PERI-TETHYAN NERITIC CARBONATE AREAS: DISTRIBUTION THROUGH TIME AND DRIVING FACTORS

Abstract

Neritic carbonates (NC) were one of the most prominent facies of the Peri-Tethyan domain. From the Moscovian to the end of Tertiary times, most parts of the area concerned were included in, or in the vicinity of, the intertropical domain, favourable to the deposition of NC. These optimal latitudinal conditions were strengthened by warm surface currents which globally ran from east westward in this part of the Tethyan realm. The settlement of NC was enhanced by the existence of huge shallow marine platforms on the southern and northern Peri-Tethyan margins and on isolated oceanic highs as well. Peri-Tethys atlas maps, explanatory notes and validation points have provided data on the main biological, sedimentological, geographical, and environmental features of NC. Areas covered by NC have been calculated from 20 maps encompassing the Moscovian to the Piacenzian/Gelasian, using an Image Analysis Optilab system. The latitudinal distribution and the total area covered by NC for each time slice have been plotted with reference to global factors driving the carbonate factory. Variations of areas through time have been analysed and discussed with respect to regional palaeogeographic conditions. Global factors driving the NC sedimentation in Peri-Tethyan areas have been successively examined. The dominant skeletal and non-skeletal mineralogy on carbonate deposition has been evaluated. Photozoan organisms have been dominant contributors; however, deposition of temperate Heterozoan carbonates in northern latitudes occurred during Artinskian, Wordian, Maastrichtian and Tertiary times. Adverse conditions of siliciclastic inputs on carbonate deposition settled at certain periods but many Peri-Tethyan NC areas faced without damage terrigenous belts. Sea level highstands generally allowed wide NC areas to form, but certain time intervals had about the same amount of area covered by NC, despite opposite - low vs high - eustatic stillstand. Latitudinal enlargement of NC areas was enhanced during Mesozoic and Early Cainozoic greenhouse regimes, while a latitudinal constriction occurred during Artinskian, Wordian and late Tertiary times, in relation to an icehouse mode. During early Jurassic, middle Cretaceous and early Tertiary times, ocean circulation seems to have controlled latitudinal shifts of the NC areas. Abrupt increases or reductions of areas covered by NC coincided with the onset of atmospheric-controlling magmatic events or of sudden oceanic events with climatic implications.