Biostratigraphic problems of Morrowan and Derryan (Atokan) strata in the Pennsylvanian System of western United States

D. L. DUNN Gulf Research and Development Company, H.T.S.C., P.O. Box 36506, Houston, Texas 77036

ABSTRACT ZONES

Although both foraminiferal and conodont zonations have been Lane and Straka (1974) proposed a conodont zonation (Fig. 1) proposed for Lower and Middle Pennsylvanian strata, the current for Arkansas and Oklahoma utilizing slightly different terminology state of the art indicates that several proposed Morrowan cono- from that proposed by Lane and others (1971). They did not rec- dont zones and one important Derryan(?) fusulinid zone (21) and ognize the expansus—S. suberectus, the the ranges of several important associated and humerus—I. sinuosis, and the Streptognathodus fusulinids are in question. The conodont zones in question are the parvus—Adetognathus spathus Zones proposed earlier (Dunn, Gnathodus girtyi simplex, the Streptognathodus expansus-S. sub- 1970b), apparently because they did not believe these zones to be erectus, the Idiognathodus humerus—I. sinuosis, and the adequately documented in northeastern Oklahoma (Lane and Streptognathodus parvus— Adetognathus spathus Zones of Dunn Straka, 1974, p. 31). Lane and Straka (1974) have failed to recog- and the Idiognathodus sinuosis, I. klapperi, and 1. convexus nize the significance of some of the most important upper Mor- Zones of Lane and Straka. The conodonts whose ranges are in rowan index fossils now known — namely, those of the first and question are Gnathodus girtyi simplex, Rhachistognathus, third zones cited above — and, consequently, have demonstrated muricatus, Declinognathodus noduliferus, Adetognathus spathus, inconsistency in the correlation of Morrowan strata and in the Neognathodus bassleri bassleri, and Idiognathoides convexus. placement of their Morrowan-Derryan boundary. This seemingly is Evidence based on conodonts suggests that there is a time over- due to their lesser reliance on conodonts and greater emphasis on lap between uppermost type Morrowan and lowermost type Der- foraminiferal ranges as related to Zone 21 of Mamet and Skipp's ryan strata. Because of this, there is as yet no precise paleontologi- (1970) foraminiferal zonation. cal definition of a single Morrowan-Derryan (or Morrowan- Lane and others (1972, p. 554) and Lane and Straka (1974, p. 1) Atokan) boundary. Key words: micropaleontology, , stated that the zonal scheme of Lane and others (1971, p. conodonts, Paleozoic, Pennsylvanian. 398-403), and as modified by Lane and Straka (1974) and shown in Figure 1 here, is applicable in west Texas and Nevada. Analysis of their data, however, indicates that they have not documented INTRODUCTION their Idiognathodus sinuosis and Idiognathoides convexus Zones in west Texas or Nevada. Moreover, their Idiognathodus klapperi Recent contributions on and Pennsylvanian bio- Zone is known at only one locality in Arkansas and is not stratigraphy in the western United States (Mamet and Skipp, 1970; documented in Nevada. Lane and others, 1971, 1972; Lane and Straka, 1974) dealing with foraminifers and (or) conodonts have presented biostratigraphic QUESTIONABLE CONODONT ZONES data dealing with zonations for these fossil groups. Lane and others (1972) and Lane and Straka (1974) presented their interpretation Gnathodus girtyi simplex Zone. Webster (1969, p. 22, 23) pro- of the relationships of their proposed conodont zones to the posed the Gnathodus girtyi simplex Zone and considered it as foraminiferal scheme of Mamet and Skipp (1970). Seemingly, they chronologically equivalent to the Rhipidomella nevadensis have shed light on understanding Chesterian, Morrowan, and Der- brachiopod zone. Although Webster did not specifically define the ryan correlations and the Mississippian-Pennsylvanian and zone on the basis of conodont limits, a restricted Gnathodus girtyi Morrowan-Derryan boundaries. simplex Zone was recognized in the Indian Springs Formation at The purpose of this paper, however, is to note problems involv- Lee Canyon in Nevada (Dunn, 1970b). Contrary to Webster ing some of the conclusions reached in the papers cited above and (1969) and Lane and Straka (1974, p. 21, 22, 29), I found that to offer alternative conclusions and interpretations. In particular, Gnathodus girtyi simplex succeeds G. girtyi girtyi in the Indian more research is needed on the problem of a Morrowan-Derryan Springs (Dunn, 1970a, p. 331), with the lowest occurrence of the (and Morrowan-Atokan) boundary before we can determine former above that for Adetognathus unicornis. On this basis, I whether or not it is only one horizon, as we have been led to recognized the zone as embracing the range of G. girtyi simplex believe. That is, the upper type Morrowan boundary is not neces- prior to the lowest occurrence of Rhachistognathus muricatus sarily correlative with the lower type Derryan (or Atokan) bound- (Dunn, 1970b). ary. The initial appearance and extinction point of G. girtyi simplex In addition, the validity of several proposed Morrowan cono- seemingly rests on interpretation of this subspecies. Webster (1969, dont zones is questioned because separate zonal schemes have been PI. 5, fig. 10), for example, includes forms under G. girtyi simplex proposed by me (Dunn, 1970b) and Lane and Straka (1974) for the that I would consider as G. girtyi girtyi. Moreover, because G. same part of the Lower Pennsylvanian (Morrowan) section (Fig. 1). girtyi simplex evolves to Declinognathodus noduliferus at the

