Early Cenomanian “hot greenhouse” revealed by oxygen isotope record of exceptionally well‐preserved foraminifera from Tanzania

Abstract

The search into Earth's mid‐Cretaceous greenhouse conditions has recently been stimulated by the Tanzania Drilling Project (TDP) which has recovered exceptionally well‐preserved biogenic carbonates from subsurface pre‐Neogene marine sediments in the eastern margin of central Africa. Published Tanzanian oxygen isotope records measured on exquisitely preserved foraminiferal tests, dating to as old as ~93 Ma, provided evidence for a Turonian “hot greenhouse” with very high and stable water‐column temperatures. We have generated a comparable data set of exceptionally well‐preserved foraminifera from a lower Cenomanian interval of TDP Site 24 spanning 99.9–95.9 Ma (planktonic foraminiferal Thalmanninella globotruncanoides Zone; nannofossil Corollithion kennedyi to Lithraphidites eccentricus Zones), thereby extending the age coverage of the Tanzanian foraminiferal δ18O record back by ~7 million years. Throughout the interval analyzed, the new foraminiferal δ18O data are consistently around −4.3‰ for surface‐dwelling planktonic taxa and −1.9‰ for benthic Lenticulina spp., which translate to conservative paleotemperature estimates of >31°C at the surface and >17°C at the sea floor (upper bathyal depths). Considering the ~40°S Cenomanian paleolatitude of TDP Site 24, these estimates are higher than computer simulation results for accepted “normal” greenhouse conditions (those with up to 4X preindustrial pCO2 level) and suggest that the climate mode of the early Cenomanian was very similar to the Turonian hot greenhouse. Taking account of other comparable data sources from different regions, the hot greenhouse mode within the normal mid‐Cretaceous greenhouse may have begun by the latest Albian, but the precise timing of the critical transition remains uncertain.

Calcareous nannoplankton proxies for palaeoenvironmental reconstruction of the Albian–Cenomanian succession in North-western Israel (Mount Carmel Region)

“…globotruncanoides (depth 132.50 m); this pattern of successive FOs of Th. globotruncanoides and C. kennedyi has been documented elsewhere (e.g., Robaszynski et al, 1993;Watkins et al, 2005;Ando et al, 2015).…”

“…Subzones UC0a and UC0b cannot be recognised in the present section because of the absence of the stratigraphically important marker Hayesites albiensis, the LO of which defines the top of the kennedyi is generally used for demarcating the basal Cenomanian (Ando et al, 2015). This level is slightly above the FA of Th.…”

“…The Early to Late Cretaceous transition was a time of global warming, when the Earth's climate was in an extreme greenhouse mode (e.g., Huber et al, 2002;Jenkyns, 2003Jenkyns, , 2010Hay, 2008;Ando et al, 2015;O'Brien et al, 2017). The northern and southern continents were separated by a wide eastern Tethys and narrow western Tethys and the Atlantic oceans.…”

Correlation of Turonian continental margin and deep-sea sequences in the subtropical Indian Ocean sediments by integrated planktonic foraminiferal and calcareous nannofossil biostratigraphy

“…Samples are tentatively assigned to the W. archaeocretacea Zone at sites 24, 26, 30, and 36 because of the extreme rarity of H. helvetica Zone in its lowermost range (Huber and Petrizzo 2016). Absence of markers for the stratigraphic interval spanning all of calcareous nannofossil Zone CC10 and from the planktonic foraminiferal Thalmanninella reicheli through the W. archaeocretacea Zone (Ando et al 2015) demonstrates that at least 2.7 m.y. of the upper Cenomanian-lower Turonian sediment record is missing at all sampled locations between Dar es Salaam and Lindi Village.…”

“…As at Site 31, no species extinctions or LOs were recorded within the H. helvetica Zone at any of the four sites.At both sites the youngest sediments are tentatively assigned to the lower Turonian W. archaeocretacea Zone (~4 m thick), due to the absence of H. helvetica, and the underlying sediments are assigned to the lower-middle Cenomanian Thalmanninella globotruncano ides Zone, due to the absence of the nominate taxa for the Th. reicheli and Rotalipora cushmani Zones (seeAndo et al 2015).…”