LARGE-SCALE TEPHRA FALL (L-STF) HAS CAUSED SEDIMENTS FROM EARTH'S PAST "GREENHOUSE" TIMES TO NOT BE REPRESENTATIVE OF THE FUTURE EFFECTS OF ANTHROPOGENIC GLOBAL WARMING

Among greenhouse times suggested as analogous to anthropogenic global warming are the early Eocene and the Cretaceous Oceanic Anoxic Events (OAEs). A new perspective from available data suggests that volcanogenic minerals from Large Igneous Provinces (LIPs) and arc volcanism represent an underappreciated challenge to assessment of past climate at those times. Anthropogenic global warming will not include the L-STF necessary to create black shales. Authigenic sedimentary minerals of U, V, and Mo in black shales are largely diagenetic alteration products of volcaniclastics and inconsistent with the criteria of Tribovillard et al. (2006) that they be “hydrogenous” in order to reflect the paleoxygenation levels of past water columns.

Redistribution of altered volcanogenic minerals rather than “climate-induced enhanced continental weathering” contributed siliciclastic influxes into sedimentary basins at times of past global warming. In the early Eocene, the North Atlantic Igneous Province sourced 23 ash layers 1900 kms. distant in the Alps and included one of the largest basaltic explosions in earth history. Eocene ash sources in North America included the Absaroka, Challis, Chilcotin, and other volcanic complexes. The Wyoming Geological Survey describes the Eocene Green River (GR) formation as containing plentiful volcanogenic zeolites along with earth’s largest trona deposit, also an alteration product of ash. Huge volumes of the volcanogenic siliciclastics from the western interior seaway combined with siliciclastics eroded from the GR and Eocene Willwood formation equivalents contributed a clastic influx into the Gulf of Mexico Basin that formed the Paleocene-Eocene Wilcox Formation.

The Cretaceous Eagle Ford in Texas was deposited across OAEII and has 300 recognized layers of ash contributed by arc volcanoes in Mexico and volcanoes in the Balcones Igneous Province. Frebourg et al. (2016) attributed the organic enrichment and the lithologic variability of the Eagle Ford to ash-derived minerals and not to climate or sea-level driven factors. The south Texas shelf margin was inundated by siliciclastics at least four times during Cretaceous OAEs not because of sea level changes, but because of direct eolian input of volcanic tephra and its re-sedimentation from the upstream drainage basin.