07. One Ice Age, or Many? (part 2)

The Basis for Interglacials

If there was only one ice age, why do uniformitarian scientists postulate interglacial periods between till sheets? What is this evidence for interglacials, and how valid is this evidence, as proof of multiple glaciation? Can a single ice age explain this evidence? This section will examine the evidence for interglacial periods. The last section of this chapter will explain the evidence from the viewpoint of a single ice age. The evidence for interglacial periods is summarized by Charlesworth (1957, p. 900):

Interglacial or “warm” epochs are proved stratigraphically by sheets of till, fluvialglacial deposits or loess which are separated by zones of weathering and by fossiliferous beds, either fluviatile, lacustrine or marine, e.g. on Long Island, or by peat, forest or other vegetation layer, lignites, soils, tufas, iron-ores and diatomaceous earths (e.g. Jutland and the Lüneburger Heide). 149 In other words, the evidence for interglacials consists of soils, zones of weathering, and fossils between layers of till, glaciofluvial sediments, and loess. Soils and zones of weathering include tufa (CaCO3 layers), and iron-rich sediments, which are characterized by various shades of red color. Fossiliferous beds include peat, lignite, and diatomaceous earth. Lignite is a brownish-black, low-grade coal. Diatomaceous earths are beds of diatom remains, and are rare in glacial sediments.

How abundant are these interglacial deposits? Are we trying to explain widespread features, or rare occurrences? It makes a difference, since rare deposits can easily be due to local conditions during a complex ice age. The answer is that interglacial deposits are rare. They are almost nonexistent in interior regions of formerly glaciated areas. Even at the periphery, organic remains are not abundant. Charlesworth (1957, p. 1025) states:

Pleistocene correlations are difficult and uncertain; time divisions are short; glacial deposits are virtually unfossiliferous; interglacial accumulations, if fossiliferous, occur in isolated and discontinuous patches....

Elsewhere he writes: “Within the glaciated territory, interglacial horizons are rarely more than fragmentary” (Charlesworth, 1957, p. 903). As discussed in the previous section, practically all ice-age fossils are found in nonglaciated areas. The northern Alps, where the fourfold glacial classification became established, did not contain any interglacial deposits between the river terraces, although warmth-indicating fossils were found in the “glacial” gravels. Most of the fossils in interglacial layers are vegetable material: pieces of wood, peat, or lignite. This material is often found in small depressions, that provided protection from erosion (Ehlers, 1983, p. 234; Felix-Henningsen, 1983). It is possible that the vegetation layers were washed into the depressions during periods of high rainfall, instead of having been formed from plant growth, in place, over an extended period of time. The rare organic deposits at least indicate that in some areas there was sufficient time between glacial advances for vegetation to grow.

Before discussing soils, which is the main evidence for multiple glaciation, mention should be made of the postulated interglacial features in loess, and fluvioglacial sediments south of the ice sheet boundaries. This evidence consists mainly of an ancient soil, called a paleosol, between layers of loess, or on top of fluvioglacial terrace deposits. Since this evidence is found in nonglaciated areas, it is not directly linked to the glacial/interglacial stratigraphy of glaciated lands. Therefore, it provides uncertain support for multiple glaciations, at best.

Furthermore, there are just as many problems in deriving a stratigraphy in loess and fluvioglacial sediments, as there are in till. For instance, George Kukla (1975, 1977) developed a loess/paleosol time scale from abandoned river terraces in eastern Europe. Figure 7.2 represents one of two key areas he studied near Brno, Czechoslovakia. He assumed that the higher terraces are much older than the lower terraces. After stating that miscorrelation has been common in past studies, he (Kukla, 1977) confidently correlates the loess/paleosol layers to the oxygen isotope record in deep-sea cores, mainly by simple curve-matching.

