THE DEPARTMENT OF ENVIRONMENTAL QUALITY • • • • miSSISSIPPI geology Office of Geology P. 0. Box 20307 Volume 12, Numbers 3,4 Jackson, Mississippi 39289-1307 December 1991
A CONTINUOUS CORE THROUGH THE UNDIFFERENTIATED YAZOO CLAY (LATE EOCENE, JACKSON GROUP) OF CENTRAL MISSISSIPPI
David T. Dockery ill, Curtis W. Stover, Phillip Weathersby, C. Wayne Stover Jr., and Stephen L.lngram Mississippi Office of Geology
INTRODUCTION PURPOSE
A continuous core of the Late Eocene undifferentiated Weathered YaZOQ clay underlies the soil cover under most marine clay of the Yazoo Fonnation in northwestern Hinds of Jackson, Mississippi, and the surrounding area, including County, Mississippi, was begun on August 19, completed on a belt of prairie land across central Mississippi known as the September 4, and grouted on September 5, 1991. The core Jackson Prairie. Jackson is centrally located within the hole was a cooperative effon of the Mississippi Office of Jackson Prairie and is unique in that it overlies an extinct Geology and the Geology Department of the University of Cretaceous volcanic structure, the Jackson Dome, across Southern Mississippi and was funded in part by a grant from which the base of the Yazoo clay rises to the surface and is the Mississippi Mineral Resources Institute. Its purpose was truncated, exposing older units. Conversely, the base of the to study the clay mineralogy and geologic history of a Yazoo clay dips downward in all directions from the dome's complete section of the Yazoo clay in central Mississippi center (near the Belhaven area) until its upper contact with where the clay has a thickness greater than 400 feeL The core the Forest Hill Fonnation is encountered. Thus !he Yazoo hole was drilled to a depth of 30 feet through a cover of clay outcrop belt, which is notorious for its foundation Pleistocene loess and into lignites of the Early Oligocene problems, surrounds Jackson like a giant bull's-eye. A full Forest HiU Fonnation (28-30 feet). Coring with a 10-foot section of the Y azoo clay is crossed by going either nonh or core barrel began at 30 feet and reached total depth at 530 south of the downtown Jackson area. feeL The 500-foot cored interval contains the basal Forest One purpose in coring a complete section of the Yazoo llill Formation (30-38 feet), the Yazoo Formation (38-500 clay in the Jackson area was to study the clay's unweathered fect),the Moodys Branch Formation (500-512 feet), and the (unaltered) mineralogy from top to bottom. Changes in upper Cockfield Formation (512-530 feet). The total thick mineralogy within this clay sequence could translate into ness of Yazoo clay cored was 462 feet. increased instability of the weathered clay at the surface. MADISON COUNTY
HINDS COUNTY
MISS.
QUADRANGLE SOCIETY RIDGE LOCATION 0 • • • • • • • • • •••• • •••• • •• •• • •• •0 •• CYNTHIA •• •• •• •• •••• o••• MOSSY GROVE
N
0 Scale r
Figure 1. A modified planimetric version of the Pocahontas 7 1/2 minute quadrangle map showing the locations of the Mossy Grove, Society Ridge, and Miss-Lite (Cynthia) test holes.
22 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 Soci«f FWve . , K/4, H£.14 NW/ .C.. 'IIW/ C S.C: l 4 T 7N.A 1W ~Co. ...S ENYat-on 370 n. Wiu U1.e • 1 KJ' HW/ 4. HEJ4, NW/ 4 S-c. l6. T 7 N, A I W Hin4• Co.. MS [.., HIUFm. [lew•ttOn 3$1 ft.
Mo")'Oro\Oe •1 N/ 2. NE/4, SW/ .., SE/4 a.tt.u Lit• C~ Pil .t.CynthM 1 s.c. 3\. T ?filA 1 w Hinds eo. ws I a.vauon 2u fL ,,
tOO
200
200 Yazoo Fm.
200
300
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Figure 2. Cross section Lhrough the Mossy Grove, Society Ridge, and Miss-Lite test holes. Location of bentonites is given for the Mossy Grove and Society Ridge test holes. Multiple log runs were made for the Society Ridge and Miss-Lite test holes and the logs used here are at a different scale than those in the electric log files of the Office of Geology. The elevation at water level in the Miss-Lite clay pit shown at ri ght is 212 feet above sea level, as surveyed by Charles Peel on June 7, 1988.
MISSISSIPPI GEOLOGY, V. 12 , No. 3,4, DECEMBER 1991 23 Zones suspected of increased instability could be projected ability of geophysical logs from nearby wells to show that the to the surface and mapped in the Jackson area. A study of the previous criteria could be met at the proposed site. Other clay's mineralogy could also have an economic value as the generic test hole site criteria included a clear, nat place to Yazoo clay is mined just north of Jackson at Cynthia to make drill and the availability of water. light-weight aggregate for usc in concrete blocks and other The site selected for the core hole was adjacent to a lake produc ts. Of both economic and environ menial importance at Mossy Grove on the east side of C linton-Tinnin Road 1s the study o f the cby's competency as an aquitard to protect across the road from Camp Kickapoo. a 11oy Scout camp. and under! ying ground w::uers. just nonh of the Clinton-T innin and Kickapoo Road intcr~cc r\ :-;ccond reason for coring the Yazoo clay concerns the tion (figures I, 2, and 3). A recent water well for the 1\'orth ~late\ gl'ologic history as rev~kd within the clay sequence. Hinds Water Association drilled at Camp Kickapoo showed In l' as rem Mississippi and southwesrem Alabama. the Yazoo the Yazoo clay in this area to be 450 feet thick and covered F11rmarion con wins four members, which in ascending order with lignitic sediments of the Forest Hill Fomwtion. The Ml' the North Twisrwood Creek C la y, the Cocoa San 24 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 Figure 3. Core hole site at Mossy Grove on north side of lake in SW/4, SE/4, Section 31, T. 7 N., R. 1 W., Hinds County. between which the drilling fluid passes to circulate the cuttings. Upon retrieving the core at the surface, the bit is removed from the core barrel (Figure 5), the mud hose of the drilling rig is inserted into a fitungat thetopofthecorebarrel, and the core is forced out of the inner barrel by hydraulic pressure (Figure 6). The cores were extruded onto half sections (cut lengthwise) of PVC pipe (Figure 7),cut into five two-foot lengths, wrapped in plastic wrap,and placed in core boxes with a ten-foot core capacity. Thecores were cut in half lengthwise at the University of Southern Mississippi Geol ogy Department and half of the core (in 50 core boxes) was returned for storage at the M ississippi OfficcofGeologycorc warehouse. STRATIGRAPHY The core hole encountered, from top to bottom (see Figure 2), 28 feet of Pleistocene loess. I 0 feet oft ignites, sands, and shalcsofthcEarly Ol•goccnc Forest Hill Fonnation (Vicksburg Group), 462 feet of the Late Eocene Yazoo clay (Jackson