Alabama Paleontology

ABSTRACT—During her three decades with the Geological Survey of Alabama from 1931 to 1961, Winnie McGlamery (1887–1977) was a key figure in Alabama paleontology and oil and gas exploration. She was a diminutive but feisty woman who arguably did more for the discovery of oil and gas fields than any other state employee during that time, for she logged the cores and cuttings of nearly every permitted well for the Survey’s public files.
McGlamery was trained in paleontology at the Johns Hopkins University at a time when few women scientists worked in the field, though microscope work was tolerated. “Miss Winnie” spent much of her career studying Foraminifera, especially after the first successful Alabama oil fields were brought in (notably, the Gilbertown field in 1944 and the Citronelle field in 1955). She also gained extensive field experience, particularly with Coastal Plain mollusks, and was active in local scientific societies. Her advice on fossils and localities was sought by many researchers. Although McGlamery published relatively little, she had a great influence on Alabama paleontology and biostratigraphy in her long association with the Geological Survey of Alabama.

ABSTRACT—Crustacean microcoprolites, Parafavreina ziczac isp. nov., are among the most common fossils in the upper Smackover Formation (Upper Jurassic) of southwest Alabama. The new ichnospecies, Parafavreina ziczac, is characterized by its zigzag arrangement of canals having a triangular outline in transverse section. Associated fossils include photosynthesizing microbial buildups, calcareous benthic foraminifera, sponges, and echinoid ossicles along with rare to uncommon bivalves and gastropods. Other crustacean microcoprolites, Palaxius and Helicerina, are also present. The salinity is thought to have been about 50–60 ‰ to account for the very low diversity of organisms and dominance by thrombolites and stromatolites. The inferred paleoenvironment consisted of shallow, restricted basins with clear, well lit, relatively quiet, hypersaline water in an arid tropical climate.
The taphonomy and diagenesis of the microcoprolites were complex. Some, but not all, pellets were leached of organic material. Most were hardened sufficiently that they underwent no noticeable distortion through burial-related compaction. A mosaic of diagenetic pathways, heterogeneous at scales down to that of individual particles, led to three end-member classes for P. ziczac. These are 1) moldic pores, 2) dolomitized pellets, and 3) microcrystalline carbonate little altered from the pellets’ depositional texture.
P. ziczac is widespread in the Smackover Formation in rocks that contain few other fossils. This suggests that it might be a useful environmental indicator of hypersaline conditions. The geographic distribution of P. ziczac outside Alabama is not well known, but it has some potential as a biostratigraphic marker, even though it may be endemic to marginal basins along the Gulf of Mexico.

Absolute water depth has been estimated for ancient deposits
based on the ratio of planktonic to benthic foraminiferal tests (the P/B ratio) in today's seas. In the present study, the formula proposed by Van der Zwaan et al. (1990, Marine Geology 95:1-16) was used to estimate absolute water depth for the Upper Cretaceous Mooreville, Demopolis, and Prairie Bluff Chalks in westcentral Alabama. Planktonic individuals made up 70-80% of the total of ~300 specimens in each sample. The resulting absolute paleodepth estimates were as follows: 557m (mean of 3) for the Mooreville Chalk, 601 m for the Demopolis Chalk, and 436m for the Prairie Bluff Chalk. Other investigators have  reported similar and even higher P/B ratios for Cretaceous deposits in the Gulf Coastal Plain and Western Interior Seaway, leading to depth estimates in excess of 500 m. In our study, these extreme depths are contraindicated by lithologic evidence (e.g., >19% sand in the Prairie Bluff Chalk), megafossil and ichnofossil assemblages, and even the microfossil assemblages themselves. Foraminifera were low-diversity faunas, dominated by Heterohelix, Globigerinelloides, and
Hedbergella. These are interpreted to be shallow-shelf opportunists. Deeperwater, single and double-keeled taxa such as Globotruncana and Globotruncanita were relatively rare in our samples.
Cretaceous seas were unlike those of today in several respects including the extreme sea-level highstand. Another significant difference was sea-water chemistry. Recent research (Stanley, Ries, and Hardie, 2005, Geology, 33:593-596) suggests that the high concentration of Ca2+ and high proportion of Ca 2+ versus Mg2+ in Cretaceous seas promoted coccolithophore productivity and induced chalk formation. We note that both coccolithophores and planktonic foraminifera have maximum species diversity in the Late Cretaceous. Although biomineralization in foraminifera is more complex than in algae, increased availability of calcium would have aided in test construction. Moreover, as heterotrophs, foraminifera would have benefited from the increased primary productivity and overall enrichment of pelagic communities. We suggest that the
abundance of Cretaceous plankton relative to that of today's seas seriously limits the use of foraminiferal P/B ratios in estimating absolute water depths.

Rindsberg, A. K., 1990, Freshwater to marine trace fossils of the Mary Lee coal zone and overlying strata (Westphalian A), Pottsville Formation of northern Alabama, in Gastaldo, Robert A., Demko, Timothy M., and Liu, Yuejin, Carboniferous coastal environments and paleocommunities of the Mary Lee coal zone, Marion and Walker Counties, Alabama: Geological Survey of Alabama, Guidebook 3-6, p. VI-82 to VI-95.      The PDF includes the entire guidebook. Describes invertebrate (and some vertebrate) trace fossils from an area near the Union Chapel Mine and from the same strata.