EARLY MISSISSIPPIAN CLIMATE CHANGE AND ITS INFLUENCE ON SEDIMENT DISPERSAL IN THE MACCRADY FACIES TRACK IN SOUTHEAST LAURENTIA (EASTERN USA)

Changes in climate may greatly alter sedimentary systems, potentially impacting the generation, transportation, and deposition of sediment. Here, we present new detrital zircon U-Pb ages from an Early to Middle Mississippian (Tournaisian to Visean) facies tract in modern West Virginia, Kentucky, and Indiana to document the influence of a rapid climatic shift on sedimentary provenance. The Price Formation, a package of fluvial deltaic sandstones, siltstones, and shale, with minor amounts of coal preserves indicators of a cool, humid climate, such as chemically-reduced iron phases and thin kaolinitic paleosols. In contrast, redbeds, evaporites, and sedimentary structures within the overlying Maccrady Formation indicate an arid climate and loess deposits. Moving westward, the Maccrady transitions into the Grainger Formation and Borden Group, preserving a transition from continental to shallow marine deposition, all with a major contribution of wind-blown sediment.

We present detrital zircon age results from 8 samples from the Price Formation and the overlying units of the Maccrady Facies Tract. All age spectra display common features, such as dominance of a Grenville-age signal (~1000 to 1200 Ma) and a significant population of ~480 Ma grains, that point towards a common origin. However, differences in the age distribution of the Price Formation and the overlying units suggest that the climate-driven transition from fluvial to wind-blown sedimentation may have produced distinct provenances. Zircons from the Maccrady Facies Tract units are smaller and more rounded than those from the Price Formation. The facies tract units contain a lower proportion of ~480 Ma grains, fewer ~1180 Ma grains relative to ~1040 Ma grains in the Grenville signal, and a greater abundance of 530-760 Ma grains associated with peri-Gondwanan terranes. During the early Mississippian, North America was at a paleolatitude of 20-30°S. We hypothesize that the climatic shift enabled southeasterly trade winds to carry sediment from the internal parts of the orogen, dispersing material throughout the continental margin of the central Appalachian foreland basin and Eastern Interior basin and beyond.