Vegetation associated with the Heisler mastodon site, calhoun county, Michigan.
Editor's Comments. Rachel E. Bearss was an undergraduate student at Alma College when this paper was written. This publication puts the Heisler mastodont into detailed contest with the environment in which it lived and died. It is also a good example of the productive interaction between Ronald Kapp and his students.
Over forty fossil mastodons have been discovered in the lower peninsula of Michigan in recent years (Holman et al. 1986). In a few instances the bones have been examined for evidence of butchery (Fisher 1984), a matter of continuing interest to archaeologists and those concerned with the causes of megafaunal extinction (e.g., King and Saunders 1984). Sediment samples, wood, and plant macrofossils have been radiocarbon dated and vegetational and paleoecological analysis has been undertaken at a few localities. It is thought that the American Mastodont, Mammut americanum (Kerr), became extinct about 10,000 years ago (Meltzer and Mead 1983), soon after the major climactic shift to early postglacial conditions.
Among the recent mastodon discoveries in lower Michigan is the Heisler Mastodon, which was found in Clarence Township of Calhoun County (SE 1/4, NE 1/4, NE 1/4, Sec. 14, T1S, R4W). Fossil remains were first recovered by Lester and James Heisler during the tiling of a small depression in a tilled field. Preliminary excavations, during which several bones were unearthed, were made in late 1984 and again in summer 1985. Further field work on August 25, 1985, revealed the skull of the animal with one tusk in place and the other broken. Several ribs and vertebrae were also recovered during these field excavations, which were directed by Daniel Fisher, Museum of Paleontology, University of Michigan.
A sediment sample (no. HMS) directly associated with skeletal remains was taken in 1984 and analyzed for pollen content; a radiocarbon date of 11,160 B.P. (before present) was obtained from wood directly associated with the bones.
Additional sediment samples were taken at various locations and stratigraphic levels in 1985; their analysis is the subject of this paper.
The original wet depression from which the mastodon remains were recovered is approximately 40 meters in diameter; it is part of a topographically closed lowland that extends NE-SW at 290 m (950 ft.) elevation. The soil is a fine black muck, doubtless degraded, cultivated peat. Sediment is 2.2 meters thick in the longest sequence examined; grayish sand, which continues to an unknown depth, is found beneath these lateglacial and postglacial deposits. The sedimentary series extends downward from disturbed black muck at the surface through peat, marl, and clay as shown in the stratigraphic diagram (Figure 1).
SAMPLE COLLECTION AND PREPARATION
The samples described in this paper were obtained from Pit C, excavated in 1985 (see Figure 1). A fresh surface was cleared on the pit wall and sediment was collected in plastic vials at 5 cm intervals. A Livingston piston sampler was used for retrieval of samples from below the pit floor; these consisted mostly of clay with alternating bands of fine sand to near the base; the core extended into the basal sand layer.
Two pieces of wood were removed from 0.7--1.0 m depth in Pit C. One was a stump 9 cm in diameter which had a 30 cm segment of stem and three roots (the longest measuring 30 cm) attached; the other was a 15 cm diameter log of which a 72 cm segment, extending across the east end of the pit, was collected. The wood samples were wrapped in foil and plastic for transport and storage. Thin, hand sections were made of the fossil wood; these were stained with safranin and mounted in glycerin jelly.
Of the thirty-nine sediment samples taken from Pit C, twenty were processed according to standard Erdtman acetolysis procedures, following carbonate removal with 10% HCI. Samples from clay-rich layers were subjected to hydrofluoric acid processing (suspended in concentrated acid, heated to 10000, with treatment continued for 24 hours after cooling) to remove clay particles. The concentrated pollen suspensions were placed in glycerin jelly for storage and preparation of microscope slides.
Pollen counting was performed at 450xand 900x (oil immersion) magnification using a Zeiss binocular compound microscope with mechanical stage and a calibrated ocular micrometer. Each slide was fully counted over the extent of the coverslip to ensure that nonrandom distribution of pollen would not skew the results. Pollen frequencies were calculated, both as a percentage of total pollen (excludingaquatics) and as an absolute frequency (by determining the ratio with known quantities of an introduced, exotic pollen type, Eucalyptus).
A sediment sample from 40--45 cm depth was collected and submitted for radiocarbon dating; the date of 10,740 [+ or -] 300 B.P. (Beta--16,250) permits an estimate of the rate of sedimentation and comparison with the 11,160 [+ or -] 110 B.P. (Beta--12934)C--14 date from a wood sample recovered in the 1984 excavations at the level of the fossil bones (80--100 cm depth).
