Abstract

Carbonate deposits of the Greenhorn Limestone, Fairport Member of the Carlile Shale, and Niobrara Chalk of Kansas are characteristically speckled by nearly white, ellipsoidal calcareous pellets having an average diameter near 0.12 min. Similar pellets occur in two widespread calcareous units, the first and second speckled shales, of the western Canadian plains. The two speckled Canadian units are approximately correlative with chalk-bearing intervals of the Kansas section. In both areas the pellets are of similar size, shape, color and texture and are known to be rich in coccoliths. Scanning electron micrography of these pellets, and of rock matrix adjacent to the pellets demonstrates (1) that pellets from the two areas are identical in being composed largely of coccoliths or coccolith debris and (2) that most non-pelletoid matrixes are composed predominantly of material not derived from coccolithophorids. Concentration in the pellets, of whole and broken coccoliths, as well as size of the pellets suggest origin as fecal matter of small, herbivorous, planktonic organisms that fed selectively on coccolithophorids. Copepods are known to feed selectively and are known also to feed on coccolithophorids. Furthermore, some living copepods produce pellets of similar size and shape to those in the Cretaceous strata. Alternatively, the pellets could have been produced by pelagic tunicates which are known to produce ellipsoidal pellets and to feed upon coccolithophorids. Further elaboration of trophic structure in the Late Cretaceous Western Interior sea requires search for skeletal remains of the pellet-producing organisms.

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