WRITTEN DESCRIPTION OF THE STRATA EXPOSED AT THE
PIKES PEAK QUARRY

SE NW NW NE sec. 34, T95N, R3W, Clayton Co., Iowa

measured by Brian Witzke and Bill Bunker, Sept. 13, 2000

(abbreviations as for McGregor Quarry section)

GALENA GROUP

DUNLEITH FORMATION

Fairplay Member

Unit 19.  Dolomite, sugary crystalline, in thick to medium beds, some fossil molds, vuggy; interval is weathered and recessive upward to highest portions of quarry; brachiopods and crinoid debris (silicified in part) noted 54-73 cm above base of unit.  Maximum thickness 1.7 m (5.6 ft).

Unit 18.  Dolomite; lower bed 25 cm, dense, less sugary, scattered vugs; upper bed 47 cm, more sugary than lower bed, vuggy; lower bed with common molds of receptaculitids (Fisherites) to 18 cm long, most common in upper 13 cm of lower bed; upper bed with scattered receptaculitids and silicified horn coral in lower 15 cm.  72 cm (2.4 ft).

Unit 17.  Dolomite, sugary textured in part, vuggy, burrow mottling; bedding breaks at 49 cm above base and top of unit; lower 17 cm with coarse sugary stringers (dolomitized packstones), scattered brachiopods noted 40 cm above base; scattered small chert nodules (to 5 cm thick) 6 cm above base of unit; resistant unit forms cliff face.  1.0 m (3.3 ft).

Eagle Point Member

Unit 16.  Dolomite, very finely crystalline, coarser and more sugary textured dolomite within thalassinoid burrow networks in upper 1 m, indistinct burrow mottling observed below; porous interval, scattered small indeterminate fossil molds and pin-point porosity, vuggy in lower part; bedding breaks at 60 cm above base and at top of unit; nodular chert bands (smooth to chalky cherts, white to pale gray) up to 5-7 cm thick noted at 16, 60, 103, 114, 125 cm above base; wispy argillaceous streaks 27-38 cm above base of unit; receptaculitid molds (Fisherites) 11 cm above base of unit; scattered brachiopod molds noted 1.0 m above base.  1.62 m (5.3 ft).

Unit 15.  Dolomite, sugary textured, vuggy; bedding breaks at 26, 133, 145 cm above base and at top of unit; nodular chert bands (smooth, white to pale gray) to 8 cm thick noted at 43, 83, 108 cm above base of unit; prominent smooth chert band up to 10-14 cm thick at top of unit (a silicified mudstone); receptaculitid molds (Fisherites) noted at 15 and 30 cm above base of unit.  1.65 m (5.4 ft).

Unit 14.  Dolomite, sugary textured,, common vugs (1-112 cm), scattered calcite void fills; bedding break  48 cm above base and top of unit; discontinuous nodular chert bands (smooth to chalky chert, white to pale gray) to 4 cm thick noted at 48, 62, 94 cm above base; top of unit marked by prominent thick chert band, masses of chert to 16 cm thick and 1.5 m in lateral extent.  1.38 m (4.5 ft).

Beecher Member

Unit 13.  Dolomite, calcitic, part sugary textured, recrystallized, calcite void fills common; argillaceous bedding breaks 12 and 34 cm above base, argillaceous to shaley break 41 cm above base, argillaceous streaks 17 and 38 cm above base; probable hardground surface 7 cm below top of unit locally capped by intraclasts (to 2 cm); prominent bedding break and lithologic change at top of unit; poorly-preserved brachiopods and crinoid debris noted.  50 cm (1.65 ft).

Unit 12.  Dolomitic limestone to calcitic dolomite, recrystallized, calcite void fills common; bedding breaks 6 and 11 cm above base; lower 20 cm and upper 13 cm of unit characterized by recessive thinly bedded lithologies with argillaceous streaks.  47 cm (1.55 ft).

Unit 11.  Dolomitic limestone to calcitic dolomite, more dolomitic in upper bed; recrystallized sugary textures in part; calcite void fills scattered in middle part, porosity locally filled by poikilotopic calcite cements in upper bed; bedding breaks at 31 and 52 cm above base and top of unit; argillaceous to shaley parting at 52 cm above base, 31-52 cm above base is limestone with wavy argillaceous streaks; irregular hardground surface 21 cm above base; poorly-preserved fine skeletal debris includes scattered brachiopod and crinoid debris, large gastropod (Maclurites) noted 40 cm above base.  88 cm (2.9 ft).

