SEQUENCE STRATIGRAPHIC ANALYSIS OF THE EVAN’S FERRY ROAD CUT, TN: A NEW PROSPECTIVE FOR LATE ORDOVICIAN (SANDBIAN) SEA LEVEL FROM THE APPALACHIAN BASIN

A megasequence boundary (Sauk-Tippecanoe) occurs within the Middle Ordovician strata in North America that represents a global sea level lowstand followed by renewed transgression and sea levels reaching a Paleozoic apex in the Late Ordovician. There are few areas globally that record continuous sedimentation through this transition in eustatic sea level which also coincides with ongoing biodiversification in marine faunas worldwide. The Evan’s Ferry section of northeastern Tennessee provides a unique prospective for Upper Ordovician sea level reconstruction as this section contains one of the most expanded latest Darriwilian- Sanbian sequences in North America. The carbonate-dominated strata from Evan’s Ferry were deposited within the Appalachian Foreland Basin, during the Taconic Orogeny. This section, containing six formations, deposited under a wide variety of conditions, as recognized by lithofacies analysis and lower order stratigraphic stacking patterns. Meter to decimeter scale sequence stratigraphic analysis suggest four third order depositional sequences are present within the Evan’s Ferry section. Ideally, each third order sequence begins and ends at a Lowstand Systems Track (LST), however, many Falling Stand Systems Track (FSST) and LST are either missing at sequence boundaries or covered.

Accompanied with the sequence stratigraphic analysis, stable isotopic analysis of carbon and oxygen were used aid in the identification of sequence boundaries/exposure surfaces. When exposed to meteoric diagenesis, δ¹³C_carb and δ¹⁸O_carb signatures show a significant lightening in their isotopic values. Several lower order exposure surfaces, especially in LST show correlation between exposure surfaces and geochemical signatures of meteoric influences, however transgressive and highstand systems tracks (TST and HST, respectively) show little to no correlation between parasequence or sequence boundaries and isotopic signatures. This study’s pairing sequence stratigraphy and chemostratigraphy in the Appalachian Basin show how changes in eustatic sea level and local accommodation space may have produced environments that were ideal for the continued intense biodiversification seen throughout this time during the Ordovician.