Texture of Tills, Central Massachusetts

Abstract

ABSTRACT The complex bedrock terrane of New England is the source of complexity in the texture of tills blanketing the region, and the variety in interpretations of the glacial history of the region seems to stem from this areal diversity of textures within till units. This study was conducted to determine if careful quantitative analysis of till matrix textures could provide a criterion to unequivocally distinguish the lower, compact upper, and loose upper tills from place to place, and indicate the age or mode of deposition of the tills. Some clues were garnered from the analyses to aid in interpretation and correlation of the till units, but an unequivocal criterion for identifying them was not found. Also, the data did not support exclusively either the one-glacier or two-glacier hypot eses currently under debate. Statistical treatment of the particle-size distribution of thirty-three samples of till classified in the field as lower till, compact upper till, or loose upper till indicate that the lower and undifferentiated upper till from the study area are distinctly different. (Undifferentiated upper till refers to the combined data from the loose and compact phases.) The loose and compact phases of the upper till are also different from each other, but display a considerable amount of overlap in parameters. In general, the till units (lower, compact upper, loose upper) become coarser grained, better sorted, and coarse skewed in stratigraphic-order from bottom to top, indicating a decrease in clay content and an increase in sand content from bottom to top. Textural analysis, however, fails as definitive tool when samples from wide-spread areas of New England are compared, because the variation in particle-size distribution from different bedrock terranes is sufficiently large to cause extensive overlap in the clusters defined by the till types as they are plotted on various kinds of scatter plots.