The data obtained from the pollen analysis are presented in a percentage and absolute pollen frequency (APF) diagram (Figure 2). Only abundant genera and groups of pollen types are presented in this figure. A complete table showing actual counts of each pollen and spore type may be obtained from the authors (Kapp, Alma College). Pollen frequency in the deeper strata was extremely low; these results are simply shown symbolically (X or p), but are not statistically significant. Absolute pollen frequency (APF) data are not available for the first sample collected (designated HMS); the cross-hatched bar represents percentage frequency for that sample, not APF. The HMS sample was collected in 1984 in direct association with mastodout skeletal remains and the wood which was radiocarbon-dated at 11,160 B.P.
The APF data were summed for each sample count and may be compared in a bar graph presentation in the right profile in Figure 2; P/cc represents the number of total pollen and spores per cc of raw sediment. Four frequency zones are discernible: negligible below 170cm, low from 100--170cm, intermediate from 60--100 cm, high from 40--60 cm. Absolute pollen frequencies are shown as open bars at each level for which this calculation was possible.
The black portion of the percentage diagram represents sample levels in which it was possible to complete a satisfactory pollen count. Samples from the deeper levels yielded statistically inadequate pollen counts (<100); consequently they are represented by an open line graph. Samples 37 and 39 yielded very few pollen grains and are represented numerically.
The pollen diagram of the Heisler Mastodon Site can be divided into four zones. The deepest, clayey, strata (below 175 cm) yielded very little recent pollen; Paleozoic spores of at least five major taxa, mostly with trilete scars, dominate the palynomorphic record. The extremely low pollen frequency of samples 37 and 39 indicates that vegetation was sparse or nonexistent in the immediate vicinity of the depositional site. The numerous Paleozoic spores were apparently derived from Mississippian or Pennsylvanian rock flour released in meltwater from the nearby receding glacier. The small amounts of modem pollen from these basal strata were almost certainly introduced by long-range drift from vegetated areas far to the south or southwest of the site. Nonarboreal pollen types (NAP), mostly composites, grasses, and fern spores, were most frequent; however, spruce (Picea), other conifers, and occasional oak (Quercus) pollen grains were encountered.
The deepest clayey deposits at both sites A and C included sharply delineated bands of fine sand. Samples 37 and 39 were from the clay layers associated with the sandy bands. We postulate that these banded sediments record the seasonal (annual?) melting and freezing cycles of the nearby glacial snout. Apparently the coarser sands were carried into a proglacial lake or pond which covered the Heisler locality during periods of melting; these formed the sandy bands. During cold periods, when the glacier remained frozen, finer sediments settled out forming the clayey atmosphere and more numerous Paleozoic spores derived from the glacial meltwater itself. The source and provenance of these Paleozoic microfossils would require careful correlation of types and frequencies of the palynomorphs with in situ rock strata in the areas overridden by the Saginaw glacial lobe. They were most likely derived from areas within the Michigan sedimentary basin northeast of the site.
Presumably deposition of the earliest post-ice sediments began at the He islet sire at approximately 14,800 years ago. The locality is at the extreme outer margin of the Kalamazoo-Mississinewa moraine complex, adjacent to the retreating margin of the Saginaw glacial lobe (Farrand and Eschman 1974). It is located in an area dominated by ground moraines and glacial outwash channels. The depositional history begins, therefore, at the earliest possible time following the earliest deglaciation of Michigan.
Samples 11 to 1 (100-170 cm) are dominated by spruce and fir (Abies is of low frequency) tree pollen (Picea and Abies) and non-tree pollen types (NAP). Paleozoic spores were also found, especially in deeper zones, indicating that glacial meltwater still entered the basin or that the clay of glacial origin was being reworked by erosion and deposited in the Heisler basin. Both the percentage and APF of Picea declines to level 7 and then increases to level 11; the frequency of NAP is the inverse of that of spruce. The total pollen deposition of NAP peaked at this time, largely due to increases in ferns, spores, ragweed (Ambrosia), and wormwood (Artemisia). This was apparently a time of very open vegetation with better growing and pollinating conditions for the herbaceous plants. If trees had become established at all in the immediate vicinity, they were certainly localized and scattered, In addition to the conifers, several genera of deciduous trees were contributing pollen to the record: Quercus-oak, Fraxinus-a sh, Betula-birch, Ostrya/Carpinus-ironwood, and/or blue beech. Both the three-furrowed ash pollen type (Fraxinus nigra), and the four-furrowed pollen type, produced by F. americanus and F. pennsylvanica, are represented; however, F. nigra (which prefers cold, damp habitats) was most commonly found. Aquatic types (Typha/Sparganium-cattail and/or bur reed and Potamogeton-pondweed) were present in substantial numbers throughout most of this zone; they were completely absent at level 9. While low pollen counts in this zone make conclusions uncertain, the absence of aquatic pollen types at level 9 suggests a period of considerable dryness.
