THE GEOMORPHOLOGY, CHARACTERISTICS, AND ORIGIN OF THE FRESH-WATER MARL SEDIMENTS IN THE GREAT LIMESTONE VALLEY, MARYLAND, USA

Certain calcareous soils occupying alluvial landscape positions in the Hagerstown (Great) limestone valley of western Maryland have develope d from highly calcareous (60-100 g 100 g(-1)) mar1 sediments of Holoce ne age. The limestone valleys of this region are located in the Ridge and Valley Province, which transcends the western portions of Maryland and Virginia. The sediments range from 0.5 m to over 8 m in depth. Th e soils developed from the marl have been mapped in the Great Valley i n units named for the Warners series (fine-silty, carbonatic, mesic Fl uvaquentic Haploquolls) and the Massenetta series (fine-loamy, carbona tic, mesic Fluvaquentic Hapludolls) and typically have a high pH (7.5- 8.5), low bulk density (1.00 g cm(-3)), and high porosity (0.5 to 0.6) . The carbonate in the marl was developed through inorganic and biogen ic processes. The marl was formed in ponds, as evidenced by the presen ce of certain gastropods, bivalves, algae, and the extremely high CaCO 3 content. The ponds are now extinct, but occurred in alluvial landsca pe positions during parts of the Holocene. Grain analyses and micromor phological evidence indicate that certain algae (Chara sp.) capable of accumulating carbonate internally and externally, were largely respon sible for forming the marl. Periods of intermittent marl development a re evidenced by the buried surface horizons within the marl sediments. The mechanisms responsible for damming and pending of these alluvial landscapes were apparently destroyed, and then reformed prior to subse quent marl development. (C) 1997 Elsevier Science B.V.