TECTONIC AND CLIMATIC CONTROL ON DEPOSITION OF SEEP-CARBONATES: THE CASE OF MIDDLE-LATE MIOCENE SALSOMAGGIORE RIDGE (NORTHERN APENNINES, ITALY)

摘要

Seep-carbonates are generally related to hydrocarbon seepage on continental margins. Modern cold seeps are abundant in actively deforming tectonic settings, suggesting that tectonics is one of the major controlling factor on fluid emissions. Hydrocarbon see-pages are considered major geological sources of atmospheric methane, one of the most important green-house gases, and have also been related to climate changes. However, the interplay between tectonics and climate change in forcing seepage is not clearly understood. Miocene seep-carbonates, formed in a collisional setting such as that of the Salsomaggiore area of the Northern Apennines (Italy), provide an opportunity to assess accumulation and release of methane in response to tectonics and climate change along a convergent margin. The studied seep-carbonates are related to fluid emissions of various intensities coeval with tectonic pulses. New planktonic foratniniferal biostratigraphic data reveals that deposition of these seep-carbonates is late Serravallian-early Tortonian in age and partially coeval with the Miller's global cooling event Mi 5 (as used below). These seep-carbonates were deposited in two stages with different seepage modes. During the first stage, local tectonic pulses at the onset of the Mi5 event may have produced slow seepage, whereas during the second stage regional tectonics and more extreme climatic conditions (coolest peak of Mi5 event) may have resulted in a fast and more intense seepage as suggested by increasing occurrence of chaotic facies. In the Salsomaggiore Ridge, tectonics and the Mi5 cooling event actively concurred to the deposition of seep-carbonates in both stages.