Group), 12 feet of glauconi tic sand of th e Late Eocene Figure 4. Bringing the core out of the hole with 17 20-foot c;cctions stacked against the monkey board and another being broken from the dnll stem at the breakout table. Phillip Weathersby is on the monkey board (top) and on the ground from left to right arc Scott Mixon, Wayne Stover. Archie McKenzie, and Steve Ingram . MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 25 Figure 5. Breaking the bit loose from the core barrel (at right) and inserting the mud hose into fitting (at left). Moodys Branch Formation (Jackson Group), and 18 feet of clays and sands of the Middle Eocene Cockfield Formation (CiaibomeGroup). TheForestH.ill- Yazoocontactconsisted of lignite unconfonnably overlying marine clay. The 462- foot thick interval of Yazoo clay present in the core hole is believed to represent as complete a section as is available for this formation in the Jackson area (compared to a thickness of380 feet in the Society Ridge test hole). As observed when freshly cored, it consisted of grayish-green (GSA color chan 10 GY 5/2), montmorillonitic clay with variations in dark ness and lightnessofhue. In its upper 150 feet, the Yazoo clay was rich in mollusk shells and contained thin layers of shell hash. The only sandy unit noted within the clay was a 3-inch thick glauconitic sand (consisting largely of glauconite) 10 feet below the clay's top. A 4-inch thick bentonite was present at 50 feet below the clay's top. No limestone units were noted even though a prominent limestone marker bed is present in the Miss- Lite clay pit at Cynthia a few miles to the east-northeast of the core hole. Coring time for the clay averaged around five minutes per ten-foot core with the stiffest clay occurring in the bottom ten feet just above the Moodys Branch Formation and having a coring time greater than eleven minutes. The Moodys Branch Formation consisted of dusky green (GSA color chart 5 G 3/2), fossiliferous, glauconitic sand. The basal contact with the Cockfield was sharp and marked by burrows and clasts. In its upper eight feet, the Cockfield Figure 6. Extruding the core with hydraulic pressure. 26 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 Figure 7. Stover and Stover examining the core. Formation contained dusky yellowish brown (GSA color Geology to date. Studies of the core's mineralogy and chart I 0 YR 2(2), silty clay with intervals of crushed oyster calcareous nannoplankton flora are underway at the Univer shells. This estuarine unit is similar to that in the upper sity of Southern Mississippi Department of Geology. Scou Cockfield Fonnation (=Yegua Fonnation)at Creola Bluffon SnyderoftheEastCarolina University DcpanmentofGcol the Red River in Louisiana, which was named the Creola ogy has sampled the core for planktonic Foraminifera. Member by Stenzel (1940, p. 881). Stenzel also recognized Studies of other microfossil groups have been planned. the presence of this unit at Garland Creek in Clarke County, Anyone wishing to study the core should contact the senior Mississippi. Dockery (1980, p. 51-52) noted a fossiliferous author at the Mississippi Office of Geology. transition zone equivalent to this unit in the upper Cockfield Formation along the Chickasawhay River in Clarke County. REFERENCES CITED The final core run was made to determine the thickness of the upper Cockfield estuarine interval. When no additional Dockery,D. T., ID,1980, Tbeinvenebratemacropaleontology estuarine sediments were noted in the last core, dual induc of the Clarke County, Mississippi, area: Mississippi tion and gamma ray geophysical logs were run and the hole Bureau of Geology, Bulletin 122, 387 p. was grouted and abandoned. Stenzel, H. B., 1940, The Yegua Problem: Contributions to The 500-foot core taken at Mossy Grove is the longest Geology, 1939, Pan 2: The University of Texas Publi continuous core completed by the Mississippi Office of cation No. 3945, p. 847-910. MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 27 CYPRAEDIA (EUCYPRAEDIA) MULTICARINATA (DALL, 1890); A LATE EOCENE OVULIDAE FROM FLORIDA, MISSISSIPPI, COLOMBIA, AND PERU STUDIES ON PALEOGENE CYPRAEOIDEA (MOLLUSCA: GASTROPODA) FROM THE GULF COAS1 BASIN - Ill Luc Dolin Saint Denis, France INTRODUCTION tember of 1912. Cypraedia (Eucypraedia) multicarinata (Dall, 1890) is a ACKNOWLEDGMENTS rare Late Eocene species with one of the broadest distribu tions known for a Paleogene gac;tropod, occurring in Florida, The material on which this paper is based was generously ~t ississ ippi, Colombia, and Peru. Between 1890 and 1977 placed at my disposal by Elena Benamy (Academy of Natural American authors have proposed several names forth is taxon Sciences, Philadelphia), S. Cazalda (Musco y Laboratoriode based on rare occurrences in different areas. An exception Geologia del Seminario, Barcelona), Frederik 1. Collier ally well preserved specimen noted by David Dockery in the (U.S. National Museum, Washington, D.C.), PeterR. Hoover U.S. National Museum collections labelled by Dallas "cf C. (Paleontological Research Institution, Ithaca), and David R. .wbcancellata Johnson" from th e Moodys Branch Formation Lindberg (University ofCalifomia Museum of Paleontology, at Town Creek in Jackson. Missi ssippi, prompted this revi Berkeley). I wish to extend my warmestgralitudetoJ. Biosca sion. This specimen (Figure I a-b) was collected by E. N. (University Politecnica de Catalunya) for his help and infor Lowe, State Geologist of Mississ ippi (1909- 1933), in Sep- mation. I , 3-4 Cypraedia (Eucypraedia) multicarinata (DaJI, 1890) la-b. Ventral and lateral view. USNM specimen 6467. E. N. Lowe collector (September 1912). Height 29.4 mm , maximum diameter 19.2 mm. dorsoventral diameter 15 .8 mm. Moodys Branch Formation. Town Creek, Jackson, Mississippi. 3. Detail of Cypraedia carmenensis holotype 349R8 UCMP. Specimen not complete, dorsoventral diameter 13.9 mm. Upper? Eocene, Bolivar, Colombia. 4. Detail of Cypraedia piusi holotype 8237 PRJ. L. P. Pitts collec tor. Height42.8 mm (siphonal canal slightly damaged), maximum diameter 24.0 mm. dorsoventral diameter 24.0 mm. Moodys Branch Formation, Town Creek, Jackson, Mississippi. 2. Cypraedia (Eucypraedia) .wbcanccllata (Johnson, 1899) Detail of holotype 71 19 ANSP. C. W. Johnson collector (October-November 1895). I Ieight 15.2 mm (siphonal canal broken), maximum diameter 9.7 mm, dorsoventral diameter 7.3 mm. Weches Formation, Smithville, Bastrop Coun ty , Texas. 5. Cypracdia (Eucypraedia) cailliaudi (Vasseur, 1881 ) Detail ofMNHN specimen. L. Dolin collector ( 1979). Height 22.0 mm, maximum diameter 17.0 mm, dorsoventr31 diameter 14.7 mm . .. Biarritzian·· {=early Bartonian }, "Picrre-Aiguc", Saint-Aignan-Grandlieu, Loire-Allantique, France. 