Biogeochemical Perturbations

A schematic representation of the major inputs and feedbacks involved in the development of organic carbon enriched fine-grained facies is shown in Figure 1 (from Sageman and Lyons, 2003). These inputs include terrigenous material, such as sediments derived from weathering of continental crust, or inputs from volcanic sources, biogenic processes (both organic matter and mineralized microskeletal products of primary photosynthetic production, on land and in the sea), and authigenic material precipitated at or near the sediment-water interface as a consequence of Eh-pH-controlled organic and inorganic reactions. The synthesis in Figure 1 integrates physical (sedimentologic and oceanographic) and biogeochemical processes, relates major inputs to proximate and broader paleoenvironmental controls, illustrates important linkages between causes and effects in the model (i.e., feedbacks), and lastly, identifies and tracks key components of the major biogeochemical cycles (C, O, S, N, and P) involved in regulating conditions at the Earth’s surface. Climate and plate tectonics are the master controlling factors for the components represented in Fig. 1. Climate includes a complex set of phenomena (temperature, evaporation, precipitation, and wind) and interactions among the atmosphere, land surface, ocean surface, biosphere, and cryosphere that are driven largely by variations in the amount and distribution of incoming solar radiation. Tectonic processes, by contrast, can be simplified to two parameters. These are vertical uplift, which creates crustal source areas for weathering and erosion, and subsidence, which together with eustasy, acts to control the accommodation space available for accumulation of sediments.

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