THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS

October 22, 1971 Paper 54

CHITINOZOANS IN THE SUBSURFACE LOWER PALEOZOIC OF WEST TEXAS A. E. KAUFFMAN Humble Oil & Refining Company, Midland, Texas

ABSTRACT Studies based on both comprehensive sample analysis and electric logs substantially facilitate dating, subdivision, and environmental interpretation of the subsurface pre- Woodford section in West Texas. Acid-insoluble chitinozoans arc shown to occur in sufficient quality and quantity to aid in subdividing well sections where the rarely oc- curring corals, brachiopods, and ostracodes are lacking. About half of the composite cutting samples processed yielded chitinozoans. Ango(hitind was found only in the Devonian. Ancyrochitina, a long-ranging (Ordo- vician through Devonian) genus, has distinctive species that can be utilized. A long- necked form seems prevalent at one level in the Silurian and has a widespread though rare occurrence. Conochitina and Rhabdochitina are restricted to the Middle and Upper Ordovician in West Texas. Lagenochitina and Sphaerochitina are long-ranging forms needing additional study before species are of much value in correlation. Associated acid-insoluble microfossils are graptolite siculae, scolecodonts, and acritarchs ("hystricho- sphaerids").

INTRODUCTION

Very little has been published on the practical (Fig. 2), represented mainly by cutting samples, zonations and facies framework essential for were to interpret the age of the rock units, obtain understanding adequately the regional history of a zonation that is applicable in sections represent- the lower Paleozoic section in the Permian basin ing differing depositional environments, and to of West Texas (Fig. 1). This is due, in part, to determine which fossils or groups of fossils are uncertainties in correlation resulting from rapid best suited to aid in solving correlation problems facies changes within some subsurface units and, in the area. more especially, to the seeming lack of diagnostic In the Permian basin, electric logs of several fossils in the sections of micritic limestone, dolo- types are used extensively in correlating the pre- mite, chert, and shale. The present report indi- Woodford section, and lithology is used to a cates, however, that an integration of sample lesser degree. The main fossils conventionally lithologie and paleontologic analysis with elec- used in this section are corals, brachiopods, cono- tric-log correlations makes practical the better donts, stromatoporoids, and ostracodes. These understanding of the regional framework that is forms are exceedingly useful for dating and in- so important in our search for oil and gas. terpreting environments of deposition, but many The objectives of the present study on the sub- well sections or areas lack them. Thus, problems, surface pre-Woodford section of West Texas such as the precise age of the Devonian chert,

2 The University of Kansas Paleontological Contributions—Paper 54

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APPROX. SCALE IN MILES FIG. 1. Area of study, major structural and depositional features, and position of cross section.

Kaugman—Chitinozoans from West Texas 3

MEMBER

SYSTEM SERIES GROUP FORMATION OR ZONE PAY ZONE

MISSISSIPPIAN 1 Kinderhook WOODFORD

DEVONIAN DEVONIAN Devonian HUNTON Middle SILURIAN ___ -kVaiL tith'------ussELMAN7 Lower "oLex A NOR iw w - wn VAN Upper MONTOYA Montoya

BROMIDE

TULIP CREEK McKEE McKee sand ORDOVICIAN Middle simPsoN McLISH WADDELL Waddell sand

OIL CREEK CONNELL Connell sand

JOINS

Lower ELL ENBURGER Ellenburger CAMBRIAN

PRECAMBRIAN

FIG. 2. Terminology applied in petroleum exploration to the lower Paleozoic section in the Permian basin, West Texas.

