Mooreville Chalk--Upper Cretaceous Sediment Facies and Sea Level Cycles, West-Central Alabama

Jerry A. Wylie, D. T. King

The Mooreville Chalk is composed of open-marine sediments containing a significant amount of fine-grained clastics. The main lithology is a "chalk" according to most workers; however, various lithologic types are present with marl being dominant. In the hemipelagic classification, a marl contains 30-70% calcium carbonate.

Five facies have been delineated through detailed analysis of outcrops and subsurface samples. In stratigraphic order, these facies are: (1) bioturbated glauconitic sandstones and silty calcareous muds (inner shelf), (2) light olive-gray bioturbated marl and calcareous mud (open shelf, below storm wave base), (3) dark olive-gray laminated marl and calcareous mud (open shelf, well below storm wave base), (4) tan calcareous siltstones and sandstones, and sandy calcareous muds (open shelf, above storm wave base), and (5) tan silty calcareous muds and silty marls (open shelf, at storm wave base).

The main depositional setting was a poorly oxygenated middle shelf environment, primarily below storm wave base. This interpretation is based on the absence of storm wave features known to exist in shallower water marls, the presence of small-scale laminae, the abundance of finely divided FeS₂, and the general dark color of the sediments.

A relative sea level curve for the early Campanian shows two main cycles of relative sea level rise and fall. These two cycles do not compare well with the cycles reported from coeval facies of the Western Interior seaway and northern Europe. This unfavorable comparison suggests a different, local sea level history for the northeastern gulf rim.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.