BAGHAI-RIDING, NINA L.1* and CHARLES T. SWANN2. 1Department of Biological and Environmental Sciences, Delta State University, Cleveland, Mississippi 38733; 2Mississippi Mineral Resources Institute/ Center for Community Earthquake Preparedness, 220 Old Chemistry Building, University, MS 38677. - Palynological analysis of a McNairy Sand sample from Alcorn County, Mississippi.
Exposures of the Cretaceous McNairy Sand Member (Maastrichtian) of the
Ripley Formation extend from northern Mississippi, into western
Tennessee, southwestern Kentucky, and southeastern Missouri. In the
middle of the McNairy section in Alcorn County, Mississippi, are clay
beds composed of dark gray to black, organic, clay that contain a
flora of well-preserved, varied, and abundant palynomorphs. The
results of previous palynological research are known from various
localities throughout Tennessee and Kentucky but information is
lacking from Mississippi. A sample from a road cut along U.S. Highway
72, in the northern half of sec. 10, T2S, R5E in Mississippi helps to
fill this informational gap. The sample represents the up dip edge of
the McNairy (outcrop belt) and is indicative of a warm temperate to
subtropical, swamp-marsh, to lower delta plain environment that
experienced occasional flooding. A 200-point count analysis contained
14.5% dinoflagellates, 3% fungal spores, 33% trilete spores, 3.5%
monolete fern spores, 19.5% gymnosperms and 26.5% angiosperms.
Significant genera include trilete spores of Appendicisporites,
Camarozonosporites, Gleicheniidites,
Hamulatisporis, and Triporoletes, gymnosperms of
Alisporites, Rugubivesiculites, and
Araucariacites, and Normapolles pollen of
Complexipollis, Minorpollis, Emscheripollis,
Plicapollis, Pompeckjoidaepollenites, and
Pseudovacuopollis. Other palynological debris include
freshwater algae cysts of Spirogyra, dispersed angiosperm
cuticles, wood fragments, and resin droplets. Several palynomorphs
including the dinoflagellates Cerodinium diebelii, and
Exochosphaeridium bifidum and Normapolles pollen of
Plicapollis usitatus and Pseudovacuopollis involutus,
pinpoint a Maastrictian age for the McNairy Sand Member. This sample,
however, contains trilete spores of Aequitriradites verrucosus,
Appendicisporites triachanthus and Murospora whose
geologic range are not commonly extended to include the Maastrichtian.
Other pollen, including Nyssapollenites cf. bindae,
Rhoipites cryptoporus and Margocolporites cribellatus
are typically associated with the Danian (Paleocene) section,
suggesting an extension of their geologic range into the older
Cretaceous section.
Key words: Maastrichtian, McNairy Sand, Normapolles, palynomorphs