28 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 Figs. 2.- S Jb I a L MISSISSIPPI GEOLOGY1 V.12 I No • 3 141 DECEMBER 1991 29 SYSTEMATICS Clark; holotype (PRI 8237)ofC. (£.) pittsiDockery; topotypes (MLGS, Barcelona 13919, 5558) of Cypraeovu/a Family OVULIDAE Fleming, 1828 funiculifera Cossmann. Subfamily CYPRAEDIINAE Schilder, 1927 Distribution: "Ocala Limestone" (Upper Eocene) at Martin's Station and Richard's Quarry, Marion County, The Cypraedia s. I. have a multispiral (sinusigerifonn) Florida. Moodys Branch Fonnation (Upper Eocene) at Town planktolrophic protoconch with an obliquely decussate sculp Creek (MGS 1), Jackson, Mississippi. Eocene Faunal Zone ture typical oftheOvulidae (Pezant, 1910, pl. 14, fig. 14a-c) C of Clark in Clark and Durham (1946) from about 1.5 and nota vertically squared sculpture as in theCypraeidaenor kilometers eastofLoma de Viento near Carmen well number perforate with a hollow columella as in the Eratoidae. 2, Bolivar, Colombia Chira Fonnation [Lower Oligocene according to Olsson (1931), but Upper Eocene according to Genus CYPRAEDIA Swainson, 1840 Clark in Clark and Durham (1946)] near Casa Sarnan and Subgenus EUCYPRAEDIA Schilder, 1939 Quercotilla, Peru. A few specimens questionably assigned to this species by Olsson (1931) are from the Punta Bravo grits Cypraedia subgenus Eucypraedia Schilder, 1939, Archiv of the Mancora Fonnation (Oligocene) of Caleto Sal, Peru. furMoUuskenkunde,v. 7l,p. 167,190. Discussion: Schilder and Schilder (1971, p. 24) prudently Type species: Cypraea sulcosa Lamarck, by original placed Cypraea (Cypraedia) chira Olsson from the Upper designation. Eocene and Oligocene? of northern Peru and Cypraedia Dolin and Dolin (1983, p. 33) justified the synonymy of carmenensisClark from the Eocene of Bolivar, Colombia, as Eucypraedia with Cypraedia. Eucypraedia is used here as a subspecies of Cypraedia (Eucypraedia) mulricarinata (Dall), convenient taxon for the group of oblong Cypraedia. which is from the Upper Eocene of Florida. The material avaiJable on these Paleogene species is not sufficient to Cypraedia (Eucypraedia) multicarinata (Dall, 1890) discriminate a geographic or stratigraphic transient; even the Figures I a-b, 2-5 Oligocene occurrence of this species in the Mancora Fonna Lion of Peru is questionable. There is no difference between 1890. Ovula (Transovula) multicarinata DaJI, Trans. the three previously mentioned species and the Upper Eocene Wagner Free Inst. Sci. Philadelphia, v. 3, no. I, p. species Cypraedia piusi from the Moodys Branch Fonnation 164, pl. 10, fig. 10-11. of Jackson, Mississippi. 1927. Cypraedia mu/ticarinata DaJI. Schilder, Archiv. The oldest known Eucypraedia is Cypraedia Naturgesh., v. 91, no. NJO. p. 68, 126. (Eucypraedia) interposiJa (Deshayes,l865) from the Ypresian 1931. Cypraea (Cypraedia) chira Olsson, Bull. Arner. (early Early Eocene) of Cuisc-la-Moue, Oise, France (sec Paleont., v. 17, no. 63, p. 93-94, pl. 17, fig. 9, 12. Cossmann and Pissaro, 1911, pl. 33, fig. 162-14). Based on 1946. Cypraedia carmenensis Clark, Geol. Soc. Amer. its thin and numerous ribs and its general shape, C. (£.) Mem. 16, p. 31-32, pl. 17, fig. 3-4. interposita belongs at the base of the Paris Basin Middle 1947. Cypraedia chira Olsson. Ingram, Bull. Amer. Eocene species complex of C.(£.) sulcosa (Lamarck, 1802) Paleont., v. 31, no. 120, p. 67, pl. 6, fig. 3-4. (Cossmann and Pissaro, 19 11 , pl. 33, fig. 162-15 = parisiensis 1971. Eucypraedia multicarinara carmenensis Clark. Schilder, 1931,and fig. l62- l6=sophia Bemay in Desha yes. Schilder and Schilder, lnsLRoyal Sci. Nat. Belgique, 1865) and C.(£.) georgii (Defrance, 1826) (see Cossmann Mem. (Ser. 2), no. 85, p. 24. and Pissaro, 1905, p. 60, pl. 15, fig. 9- 11). 1971. Eucypraedia multicarinata multicarinata Dall . Cypraedia (Eucypraedia) cailliaudi (Vasseur, 1881 ) from Schilder and Schilder, Ibid. the "Biarritzian" (= Bartonian: late Middle Eocene) ofBois 1971. Eucypraedia multicarinata chira Olsson. Schilder Gouet and Saint-Aignan de Grandlieu, Loire-Atlantique, and Schilder, Ibid. France(seeCossmann, 1897 ,pl. 8, figs. 28-29, 31}, is similar 1977. Cypraedia piusi Dockery, Mississippi Geol. Sur to C.(£.) multicarinata in the width of its shell but differs in vey, Bull. 120, p. 6 1, pl. 17, fig. 4a-b. its thin and more broadly spaced ribs and in its smooth Types: Holotype of Ovula (Transovula) multi intercostal zones (Figure 5), which lack the weak intercalary carinata Dall, U.S. National Museum 112450 (Schuchert threads present in the C. (£.) subcancellata. multicarinata et al., 1905, p. 476). and sulcosa species complex. Based on this last criterion, Type locality: Martin's Station, Marion County, Florida. Cossmann ( 1898, p. 339) suggested that C.(£.) cailliaudi was Material examined: Plesiotype (UPMC, Cossmann Col related to Cypraeovula funiculigera Cossmann, 1897 [as lection) of Cypraedia (Eucypraedia) cailliaudi (Vasseur); funiculifera in Cossmann, 1898, p. 25, pl. 9, fig. 1-2 =C.(£.) paratypes (USNM 112449, 11502) of C.(£.) mulricarinata barcinensis (Gray, 1828) fide Schilder, 1927, p. 68, 126) (DaJI); holotype (ANSP 7 119) of C. (£.) subcancellata from the lower"Biarritzian" (=Bartonian) ofSant Llorenc de (Johnson); holotypeand paratype(PRJ 2102, 2099) of C.(£.) Morunys, Lerida, Spain. This last species, however, is more chiraOJsson; holotype (UCMP 34988) of C.(£.) carmenensis spherical, an ancestral characteristic. 30 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 REFERENCES CITED CYJ>taCacea (Mollusca, Prosobranchiata) Eocene Recoltes dans les localites de Gan (Tuilerie et Acot) et Bosdarros Clark, B. L., 1946, Part I.