Geological Society of America Bulletin, v. 87, p. 641—645, 1 fig., May 1976, Doc. .. 60501.

641

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/5/641/3418251/i0016-7606-87-5-641.pdf by guest on 30 September 2021 5 CONODONT ZONES üü (f) »- UJ co a: RANGES OF KEY ZONE CONODONTS >- tu LANE $ STRAKA co THIS PAPER co 1974 z 2 ë Si Idiognathoides n sp. I UJ o ?

Streptognathodus parvus I. convexus Adetognothus spathus Q. I. klapperl 10 in Idiognathodus humerus c in a> a> o I. sinuosi« a> TJ XJ Q. '5 o I. sinuosi» a. -C o O Z Streptognathodus expansus c o < CJl o O 2 S. suberectus £ u> T3 v> o 10 3 3 < o o TJ T3 ÎZ 3 in O O >.t E C 3> -J o O 3 JC. >- a tr £ to O 0 N. basslerl bassleri N. bassleri bassleri 3 O c co~ oc a. c Q. <31 01 o m .c o o c 05 TJ o> CO o E o <2 o a -C 3 c £ ja c J2 CT o o a) o o o o 75 c Ê 3 o> (0 D. noduliferus I. noduliferus -C .c cu 3 Q- a: CE Q E in g •o a> >> a> c T3 k. (A o o i/> Q. -C 3) o X o -Q as c en R. primus R. primus to O 3 CO in 3 -C 3 10 3 -X. o _T3 . J8 -o a> -n- O Q. > -C Z R. muricatus c < R. muricatus o u) o < 10 o 3 c po i a. 3 TJ en tr (G.girt. simplex ? ) W o Q. a> v Q. o "O a> co £ ti A. unicornis c O CO (/) o A. unicornis o> £5 C o5 UJ o o> X D o co o a> C S Pre A. unicornis g TJ

Figure 1. Comparison of conodont zonal schemes and ranges of key zone conodonts.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/5/641/3418251/i0016-7606-87-5-641.pdf by guest on 30 September 2021 BIOSTRATIGRAPHIC PROBLEMS OF MORROW AN AND DERRYAN STRATA 643

