology. It is therefore proposed that hitherto unknown diagenetic process, or processes, under peculiar interstitial-water geochemistry, resulting from volcanic ash alteration, played a role for the paired δ 13 C- 87 Sr/ 86 Sr anomaly at DSDP Site 463. By removing the δ 13 C data from samples that possess the highly unradiogenic 87 Sr/ 86 Sr ratios, the amplitude of early Aptian negative δ 13 C excursion is reevaluated to be −2.7‰ or −3.3‰, facilitating comparison with published δ 13 C records from other sections. The refined Site 463 δ 13 C profile further implies that the early Aptian negative δ 13 C event is better described as a twin excursion.