L144

Location   

35.459917, -92.865050 (at base of exposed section)

Site name       

Evans Mountain Road

Type

Exposure along National Forest Service gravel road and in nearby ravine in Boston Mountains.  Horizontal length approximately 2600 ft.   

Age/Formation/Unit (in stratigraphic order)

Pennsylvanian / Bloyd Formation (KesslerMember)

Pennsylvanian / Atoka Formation (Trace CreekMember)

Features of interest

Vertical section of 220 ft.  Marine high-stand sandstones and shales of upper Bloyd Formation (expanded Kessler Member) are overlain unconformably by basal Atoka fluvial and shallow marine sandstones, which are correlative with “Barton A” gas pay zone in the eastern Arkoma subsurface.

Lithology present

Sandstone, shale

State/County    

AR / Pope County

Access         

Evans Mountain Road (NFM 1304) and nearby ravine, Sec 1, T9N-R18W and Sec 36, T10N-R18W,  Ozark National Forest, 2.5 miles north of Arkansas Highway 124 intersection at Appleton (Jerusalem Quad). 

Support material available

Illustrated geology note (field guide text, photos, site map, stratigraphic section)

Site contributed by
M. R. Shinn, 6/22/16.  Site visits by Shinn in 2012-13

Figure 1.  Evans Mountain Road site map (base from Jerusalem 7.5-minute topographic quadrangle, 20’ CI)

Figure 2. Outcrops of Lower Kessler sandstone (Bloyd Formation) occur along NFM 1304 at elevations 988’-1052’ ASL. Thick bedded, upper fine- to lower medium-grained, abundant fossil molds (crinozoans, bryozoans), calcareous, friable, porous, with clay pebbles.  This marine sandstone is correlative to the restricted “Kessler limestone” of type Bloyd area.

Figure 3. Upper Kessler sandstone (Bloyd Formation) outcrops occur, along NFM 1304 road side at elevations 1121’-1152’ ASL.  Thick to medium-bedded, lower medium-grained, with fossil molds.  These rocks are the uppermost marine sandstones preserved beneath the Morrowan-Atokan unconformity in Pope County and are absent in the type Bloyd area. 

Figure 4. Massive, trough cross-stratified basal Atoka fluvial sandstone, unconformably overlying mostly-covered shales of the upper Kessler Member of the Bloyd Formation. Outcrop is along stream, approximately 600 feet northwest of NFM 1304.  The incised fluvial facies, here approximately 21 feet thick, is absent at the NFM 1304 roadway exposures.

Figure 5. Transgressive facies near top of basal Atoka sandstone. Unit outcrops along NFM 1304 road side at elevations 1175-1208’ ASL. Sandstones are medium to thick bedded, upper fine-grained, siliceous and friable, with minor marine fossil molds. Interpreted as shoreface deposits.