the local presence or absence of Silurian Fusse!- new (TAUGOURDEAU & JEKHOWSKY, 1960; JODRY man, andand the position of the Montoya-Simpson & CAMPAU, 1961) but has been most extensive in contact locally, have persisted for many years. northern Africa. About 40 genera and several This sparsity or lack of diagnostic conven- hundred species have been described with about tional fossils indicated that new approaches were half the studies being published after 1962 required for resolving subsurface problems. (LANGE, 1949, 1952; COLLINSON & SCOTT, 1958; Chitinozoans and associated acid-insoluble micro- TALIGOURDEAU, 1966; TAUGOURDEAU AND OTHERS, fossils were tried first because JEFFORDS & MILLER 1967; COMBAZ AND OTHERS, 1967; EISENACK, 1968). (personal communications, 1962-68) had directed Species, however, commonly are rather broadly attention on the value of these forms as strati- defined or exceedingly difficult to recognize from graphic indicators in the subsurface lower Paleo- published descriptions and their age significance zoic of West Texas and Oklahoma. They is imprecise (JEFFORDS, 1968). Although chitino- showed, for example, the advantages of using zoans have been utilized with evidently some abundantly occurring chitinozoans rather than success in several subsurface studies, the "zona- the smaller conventional palynomorphs and dem- tions" cannot be applied in other areas without onstrated the subsurface occurrence of chitino- first verifying the ranges of broadly defined zoans locally in this area. species and eliminating factors of purely local Chitinozoans are small, flasklike, cylindrical, significance. As with many rapidly developing spherical, and globose microfossils of uncertain groups of fossils, chitinozoans are very useful in biologic affinities. They are minute, ranging in the subsurface even though the potentially prc- size from 50 p, to approximately I mm, averaging cise age significance of most species presently is 100-200 p.. These forms are relatively abundant inadequately known. Thus, chitinozoans are not in many types of marine sediments from the a panacea for subsurface problems in West Texas Lower Ordovician to the uppermost Devonian. but must be applied cautiously by skilled workers. In West Texas, they range from the Middle In the present study chitinozoans have been Ordovician Simpson group through the Upper used together with whatever other fossils were Devonian. No forms have been found in the found in conjunction with known lithologie in- Lower Ordovician Ellenburger to date. tervals and electric logs. These fossils were re- The application of chitinozoans to biostrati- covered from most lithologies. Chert, including graphic phases of petroleum exploration is not novaculite and tripolitic types, and dark micritic 4 The University of Kansas Paleontological Contributions—Paper 54

limestone yield fair assemblages. Dolomite, sand- related records. Although cores are greatly pre- stone, and reef limestone yield poor assemblages. ferred over cuttings in any stratigraphie study, Considering the quality and quantity of some drilling costs and the high-risk potential tend to cutting samples, the recovery success seems good. discourage most coring in the deep (20,000- to Chitinozoans sufficient for study occur in 50 to 26,000-foot) lower Paleozoic section of West 55 percent of the samples processed. Texas. Thus integrated lithologie, paleontologic, Representative chitinozoans found during the and log studies were made on lower Paleozoic present study are illustrated on Plates 1-16. These sections represented by cuttings from 60 wells identifications are to rather broadly interpreted located throughout the Delaware, Val Verde, and genera and a few species. Because a principal Midland basins and the Central Basin platform objective was to determine whether chitinozoans (Fig. 1). Depending on well location, the thick- occur in sufficient abundance and adequate qual- ness of the section studied ranges from 350 to ity for application in practical subsurface prob- 4,000 feet. lems, no detailed systematic treatment is given. First the lithology and fauna were described Moreover, studies in applied paleontology com- and logged systematically for each well. Insofar monly must be based on cutting samples that are as possible, age and environment of deposition subject to contamination by cavings and generally were interpreted. Sonic or induction logs were yield only moderate numbers of specimens that checked for additional information. Then com- are inadequately preserved for detailed descrip- posite samples were processed for acid-insoluble tion. Such material, however, can be identified microfossils. As only a part of the cutting sam- ples reasonably could be destroyed by processing, with respect to adequately described assemblages composite samples were used. Depending on the and can be interpreted readily by application of amount of samples available, they were grouped all facets of subsurface data. into 50- or 100-foot increments; rarely a 200-foot Acknowledgment is made to Humble Oil & interval was necessary. An average composite Refining Company for permission to publish sample was about 50 grams. Wherever possible, these results. Thanks are given to Messrs. H. P. systemic boundaries were not crossed, and sam- BUSHNELL and A. E. MILES for their encourage- ples from 50 feet above to 50 feet below a contact ment; to R. M. JEFFORDS for editing and other were not processed. Samples were processed assistance; to T. H. MILLER for technical assis- using techniques described by MILLER (1967). tance; to J. W. SKINNER for photographic as- Fossils, chiefly chitinozoans, found in the sistance; to C. B. ERCK, JR., for assistance in samples processed from the 60 wells were studied drafting, and, finally to E. R. OLGIN, JR., an able empirically and long-ranging forms having little laboratory technician. value were disregarded. Useful forms then were All figured specimens are deposited in the color-coded on logs, recorded, and listed on work files of Humble Oil & Refining Company, Mid- sheets. The data sheet for each well then was land, Texas. attached to the electric logs, the wells correlated, and cross sections prepared (Fig. 3, 4). Scoleco- PROCEDURES AND TECHNIQUES donts, graptolite siculae, and acritarchs ("hystri- Studies were planned to obtain maximum in- chosphaerids") were noted and listed, but these formation from available cuttings samples and were used only when chitinozoans were lacking.