Figure 7.2 <C:\Program Files\e-Sword\Graphics\ICE\152.jpg>    West Bank of Svratka River

Cross section along the west bank of the Svratka River at Brno, Czechoslovakia. Loess, soil, and minor debris flow (not distinguished) are shown above abandoned terraces. Elevations and distances are in meters (Kukla, 1977). The depth of the sequence studied by Kukla, varies from ten to 30 meters (Figure 7.2), and was supposedly deposited in about one million years. The higher terraces are obviously older than those below them, but the time difference could be in years, rather than in the long time period Kukla presumes (see Chapter 6). Since the total depth of the deposits is rather thin, periodic strong winds during a dry period, could have laid these deposits in a very short time. The staircase structure of the terraces would have provided a natural trap for blowing dust. It is well known, that during the dust-bowl years in the midwestern United States during the 1930s, blowing sand and dust rapidly covered fences, and partially buried farm buildings (Landsburg, 1958, pp. 267, 268). In the river valleys that Kukla studied, occasional strong winds are responsible for at least part of the sequence, as indicated by frequent sandy interlayers and wind-moved rock fragments on the slopes (Kukla, 1977, pp. 324, 325). During periods of nondeposition, a soil, if they are really soils, could develop rapidly (see next section). Furthermore, the loess/soil transitions generally are sharp, indicating little erosion or time interval (Kukla, 1977, p. 335). The best conclusion, from the evidence, is that loess/paleosol stratigraphy in non-glaciated areas does not represent a long period of time. This stratigraphy is not independent data, and is a poor basis for surmising glacial/interglacial oscillations.

Interglacial Soils

Since organic remains are rare in formerly glaciated areas, the most widely used method for distinguishing the various glacial periods has been paleosols between, or on top of, till layers at the periphery. Not only is a paleosol presumed to designate an interglacial period, but various properties of the paleosols are used to “date” each ice age. On this basis, a glacial/interglacial stratigraphy has been developed from ancient soils, especially in the north-central United States (Table 7.2 and Figure 7.1). Birkeland (1984, p. 325) states: “Soils are important to the subdivisions of Quaternary sediments, whether the soils are at the surface or buried.” However, this method is now slowly being abandoned. The reason for this, is the replacement of soil stratigraphy with oxygen-isotope stratigraphy from the ocean. Soil stratigraphy is now claimed to have been always faulty. Since ancient soils are the main physical evidence for interglacials, paleosols will be discussed in detail. The method of using paleosols for a multiple ice-age stratigraphy will be examined in the next section.

What are the properties of a soil, or paleosol? A soil is simply the products of rock weathering, which have supported plant growth. A soil is divided into three main layers, called a soil profile. Figure 7.3 shows a general soil profile. This profile is composed of a top organic layer, called the A horizon; a middle layer of well-weathered material, called the B horizon, and a bottom layer of slightly weathered material, referred to as the C horizon. There are other minor horizons, and each major horizon can be further subdivided (Birkeland, 1984, pp. 3-37). The C horizon is very similar to the parent sediment, or rock, and has little use in soil stratigraphy. The B horizon is usually a clay layer, red-colored layer, iron or aluminum-rich layer, or CaCO3 layer. This section will mainly examine day soils-the predominant interglacial soil.

Figure 7.3 <C:\Program Files\e-Sword\Graphics\ICE\155.jpg>    General Soil Profile

There are many problems with paleosols that should have made them unsuitable for use as evidence for multiple glaciations or relative time indicators. The most basic problem is that of defining and recognizing a paleosol in the field (Ruellan, 1971). Much confusion has occurred. Few unique properties of soils exist, as opposed to sediments. Soils are altered upon burial, and can look like sediments that have undergone diagenesis (Valentine and Dalrymple, 1976, pp. 209, 210; Bowen, 1978, p. 182). Diagenesis includes the weathering of minerals by oxidation and reduction, hydrolysis and solution, biological action of bacteria, compaction, cementation, recrystallization, and lattice alternation of day by the expulsion of water and ion exchange (Valentine and Dalrymple, 1976, p. 210). Thus, a buried soil and a sedimentary layer may be difficult to distinguish: “A review of the literature, then, confirms that the identification of a buried paleosol is ‘rarely simple and irrefutable’...” (Valentine and Dalrymple, 1976, p. 213).

