Collection Protocols

Beginning in 1992 DMNH crews opened a stratigraphically controlled excavation along the westernmost wall of the Velvet Room. Excavation continued through the 1997 field season, ending when large boulders were encountered at the base of the site. Excavation was carried out by volunteers (most from the Western Interior Paleontological Society) under the direction of Don Rasmussen, Robert Raynolds, and Lou Taylor.

The DMNH excavation was spatially controlled by referencing specimens within 26 grids (grids = squares in this usage), each approximately 0.6 m (2 ft) on a side (figure 2.9). Each grid was excavated in arbitrary stratigraphic levels that were from about 5 to 10 cm (about 2-4 in.) thick. Levels did not always follow natural lithologic breaks, and because of the complex stratigraphy and slope of the deposit, these "micro-levels" are not correlative from one grid to the next (for example, level 5 in grid 5 could be a different age than level 5 in grid 17). However, stratigraphic horizons ranging from 5 to

FIGURE 2.8 Portion of a fossilized Neotoma midden recovered from middle Pleistocene strata in the CM Velvet Room excavation.

Fecal

Pellet

Molds

FIGURE 2.8 Portion of a fossilized Neotoma midden recovered from middle Pleistocene strata in the CM Velvet Room excavation.

FIGURE 2.9 Plan view of excavation grids for DMNH 644, Velvet Room. The "Line of Cross Section" shows the location of the vertical profile drawn in figure 2.10. (Drawn by D. Rasmussen.)

15 cm can be discerned based on lithologic features that are traceable across grids, and on that basis 18 horizons were defined, designated in alphabetical order from A at the top to R at the bottom (figure 2.10; table 2.2). Specimens were collected as the sediment was scraped into bags, and all bagged sediment was run through nested screens of 4, 8, and

16 squares/2.54 cm. The resulting fossiliferous matrix was taken to the DMNH for extraction of specimens by volunteers. Details about the DMNH excavation that will be pertinent to future analyses of the fossils were provided by RGR and LHT (pers. comm. to ADB, 2001):

Prior to excavation, the surface of the site was delimited by an orthogonal 2-foot by 2-foot (~0.6 x 0.6-m) pattern of 26 grids

[figure 2.9], and a master horizontal datum was established. The ground surface was covered by a veneer of modern wood rat droppings. Below the modern debris lay undisturbed Pleistocene strata, the upper strata of which were more fossiliferous and more clearly bedded than the lower strata. Below ~1 m angular rocks become more common and the strata less fossiliferous.

The grids were excavated from east to west. The earliest excavated grids (1-5) have modest data and were relatively thin [stratigraphically]. Subsequent grids were excavated to depths exceeding 3 m. Grids, or in some cases a pair of adjacent grids, were excavated in a series of numbered levels. Level 1 was at the top and excavation extended down to as far as level 33. While the digging was active, it was not practical to identify natural stratigraphic boundaries in the unconsolidated material; therefore levels were arbitrary, ranged in thickness from 5 to 10 cm, and were maintained with approximately horizontal floors (relative to datum) across grids. Natural stratigraphic divisions became evident as vertical faces were exposed [figure 2.10]. The digging was interrupted by periods of careful section measurement and documentation of stratal patterns visible on the vertical faces. Because the natural stratigraphic divisions slope relative to the horizontal floors of the arbitrary levels, the arbitrary levels are not coeval from grid to grid. Therefore the arbitrary numbered levels should only be used to recognize relative stratigraphic position within any given grid.

After digging ended, it was necessary to correlate the arbitrary levels across grids. Don Rasmussen and Robert Raynolds accomplished this by careful review of field notes, sketches, and figures. The numbered arbitrary levels were correlated into a series of lettered horizons with horizon A

being the youngest and extending down to horizon R [table 2.2; figure 2.10]. In general 2 to 4 arbitrary (numbered) levels were grouped into each newly defined horizon [and identified] by a letter designation. In a few cases the horizon boundaries split numbered levels; in these cases the horizon is indicated to contain portions of both levels [table 2.2]. Horizons designated by letters average 14 cm in thickness. Horizon A is characterized by modern Neotoma (wood rat) pellets; Horizon C is distinctively gray in color; and Horizon E is particularly well laminated. Other levels are generally rubbly, and all sediments are unconsolidated.

The depositional setting of locality DMNH 644 is unusual in that it appears to define a small alluvial cone that came from the west into the Velvet Room [figure 2.11]. Depositional dips of about 10° are common and exhibit a radial pattern. It is likely that alternation of moist and dry conditions defined variable patterns of filling, resulting in the establishment of bedding patterns. Overall the package of strata becomes finer upward, suggesting [that] the orifice supplying sediments gradually became clogged or cut off.

DMNH 644 was sampled for paleomagnetic analysis in 1993, 1994, and 1995. Analysis of the samples is reported by Friedmann and Raynolds [chapter 6], and compared to biostratigraphic indicators by Barnosky and Bell [chapter 7].

As of the end of 2000, a total of 6090 specimens from this locality were catalogued in the Denver Museum of Nature and Science.

