Fig. 14
Next is the Tonto Group, made up of the Tapeats Sandstone, Bright Angel Shale, and Muav Limestone. The most common invertebrate fossils found in the Tonto Group are brachiopods and trilobites. Fragments of sponges,primative molluscs, echinoderms, and algae also occur, but they are not as abundant. Trace fossils are common in all formations of the Tonto Group, and include a diverse array of trails, tracks, and burrows. The depositional environments of the Tonto Group varied from fluvial, nearshore, and shallow shelf. A number of transgressions and regressions resulted in the intertonguing of the formations of the Tonto Group, and also vertically juxtapositioned facies belts that were not laterally adjacent.