DEPOSITIONALSYSTEMS IN THE SPARTA FORMATION () GULF COAST BASIN OF TEXAS1

Jose Ulises Ricoy2 and L.F. Brown,Jr.3 Abstract

Three principal depositional systems are defined within the Sparta Formation ofTexas using surface and subsurface data: high-constructive delta system in east , strandplain/barrier-bar system in central Texas, and high-destructive, wave-dominateddelta system in south Texas. Principal facies constituents of the high-constructive delta include upper delta plain in outcrop and lower delta plain, delta front,andprodelta in subsurface. Five major deltaic lobes in the SpartaFormation are similar to variouslobes ofthe Eocene QueenCity Formation, lower Wilcox Group, Jackson Group, and Yegua Formation ofTexas. The Sparta high- constructive delta system is present from Fayette andColorado counties in Texas, eastward into Louisiana, Mississippi, and Arkansas. The Sparta strandplain/barrier-bar system ofcentralTexasis basically composedofa single multistorybarrier bar unit.It was constructed with sand transported along strike by longshore currents from reworked sediments of the high- constructive delta system in east Texas. This system extends from Fayette andColorado counties westward to Atascosa and LiveOak counties. A Holocene analog is the Texasbarrier island system. Eocene analogs arethe strandplain/barrier- bar system of the Eocene Jackson Group, Yegua Formation, lower Wilcox Group, andQueen City Formation. A high-destructive delta system in south Texas is composedessentially ofcoastal barriers and associated lagoonal facies in outcrop and coastal barrier, lagoon, andprodelta shelf facies in the subsurface. This wave-dominated delta system is present from Atascosa andLiveOak counties southward to the Rio Grande, andit extends into northern Mexico. Eocene analogs occur in the south Texas Wilcox Group,Yegua Formation, andQueenCity Formation. Oil and gas have not been found in the SpartaFormation, in part because little growth faulting was associated with the thin Sparta delta-front sandstone and prodelta shale facies. Water chemistry variations are closely related to depositional systems within the Sparta Formation. A bicarbonate province is related to updip areas (major fluvial influence) of the high-constructive delta system of east Texas; a sulfate province occurs in updip areas (barrier-bar/lagoon influence) associated with thehigh-destructive delta system of south Texas andcentral Texas; a chloride provinceis associated with downdipmarine sandstone facies ofbarrier anddeltaicorigin. Flushingby freshwater hasquantitatively butnotqualitatively altered the initial water distribution within the various Sparta sand facies.

Introduction Interval Studied This study involves the recognition and mapping of Theinterval studiedin eastTexas (Fig. 2) is composed depositional systems and genetically related constituent of facies that extend from the base of the progradational facies in the Sparta Formation, Claiborne Group of sandstone and mudstone facies of the overlying Yegua Eocene age in the Texas Gulf coast basin. The Sparta Formation to the base of the subjacent Weches Forma- Formation is one of the many Tertiary, offlapping, ter- tion. It comprises the Cook Mountain, Sparta, and rigenous, clastic-wedge sequences that filled the Gulf Weches Formations in central eastTexas and the Laredo coast basin. It is composed of sand and mudstone de- Formation insouthern Texas,which includes strataequi- posits which are overlain by regionally persistent valent to the Cook Mountain and SpartaFormations. glauconitic,fossiliferous,marly shelf facies of the Cook In east Texas, the Sparta Formation is approximately Mountain Formation and are underlain by similar shelf 400 feet thick inupdip areasnear the outcrop,increasing facies ofthe WechesFormation. in thickness downdip to 650 feet where the sand facies disappear;regional dipis to the southat 100 feet per mile. Location Incentral Texas the Sparta varies in thickness from 200 This investigation covers the outcrop and subsurface feet updip to 350 feet downdip with aregionalsouthward extent of the Sparta Formation in Texas,an area of ap- dipof 150 feet permile. In southTexas,the Sparta varies proximately30,000 squaremiles (Fig. 1). Itis bounded by in thickness from 300 feet updip to 500 to 750 feet theRioGrange on the south (Mexicanborder)andby the downdip (thickeningtoward Mexico) with a regionaldip Sabine River on the east (Louisianaborder). southeastward toward the Gulf coast at 150 to 250 feet The Sparta Formation and associated stratigraphic per mile. units crop out from northern Mexico throughout Webb, Dimmit, Zavala,Frio,Atascosa, Wilson,Gonzales,Bas- Terminology trop, Lee, Burleson, Robertson, Leon, Houston, Cherokee, Smith, Wood, Morris, Cass, Nacogdoches, Lithofacies within the SpartaFormation have been as- using terminology San Augustine, and Sabine counties. The outcrop ex- signed to several depositional systems tends into the states of Louisiana, Arkansas, and Missis- applied by Fisher and McGowen (1967) to the Eocene sippi, where the Sparta is considerably thicker than in Wilcox Group of Texas. Depositional systems are as- Texas. semblages of genetically related sedimentary facies. As such they arethe stratigraphic equivalentsofgeomorphic 'Publication authorized by theDirector, Bureau of EconomicGeology, orphysiographic elements such as fluvial,delta, strand- The University ofTexas atAustin. plain,andbarrier-bar systems. Tnstituto Mexicanodel Petroleo, Mexico,D.F. Depositional systems are defined according to the 3Bureau ofEconomicGeology,The University ofTexas at Austin. nature and kind of associated component facies that are

139 140 TRANSACTIONS— GULF COAST ASSOCIATION OFGEOLOGICAL SOCIETIES Volume XXVII, 1977

FIGURE 1. Locationof wells and cross sections, SpartaFormation, TexasGulf Coast Basin.