- The molluscan faunas, in B. L. (Pyrenees-ALiantiques, France): Meded. Werkgr. Teet. ClarkandJ. W. Durham,Eocenefaunasfrom the Depart Kwart. Geol., v. 20, no. 1, p. 4-48,31 fig., l tab. ment of Bolivar, Colombia: Geological Society of Ingram, W. M., 1947, Fossil and Recent Cypraeidae of lhe America, Memoir 16, p. 4-76, pl. t-24. western regions of lhe Americas: Bullctins of American Cossmann, M., 1897, Mollusques Eoceniqoes de la Loire Paleontology, v. 31, no. 120,82 p., 3 pl. inferieure, ill: Bull. Sci. NaL Ouest. v. 7, no. 4, p. 297- Olsson, A. A., 1931, Contribution to lhe Tertiary Paleontol 358, pl. 5-11. ogy of Northern Peru. Part IV. The Peruvian Oligocene: Cossmann,M., I898,EstudiodeAJgunosMoluscosEocenicos Bulletins of American Paleontology, v. 17. no. 63, p. 98- del Pirineo Catalan: Bo1. Com. Gcol. Espana, (Ser. 2), 261, pl. 13-33. V. 3, p. 1-32, pl. 6-10. Pezant, A., 1910, Coquilles fossiles des Calcaires grossiers Cossmann, M., and G. Pissaro, 1905, Faune Eocenique du de Parnes: Feuille jeunes Natural., (Ser. 4), v. 40, no. Cotentin, IV: Bull. Soc. Geol. Normandie, v. 23, no. 3, 480, p. 185-197, pl. 13-14. p. 16-86, pl. 11 -19. Schilder, F. A., 1927, Revision der Cypraeacea (Mollusca, Cossmann, M., and G. Pissaro, 1911 , lconographiecomplete Gastropoda): Archiv fur Naturgeshichte, v. 91, no. N des Coq ui lie fossiles de I 'Eocene des environs de Paris: 10, 165 p. Paris, v. 2, 22 p., 61 pl. Schilder, M.,and F. A. Schilder, 1971, A catalogue of living Dall, W. H., 1890, Contributions to lhe Tertiary fauna of and fossil cowries. Taxonomy and Bibliography of Aorida, wilh especial reference to the Miocene silex Triviacca and Cypraeacea (Gastropoda Prosobranchia): beds of Tampa and lhe Pliocene Beds of lhe Inst. Royal Sci. Nat-. Belgique, Mem., (Ser. 2), v. 85,240 Caloosahatchle River: Trans. Wagner Free lnst. Sci. p. Philadelphia, v. 3, no. 1, 200 p., 12 pl. Schuchert, C., (assisted by) W. H. Dati , T. W. Stanton, and Dockery. D. T., ill, 1977, Mollusca of lhe Moodys Branch R. S. Bassler, 1905, Catalogue of lhe type specimens of Formation, Mississippi: Mississippi Geological Survey, fossil invertebrates in the department of geology, United Bulletin 120,212 p., 22 pl. States National Museum: U.S. National Museum, Bul Dolin, C., and L. Dolin, 1983, Revision des Triviacea et letin 53, pt. 1, 704 p. MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 31 SEISMIC STRATIGRAPHIC CONFIRMATION OF A BURIED LATE PROTEROZOIC TERRANE SUNFLOWER COUNTY, MISSISSIPPI James L. Coleman, Jr. Amoco Production Company Houston, Texas 77253 INTRODUCDON Madrid seismic zone and the Mesozoic Gulf of Mexico peripheral fault zone. These two tectonic provinces converge The subsurface of the Mississippi River alluvial plain in near the area of the Monroe-Sharkey Uplift (Figures 1. 3). western Mississippi and eastern Arkansas is one of very Proterozoic basement encoun ters have become more diverse and interesting geology. Quaternary sediments, numerous with increased oil and gas company drilling for which cover most of the area, make study of all pre-Pleisto deeper objectives. The radiogenic age dates and lithologies cene units very difficult. Oil industry exploration seismic of these basement rocks indicate that two thermotectonic and wells give us a unique opportunity to examine this provinces are present within the southeastern U.S.A. (Table unexposed section. A few of these wells drilled beneath the 1). The structural trends of these provinces can be extrapo Mesozoic sedimentary sequences into either Mesozoic igne Lated using regional aeromagnetic and gravity maps (Zietz, ous or Paleozoic sedimentary/metasedimentary rocks (or 1982; Lyons and O 'Hara, 1982) (Figure 1). These data, as both). These provide a glimpse into the earliest geologic well as previously published interpretations of the periods recorded in western Mississippi. The Pan American Midcontinent (Bickford et al., 1986; Bickford , 1988), sug No. I Word,SunflowerCounty,Mississippi,isonesuchwell. gest a progressive Proterozoic accretionary history on the Drilled originaJly in 1969 as a Jurassic Smackover test on a (present) southeastern flank of the North American craton, seismically-defined anticline, the well encountered over culminating in the Grenvillian Orogeny be{wee n 1.3 and 1.0 3700 ft (1130 m) of igneous rocks below undifferentiated Ga. This orogeny was followed by late Proterozoic rifling Jurassic Cotton Valley Group sediments. No identifiable and creation of the early Paleozoic passive continental Smackover was present. The target horizon reflector, origi margin of Laurentia (0.8 to 0.6 Ga)(Hoffman, 1989). For the nally thought to be the top of the Smackover Formation, purposes of this discussion the Proterozoic is assumed to end turned out to be the Jurassic sedimentary unconformity about 570 Ma (Hoffman, 1989). contact with an underlying thick igneous section. This igneous section was dated using the K-Ar method and PAN AM NO.I WORD DRTLLING RES ULTS resu Ited in age ranges from 174 +/- 7 Ma to 785 +/- 34 Ma. These dates indicate that the Pan Am No. l Word was the first The Pan American Petroleum Corporation (now Amoco well in Mississippi to encounter Proterozoic rocks. Production Company) drilled the No. 1 Mrs. A. J. Word, Jr. , Failure to find a trend of Smackover fi elds extending the to a total depth of11,988 feet(3654 m) inScc.4, Tl7N,R3W, Dollarhide Field discovery discouraged further exploration Sunflower County, Mississippi. The test was originall y in the area until the early 1980's. In 1983, Pruet Oil and PGI planned as a Jurassic Smackover wildcat. Overlying Creta reprocessed Amoco's seismic data in the area. This effort ceous igneous units were known to be present in the area, so substantially improved the seismic stratigraphic resolution encountering an igneous body prior to reaching the Smackover of the data and finally permitted resolution of the previously was not considered detrimental nor unusual. Consequentl y, undifferentiable igneous pile in the lower portion of the Pan the well drilled through 3705 ft(ll29m)ofthe lowerTertiary Am No. I Word. Through an integration of seismic, well log, Wilcox and Porters Creek formations, 3675 ft (1120 m) of and dri ll cutting radiometric age dates, this report presents an Cretaceous chalks, volcanic rocks, and interbedded shales interpretation of some of that data. and sandstones, and 840ft (256m) of Jurassic Cotton Valley Group sandstones and shales before reaching the top of the REGIONAL GEOLOGIC SETTING main igneous pile at a measured depth of 8280 ft (2524 m)(Figure 2). Drilling continued through a thick igneous The Mississippi Alluvial Plain overlies a tectonically section, ultimately penetrating approximately 3700 feet (11 30 active structural trough which has displayed major, recurring m) of continuous igneous lithologies. No Smackover was movement since the Late Proterozoic. This activity is identified. At 11 ,988 fL (3654 m) the well was logged, associated with faulting within the Reelfoot Rift - New plugged and abandoned without any oil or gas shows. Com- 32 MISSISSIPPI GEOLOGY, V. 12 , No. 3,4, DECEMBER 1991 en~ en u; ~ ~ ·!' •5 ' I ~ 6 ) C) 0' 0 -~------6 ~ -- b --Y~----- ~/-,..,_ .•1 - - ~2 - -:- - 5 - a • ,-_:·- - --/ 0 ;1:::'. C) I 0 1 • ~.... · ,' dl,r 6' / 0 ' , .< 6 -b 2 I '0 ~0 '1.-"' 6 It)• 0 / 0 :o ~ 0 ~ --- ...... A a: p - N l,' o ,:_, . ~~- · 7 z - _,- ...... ! ? ~ ;co. 0 ~ ~ CD ~ ..A l8 ..A \_ ------~ - -\·- I- -·--··-· _... -\1 Al \.. ' .,, ~ ~.