Point Ann South

Name:

point ann south outcrop (rm-4)

County:

clayton

Company:

mcgregor, city of

IDALS Reg. #:

not applicable

IDOT Code #

not applicable

Loc. (Q's):

nw sw nw nw

Sec.

95n

Quad:

prairie du chien (E45)

Elevation:

630 ft. at road level (base of section)

Loc. Rmrks:

Outcrop on west side of road, at south end of the Point Ann ridge.

Descrip. By:

Robert M. McKay

Date(s):

11/7&16/1994

Descrip. Rmrks:

Section measured and numbered from base upwards. Section begins at road level.

TF = trough foreset dip azimuth; TA = trough axis dip azimuth

WF=wedge foreset dip azimuth; PFA = planar xs foreset azimuth

Unit	Description				ft.	m.
1	Sandstone, grey on weathered outcrop, mostly poorly exposed, brown to white on fresh surface; fine-coarse grained; large-scale trough cross-strata in sets 10-30 cm thick; contains calcite cemented “popcorn-shaped” zone; TA = 237, 234, 253 measured 0.9 - 1.3 m below top of unit. Thickness calculated with tape & vertical angle measurement.				25.6 ft	7.8 m
2a	Sandstone, grey when weathered, white when clean, fine-medium, minor coarse, very friable, very poorly cemented; trough cross stratified in sets 5-10 cm thick and 10-30 cm wide, sets are deeply truncated.				0.98 ft	0.3 m
2b	Sandstone, generally finer grained interval; lower 25 cm appears parallel and horizontal to wavy laminae filling truncated surfaces. Middle 30 cm is well developed lenticular and flaser bedded siltstone to very fine sandstone with well developed silt to clay dominated lense drapes and flaser laminae. Small scale troughs with TA = 254, 185, 184. Several photos				2.13 ft	0.65 m
2c	Sandstone, white, very fine - medium, dominantly planar-parallel horizontal laminae to very low angle laminated which laterally appears as larger scale truncated trough cross strata.				0.33-0.49 ft	0.1-0.15 m
3a	Sandstone, intraclast conglomerate, matrix fine- to coarse-grained with trace very coarse, common dolositstone fpc 1mm-4cm with rounded edges. Unit truncates the upper part of unit 2. Some clasts may be exhumed and hardened burrow casts. The lower two thirds of unit is horizontal to low-angle planar stratified; upper two thirds may be truncated and filled by truncated wedge sets 7-10 cm thick with WF=341. Staratification is locally contorted over white sandstone of unit 2b. Sample upper part 3a.					0.2-0.33 m
3b	Dolostone, tan, very sandy with very fine- to coarse-grained sand, moderately bioturbated with Skolithos , burrows extend down into intraclast conglomerate of 3a.				0.33 ft	0.09-0.1 m
4	Sandstone, tan, fine- coarse, minor very coarse and trace granule to 3mm. Stratified in wedge sets generally 10 cm thick with common dolomitic flat pebble clasts (fpc) and numerous Skolithos tubes in more dolomitic laminae. Stratification within wedge-shaped sets is low-angle with 1-2 m wide laminae containing interlaminated dolomudstone to dolosiltstone laminae (probable IHS – inclined heterolithic lateral accretion laminae). Unit divided into 5 subunits, 4a-4e. Several photos of intraclasts & Skolithos tubes.				4.7 ft	1.43 m
4a	Sandstone, fine - coarse, trace very coarse, highly intraclastic; stratification in planar xs wedge-shaped sets 6-10 cm thick (PFA = 204, 214, 217). Intraclasts 1 mm - 4.5 cm, fpc of silty-sandy dolomite & dolomitic vf-f minor m-c sandstone; Skolithos tubes 2-3 mm thick by 1-5 cm long. (15-18 cm)				0.6 ft	0.15-0.18 m
4b	Dolostone, tan, extremely sandy to dolomitic sandstone, silt - m grained with minor coarse. Drapes over the wavy and truncated upper surface of 4a, thickens over trough-shaped lows in 4a and thins over thicker portions of 4a, horizontal-planar laminated (1-5 cm) Sample RM4-4B				0.1 ft	0.01-0.05 m
