Basalt geochemistry shows that, in nearly all of the basins that contain basaltic lava flows, the oldest basalt-flow unit has the same chemical signature known as HTQ (high-titanium quartz-normative basalt). HFQ=high-iron quartz-normative basalt; LTQ=low-titanium quartz-normative basalt; HFTQ=high-iron & high-titanium quartz-normative basalt.  Olsen et al. (1996) determined that the three lava flow units in the Newark basin were erupted in ~600,000 years. From Schlische et al. (2002).