Geological and ichthyological investigations into palaeodrainage hypotheses for the Tennessee River
The course of the ancestral Tennessee River has been debated in both the geological and biological literature for over 100 years. Several of the proposed courses for the ancestral Tennessee place its course across the state of Mississippi. Geochemical analysis of sedimentary rocks in the Pascagoula River basin supports these hypotheses suggesting that the rocks in the Pascagoula basin were derived from the Highland Rim of Tennessee and northern Alabama, while geochemical analysis of rocks from the Pearl River basin point to deposition from a mixture of sources including the ancestral Mississippi River and perhaps the ancestral Tennessee. To delve deeper into the history of the Tennessee River, the phylogenetic systematics of the Etheostoma subgenus Doration were used to further test these hypotheses. Results of the phylogenetic analyses suggest that the members of Doration along the Highland Rim are diverged from not only the remaining Doration , but also from one another due to the breaching of the Fort Payne chert atop the Nashville Dome during the Miocene. From the phylogenetic analyses, it is unclear whether the ancestral Tennessee crossed Mississippi, but a couple of patterns are evident. First, the results suggest that a stream capture event occurred between Bear Creek of the lower Tennessee drainage and one of the eastern tributaries to the Tombigbee River of the Mobile basin. Second, Etheostoma stigmaeum from the Pascagoula River basin are consistently recovered as monophyletic. When coupled with the geological evidence, these findings suggest that the history of Pascagoula River basin may be independent of its neighboring drainages on the coastal plain, possibly due to the mobilization of salt domes in the subsurface of the Gulf of Mexico coastal plain.