Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 251, part 1
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Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 251, part 1
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Next Page--Substrates and Sedimentation
The exposure at this locality was measured and described noting particularly the form of the algal (Calcipatera) thalli, their association to each other, the associated biota (both attached encrusters and free-living epibiota), and the associated lithologies (three are recognized) that occur below, within, and above the interval bearing the upright, in situ, algal thalli. Oriented blocks were removed for laboratory examination. Polished sections, thin sections, and acetate peels were prepared, and along with numerous hand specimens, were studied to document the phylloid algal growth form, associated biota, and associated lithologies. Point counts, using the method of Chayes (1949), were made of thin sections from the three different lithologies. The general algal growth form was further documented by reconstructing a series of sections through an individual thallus. These serial sections formed the basis for the reconstruction of Calcipatera cottonwoodensis in Torres et al., 1992, reproduced here as fig. 3. For more details on the methods of study, see Torres et al. (1992). Differences between the three basic lithologies recognized in this study are illustrated by the point count data included in tables 1 and 2. The results of our studies are, in general, compatible with those presented by Laporte (1960, 1962) for the Cottonwood limestone at this locality, but our focus was on the in situ algal growths rather than the more resistant and conspicuous bed of platy algal packstone that was the focus of Laporte's studies.
Figure 3--Reconstruction of Calcipatera cottonwoodensis. Thallus is about 13.5 cm across and 4.2 cm high (from Torres et al., 1992; used with permission of the Journal of Paleontology).
Based on field and laboratory observations, we conclude that Calcipatera displayed a gregarious habit with dense growths of overlapping thalli that formed a continuous to patchy canopy above the substrate. Baffling by the erect algal thalli caused fine carbonate sediments to settle around the alga and fill the cup-shaped thalli. Skeletal fragments of the alga, epiphytes, and mobile organisms also settled on, within, and around the in situ growths. As sediment filled the cup-shaped thalli, growth of the thalli continued upward, and at the same time, new thalli established themselves on the carbonate mud substrate within the cups, producing stacked buildups of Calcipatera (fig. 2a). Growth of an individual thallus ceased when overtaken or shaded by a dominate (larger) thallus (fig. 4), or when completely buried by sediment.
Figure 4--Polished specimen showing cross sectional view of in situ Calcipatera in growth position (growth was from base to top of photo). The cup-shaped thalli are filled with carbonate mud, skeletal grains, and fragments of the alga. Growth of the individual thallus on the right was inhibited (arrow) by the thallus on the left. Scale bar = 1 cm.
As pointed out by Torres et al. (1992), placement of Calcipatera and other Paleozoic algae in a taxonomic hierarchy constructed for living algae is arbitrary; however, there are many Holocene algal genera with somewhat similar growth forms and methods of substrate attachment to which Calcipatera can be compared. Based strictly on gross morphology (cup-shaped leafy thallus), Calcipatera most closely resembles the Holocene genera of brown algae (Phaeophyta) Lobophora and Padina (especially Padina sanctae-crucis). In Padina, the only brown alga that calcifies (Littler et al., 1989), calcification is limited to the surficial layer, perhaps as a result of the removal of carbon dioxide by photosynthesis. The green alga (Chlorophyta) Udotea cyathiformis has a calcified funnel- or cup-shaped thallus attached to a small single stalk (Littler et al., 1989). Other Holocene green algal genera with folded, leafy thalli include several species of Ulva and Avrainvillea. Konishi and Wray, 1961, compared the growth form of Eugonophyllum, another cyathiform alga (Torres, 1997), to the Holocene brown algal genus Thalassiophyllum. Thus, the growth form of Calcipatera, as illustrated by Torres et al. (1992), and further supported by this study, is known from extant algae from several different taxonomic groups.
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