SILURIAN AND QUATERNARY GEOLOGY AT THE MARTIN MARIETTA
CEDAR RAPIDS QUARRY, LINN COUNTY , IOWA
prepared and led by the

and
Staff Geologists
Groundwater and Stratigraphic Studies Section
Iowa Geological Survey

April 30, 2005

The GSI 2005 Spring Field Trip will provide participants with an abbreviated look at some of the interesting geologic materials southeast of Cedar Rapids . In a return to GSI procedures of many years ago, the Spring Field Trip will be associated with the Iowa Academy of Science, which is meeting at Cornell College in Mount Vernon . This Spring's field trip will be begin on Saturday April 30 at 3:00 pm , following completion of the Geology Section at the Academy meeting. We will be visiting the Martin Marietta Cedar Rapids Quarry, 1636 Marietta Road , just south of the Cedar River at the junction of Hwy 30 and 13/151 (Figure 1). Trip participants should meet in the parking area near the scale house at the Martin Marietta Cedar Rapids Quarry ( DO NOT DRIVE ON THE SCALE). To get to the quarry, exit Hwy 30 at the Old River Road (just west of the Cedar River ) and proceed south . Immediately south of Hwy 30, turn east on Martin Marietta Road and continue to the scale house parking area.

At the quarry, we will see Silurian dolomites of the Scotch Grove and Gower Formations that are quarried at the site and a very interesting overlying Quaternary section. The Gower Formation is composed of distinctly horizontally-bedded laminated fine-grained dolomites of the Anamosa Member and their laterally equivalent mud and skeletal-rich mounds of the Brady Member. Brady fossils include brachiopods, tabulate corrals, solitary corals, gastropods, and nautiloids. Additionally, some spectacular sphalerite (ZnS 2 ) and pyrite ( FeS 2 ) mineralization has been found in the quarry.

The Quaternary section displays 3 Pre-Illinoian tills resting on very dark gray pro-glacial sediments above a weathered Silurian surface that displays about 3 feet of relief. The tills include abundant well-preserved wood (spruce) fragments that had been buried by the advancing ice sheet 500,000 to 1,600,000 years ago. a sand body near the top of the section was deposited by a river that crossed the area after the glacier retreated. The entire section is overlain by a thick (~50 feet) section of wind-blown Peoria loess, 12-25,000 years old.

Bring your hard hats and safety glasses if you have them. If not, they will be provided. Also, bring your rock hammer and a collecting bag. Rock and fossil collecting will not only be allowed, it will be encouraged.

-Geology Society of Iowa Website-