LARGE BURROWS FROM THE LOWER MISSISSIPPIAN HUNTLEY MOUNTAIN FORMATION, NORTHEASTERN PENNSYLVANIA

Several exceptionally large trace fossils are identified within the Huntley Mountain Formation (HMF) in an exposure at the Red Rock quarry locality in Ricketts Glen State Park, PA. The outcrop preserves dark reddish-brown silty clays in the upper part of the HMF, likely deposited during the earliest Mississippian (possibly latest Devonian). We present a detailed morphological assessment of these trace fossils thought to be constructed as dwellings and aestivation burrows.

Burrow traces have been previously identified in the HMF and interpreted as lungfish aestivation structures. The burrows are described as vertical cylinders that vary in diameter (3.0-15.0 cm) and length (<1 m), oriented normal to bedding. Burrows with similar dimensions are identified at the Red Rock quarry site, with diameters ranging from 5.7 to 16.6 cm and lengths varying from 19.9 to 44.9 cm. However, within this horizon there is an extremely large burrow exhibiting similar morphology, with a diameter that is 47.0 cm at its maximum and an overall length of 128.5 cm.

Modern lungfish construct burrows as an aestivation activity for temporary refuge and survival during seasonal dry conditions and remerge when aquic conditions return. This activity fits with the interpreted depositional environment of the HMF as a meandering fluvial system with overbank deposits from periodic flooding. These deposits are subjected to pedogenesis and exhibit wetting/drying features indicative of a seasonal climate.

Within this same horizon is a second large burrow that is distinctly different than that of the lungfish. This burrow has a mean entrance shaft diameter of 35.2 cm, normal to bedding, and extends 61.5 cm to a terminal chamber oriented subparallel to bedding. The chamber length ranges between 44.5 to 105.3 cm and 54.6 to 56.0 cm in height. The morphology is similar to vertebrate (tetrapod) burrows identified in the overlying Upper Mississippian Mauch Chunk Fm. forming under similar seasonal climate conditions.

The HMF is of interest because it stretches across the Devonian-Mississippian boundary and provides unique insight during this transition. Aside from the information regarding paleoclimate; the scale of these burrows provides insight into organisms evolution as well as ecological responses to changing landscape conditions during this interval.