Abstract The Paleocene/Eocene Thermal Maximum (PETM) is characterized by pronounced global warming and associated environmental changes. In the more-or-less two decades since prior regional syntheses of Apectodinium distribution at the PETM, extensive biological and geochemical datasets have elucidated the effect of rising world temperatures on climate and the biome. A Carbon Isotope Excursion (CIE) that marks the Paleocene/Eocene Boundary is associated with an acme of marine dinocysts of the genus Apectodinium in many locations. Distinctive foraminiferal and calcareous nannofossil populations may also be present. For this updated, dinocyst-oriented view of the PETM, data from worldwide locations have been evaluated with an emphasis on stratigraphic and sedimentological context. What has emerged is that a change in lithology is common, often to a distinctive siltstone or claystone unit, which contrasts with underlying and overlying lithotypes. This change, present in shallow marine/coastal settings and in deep-water turbidite deposits, is attributed to radical modifications of precipitation and erosional processes. An abrupt boundary carries the implication that some time (of unknowable duration) is potentially missing, which then requires caution in the interpretation of the pacing of events in relation to that boundary. In most instances an ‘abrupt’ or ‘rapid’ CIE onset can be attributed to a data gap at a hiatus, particularly in shallow shelf settings where transgression resulted from sea-level rise associated with the PETM. Truly gradational lower boundaries of the PETM interval are quite unusual and, if present, are poorly known so far. Gradational upper boundaries are more common, but erosional upper boundaries have been reported. Taxonomic changes have been made to clarify identification issues that have adversely impacted some biostratigraphic interpretations. Apectodinium hyperacanthum has been retained in Wetzeliella , its original genus. The majority of specimens previously assigned to Apectodinium hyperacanthum or Wetzeliella ( Apectodinium ) hyperacanthum have been reassigned to an informal species, Apectodinium sp. 1. Dracodinium astra has been retained in its original genus as Wetzeliella astra and is emended.

Abstract Post-Turonian (Late Cretaceous) rudist-bearing limestones of the Nurra region in northwestern Sardinia (northern Tethyan margin) and in the central-southern Apennines and Apulia (central Tethyan domain) have recorded relevant changes in the characteristics of the carbonate platforms following the “middle” Cretaceous crisis events which affected the peri-Tethyan region as well as other regions worldwide. Rudist bivalves became the dominant lithogenetic taxon owing to their proliferation in shallow-water environments and strong dominance of Late Cretaceous carbonate factories. Their inception, evolution, and demise were seemingly controlled by a complex interplay of environmental processes that, acting on a global scale, profoundly modified the Early Cretaceous hydrosphere-atmosphere system and forced Tethyan depositional systems to change their organization, internal architecture, and facies patterns. As a result, wide, open shelves developed where the almost ubiquitous mode of carbonate fixation was that of foramol factories. In this paper, evidence of the remarkable regional variability in the rudist-bearing carbonate platforms of the Mediterranean Tethys is presented. The analysis of the resulting shallow-water facies has demonstrated that, in spite of several stratigraphic similarities and common sedimentological features, some remarkable differences occurred between the northern Tethyan margin and the central Tethyan banks as regards the areal partitioning of the main paleoecologic controlling factors. This resulted in the deposition of rhodalgal successions in Sardinia (northern Tethyan margin) and rudist-rich foramol facies in the Apennine-Apulia (central Tethys) regions, respectively. Such Late Cretaceous carbonate systems can be viewed as geological products which have closely and coherently recorded the globally changing environmental conditions of the oceanic realm. In spite of this, the difference of the facies partitioning in different Tethyan regions according to a latitudinal gradient is interpreted as derived mainly from local variable paleoceanographic and paleoclimatic conditions.