The hunt for Cummingsella ( Carboniferous , Chlorophyta )

Until recently Cummingsella was only known by two rare and puzzling species, erected on very limited material. The genus was therefore considered as representing a very uncommon and puzzling form that played no role in carbonate sedimentation. Recent studies of Viséan carbonates in the American Midcontinent have disclosed a prolifi c Cummingsella fl ora that indicates the proximity of an algal bank. Cummingsella can therefore be considered locally abundant and cosmopolitan (Europe, Australia, North America), ranging in age from the Tournaisian to the Namurian (Serpukhovian).


PLATE 2
All samples are from the Middle Viséan Zone 12, "Warsaw" Formation, Sugar Creek Quarry, Kansas City.Kansas.
1 Well-sorted fossil grainstone.Three reworked mud-fi lled Cummingsella thalli (lower left, upper right) associated with pitted echinoderms, mud-fi lled broken fenestellid fronds and brachiopod shells.It has to be admitted that the "erection" of a new taxon on one single section is not to be recommended and is equivalent to "skating on thin ice".To make things worse, no new material to substantiate this claim was discovered for 25 years.Moreover the attribution of the genus to higher levels was unclear but could suggest the Dasycladales or the "Udoteaceae" (Halimedaceans).BUCUR (1999) attributed the two species to the Halimedaceans.But no new discoveries of the genus could be found.
Thus the recent observations of abundant Cummingsella in the Viséan of North America, which are the subject of this note, are welcomed.

LOCATION, STRATIGRAPHY AND MICROFACIES
Due to the expansion of the Lafarge Cement Sugar Creek Quarry in the vicinity of Kansas City, Kansas (Fig. 1), a number of drill-holes were made to test the quality of the Mississippian carbonates.They provided a detailed stratigraphic succession from the Viséan (= Meramecian) "Warsaw" and St. Louis formations.
The level that contains numerous Cummingsella is located at the top of the "Warsaw" Formation, just below the contact with the overlying St Louis Limestone.It can be traced over a square kilometre and is 10-12 metres in thickness.A few hundred thin-sections yielded the following observations.
Each thin-section contains from 5 to 20 Cummingsella and the total observed fl ora amounts to 400 thalli.
The paleoenvironment is within the fair-weather wave base, at the base of the euphotic zone.The age is Zone 12, in the upper part of the Zone, Middle Viséan.The age is different from Australian material (Late Tournaisian) but the overall microfacies is quite similar.The abundance of reworked, heavily micritized thalli suggests the proximity of an algal bank.MAMET & ROUX 1983 (Pl. 1, Figs. 2-17) Description: Small species of Cummingsella has diameter of segments around 200-250 µm.The thallus is perforated by a central cylindrical medula (60 to 110 µm).Ramifi cations are regular, 10 to 12 at the same level, equidistant, bifurcated as single or double tufts.Diameter is 25-30 µm.

Cummingsella bingleburrae
Comparison: The periphery of the thallus is less seg mented than the original material.However, the central medulla is often enlarged by micritization and corrosion, and thus appears artifi cially segmented.This indicates extensive diagenesis (the thallus was probably aragonitic) and has caused confusion in the past between the attribution to Dasycladales and "Udo teaceans".Prof. Bucur suggests the possibility of intusannulations, suggesting junctions of lateral fi laments.

CONCLUSION
The hunt for Cummingsella is a good illustration of the fl uctuating state of knowledge of the Palaeozoic algae.Many gen era, often recognized on insuffi cient data, seem endemic to a region, appear to be scarce, and of dubious sedimentological consequence.They may suddenly appear, and by chance have very different connotations.Hence palaeogeographic reconstructions and migration patterns based on microfl ora have to be taken "cum grano salis".