The Guadalupian mass extinction took place during the major global environmental changes during Phanerozoic time. Large-scale sea-level fluctuations and a negative shift of δ13C were associated with this crisis. However, the diagenetic or primary origin of the decreased δ13C across the Guadalupian–Lopingian (G–L) boundary and the potential causes for this biotic crisis are still being intensely debated. Integrated analyses, including detailed petrographic examination, identification of foraminifer and fusulinid genera, and analysis of carbonate δ13Ccarb and bulk δ13Corg across the G–L boundary were therefore carried out at Tianfengping, Hubei Province, South China. Our results show that: (1) some foraminifer and most fusulinid genera disappear in the upper Maokou Formation (upper Guadalupian); (2) the negative shift of δ13Ccarb in the uppermost Maokou Formation is of diagenetic origin, but the values of δ13Ccarb in the remainder of the Maokou Formation and in the Wuchiaping Formation represent a primary signal of coeval seawater; and (3) the bulk δ13Corg perturbation across the G–L boundary at Tianfengping is mainly controlled by organic matter (OM) source, that is, terrestrial OM contribution. We suggest that the δ13Ccarb negative shift in the lower Wuchiaping Formation (Wuchiapingian) compared to that in the lower–middle Maokou Formation (Capitanian) were probably caused by the re-oxidization of 12C-rich OM during regression. Global regression resulted in the negative shift of δ13Ccarb at the G–L boundary in South China and led to the loss of shallow-marine benthic habitat. Large-scale global regression is probably one of the main causes for this bio-crisis.

Abnormal test development in foraminifers is observed and environmental factors are suggested to be the main cause. Most of the abnormalities are aberrant test morphologies. In some cases twin, triplet and quadruplet formations are observed. The twins may sometimes be formed by two different species. In the framework of this study, foraminifer fauna of a submarine spring (Pamucak Cove, north-western Kuşadası, Aydın) was determined. A rich population of Amphistegina lobifera Larsen was found. Individuals with abnormal morphologies were also observed, but the most striking abnormality was the togetherness observed between two different families, Vertebralina striata d'Orbigny (Ficherinidae: Nodobacularinellinae) and Coscinospira hemprichii Ehrenberg (Peneroplidae).

Sea surface temperature (SST) estimates using the δ18O composition of fossil planktonic foraminifer calcite, within the time slice 3.12 to 3.05 Ma (Pliocene, Kaena Subchron – C2An1r) are assessed for nine Atlantic Ocean sites. These are compared with SST estimates from fossil assemblages for the ‘Time Slab’ 3.29–2.97 Ma and with estimates from a fully coupled ocean–atmosphere General Circulation Model (GCM) for the same time interval. Most SST estimates derived from the δ18O data indicate a cooler ocean surface than at present, through the latitudinal range 69.25° N to 46.88° S. At some sites the temperature difference is greater than 5 °C (cooler than at present). This contrasts with SST estimates from fossil assemblages that give warmer than present temperatures at mid- to high latitudes, and similar temperatures in the tropics, and with the GCM, which predicts SSTs warmer than at present across all latitudes for this time interval. Difficulties interpreting the ecology of fossil foraminifer assemblages and inaccurate estimates of mid-Pliocene seawater δ18O composition (δ18Osw) at some sites may partly produce the temperature discrepancy between isotope-based and fossil-based SST estimates, but do not adequately explain the cool signal of the former. We interpret the cool SST estimates from the δ18O data to be the product of: (a) calcite formed at a level deep within or below the ocean mixed-layer during the life-cycle of the foraminifera; (b) secondary calcite with higher δ18O formed in the planktonic foraminifer tests in sea bottom pore waters. Although these effects differ between sites, secular and temporal oceanographic trends are preserved in the primary calcite formed in the mixed-layer near the ocean surface, witnessed by the latitudinal variation in estimated SSTs. Reconstructing accurate mid-Pliocene SSTs with much of the existing published oxygen isotope data probably requires a detailed re-assessment of taphonomy, particularly at tropical sites. This study also indicates that methods for estimating Atlantic Pliocene δ18Osw need to be refined.