ABSTRACT

The LaSalle Arch is a southerly trending anticline in north-central Louisiana. The northern end of the Arch separates the Louisiana and Mississippi interior salt basins. The structural trend of the arch is supported by relict paleo-highs. The paleo-high beneath the Nebo-Hemphill Field, as seen on reflection seismic data, is the nose of an Ouachitan thrust fault which was partially rifted during the opening of the Gulf of Mexico. The western limb of the Arch formed by differential subsidence expanding the stratigraphic section toward the southwest. The eastern limb of the Arch formed by regional tilting to the east after deposition of the Claibornian Sparta Formation. Late Cretaceous uplift of the LaSalle Arch is seen as a truncational unconformity within the Tayloran Demopolis Formation.

The Wilcox and Midway groups of central Louisiana have been subdivided into three genetic sequences which were bounded above and below by regionally correlatable flooding surfaces. They are T₁ (the Midway), T₂ (the Holly Springs), and T₃ (the Carrizo). This sequence stratigraphic framework correlates with other studies in the type section in Alabama.

The highstand systems tract of T₁ and T₃ were deposited during a relative sea level fall resulting in similar homogenous wave dominated deltaic morphologies and electrofacies. Channel facies within T₁ and T₃ lie over the rift graben and thin over the thrust fault nose. This indicates subsidence played a key role in the location of depositional environments within T₁ and T₃, but did not prevent progradation to the southwest. The structural trend of the LaSalle Arch was unmodified during T₁ and T₃. The highstand systems tract of T₂ was deposited during a relative sea level rise resulting in heterogenous fluvial dominated deltaic morphologies and electrofacies capped by a meandering channel system. The structural trend of the LaSalle Arch was highly modified during the T₂ highstand systems tract. Channel facies are not controlled by the rift graben or thrust fault nose indicating subsidence did not play an important role in the location of depositional environments within T₂.