inferred to be genetically related. Composition, Acknowledgments geometry,vertical sequenceand pattern of facies,lateral Geological distribution, association, R.O. Kehle andA.J. Scott,Departmentof facies facies and net sand pat- Sciences, The University of Texas at Austin,provided ternprovide theprincipal basis for recognition of deposi- suggestions and criticism. Raul Solis,The University of tional systems. Texas at Austin,aided in field work, and J. N.Russel, Texas Water Development Board, provided access to Methods of Study E-logs.TheInstitutoMexicano del Petroleo and Univer- Data used in this study include outcrop information sidad Nacional Autonoma de Mexico provided schol- and subsurface control obtained primarily from more arship funds. The research by Ricoy was in partial ful- than 700 electrical well logs. The logs were correlated fillment of therequirementsfor aMaster ofArts degreein throughout the basin using 20 dip cross sections and 3 Geology,TheUniversity of Texas at Austin. strike cross sections. Net sandstone thickness for the Sparta Formation or equivalent strata was determined for each welllog, and a net sandstone map was constructed to define the princi- pal sandstone dispersal pattern duringSparta deposition. Sparta depositional systems can be easily dif- ferentiated in most of the area studied,especially in east and central Texas. The Sparta facies are difficult to de- lineate in someareasclose to theoutcropin southTexas, but net sandstone trends can be extrapolatedupdip from areas of better control in the deeper subsurface. By integrating the cross sections and the net sandstone patterns, a three-dimensional picture of sandstone and mudstone facies was delineated. Electric-log character, net sandstone trends,and lateraland vertical stratigraph- icrelationships permittedthe interpretation offacies that compose the depositional systems of this mid-Eocene interval. Outcrop studies consist of analyses of lithology, sedi- mentary structures, and lateraland vertical interrelation- ships exhibited by sandstone and shale facies. These data were integrated with the subsurface information to verify facies interpretation. Refer toRicoy (1976) for an appendix with wellnames and other data used to preparemapsand cross sections. FIGURE 2. Electric log cross section showing intervalstudied Wellnumbers onindex map(Fig. 1) and cross sections in and relationshipbetweengenetic andformalstratigraphicunits, this report correspondto numbers in the appendix. mid-Eoceneformations, TexasGulf CoastBasin. RICOY, BROWN 141

