Vegetation-Climate Interactions Drive Sedimentologic Evolution through the Phanerozoic

C.M. Fraticelli, K.M. Bohacs, and B.P. West
ExxonMobil Upstream Research, Houston, TX

Modern environmental distributions reflect strong feedbacks among vegetation communities, precipitation, and temperature. These feedbacks are robust enough to dry out tropical rainforests, green deserts, and warm high latitudes. Viewing vegetation as purely reactionary means overlooking how changes in this key Earth system component may impact, or even cause, the very effects we study. Through feedback mechanisms, plants deliberately modify their habitat to create a more hospitable environment. For this reason, climate models based on patterns prevalent in the modern sometimes cannot replicate ancient patterns without evoking other causes for discrepancies (i.e hydrologic restrictions, massive monsoon systems). In this, as in many other things, the present and the past are not interchangeable. Rather than solely a consequence of climate change, vegetation augments broader trends initiated by tectonics or orbital parameters and therefore, the geographic evolution of plants can have an even greater impact on the sedimentary record than morphologic changes.

The concept of fluvial changes forced by plant evolution is not new. Schumm (1958) postulated a worldwide decrease in sediment yield through time tied to plant evolution, speculating that expanding vegetation intensified fine-grained sediment generation and increased sediment stability. The addition of vegetation-climate feedback concepts, to explain changes in moisture and associated patterns, to the original concepts of Schumm allows time intervals across which specific transformations take place, based on the evolution of plants into environmental niches, to be identified and permits speculation on how and when during the Phanerozoic certain fluvial characteristics became prominent. The model presented here describes a broad, first- or second- order pattern through the Phanerozoic caused by the evolution of climate-land plant interactions, and reflected in climate and fluvial patterns.