Fossil Pollen and Spores from the LoDaisKa Site, Colorado

By Donald R. Whitehead

Introduction

A preliminary pollen analytical investigation has been attempted on material from the LoDaisKa Site in order to determine the feasibility of working with such sediments, and to see what culturally significant plants might be represented. Due to the extremely poor preservation in all but the lowermost levels no pollen diagram has been prepared. Such a diagram would be misleading, because many of the original constituents of the pollen flora might have been destroyed by differential degradation. A brief description of the investigation follows, with a discussion of the potentially significant grass pollen.

Techniques

All samples were prepared by boiling for six minutes in 10% KOH, washing with 10% HCI to remove carbonates, boiling for ten minutes in about 30% HF, actolysing for one minute, staining with fuchsin, and mounting in silicone oil. For each sample a total of four slides was counted by making traverses at one millimeter intervals.

Identification of Large Grass Pollen

In order to attempt an identification of the various large grass pollen encountered, the long axis of each grain and the pore diameter (including annulus) were measured, and the ratio between the two plotted. Barghoorn, Wolfe, and Clisby (1954) have suggested that this ratio can be used to supplement size measurements in attempting to identify fossil pollen of the tribe Maydeae. However, one can not compare directly the size data from the LoDaisKa fossils with the data from modern pollen assembled by Barghoorn, Wolfe, and Clisby (l.c.). Christensen (1945) has shown that not only do recent and fossil grains of the same species differ in size (depending partly upon the type of sediment in which the pollen is preserved), but also, different methods of preparation greatly affect the size, often differentially with respect to fossil and modern pollen. The recent pollen measured by Barghoorn, Wolfe, and Clisby (l.c.) was prepared by acetolysis and mounted in glycerine jelly. By comparing the size of modern Corylus avellana pollen prepared and mounted in this manner (ca. 28, Christensen, 1945) with the size of fossil Corylus avellana pollen from a variety of sediment types prepared and mounted by the technique used in the present investigation (ca. 24, S. T. Andersen, pers. comm.), one can arrive at a factor (7/6) by which the size of the fossils can be multiplied in order to compare more directly with the data presented by Barghoorn, Wolfe, and Clisby (l.c.). It should be emphasized that such an absolute comparison is dangerous, because there is no way of determining precisely how the environment of preservation at LoDaisKa has affected the pollen, and there is no guarantee that size changes of Corylus and Gramineae pollen are absolutely proportional.

For each grass grain both the long axis measurement and the pore axis ratio are tabulated in the results below. Only fully expanded grains were measured.

Sampling (Author’s Note)

The provenience of the samples analyzed below is as follows:

All samples were taken at 6 inch intervals.

Samples W 1-10 were collected in Square J8, starting at 38 inches below baseline.

Samples E₁ 1-6 were collected in Square M11, starting at 38 inches below baseline.

Samples E₂ 3-7 were collected in Square P 9-10, starting at 62 inches below baseline.

Samples E₁ 1 - E₁ 5 (38-68″) Preservation extremely poor, only badly corroded pine pollen, a few Compositae grains, and many plant fragments (mostly coniferous tracheids).

Sample E₁ 6 (68-74″)

Pinus—9

Gramineae—2, (70,21ₘ, pore obscured by detritus), (40.46ₘ, 1:4.9)

Sample E₂ 3 (62-68″)

Pinus—10

Sample E₂ 4 (68-74″)

Pinus—19

Picea—2

Fern spore—1

Gramineae—-1, (71.40ₘ, pore distorted)

unknowns—2

Sample E₂ 5 (74-80″)

Pinus—66

Picea—1

Juniperus—2

Quercus—1

Compositae (total)—24, (Artemisia—11,

Ambrosia type—2, Liguliflorae—1)

Chenopodiaceae—11 Caryophyllaceae—4

Allium—3 Geranium—1

Polygonum, sect. Pericaria—3

Gramineae—5, (53.55ₘ, 1:3.8), (70.21ₘ, pore obscured),

(46.41ₘ, 1:4.3), (58.30ₘ, 1:5.5), (45.22ₘ, 1:3.5) unknowns—5

Sample E₂ 6 (80-86″)

Pinus—60

Quercus—2

Compositae (total)—22, (Artemisia—14, Liguliflorae—1)

Convolvulaceae—1 (fragment of a large periporate type)