4c	Sanstone, fine- to coarse-grained, 6 to 7 sets separted by 1-6 cm thick dolomitic sandstone layers. XS sets display weak stratification, common intraclasts and Skolithos burrows. XS is not preserved enough to measure FA; sandy dolomitic layers are more intensely bioturbated. (50-52 cm)				1.65 ft	0.5-0.52 m
4d	Sandstone, silt to coarse, minor very coarse; lower third locally preserves tangential to trough foresets with sets 3-12 cm thick at 60 cm above base; several maximum foreset azimuths & dips TFs = 193, 214 w/ 25 dip,221 w/ 24 dip, 211 w/ 28 dip; remainder is poorly stratified to nonstratified with midlle part being more dolomitic and strongly bioturbated; upper is clean fine to coarse, minor very coarse, with much less dolomite content, nonstratified, very faint burow traces; dolomitic sandstone in middle part displays some contorted bedding. (45 cm)				1.48 ft	0.45 m
4e	Sandstone, whitish to greenish color, recessive subunit, dominantly fine to coarse, minor very coarse. Thinly bedded with stacked 1-2 cm thick sets of wavy laminated finer and coarser sand with interbedded small-scale-low-angle tangential cross-laminae; one small scale TFA = 354; upper 5 cm with vertical Skolithos. (15-25 cm)				0.66 ft	0.15-0.25 m
5a	Thinly Interbedded Sandy Dolostone and Dolomitic Sandstone; Sandstone, very fine to medium, no coarse, occurs as sets of small scale trough cross-strata (FA = 350, 314, 183). Ledge forming unit. Thin dolostone interbeds are of lenticular tan dolomudstone with vertically oriented sand-filled mudcracks ( one lense of dolomudstone only 1.0m across. Basal portion of unit is locally cutout and filled by intraclastic conglomerate. Upper 2-5 cm locally is extremely very fine to medium sandy, laminated dolostone; wavy laminae drape over ripple forms below ( low-amplitude drapes of < 1 cm). (Photos of mudcracks)				0.56 ft	0.15-0.19 m
5b	Dolostone, occurs as a ledge former, generally seen as 3-4 distinct beds, but laterally may appear as one bed with prominent joints. Lower half is a very fine to medium grained dolomitic sandstone with minor coarse, nonstratified, bioturbated; upper half is a very sandy very fine to medium sandy dolomite with minor coarse sand. This unit is probably the same as orange-tan dolostone (unit 2) of section RM-172.				1.38 ft	0.39-0.44 m
6	Relatively uniform appearing unit on hillside with a 50 cm thick zone of popcorn cementation/weathering in lower 50 cm. Is slightly recessive from units below and above but has thin ledgy cementation especially in lower part. Units 6a-6c.				4.9 ft	1.45-1.54 m
6a	Sandstone, fine – coarse, minor vc but some sets are f-m. At least 8 wedge-shaped truncated sets of xs (16 degree foreset dip) FA= 290, 87, 117, 346, 315, 184. Some silty dolomudstone foreset laminae drapes, minor thin-flake intraclasts from doloforeset laminae, minor Skolithos. (70 cm)				2.3 ft	0.7 m
6b	Interlaminated SS & Shale, ss is f-m, minor c, wavy to horizontal interlaminated with green clay in lower part; lenticular to flaser laminated in middle with some ripple foreset preserved (RFA= 300) Upper part wavy interlaminated with approx 10% green clay. (25 cm)				0.82 ft	0.25 m
6c	Sandstone, vf-f, minor m, dominantly horizontal - wavy planar laminated with minor foresets in part (FA=124), very little clay, less recessive than units below, sharp upper contact. Minor thin dolomitic laminae, mostly very porous but moderatly calcite cemented in part. (55-60 cm). (Photo of unit 6/unit 7 contact.)				1.87 ft	0.55-0.60 m