-.J , . . -' i Ia£& - 0 199 209 250 ~ 0 100 zoo 2110 ~ KLOIIETERI ~~~t:~~ PAOTEROZOK: BASEIIENT l .EGENO TRENDS OF -Grenvillian and older datea (>1.0 Ga) ...... ,., Appfoaa.ate pre·thrvat..... toc..Uoft 0 ot C.rMNo-Ordo't'k;le" oarboftate SOUTHEASTERN U.S .A. bank mare"' A · Laurentian rlttlng datea (< 1.0 Ga) - ...tof Pateozok tautt I.OMI ..._• ._e ...... ,,...... Precambrian age by etrellgrephi<: retallonaltlp (ct.•Md w·hMe lftfen •cl, ·- 0 only '"' ----- l a,_o...... , (H · £•1-...... ~ • Pan Am 111 WO Figure 1. Proterozoic basement dates and structural trends in the southeastern United States. Age dates, locations, and data ~ sources are identified in Table I. Base map modified, in part, from Hale-Erlich and Coleman (1991, in review) andJurick ( 1989). ~ ; ',OLE I rr.CI•tr.c;:-: . !':;S('I[~T rr· CTRATIO'S \~ 0 OCC'lr.~E.,CCS S.E. l:.S. \ , ' ~OC.\T I O~S PLOTTE.D 0~ F!GI'RI' I' H' 'll\£ , £T ~ . llOCil T l'rE R EFE R E~CI' SOt'RCt< S) ~. ·•!... • ''I!A. • ~• ., _:t" ~v n. c '· I ~ .: lll'l· ~1 -lnit l· \·an ~rh• u• antJ others t 1981) : l [ \ "''· ' hrwrtals OBI I l · l1~·li \t. Caadc:-u C"'. 163] rtr b ,n,.t•• \'an Sc hau• and oth~Pr" I 19£7) ,., u \f: in• rela TDI :a l :'\-I;" Ca.adcr• .. .. , 163] r/Pb \'3n ~h· "- u• •ntJ olhrr• 1191 .. ) J-) ~t fouu.al• 'tt n~ . ~r "· ~•ou r ! t t•" 1/ P~ "rh~"~'··o ll · BicLf o r.J • nd !'t o$~ t 1915 ) 1r•n .t• ..; J Uu l( C' o! rr '- -~ V/Pb 1 r an l tr l'l"nlcls 6. S• ith I~JO R\./Sr teranlte "'1 u~t.t bur1~ r l o th rr~ ( 19ti6) t 2 \' J.erhall~r :) S ~ ·~H! n .t\> C rt.•t-•lo: 'lo)rli Co. 1280 Rb/Sr a: run t te !'4u e til burc ot• o ther• ( 1960) o u t C' r o r " l t"' t_ ta. ~~~. Ctt!i 1230 Rb/Sr ~ uehlbur1 ~r otbcro 1 1966 1 • I St..oc;: l.tor. 'I Pan \ a • J T.u-k«>\.t 1200 Rb/Sr 'luehlburter oth~ rs ( 1966) 1) La nr 4 ~r ~ t~tn J - 16~·26 11 Bc>nt on Co. r<" •trat. a lcr o l r•nlle• Denlaon (lU I ) • Z O.catur ret. porphJr)' : ) Ozark • t C'urr}" r<" atrat. rhJollte Denloon !1981) r •l. vorphyr) J; Teru •.:c.~ • 1 Cr.o nfll a\f'r 17-l0~- 27W Franllln Co. rc atrat. •lc roaranlt.e Denloon (lUI) r td. porphrrY I ) S££CO I 5 Leas h•> 21-l0~ ·281i Fr~~n kl ln Co. PC a t rat. a ran l t ~ Den l oo n ( 1984 I r e I. :'.) \ rl~ t a cJ ..\rk . \ 'n) l t")' PC I t rat.. • icroaraph ic; Den l oo n (1984) red. cranlle PC a t rat. • •larhyo l i teo Den loo n !1184 1 ret. t I La yne Wf:' a lc-rn l · l&~-26 11: !'ladl&on C'o. PC atrat. a.etarbyol l te Denloo n 1198 ~ 1 t 1 Hunls\· lllt' rtol , I J St. Joe !lin. l0•2l~ -25V Carroll Co. PC a t r at . a lcro1 r aph ic Den l oo n I 1914 ) t AK -('A - 1 rel . a r a.ni te o t Pan \A I I t'S-\ 28-ll~ - 22W s .. wton C'o. PC a trat. . a ter o a raphlc: Den loon I I 984 I rel. cranlte 10) hlrople' 18· 14N-16W Searcy Co. PC at rat. &r ani to Denhon ( 1984 ) t l \~ heeler r el. Il l Opel l o brecci a PC" I I th. cranl t e cn.elaa Denlaon II 184 l xenolltho 12 ) Arco • 1 tdc•an PC atr•t. 1 r ani t.e Den loo n I 1984 I rot. w/dlabaoe I ll Ho • l ny Hil l Sa lln• Co. 1025 'MAr a etaaa.bbro Morrie 6 Stone ( 198&, 11) Coc k~r~ll t l Carter 4- 4H-ll St. Frane-l a Co. PC unk. •t..a«..._nl· Schwalb ( 19121 l~ l Dow t1 Wil•oa 14- 12~ - 9£ Hlosisslppl 14~ 1 / Ar aranitlc a neiaa Howe (IUS) Co. 'IISSISSI PPI : I) Tf" ,•.co f l hf' l6 - Z7~-3 V Coa hoae Co. PC • t r et.. e icroperthlte Rarrehon & IIcker I 11791 ..... aranl te ~ ) P• n Aa t l '-'o rd 1·17\'- JW Su.nrlower Co , 786 K/Ar •r•nlte: Table 2, thla paper 3 1 Pru•l & Hu•h•• 18- 7S-IW Lafayetlo Co. 790 K/Ar alc ropert.h lle Ri.. . ( lt76) t I DunlAp a r a nlte 11 £~~o n t l Fu l ch•• 33 · 1 9 ~· 12£ Ok tibbeha Co. PC alrat. . Harre loo n I. Bicker 11979), r•J. t;~: t ~: i c rock.. He llen (1917) AL.\BA!I.\ : PC au·at. alk. o lldne ~ eatherr I. Copelaod I 1983 J ret. ba eal t Z l S••• I I Sk ld 110r~ 36- 7$- IW !to r ••" ('o. 752 l l Sa l• t l Rudoon 16-IOS-2£ Blo unl Co, PC atrat . aranodlorlt..e l/eatherr & Copeland ( 19831 ret. PC at rat. aranltlc anel•• SL~Ilenpo h l ( 11881, St~lhnpohl rt- 1. l Moor• (19111 TE.\"SESS[[ II HI ' C hl~r • I Ta)lor Cib•o« Co . uo K/Ar *b••• • ont Cor••n l Bradlctl' (19831 roc k a" ~l DuPont 12 f•e Huaphr•Y• Co. PC at rat. unpubl. Aaoco f ile & r e l. l, Sta u rte-r ~h f'a ical "1aun· ro. 1328 K/Ar rhyollt./ Corcan l Brad ley ( 1983 I, ; 1 F ~e aranlte !.teathery • Coveland ( 1983 I I I Cottrornla Gil*• Co. 1120 Rb/Sr 1ranlLe Cor1an & Bradlor ( 19831, 1 1 lc-eler v... ..nt.ura & o lbrrs ( 19&2 ) 5) OuPont • J Fet- Da " ldaon Co. PC a t r-a t. · ara.nlt•• unpubl. -'-O~o fllu re-l. Rutherf o rd Co . PC stral... unpubl. -'-Ceo files, Sc:hwalb 119121 rei . l."llaon Co. PC !l.lra t. u npubl. Aao 34 YSSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 f ,\BLI 1 (._lo)nl l nu~J} PRO'T~ROZOIC BASEMENT PF.NETR A TI O~S AND orrcnRE!'<<'r.S S.F.. t· .~. ~. 11(>1'\Tl n'" ~ Lt>'M"rD n~ Fl~• ·Rr I I VI.LL. '1J!t£.£TC. lOCATIO~ ACt I ~• l METHOD Rrrrn~:cr sot•Rcrr • 1 0£0RCI.\: ll S0t(AT ., lro-. n Dadt!' Co. G5l 1\/ \r ~ra.nOit& o r- • \ ~ 'ttath.<-r! l rop4"1 :'\f'iiJ t !,.., .. . Fort M.ounloln a rra. "'urra ) ('o. 1030 \'/Pb &rani\ tc lillcConr.c-11 & ("',.u r ll ft9e• cneiaa 3) SolC"• Churc h 8art.oto. ... Chf>rOkC'C" Cos . ) JlOO Pb/Pb 1ra.nll l(' 'ntlt• &lnoriu• Ar/.\r (nt"ia• I ) Pine "'.ounuln 1055 Rb/Sr c rantt h Strltc-npohl t1 981 1 wlndov 1018 C/Pb flnc i s a '>tto• A 1)\'u' . [ !?'"''"• 1"t2:: ~ \' l ROt~ lA : II Bl ur Mld1c MLna . SC \' lrc tnl• 10 41 - at roAt. cranodlorllc )) 4 9 corre-1 . c·n ei•• %) Striped AOt;k s. Vlr1 lnla 81u• e•a Rb/Sr ar11n1 t f" C'klo• & f u11ac nr Cl"t',' 1 rantt~ Rldco 712 Pb/ Pb Moaco l oth tor>tr. I 19821 780 U/Pb f'XJo• 1 F'-' lt .....u C1 :» 8 I l ell Rb/Sr Octo• I Fu Jla&a r 1191 1 l. 'to ..• l .:tlh'" • • t 1 IJit' H O ~/ Pb Odo• l Ful1•C•r fJte • t S95 Ph/\• Odu• & Fullnc•r (19811 l) Ora ya on 1nelaa 1150 cn,.taa F'vll acar l Odo• flt13J 'hue & ... ll,<>r• 41983 1 Rank tn & Q\f'''' ( 19PO I ~ ORT K CAROLINA : 1) "4 t, Ro . o r s a._r &l\ 'IW ' II ) ~'W No. Car olina TOG Rb/Sr 1 r•nlt,. iklf'C' h cranJt.r Odo• ' ru l I •••r c 1911 , I out c r o v 'tcuu• I. ot'tl'""" 1198~) 121 l·/Pb \fosto & Olh.. u : ( 1 98~) 750 IJ/Pb Orln• A Futl,..ar (1981• 12} L• n•lnc plut.on 20 k• ao. HL. Ro 1 ers Ul Rb/Sr Oclo• & Fulla111•• ( %98 11 ..-u t... r o p R.anL. ln a uth•r• c 14,1't l K£l'Tl:CKT: II o\•er-adl4 I I Edw•rds 24- ll - 60 Pula•k l Co . IHT 11/Pb a)tmlla Rovr4 A o thrr"' ft9R1t 2 1 D.,_ nz. I I :(unna11y IS•F• IG MotcalC Co. PC unk. •basf"•f"nt • S-~hw • Ht C l 91: I posite samples were collected from several intervals in the Sundeen (1979, 1980, 1982, 1986), Harrelson and Bicker igneous pile and dated by K -AI method (Table 2). Three ages (1979), and others (see bibliography in Sundeen, 1986, were detennined: Appendix C). These rocks extend over approximately 5300 sq. mi. (13,640 sq. lcm) in the Mississippi Embayment of 1) basalt from 9613 ft (2930 m) at 174 +/- Mississippi, Louisiana, and Aikansas (Figure 3). Within the 7 Ma (M. Jurassic) well bore, MiddleJ urassic igneous rocks rest on a metaquanz 2) basic igneous rock from 11,210 ft to 11 ,984 ft ite of undetennined age which occurs between 10,905 ft (3417 m to 3652 m) at468 +/- 19 Ma (3324 m) and 10,960 ft (3340 m). (M.