884 <strong>Norphlet</strong> <strong>Formation</strong> (<strong>Upper</strong> <strong>Jurassic</strong>), AlabamaTOP OFPERMIT NO. 25430S-3MOBItOILCO.EPSIALABAMA STATC L£AS£ 34/SOUTH TRACT 76 MOBILE BAYCOTTON VALLEY GROUP ^ ? TrcT> } -16.500) I -^ 7,000I J -17,500i i -18,000< < -18,500TCP OF / 5HAYNESVILLE FORMATION \ \> \ -19,000METERS-5029.2-5181 6-5334.0-5486.4-5638.8-5791.2the Mosbacher Powell Gas Unit 19-4 core, EscambiaCounty, Alabama.The Denkman and red beds are replaced farther updipin Choctaw, Marengo, Clarke, Wilcox, Dallas, Monroe,Conecuh, Escambia, and Covington Counties by<strong>Norphlet</strong> conglomeratic sandstone. The sandstone is grayor red, poorly sorted, very fine to coarse-grained, and containsangular to subangular quartz grains (Figure 9A).Typically, the sandstone contains granule to cobble-sizeclasts of chert, shale, quartzite, granite, and rhyolite (FigurelOA).Shale occurs at the base of the <strong>Norphlet</strong> sequence inparts of Escambia and Choctaw Counties, and most likelyis present elsewhere in Alabama, particularly in the offshorearea. The shale is typically black, structureless towavy laminated, and illitic (Figure lOD). It is essentiallybarren of any organic remains, and it may be intertidal<strong>Norphlet</strong> or Louann lithofacies.ENVIRONMENTS OF DEPOSITION1 " ^ -19,500TOP OF 1 _~^SMACKOVER FORMATION r~ ~CI ^ -20,000TOP OF L 7_.20 500NORPHLET FORMATION r" ^~JTOPOF PINE HILL ANHYDRITE > ) -21.000MEMBER OF THE LOUANN SALT -»-SP RESISTIVITY-5943.6-6096.0-6248.4-6400.8Figure 3—Type log for southwestern and offshore Alabamaillustrating characteristic log curves for <strong>Jurassic</strong> strata.core. Hatter's Pond field, Mobile County, Alabama. TheDenkman becomes reddish-brown near its base and gradesinto underlying red beds.These red beds, which include sandstones, siltstones,and shales, become the dominant <strong>Norphlet</strong> lithologyupdip in parts of Choctaw, Clarke, Monroe, and EscambiaCounties. The sandstones consist chiefly of gray tored, poorly to moderately sorted, very fine to coarsegrainedsubarkoses, according to the classification schemeof Folk (1974), containing angular to subangular quartzgrains (Figure 4E). The average composition is 59.7%quartz, 11.8% feldspar (plagioclase, microcUne, andorthoclase), 9.2% rock fragments (chert, phyllite, quartzite,schist, gneiss, and basic and felsic igneous), 10.7%matrix (clay), 6.0% cement (anhydrite, quartz, and carbonate),2.2% accessory minerals, and 0.4% mica(Wilkerson, 1981). The sandstones generally have horizontalto inclined, discontinuous laminae (Figure 6B).Figure 8 illustrates a typical vertical sequence of paleoenvironmentsin the <strong>Norphlet</strong> <strong>Formation</strong> as observed inThe accumulation of thick <strong>Jurassic</strong> salt deposits, anhydrite,and red beds in association with <strong>Norphlet</strong> sandstonessuggests that arid climatic conditions wereprevalent during <strong>Norphlet</strong> deposition. Generally, an associationof salt, anhydrite, and red beds indicates arid climaticconditions, and eolian sands commonly accumulateunder such depositional conditions (Walker, 1967).The Appalachian Mountain system of the easternUnited States, which extended into southwestern Alabamain the <strong>Jurassic</strong>, provided a barrier for air and watercirculation during the deposition of the <strong>Norphlet</strong> <strong>Formation</strong>.This mountain system produced topographic conditionsthat contributed to the arid climate of southwesternAlabama during the <strong>Jurassic</strong>; these mountains alsoaffected sediment accumulation. Paleogeography insouthwestern Alabama during the <strong>Jurassic</strong> was dominatedby a broad desert plain rimmed to the north and east by theAppalachian Mountains and to the south by a developingshallow sea. The Wiggins arch, located in the southwesternportion of the desert plain, was a positive feature during<strong>Norphlet</strong> deposition, as evidenced by the observationthat the <strong>Norphlet</strong> has not been penetrated by wells drilledon this structure. The desert plain extended westward intoeastern and central Mississippi. Ancient analogs are thePliocene and Pleistocene Sonoran desert sediments ofnortheastern Baja California, Mexico (Walker, 1967), thelate Paleozoic and Triassic-<strong>Jurassic</strong> deposits of the westerninterior of the United States (McKee, 1979b), and thePermian sandstones of northwestern Europe (Glennie,1972), of the North Sea (Gage, 1980; Glennie and BuUer,1983), and of Scotland (Clemmensen and Abrahamsen,1983).The initiation of <strong>Norphlet</strong> sedimentation was the resultof basin subsidence accompanied by erosion of the southernAppalachian Mountain chain. <strong>Norphlet</strong> conglomeraticsandstones were deposited in proximity to theirAppalachian source (Figure 11). This <strong>Norphlet</strong> lithofaciesis most prevalent in Choctaw, Marengo, Clarke, Wilcox,Dallas, Monroe, Conecuh, Escambia, and CovingtonCounties, Alabama, or in areas that would be considered
Ernest A. Mancini et al 885L0.10 mmFigure 4—Photomicrographs illustrating sandstone composition and textural characteristics of <strong>Norphlet</strong> <strong>Formation</strong> in southwesternand offshore Alabama. (A) Eolian dune sandstone depicting composition, Getty Peter Klein 3-141 well, Mobile County, depth 18,403ft (5,609.2 m). (Note feldspar grain at F.) (B) Eolian dune sandstone depicting texture, Exxon State Block 621 well, Mobile Bay, depth20,514 ft (6,252.7 m). (C) Marine shoreface sandstone depicting composition, Louisiana Land & Exploration T. R. Miller Mill Company32-31 well, Escambia County, depth 15,497 ft (4,723.5 m). (D) Marine shoreface sandstone depicting composition and texture,Exxon State Block 621 well. Mobile Bay, depth 20,464 ft (6,237.4 m). (Note carbonate cement at C.) (E) Red-bed sandstone depictingcomposition and texture, Exxon L&N Railroad 30-31 well, Escambia County, depth 15,603 ft (4,755.8 m). (F) Wadi sandstone depictingcomposition and texture, Louisiana Land & Exploration T. R. Miller Mill Company 32-31 well, Escambia County, depth 15,561 ft(4,743.0 m).
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