CHRONOSTRATIGRAPHY OF THE LATE EDIACARAN - EARLY CAMBRIAN CHILHOWEE CLASTIC SUCCESSION OF SOUTHERN LAURENTIA: REDUX WITH REFINEMENT

Based on new trace and body fossil discoveries and reassessment of previously described material, and succession deposition environments tied with regional and global events, the late Neoproterozoic to early Cambrian clastic sediments from Alabama to Pennsylvania (Chilhowee Group) can be placed in the context of the global geologic time scale (ICS v2015/01). Formation names for equivalent units are presented here as central/southern/northern Appalachians. Acknowledging some regional diachronism of depositional events, best estimates for chronostratigraphic boundaries (bases from old to young) are, Cambrian (Fortunian, 541.0 Ma) positioned in the upper Unicoi/Cochran/Weverton Fm., upper part of medial-distal braidplain facies and below fully marine quartz arenite facies; Cambrian Stage 2 (529.0 Ma) in the lower Hampton/Nichols/Harpers Fm, upper part of outer shelf facies or lower part of middle shelf facies; Cambrian Stage 3 (521.0 Ma) near the base of the Nebo/Erwin/Antietam Fm.; Cambrian Stage 4 (514.0 Ma), in the Helenmode/upper Erwin/upper Antietam Fm, or the lower part of the Shady/Tomstown Dolomite.

Extrapolating from constrained dates and relative positions, key lithostratigraphic events (base of facies/unit) from old to young are: Unicoi/Cochran/Weverton Fm. ca. 553±5 Ma; amygdaloidal basalts of the middle-Unicoi, ca. 547 Ma; first fully marine deposits, upper-Unicoi, ca. 540 Ma. Hampton/Nichols/Harpers Fm., middle Fortunian, ca. 533 Ma. Cambrian Agronomic Revolution, middle Hampton/Nichols/Harpers Fm., middle Cambrian Stage 2, ca. 526 Ma. Nebo/Erwin/Antietam Fm. near base of Cambrian Stage 3, ca. 521 Ma; Murray/lower-mid Erwin/lower mid-Antietam Fm., lower-mid of Cambrian Stage 3, ca. 518 Ma; Hess/mid-upper Erwin/mid-upper Antietam Fm., upper-middle Cambrian Stage 3, ca. 517 Ma; Helenmode/upper Erwin/upper Antietam Fm., lower-mid of Cambrian Stage 3, ca. 516 Ma; Shady/Tomstown Dolomite. upper Cambrian Stage 3, ca. 514 Ma.

This chronostratigraphic framework allows for higher-resolution, global correlation of macroevolutionary and geologic events observed in southern Laurentia during the late Ediacaran to early Cambrian transition.