Depositional and Post-Depositional Features in the Late Wisconsian Tills of Massachusetts.

(David L. Lindbo, Julie Brigham-Grette and Peter L.M. Veneman. Whole Regolith Pedology, Soil Science Society of Amercia Special Publication no. 34, p. 75 - 95, 1995)

Recent pressures on community development in Massachusetts require that the soil parent materials can be examined in greater detail than has been done in the past. Up to 50 % of the soils in Massachusetts are developed in dense glacial till regionally subdivided into the Lower Till of late Illinoian age and the Upper Till of late Wisconsinan age. Twelve till exposures were investigated to relate common morphological features seen in the tills to soil development, hydrology, and potential impact on land use. Depositional features such as sand layers and lenses, contorted silt/clay beds, and shear planes in the tills act as conduits for rapid water (and potential contaminant) movement. Oxidation along joints and fractures in both the oxidized and unoxidized facies in the Illinoian aged Lower Till suggests water movement and redox reactions are ongoing processes and occur several meters below the surface. There is a noticeable increase in both the amount and degree of development of argillans and redoximorphic features within the solum of soils developed on the oxidized Lower Till. The increased development suggests that much of the morphology of the modern soil is not inherited from the till but is due to pedogenesis. We concluded that the brown matrix, oxidized mineral grains, and increased fissility in the oxidized Lower Till results from postdepositional subaerial weathering and that the oxidized Lower Till appears to represent the remains of the Sangamon C horizon. Redox features also are present in the Upper Till generally occurring at textural transitions in the till. The relatively unweathered deeper portions of the Upper Till contain few to no argillans but argillans are common in the solum of soils developed in the Upper Till. These observations attest to the Holocene pedogenic alteration of the surface tills of all ages in Massachusetts.

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