Abstract
Eight pollen and spore sequences from the high ash, high sulfur San Miguel lignite deposit indicate a Late Eocene, Jackson age. In general, the sequences follow a pattern, with high Nyssa kruschii and Rhoipites angustus percentages at the base, and high Cupuliferoipollenites sp. percentages at the top; the presence of Nyssa (tupelo) strongly suggests a freshwater swamp. Cluster and reciprocal averaging analysis reinforce these patterns, and suggest two vegetational-environmental gradients. One of these involves N. kruschii/R. angustus and Cupuliferoipollenites. The second involves these taxa in opposition to fern spores such as Laevigatosporites. It is not certain whether the gradients represent progressively shallower, deeper, or more saline environment. Similar palynomorph sequences were also recovered from the Momipites coryloides-dominated Late Eocene Lake Somerville lignites. The Lake Somerville lignites may represent a cyclic increase in depth and salinity, and the San Miguel lignites may have had an analogous depositional history. No strong correlation was found in the San Miguel lignites between ash, sulfur, and palynomorph content. Analysis of palynomorph samples from horizontal sequences indicates a great deal of lateral variability, but the use of reciprocal averaging and running averages show that vertical variability is greater and that, although the data is "noisy," vertical changes in palynomorph content are valid and meaningful.
Gennett, Judith Ann (1993). Palynology and paleoecology of the San Miguel lignite deposit of late eocene age, South Texas. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1505906.