Abstract:

 The midCretaceous (~12588 Ma) is characterized by a remarkable increase of global organic matter (OM) accumulations—the significant source rock of many large oil fields in most oceanic basins. Based on the previous discussion about geological setting and major controlling factors on the marine organic carbonrich accumulation, this paper proposes that both high primary productivity (PP) and oceanic anoxic events (OAE) controlled the wide distribution of marine organic carbonrich sediments in the midCretaceous. In fact, OAE not only sped up the extinction and the replacement of marine life, causing  huge amounts of OM accumulation, but also promoted the regeneration of nutrients (e.g. P, N, Fe) and the flourish of anaerobic autotrophic microorganisms (e.g. green sulfur bacteria, cyanobacteria, archaea) as well. The high PP in turn exacerbated the oceanic anoxia. During that period, the Cretaceous large igneous events triggered the sustaining greenhouse climate and abnormal oceanic environments together with euxinic conditions, confusion currents and weak upwelling, which led to the improved productivity and OAE, and eventually, caused the extensive accumulation of organic matter.

Key words: Key words: marine organic carbonrich sediments; Oceanic Anoxic Events (OAEs); paleooceanic productivity; midCretaceous