Samples 15-21 (50-100 cm) are recognized as the spruce pollen zone. It is characterized by increased pollen deposition and a consistently high percentage (>40%) of spruce. Pine and other conifers are present in small quantities (<5%) up to level 19 (70-75 cm) above which tamarack (Larix) and cedars or yew (Cupressaceae or Taxaceae) were not found. Oak pollen was present in stable percentages in levels 15 and 19 but increased at level 21 and above. Fraxinus pollen increased sharply in both relative percentages and in APF, the frequency of other deciduous trees and shrubs (elms, alder, willow) peaked at level 21. Fraxinus and certain other hardwoods were apparently becoming established in the area. Although the APF of herbaceous pollen (NAP) remained relatively stable, the relative frequency declined throughout this zone from 20 to 10%, reflecting greater actual influx of tree pollen. The absolute frequency of aquatic types remained stable in this zone and the relative percentages fluctuated slightly. Vegetatio nal changes recorded in the spruce pollen zone reflect a slowly closing spruce forest with few other conifers and various deciduous trees present in the area.
The mastodon bones were recovered from this stratigraphic horizon and it is also the zone of concentrated fossil wood accumulations. All of the wood examined is coniferous and the two samples studied in detail, a small stump and a 15 cm diameter log, were apparently both of Picea (spruce); it should be noted that the distinction between the wood of spruce and that of tamarack (Larix) is technically difficult and in fossil material sometimes uncertain.
The fourth and uppermost zone, represented by samples 23 and 25 (40-60 cm, beneath the muck), shows greatly increased total pollen deposition and is dominated by pine (Pinus). The relative percentage of spruce diminished dramatically and its APF declined slightly as pine began to replace spruce in the pollen record. Both the relative percentage and APF of pine increased sharply in this zone. Other conifers were not present and the percentages of all other types, except oak, decreased. Oak pollen continued the steady increase which began at about 75 cm, approximately 11,000 B.P. The increase in oak pollen probably represents a true increase in the number of oak trees in the vicinity although Quercus is a notably heavy pollen producer which is usually overrepresented in pollen diagrams.
This uppermost zone was deposited near the end of the late-glacial era; throughout the Great Lakes region pine pollen replaces spruce as the dominant pollen type at about 10,500 B.P. The continued decline of nonwoody pollen types (NAP) and the sharp decrease in percentage and APF of aquatic types may represent both a drier, warmer climate and reduction in the extent of unforested, marshy, and open water habitats in the vicinity of the Heisler mastodon site.
The Heisler Mastodon Site began accumulating clayey and organic sediments as early as 14,800 years ago, immediately after glacial retreat from northeastern Calhoun County. The earliest microfossil record is an admixture of redeposited Paleozoic spores and pollen from distant deglaciated sites. The pollen diagram derived from the Heisler sedimentary sequence permits an interpretation of the late-glacial vegetation and paleoecology at a time when mastodons and other large Pleistocene mammals occupied lower Michigan and the earliest human activity in the state was occurring. Forest cover was scattered and sparse until 13,000 B.P., possibly later. The landscape was dominated by ponds and open sedge marsh; the climate was sufficiently cool and moist to support glaciers further north in Michigan. By 12,000 B.P., or earlier, spruce forests dominated the region; occasional north temperate deciduous trees were present on suitable sites. Willow and alder shrubs fringed the numerous marshes, swamp forests, and bogs. A m arly pond with spruce and probably cedar at its margins had developed by about 11,200 B.P. when the mastodon died or possibly was butchered at the site. Further paleontological and taphonomic interpretation is required to establish human association with the mastodon. Somewhat later, apparently shortly after 11,000 B.P., pine began to dominate the pollen record, heralding the major climate shifts of the postglacial period.
[FIGURE 2 OMITTED]
Application for funding of the radiocarbon dating is expressed to the National Geographic Society (grant no. 2938-84) to J. Alan Holman of Michigan State University) and to the Alma College small grants program.
FARRAND, W. R., AND D. F. ESCHMAN. 1974. Glaciation of the Southern Peninsula of Michigan. Mich. Acad. 7:31-56.
FISHER, D. A. 1984. Taphonomic analysis of late pleistocene mastodon occurrences: evidence of butchery by North American Paleo-Indians. Paleobiology 10:338-57.
HOLMAN, J. A., D. C. FISHER, AND R. O. KAPP. 1986. Recent discoveries of fossil vertebrates in the Lower Peninsula of Michigan. Mich. Acad. 18:43 1-63.
KING, J. E., AND J. J. SAUNDERS. 1984. Environmental insularity and the extinction of the American mastodont. In Quaternary Extinction -- A Prehistoric Revolution, edited by P. S. Martin and R. O. Klein, 3 15-339. University of Arizona Press, Tucson.
MELTZER, D. A., AND J. I. MEAD. 1983. The timing of late Pleistocene mammalian extinctions in North America. Quaternary Research 19:130-5.
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|Author:||Bearss, Rachel E.; Kapp, Ronald O.|
|Date:||Sep 22, 2003|
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