Another problem with ancient soils is that they have been subject to erosion and redeposition, and can have large horizontal and vertical variations over short distances (Birkeland, 1984, pp. 234-259). Nilsson (1983, pp. 178, 215) states that many paleosols in formerly glaciated areas of northern Europe have been destroyed by subsequent glaciation, and that fossil soils are subject to solifluction, causing them to flow into depressions and form extra thick “soils,” or false paleosols.

It would seem that the most obvious tell-tale sign of a paleosol is the A, or organic horizon (Figure 7.3). However, the A horizon is usually missing in paleosols, making reliable identification of an ancient soil exceedingly difficult:

It is difficult to classify buried soils to the same degree of accuracy as surface soils. This is because during burial changes take place in properties critical to such classification. For example, A horizons are critical to classification, yet are rare in buried soils (Birkeland, 1984, p. 33).

Flint (1971, p. 300) corroborates: “... indeed, in most buried soils the A horizon is lacking, because it is especially erodible.”

Since the A horizon is rare, and the C horizon nondiagnostic, the only criterion left for soil identification and stratigraphy is the B horizon. In previously glaciated territory, especially in North America, the B horizon is most often a sticky clay, called gumbo, or gumbotil. But the origin of gumbotil has been controversial (Nilsson, 1983, pp. 37 79). Some investigators have considered gumbotil to be an actual ancient soil, while others have believed it to be only an accumulation, by lateral wash, into depressions (Valentine and Dalrymple, 1976, p. 215). If the latter is true, gumbotil is not a soil at all, and could not be used as evidence for interglacials, or as subdivisions of Quaternary time. Recently, experts have agreed that both origins are correct (Birkeland, 1984, pp. 246-248). Resedimented deposits by lateral wash were given the name accretion gley, while the original name, gumbotil, was retained as the remnants of an old soil which has been formed in “poorly drained” areas. This compromise only partly alleviates the problem of identifying the B horizon of a paleosol in a particular locality.

Several processes, other than time, can develop a thick B horizon. Besides the lateral accumulation of clays discussed above, day, or other B horizon material, can develop by translocation of minerals upward from a high water table, or by the accumulation of fine material overlying coarse impermeable sediments (Birkeland, 1984, pp. 21, 22, 146-148). These conditions occur where there is poor drainage and a reducing environment, and can produce accretion gley or gumbotil, in a relatively short time. West (1969, p. 198) states: The problems of interpreting fossil soils are several. The first is in the recognition of a fossil soil. An iron rich or ferrocrete or a calcrete layer, may be the result of post-depositional changes related to former or present water levels or to impermeable layers holding up drainage. A horizon rich in organic matter may be a result of primary sedimentation.

Flint (1971, pp. 299, 300) agrees with this assessment. Although a thick B horizon of clay or other material may be a soil, again, it could have formed rapidly in a wet climate with poor drainage.

Soil Stratigraphy

It should be apparent to the reader that there is a basic problem of recognizing the B horizon of a paleosol which can support a postulated, interglacial period. But glacial geologists have taken paleosols even further, and have set up a dating scheme and a stratigraphy for multiple ice ages. Assuming that soils can be distinguished from sediments, how can they be used to date various till, or even loess layers, upon which the “soil” developed?

Vreeken (1984) gives a good description of the soil-dating procedure. First, one or more soil properties from several soils of different “known” ages, are given relative age values. These properties are usually the thickness of the B horizon (called its maturity), or its degree of redness for iron-rich layers (Birkeland, 1984, p. 24). The thicker, or redder the soil, the older it is assumed to be. Second, an estimate for an unknown age is obtained by matching to the “index of development.” The soils of “known” age are derived from the stratigraphy of the underlying, or overlying sediments, which is based on the geological time scale, and involves all the additional assumptions that have gone into its development. For the Quaternary period, the basis for soil stratigraphy, originally, was the four-ice-age alpine model (Table 7.2). This basis has been supplanted by the oxygen-isotope record in oceanic sediments, with resultant confusion, concerning previous correlations based on paleosols. Since the oceanic record has a longer time scale, the dates of the various soils and ice ages have been extended further into the past. For example, the last interglacial-the Sangamon, in the North American classification-is now dated at about 120,000 years ago. If the “maturity” of an unknown soil is similar to the Sangamon soil, the unknown soil is assumed to be about 120,000 years old. To refine the soil-dating scale, soils assumed to be the most recent-Holocene and late Pleistocene-are sometimes dated by carbon-14. From the thickness of these dated soils, a typical soil formation rate is determined, and extrapolated into the Pleistocene, beyond the range of C-14 dating. Flint (1971, p. 291) states:

It has been possible to estimate the maximum time required for the development of some postglacial soils in glacial drift, in areas where deglaciation has been dated by C14... or by otherwise bracketing a soil between two relevant C14 dates.