7a	First subunit in a thick prominent ledge-forming unit. Sandstone, f-c dolomitic to very dolomitc, fpc abundant up to 8 cm; very sandy dolostone clasts in base grades up to 5 cm thick set of horz planar tovery low angle xs with tangential foresets FA= 170, no bioturbated cycle cap. (26 cm) Sample RM4-7a.				0.85 ft	0.26 m
7b	Sandstone, intraclast conglomerate in basal 7 cm, grades sharply upward to vf-f grained horizontal-planar laminated sandstone with dolomite cement and dolomite peloids, minor bioturbation. (31 cm) Sample RM4-7b.				1.0 ft	0.31 m
7c	Dolostone, lower 32 cm is intraclast conglomerate, vf-m sandy; upper 88 cm is vf-m sandy peloidal dolograinstone. Upper stratification is dominantly horizontal-planar to wedge-shaped sets having very-low-angle and long (1-2 m) foreset laminae with wedge FA = 16, 28, 186. Less common interstratfied 6-7 cm thick tabular sets in upper part (with FA =150 with dip incline =27), usually separated by 2-4 cm thick horizontal-planar sets. Sample 7c-lower from lower 32 cm; sample 7c-upper from 50 cm below top.				3.9 ft	1.2 m
7d	Sandstone, white, slightly recessive, vf-f, friable, intraclastic.				0.46 ft	0.14 m
7e	Sandstone, dolomitic, hard, vf-m, ledge-former, lower 30 cm composed of basal 10 cm thick small-scale wedge set (FA=10) and overlain by 20 cm thick wavy to sm-sc-ripple xs. Remainder of unit is several wedge-sets of very low-angle to horizontal-planar xs to laminae (FA=205 and foreset dip 8 degrees)				3.5 ft	1.07 m
8	Dolostone, intraclastic grainstone, f-c sandy, hard, faint wedge-shaped set with FA = 133.				0.59 ft	0.18 cm
9	Sandstone, vf-f, dolomitic, bioturbated with Skolithos.				0.23 ft	0.07 m
10	Dolostone, light gray, f-c sandy mudstone, bioturbated				0.33 ft	0.07-0.12 m
11	Sandstone, f-c with less vc-pebbles, locally calcite cemented, intraclastic with silty dolomite intraclasts and green claystone intraclasts; one 2 cm disc-shaped quartzite pebble. Lower 10-15 cm is one laterally widespread tabular set with FA = 176, 149, 158 and 19 degree foreset dip angle. Upper part is also intraclastic with local trough-shaped set with TA = 265. 2 Samples RM4 11, one from base.				1.12 ft	0.34 m
12	Dolostone, coated-grian grainstone to ooid grainstone, extremely f-c quartz sandy; becomes well-developed ooid-grainstone upwards.				2.6 ft	0.7-0.9 m
13	Dolostone, very sandy f-c and highly intraclastic in lower 10 cm; grades upward to sandstone, f-c with some ooid to coated-grains, and a second intraclast conglomerate zone in upper half. Sample 13b from upper part.				1.02 ft	0.31 m
14	Dolostone, parted into three beds, coated-grain grainstone to ooid grainstone, f-c quartz sandy, common ooid quartz cores.				1.02 ft	0.31 m
15	Dolostone, intraclastic and f-c quartz sandy in basal part, grades upward to much less sandy ooid grainstone with horzontal-planar to low-angle cross-strata. Top of unit 15 is near top of steep bench with poorly exposed interval above this point.				1.87 ft	0.57 m
16	Covered Interval, top of covered interval is recessive bench along cliff.				1.97 ft	0.6 m
17	Dolostone, intraclastic coated-grain to ooid grainstone, very sandy; has a 6-12 cm thick laminated f-m grained quartz sandy dolomudstone cap.				1.12 ft	0.34 m
18	Sandstone, vf-m, very minor c, hard, very dolomitic grading upwards to less dolomitic; two tabular sets of cross-strata, FA = 156. Top of this unit is the base of prominent overhang.				1.54 ft	0.47 m
19	Dolostone, gray, non-sandy, f-m crystalline, 2 cyles of peloid grainstone with 1-2 cm thick mudstone cap.				0.82 ft	0.15-0.29 m
20	Dolostone, stromatolite boundstone, f xtln, non-sandy, wavy mat in lower part grading upward to small (2-4 cm across) LLH with 1-2 cm relief; wavy to low-relief mounded upper surface. Sample 20. Units 19 and 20 tend to appear on outcrop as a single thick bed.				0.82 ft	0.2-0.29 m
