THE PALEOECOLOGY AND GROWTH HABITS OF ARBORESCENT LYCOPODS FROM AN IN SITU SWAMP FOREST OF MIDDLE PENNSYLVANIAN AGE (BERNICE BASIN, SULLIVAN COUNTY, PENNSYLVANIA) (TAPHONOMY)

The Bernice Basin is a small structural basin entirely contained within the northern halves of the Laporte and Lopez quadrangles in north-central Pennsylvania. It contains Pottsville and Llewellyn sediments and is of Middle Pennsylvanian age. An abandoned strip mine in the basin contains the remains of an in place Paleozoic swamp forest. The basal unit in the swamp sequence is the old soil horizon, a medium gray, unfossiliferous, intensely rooted siltstone. Its top 10 centimeters are well bedded and contain the remains of a litter layer produced by the lycopodpteridosperm dominated forest which stood on this site before it was suffocated by flood waters. The forest\u27s trunks are well preserved in the overlying black shale which grades into 150 centimeters of allochthonous banded coal. Logs of Lepidodendron rimosum and L. dichotomum dominate this assemblage. In these two species, juvenile trunks are obconical, because the growth of secondary tissues did not keep pace with the increasing diameter of the apical meristem. During this stage, the cushion\u27s length and width increased with trunk height. After the meristem matured, the trunk continued growing upward in an unbranched state, and the cushions produced at this time were of constant dimensions. In both species, unfavorable environmental conditions affected cushion size. Lepidodendron rimosum accomodated growth of the secondary tissues by expanding the inter-area between cushions. Lepidodendron dichotomum lacked this potential and shed its cushions more quickly. Cushion length decreased drastically in Lepidodendron rimosum just before branching, but not in L. dichotomum. The former branched by dichotomizing apices and was determinate in growth, the latter produced determinate lateral branches by monopodial branchings but was indeterminate as a whole. The Bernice forest had a multi-story canopy. The uppermost canopy was some 50m above the ground and was dominated by L. rimosum. A lower canopy occurred some 35 m above the surface and was dominated by L. dichotomum. A third level occurred 15m above the ground. It contained the pteridosperms and occasional calamites. The lowest layer consisted of the herbaceous Sphenophyllum