Mississippian-Pennsylvanian boundary, differentiation of these two distinctly different species of Idiognathodus in their upper Mor- conodonts at the boundary is difficult. Whether or not a broad rowan material. interpretation of G. girtyi simplex is the reason for Lane and Other authors (Koike, 1967; Webster, 1969; Webster, in Lane Straka's (1974, p. 28) reported lower Morrowan occurrence of this and others, 1971, p. 405) may have recovered I. sinuosis and I. subspecies at Arrow Canyon in Nevada is not known. In any case, humerus in their material and, if so, possibly identified them to- the difficulties of recognizing any sort of G. girtyi simplex Zone, as gether with other forms of Idiognathodus as I. delicatus Stauffer pointed out by Lane and Straka (1974), may preclude its useful- and Plummer. ness. Further research is necessary to answer this question. Redefinition in this paper of the underlying Streptognathodus Idiognathodus sinuosis Zone versus Streptognathodus ex- expansus—S. suberectus Zone raises the lower limit of the pansus-Streptognathodus suberectus Zone. In proposing the Idiognathodus humerus—I. sinuosis Zone to the stratigraphic level Idiognathodus sinuosis Zone, Lane and Straka (1974, p. 31) seem- of extinction of S. expansus and S. suberectus. ingly discredited my evidence for the S. expansus-S. suberectus Idiognathoides convexus Zone versus Streptognathodus par- Zone in the Arkansas-Oklahoma area (Dunn, 1970b), and recog- vus-Adetognathus spathus Zone. Lane and Straka (1974) ap- nized the Idiognathodus sinuosis Zone as immediately succeeding parently have unraveled the knotty problem of nomenclature con- the Neognathodus bassleri bassleri Zone. They are technically cor- cerning Idiognathoides sulcatus, I. sinuatus, I. sulcatus parvus, I. rect in regard to my original definition of the S. expansus—S. sub- macer, and I. convexus. On the basis of their determined range for erectus Zone (Dunn, 1970b, p. 2970). Nevertheless, these impor- Idiognathoides convexus, they have proposed an uppermost Mor- tant middle Bloyd (Arkansas) conodonts are present in Lane and rowan conodont zone tentatively defined by the range of that Straka's faunal material, although invariably they seem to occur species below the level of appearance in so-called "Derryan" strata with Idiognathodus sinuosis (and [or] I. humerus). Because S. ex- of Idiognathoides n. sp. Although the zone may be valid for Arkan- pansus and S. suberectus are known from the midcontinent, the sas and Oklahoma, other authors have identified I. convexus from Cordillera, and Japan and are short ranging, they are excellent lower Morrowan strata elsewhere (Koike, 1967; Webster, 1969; guide fossils. The failure of Lane and Straka (1974) to recognize the Dunn, 1970a, 1970b). significance of S. expansus and S. suberectus in a conodont zonal Lane and Straka (1974, p. 31) discredited the occurrence in Ar- scheme is, in my opinion, a serious oversight. Absence of these kansas and Oklahoma of the Streptognathodus parvus - Adeto- important zone conodonts stratigraphically below and unaccom- gnathus spathus Zone that I proposed (Dunn, 1970b) for the upper- panied by Idiognathodus sinuosis (and I. humerus) strongly sug- most Morrowan strata. They indicated that they had difficulty in gests the presence of a hiatus in Arkansas and northeastern recognizing this and my preceding two zones in northeastern Oklahoma. Oklahoma on the basis of my data. Admittedly, my published data To aid other workers in utilizing these important conodonts, I are weak for northeastern Oklahoma, but so are Lane and Straka's here redefine the upper limit of the S. expansus—S. suberectus Zone data for their proposed Idiognathodus klapperi Zone. Never- to coincide with the extinction of the zonal name-bearers. The theless, I think that the goals of biostratigraphic research would zone, therefore, can be divided into two subzones, the lower of have been better served if Lane and Straka had attempted to ac- which is defined as the range of the zonal name-bearers