Unit 10.  Dolomite, calcitic, recrystallized sugary texture, argillaceous streaks in upper 9 cm with calcite void fills; bedding breaks at 44 and 28 cm below top, prominent bedding surface at top; scattered brachiopod and crinoid debris.  Upper 75 cm (2.45 ft) of unit is exposed, approximately 40 cm (1.3 ft) covered at base of quarry walls; Dunleith-Decorah formational contact occurs within covered interval.

DECORAH FORMATION

Ion Member (includes Buckhorn and St. James members of Illinois classification)

Unit 9.  Shale and limestone; top 20 cm is limestone ledge, wkst, slightly argillaceous, slightly dolomitic, fossils include fragmented skeletal debris, scattered large trepostrome bryozoans, horn coral; lower 38 cm is shale dominated, green-gray, calcareous, contains some thin limestone lenses (to 4 cm thick), horizontal burrow mottles, scattered broken skeletal debris, scattered brachiopod and bryozoan material.  Limestone ledge forms quarry floor, local excavation into quarry floor exposes up to 58 cm (1.9 ft) of unit 9; contacts with overlying and underlying strata not accessible.

Unit 8.  Covered interval, approximately 1.2 m (3.9 ft).  Based on section in nearby McGregor Quarry, this interval is composed of interbedded limestone and shale.

Unit 7.  Limestone, argillaceous; wkst; lower 25 cm forms limestone ledge; 25-32 cm above base is shale, green-gray; upper 43 cm includes ledges of limestone, burrowed in part, separated by thin shales; lower limestone ledge with large brachiopods (strophomenids), upper beds with brachiopods (orthids, strophomenids).  75 cm (2.45 ft); covered above; unit 7 and underlying strata accessed in roadcut immediately below quarry.

Unit 6.  Limestone ledges interbedded with shale; lower 70 cm is limestone dominated, argillaceous wkst, part slightly nodular, pkst stringers at 31, 45, 53, 68 cm above base of unit, thin shale interbeds; upper 35 cm is interbedded limestone and shale, limestone is argillaceous wkst to pkst (in lenses), becomes shale dominated in upper part of unit; fossils include whole shell and fragmental brachiopods (Sowerbyella, strophomenids, dalmanellids, other orthids), small stick bryozoans.  1.05 m (3.45 ft).

Unit 5.  Limestone ledges in lower half, argillaceous, wkst, bioturbation, fossils include brachiopods (Sowerbyella, Strophomena, Dalmanella, other orthids), bryozoans (small stick-like forms, larger trepostomes), scattered crinoid debris; upper half of unit forms recessive slope, much shalier, interbedded thin limestones, shale reentrant at top.  62 cm (2 ft).

Unit 4.  Limestone and shale; lower 15 cm is limestone, wkst, very argillaceous to shaley, forms nodular ledges, brachiopods, crinoid debris; 15-32 cm above base is shale slope with scattered limestone lenses; top 10 cm is thin limestone ledges with shale partings, wkst to fragmental pkst, fossils include brachiopods (Sowerbyella, Strophomena, orthids), crinoid debris.  42 cm (1.4 ft).

Unit 3.  Limestone and shale; lower 31 cm is interbedded limestone and thin shale, argillaceous, wkst with pkst stringers and burrow fills, basal 8 cm is shaley; upper 25 cm forms a partly covered slope, shale dominated; fossils include brachipods (Sowerbyella, Strophomena, Dalmanella, other orthids, rhynchonellids), bryozoans (small stick-like forms, trepostomes in upper shale), scattered crinoid debris.  56 cm (1.8 ft).

Guttenberg Member

Unit 2.  Limestone ledges, wkst to pkst, interbedded pkst lenses (1-6 cm), slightly argillaceous; prominent bedding breaks at 56 and 91 cm above base and top of unit, nodular to wavy bedding in lower part; fossils include whole shell to fragmental brachiopods (Sowerbyella, strophomenids, orthids), small stick bryozoans, scattered crinoid debris.  1.1 m (3.6 m).

Unit 1.  Limestone ledges, wkst, some pkst, slightly argillaceous; bedding breaks at 40 and 70 cm above base and at top marked by argillaceous to shaley partings; some horizontal burrows; fossils include brachiopods (Sowerbyella, Strophomena, orthids), stick bryozoans, scattered crinoid debris.  92 cm (3 ft); unit extends to ditch below roadcut section.

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from

Witzke, B.W. and. Bunker, B.J., 2000, Stop 8: Dunleith Formation at the Old Pikes PeakQuarry. in Anderson, R.R (ed.), The Natural History of Pikes Peak State Park, Clayton County, Iowa: Geological Society of Iowa Guidebook 70, p. 112-113.