-L. Ordovician) Beneath the Middle Jurassic section, a sequence of 3) hornblende syenite from 11 ,300 ft to 11 ,360 ft hornblende syenite with intruded(?) basic igneous rocks (3444 m to 3462 m) at 785 +/- 34 Ma continues to the bottom of the well. The basic igneous rocks (L. Proterozoic) wereoriginallydatedat459+/-23 Ma(Table2). In the report of analysis of a re-sampling of the lower section, Krueger The Middle Jurassic basalt fits into a whole suite of (1976) stated that the 459 +/-23 Ma early Paleozoic age may similarly aged basic igneous rocks reported in some detail by be a minimum detenninatioo. If this assessment is correct, MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 35 then the Middle to Late Ordovician date may be too young zoic age and 180 ft (55 m) above the uppermost sample depth because of Mesozoic thermaJ aJtcration and radiometric yielding the Middle to Late Ordovician age. It is 60ft ( 18 m) below rescuing associated with the Jurassic basalt flows. This being the contact between the quartzite and the coarse-crystalline igne the case, the basic igneous rock may be at least Cambrian in ous rockatl0,960 ft(3340 m). Althis depth, theapparent 60 ft(l8 age, and is possibly related to rcgionaJ igneous activity m) mis-tie is approximately 6 milliseconds of two-way time, a involved in early Paleozoic rifting of the Reelfoot Rift pencil point width. While caution should be exercised when using (Howe, 1985). RecaJculation of the originaJ data yields a an interpretation made from a single seismic line, in th is case it slightJ y older age of 468 +/- 19 Ma (Table 2). If either age appears reasonable to assign the lower seismic unconformity to the is valid, then they fall close to ages of Ordovician bentonites Mesozoic- Proterozoic regional unconformity. from eastern Nonh America (457. 1 +/- 1.0 Ma)(Samson et The fundamentaJ lithologic differences between the Ordovi al., 1989). Thesebentonitesare usually attributed to volcanic cian and the Proterozoic samples suggest that the Ordovician basic ash faJis emanating from an, as yet, unidentified volcanic igneous rocks intruded the Proterozoic syenite. The seismic data source in the southeastern U.S. A. This age is aJso within the arc insufficient to discern the accuracy of this assessment How age ranges of Carolina slate belt felsic metavolcanic rocks- ever, the short-length, high amplitude re fl ectors below the Meso 465 Ma (LeHuray, 1987). The volcanic source for the North zoic- Proterozoic unconformity are characteristic of moderately American Ordovician bentonites was apparentJy underlain thin-bedded, but fairly numerous, intrusive bodies within an by Proterozoic crust because it contains inherited zircon with otherwise "quiet" (i.e., low amplitude) seismic intervaL ages of 1100 and 1500 Ma (Samson et al. , 1989). Data are insufficient to speculate further on the potential relationship DISCUSSION between the occurrence of Ordovician age basic igneous rocks and the eastern North American bentonites of the same The identification of at least two distinct seismic packages age. within the 3700 ft (1130 m) igneous section of the Pan Am No. I The Ordovician basic igneous rocks of the Word well Word indicates that the radiometrically dated igneous sections presumably intrude into the more sialic, hornblende syenite may be correlated with reasonable confidence to these seismic secti on dated at 785 +/- 34 Ma, although specific sample intervals. The upper igneous interval is of Middle Jurassic age and evidence is currently lacking tO demonstrate this. thickens from south to north across the study area (Figure 4 ). The This Late Proterozoic age date is similar to other Late lower intervaJ is primarily of latest Proterozoic age. The date and Proterozoic Laurentian dates in the area (Figure 1, Table 1). lithologies are consistent with other occurrences along the margin The samples which yielded these dates are aJI from localities of the Mississippi Embayment - Reelfoot Rift. near or within the Late Proterozoic rifted marginofl.aurentia. There is no clear geophysical evidence that the Word area was It is reasonable to assume that these ages reflect the high thrusted northward during the Ouachita Orogeny. Previous work temperature events associated with that major tectonic epi ers have placed it south of the various late Paleozoic disturbed soclc. zones in Mississippi (Gazzier and Bograd, 1988; Jurick, 1989; and others). The limits of the late Proterozoic igneous body cannot be INCORPORATION OF SEISMIC STRATIGRAPHY further refined by the ex isting seismic data. It appears to extend beyond both ends of the illustrated seismic line, a distance of 12m i. Since the samples that were dated were collected from (19 km)(Figure 4a,b). Based on its seismic character in the Word dri ll cuuings from a 60-foot (18 m) interval, it is difficult to area, it extends, on other seismic data, as much as 15 mi. (24 determine their precise stratigraphic level, and hence, the age km)(north to south). This ex tent suggests that this late Proterozoic to which they can be applied. Application of simple seismic body may not be a local anomaly or exotic local crustal block, but stratigraphic techniques to a north-south seismic line through rather may be part of the main North American Proterozoic craton. the well helps constrain the options. A synthetic seismogram While i ts age groups it with other Laurentian rifting ages, its (Figure 2) was created from the sonic and density logs run in potential significance is its apparent location south of what is the Pan Am No.I Word borehole. This seismogram Lies the thought to be the southern cratonic margin of Paleozoic Nonh well log stratigraphy and li thology to the seismic refl ection America (Figure 1). lfthis assessment is true, then the Word area packages. Two seismically interpreted unconformities arc may have been a part of the continental mass which rifted away obvious below the top of the Couon Valley reflector (Figure from North America between 800 and 600 million years ago. The 4): one at the top of the volcanic pile (approximately 1.9 785 Maage forthe basal igneous of the Word section is very similar seconds on the right section margin) and a deeper one within to ages obtained from Blue Ridge igneous