Carbon-14 dating of Holocene soils has resulted in a length of time for soil formation to be tens of thousands of years. Consequently, soil formation is believed to be a very slow process. For soils presumed too old for C-14 dating, which is practically all the Pleistocene, there is rarely any other method for absolute dating. Efforts are being made to develop techniques that will supplement and extend the range of C-14 dating (Mahaney, 1984). Kemp (1986, pp. 243, 245) writes:

Many Quaternary sediments cannot be dated absolutely, primarily because their ages lie outside the range afforded to radiocarbon dating. Although new techniques such as thermoluminscence [sic] and amino acid racemization may in the future assist in the dating of deposits and soils, most sediments can still only be dated relative to others using lateral correlations based on lithological criteria and fossil assemblages determined by environmental conditions. These approaches, however, are liable to introduce errors in correlation, which could lead to incorrect dating of soils.... Particular doubts have been expressed over the differentiation of tills of successive cold stages

Such is the methodology of soil stratigraphy. Extensive problems with this simple scheme have been pointed out by a number of authorities. Many of these problems have been alluded to already in this section. Bowen (1978, p. 183), in reference to the four-ice-age scheme in the north-central United States, points out: In retrospect it would seem that the earlier use of paleosols for subdividing the classical sequence of central North America outran the state of soil science at the time. Currently increasing knowledge of present soil forming processes serves to emphasize the inadequate basis of many such early correlations.

Richmond and Fullerton (1986, p. 184) add: “However, they [paleosols] have no definite chronologic significance and they cannot be correlated reliably from one region to another on the basis of their physical properties.”

Vreeken (1984) essentially says there are too many variables in soil stratigraphy that cannot be treated adequately. The character of soils depends upon parent material, climate, topography, vegetation, and time, and each of these is related to a host of other variables, as well as with each other (Birkeland, 1984). Many environmental factors may cause a soil to form rapidly. Moisture and temperature are highly significant factors in soil development (Boardman, 1985, pp. 62-65). These variables control the rate of physical, chemical, and biochemical processes that occur within a soil. Higher moisture and temperature can greatly increase the weathering rate and soil formation (Birkeland, 1984, pp. 275-324). The “type” soils of presumed known age have been taken from areas with little regard to lateral variations, or to the influence of other variables besides those on which the type classification of the soil is based (Valentine and Dalrymple, 1976, p. 215). Soils of the same age can vary in their “maturity,” due to the different soil-forming factors (Birkeland, 1984, p. 24).

Some of these problems are illustrated in the north-central United States, where various tills have been subdivided by soils. Table 7.2 presents the old four-fold classification for this area, and Figure 7.1 shows the surface location of each of the four putative glaciations. From this classification, one would think that a vertical profile through the Wisconsin till would often reveal several soils, each separated by a till layer, one set for each glaciation. This is rare; most often, a single till layer and overlying paleosol is found. Flint (1971, p. 299), in referring to soils that developed on till, says: “... at rare localities two interglacial soils occur.” (This is probably why Charlesworth felt the field evidence favored only two glaciations.) In other words, each till layer and its associated interglacial soil are found predominantly in the periphery area represented by each supposed glaciation in Figure 7.1. The four-ice-age model for the north-central United States, like models for other periods of the geological time scale, is built up from these “interglacial” soils. The important point is that these “type” soils are selected from different locations. The patches are then pieced together into a vertical sequence that is suppose to represent a universal time sequence. The Sangamon soil of the last presumed interglacial illustrates some of the pitfalls (Boardman, 1985, pp. 67, 68). This soil is widespread, but mostly is found south of the margin of the last glaciation-the Wisconsin ice age (Follmer, 1983, pp. 138, 139). In other words, the Sangamon soil is rarely covered by till, and in its “type area,” in central Illinois, the Sangamon soil is covered by loess. The Sangamon soil varies considerably from one location to another. As a result, the method of distinguishing this soil is questionable. The Sangamon soil is usually just assumed to be the youngest strongly developed clay layer in any locality (Birkeland, 1984, p. 338). Bowen (1978, p. 53) believes this practice is ill-advised. Furthermore, the Sangamon soil resembles the soils from the presumed previous two interglacials (Flint, 1971, p. 299), differing from them largely in the thickness of the B horizon. But thickness differences can be due to factors other than time, making the whole subdivision into four ice ages subjective.

