Temperature Changes and Biota Evolution in the Cenomanian–Turonian Shallow-Water Carbonates of the Friuli Carbonate Platform: Is There a Link?

Temperature reconstructions, derived from several proxies (TEX86, δ18O), and climate modeling suggest the Late Cretaceous was one of the warmest periods in Earth history Following the trend of temperature rise straggling the Cenomanian–Turonian boundary (CTB), the highest oceans temperatures of the Cretaceous were reached in the Early Turonian when sea surface temperatures reached over 35°C in low and mid latitudes. This warming phase was followed by a general cooling, although punctuated by short-term hot snaps, which lasted until the Campanian.

Paleotemperature and paleoenvironmental changes are well documented from deep-water carbonate deposits by variations in geochemical proxies and distribution patterns of macro- and microfauna. However, climatic and environmental fluctuations had severe impacts on carbonate platforms biota. Paleontological data show major changes within the main carbonate platform producers during the early Late Cretaceous: rudists and benthic foraminifera. Both groups experienced major taxonomic turnovers at the CTB that were followed by a further reradiation in the middle/late Turonian. However, the lack, to date, of detailed paleoclimatic reconstructions in shallow water carbonate succession hampers the possibility of investigating a possible causal relationship between temperature changes and faunal evolution.

In the present study, integrated geochemical, sedimentological, and paleontological data from the Adriatic Carbonate Platform (Friuli; north-east Italy) are presented. Biostratigraphy and isotope stratigraphy were used to precisely constrain the stratigraphy of the late Cenomanian-middle Turonian interval. δ18O analyses on both well-preserved rudist shells and bulk rock samples were used to “build” high-resolution paleotemperature curves. Our results suggest that the temperatures rose across the CTB and reached the warmest peak, during the Early Turonian with water surface paleotemperatures as high as 41 to 45°C. Benthic foraminifera and rudists evolution followed paleotemperature fluctuations hence suggesting that their demise in the Upper Cenomanian and reoccurrence in the Turonian strata was strongly modulated by temperature changes.