rocks (Table 1; also sec the pile (approximately 2.2 seconds, aJso on the right mar Mose et al., 1989, for Blue Ridge dates just nonh of the map area gin). Initial correlation of this deeper unconformity back to ofFigure 1). These dates are bimodal,ranging from 570 to 785 Ma the borehole places it at approximately 11,020 ft (3359 m) on and from 947 to 1280 Ma (Table 1; Mose et al., 1989). It is the well log. This borehole intercept occurs 260ft (79 m) uncertain if the Word area is an isolated microcontinental block or above the uppermost sample depth yielding the late Protero- a portion of a larger crustal block. Since its age is more in line with 36 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 the dates associated with the late Proterozoic rifting ofNonh shear faulting along th e Alabama - Oklahoma transform America rather than the Cambrian intracratonic rifting of zone. interior North America (Lowe, 1985; Reed et al., 1989; Thomas, 199 1) , it is conceivable that the Word area repre ACKNOWLEDGMENTS sents a locali7,ed block of North America left behind along the initial rifted cratonic margin. It is located nonh of the Tom Steele, now deceased and formerly with Amoco proposed track for the late Proterozoic - early Paleozoic Production Company, New Orleans, originally showed me A Ia bam a - Oklahoma transfonn wne of Thomas ( 1991, the improvement Pruet Oil and PGI made in the old Amoco Figure2). Il wa<; this tr~msfe r zon e which created the sou them seismic lines. Appreciation is extended to Amoco Produc Paleozoic cominental margin of North America. tion Company and Pruet Oil for releasing th e seismic and radiometric data. The author thanks Wendy Halc-Erlich. CONCLUSIONS lone Taylor, and Danny Harrelson for reviewing earlier versions of this manuscript, and the Mississippi Office of ThePrecambrianageofa thick sec tion of alkalic igneous Geology for providing an outlet for short geological notes on rock encountered in the lower portions of the Pan Am No. I the fascinating geology of Mississippi. Word well can be confidently correlated with an identifiable seismic sequence. The upper unconfonnity boundary to this sequence separates the Precambrian igneous section from the REFERENCES CITED Jurassic igneous sec tion. The seismic character of the Precambrian sec tion can be correlated for at least 12 mi. ( 19 Bickford, M. E., 1988, The fonnation of continental crust: km) across the study area and may have a north - south part I . a review of some principles; part 2. an applica extension of at least 15 mi. (24 km). The 785 Ma age of this tion to the Proterowic evolution of southern North .section is compatible with oth er igneous age dates in the America: Geological Society of America Bulletin, v. region which arc correlated with the late Proterozoic conti 100, p. 1375- 139 1. nental margin rifting of North America. A determination of Bickford, M. E., and D. G. Mose, 1975, Geochronology of the regional tectonic position of this section cannot be made Precambrian rocks in the St. Francois Mountains, south at this time. Initial conclusions suggest that it is an aban eas tern Missouri: Geologica l Society of America, Spe doned, rafted block of North America, possibly caused by cial Paper 165, 48 p. TABLE 2 RADIOMETRIC ANALYSIS. OF PAN AMERICAN NO. I WORD SAMPLES De[!th (lntervl)ls} L ithQIQg:i ~ ave, Ar4Q tmm ave, K40 1212m Ar4Q[K40 I ) 9,613 ft basalt 170 +/- 8 Ma 0.0 120 1.1 57 0.0 104 (whole rock) 2) ll,2 10 -11 ,984ft basic ign. 459 +/- 23 M a 0.01536 0.0505 0.03037 rock (amph. concentrate) 3) 11 ,300 - I 1,360 ft hornblende 770 +/-50 Ma 0.01145 0.2050 0.0559 syenite (or diorite) (hornblende concentrate) ·Analysis performed by Krueger Enterprises in 1969 and 1976 for Amoco Prod. Co. In 1985, the Miss. Bureau of Geology had these anal yses re-calculated by Geochcm Labs utilizing new decay constants of Stcigncr and Jager ( 1977, Earth and Planet.ary Sci. L trs., v. 36. p. 359-362): 1) 174 +/- 7 Ma 2) 468 +/- 19 Ma 3) 785 +/- 34 Ma MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 37 sonc ux;g;o DEPTH TIHE AGE DATE (fT) IMSI INTERVALS & AGES SEISMIC MARKERS - 380 - 100 - 763 -200 - lli6 - 300 -1529 - -100 - 19 12 - -500 - 2296 -600 - 2679 - - 700 - 3062 - BOO - 3115 - -900 I 111111111 llltlllllll -3828 - - 1000 - 1211 - 11 00 - 4628 - 1200 - 5039 - - 1300 -5522 - 1400 - - 6 130 - 1500 -6745 - - 1600 -7390 - - 1700 - 8033 - 1800 - 8783 - - 1900 - ~174 + /-7 1111a - 9574 - 2000 -10186 - - 2100 - ..., 468 +I· 191111a . ~ ' ~ ·.,: -11472 - - 2200 ~ _> ~ ' ...... ~ " ;t - 5 785 +/- 34Ma N OTD 11,988' - 2300 ~ UJ 1- -2400 ~ CL ITIT IT I - 2500 Figure 2. Stratigraphy of the Pan Am No. 1 Word. 38 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 \ r ' -1 I - ··- -··-·-··- , .... _ ..,' : ' ~( \.. '\ s .L- - · - -- ) > MILES ______.1o~o~======2~o.o..... 0 250 o------~====~--250 100 200 KILOMETERS Figure 3. Approximate extent of Middle Jurassic igneous province, based on regional aeromagnetic and gravity trends ofZieLZ (1982) and Lyons and O'Hara (1982), plus weU data. Cross-hatched areas are high amplitude, aeromagnetic anomalies of apparent or actual Mesozoic ori gin. 39 MISSISSIPPI GEOLOGY, V.12 , No. 3,4, DECEMBER 1991 Bickford, M. E., W. R. Van Schmus, and I. Zietz, 1986, Krueger, H. W., 1976, Cover letter dated 17 June 1976 to Proterozoic history of the midcontinent region of North Amoco Prod. Co. from Krueger Enterprises accompany America: Geology, v. 14, p. 492-496. ing radiometric analysis of Word samples. Corgan, J. X., and M. W. Bradley, 1983, Radiometric ages of LeHuray, A. P., 1987, U -Pb and Th-Pb whole-rock isochrons Tennessee rocks: Tennessee Division of Geology, Bul from metavolcanic rocks of the Carolina slate belt: letin 82, 41 p. Geological Society of America Bulletin, v. 99, p. 354- Denison, R. E., 1984, Basement rocks in northern Arkansas: 361. Arkansas Geological Commission, Miscellaneous Pub!. Lowe, D. R. , 1985, Ouachita trough: part of a Cambrian 18-B, p. 33- 49. failed rift system: Geology, v. 13, p. 790- 793. Denison, R. E., E. G. Lidiak, M. E. Bickford, and E. B. Lyons, P. L., and N. W. O'Hara, chm., 1982, Gravity K:isvarsanyi, 1984, Geology and geochronology of Pre anomaly map of the United States exclusive of Alaska cambrian rocks in the central interior region of the and Hawaii: Society of Exploration Geophysicists map, United States: United States Geological Survey, Profes scale 1:2,500,000. sional Paper 1241-C, 20 p. McConneli,K. I., and J. 0. Costello,l980, Guide to geology Fullagar, P. D., and M. J. Bartholomew, 1983, Rubidium along a traverse through the Blue Ridge and Piedmont strontium ages of the Watauga River, Cranberry and Provinces of north Georgia, in R. W. Frey, ed., Excur Crossing Knob gneisses, northwestern North Carolina: sions in southeastern geology: American Geological Carolina Geological Society Field Trip guidebook, pa Institute, Atlanta, v. I, p. 241 - 258. per II, p. 29. McConnell, K. I., and J. 0. Costello, 1984, Basement cover Full agar, P. D., and A. L. Odom, 1973, Geochronology of rock relationships along the western edge of the Blue Precambrian gneisses in the Blue Ridge province of Ridge thrust sheet in Georgia: Geological Society of northwestern North Carolina and adjacent parts of Vir America, Special Paper 194, p. 263-280. ginia and Tennessee: Geological Society of Ame.rica Mellen, F. F., 1977, Cambrian System in Black Warrior Bulletin, v. 84, p. 3065- 3080. Basin: American Association of Petroleum Geologists Fullagar, P. D., R. D. Hatcher, and C. E. Merschot, 1979, Bulletin, v. 61, no. 10, p. 1897-1900. 