Sedimentology and paleontology of a Carboniferous log jam Robert A. Gastaldo a, ⁎ , Carleton W. Degges b a Department of Geology, Colby College, Waterville, ME 04901, United States b Heidelberg Cement Group, Leeds, AL 35094, United States Received 1 January 2005; accepted 22 February 2006 Available online 17 July 2006 Abstract A localized sandstone split in the Mary Lee coal (Early Pennsylvanian, Langsettian) of the Black Warrior Basin, Alabama, has a channel-form geometry and preserves a concentrated log-and-gravel (pebbles, cobbles, and boulders) assemblage at the top of the fill sequence. Gravel lithotypes within and amongst rooting structures of lycopsid, cordaitean, and calamitean trees are indicative of an Appalachian orogenic provenance, and support an allochthonous origin for some of the logs. In addition, a Skolithos ichnological assemblage within the channel is indicative of opportunist colonization during channel fill. A low sinuosity geometry characterizes the overall channel-form belt, exhibiting a general northwesterly trend. Paleocurrent measurements from the cross-bedded sandstone at the margin of the channel belt indicate flow was to the northwest. Log orientations at these sites are subperpendicular to perpendicular to the overall sediment transport direction and are interpreted to represent an ancient log jam. The genesis of the fluvial channel, the introduction and emplacement of the concentrated log assemblage, the effects of this floating log accumulation on sedimentation within the channel, and the relationship between paleocurrent and log orientation are discussed. The Red River, located in the southern United States, is used as a modern analog for comparative purposes. © 2006 Elsevier B.V. All rights reserved. Keywords: Paleobotany; Pennsylvanian; Plant taphonomy; Ichnology; Black Warrior Basin 1. Introduction The disposition of fossil logs in fluvial environments has been used as a paleoenvironmental indicator to varying degrees of success (e.g., Pelletier, 1958; Colton, 1967; MacDonald and Jefferson, 1985; Fiorillo, 1991; Evans, 1991; Gastaldo, 2004). Although commonly found in ancient channel deposits in channel-lag deposits, no definitive conclusion has been drawn on the significance of wood orientation with respect to current direction. The complexity of this problem is compounded by many factors including the source area of logs, their diameter and length, number of logs, wood and/or periderm density, susceptibility to waterlogging, and resistance to decay (see: Robison and Beschta, 1990; Montgomery and Piégay, 2002). A localized channel-form sandstone divides the Carbo- niferous Mary Lee coal into two benches in northwestern Walker County, Alabama (Ward, 1986; Liu and Gastaldo, 1992a). The sandstone attains a maximum thickness of a few meters, thins laterally, and is oriented in a north- western direction in which an unusual paleontological assemblage occurs. A concentrated log accumulation (xylocoenosis) is preserved at the top of the channel sequence in which extrabasinal gravel found within International Journal of Coal Geology 69 (2007) 103 – 118 www.elsevier.com/locate/ijcoalgeo ⁎ Corresponding author. E-mail address: ragastal@colby.edu (R.A. Gastaldo). 0166-5162/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2006.02.011