prior to the commodate their data to the earlier proposed zones in order to occurrence of Idiognathodus sinuosis (and its mate, I. humerus), either confirm or negate them, particularly because they show their and an upper subzone in which the zonal name-bearers occur to- zonal boundaries as coincidental with mine (Lane and Straka, gether with Idiognathodus sinuosis (and I. humerus). Redefinition 1974, p. 20). In addition to Adetognathus spathus, Lane and of this zone raises its upper limit and consequently raises the lower Straka (1974, Fig. 40, specimen 19) have Streptognathodus parvus limit of the succeeding Idiognathodus humerus—I. sinuosis Zone. in their conodont collections but have not identified the latter Lane and Straka's (1974) oversight in not recognizing the impor- specifically. The same is true for Streptognathodus anteeccentricus, tance of Streptognathodus expansus and S. suberectus may be due another important conodont first appearing in the upper Mor- in part to their failure to identify the latter in their faunas. This rowan, which they have not identified specifically (Fig. 40, speci- species is identified by them as Streptognathodus sp. in their Figure men 21). 37, specimens 33—35, and Fig. 40, specimen 20. Idiognathodus hlapperi Zone versus Idiognathodus humerus-I. MORROWAN-DERRYAN (ATOKAN) sinuosis Zone. Lane and Straka (1974, p. 24) proposed the BOUNDARY PROBLEM Idiognathodus klapperi Zone for Arkansas and Oklahoma on the basis of six specimens, all of which were recovered from an In spite of proposed conodont and foraminiferal zonations for ~60-cm interval in the Dye Shale Member of the Bloyd Formation Lower and Middle Pennsylvanian strata, a Morrowan-Derryan or of Arkansas at one locality. This zone may prove to be highly a Morrowan-Atokan boundary cannot at present be precisely useful, but at present it is not known elsewhere in Arkansas, defined either on the basis of conodonts or, in my opinion, of Oklahoma, or west Texas. By contrast, the Idiognathodus fusulinids. The stratigraphic order of appearance of the fusulinids humerus-I. sinuosis Zone (Dunn, 1970b) is a stratigraphically re- critical to the definition of the lowermost so-called "Derryan" stricted zone that seems to be geographically widespread. Contrary Zone 21 of Mamet and Skipp (1970), Pseudostaffella, Eoschuber- to the long range (into rocks of Derryan age) given for I. sinuosis tella, and Profusulinella, is inconsistent from place to place; this is (and I. humerus) by Lane and others (1971, p. 399) and Lane and evident in the data of Lane and others (1972, p. 551) and Lane (in Straka (1974, p. 18), these species are relatively short ranging and Verville and others, 1973, p. 196) for west Texas, New Mexico, became extinct during late Morrowan time. They are superseded in Nevada, and Wyoming. Lane and others (1972, p. 563) pointed the uppermost part of the Morrowan Series by other forms of out that the first occurrence of Profusulinella may not conform Idiognathodus distinct from the former. These latter forms were everywhere to the base of the Derryan Series, one reason possibly described and pictured earlier (Dunn, 1970a, p. 334, PI. 63, figs. being local paleoenvironmental conditions. This must also be con- 5-13) as Idiognathodus spp. and are illustrated in the material of sidered as likely for Pseudostaffella and Eoschubertella. Because of Lane and Straka (1974, Fig. 43, specimens, 2, 5, 6, 14). They are, this reasoning, the absence of Pseudostaffella and Eoschubertella in however, incorrectly identified as I. sinuosis. The remainder of the type Morrowan strata does not prove that Mamet and Skipp's specimens shown in Figure 43 are correctly identified. An analysis of Zone 21 is exclusively Derryan in age. Indeed, even in strata where source material for Lane and Straka's illustrated specimens indi- Zone 21 fusulinids seemingly occur in their assumed stratigraphic cates that I. sinuosis (and [or] I. humerus) s.s. is succeeded by relationship, such as in the Kodani Formation of Japan (Koike,

