We present a global synthesis of the evolution of the climate/ocean system from the late Campanian at approximately 75 Ma to the end of the Maastrichtian at 65 Ma. This study is based on published and new oxygen and carbon isotope data of benthic and planktic foraminifera from a number of deep-sea sites, spanning the high to the low latitudes. Most of the sites were at depths that in the modern oceans are bathed by intermediate-water masses. The δ 18 O records of planktic and benthic foraminifera from most locations indicate that surface and intermediate waters cooled during the period 75 to 65.5 Ma, particularly at high latitudes. Model surface-water temperatures, based on δ 18 O values averaged for 1-m.y. intervals at each of the sites and corrected for the latitudinal variation of seawater δ 18 O using the present seawater latitudinal δ 18 O variation, indicate that the latitudinal thermal gradient increased from 10 to 13°C. Superimposed on the long-term trend there were two episodes during which, on a global scale, benthic foraminiferal δ 18 O values increased substantially, and then decreased. The first episode occurred between 71 and 69.5 Ma; the second began between 68 and 67.5 Ma, and terminated at about 65.5 Ma. During the first episode, the thermohaline circulation changed, and cool intermediate depth waters derived from high-latitude regions penetrated temporarily to the tropics, resulting in tropical Pacific intermediate waters becoming cooler than those in the high southern latitudes. Benthic foraminiferal δ 13 C values suggest that these cool waters may have been derived from high northern latitudes. The level of the carbonate compensation depth (CCD) shallowed substantially in the Pacific, Indian, and South Atlantic basins, although surface-water productivity may have increased during the time of altered thermohaline circulation. At the same time, the CCD deepened in the North Atlantic, where deep waters were warm and salty, and formed locally. From 67.5 to 65.5 Ma, intermediate waters in the southern high latitudes were cooler than those in other basins, indicating that the thermohaline circulation operated on a mode more similar to the present circulation. Both episodes of cooler intermediate water can be correlated with eustatic sea-level curves, suggesting that sea level was the most likely mechanism to change the circulation and/or source(s) of intermediate-deep waters. At 65.5 Ma, surface and intermediate waters warmed globally by about 3-4°C, and then cooled slightly at about 65.1 Ma. We suggest this increase in marine temperatures correlates with the timing of the main episode of Deccan Trap flood basalt eruptions and may have been caused by greenhouse global warming.
High-resolution stratigraphy of the Cenomanian-Turonian boundary interval at Pueblo (USA) and wadi Bahloul (Tunisia):stable isotope and bio-events correlation Stratigraphie à haute résolution de la limite Cénomanien-Turonien sur les coupes de Pueblo (États-Unis) et de l'Oued Bahloul (Tunisie) :isotopes stables et corrélation des événements biologiques
The most important factor controlling the timing of Phanerozoic mineralogical evolution in the Bivalvia appears to be thermal potentiation of calcite deposition in colder marine and estuarine environments. Cold temperature has promoted mineralogical evolution in the Bivalvia by kinetically facilitating (potentiating) initially weak biological controls for calcite, thereby exposing their genetic basis to natural selection. Calcite has evolved in bivalve shells for a variety of selective advantages, including resistance to dissolution; resistance to chemical boring by algae and gastropods; reduced shell density in swimming and soft-bottom reclining species; enhanced flexibility in simple prismatic shell layers; and fracture localization and economy of secretion in association with certain foliated structures.Endogenous calcite in bivalve shells varies from biologically induced to weakly and strongly biologically controlled. Biologically controlled calcite generally first appears in bivalve shells as an impersistent component of the outer shell layer, only later, in some groups, expanding to include the entire outer and then part or all of the middle and inner shell layers. The initial stages of mineralogical evolution are shown by certain modern Mytilidae, Veneridae and Petricolidae. In the latter two families, the calcite occurs as conellae in the outer part of the outer shell layer. Calcitic conellae in the inner shell layer of Pliocene Mercenaria are not barnacle plates, as previously indicated, but endogenous calcite comparable in origin to other venerid conellae. Their occurrence in Mercenaria may reflect thermal potentiation of weak biological controls for calcite, as well as local detachment of the secretory mantle epithelium near the pallial and adductor musculature.
Figure 1. Paleogeography reconstruction at 70 Ma, showing location of deep-sea sites discussed in this study. Dark areas were above sea level, and areas defined by thin lines were blocks and terranes below sea level. South Atlantic and southwestern Indian Ocean waters may have been separated from southeastern Indian Ocean waters at intermediate depths by Kerguelen Plateau,
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