Howard D. Mooers

Terrestrial record of Laurentide Ice Sheet reorganization during Heinrich events

The glacial stratigraphy and geomorphology of the western Lake Superior region record a complex sequence of late Wisconsinan ice advances and retreats of the Laurentide Ice Sheet from accumulation centers in Quebec and Hudson Bay. Geomorphic evidence indicates that three major late Wisconsinan events occurred, each marked by gradual buildup of ice, formation of a prominent moraine, and subsequent rapid ice retreat. The established radiocarbon chronology indicates that these three events culminated ca. 23–21, 16–15.5, and 13 14C ka, indicating that major glacial advances culminated immediately prior to Heinrich events H-2 and H-1, and that ice underwent rapid retreat during Heinrich events. The possible linkage between western Lake Superior region ice dynamics and Heinrich events is supported by the presence of indicator rock types in drift associated with each major glacial recession. These indicators suggest that progressive southward shifts of the Laurentide Ice Sheet ice divide accompanied each rapid glacial recession. Furthermore, lithologic evidence indicates that there were two episodes of ice divide shifts: one ∼400–600 km occurring during H-2, and a smaller shift occurring during H-1.

Paleo-Indian Occupations in Northeastern Minnesota: How Early?

Environmental factors influenced Paleo-Indian occupation in northern portions of North America. Glacial features posed physical restrictions while revegetation on the post-glacial landscape limited available resources. Areas of northern Minnesota were ice-free by 13,500 B.P. with lake formation and revegetation at 12,000 to 11,000 B.P. By 11,200 B.P. northeastern Minnesota was probably habitable. However, archaeological evidence for early Paleo-Indian occupation in the area is sparse. Fluted and Holcombe-like projectile points have only been reported from three localities; well-dated sites are lacking at present, in contrast to the evidence for Late Paleo-Indian occupation. However, rugged terrain and thick vegetation hamper survey and bias the record toward accessible locations—those on modern waterways. A survey strategy based on the immediate post-glacial landscape needs to be implemented to address the question of earliest occupation. In addition, the problem of charcoal dates that are widely divergent from associated cultural remains must be addressed.

Discriminating texturally similar tills in central Minnesota by graphical and multivariate techniques

Abstract The sequence of glaciation in the midwestern United States has been defined mainly by till stratigraphy. Correlation of tills over long distances, however, is complicated by spatial variation of sediment characteristics. In east-central Minnesota three till units were previously defined. Two were considered to be lithologically identical and were correlated with the late Wisconsin advance of the Rainy lobe, whereas a third till was assigned to the contemporaneous advance of the Superior lobe. This interpretation was inconsistent with subsequent glaciological reconstructions of the Rainy and Superior lobes. In an effort to define the parent lobe of the deposits in central Minnesota, the tills were sampled, analyzed, and compared by graphical and multivariate techniques. Graphical comparisons of sedimentological parameters were inadequate to distinguish important differences among the groups. However, principal component analysis of the analytical data indicates that the original interpretation is untenable and that one of the tills formerly assigned to the Rainlylobe should now be attributed to the Superior lobe. Problems encountered with correlation of tills exposed at the surface illustrate the complexity and problems associated with subsurface stratigraphic correlation.

Gravestone decay and the determination of deciduous bulk canopy resistance to acid deposition

Gravestone decay and atmospheric concentrations of SO2 are used to determine deposition velocities in two adjacent cemeteries in the Birmingham, UK, Jewellery Quarter. Warstone Lane cemetery is essentially open to the environment with only a limited number of trees. Key Hill Cemetery, located within 100m, has a continuous canopy of 100+ year-old London plane; gravestone decay at Key Hill is 50% less than at Lane for the period after 1960. This difference is used to calculate canopy resistance as a residual term assuming that aerodynamic and quasilaminar resistances are generally similar at both sites. Calculated resistances range from approximately 300 to 900sm-1 and are consistent with estimated and calculated values from a wide variety of studies.