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/5/641/3418251/i0016-7606-87-5-641.pdf by guest on 30 September 2021 644 D. L. DUNN

1967), it is not guaranteed that Zone 21 is Derryan in age. I believe Morrowan-Derryan (and probably a Morrowan-Atokan) bound- that Zone 21 in the Kodani Formation is almost entirely Mor- ary could be defined as falling somewhere between the uppermost rowan in age, because it overlaps with most of the range given for limits of Idiognathoides convexus and (or) Adetognathus spathus Streptognathodus expansus, a Morrowan index in the western and the initial appearance of coloradoensis. United States. Conodonts occurring in this zone include Streptognathodus par- Conodont ranges between Morrowan and Atokan strata are vus, S. anteeccentricus, and unnamed species of Idiognathodus, but poorly known. Moreover, lowermost type Derryan conodonts in- not Idiognathodus sinuosis and (or) I. humerus. dicated by Lane and others (1972, p. 551) as occurring in the lower 4.6 m of the Arrey Formation also occur in the upper Morrowan of CONODONT RANGES northeastern Oklahoma and in the Trace Creek Member of the type Morrowan in Arkansas. There is a strong possibility that the Comments regarding certain stratigraphically important cono- lower 4.6 m, and possibly more, of the type Derryan section is donts are presented here because of contradictory reports for their Morrowan in age. ranges. A Derryan age assignment by Lane and others (1972, p. 554) and Gnathodus girtyi simplex. Possible reasons for the conflicting Lane and Straka (1974, p. 26, 31) for strata as low as my sample 47 reports of the range for G. girtyi simplex are discussed in the pre- (Dunn, 1970a, p. 322) in the Bird Spring Formation at Lee Canyon ceding section on conodont zones. in Nevada demonstrates that their concept of Derryan at Lee Can- Rhachistognathus muricatus. Lane and Straka (1974, p. 23, 36) yon almost certainly overlaps in age with upper Morrowan strata. reported R. muricatus as occurring with Neognathodus bassleri This has resulted in their distortion of conodont zone correlations bassleri in the Bird Spring (Morrowan) at Arrow Canyon. This between Oklahoma and Nevada, as shown in their comparison mutual occurrence is puzzling in that neither Webster (1969) nor I of various zonal schemes (Lane and Straka, 1974, p. 20). More- (Dunn, 1970a, 1970b) found these two forms to overlap in seven over, at the Lee Canyon section, Lane and others (1972) and Lane southern Nevada sections and one Utah section. Webster (1969) and Straka (1974) departed from the Zone 21 standard, used reported 132.6 m of separation between these species at Arrow throughout their work for determining their Morrowan-Derryan Canyon. A documented overlap, however, would not affect the boundary, by lowering this boundary to include the lowest known definitions of the zones that bear the names of these two occurrence of Neognathodus roundyi {= Neognathodus n. sp. of conodonts. Lane and others, 1972). This is ~46 m below the first occurrence of Declinognathodus noduliferus. The range of this species seems Zone 21 fusulinids at Lee Canyon. Seemingly by this same reason- to be the most controversial of those of all Early Pennsylvanian co- ing, Lane (in Verville and others, 1973, p. 166) assigned a Derryan nodonts. It is reported as occurring only in the lower Morrowan in age to certain strata yielding what he identified as Idiognathoides Arkansas and northeastern Oklahoma (Lane, 1967; Dunn, 1970a, noduliferus in the Morgan Formation from a well in Uinta County, 1970b; Lane and Straka, 1974). In southern Oklahoma, Straka Wyoming. Lane here claimed for the first time that this latter (1972) reported it ranging into the middle Morrowan. Its range in species occurs in the type Derryan in New Mexico, but its strati- central Texas and Nevada is equivalent, or nearly so, to that for graphic position is not documented in the type section. How this southern Oklahoma (Webster, 1969; Dunn, 1970a, 1970b), al- reported occurrence of Idiognathoides noduliferus in the type Der- though Webster found lower