Paleoclimate and the origin of two 1000 km Lower Mississippian facies tracts in southeastern Laurentia (USA): Cool-humid Famennian and Kinderhookian – warm-arid Osagean

Abstract

Two lithologically distinctive Mississippian facies tracts (MFTs) are described from Lower and Middle Mississippian strata (Kinderhookian and Osagean North American Stages) in southeast Laurentia (SEL). The MFTs extend from the central Appalachian Basin westward across the Cincinnati Arch, through the Eastern (Illinois) Basin, onto the Burlington shelf in central Missouri and into the Western Interior (Forest City) Basin, USA. The MFTs developed under radically different climatic regimes. Kinderhookian climate cycles ranged from 3rd order humid to 4th and 5th order humid-subhumid alternation. These climate fluctuations controlled Kinderhookian sediment flux, evidenced by fluvial-deltaic sandstones, coal beds, and pro-deltaic terrestrial-organic-matter-enriched marine black shales. A dramatic climate shift coincided with the Kinderhook-Osage boundary, from 3rd order cool-humid to 3rd order warm-arid conditions, causing cessation of deltaic sedimentation and the onset of eolian sedimentation at that boundary. This abrupt climate reorganization is reflected in 3rd, 4th, and 5th order continental and eolo-marine loessites that replaced fluvial-deltaic facies. Eolianites, evaporites, and calcareous protosols indicate Osagean aridity. Consequently, we reject the deltaic depositional paradigm for Osagean siliciclastic facies. Osagean eolian sediment consisted mainly of quartz silt with significant pristine (unaltered) feldspar silt (∼ ≤ 10%). Pristine feldspars are consistent with an arid sedimentary source that lacked significant chemical weathering under an arid paleoclimate. Dissolution of the chemically reactive disordered lattice of eolian-abraded quartz in subarkosic loess served as the predominant source of silica for massive amounts of biotic and abiotic chert in Osagean eolo-marine sediments. The ≤20 μm fraction of quartz dust is particularly susceptible to dissolution and re-precipitation as microcrystalline quartz (chert). We conclude that tectonic, eustatic, and climatic (allocyclic) processes all exerted some control on deposition; tectonics and eustasy controlled accommodation space, whereas paleoclimate changes (cycles), driven predominantly by orbital forcing, were the principal control on sediment supply and lithostratigraphy.