Queen City and Sparta sands. They inferred that the Previous Investigations and Stratigraphic Terminology Weches Formation was depositedinmoderately shallow, The Sparta sands of Louisiana were defined by T. W. clear marine waters which deepened as the epoch ad- Vaughan (1896) as deep quartz sands extending across vanced. The molluscs Vertagus wechesensis Sten- Louisiana which were well developed near Sparta in zel, Turritella femina Stenzel, Rimella texana Harris, Bienville Parish. He erroneously included Pleistocene Latirus singleyi Harris, and Scutella mississippiensis sands in the formation. W. C. Spooner (1926) modified Twitchell werelisted as index fossilsof the Weches For- the original definition to include only Claiborne (Eocene) mation. sands occurring near Sparta, Louisiana. Furthermore, Sediments of the Sparta Sand were mostly continental Spooner divided the Claiborne Group into Yegua, St. in origin according to Sellards and others (1932). They Maurice,Sparta, andCane RiverFormations. inferred that the basal sands were laid down on a beach Dumble (1924) recognized four divisions of the and coastal plain in conjunction with the withdrawal of Claiborne Group of Yegua, Nacogdoches, the Weches sea. The middle Sparta sands were inter- east Texas: preted mainly Cook Mountain,andMount Selman. Dumble referred to to be fluviatile deposits spread broadly the Nacogdoches as the transitional beds between the over a flat terrain. Theupper Sparta sediments werede- Cook MountainGreensand and the gypsiferous clays of posited along a transgressing shoreline laid down in ad- the Yegua. Later, Wendlandt and Knebel(1926) modified vance of the Crockett sea. Thinlaminae composed of the this definition of the Claiborne Group of east Texas. remains of land and marsh plants occur in the middle Based on outcrop and subsurface data, they subdivided sands, but there are no significant layers of lignite.Clays the CookMountain into theCrockett and Sparta Forma- are most prevalent in the upper part of the formation. tions and the Mount Selman into Weches, Queen City, They are gray or chocolate colored and containconsider- Reklaw, and Carrizo Formations. Dumble's Nacog- able carbonaceous matter. The Crockett Formation overlies the Sparta Sand and doches was abandoned. Wendlandt and Knebel made Yegua these comments about the Weches, Sparta,and Crockett is overlain by nonmarine beds of the Formation. (now Cook Mountain): The Crockett is constituted mostly of clay, shale, and sandy shale, which are fossiliferous and partially glau- Following the shallow conditions of the seas during conitic; some lentils occur within the forma- Queen City time, the basin subsided again suffi- tion. These strata are essentiallyof marine origin.Stenzel ciently to cause conditions favorable for glauconitic (1935) introduced Stone City Formation for transitional deposition. The Weches is a remarkable deposit of beds that separate the Crockett and the Sparta Forma- rather pure clayey glauconite whose average thick- tions. Stone City was located at theSan Antonio ferry on ness is approximately 50 ft. throughout the basin the Brazos RiverinBurlesonCounty,Texas. proper . . . The sands and light-colored clays, In South Texas, the Yegua, Cook Mountain, and amounting to 250or 300 ft. inthickness, between the Mount SelmanFormations of the Claiborne Group were WechesGreensand and theCrockett clays,arecalled mapped byDeussen (1924) whocorrelated them with the the Sparta Sand, because they are equivalentto the east Texas outcrops. In the Rio Grande Valley, Tow- same beds in Louisiana ... This sand was recog- bridge(1932) described theCookMountainFormation as nized by both Dumble (1918) and Kennedy (1892), who referred to it as Nacogdoches in age.However, "consisting chiefly of sand and sandstone. Most of the Nacogdoches,as defined, consisted of the transi- the rock is medium grained. Thebeds are commonly tional beds betweenCook MountainandYegua. ... glauconitic, ferruginous, and micaceous; many of TheCrockettFormation them are cross-bedded and ripple marked. Inter- consists of chocolate brown white, and gray clay,rangingfrom350 to 450 ft. in thickness bedded with the standstone are some yel- and containing some beds of fossiliferous glauconite lowish, bluish, and greenish gray or chocolate col- with concretionary zones of fossiliferous brown ored clays and a few thin lenses of gray limestone. sandy limestone. The Crockett Formation also con- The sandstone and at some places the clay contain tains thin beds of sand, clay ironstone concretions, large dark-gray hard crystalline limestone concre- and in places is calcareous ...The contact between tions, some of which are fossiliferous. The lower the fossiliferous Crockett and the Yegua is transi- two-thirds of the formation weathers into red sandy tional. The contactis usually selected where the last soil; theupper thirdat most places weathers gray." macrofossils appear. Towbridge interpreted the depositional environments to On the basis of micropaleontology and lithology (sub- be partially restricted bays and lagoons, but he inferred surface and surface), A. C. Ellisor (1929) supported the that the Cook Mountain is principally of open-marine Wendlandt and Knebel subdivisions of the Claiborne of origin. east Texas and correlated the sequence with the Kane and Gierhart (1935) traced the Claiborne Group Claiborne of Louisiana. She correlated the Crockett of into Mexico where they observed that the Cook Moun- Texas (now Cook Mountain) with St. Maurice of tain Formation becomes thicker and is composed of a Louisiana and the Sparta of Texas with the Louisiana series of thick, massive, glauconitic sandstone deposits. Sparta. She noted the disappearance of the Queen City Large fossiliferous concretions occur in many of the Formation toward Louisiana and the equivalenceofRek- sandstone beds. There are many fossiliferous limestone law of Texas with Cane River of Louisiana. Renick and beds within theCook MountainFormation. Stenzel (1931) extended the Claiborne subdivisions Gardner (1938) proposed the name Laredo Formation (WendlandtandKnebel,1926) into theBrazosRiver area. for the Cook Mountain in the Rio Grande embayment Sellards andothers (1932) described the Weches as the where themiddleEocene sectionis different from equiva- marine, fossiliferous, glauconitic beds between the lent strata in east Texas. Thick sandstone sequences in 142 TRANSACTIONS— GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES Volume XXVII, 1977 south Texas contrast