occurrences in Nevada than I did. ryan relates to the question of possible Morrow-Derry overlap is Lane and Straka (1974, p. 35, 36) believed that there are three not known. I also believe that Lane and others (1972, p. 551) have separate occurrences in time of this species in the Lower and lower placed the Morrowan-Derryan boundary 60 to 90 m too low in the Middle Pennsylvanian. The evidence for this is weak. Its range in Bird Spring Formation at Arrow Canyon on the basis of the cono- Arkansas and northwestern Oklahoma is incomplete because of dont ranges. paleoenvironmental or other reasons. They contended that the up- It seems obvious that there is, as yet, no conclusive way to de- permost "separate occurrence" of this species is Derryan in age termine accurately a consistent Morrowan-Derryan or Mor- because the type species was recovered from the Dimple Limestone rowan-Atokan boundary paleontologically. I believe, however, in West Texas (Ellison and Graves, 1941) — a formation dated as that we are close to being able to do so. The problem has been Derryan on the basis of its fusulinid fauna (Sanderson and King, recognized by Shaver and Smith (1974) who, on the basis of os- 1964). Examination of Ellison and Graves's data indicates that the tracod research in the Mansfield and Brazil Formations of the Il- Dimple Limestone carries a conodont faunal admixture throughout linois Basin, suggested the probability of upper Morrowan—lower the range shown for nodulifera (= Declino- Atokan time overlap in consideration of the most common recogni- gnathodus noduliferus, Idiognathoides noduliferus, Strepto- tions of these series in the midcontinent. They attributed the over- gnathodus noduliferus, or Gnathodus noduliferus of various au- lap as being partly the result of an inadequately established Atokan thors). Included in the admixture are spp., type section, and they believed that the scarcity of fusulinid data in Gnathodus texanus, spp., Spathognathodus com- the midcontinent has led to misinterpretation of the relationships mutatus, and other , Mississippian, and Early Pennsylva- among the two series and the fusulinid zones. The conodont re- nian conodonts. The Dimple Limestone may indeed be Derryan in search of Taylor (1974) supports the findings of Shaver and Smith age — and possibly younger in its upper part — but there is no in their Morrowan age assignment for the Mansfield Formation. proof that Declinognathodus noduliferus is indigenous to the The critical part of the Mansfield, as well as the overlying Brazil Dimple. Formation, had previously been assigned an Atokan-Desmoinesian Lane's statement (in Verville and others, 1973, p. 166) that the age on the basis of fusulinid work. It is critical to note that the specimens they called Idiognathoides noduliferus occur in the type upper part of the Mansfield Formation yields Profusulinella. Derryan is not documented. If a bona fide Derryan occurrence can Thompson (1970) reported conodonts from a stratigraphic sec- be documented, it would not, in my opinion, be post-Morrowan in tion in southwestern Missouri which seemingly bear on the prob- age there unless and until it is definitely proved that these rocks are lem of a Morrowan-Atokan boundary. However, all of his material younger than upper type Morrowan Trace Creek strata (see discus- is probably Morrowan in age and his uppermost fauna, which he sion of this disputed part of the type Derry in the section on the considered as questionable Atokan (because of association else- Morrowan-Derryan boundary problem herein). where of his conodont guide species with Profusulinella), is most Adetognathus spathus. This species first occurs at or near the likely Bloyd (late Morrowan) in age. base of the Pennsylvanian (Morrowan) in the United States, accord- It seems likely that on the basis of conodonts, a consistent ing to most researchers. The definition of its uppermost limit de-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/5/641/3418251/i0016-7606-87-5-641.pdf by guest on 30 September 2021 BIOSTRATIGRAPHIC PROBLEMS OF MORROW AN AND DERRYAN STRATA 645