GENERALIZED STRATIGRAPHY AND OCCURRENCE OF CHITINOZOANS AND OTHER FOSSILS

Units noted in the following discussion of the areas (Fig. 2). No attempt has been made to stratigraphie succession in the subsurface of West adjust this informal usage to agree with formal Texas are those widely recognized and applied nomenclature suggested by the American Com- in petroleum exploration of this and adjacent mission on Stratigraphie Nomenclature (1961).

Kaugman—Chitinozoans from West Texas 5

PRECAMBRIAN operational petroleum geologists, the Simpson Group comprises the Joins Formation (limestone The basement complex in the subsurface and dolomite); Oil Creek Formation (sandstone, underlies beds ranging in age from Cambrian shale, and limestone); McLish Formation (sand- through Permian. Generally speaking, igneous stone and limestone); Tulip Creek Formation rocks are found in most of the Permian basin, but (sandstone and limestone); and Bromide Lime- tnetamorphics occur near the extreme southern stone. The group ranges in thickness from less limits. The igneous rocks range from granites to than 50 to more than 2,000 feet in the Delaware granodiorite to quartz monzonites. Metamorphic basin. rocks are considered to be in the phyllite to schist Each formation of the Simpson group con- range. Precambrian residues lack chitinozoans tains an abundant and varied fauna; ostracodes for all wells examined. have a predominant role in subdividing the CAMBRIAN group. In West Texas only the Bromide and Tulip Creek formations yield chitinozoans. Cono- Cambrian rocks, where present, are differen- chitina is the dominant genus and Cyathochitina tiated readily from the overlying Ellenburger. and Rhabdochitina occur more rarely. In the eastern shelf of the Midland basin, the dominant lithology is finely grained, slightly cal- ORDOVICIAN (JOINS FORMATION) careous, slightly hematitic sandstone that prob- The Joins is considered to be the basal for- ably is Late Cambrian (Riley) in age. South and mation of the Simpson Group. In many cases it west of the Midland basin, Cambrian rocks pene- is erroneously picked as Ellenburger because of trated in wells consist of 100 to 150 feet of similarity of lithology—dolomite. medium to coarse sandstone, glauconitic lime- The formation consists of thin limestone and stone, and green shale. Dolomite also is present shale at the surface; in the subsurface, however, at the northern limit of the Val Verde basin. No the Joins becomes increasingly dolomitic and re- chitinozoans have been noted in Cambrian lithol- sembles the underlying Ellenburger in this re- ogies in West Texas. spect. Joins dolomites are argillaceous and some- ORDOVICIAN (ELLENBURGER) what sandy, and fossil fragments are noted. In West Texas, the contact between gray-green shale The Ellenburger in West Texas is typically and argillaceous dolomite of the Joins with the cream, white, buff-brown, and gray, microcrystal- underlying clean, light Ellenburger dolomite coin- line to coarsely crystalline, fractured dolomite that monly suggests little or no erosional break. ranges in thickness from 300 to more than 2,000 feet. Vugs, chert, bands of finely to coarsely ORDOVICIAN (OIL CREEK FORMATION) grained, frosted, quartz sand, and occasional gray The Oil Creek Formation in surface and sub- and green shale occur. Light-colored micritic surface sections is subdivided into two members, limestone is present in wells penetrating this sec- a basal sandstone (Connel Sandstone) and upper tion in the Val Verde basin and at the southern member of interbedded limestone and shale. The limit of the Midland basin. This limestone ex- sandstone is massive, white, and extremely fri- tends eastward toward the Llano uplift. A simi- able; it consists of fine- to medium-grained, lar limestone is seen in well penetrations in the rounded to subrounded, frosted quartz grains. Northwest shelf. The subsurface Ellenburger Locally in the subsurface, sandstone in the Oil yields a sparse fauna consisting of a few mollusks Creek is silicified. Limestone is thinly bedded and brachiopods. Although cysts and unidenti- and contains many ostracodes. Olive-green shale fiable forms are noted, no chitinozoans have been is interstratified or intercalated with limestone; found during the present study in Ellenburger the shale, however, generally occurs in the upper dolomite or limestone. part.

