Mining, Minerals and More in the Western Ouachita Mountains

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Studies of paleocurrent, grain size distribution and geometry of the Hatton Tuff suggest avolcanic source to the south or southeast (Niem, 1977) (Fig. 9). Analyses of recent ash fallsshow that grain size increases and the deposits thicken toward the source. This is the case withthe Hatton Tuff as well.A.B.C.Figure 7. A. Early in a volcanic eruption, a large volume of pyroclastics produced apyroclastic flow that deposited thick unstratified tuff. B. Numerous thin slurries followedthe main flow and deposited thin-bedded tuff. C. Toward the end of the volcanic eruptions,settling of fine ash produced fine-grained tuff (from Niem, 1977).6
Ouachita Orogeny (Middle Mississippian-Pennsylvanian, 345-299 million years ago)The rocks exposed in the Ouachita Mountains region are no longer flat-lying as they wereoriginally deposited. They are steeply inclined and have been folded into anticlines andsynclines. Compare the attitude of the rocks in the Ouachita Mountains region with those in theArkansas River Valley and the Ozark Plateaus Regions.Figure 8. This figure displays an anticline that has been distorted due to folding. Look for these types offolds at each fieldtrip stop.To understand why the rocks are no longer flat-lying we need to look back in geologic time. Bythe Middle Pennsylvanian Period, geologists believe that there was approximately 50,000 feetof sediment that had been deposited in a deep ocean basin in the area of the present dayOuachita Mountains (Stone and Haley, 1982). At that time, around 345 million years ago, platetectonics began to shape what is now Arkansas (Fig.5). The continents of Laurasia and Llanoriabegan to collide, pushing together this large mass of material. Over time, this collision causedthe rocks to be folded, faulted and uplifted into the Ouachita Mountains that we see today.Deformation of the rocks increases as one travels from south to north, with more complexfolds, thrust faults and sizeable quartz veins in the northern region.7
Page 3 and 4: STATE OF ARKANSASARKANSAS GEOLOGICA
Page 5 and 6: Table of ContentsGeologic Setting..
Page 7: Educational Workshop Series 06 -
Page 10 and 11: Figure 2. Digital ortho-photograph
Page 12 and 13: This workshop focuses on the Stanle
Page 16 and 17: LaurasiaFigure 9. Late Mississippia
Page 18 and 19: Varying stream patterns develop acc
Page 20 and 21: Figure 13. Map showing location of
Page 22 and 23: This area is rich in plant fossils.
Page 24 and 25: The active portion of the quarry is
Page 26 and 27: Figure 21. Load features on sandsto
Page 28 and 29: References:Clardy, B.F., and Bush,
Page 30 and 31: Sigillaria, an extinct coal-age tre

Mining, Minerals and More in the Western Ouachita Mountains

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