pends upon the placement of a Morrowan-Derryan boundary, but REFERENCES CITED seemingly its extinction point would not be widely separated in time and (or) stratigraphically from that boundary. Dunn, D. L., 1970a, Middle Carboniferous conodonts from western United Neognathodus bassleri symmetricus and N. bassleri bassleri. States and phylogeny of the platform group: Jour. Paleontology, v. 44, The range of these subspecies remains in doubt because of Lane p. 312-342, Pis. 61-64. 1970b, Conodont zonation near the Mississippian-Pennsylvanian and Straka's (1974, p. 30, 32, 36) contention that certain reported boundary in western United States: Geol. Soc. America Bull., v. 81, occurrences of these subspecies represent occurrences for the nearly p. 2959-2974. identical Derryan form, Neognathodus colombiensis (Stibane). Ellison, S., and Graves, R. W., Jr., 1941, Lower Pennsylvanian (Dimple Idiognathoides convexus. Lane and Straka (1974, p. 24) limited Limestone) conodonts of the Marathon region, Texas: Missouri Univ. the range of I. convexus to uppermost Morrowan, but others have School Mines and Metallurgy Bull., Tech. Ser., v. 14, no. 3, 21 p. reported this species from lower Morrowan strata elsewhere Koike, T., 1967, A Carboniferous succession of conodont faunas from the (Koike, 1967; Webster, 1969; Dunn, 1970a, 1970b). Atetsu Limestone in southwest Japan (Pt. VI in Studies of Asiatic conodonts): Tokyo Kyoiku Daigaku Sci. Repts., Sec. c, Geology, CONCLUSIONS Mineralogy, and Geography, v. 9, no. 93, p. 279-318. Lane, H. R., 1967, Uppermost Mississippian and Lower Pennsylvanian conodonts from the type Morrow region, Arkansas: Jour. Paleontol- The fact that different conodont zonal schemes have been pro- ogy, v. 41, p. 920-942, Pis. 119-123. posed by various biostratigraphers for the same part of the strati- Lane, H. R., and Straka, J. J., II, 1974, Late Mississippian and Early Penn- graphic section seems to be due more to a lack of intercommunica- sylvanian conodonts, Arkansas and Oklahoma: Geol. Soc. America tion between researchers than to a difference in findings. Correla- Spec. Paper 152, 144 p., 44 figs. tions of upper Morrowan strata on the basis of conodonts and Lane, H. R., Merrill, G. K., Straka, J. J., II, and Webster, G. D., 1971, precise definition of a Morrowan-Derryan or a Morrowan-Atokan North American Pennsylvanian , in Sweet, boundary on the basis of either fusulinids or conodonts are seem- W. C., and Bergstrôm, S. M., eds., Symposium on conodont bio- ingly not yet firm. However, the boundary could be defined as stratigraphy: Geol. Soc. America Mem. 127, p. 395-414. falling somewhere between the uppermost limits of Idiognathoides Lane, H. R., Sanderson, G. A., and Verville, G. J., 1972, Uppermost Mississippian-basal Middle Pennsylvanian conodonts and fusulinids convexus and (or) Adetognathus spathus and the initial appearance from several exposures in the south-central and southwestern United of Spathognathodus coloradoensis. States: Internat. Geol. Cong., 24th, Montreal 1972, Sec. 7, Paleontol- The Gnathodus girtyi simplex Zone does not rest on a solid base ogy, p. 549-555. mainly because of questionable subspeciation. The lower part of Mamet, B. L., and Skipp, B. A., 1970, Preliminary foraminiferal correla- the herein redefined Streptognathodus expansus—S. suberectus tions of early Carboniferous strata in the North American Cordillera: Zone (without Idiognathodus sinuosis and [or] I. humerus) fits a Colloque sur la stratigraphie du carbonifère, 8 e, Université de Liège, hiatus in Arkansas and northeastern Oklahoma not recognized by 1970, Comptes Rendus, v. 55, p. 327-348. Lane and Straka; therefore their position of the I. sinuosis Zone is Sanderson, G. A., and King, W. E., 1964, Paleontological evidence for the questionable. Recovery of Idiognathodus klapperi from a single age of the Dimple Limestone, in The filling of the Marathon geosyn- cline — A symposium and guidebook: Soc. Econ. Paleontologists and locality is a poor basis for a zonal index, and hence for a zone, Mineralogists Basic Sec. Pub., p. 31—34. particularly with possible misidentifications. The range of Shaver, Robert H., and Smith, Susan G., 1974, Some Pennsylvanian Kirk- Idiognathoides convexus is still open to question because it has byacean ostracods of Indiana and Midcontinent series terminology: been found in rocks much older than those of the position shown Indiana Geol. Survey Prog. Rept. 31, 59 p., 3 pis. by Lane and Straka for the base of the I. convexus Zone. The range Straka, J. J., II, 1972, Conodont evidence of age of Goddard and Springer of Declinognathodus noduliferus has not yet been documented in Formations, Ardmore Basin, Oklahoma: Am. Assoc. Petroleum rocks younger than Morrowan age. Problems regarding definition Geologists Bull., v. 56, p. 1087-1099. of a Morrowan-Derryan boundary include the facts that the order Taylor, Gilbert D., 1974, Morrowan conodont faunas from the Mansfield of first appearances of critical fusulinids is inconsistent, that so- and Brazil Formations, southeastern Illinois Basin: Geol. Soc. called "Derryan" Zone 21 fusulinids overlap with the Morrowan America Abs. with Programs, v. 6, p. 549. Thompson, Thomas L,, 1970, Lower Pennsylvanian conodonts from index Streptognathodus expansus in Japan, that several conodont McDonald County, Missouri: Jour. Paleontology, v. 44, p. species range in both the upper type Morrowan and lower type 1041-1048, PI. 139. Derryan, and that critical conodont species such as Declino- Verville, G. J., Sanderson, G. A., Brenckle, P. L., and Lane, H. R., 1973, gnathodus noduliferus, Adetognathus spathus, Neognathodus Upper Paleozoic biozonation in the Unit no. 19 well, Church Buttes bassleri bassleri, and Idiognathoides convexus have been Field, Uinta County, Wyoming, in Wyoming Geol. Soc. Guidebook, assigned conflicting ranges by different researchers and are there- 25th Ann. Field Conf.: p. 165-171, Pis. 1-3. fore not firmly established. This evidence strongly suggests that Webster, G. D., 1969, Chester through Derry conodonts and stratigraphy there is a time overlap of the two series. of northern Clark and southern Lincoln Counties, Nevada: California Univ. Pubs. Geol. Sci., v. 79, 121 p., 8 pis. ACKNOWLEDGMENTS MANUSCRIPT RECEIVED BY THE SOCIETY APRIL 17, 1975 Reviewed by R. S. Shaver and C. B. Rexroad. MANUSCRIPT ACCEPTED AUGUST 19, 1975

Printed in U.S.A.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/87/5/641/3418251/i0016-7606-87-5-641.pdf by guest on 30 September 2021