ORDOVICIAN (SIMPSON GROUP) ORDOVICIAN (McLISH FORMATION) Rocks of Simpson age are found throughout The McLish Formation consists of a basal the West Texas area. As generally accepted by sandstone (Waddell Sandstone) and an overlying 6 The University of Kansas Paleontological Contributions-Paper 54

EXPLANATION OF PLATES (All figures X250)

PLATE 1 PLATE 5 Acid-insoluble microfossils from the Humble Oil Chitinozoans from the Humble Oil & Refining & Refining Company No. 1 Worsham, Pecos Company No. 1 State BS, Andrews County, County, Texas. Figures 1-4, Desmochitina sp. Texas (figures 1-11), and the Harrell No. 1 from core at depth of 12,918 feet; figures 5-7, Cook, Glasscock County, Texas (figures 12-17). Angochitina sp. from a depth of 12,918 feet; fig- Figure 1, Angochitina milanensis COLLINSON ures 8-12, Angochitina sp. cf. .4. mourai LANCE, & SCOTT, from a depth of 9,000 to 9,050 feet; from core at depth of 12,924 feet; figure 13, figures 2-4, Angochitina sp. cf. A. mourai LANGE, scolecodont from same sample as figures 8-12; from a depth of 9,100 to 9,200 feet; figure 5, figure 14, unidentified spore from same sample as Desmochitina sp. from a depth of 9,100 to 9,200 figures 8-12. feet; figure 6, Angochitina sp. from a depth of 9,300 to 9,350 feet; figures 7-8, Angochitina PLATE 2 globosa CoLLINsoN & SCOTT, from a depth of Chitinozoans from cores at a depth of 12,926 feet 9,300 to 9,350 feet; figures 9-10, Angochitina sp. in the same well as Plate 1. Figures 1-5, 2, 9, from a depth of 9,300 to 9,350 feet; 10, from Angochitina sp. cf. A. mourai LANGE; figures 6- a depth of 9,800 to 9,830 feet; figure 11, Ango- 12, Sphaerochitina sp.; figures 13-14, Desmo- chitina? sp. from a depth of 9,800 to 9,830 feet; chitina sp. figure 12, Angochitina sp. from a depth of 10,400 to 10,480 feet; figure 13, 15, Sphaerochitina sp. PLATE 3 from a depth of 10,400 to 10,480 feet; figure 14, Lagenochitina? sp. from a depth of 10,400 to Chitinozoans from the Humble Oil & Refining 10,480 feet; figures 16-17, Desmochitina sp. from Company 1 No. State AP, Andrews County, a depth of 10,500 to 10,550 feet. Texas. Figure 1, Ancyrochitina sp. 1 from depth of 10,550 to 10,600 feet; figures 2-3, 5-6, PLATE 6 Angochitina mourai LANGE, from a depth of Rhabdochitina from the Harrell No. 1 Cook, 10,700 to 10,780 feet; figure 4, Lagenochitina sp. Glasscock County, Texas. Figures 1-6, Rhab- from a depth of 10,700 to 10,780 feet; figures dochitina sp. from a depth of 10,700 to 10,750 7-10, Angochitina devonica EISENACK, from a feet. depth of 10,700 to 10,780 feet; figure 11, Ango- chitina globosa COLLINSON & SCOTT, from a depth PLATE 7 of 10,810 to 10,850 feet; figures 12, 15, Ango- chitina milanensis COLLINSON & SCOTT, 12 from a Chitinozoans from the El Cinco No. 1 Hoover, depth of 10,810 to 10,850 feet; 15 from a depth of Crockett County, Texas.-Figure 1, Lageno- 11,170 to 11,190 feet, and is probably a caved chitina? sp. from a depth of 12,100 to 12,200 feet; form; figure 13, Sphaerochitina sp. from a depth figure 2, Sphaerochitina sp. from a depth of of 10,810 to 10,850 feet; figure 14, Ancyrochitina 12,100 to 12,200 feet; figures 3-4, Angochitina cornigera COLLINSON & SCOTT, from a depth of sp. from a depth of 12,100 to 12,200 feet; figure 10,870 to 10,890 feet. 5, Ancyrochitina sp. from a depth of 12,100 to 12,200 feet; figures 6-7, Conochitina sp. from a PLATE 4 depth of 12,300 to 12,400 feet; figures 8-9, Rhab- Chitinozoans from the Humble Oil & Refining dochitina sp. from a depth of 12,300 to 12,400 Company No. 1 State AP, Andrews County, feet. Texas (figures 1-7), and the Union Oil No. 1 PLATE 8 Rape, Glasscock County, Texas (figures 8 9). Figures 1-7, Conochitina spp. from a depth of Chitinozoans from the El Cinco No. 1 Hoover, 11,460 to 11,510 feet; figures 8-9, Rhabdochitina Crockett County, Texas. Figures 1-2, Sphae- sp. from a depth of 10,710 to 10,760 feet. rochitina sp. from a depth of 12,300 to 12,400 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Kauffman—Chitinozoans from west Texas Paper 54, Plate 1

