A PALYNOLOGICAL ANALYSIS OF THE MCNAIRY SAND MEMBER IN NORTHERN MISSISSIPPI

Exposures of the McNairy Sand Member (Maestrichtian) of the Upper Cretaceous Ripley Formation crop out in northern Tippah and Alcorn Counties, Mississippi. The McNairy extends northward from Mississippi into western Tennessee, southwestern Kentucky and southeastern Missouri, where it is assigned a formational ranking. Its lithology consists of fine-to-coarse-grained, cross-bedded sand that weathers to a yellow or reddish-brown. The middle of the McNairy section consists of up to thirty feet of interbedded gray, black, or brown, organic, micaceous clay that contains well-preserved, diverse, and abundant palynomorphs. In this study, five samples were collected from a 30-foot road-cut exposure along U.S. Highway 72, in the northern half of sec 10, T2S, R5E (Alcorn County, Mississippi). Two additional samples were collected from road-cut exposures in adjacent Tippah County. Palynological results suggest that the middle McNairy clay section was deposited in a warm-temperate to subtropical climate. Samples obtained from the lower part of the clay section were probably deposited in a reducing, poorly-drained coastal marsh / swamp that bordered the McNairy delta. As many as 54 species have been identified from one sample. Common palynomorphs include dinoflagellate cysts of Cerodinium, Cleistosphaeridium, and Exochosphaeridium, trilete spores of Camarozonosporites, Cicatricosisporites, Gleicheniidites, Hamulatisporis, Klukisporites, monolete fern spores of Laevigatosporites, and gymnosperm pollen of Araucariacites, Pityosporites, and Taxodiaceaepollenites. Normapolles pollen represents a dominant angiosperm component. Genera of Normapolles include Complexipollis, Emscheripollis, Minorpollis, Plicapollis, Pompeckjoidaepollenites, and Pseudovacuopollis. Other common angiosperm genera include Momipites, Casuarinidites, Margocolporites and Proteacidites. Dense plant growth and anoxic conditions were partly responsible for the generic richness and diversity in this sample. Dinoflagellates were possibly transported inland by storm waves and high tides along the deltaic coastline. Fresh-water zygote cysts of Spirogyra are rare and are attributed to transport by rivers debauching into coastal marshes/swamps.