Abstract

Gravel, ranging from pebble to boulder size, is preserved inside or dispersed among vitrinized logs within a coastal-channel sandstone sequence of the Upper Pottsville Formation, Black Warrior Basin, northwestern Alabama. The gravel was transported from extrabasinal areas to the coastal regime in log rafts composed of hollow trees. Pebble accumulations represent a partial infilling of the logs while they lay on a gravel-covered stream bed at extrabasinal sites. Cobbles and boulders were transported entrapped within root structures of trees introduced into the river, or may have been trapped on or within log rafts. Only a limited number of clasts were available for study because the mining bench from which they were collected was exposed for a limited time and is now reclaimed. A suite of 300 clasts consists of metamorphic rocks (phyllite, quartzite, schist, and gneiss), igneous rocks (granodiorite and pegmatitic quartz), and sedimentary rocks (coarse- to fine-grained subarkose). The dominance of low- and high-grade metamorphic, plutonic igneous, and sedimentary rocks, and the absence of volcanic or volcaniclastic rocks, indicates an intensely deformed and uplifted source area. When this suite of rocks is compared with the two possible orogenic sources, Ouachitas or southern Appalachian, the southern Appalachian orogen conforms best. This interpretation modifies presently accepted models and indicates an eastern expansion of the source area from the Ouachitas to the adjacent part of the Appalachians during the Early Pennsylvanian.

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