14

13 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Paper 54, Plate 2 Kauffman—Chitinozoans from west Texas

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14 12 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Kauffman—Chitinozoans from west Texas Paper 54, Plate 3

14 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Paper 54, Plate 4 Kauffman—Chitinozoans from west Texas

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6 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Kauffman—Chitinozoans from west Texas Paper 54, Plate 11

5 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Paper 54, Plate 12 Kauffman—Chitinozoans from west Texas THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Kauffman—Chitinozoans from west Texas Paper 54, Plate 13 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS Paper 54, Plate 14 Kauffman—Chitinozoans from west Texas

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Kaugman-Chitinozoans from West Texas 7 feet; figures 3-6, Rhabdochitina sp. from a depth Montgomery, Pecos County, Texas.-Figures of 12,300 to 12,400 feet. 1-3, Conochitina sp. from a depth of 11,150 to 11,200 feet. PLATE 9 PLATE 14 Chitinozoans from the El Cinco No. 1 Hoover, Crockett County, Texas.-Figure 1, Rhabdo- Chitinozoans from the Standard of Texas No. 1 chitina sp. from a depth of 12,300 to 12,400 feet; Montgomery, Pecos County, Texas. Figures figures 2-5, Conochitina sp. from a depth of 1-4, 8-9, Conochitina sp. from a depth of 11,400 12,300 to 12,400 feet; figures 6-8, Cyathochitina to 11,450 feet; figures 5-7, Conochitina? sp. from sp. from a depth of 12,300 to 12,400 feet. a depth of 11,400 to 11,450 feet; figure 10, Cya- thochitina sp. from a depth of 11,400 to 11,450 PLATE 10 feet; figure 11, Rhabdochitina sp. from a depth Chitinozoans from the Sinclair No. 1 Long (fig- of 11,400 to 11,450 feet. ures 1-3) and the Sinclair No. 1 Hall (figures 4-8), Glasscock County, Texas.-Figure 1, PLATE 15 Rhabdochitina sp. from a depth of 9,910 to 9,950 Chitinozoans from the Humble Oil & Refining feet; figures 2-3, Conochitina sp. from a depth of Company No. 1 Spencer, Terrell County, Texas. 9,910 to 9,950 feet; figures 4-8, Desmochitina sp. Figures 1-2, 6-7, Angochitina sp. from a from a depth of 10,680 to 10,710 feet. depth of 12,500 to 12,600 feet; figures 3-5, 8-9, Desmochitina sp. from a depth of 12,500 to PLATE 11 12,600 feet; figure 10, Ancyrochitina? S. from a Chitinozoans from the Phillips No. 1D Puckett, depth of 12,650 to 12,670 feet; figures 11-14, Pecos County, Texas.-Figures 1-5, Desmo- Conochitina sp. from a depth of 12,700 to 12,750 chitina sp. from a depth of 10,700 to 10,750 feet; feet. figures 6-7, Conochitina sp. from a depth of PLATE 16 11,000 to 11,050 feet. Chitinozoans from the Union (Pure) No. 1 Tyr- PLATE 12 rell, Pecos County, Texas (figures 1-15), and the Chitinozoans from the Standard of Texas No. 1 Humble Oil & Refining Company No. 1 Black- Montgomery, Pecos County, Texas. Figure 1, stone-Slaughter, Terrell County, Texas (figures Angochitina sp. from a depth of 10,900 to 10,950 16-18). Figures 1-2, 6, Angochitina sp.; 1, 2, feet; figure 2, Desmochitina sp. from a depth of from a depth of 16,900 to 16,950 feet; 6, from a to 17,100 feet; figures 3-4, 10,900 to 10,950 feet; figure 3, Sphaerochitina depth of 17,070 Des- tnochitina sp. from a depth of 17,070 to 17,100 sp. aff. S. longicollis TAUGOURDEAU & JLKH0WSKY, feet; figures 5, 7-8, 11-13, Angochitina sp. cf. A. from a depth of 11,100 to 11,130 feet; figures 4, 6, mourai LANGE, 5, 7-8, from a depth of 17,070 to Conochitina sp. from a depth of 11,100 to 11,130 17,100 feet; 11-13, from cores at a depth of 17,110 feet; figure 5, Desmochitina sp. from a depth of feet; figures 9-10, Lagenochitina? sp. from a 11,100 to 11,130 feet; figures 7-9, Conochitina depth of 17,070 to 17,100 feet; figures 14-15, sp. from a depth of 11,150 to 11,200 feet. Conochitina sp. from a depth of 17,580 to 17,620 feet; figures 16-17, Desmochitina sp. from a depth PLATE 13 of 9,500 to 9,530 feet; figure 18, Conochitina sp. Conochitina from the Standard of Texas No. 1 from a depth of 9,900 to 9,950 feet. 0