Coupled with the poor methodology of soil stratigraphy is a lack of knowledge concerning modern soil-formation rates. Very few quantitative studies on soil formation have been undertaken (Birkeland, 1984, pp. 118, 119). Boardman (1985, p. 65) states:

Formidable problems concerning dating, correlation, and a lack of knowledge of rates of contemporary soil-forming processes, frequently preclude more precise evaluation of the effects of time versus environmental factors. A modern-day example of rapid soil development is a 14-inch-thick soil that formed in 45 years on the volcanic ash deposited from the Krakatoa volcanic eruption (Leet and Judson, 1965, pp. 83, 84). Ash below the soil, while not yet classified as soil, has already been significantly altered. The red color of the B horizon has been used as a relative guide to soil development and age. The redder the deposit, the older it is assumed to be. However, redness may not develop at the same rate for all deposits, and there are processes that can cause a soil to be red which do not involve extensive time (Boardman, 1985, pp. 65, 66; Pawluk, 1978, pp. 63, 64). Valentine and Dalrymple (1976, p. 212) write: “It [color] may be inherited from the parent material, or color variations may be produced by deep subsurface weathering, associated with ground-water movement in layered sediments.”

Considering all the difficulties involved, paleosols should not be used to date glaciations, or to separate them into multiple events. A strict application of the principle of uniformitarianism would require that soil stratigraphy be disqualified as a relative dating method. Due to all the problems in trying to find evidence for 20 or 30 glaciations in the continental deposits, most glacial geologists have abandoned soil stratigraphy, and now feel free to comment on the significance of the method. This section will end with one such comment. Ericson and Wollin (1968, p. 1227) state: “Furthermore, the long interglacial stages are often represented by nothing more than a weathered, or chemically altered zone on the surface of glacial detritus left by a preceding ice sheet.” They are not impressed with the evidence for multiple glaciation based on continental deposits.

One Dynamic Ice Age The character of the till, with interbedded day and organic remains in some areas along the periphery, can be explained by one ice age. The explanation is basically the same as that advocated years ago by the monoglacialists. They postulated an ice sheet that oscillated at its margin, sometimes widely. These oscillations are no different, except for scale, than those observed for modern glaciers. Glaciers, at present, advance, retreat, readvance, and in some instances, surge. Ice motion is governed by many variables, most of which are related to climate. A recent example is provided by glaciers in the Swiss Alps. These glaciers reached a recent maximum about 1820, and remained relatively stable, with only minor oscillations, for about 50 years. Around 1870, they retreated rapidly, and then readvanced until shortly before 1900 (Paterson, 1981, p. 241). These glaciers, as well as most other glaciers in the Northern Hemisphere, have been retreating during the 20th century.

How can an ice sheet in the post-Flood climate, although rather thin, oscillate widely? Before this is answered, we need to examine the variables that determine the speed at which a glacier moves. We will then take a look at these variables in the post-Flood climate. We will conclude by showing that some glacial geologists recognize that one glaciation can, indeed, form multiple tills, with nonglacial deposits between.

