Harold A. Winters

NEW AGE CONTROL ON THE PORT HURON MORAINE IN NORTHERN MICHIGAN

Until now, radiocarbon age estimates of the Port Huron moraine in Michigan have been based largely on 14C dates from beyond the state. This study reports a radiocarbon age of 12,960 ± 350 yr B.P. from sediments immediately proximal to the northwestern part of the Inner Port Huron moraine in Michigans Southern Peninsula. Geologic relationships indicate that this section of the moraine predates the age estimate. Stratigraphic and morphologic relationships of sediments of ancestral Great Lakes phases related to the Port Huron morainic system, 14C ages from sediments of those lake phases, and a 14C age from wood buried by till of the Wyoming moraine (a morphostratigraphic equivalent of the Port Huron moraine), have collectively supported the interpretation that the morainic system was formed between 13,500 and 12,700 yr B.P. Our radiocarbon age estimate, the first from sediments immediately proximal to the Port Huron system in Michigan, is compatible with this interpretation. Furthermore, because the Port Hu...

SIGNIFICANCE AND AGES OF MID-WISCONSINAN ORGANIC DEPOSITS IN SOUTHERN MICHIGAN

Four recently drilled, closely spaced wells near Kalkaska, Michigan encountered a thick zone of organic-rich sediments at a depth of about 130 m; all are interpreted as part of the same unit. Two radiocarbon dates and botanical data derived from the carbonaceous material along with associated sediments indicate that about 35,000 B.P. the site was ice-free, poorly drained, and supported first an open and later a closed boreal forest. These two and eight additional radiocarbon determinations (four finite and four “infinite”) from wood recovered during other research are compared with all other previously published dates for Middle Wisconsinan material from southern Michigan. This array of ages suggests that at least parts of the state were not glaciated during much if not all of the Middle Wisconsinan, including the Cherrytree Stadial. Botanical evidence also indicates that about 35,000 B.P. the climate in the northwest part of the Southern Peninsula was considerably cooler than at present, possibly being i...

The anomalous Roxana silt and mid-Wisconsinan events in and near southern Michigan

Abstract Thick deposits of Roxana Silt are recognized only along the Illinois River (downstream from the Woodfordian terminal moraine) and are generally interpreted as being mainly loess, with the bulk accumulating from about 40,000 to 30,000 yr ago in association with an Altonian-age glacier in northeastern Illinois. Yet 11 14C dates indicate that southern Michigan was not ice-covered during that interval; thus, any proximate ice must have, at best, been restricted to Great Lakes basins, an interpretation supported by the absence of late Altonian till at critically located Michigan, and nearby, sites. Late mid-Wisconsinan ice did, however, obstruct eastern drainage of the ancestral Great Lakes. Such glacial blockage, the distribution of many Michigan organic deposits within pre-Woodfordian lacustrine sediments, and radiocarbon dates suggest that, more than once, late Altonian lakes associated with the Lake Michigan basin drained into the Illinois River. Erosion of lake and spillway bluffs along with repeated river fluctuations provided a source for the thick, geographically restricted Roxana Silt. Meanwhile, along other nearby rivers the supply was meager and the loess thin.

Low-altitude organic deposits in Michigan: Evidence for pre-Woodfordian Great Lakes and paleosurfaces

Reports of 136 glacially buried organic deposits below 200 m in altitude and other related data provide a basis for identifying relicts of several low-level Pleistocene paleosurfaces in southern Michigan. The carbonaceous material is concentrated in five areas and probably represents low places on pre-Woodfordian landscapes with local base levels far lower than the present topography. These findings have implications regarding adjacent ancestral Great Lakes that existed sometime prior to final glaciation of the peninsula.

Distribution and Significance of Glacially Buried Organic Matter in Michigan's Southern Peninsula

Within Michigans Southern Peninsula, the presence of glacially buried Pleistocene organic matter is relatively uncommon but more abundant than previously recognized. These deposits tend to be concentrated in 13 districts and are most closely related to (1) places with high relief on the drift-covered bedrock surface, (2) the extent of buried bedrock valleys, and (3) low areas on a palimpsest paleosurface. Well logs show that multiple organic horizons at any one site are extremely rare, but variations in location, elevation, types of material with their climatic implications, and radiocarbon dates support the conclusion that remnants of several Pleistocene paleosurfaces, preserved through burial by deposits from separate glacial advances, exist at a number of places, especially in the southern part of the peninsula.

DRAINAGE REVERSALS AND TRANSVERSE RELATIONSHIPS OF RIVERS TO MORAINES IN SOUTHERN MICHIGAN

In southern Michigan, a multiglaciated area of thick drift, regional differences in the altitude of the buried bedrock surface control the direction of major drainage lines and facilitated some stream reversals during deglaciation. Furthermore, individual bedrock valleys, though deeply buried, may influence surface forms in a fashion that induces transverse relationships between river courses and morainal trends. Apparently one or more ancestral glacial landscapes were influenced by the bedrock surface and are also reflected in the present topography. Such palimpsest landscapes may be more widespread in glaciated terrains than have generally been recognized.

Differentiation of surficial glacial drift in southeastern Michigan from 7-Å/10-Å X-ray diffraction ratios of clays

Woodfordian till deposited by the juxtaposed Saginaw and Huron-Erie glacial lobes in southeastern Michigan appears similar in many respects but may be differentiated on the basis of certain mineralogical characteristics of clay-sized particles. This is apparent from X-ray diffractograms of basally oriented, magnesium-saturated, and glycerol-solvated specimens. Thirty-five till samples from the converging Kalamazoo (Saginaw lobe) and Mississinewa (Huron-Erie lobe) moraines and their interlobate tract have 7-A/10-A peak height ratios that differ significantly according to provenance. Every sample from locations within and proximal to the Kalamazoo moraine has a ratio of 0.91 or more. All but one of the samples from the Mississinewa moraine and areas to the east have ratios less than 0.91. Data from several other sources indicate that the same relationships also exist on a larger scale in southeastern Michigan. The findings are consistent with previous interpretations of the area9s geology and may provide a reliable basis for the placement of the surficial boundary between drifts deposited in a complex interlobate area.

FRANK LEVERETT — PLEISTOCENE SCHOLAR AND FIELD WORKER

Frank Leverett (1859–1943) contributed more than any other person to our understanding of the Midwests glacial geology. Examination of his publications shows that he authored more than 100 reports, including three monographs which alone total more than 2100 pages, and at retirement had more printed words in U.S. Geological Survey publications than any other person. A review of many original field notebooks indicates that he relied primarily upon descriptive traverse mapping stressing interpretation from landforms; and it is estimated that his hundreds of notebooks contain more than 45,000 pages. Study of 506 personal letters written to Frank B. Taylor over a 53 year period reveals that Leverett had a persistent dedication to glacial geology, great self discipline and a sense of responsibility to report his findings. His professionalism is well illustrated by a quotation from a letter written when he was 70: “. . . it is the truth we are after and not the defense of a particular view or estimate.”