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10 The University of Kansas Paleontological Contributions — Paper 54

section of thin sandstone, olive and dark green The fauna of the Montoya noted in subsurface shale, and varied limestone. The sandstone is rocks includes brachiopods, trilobites, conodonts, light green with finely grained, rounded to sub- siliceous spicules, ostracodes, and questionable rounded, frosted quartz grains. The limestone is radiolarians. Acid-insoluble fossils also are abun- gray-white to locally mottled. The "birdseye" dant in the Montoya strata, chitinozoan genera limestone of Oklahoma is found in this formation. nant forms. The equivalent surface Viola Lime- stone of Oklahoma has yielded a large and varied ORDOVICIAN (TULIP CREEK assemblage of chitinozoans (JENxiNs, 1969). FORMATION) The Tulip Creek Formation consists of a ORDOVICIAN (SYLVAN SHALE) basal sandstone (McKee Sandstone of West Texas The Sylvan Shale, topmost unit of the Ordo- and of Wilcox Sandstone Oklahoma) and an vician in West Texas, is gray to green, or more overlying section of intercalated shale and lime- rarely black, pyritic, phosphatic, and locally dolo- stone. Subsurface Tulip Creek sandstones char- mitic and cherty. In the subsurface, the Sylvan acteristically display a "salt-and-pepper" stippled is generally sandy, dark-green, and gray. Locally appearance, the pepper (darker particles) being this shale is difficult to separate from the over- conodonts, phosphatic pellets, darkened aragonite, lying "Silurian green shale." In the Ouachita or discolored quartz grains. Olive-green and Mountains of Oklahoma, the Sylvan becomes the maroon shale is abundant throughout the forma- dark-green and maroon Polk Creek Shale. In the tion. Limestone beds are thin and contain abun- Marathon region, the Sylvan also is equivalent to dant schmidtellid ostracodes. the Persimmon Gap Shale. Fossils are rare in the subsurface Sylvan, al- ORDOVICIAN (BROMIDE FORMATION) though graptolites are found abundantly in sur- The Bromide Formation consists of alternat- face exposures. No chitinozoans were noted. ing shale, limestone, and sandstone. The sand- stone is thinly bedded to massive and consists of SILURO - DEVONIAN HUNTON white to buff, fine to coarse, angular to rounded In West Texas, the terms Devonian, Silurian quartz grains. Shales are dark green and slightly shale, and Fusselman have been more indurated than the shale of other forma- and are still being used for appropriate lithologic parts of tions in this group. this section. The following simple description of the Limestones vary in thickness and color from dominant lithologies of the Hunton as used in- light gray to buff and brown, are nodular, and cludes the series or lithologic units just noted. contain abundant ostracode and bryozoan faunas. Distribution of chitinozoans in the Silurian is Other fossils commonly include brachiopods, variable and in places erratic. No forms were sponges, and corals. found in the Fusselman Limestone or Dolomite. Chitinozoans are notably lacking in reef facies ORDOVICIAN (MONTOYA GROUP) and are sparse on the shelf to shelf margin. Dark- In the subsurface, the Montoya is primarily brown micrites of the basinal facies yield the most brown to dark-brown micritic to micritic-skeletal diverse assemblages. Ancyrochitina is the domi- limestone. Blue, light-gray, and brown to dark nant genus of the Silurian. A small delicate brown chert characteristically is scattered through- species of Conochitina also was noted. out the Montoya section. A recrystallized buff- cream micritic skeletal limestone also is present. LOWER SILURIAN (ALEXANDRIAN) The Montoya ranges in thickness from 0 to 600 feet. The oldest questionable Silurian beds found This group is the approximate time equiva- in this area are isolated patches of oolitic lime- lent of the subsurface Viola Group of Oklahoma stone in the southern Midland basin. This sec- and North Texas. The Bigfork chert of the tion is correlated tentatively with the lower Chim- Ouachita facies and Maravillas chert of the Mara- neyhill of Oklahoma, giving this section a ques- thon also are facies equivalents of the Montoya. tionable Early Silurian (Alexandrian) age. Kaugman—Chitinozoans from West Texas 11