Glaciers move over relatively flat terrain by three mechanisms: 1) internal deformation of the ice crystals, 2) basal slip, and 3) the deformation of the basal till. The force for ice deformation has been correlated to two large-scale ice-sheet variables. These are ice thickness and surface slope, The relationship between these factors and deformation is highly non-linear. When the surface slope is small and the flow is smooth, ice deformation is generally proportional to the fourth power of the thickness and the third power of the surface slope (Paterson, 1981, p. 87). Therefore, a thick ice sheet with a relatively steep surface slope will deform quickly. But, if the surface slope exceeds a modest value, the power relationships become invalid. The ice can still deform rapidly, scientists just have difficulty formulating the glacial response. A given force can cause a large range of motion in a glacier, depending on several variable characteristics within the ice. Internal deformation of the ice crystals depends upon their orientation, the number of crystal lattice dislocations, and the amount of impurities. As a result, internal deformation is a highly complex and non-linear phenomenon that no model can represent adequately (Paterson, 1981). In general, a glacier will deform faster for a given stress, if the crystals, after recrystallization, are orientated in the direction of the stress, and if the number of dislocations and impurities is relatively high. Ice crystals tend to slip more easily along dislocations and over areas of impurities. These variables illustrate some of the problems inherent in modeling glacial motion.

Basal slip depends upon such variables as bed roughness and basal shear stress. It is potentially much faster than ice deformation. Modern sliding velocities range from zero for cold-based glaciers, to several kilometers per year for large outlet glaciers of the Greenland and Antarctic ice sheets, and for glacial surges (Paterson, 1981, pp. 112, 113). There are many problems in developing a model for basal slip, and observations below the ice are, of course, difficult. One feature, in particular, is highly correlated to rapid motion. That is reduction of sliding friction by a layer of water at the base (Paterson, 1981, p. 128). Sugden and John (1976, p. 30) state:

Furthermore, it has long been known that there is a relationship between high summer rates of glacier flow and the existence of basal meltwater, at least in the ablation area of glaciers.

Surges are poorly understood, but most likely are related to basal water buildup in the ablation zone (Paterson, 1981, pp. 275-298). A surge is a sudden increase in glacial flow, from normal to perhaps 100 times faster, over a period of a few months, to as long as three years. Surges can rapidly advance a glacier. The greatest known surge advance Isa 21:1-17 kilometers for a glacial in Spitsbergen. The temperature of the ice sheet, which depends on the climate, is an important variable that controls both the rate of ice deformation and the rate of basal slip. A temperate ice sheet will deform faster than a cold ice sheet. Sugden and John (1976, pp. 25, 26) state: “The warmer the ice, the more easily it deforms. For example, the strain rate [deformation rate] at a temperature of -22°C is one-tenth of its value at 0°C....” A temperate glacial will slip faster along its base, due to more water from melting ice and snow.

Another mechanism for rapid sliding of a glacier has been discovered recently in Antarctica. Using radar to penetrate through an ice stream with low surface slope, it was discovered that the deformation of a thin layer of basal till under high pore water pressure was likely causing unusually rapid motion of the ice (Blankenship et al., 1986; Alley et al., 1986). Boulton (1986) suggests that this new information may cause a paradigm shift in glaciology, especially for concepts of ancient Quaternary glacial velocity. He notes that Quaternary glaciers flowed over strongly deformed and predominantly soft-sediment beds, and probably, as a result, moved rapidly under low-driving stresses:

It has been further argued that such a mechanism controlled the behaviour of mid-latitude Quaternary ice sheets, with a soft, easily deforming sedimentary substratum permitting high glacier velocities for relatively low driving stresses; rapid responses to changing climate; and fast volumetric growth and decay facilitated by rapid changes in the extent of the ice sheets (Boulton, 1986).