with the thick clay deposits of east representing delta-plain marsh deposits. When a dis- Texas. tributary channel becomes overextended, it shifts sud- From outcrop studies alongthe RioGrande,Patterson denly to a new channel with a steepergradient, and the (1942) showed that theCookMountain sectionconsists of cycle of distributary progradationbegins again. Although three units: thick sandstone members at top and bottom an abandoned delta lobe founders rapidly because of the separated by a shale member. He concluded that the large thickness of theunderlyingprodelta muds, it is ex- Cook Mountain,Yegua, and Fayettebeds were appar- posed for a time to marine processes (destructive phase) ently deposited under environments associated with which rework the sediments. transgressions and regressions. He inferred that both ad- The high-constructive lobate delta type, as shown by vance and retreat of shorelines began with mud deposi- several abandoned deltas of the Mississippi system tion both basinward and shoreward from contemporane- (Frazier, 1967), are also developed under conditions of ous sandy deposits. high sedimentinput, but these delta-front sands prograde Eargle (1968) pointed outGardner's (1938) proposition over thin prodelta muds deposited in relatively shallow and emphasized the use of Laredo Formation for those water. The constructive phase (progradation of dis- thick sand sections of the Cook Mountain Formation in tributaries)is similar toelongate deltas,butprogradation southTexas. is limited and channel abandonment is more common, resulting in many branching distributaries. Because available wave energy significantly reworks the shallow delta-front sands, alobate sand patternis characteristic. Depositional Systems During delta abandonment (destructive phase), founder- Fisher (1968) classified deltasinto (1) high-constructive ing is not as rapid as in the elongate type, and the aban- systems, both elongate and lobate, characterized by a doned delta is intensivelyreworked by marineprocesses. dominance of constructive deposits (fluvially influenced The delta-front sands arereworked to produce transient facies) over destructive deposits (marine-influenced delta-fringe islands which progressively shift landward facies), and (2) high-destructive systems, either wave across the subsiding delta plain. dominated or tide dominated, that exhibit a predomi- In high-destructive delta systems, sediment input is nance of marine-influenced (destructive) facies. The subordinate to marine wave and current energy, and ac- marine facies result from reworking or modification of cordingly, these systems are composedoffluvially intro- fluvially introduced or influenced sediments. duced sediments that are contemporaneously reworked The depositional processes that are dominant during by marine processes. Thus, in wave-dominated deltas, the constructive phase of deltaic development are pro- the resultant deposits are formed mostly of destructive gradationof distributaries and areal extension of deltaic facies (marine influenced), and principal sediment ac- plains by crevasse splays. As distributaries become cumulation occurs as a series of coastalbarriers flanking overextended,the riveris diverted into acourse having a the river mouth,giving a cuspate to arcuate trend to the steeper gradient and the cycle of distributary prograda- sand bodies. Modern barrier-bar and strandplain facies tion (constructive phase)begins again. Theabandonment consist mostly of well-sorted, locally glauconitic sands of a distributary system initiates a destructive phase overlying fossiliferous, shallow-water prodelta/shelf characterized by subsidence and reworkingofdeltaic de- muds. Sediment is fed by fluvial systems that are com- posits by marine processes.These destructive phases on monly characterized by a highproportion of sand to mud a regional scale result in the deposition of marly, (high bedload to discharge ratio). Streams form chiefly glauconitic, fossiliferous shelf muds that delimit upper meandering fluvial systems; lateral shifting of streams and lower boundaries of a cycle of deltaic deposition. In and paucity of mud result in a poorly developed delta- this study, shelf facies include thelower partof theCook plain facies. Prodelta facies are thin, well-burrowed fos- Mountain and lower part of the Weches Formations that siliferous and glauconiticmuds. overlie and underlie the Sparta Formation, respectively (Fig. 2). Sparta and Associated Depositional Systems High-constructive delta systems are developedunder The Sparta Formation is a very well differentiated conditions of high sediment input relative to marine res- lithostratigraphic unit. In east Texas, it is underlain by ervoir energy. The resultant deposits show a prograda- the Weches Formation and overlain by theCook Moun- tional patternnormal to the depositional strike or relict tain Formation, both of which can be differentiated in coastline. The sediment source is generally far inland, outcrop and in the subsurface (Fig. 3) because of the and the fluvial feeder system is concentrated near the marly character of these shelf facies. The marly basal edge of thedepositionalbasin. facies of the Weches and Cook Mountain Formations The high-constructive elongate delta is characterized representmarine transgressions precedingand following by thick mud deposits. Sand deposits composedprimar- the Spartaprogradationand can— be recognizedondip and ily of distributary channel-fill and channel-mouth bar strike cross sections (Figs. 3 6). facies prograde over relatively thick prodelta mud se- Sand distribution within the SpartaFormation (Fig. 7) quences. These elongate sand bodies were called bar- delineates two principal areas of sand input, east and finger sands by Fisk (1961). Bifurcation of distributaries south Texas. The SpartaFormation in east Texas is a results in barfinger sands that in map view resemble a high-constructive lobate delta system, similar to the bird's foot. Prodelta muds grade upwardinto silty sands lower part of the Wilcox Group (Fisher and McGowen, and well-sorted sands of the channel-mouth bar (bar- 1967), Jackson Group (Fisher and others, 1970), Yegua finger) facies. If progradation continues, the channel- Formation (Fisher, 1969), and Queen City Formation mouth bar facies will be overlain transitionally by silty (Guevara, 1972) where sandstone maxima with a lobate sands and muds of levee origin, and organic-rich clays tendency are oriented perpendicular to the depositional RICOY, BROWN 143