LOWER SILURIAN (FUSSELMAN Silurian reefs, where encountered, are char- FORMATION) acterized typically by light-gray carbonate that contains abundant stromatoporids, corals, crinoid The next oldest Silurian found in the subsur- columnals, pentamerid brachiopods, and other face of West Texas is the lower Niagaran Fussel- microfossils. Parts of these reefs are dolomitic. man Formation. The Fusselman encountered in The inner reefal zone is a dark-brown micritic- the subsurface is a light-gray and white, finely to skeletal limestone. Shelf dolomitic limestones are coarsely crystalline limestone or dolomite. Chert occurs sparsely as small nodular masses. The light-gray to a darker gray. rocks locally have a pink to light-green cast. Fauna is common and consists of crinoid colum- DEVONIAN nals, the corals Hal ysites and Favosites, and frag- Devonian cherts are a variation of white to ments of brachiopods. Dolomitization where dark-brown novaculites and glassy cherts, chang- present alters the fossils observed. The section is ing facies to a buff, partially tripolitic zone, and correlatable with the upper Chimneyhill of to a buff, cream, tripolitic chert. Cherty dolo- Oklahoma. mites occur in the Delaware basin. Carbonates SILURIAN SHALE are cream, buff, and brown micrites to micritic- erinoidal limestones. Siliceous limestone and The Silurian shale is considered the topmost dolomite also are present. Age determinations in unit of the Silurian in the subsurface. Time- this section are made using brachiopods, corals, wise it is late Niagaran and correlates with the and ostracodes; acid-insoluble fossils are used Henryhouse of Oklahoma. It is a gray-green cal- Angochitina is careous shale with micritic to micritic-skeletal when no other fauna is present. limestone near the base. Bedded chert also occurs the dominant chitinozoan of the Devonian and at the base. Fossils found in this unit include locally is found in association with species of Hal ysites, Favosites, stromatoporids, ostracodes, Ancyrochitina, Lagenochitina, Desmochitina, and and pentarnerid brachiopods. Sphaerochitina.

APPLICATION OF CHITINOZOANS TO SUPPLEMENT PHYSICAL CRITERIA IN CORRELATION

An example of the problems confronting the for detailed correlations to other sections in this subsurface geologist in dating and correlating the area where marked changes occur laterally in log subsurface lower Paleozoic of West Texas is patterns, lithology, and thickness. Cross section shown on the cross section (Fig. 3). This section (Fig. 4) shows correlation of the wells using oc- illustrates the complications encountered in cor- currences of chitinozoan genera together with relations, using only physical criteria (i.e., electric- lithology and electric-log patterns. It is doubtful log patterns and lithology), between well sections that the physical correlations would have been (wells No. 2 and No. lacking paleontologic data able to indicate a Devonian thickening toward Well No. 1 is subdivided using both physical 3). the southeast or a Silurian pinchout as noted and paleontologic data, and even with this between wells No. 2 and No. 3. amount of control, insufficient clues are provided

SUMMARY AND CONCLUSIONS

Al) important result of the study here reported Chitinozoans were found in most lithologies has been the demonstration that acid-insoluble except sandstone and organic (reef) limestone. microfossils can be recovered in sufficient quan- Recoveries from dolomite were sparse, although tity and quality to aid in correlation and dating. cherty dolomite yields a number of forms. De-