Now that we have discussed the variables that influence glacial motion, we can ask, would the post-Flood ice sheets have moved rapidly? The answer is yes. Most of the factors discussed above would favor rapid motion at the periphery, but not in the interior of ice sheets. As stated by Boulton, the substratum was easily deformable and favorable for rapid ice motion, with low driving stress. This applies mainly along the periphery, where the substratum is composed of soft sedimentary rocks. In the mild, post-Flood winters, the ice sheets would have been relatively warm at the periphery, favoring rapid deformation. Also, volcanic dust would have added impurities, which would give the ice a greater rate of internal deformation. Ice, presumably from the ice age, in Greenland and Devon Island ice cores contains sufficient microparticle content to deform about three-to-four times faster than pure ice (Reeh, 1985; Fisher and Koerner, 1986). The Laurentide ice sheet did not build in northeast Canada and flow south into the United States. It more-or-less developed in place, and moved according to the complex dynamics of ice-sheet flow. Generally, this direction would have been south, at the southern periphery, but there is no reason for it to not move in a different direction in some areas. Since the storm tracks paralleled the southern and eastern edge of the ice sheet, the margin, in this area, would become thicker, with a relatively greater surface slope. Consequently, the outward-flow rate would have been greater along this portion of the periphery.

Another factor that would have contributed to rapid glacier movement is the large amount of basal water expected in a mild ice age. Geothermal heat will melt an average of about six millimeters of ice annually. Frictional heat melts another six millimeters if the ice sheet moves at only 20 meters/year (Paterson, 1981, p. 142). Since the evidence indicates the ice sheets moved much more rapidly than that, significant quantities of water from frictional melting would be added at the base of the post-Flood ice sheet. Water from surface melting and summer rain would reach the base through crevasses and conduits. With so large an amount of basal water, surges would likely have been common along the periphery. Table 7.3 lists a summary of the variables favoring rapid ice movement along the periphery during the post-Flood ice age.

Oscillations at the margin of a post-Flood ice age would have been greatly affected by the variable input of volcanic dust and aerosols into the stratosphere. Since the dust and aerosols would have been greatest at the beginning, the largest southerly extension of the Laurentide ice sheet, in the continental United States, likely would have occurred at this time. In the north-central United States till, that has been divided into the Nebraskan, Kansan, and Illinoian ice ages, would have been deposited at this time. As volcanism waned, solar melting would have been greatest along the southern portion of the ice sheet. The southern margin would retreat northward to a more-or-less-equilibrium position (the Wisconsin ice edge). Much heavier precipitation than is currently characteristic of the area south of the Wisconsin ice edge would have caused extensive weathering of the surface of the newly exposed till, and formed gumbotil and clay soils in poorly drained areas. The surface would develop an “old,” or eroded, appearance in a short time. During the large-scale ice retreat in the north-central United States, plants and animals, some indicating mild conditions as discussed in Chapter 4, would have lived south of the ice sheet and rapidly populated previously glaciated areas. At the Wisconsin equilibrium position, marginal oscillations would have continued. A high surface slope at the margin, at times, would have aided southward advances and surges. Long-term readvances would have occurred during periods of high volcanic activity. Mild climate plants, and possibly some animal bones, likely would have been buried by these readvances. Scientists finding these remains would naturally postulate warm, interglacial periods.

Ice movement in interior Canada would have been sluggish. The bedrock is mostly hard crystalline rock that does not easily deform. At first, this area would have been relatively warm, and would have received much of its moisture from the Arctic Ocean. Ice velocity would have been faster at this time. As the oceans cooled, so would the atmosphere. The annual available moisture would consequently diminish. The storm tracks would progressively be displaced farther south. Under these conditions, the ice over the interior of the ice sheet would end up relatively thin, with a rather flat surface slope. An ice dome over Keewatin would be favored by the moisture from the Arctic Ocean, while an ice dome over Labrador-Ungava would grow mainly from North Atlantic moisture. Another ice dome may have formed between the Great Lakes and Hudson Bay, and later in the ice age, over the Queen Elizabeth Islands of northeast Canada. A thin ice sheet and relatively cold air temperatures result in cold basal temperatures, with little basal water. Accordingly, the interior portion of the ice sheet likely became frozen to its bed. Because of all these conditions, the ice sheet would move little in interior regions. During deglaciation of the interior region, the margin would oscillate, but with the very cold climate, the rate of motion would have been slow. The net result would be little erosion of the bedrock, and only a thin, coarse-grained, final till cover.