1200 m.y.-old gneisses in the Blue Ridge Province of Morris, E. M., and C. G. Stone, 1986, A preliminary report North and South Carolina: Southeastern Geology, v. 20, on the metagabbros of the Ouachita core: Arkansas p. 69 -77. Geological Commission, Guidebook 86-2, p. 87 - 90. Gazzier, C. A.,andM. B.E. Bograd,1988, Structural features Mose, D. G., F. D. Eckelmann, S. W. Kline, and G. W. of Mississippi: Mississippi Bureau of Geology map, Mushrush, 1989, Radiometric ages of rift-associated scale 1:500,000. latest Precambrian alkalic granites in the Grenville Hale-Erlich, W. S., and J. L. Coleman, Jr., 1991, in review, terrane of the Appalachians: Northeastern Geology, v. The Ouachita - Appalachian Juncture: a Paleozoic 11, p. 1-21. transpressional zone in the southeastern U.S. A.: Ameri Muehlberger, W. R., C. E. Hedge, R. E. Denison, and R. F. can Association of Petroleum Geologists Bulletin. Morvin, 1966, Geochronology of the Midcontinent re Harrelson,D. W.,and A.R. 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Rb- Sr geochronology of the basement rocks in the Pine 40 MISSISSIPPI GEOLOGY, V.12, No. 3,4, DECEMBER 1991 SOUTH ... ~ . NORTH rwt Figure 4a. Migrated, north-south seismic line through Pan Am No. I Word (interpreted). b. Same as 4a, but uninterpreted. Mountain bell of southwest Georgia, inS. A. Kish, T. B. A. L. Odom, 1983, Correlation chan for Precambrian Henly, and S. Schamel, cds.. Geology of the southwest rocks of the eastern United States: United States Geo em Piedmont ofGeorgia : Geological Society of America, logical Survey, Professional Paper I 241-E, 18 p. field Lrip guidebook, p. 12- 14. Rankin, D. W., A. A. Drake, Jr., and N. M. Ratcliffe, 1990, Rankin, D. W.,T. W.Stem,J. McLelland,R.E.Zartman,and Geologic map of the U.S. Appalachians showing the MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 4 1 Laurentian margin and the Taconic Orogen, in R. D. Sundeen, D. A., 1980, Petrology and geochemistry of igne Hatcher, Jr., W. A. Thomas, and G. W. 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Bickford, and I.Zietz,I987,Early area: NUREG/CR-2909, 61 p. and middle Proterozoic provinces in the central United Steltenpohl, M.G., 1988, Geology of the Pine Mountain States: American Geophysical Union Geodynamics imbricate zone, Lee County, Alabama: Geological Series, v. 17, p. 43-68. Survey of Alabama, Circular 136, 15 p. Wasserburg, G. J., G. W. Wetherill, L. T. Silver, andP. T. Steltenpohl, M. G., and W. B. Moore, 1988, Metamorphism A awn, 1962, A study of the ages of the Precambrian of in the Alabama Piedmont: Geological Survey of Ala Texas: Journal of Geophysical Research, v. 67, p. bama, Circular 138, 27 p. 4021-4047. Sundeen, D. A., 1979. Petrology and geochemistry ofsubsur Zietz, I., compiler, 1982, Composite magnetic anomaly map face igneous rocks in Humphreys and Sharkey of the United States, part A: contenninous United States: Coumies, Mississippi: Mississippi Mineral Resources Uni ted States Geological Survey map, scale 1:2,500,000. Institute, Project 787 final report, 22 p. 42 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 NEW PUBLICATION BY THE OFFICE OF GEOLOGY CAMBRO-ORDOVICIAN SUBSURFACE STRATIGRAPHY OF THE BLACK WARRIOR BASIN IN MISSISSIPPI The Office of Geology announces the publication in isopach maps and five cross sections. The report concludes of Report of I nvest.igat.ions 2, "Cambro-Ordovician S ubsur that this section in Mississippi offers exciting possibilities faceStratigraphyoftheBlackWarriorBasin in Mississippi," due to numerous hydrocarbon shows, excellent reservoir by Kevin S. Henderson. rocks, and large undrilled structures. This report describes the Cambrian and Ordovician Report of Investigations 2 may be purchased from of the Black Warrior Basin in northern Mississippi, a se the Office of Geology at Southport Center. 2380 Highway 80 quence of rocks up to 8000 feet in thickness. Henderson's West, Jackson, for $8.00 per copy. Mail orders will be study compiles information on nine Cambro-Ordovician accepted when accompanied by payment ($8.00, plus $1.50 formations from available geophysical logs, cores. and postage and handling). Send mail orders (with check or samples. The Cambrian stratigraphic units discussed are the money order) to: Weisner Quartzite, Shady Dolostone, Rome Formation, Conasauga Limestone, and Copper Ridge DolasLOne. The Office of Geology Ordovician units are the Knox Dolostone, Knox Limestone, P. 0. Box 20307 Stones River Dolostone, and Stones River Limestone. Litholo Jackson, MS 39289-1307 gies and stratigraphy are discussed in the text and illustrated LIST OF PUBLICATIONS Copies of the lates t List of Publications (November 1991) are available from the Mississippi Office of Geology. Copies may be obtained free of charge from the Office of Geology at Southport Center, 2380 Highway 80 West, Jack son, or by writing to: Office of Geology P. 0. Box 20307 Jackson, MS 39289-1307 MISSISSIPPI GEOLOGY, V. 12, No. 3,4, DECEMBER 1991 43 MISSISSIPPI GEOLOGY Department of Environmental Quality Office of Geology Post Office Box 20307 Jackson, Mississippi 39289-1307 Mississippi Geology is published quarterly in March, June, September and December by the Mississippi Department of Environmental Quality, Office of Geology. Contents include research articles pertaining to Mississippi geology, news items, reviews, and listings of recent geologic literature. Readers are urged to submit letters to the editor and research articles to be considered for publication; format specifications will be forwarded on request. For a free subscription or to submit an article, write to: Editor, Mississippi Geology Office of Geology Editors: Michael B. E. Bograd and David Dockery P. 0 . Box 20307 Jackson, Mississippi 39289-1307