294:
380:
280:
273:
424:
266:
168:
463:
448:
362:
443:
417:
410:
458:
453:
313:(below: a thin, white stripe of in-place rock followed by a slope of eroded St. Peter Sandstone material).
390:
359:
329:
38:
340:
336:
306:
252:
144:
48:
245:
238:
309:(above: the less-eroded, layered unit that constitutes the majority of the photo) and the
8:
310:
228:
160:
128:
58:
398:
218:
233:
213:
193:
122:
203:
188:
347:
during
Ordovician time. Because it is often very thin (~10 cm or less in the
366:
223:
208:
198:
176:
104:
394:
344:
437:
134:
73:
24:
387:
112:
348:
298:
322:
28:
293:
302:
83:
305:. In this photo, it is the thin, darker layer that lies between the
328:
formation in the sedimentary sequence characteristic of the upper
379:
325:
343:. Together, these three units represent a sequence of
351:), it is often ignored in the general stratigraphy.
435:
94:Paleozoic Stratigraphy of the Upper Midwest, USA
360:University of Minnesota: River Bluffs homepage
418:
274:
425:
411:
281:
267:
292:
464:United States geologic formation stubs
436:
449:Shale formations of the United States
374:
297:The Glenwood shale cropping out in
13:
444:Ordovician System of North America
14:
475:
378:
386:This article about a specific
1:
354:
397:. You can help Knowledge by
7:
10:
480:
393:in the United States is a
373:
79:
69:
64:
54:
44:
34:
23:
18:
330:Midwestern United States
314:
341:Saint Peter Sandstone
337:Platteville Limestone
307:Platteville Limestone
296:
253:Mount Simon Sandstone
145:Platteville Limestone
49:Platteville Formation
459:Ordovician Wisconsin
454:Ordovician Minnesota
246:Eau Claire Formation
239:Galesville Sandstone
311:St. Peter Sandstone
229:Franconia Formation
161:St. Peter Sandstone
129:Wise Lake Formation
59:St. Peter Sandstone
25:Stratigraphic range
365:2008-09-28 at the
335:It lies under the
315:
219:Munising Formation
406:
405:
291:
290:
234:Ironton Sandstone
214:Potsdam Sandstone
194:Shakopee Dolomite
169:Knox Unconformity
123:Dubuque Formation
99:Dates approximate
89:
88:
471:
427:
420:
413:
382:
375:
283:
276:
269:
204:Jordan Sandstone
189:Everton Dolomite
91:
90:
16:
15:
479:
478:
474:
473:
472:
470:
469:
468:
434:
433:
432:
431:
371:
367:Wayback Machine
357:
287:
224:Davis Formation
209:Potosi Dolomite
199:Oneota Dolomite
177:Knox Supergroup
105:Maquoketa Group
12:
11:
5:
477:
467:
466:
461:
456:
451:
446:
430:
429:
422:
415:
407:
404:
403:
383:
356:
353:
345:sea level rise
339:and above the
319:Glenwood Shale
289:
288:
286:
285:
278:
271:
263:
260:
259:
258:
257:
256:
255:
250:
249:
248:
243:
242:
241:
236:
231:
211:
206:
201:
196:
191:
183:
182:
180:(~497-~470 Ma)
173:
172:
171:(~470-~459 Ma)
165:
164:
163:(~459–~455 Ma)
157:
156:
153:Glenwood Shale
149:
148:
141:
140:
139:
138:
132:
131:(449.4–447 Ma)
126:
117:
116:
109:
108:
101:
100:
96:
95:
87:
86:
81:
77:
76:
71:
67:
66:
62:
61:
56:
52:
51:
46:
42:
41:
36:
32:
31:
21:
20:
19:Glenwood Shale
9:
6:
4:
3:
2:
476:
465:
462:
460:
457:
455:
452:
450:
447:
445:
442:
441:
439:
428:
423:
421:
416:
414:
409:
408:
402:
400:
396:
392:
389:
388:stratigraphic
384:
381:
377:
376:
372:
369:
368:
364:
361:
352:
350:
346:
342:
338:
333:
331:
327:
324:
320:
312:
308:
304:
300:
295:
284:
279:
277:
272:
270:
265:
264:
262:
261:
254:
251:
247:
244:
240:
237:
235:
232:
230:
227:
226:
225:
222:
221:
220:
217:
216:
215:
212:
210:
207:
205:
202:
200:
197:
195:
192:
190:
187:
186:
185:
184:
181:
178:
175:
174:
170:
167:
166:
162:
159:
158:
154:
151:
150:
146:
143:
142:
136:
135:Decorah Shale
133:
130:
127:
124:
121:
120:
119:
118:
114:
111:
110:
106:
103:
102:
98:
97:
93:
92:
85:
82:
78:
75:
74:United States
72:
68:
63:
60:
57:
53:
50:
47:
43:
40:
37:
33:
30:
26:
22:
17:
399:expanding it
385:
370:
358:
334:
318:
316:
179:
152:
147:(455–454 Ma)
137:(454–452 Ma)
125:(447–446 Ma)
115:(454–446 Ma)
113:Galena Group
107:(446–440 Ma)
349:Twin Cities
299:Minneapolis
438:Categories
355:References
323:Ordivician
321:is a thin
29:Ordovician
391:formation
303:Minnesota
155:(~455 Ma)
84:Minnesota
45:Underlies
39:Formation
363:Archived
65:Location
55:Overlies
70:Country
80:Extent
326:shale
395:stub
317:The
35:Type
440::
332:.
301:,
27::
426:e
419:t
412:v
401:.
282:e
275:t
268:v
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.