FIGURE 3. Stratigraphicdipsection B-B' showingthe differentfacies assemblagesand the differentiationof prodelta from shelf facies, Spartahigh-constructive delta system. strike. TheLafourche and St. Bernard deltas of theMis- Fayette and Washington counties into Louisiana, the sissippi delta system (Frazier, 1967) are Holocene Sparta Formation is characterized by a net sandstone analoguesof the high-constructive Spartadelta system. maximum that is oriented perpendicular to the deposi- The Sparta Formation in south Texas (Fig. 7) is a tional strike and exhibits a lobate areal geometrysimilar high-destructive, wave-dominated delta system similar to to the Lafourche and St. Bernard lobes of the Holocene the upper Wilcox Group and YeguaFormation (Fisher, Mississippi delta system (Frazier,1967). 1969) and Queen City Formation (Garcia, 1972) where The facies components of thehigh-constructive Sparta sandstone maxima are similarly oriented parallel to the delta system in east Texas are delta plain (distributary regional depositional strike. Other examples include the channel-fill sandstone and interdistributary mudstone), Holocene Rhone,Po,and Nile delta systems, as well as delta-front sandstone, and prodelta mudstone. All of theHolocene Tabasco (Mexico)andPleistocene Surinam these facies are present in outcrop and subsurface; the coast (Fisher, 1969). prodelta facies, however, are thin and poorly developed Incentral Texas, the SpartaFormation was deposited in the outcropbelt. Theinterrelationships of these facies in an interdeltaic area which is characterized by a in subsurface and the areal distributionof Sparta deposi- strandplain/barrier-bar system. This system was built tional systems are illustrated by figures 3 and 7,respec- parallel to depositional strike, fed by way of longshore tively. currents from the easternhigh-constructive delta system. Based on sandstone percentagedistribution within the The barrier islands along the Texas coast are modern Formation, Payne examples. Sparta (1968) determined that these stratain eastTexas,Louisiana,Mississippi, andsouthern The SpartaFormation is significantly thicker eastward deposited a plain" Louisiana,Mississippi, Equivalent Arkansas were in "fluvial deltaic envi- in andArkansas. and ronment.He noted that the deltarepresents therecord of also thicker sand deposits occur innortheasternMexico. anancestralMississippiRiver system that existed during deposition of theSpartaand possibly duringdepositionof High-Constructive Delta System, East Texas much of the Claiborne Group. Sandstone facies are well Sandstone— distribution map (Fig. 7), cross sections developed along a general northerly trend, presumably (Figs. 3 6), outcrop observations, and comparison with normal tothe orientation of the Sparta shoreline;the pat- the lower Wilcox Group (Fisher and McGowen, 1967), ternof sandstone distribution was probably createdby a Jackson Group (Fisher and others, 1970), YeguaForma- system of anastomosing, constantly shifting stream tion (Fisher, 1969), andQueenCity Formation (Guevara, channels and interlacing lakes, marshes, and swamps 1972) provide the basis for defining the high-constructive such as would be developed on a large fluvial-deltaic Sparta delta system in east Texas. Eastward from plain. 144 TRANSACTIONS-GULF COAST ASSOCIATIONOF GEOLOGICAL SOCIETIES Volume XXVII,1977

FIGURE 4. Stratigraphicdipsection G-G', Sparta strandplain/barrier-barsystem, centralTexas.

Prodelta facies thin near the outcrop to several hundred feet thick in the deepersubsurface where the entire Sparta interval is Prodelta facies of the Sparta delta lobes are fine- composedofprodelta facies. Shelf mudstone facies of the grained, terrigenous, clastic sediments deposited from subjacent Weches Formation can be differentiated from suspension seaward of the progradational delta-front Sparta prodelta mudstone deposits (stratigraphically in- sands. The prodelta mudstone facies are the initial ter- cluded in the Weches Formation) because the marly rigenous sediments deposited in the development of the glauconitic Weches shelf facies can be recognized on delta. Hence, they thicken seaward and stratigraphically electric logs by a distinctiveresistivity peak without cor- underlie the delta-front sandstone facies. respondingresponsein the SP curve. Dip cross sections (Fig. 3) show that prodelta mud- Several outcrops exposed alongU.S.Highway 69, ap- stone deposits progressively thicken downdip from very proximately 5 to 7 miles north of Jacksonville, Texas, RICOY, BROWN 145

FIGURE 5. Stratigraphicdip section I-I' along channel-mouth bar and coastalbarrier facies, Spartahigh- destructive, wave-dominateddelta system, southTexas. exhibit atransition from the highly fossiliferous glauconi- North of Tyler on Farm Road 14, approximately 12 tic shelf mudstone of the Weches Formation to the basal miles from Loop 323, 1mile north of the intersection of delta-front sandstone bodies of the overlyingprograda- Farm Roads 20 and 14, 2 miles east of Centerville on tional Sparta Formation. The thin transitional interval of Texas Highway 7, and 7 miles southeast of Jacksonville interbedded sandy siltstone and sparsely to nonfossilifer- onU.S. Highway 69 are typical exposures of prograda- ous mudstone represents the only evidence of prodelta tional Sparta sequences composed of horizontally inter- facies in outcrop. bedded silty sandstone and mudstone layers. Sandstone beds are composed of small-scale tabular crossbeds; the Delta-front facies sequences become sandier upward with a corresponding Delta-front sandstone deposits of the SpartaFormation increase in abundance and scale of cross-stratification. include distributary-mouth bars and marine-reworked A laterally persistent, well-sorted, fine-grained sand- sheet sandstone facies. IneastTexas, the well-developed stone unit with low-angle cross-stratification composed delta-front deposits are the dominant facies of the high- of small-scale tabular and foreset crossbedding is ex- constructive delta systems.Delta-front sandstone facies posed 2 miles northwest of Rusk on U.S. Highway 69. are the framework element that defines the geometry of This deposit representsa channel-mouth bar with a high the delta system. degree ofreworkingby marine processes. Delta-front facies are characterized by interbedded sandstone and mudstone sequences that become sandier upward. Thus, on electric logs these facies are charac- Delta-plain facies terized by an inverted Christmas tree shaped spontane- The delta-plain part of the Sparta delta system, the ous potential - resistivity pattern(Fig. 8). This patternre- subaerial part of the delta, is composed of distributary flects a coarsening-upward sequence that is typical of channel-fill sandstone and interdistributary mudstone progradational deposits and contrasts with the sharp deposits, whichare at someplaces associated with lignite bases of scourbounded distributary channel sandstone beds. The distributary channel-fill deposits are mostly deposits.Delta-front facies grade downdip into prodelta fine-grained sandstone exhibitingtrough-fill crossbeds, mudstone facies and updipinto delta-plain deposits. tabular crossbeds, a large amount of mud chips, and a 146 TRANSACTIONS— GULFCOAST ASSOCIATIONOF GEOLOGICAL SOCIETIES Volume XXVII,1977

FIGURE 6A. Stratigraphicstrike sectionL-L' across the high-destructivedelta system of southTexas and the strandplain/barrier-bar system ofcentral Texas.