The DMNH excavation is spatially discrete from the CM Velvet Room excavation, and the age relationships of sediments in the two parts of the room are not straightforward. Observations table 2.2

Conversion from Numbered Arbitrary Levels Applicable Only within Grids to Correlative Horizons Labeled by Letters Traceable across Grids in DMNH 644, within the Velvet Room

Horizon

Level

Horizon

Level

Grid 6

A

=

1, 2

K

=

26X

B

=

3,4, 5,6

L

=

27X

C

=

7, 8

M

=

28X

D

=

9, 10, 11, 12

N

=

29X

E

=

13, 14

O

=

30X

F

=

15, 16

P

=

31X

G

=

16

Q

=

32X

R

=

33X

Grid 7

A

=

1, 2

B

=

3, 4, 5

Grid 11

A

=

1, 2

C

=

6, 7, 8

B

=

3, 4

D

=

9, 10, 11, 12, 13, 14

C

=

4, 5

E

=

15, 16

D

=

5, 6, 7, 8

F

=

17, 18

E

=

8, 9, 10

G

=

19

F

=

10, 11, 12

H

=

20, 21

G

=

13, 14, 15

H

=

15, 16, 17

Grid 8, 8A

A

=

1, 2

I

=

17, 18

B

=

3, 4, 5

J

=

18

C

=

6, 7, 8

K

=

26

D

=

9, 10

L

=

27

E

=

11, 12, 13, 14, 15, 16, 17

M

=

28

F

=

17, 18

N

=

29

Grid 9, 9A

A

=

1

O

=

30

B

=

2, 3, 4, 5

P

=

31

C

=

6

Q

=

32

D

=

7, 8, 9

Grid 12

A

=

1

E

=

10, 11

B

=

2, 3, 4, 5

F

=

12, 13

C

=

5, 6

G

=

13, 14

D

=

7, 8

H

=

27

E

=

9, 10, 11

I

=

28

F

=

11, 12, 13

J

=

29, 30

G

=

13

K

=

26X

H

=

14

L

=

27X

I

=

15

M

=

28X

N

=

29X

Grid 13

A

=

1

O

=

30X

B

=

2, 3

P

=

31X

C

=

3

Q

=

32X

Grid 14

A

=

1

R

=

33X

B

=

2, 3

Grid 10

C

=

3, 6, 7

A

=

1

D

=

7, 8

B

=

2, 3, 4, 5, 6,

C

7, 8, 9, 10

E

=

8, 9, 10A

=

D

11, 12, 13, 14

F

=

10A, 10B, 10C

=

G

=

10D

E

=

15, 16, 17,18

F

H

=

10E, 10F, 10G

=

19, 20

G

21, 22, 23

I

=

10H,10J, 11A

=

H

=

23, 24, 25, 26

Grid 15

A

=

1

I

=

26, 27, 28, 29

B

=

2, 3, 4, 5

J

=

30

C

=

(continued)

table 2.2 (continued)

Horizon Level Horizon Level

D

=

7

Grid 18, 19

Not excavated

E

=

8, 9, 10A

Grid 20

A

=

1

F

=

10A, 10B, 10C

B

2

=

G

=

10D

C

=

3, 4, 5, 6, 7A

H

=

10E, 10F, 10G

D

=

Eroded?

I

=

10H, 10J, 11A

E

=

7B, 8, 9, 10

J

=

11A

F

=

11

K

=

26

G

=

12

L

=

27

H

=

13, 14, 15

A

=

1

I

=

15, 16, 17, 18

B

=

2, 3, 4

J

=

19, 20

C

=

5

K

=

20

D

=

6, 7, 8

Grid 21

A

=

1

E

=

9, 10

B

=

2

F

=

11, 12, 13

C

=

3, 4, 5, 6, 7A

G

=

14, 15, 16

D

=

Eroded?

H

=

17, 18

E

=

7B, 8, 9, 10

I

=

19

F

=

11

J

=

20

G

=

12

K

=

26

H

=

13, 14, 15

L

=

27

I

=

15,16

M

=

28

Grid 22

A

=

1

N

=

29

B

=

2

O

=

30

C

=

3, 4, 5, 6, 7

P

=

31

Q

=

32

Grid 23, 24

B

=

2

R

=

33

C

=

3, 4, 5, 6, 7

A

=

1

Grid 25

A

=

1

B

=

2, 3, 4

B

=

2, 3

C

=

5

C

=

7A

D

=

6, 7, 8

D

=

Eroded?

E

=

9, 10

E

=

7B

F

=

11, 12, 13

Grid 26

A

=

1

G

=

14, 15, 16

B

=

2, 3

H

=

17, 18

C

=

7A

I

=

19

D

=

Eroded?

J

=

20

E

=

7B

of the DMNH excavation by ADB and CJB in 1994 compared with lithologie descriptions recorded in ADB's field notes at the time of the CM excavation suggest, based on lithologic criteria, that the two excavations may relate in the following way: CM VR level 1 correlating with part of DMNH level A; parts of CM VR levels 2A and 2B correlating with parts of DMNH levels B and C; and parts of CM VR levels 2C, 3, and 4 correlating with parts of DMNH level D. If this is the case, the lower levels of the DMNH excavation are probably older than all of the sediments in the CM excavation. However, these relationships remain speculative at this point. The problems with correlating deposits in different parts of this room are well illustrated in figure 2.11, which shows the relationship of DMNH 644 to Kate's Cupola / Mark's Sink (DMNH 1349).

TAPHONOMY

Characteristics of the fossil bones resemble those described for the CM excavation and the Pit. Sedimentological features of at least levels A-D resemble those noted for the CM exca

FIGURE 2.11 Southeast to northwest profile through the southern part of the Velvet Room. The view is to the southwest. (Drawn by R. Raynolds.)

vation (Barnosky and Rasmussen, 1988). Therefore it seems likely that wood rats played a prominent role in accumulating many of the fossils.

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