12 The University of Kansas Paleontological Contributions-Paper 54 vonian chert of all types (novaculite, glassy, and the Middle through Upper Ordovician; it is tripolitic) is the most prolific in chitinozoan fos- found abundantly in the Montoya and to a lesser sils, although tripolitic chert is less so than the degree in the Simpson. Cyathochitina is rare, other types. Recovery of acid-insoluble fossils being noted only in two wells where it ranged from the Silurian is fair but poor in chitinozoans, from the upper Simpson through the lower Mon- even though cores were used in this portion of toya. Rhabdochitina is common in the Montoya. the study. Recovery was excellent in the Middle Its lateral occurrence is unpredictable, but it is Upper Ordovician. Forms were found in and found only in the Upper Ordovician. Desmochi- the Middle (Simpson Group) through the Upper tina, Lagenochitina, and Sphaerochitina are long- (Montoya) part of the system. No chitinizoans ranging forms in the Devonian and Ordovician. were found in rocks older than Middle Ordo- Detailed description of species within these gen- vician. era is necessary before they can be used as ef- Angochitina is the dominant genus in the work. Scolecodonts, Devonian and is restricted to this portion of the fective fossils in stratigraphie lower Paleozoic. Several species of Ancyrochitina graptolite siculae, and hystrichosphaerids were are present, a long-necked Silurian form being recognized and listed but were used only when the most distinctive. Conochitina is dominant in chitinozoans were not present.

REFERENCES

AMERICAN COMMISSION ON STRATIGRAPHIC NO- tools for the subsurface geologist: Am. Assoc. MENCLATURE, 1961, Code of strati graphic Petroleum Geologists, Bull., v. 45, p. 1378- nomenclature: Am. Assoc. Petroleum Geol- 1391, 5 fig., 3 pl. ogists, Bull., v. 45, p. 645-665. LANGE, F. W., 1949, Novos microf6sseis devoni- COLLINSON, CHARLES, & SCOTT, A. J., 1958, Chiti- anos do Parand: Museu Paranaense, Arqui- nozoan faunules of the Devonian Cedar Val- vas, V. 7, p. 287-298, pl. 6-8. ley Formation: Illinois Geol. Survey, Cire. , 1952, Chitinozodrios do folhelho Bar- do Pard: Dusenia, v. 3, 247, 34 p •, 13 fig., 3 pl. reirinha, devoniano COMBAZ, ANDRÉ, & OTHERS, 1967, Micro fossiles p. 373-386, pl. 18-19. organiques du paléozoique; pt. 2, les chitino- MILLER, T. H., 1967, Techniques for processing zoaires, morphographie: Centre National and photographing chitinozoans: Univ. Kan- Recherche Sci. Ed., 42 p., 8 fig., 5 pl. sas Paleont. Contrib., Paper 21, 10 p., 1 fig., EISENACK, ALFRED, 1968, Ueber Chitinozoen des 3 pl. baltischen Gebietes: Palaeontographica, Abt. TA UGOURDEAU, PHILIPPE, 1966, Les chitinozoaires; A, v. 131, p. 137-198, 13 fig., pl. 24-32. techniques d'études, morphologie et classifica- JEFFORDS, R. M., 1968, Chitinozoa, abundant Or- tion: Soc. Géol. France, Mém., n. ser., v. 45, dovician to Devonian microfossils: in R. C. Mém. 104, 64 p., 4 pl. Moore & others, Developments, trends, and , & J EKHOWSKY, BENJAMIN, DE, 1960, Ré- outlooks in paleontology: Jour. Paleontology, partition et description des chitinozoaires v. 42, p. 1346-1347. siluro-dévonian de quelques sondages de la J ENKINS, W. A. M., 1969, Chitinozoa from the C.R.E.P.S., de la C.F.P.A. et de la S.W. Repal Ordovician Viola and Fernvale limestones of au Sahara: Inst. Français Pétrole, v. 15, p. the Arbuckle Mountains, Oklahoma: Palae- 1199-1260, 19 fig., 13 pl. ont. Assoc. (London), Spec. Papers in Palae- , & OTHERS, 1967, Micro fossiles organiques ontology 5, 44 p., 10 fig., 9 pl. du paléozoïque, pt. 1, les chitinozoaires; JODRY, R. L., & CAMPAU, D. E., 1961, Small pseu- analyse bibliographique illustrée: Centre Na- dochitinous and resinous micro fossils; new tional Recherche Sci. Ed., 96 p., 4 fig., 11 pl.