FIGURE 68. Stratigraphicstrike section L-L' across the strandplain/barrier-barsystem of centralTexas and the high-constructive delta system of east Texas. RICOY, BROWN 147

FIGURE 7.Net sandstone,arealdistributionofprincipalfacies,and inferreddispersalsystem, Spartadeposi- tional systems, Texas Gulf Coast Basin.

FIGURE 8. Well logs ofrepresentativefacies, Sparta depositional systems. 148 TRANSACTIONS— GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES Volume XXVII, 1977

symmetrical channel cross section. Themaximum thick- to Webb counties,Texas.Payne noted that, in the latter ness of individual channel-fill deposits is about 30 feet. area of central and southern Texas, the long axesof the Delta-plain facies were observed in most Sparta out- sandstone isopach patternsindicate that sandbodies are crops. Good exposures occur 10 miles south of Alto on parallel to the postulated Sparta strandline. Payne also U.S.Highway69 where a distributary channel fillclearly noted (1) that the thickness of the Sparta Sand in south- cuts a channel-mouth bar deposit. The distributary central Texas is uniform,but in Arkansas, Mississippi, channel-fill sandstone is characterized by alarge amount Louisiana,and eastTexas,thicknesses are extremely var- of trough-fill crossbeds and .mud chips; the channel- iable and (2) that the downdip extent ofsandstone in the mouth bar deposits are of horizontally bedded sandstone formationis muchless incentralTexas thanin eastTexas containing tabular crossbeds. ExposedonFarm Road 39, and Louisiana. Hence,Payneconcluded that theorienta- half a mile south of Flynn is a distributary channel-fill tion of the sandstone bodiesparallel to the strandline, the deposit composed of fine-grained sandstone, abundant uniform thickness of the Sparta interval,and the smaller mud clasts, and medium- to large-scale trough-fill downdip extent of sandstone all suggest that the Sparta crossbeds in the central part of the channel. The Formationin central and southTexas was depositedpre- crossbedding decreases in scale toward the channelmar- dominantly as nearshore bar and beach deposits. This gins where ripple-drift cross-stratification becomes dom- depositional setting contrasts with the inferred fluvial en- inant. vironments during Sparta deposition in east Texas and Louisiana. Strandplain/Barrier-Bar System, Central Texas Payne's (1968) interpretationfor centraland eastTexas All well logs in the central coastal area of Texas basically agreeswith theresults of the presentstudy.The (southwesternFayette,Lavaca,Gonzales,De Witt, Wil- present study, however, indicates that the south Texas son, Karnes counties) show that the Sparta Formation area receivedlocal fluvial sediment input, which resulted constitutes a single sandstoneunit (Figs. 4, 6), which has in deposition of facies that constitute a high-destructive, amaximum thickness of 100feet updipbut thins downdip wave-dominated delta system. Two basic factors influ- as it grades into shelf mudstone facies. This sandstone enced this different interpretation: unit is very consistent laterally. Isolith patterns trend (1) The upper and lower boundaries of the Sparta de- parallel to depositional strike, indicating tabular sand- positional cycle are imprecise; therefore, the sandstone stonebodies that arecharacterized bycoarsening-upward percentage mapping used by Payne is more subjective sequences. These Sparta sandstone bodies resemble than net sandstonemapping used in this study. individual barrier-bar sandbodies of the high-destructive (2) Because Payne used sandstone percentage maps, delta system of southTexas (Fig. 6).Such sequencesare he apparently did not recognize the significanceof high similar to modern shoreface deposits associated with net sandstone concentrations in the south Texas area barrier-bar and strandplain sands (Hayes andScott, 1964; which require a local fluvial sediment supply (high- Bernard and Leßlanc, 1965; Bernard and others, 1970). destructive, wave-dominated delta system); data in the Upwardincreases innumber, grain size, and thickness of southernmost part of the area (Zapata county) were not sandstone beds are well shown by SP-log profiles (Figs. available duringPayne'sinvestigation. 4,6). Although exposures are poor, sandstone deposits of High-Destructive, Wave-Dominated Delta System, this strandplain/barrier-bar system are light colored, fri- South Texas able,fine grained, and well sorted.Primary sedimentary A high-destructive Sparta delta system developed in structures are very low angle, tabular crossbeds, small- south Texas in western Atascosa, western Live Oak, scale trough-fill crossbeds, and wave-rippledcrossbeds. McMullen,La Salle, Webb, and Zapata Counties and The net sandstone pattern of the Sparta strandplain/ extended southwardintoMexico. barrier-bar system, its parallelism to depositional Coastal barrier sandstone facies, lagoonal mudstone strike, and the absence of evidence of updip sediment facies and prodelta shelf mudstone facies have been rec- sources imply that these deposits developedbetween the ognized in the Sparta delta system of south Texas. The eastand southTexas deltaic areas. The sediments in the Sparta system can be recognized by the distinctive system were transported by prevailing southwestern sandstone distribution pattern(Fig. 7), which is similar to longshore currents from reworked shoal-water, delta- the upper Wilcox Group and YeguaFormation (Fisher, front deposits of the easternhigh-constructive delta sys- 1969) and the Queen City Formation (Garcia, 1972), tem of the SpartaFormation. where sandstone maxima are oriented parallel to the The above characteristics closely resemble the regional depositional strike. The facies interpretation strandplain/barrier-bar systems of the Jackson Group agrees with outcrop observations and former outcrop (Fisher and others, 1970) and YeguaFormation (Fisher, studies (Towbridge,1932; Kane and Gierhart, 1935;Pat- 1969) and the strandplain system of the Queen City For- terson, 1942; Lonsdale andDay, 1937; Lonsdale, 1935). mation (Garcia,1972); Holocene analoguesarethe Texas Modern examples of high-destructive, wave-dominated barrier bars and the strandplain system of the Nayarit deltas are the Holocene Rhone,Po, Nile,Grijalva, and coast ofMexico (Curray andothers, 1969). Pleistocene Surinam systems (Fisherand others, 1968). On the basis of sandstone percentagetrends exhibited The thick sand deposits that compose the wave-dom- by the SpartaFormation,Payne(1968) inferred two prin- inated Sparta delta system were initially recognized by cipal types of relict depositional environments. He de- Gardner (1938), who argued that the Cook Mountain fined a distinctive area in Louisiana,Mississippi, south- Formationin eastTexas was mostly fossiliferous clay but ern Arkansas, and eastern Texas, which includes the in southTexas was composed of thick, fossiliferous sand high-constructive Sparta delta system of east Texas de- deposits.She recommended the name of Laredo Forma- scribed herein,and another area extendingfrom Grimes tion for these Sparta-equivalentsof southTexas. RICOY, BROWN 149