Some glacial geologists, although committed to multiple glaciations, now recognize that one glaciation can form multiple tills, with non-glacial deposits between them. For instance, Derbyshire (1979, p. 77) writes:

Long-standing problems of interpretation of complexly interbedded tills of the Pleistocene glaciations have been resolved as a result of the realization that not all tills are of subglacial origin, and that a formation of several tills interbedded with meltwater stream deposits may be the product of a single advance and retreat of the glacier.

Sugden and John (1976, pp. 135, 220, 234) and Paul (1983) agree with Derbyshire, and show how several till sheets can develop within the periphery of one ice sheet, due to shearing, or thrusting, of debris-rich basal layers. This process is illustrated in Figure 7.4, and has been observed on a glacial in Greenland (Flint, 1971, p. 107).

Figure 7.4 <C:\Program Files\e-Sword\Graphics\ICE\165.jpg>    Shearing of Basal Ice and Debris at Glacial Snout

Shearing of basal ice and debris at the snout of a glacier. Retreats and advances of the glacier cause a complex mixture of till, flowtill, and outwash deposits after the ice melts that have been mistaken for multiple glaciation.

Multiple till layers can be formed, at least locally, well to the north of the ice margin. This is accomplished by episodes of erosion, and by discontinuous basal, or lodgement till deposition (Eyles and Menzies, 1983, pp. 38-41). Eyles et al. (1983b, p. 222) indicate how this pattern can lead geologists to postulate multiple glaciations: In drumlinized terrain ubiquitous ‘tripartite’ stratigraphies composed of lower till(s), middle sands, gravel and laminated clays and upper till(s) have been used extensively as mapping units and taken to indicate multiple glaciation. Many multiple successions can probably be explained by the former presence of subglacial melt streams coupled with shifting ice divides and changing ice flow directions.... The controversy over the Scarborough Bluffs section along Lake Ontario, supposedly showing multiple glaciations, has previously been discussed. When challenged on their seemingly unreasonable subdivisions of the stratigraphy of the Scarborough Bluffs, Eyles et al. (1984, p. 896) responded:

We place stratigraphic boundaries ‘rather differently’ from those of Karrow’s original 1:50,000 regional mapping... simply because the sediments have been looked at in detail. Logging shows that lithological breaks (considered as major stratigraphic boundaries by Karrow) are part of a single depositional sequence with transitional or interbedded contacts between such lithologically, dissimilar beds. The type-section approach, upon which the multiple glaciation concept was derived years ago, is seen as overly simplified and confusing, in view of newer research, which indicates that one glaciation can deposit multiple till sheets (Eyles, 1983, pp. 15, 18). The new three-dimensional view “... sees multiple tills as the normal expectation in glacial sediments” (Paul, 1983, p. 85).

Surging glaciers that stopped at the approximate location of a previous advance, or advanced the margin farther, would cause stacked till sheets and/or multiple moraines. Several major lobes of the Quaternary ice sheets are now assumed, by many glaciologists, to have advanced by surges (Eyles and Menzies, 1983, pp. 27, 28). At least 32 moraine arcs, in Illinois, are believed to have been deposited by repeated surging (Bowen, 1978, pp. 176, 177). The landforms produced by modern surging glaciers, are similar to Pleistocene deposits in some areas (Paul, 1983, p. 77). This is as expected along the periphery of the post-Flood ice sheets.

Organic remains may have been engulfed by glacial readvances and surges. Eyles et al. (1983b, p. 222) say that a readvancing ice lobe can sandwich organic material between till sheets. Charlesworth (1957, p. 912) points out that vegetation grows near the snouts of a number of glaciers today. He adds that monoglacialists cannot appeal to this evidence, because vegetation is near modern glaciers only because the glacier forms at high altitude and flows to lower altitude, unlike Pleistocene ice sheets that mostly formed over low terrain. According to Charlesworth, plants could not grow adjacent to the Pleistocene ice sheets, because the climate was too cold, and because some of the vegetation indicates milder temperatures. However, these deductions would not be valid for a mild ice age. In summary, the post-Flood ice sheets would have been dynamic, and characterized by rapid glacial motion. One ice age can account for the character of the deposits along the periphery, even in the north-central United States. It can also explain the character of the glacial features found over interior regions of the ice sheets.