CADDISFLY (INSECTA: TRICHOPTERA) PUPAL CASES USED AS UNIQUE AUTOCHTHONOUS PALEOENVIRONMENTAL INDICATORS: EOCENE LAKE GOSIUTE

A band of caddisfly-dominated carbonate bioherms up to 9 m thick extends in a great arc for over 250 km across the western, northern, and eastern Greater Green River Basin in central Wyoming. The bioherms formed in nearshore paleoenvironments associated with Eocene Lake Gosiute. Internal fabrics of the bioherms include abundant calcified caddisfly pupal cases alternating with layers of stromatolites and tufa. The caddisfly cases are pupal cases (not larval cases) because they are all the same length and diameter. In general the bioherms developed during transgressive phases of Lake Gosiute in early Laney time. However, along the western and eastern margins, the caddisfly-dominated bioherms interfinger with siliciclastic mudstones of the Cathedral Bluffs tongue of the Wasatch Formation. The Wasatch Formation bioherms and the Green River Formation bioherms were formed contemporaneously.

The particles used in pupal case construction vary across the east/west transect according to the paleoenvironment encountered. In lacustrine carbonate-dominated paleoenvironments, the caddisfly pupal cases are composed of mostly carbonate particles. In fluvial/floodplain sediments, the caddisfly pupal cases are composed of mostly siliciclastic particles. It is clear that the particles used in caddisfly case construction directly reflect the paleoenvironment in which the cases were built.

This case study suggests that caddisfly cases can be used to help elucidate the degree of transport of fossil assemblages that contain caddisfly cases. In autochthonous situations, caddisfly case particles match the particles that occur in the surrounding environment.