posits are calcareous and are essentiallyan impuremarly limestone. withincalcareous concretions are scat- tered throughout the formationin southTexas.Patterson (1942) interpreted such sediments as indicative of off- shore bar deposition associated with landward lagoonal muds and seaward shelf muds. Examples of coastal barriers that are associated with high-destructive delta systems are the modern Niger delta (Allen, 1965), Apalachicola delta system of north- western Florida (Fisher and others, 1969), Rhone delta (Oomkens, 1967), Po and Danube deltas (Fisher, 1969), and Holocene Grijalva delta in Tabasco, Mexico (Psuty, 1967) and theNayaritcoastalplain inMexico (Curray and others, 1969). Lagoonal facies FIGURE 9. High-destructive cuspate (wave-dominated) delta system showing strike-orientedcoastal barrier facies and as- Lagoonalfacies are developedlandward ofcoastal bar- sociatednarrow lagoonal mud facies. FromFisher, 1969. riers and between elevated strandplain beacja ridges. Sedimentation in this environment is slow; wind-trans- Coastalbarrier andchannel-mouth bar facies ported sand, clay deposited from suspension, storm- washover fans (sand), and biogenic activity (burrowing Coastal barrier-bar/strandplain sand facies associated and root mottling) maybe important processes, depend- with high-destructive delta systems are formed by the ing on local conditions. Salinity is influenced by fluvial reworking ofchannel-mouth bar sand deposits by waves discharge, storm inundations,evaporation, and tides. In and currents and redeposition of the sand along strike general, lagoons are brackish, contain abundant mol- marginal to the channel mouth. The resulting deposits luscs, and have low to moderate species diversity. In form arcuate to cuspate sand bodies (Fig. 9). Although highlyrestricted lagoon environments,gypsumandother most of the final sand depositionis in the form ofbarrier evaporites are precipitated. The resulting lagoonal de- bars, some channel-mouth bar facies are preserved. posits are composed of thinly bedded or bioturbated Coastal barrier and channel-mouth bar sand facies can sands, silts,muds, locally gypsiferous muds,and alarge be differentiated by the SP curve onelectric logs. Chan- number of molluscs. nel-mouth bars generally display a gradual transition Lagoons associated with high-destructive delta sys- upward from prodelta/shelf facies to boxlike SP shapes. tems occur inthemodern Apalachicola delta, the modern Thebarrier bars, on the other hand, show a more abrupt Po delta system (Fisher, 1969) and the Holocene coastal coarsening-upward sequence which is characteristic of plain of Nayarit, Mexico, which is formed of elongate shoreface deposits (Fig. 8). Channel-mouth bars are mud swales and associated coastal barriers (Curray and restricted toriver discharge areaswhere maximumfluvial others, 1969). sand deposition occurs. Lagoonal Sparta deposits composed of thin-bedded Mud is deposited in narrow, discontinuous, elongate sandstones, siltstones, mudstones, and some gypsum lagoons on the landward side of the barrier bar or laminations are exposedin an excavation onprivateland strandplain contemporaneous with delta construction. 5 miles west of EncinalonTexasHighway44. Somebeds The Sparta high-destructive delta system of southTexas show ripple cross-stratification and other beds are highly does not possess a well-defined updip lagoonal facies. bioturbated. Shell concentrations form calcareous con- The deltaic sandstonebodies areconnected updip to sup- cretions. The lagoonal deposits abruptly overlie sandy porting fluvial systems and contain local progradational depositsof barrier origin. sequences similar to the upper Wilcox depositsin Texas (Fisher, 1969). Coastal barrier and strandplain facies in the high-de- Prodeita/shelf facies structive Sparta delta system are stacked vertically, Prodelta facies consist of fine-grained, terrigenous, and individual sandstone bodies are characterized by a clastic sediments deposited from suspension seaward of coarsening-upward sequence composed of shoreface de- progradational delta-front sands (or coastal barrier posits.Barrier/strandplainsandstonebodies are30 to100 sands). These sediments are the initial deposits in the feet thick and arebetter developed southward within the development of the delta; they thicken seaward and system. A southward cuspate trendin net sandstone (Fig. stratigraphically underlie the coastal barrier sands (Fig. 7) is a goodindicator ofa well-developedsouthwestward 5). Under high wave influence (high-destructive, wave- longshore current during Sparta deposition. dominated deltas) where slow deposition and extensive Outcrop studies (Lonsdale, 1935; Lonsdale and Day, bioturbation occur, prodelta and shelf environments are 1937; Patterson, 1942, Towbridge, 1932) of the undif- similar and, for this reason, cannot be differentiated. ferentiated Sparta-Cook Mountain Formations (Laredo Hence, the termprodelta/shelfisapplied to these facies. Formation, Fig. 2) in south Texas provide evidence of The higher wave (marine) influence causes a greater barrier-bar/strandplain facies and associated lagoonal similarity between the prodelta and shelf environments. strata. Earlier workers describe the LaredoFormation as Thus, the differentiation between prodeltamudstone and consisting of sandstone, gypsiferous clay, impure lime- shelf mudstone facies is difficult,if not impossible. High stone, and lignite. Much of the sandstone is glauconitic marine influence permitted the development of a ben- and crossbedded.Insome exposures, the glauconitic de- thonic fauna and, consequently, resulted in highly bio- 150 TRANSACTIONS— GULF COAST ASSOCIATIONOF GEOLOGICAL SOCIETIES Volume XXVII, 1977 turbated prodelta mudstone deposits similar to shelf crevasse splay deposits, and rare lignite deposits. This fades. deltaic system extendedeastward into Louisiana,Missis- Shelf Depositional System sippi, and Arkansas, where the Sparta deltaic deposits are much thicker than in eastTexas. The term "shelf," as used in this report, denotes a Reworked shoal-water,delta-front sands of eastTexas depositional environment which is characterized by a were transported toward central Texas by prevailing very slow rate of deposition, implying an absence of sig- southwestward longshore currents and supplied the nificant terrigenous clastic sediment supply. Therefore, strandplain/barrier-bar system of that region. They also shelf sediments are the resultof reworkingof relict sedi- contributed to a small degree in the construction of the ments by marine physical and biological processes.They high-destructive, wave-dominated delta system of south are mostly of a muddy character, extensively biotur- Texas. bated, and may include biogenic and chemical compo- nents (glauconite, phosphorite, carbonates)as well as di- versified fauna. Studies ofmodern shelves,such as those Comparison With Other Systems of Curray (1965), Emery(1968), andUchupi (1968),have provided aninsight into shelf processesand resultingde- The composition, distribution, and relationship of posits. facies within the various Sparta depositional systems are Shelf sediments are depositedprimarily duringdestruc- similar to Eocene deposits of the QueenCity Formation tive stagesof delta development, and in aregional scale, (Guevara, 1972; Garcia, 1972), Jackson Group (Fisher they representaphysical boundary betweengenetic units and others, 1970), lower partof the Wilcox Group(Fisher of clastic progradations. The deltaic and strandplain/ and McGowen, 1967), and Yegua Formation (Fisher, barrier-bar systems of the SpartaFormation areoverlain 1969) shown on figure 10. All of these Eocene clastic and underlain,respectively,throughout most ofTexasby units are characterized by a high-constructive delta sys- the Cook Mountain and Weches Formations, the lower tem in east Texas. Except for the Jackson and Queen parts of which arehighly fossiliferous,marly, glauconitic City, the Eocene deltaic systems extendinto Louisiana. mudstone of shelf origin. Throughout east Texas, pro- These systems arealso comparable to theHolocene Mis- delta mudstone facies in the upper parts of the Weches sissippi fluvial-delta system and its related strike systems and Cook Mountain Formations are distinctively dif- of the northwesternGulf ofMexico. ferentiated from underlying shelf mudstone deposits be- In central Texas all of the above-mentioned Eocene cause the marly character of the shelf facies provides a units are composed of strike-fed deposits that form very consistent and diagnostic peak in the resistivity strandplain/barrier-bar systems. In south Texas, as in curve of electric logs (Figs.3, 6). This differentiation oc- central Texas, most Eocene sediments were deposited curs, therefore, because the high rate of progradation of parallel to strike, forming barrier-bar facies and as- high-constructive produced a change sociated lagoonalmudstone facies. In theparticular case the system drastic Wilcox, in environmental conditions from shelf to prodelta envi- of the lower the sediment source was the con- ronments resulting in deposition of nonfossiliferous pro- temporaneous, high-constructive Rockdale delta system delta muds on highly fossiliferous shelf muds of the by way of southwestward longshore currents. In the Weches. Formal stratigraphic divisions do not make this other clastic units, the principal source of sediments in genetic facies differentiation. south Texas was local fluvial systems similar to those of the Sparta Formation. Strandplain/barrier-bar deposits Sediment Dispersal are the basic framework facies of the high-destructive, wave-dominated delta system. Two basic types of sediment dispersal systems were operating during deposition of the Sparta. Within the high-constructive delta of east Texas, the dispersal of Natural Resources sediment was predominantly in a dip direction by fluvial Thepotentialfor economically significant occurrences processes; within the strandplain/barrier-bar system of of hydrocarbons in the Sparta Sand in Texas is low, al- central Texas and the high-destructive delta of south thoughHeath and others (1931) noted the occurrence of Texas, sediment dispersal was along strikeby longshore oil in the Clay Creek salt dome in Washington county. drift. Clastic sediments were introduced into the Gulf This occurrence is of a very local extent and must be basin of Texas during Sparta time in east and south certainly the result of secondary structural development Texas. Principal clastic deposition was concentrated and migration. within high-constructive delta systems of east Texas, The lack of oil accumulations may be explained by Louisiana,and Mississippi (Payne, 1968). several factors which are related to the relatively thin In southTexas,the sediments were introduced into the Spartaprogradationalfacies inTexas: Gulf basin by a series of small stream complexes (Fig. 7) (1) the unit (less than 700 feet) did not develop a suffi- which suppliedahigh-destructive, wave-dominated delta cient thickness of prodelta muds to serve as adequate system, essentially composed of coastal barrier sands source beds; and associated lagoonal muds. In east Texas the sedi- (2) the thin delta front/prodelta facies did not permit ments were introduced by a major integrated stream growth faulting to provide early fault closure and traps; complex which derived sediments from an extensive and drainage area in the United States continental interior. (3) in relation to the underlying and overlying progra- This sediment was deposited within a high-constructive dational units, the thin Sparta sequence provided very delta system as delta-front sands, prodelta muds, and restricted reservoirs for oil entrapment from secondary delta-plain deposits such as distributary channel-fill structural development and later oilmigration. sands, floodbasin/interdistributary bay assemblages, The Sparta Sand is one of the major sources of RICOY, BROWN 151