21	Dolostone, coated-grain to peloidal grainstone, vf-m sandy, sandier to intraclastic basal part; sharp contact over underlying stomatolite boundstone. This unit appears to grade, at least locally, to vf-m dolomitic sandstone in the upper 10 cm. Sample 21a and 21b.				1.3 ft	0.38-0.42 m
22	Silicified oncolite packstone ?, white, silicified oncolites? to nodules <1 - 2 cm in diameter, oval to spherical-shaped in dolomitic sandstone matrix; lower part appears to be oncolite packstone, upper part very sandy dolostone with ooid grainstone intraclasts. Sample 22 a and 22b from lower and upper parts. This bed appears to be a local marker bed as it is present at Point Anne Road parking area in the cliff face above the parking area.				0.59 ft	0.17-0.19 m
23	Dolostone, packstone, intraclastic with fpc to 6cm, vf-m sandy, upper 8-10 cm has diffuse white silicification throughout (possible pedogenesis ?, may correlate to Marquette West roadcut unit), sharp upper contact; also some elongate 1by 6 cm white chert nodules.				1.44 ft	0.44 m
24	Dolostone, oxidized brown, slightly sandy peloidal packstone - grainstone, slightly recessive, no discernable stratification, highly fractured with small equant pattern.				1.64 ft	0.5 m
	Offset section 30 m to the north.
25	Dolomite, light grey, fine xtln, fine sandy, dense, hard, moderately vuggy, massive thick bed, ledge former.				3.44 ft	1.05 m
26	Dolostone, vertical honeycomb (sensu Adams, 1975) digitate stromatolite boundstone, wavy mat in lower 10-15 cm, grades upward to main digitate stromatolite.				1.64 ft	0.5 m
27	Dolostone, low-amplitude wavy stromatolite mat.				0.98 ft	0.3 m
28	Dolostone, fine-med xtln, dense, hard, intraclastic peloidal packstone.				0.98 ft	0.3 m
29	Covered interval				1.97 ft	0.6 m
30	Dolostone, inaccessible				0.98 ft	0.3 m
31	Dolostone, digitate stromatolite boundstone, (vertical honeycomb)				0.66 ft	0.2 m
32	Dolostone, grades from unit 31 below, stromatolite boundstone, llh, low wavy strom heads 30 cm diameter				1.48 ft	0.45 m
33	Dolostone, brown, ooid grainstone with white chert nodules, poorly exposed to covered				1.15 ft	0.3-0.4 m
34	Dolostone, stromatolite boundstone, low-amplitude llh in lower part grading up to wavy mat in upper part, white chert nodule band at top				1.38 ft	0.42 m
	The two white chert bands of unit 33 and 34 correlate to Marquette West Road Cut Section
35	Dolostone, intraclast conglomerate grainstone, intraclasts to 6 cm, fine- to coarse xtln, nonsandy (hand lense), sporadic 10 by 20 cm white chert nodules				0.98 ft	0.23-0.3 m
36	Dolostone, very light grey to very light green with brown mottles, appears as “white beds” from road level below, fine xtln, thin bedded, horizontal burrows common, upper 85 cm is slightly recessive, this facies continues upward an undetermined amount				6.56 ft	2.0 m
	There is at least another 20 m of section exposed above this point in bold vertical cliff face

Summary of Conodont Samples sent to Jim Miller at Southwest Missouri State Univ. on Sept. 29, 1999. Lith samples retained from all conodont samples

Unit #		Meters above Base of Section	Weight
11		16.0 m	2.3 lbs
7C		13.7 m	2.3 lbs
7A		12.7 m	2.15 lbs
6B		11.7 m	1.9 lbs
6A		11.3 m	2.0 lbs
5B-3		10.9 m	2.0 lbs	Unit 5B correlates lithically to the 1’st dolomite bed at Mrs. Moes House, the upper part of unit 14 at Point Ann North, and unit 8 at the “A” Street Outcrop. Sample 5B-1 is from lower part, 5B-2 from middle, and 5B-3 from upper.
5B-2		10.8 m	2.2 lbs
5B-1		10.6 m	2.3 lbs
4E		10.3 m	1.7 lbs