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Recent Topics Posters

Baghai-Riding, Nina [1], Swann, Charles [2].

A palynological investigation of the McNairy Sand Member in northern Mississippi.

The Upper Cretaceous McNairy Member of the Ripley Formation crops out in Tippah, Alcorn, and Union Counties, Mississippi, and northward into Tennessee, Kentucky and Missouri where it has been assigned a formational ranking. The McNairy represents a regressive - transgressive cycle of sea-level change. The regressive portion of the cycle is portrayed in the lower McNairy section with the maximum regression occurring in the “middle clay beds”. In this study, seven samples for palynological analysis were collected from middle clay exposures. Five samples were obtained from a 30-foot, black to brown organic bed exposure in Alcorn County. Two other samples were collected from exposures in Tippah County. Palynomorphs recovered consist of marine and terrestrial elements and suggest that the southernmost extension of the McNairy was deposited in marginal marine delta swamps or on low alluvial plains. Assorted chorate and proximate dinoflagellate cysts, acritarchs, and inner linings of foraminifera were present in the one-foot interval suggesting an important marine influence. Terrestrial palynomorphs dominated other intervals, suggestive of regressive conditions, although a few dinoflagellate cysts and acritarchs occurred at higher stratigraphic intervals that may have been brought by strong waves or tides. Terrestrial plant groups include fungi, bryophytes, lycopods (Lycophyta), climbing ferns, Mesozoic seed ferns, gymnosperms (Coniferophyta, Cycadophyta, and Ginkgophyta) and angiosperms (Anthophyta). A total of 171 species in 113 genera were recorded from these samples. Dinoflagellates of Exochosphaeridium bifidum and angiosperm species of Holkopollenites chemardensis, Myricipites dubius, Plicapollis usitatus, Proteacidites retusus, Proteacidites thalmannii, Tricolpites micromunus, and Triporopollenites mullensis imply a Maastrichtian age.

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Related Links:
Geology of the Chalybeate Topographic Quadrangle, Tippah and Alcorn Counties, Mississippi

1 - Delta State University, Division of Biological & Physical Sciences, Cleveland, Mississippi, 38733, USA
2 - Mississippi Mineral Resources Institute, Center fro Community Earthquake Preparedness, 220 Old Chemistry Building, University, Mississippi, 38677, USA

McNairy Member
Ripley Formation

Presentation Type: Recent Topics Poster
Session: 33-117
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:673

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