FIGURE10.ComparisonbetweentheSpartadepositionalsystems andancientmoderndepositionalsystemsof theTexasGulfCoast Basin.AfterFisher andMcGowen, 1967;Fisher, 1969;Fisherandothers,1970;Guevara, 1972; and Garcia, 1972. 152 TRANSACTIONS— GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES Volume XXVII, 1977

FIGURE11. Relationshipbetweendepositionalsystems anddistributionofdissolvedsolids inSpartaground water. AfterPayne, 1968.

groundwater in southern Arkansas, northern and in the high-constructive delta system of eastTexas (and centralMississippi,and easternTexas as far as south Louisiana,Mississippi, and Arkansas);(2) the sulfate wa- Burleson County. However, from Burleson County ters reflecting restricted environments such as back- southward in Texas the Sparta Sand is of minor im- barrier lagoons of the strike-oriented strandplain/ portanceas an aquiferbecause itcontains fresh water barrier-bar system of central Texas and of the high- only in a small area, yields are low, and the water is destructive delta system of south Texas; and (3) the hard and has ahigh concentration ofdissolved solids chloride waters reflecting generally isolated delta-front/ (Payne, 1968). prodelta sediments deposited under normal sea-water Basedon electric log data, Paynedetermined the areal conditions. Of course, this picture is altered to some ex- distribution of the dissolved-solids content of the Sparta, tent according to the degree of later flushingby meteoric and from these chemical data determinedregionalchemi- water. The greater the movement of water, the greater cal variations (based on proportion of anions) in the the proportion of bicarbonate and the lesser the Sparta Sand (Fig. 11).He defined three "chemical prov- dissolved-solids content. inces": The downdip transmissibility for water flushing is (1) bicarbonate water that is distributed as a function greater in the dip-oriented sandstone of east Texas than of rate of water movement and time; that is, the greater in the strike-oriented aquifer of south Texas.In the case the degree of flushing, the greater the proportion of of a considerable amount of water flushing, it would be bicarbonate; expected that in east Texas the bicarbonate-chloride (2) chloride waters that generally represent areas of boundary would be farther downdip and dissolved-solids discharge where the dominant component of flow is up- content would be at lower levels than for thecorrespond- ward througha thick sectionofCookMountain clays and ing sulfate-chloride area of south Texas,but that is not shales, and,in places,a shalyCockfield (Yegua) section. the case (Fig. 11).Hence, it appearsthat only a limited Downdipmovementof wateris limitedby therapid pinch amount of water flushing has occurred and that the dif- out of permeable beds of any appreciable thickness; ferent water types are closely related to water composi- hence, chloride waterslie beyond the limits of extensive tion of the initial depositional environments. The water flushing by fresh water;and provinces are not theresult of extensive later flushing by (3) sulfate waters that coincide closely with an areain meteoric water.Inother words, flushing by fresh water which the formations overlyingandunderlyingthe Sparta has altered only quantitatively (not qualitatively) the ini- Sand contain lagoonalgypsumandgypsiferous clays; the tial distribution of water types. sulfate content can be attributed to the solution of gyp- sum by waters passing by these gypsiferous formations and the soils derived from them. Conclusions Comparing Spartafacies distribution with maps of the The Sparta Formation represents one of several dissolved-solids content and chemical provinces exhib- Eocene lithogeneticcycles offluvial-deltaic progradation ited by the aquifer (Fig. 11), a very good correlation into theGulf coast basin.During Sparta time there were exists between the distributionof chemicalprovinces and two principal areas of sediment input: (1) east Texas, the depositional systems within the Sparta.Thus,the dis- Louisiana, Mississippi, and Arkansas and (2) south tribution of chemical provinces can be seen as a reflec- Texas. tion of the type of depositional environments operating The Sparta deposits of east Texas compose a high- during Sparta time: (1) the bicarbonate waters reflecting constructive delta system; equivalent deposits of south fresh-water influx alongthe dip-orientedfluvial deposits Texas constitute a high-destructive wave-dominated RICOY, BROWN 153 delta system; Sparta deposits in centralTexas composea Ellisor,A.C, 1929,Correlation of theClaiborne of east strandplain/barrier-bar system. The high-constructive Texas with Louisiana: Am.Assoc. PetroleumGeol- delta of east Texas supplied sediments that were trans- ogists Bull.,v. 13, p. 1335—1346. ported southwestward by longshore currents to form the Emery, K. 0., 1968, Relict sediments on continental strandplain/barrier-bar system. shelves of world: Am.Assoc. PetroleumGeologists Sparta sediments prograded over transgressive shelf Bull., v.52,p. 445— 464. muds of the Weches Formation;following Spartadeposi- Fisher,W. L.,1968,Basic delta systemsin the Eocene of tion,marine transgressionresulted in deposition of shelf the Gulf Coast Basin: Gulf Coast Assoc. Geol. muds of theCookMountain Formation. Socs., Trans.,v. 18, p.48. The thickness of the SpartaFormationin Texasis less 1969,Facies characterization ofGulfCoast Basin than 700 feet, which did not allow the development of delta systems, with some Holocene analogues: Gulf— adequate source beds and structures favorable for sub- Coast Assoc. Geol. Socs., Trans., v. 19, p. 239 sequentoilentrapment. 261. Present distributionof chemical water types (and total ,andMcGowen,J.H.,1967,Depositionalsystems dissolved solids) reflects the primary depositional envi- in the Wilcox Group ofTexas and their relationship ronments of the Sparta system. tooccurrence ofoilandgas:GulfCoastAssoc.Geol. Theinitial study of depositional systems should be ap- Socs., Trans.,v. 17, p. 105—125. proachedat a regionalscale so that the interrelationships ,Brown, L. F.,Jr., Scott, A. J., and McGowen, of component facies that define the depositional systems J. H.,1968,Delta systems in the exploration for oil can be properly determined andmapped. and gas: A research colloquium: Univ. Texas,Bur. Depositional systems provide a perspective of basin Econ. Geology,212 p. that permits prediction of stratigraphic rela- ,Proctor,C.V., Jr.,Galloway, W.E., andNagle, tionships, sandstone geometry, potential, and aquifer J. 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Patterson, J. M., 1942, Stratigraphy of Eocene Forma- Spooner, W. C, 1926,Interior salt domes of Louisiana: tions between Laredo and RioGrande City,Texas: Am. Assoc. Petroleum Geologists Bull., v. 10, p. Am. Assoc. Petroleum Geologists Bull., v. 26, p. 217—292. 256—274. Stenzel, H. 8., 1935, A new formation in the Claiborne Payne, J. N., 1968, Hydrologic significance of the Group: Univ.TexasBull.3501, p. 267—279. lithofacies of the Sparta Sand: U.S. Geol. Survey Towbridge, A.C,1932, TertiaryandQuaternarygeology Prof. Paper569-A., p. A3— A5, plate g. of thelower RioGrande region ofTexas:U.S.Geol. Psuty,N.P., 1967,Thegeomorphology ofbeachridges in Survey Bull. 837, p. 141—156. Tabasco, Mexico: Louisiana State Univ., Coastal Uchupi, E.,1968, Atlantic continental shelfand slopeof Studies Ser.,No.18,51 p. the United States— physiography: U.S. Geol. Sur- Renick, B. C, and Stenzel, H. 8., 1931, The Lower vey,Prof. Paper529-C, 30 p. Claiborne on the Brazos River,Texas:Univ.Texas Vaughan,T. W., 1896, A brief contribution to the geol- Bull. 3101, p. 73— 108. ogy and paleontology of Northwestern Louisiana: Ricoy, Jose Ulises, 1976, Depositional systems in the U.S.Geol. Survey Bull. 142. Sparta Formation (Eocene), Gulf coast basin of Wendlandt, E. A., and Knebel, G. M., 1926, Lower

A. W./V*_*k_J. 111T ■ A Austin,A. J.TXIAUI.VI U \J Texas:Univ.Texas,VilWU^ lUULlllj Master's thesis,I.IIVUIUJ 98 p.ff* Claiborne of east Texas, with special reference to Sellards, E. H., Adkins, W. S., and Plummer, R. 8., Mount Sylvan dome and salt movements:Am. As-— 1932, The Geology of Texas, V. I, Stratigraphy: soc. Petroleum Geologists Bull., v. 13, p. 1347 Univ.Texas Bull. 3232, 1007p. 1375.