Caryophyllaceae—5

Chenopodiaceae—4

cf. Cruciferae—3

Polygonum, sect. Pericaria—1

Allium—1

Gramineae—6, (40.46ₘ, 1:4.2), (61.88ₘ, 1:4.0),

(52.36ₘ, pore distorted),

(50.35ₘ, pore greatly enlongated),

(46.41ₘ, 1:4.9),

(45.22ₘ, 1:5.4). unknowns—10

Sample E₂ 7 (86-92″)

Pinus—54

Picea—2

Juniperus—1

Compositae (total)—20, (Artemisia—11,

Ambrosia type—1, Liguliflorae—2)

Caryophyllaceae—2

Chenopodiaceae—2

Geranium—1

Lonicera—2

Onagraceae—2

Gramineae—3, (50.35ₘ, pore obscured),

(29.75ₘ, 1:4.1), (39.75ₘ, pore distorted)

unknowns—6

Samples W1 - W8 (38-86″)

Preservation extremely poor, only corroded pine, composite,

and chenopod pollen. Abundant coniferous wood fragments.

Sample W9 (86-92″)

Pinus—14

Chenopodiaceae—2

Artemisia—1

Caryophyllaceae—1

Gramineae—1, (51.17ₘ, 1:3.9)

unknowns—3

Sample W10 (92″-base)

Pinus—13

Picea—1

Quercus—5

Compositae (total)—6, (Artemisia—5,

Ambrosia type—1, Liguliflorae—1)

Chenopodiaceae—1

Polygonum, sect. (Pericaria—1)

Lonicera—1

Gramineae—6, (49.98ₘ, 1:4.2), (52.36ₘ, 1:40), (49.98ₘ, 1:4.2),

(58.30ₘ, 1:4.5), (57.12ₘ, 1:4.0), (54.74ₘ, 1:4.2)

unknowns—4

Discussion

It is interesting to note that many of the plants identified from their megascopic remains by Walton C. Galinat are likewise represented in the pollen flora (e.g., Allium, Quercus, Juniperus and chenopods). As Galinat has also identified several fragments of Zea Mays, it was hoped that pollen of Zea might be found in some of the oldest levels. Unfortunately, none of the fossil grass pollen can be definitely identified as that of Zea. It seems obvious that the three largest grass grains (over 70ₘ) are too large to be Tripsacum, but whether they represent teosinte or Zea can not be established. The pore of two of these was obscured by detritus, and that of the third was greatly distorted. Thus no ratio could be established.

The remainder of the grass grains seem to fall within the limits of the genus Tripsacum (size extremes 33.6ₘ to 64ₘ, and ratio extremes 1:3.0 to 1:4.8), although the pore-axis ratio of some appears to be too large. However, the possibility must be left open that these smaller grains might not be Tripsacum. As yet there is very little pollen size data available for the grasses of North America. Geisler (1945) has measured pollen from 32 species and of these, Zizania aquatica has the largest grains (range 38ₘ-50ₘ). It is important to note that she did not employ acetolysis, so that this range is on the small side. In Europe, Firbes (1936) has presented pollen size data for 103 species of grasses, and of those he studied, Avena, Secale, Triticum, Hordeum, and Elymus possess pollen as large as that of Tripsacum. Hence it would appear to be necessary to study intensively the pollen of most of our native grasses in order to establish size and other morphological criteria for identifying the smaller LoDaisKa grass pollen.

As the preservation is distinctly better in the lower levels of the deposit, a careful and detailed pollen analytical investigation, with recourse to adequate reference material might be profitable.

Acknowledgments

The present investigation was carried out in the Laboratories of the Geological Survey of Denmark while the author was sponsored by a Fulbright Fellowship. The author is particularly indebted to Svend Th. Andersen for his suggestions and helpful criticisms of the manuscript.

Bibliography

Barghoorn, E. S., M. K. Wolfe, and K. H. Clisby, 1954. Fossil Maize from the Valley of Mexico. Bot. Mus. Leaflets, Harvard University 16: 229-240.

Christensen, B. Brorson, 1945. Measurements as a Means of Identifying Fossil Pollen. Danmarke Geologiske Undersgelse IV R., Bd. 3, Nr, 2.

Firbes, F., 1937. Der pollenanalytische Nachweis dos Getreidebaus. Zeitschrift für Botanik, Bd. 31: 447-478.

Geisler, F., 1945. A study of Pollen Grains of Thirty-two Species of Grasses. Butler Univ. Bot. Studies 7: 65-73.