CHRISTINA LOCHMAN-BALK Department of Geosdence, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801

Late Dresbachian (Late Cambrian) Biostratigraphy of North America

ABSTRACT bachian Aphelaspis Zone (Howell and Dresbachian time in the central Texas others, 1944) into an older Aphelaspis Zone section, with only a very short hiatus? before An examination of the taxonomic com- and a younger post-Aphelaspis Zone. the appearance of the Elvinia Zone fauna. position of the North American late Trilobites and brachiopods assigned by The short hiatus? refers to the well-defined Dresbachian faunules described to date Palmer to the Aphelaspis Zone are listed in faunal break and disconformity between the indicates that there is an Aphelaspis Zone Table 1. In the basal beds of the zone, Palmer Lion Mountain Sandstone Member of the faunal assemblage characteristic of the early Riley Formation and the Welge Sandstone half of the late Dresbachian Stage and a Member of the Wilberns Formation (Loch- TABLE 1. TRILOBITES ÄND BRACHIOPODS ASSIGNED TO Dunderbergia Zone faunal assemblage APHELASPIS ZONE, RILEY FORMATION, TEXAS, man, 1938; Freeman, 1969). characteristic of the later half. The diagnos- BY PALMER (1955) From 1951, Palmer was engaged in the

tic elements of each of the assemblages are Aphelaspis walcotti study of the Late Cambrian faunas of the listed, and the biozones of the common Labiostria (now Aphelaspis) conveximavginata Great Basin and published late Dresbachian Labiostria (now Aphelaspis) platifrons trilobite genera are noted so that correct Dunderbergia variagranula faunal lists in Nolan and others (1956) and Eaaschella (now Glaphyraspis) omata intracontinental correlations may be made. Cheilooephalus brevilobus in Drewes and Palmer (1957) to document Aphelaspis constriota the existence in the Great Basin of a large INTRODUCTION Aphelaspis spinosa Aphelaspis longifrons faunal assemblage younger than the Dytremacephalus granulosus Aphelaspis Zone and older than the Elvinia Recent discussion of the late Dresbachian Dytremacephalus laevis lithostratigraphy and biostratigraphy Pseudagnostus comrunis Zone assemblage. In 1958, Lochman-Balk Pseudagnostus josephus (Palmer, 1971; Kurtz, 1971) indicates the Geragnostus cf. G. tumidosus and Wilson published on the Cambrian Angulotreta triangularis biostratigraphy of North America and need for a clarification of the exact Dictyonina perforata composition of the faunal assemblages cf concluded that the term "post-Aphelaspis" the Aphelaspis, Dunderbergia, and Elvinia was inadequate for the large faunal Zones and the need for a listing of the assemblage which was being studied by currently known ranges of the trilobite and reported Aphelaspis walcotti in association Palmer. In analyzing Palmer's faunal lists, brachiopod genera within these zones. with Coosia cf. C. albertensis, Lochman-Balk and Wilson (1958, p. 337) Confusion concerning the occurrence and Crepicephalus? (now Coosella) perplexa, noted that Dunderbergia appeared to be an range of the common genera appears to be Maryvillia cf. M. (now Coosina) ariston, abundant and widespread genus in the hampering accurate correlation of the late Llanoaspis pecularis, and Tricrepicephalus younger late Dresbachian assemblage. Dresbachian faunules in the United States. A coria. The trilobites and brachiopods Lochman-Balk and Wilson (1958, p. 333) review is made of all the faunules of this age assigned by Palmer to the post -Aphelaspis were also aware that Dunderbergia did described to date in the United States. Zone are listed in Table 2. Palmer placed occur in association with Aphelaspis and During this time, the stock of the Aphelas- stated that it first appears near the top of the pididae was evolving rapidly and gave rise Aphelaspis Zone, but it continues into and becomes more abundant in higher beds: both to several closely related genera that TABLE 2. TRILOBITES AND BRACHIOPODS ASSIGNED TO are now placed in that family and to four POST-APHELASPIS ZONE, RILEY FORMATION, "The passage beds between the Aphelaspis TEXAS, BY PALMER (1955) other genera, Prehousia, Dytremacephalus, and the Elvinia faunizones in both Texas Dunderbergia, and Pterocephalia that are Labiostria (now Aphelaspis) convezimarginata and Nevada occupy a position spanning the Labiostria (now Apehlaspis) sigmoidalis regarded as the ancestral genera of the Dytremacephalus granulosus median level of the Dunderbergia biozone. It Housiidae, the Dokimocephalidae, the Cheilooephalus brevilobus is proposed that this biostratigraphic unit be Dunderbergia Variagranula Elviniidae, and the Pterocephaliidae, respec- Pterocephalia cf. P. ocaidens (now Pterocephalia oonaava) known as the Dunderbergia faunizone" Angulotreta triangularis tively. By the later half of late Dresbachian Apsotreta expansa (Lochman-Balk and Wilson, 1958, p. 333). time and the earliest part of Franconian Dysoristus lochmanae By including Texas in this statement, time, Aphelaspis and the closely related Lochman-Balk and Wilson (1958) were genera had become extinct, and genera and accepting Palmer's 1955 concept that the species of the four descendent families were post-Aphelaspis Zone faunal assemblage of diversifying and dominating the faunules. Labiostria in synonymy with Aphelaspis in Texas (1) was distinct from the Aphelaspis 1962, and he described Pterocephalia Zone faunal assemblage of Texas and (2) FAUNAL ASSEMBLAGES concava in 1960c. was to be correlated with the large faunal In 1965, p. 6, Figure 3, Palmer showed assemblage in Nevada younger than the Aphelaspis Zone that he considered the Aphelaspis and the Aphelaspis Zone which Palmer listed in Palmer (1955), in his study of the Riley post-Aphelaspis Zones and their assem- 1956 and 1957. The faunule lists in Tables 1 Formation of Texas, split the late Dres- blages to occupy nearly all of late and 2 show that the two zones in Texas have

Geological Society of America Bulletin, v. 85, p. 135-140, January 1974

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five genera and species in common, and the similar to the two Texas faunules listed by the time span of the late Dresbachian and synonymizing of Labiostria with Aphelaspis Palmer (1955) as representing the early Franconian Ages. Palmer's range chart (Palmer, 1962) demonstrates that the Aphelaspis and post-Aphelaspis Zones. The (1965, PI. 21) shows the composition and faunule of the post-Aphelaspis Zone of Texas faunal lists in Tables 1 and 2 show range of genera and species in each of the Texas is actually a slightly younger that Aphelaspis occurs in the faunules of zones. The 13 trilobite taxa assigned to his Aphelaspis Zone faunule. both zones, and is associated in both zones new Aphelaspis Zone in the Great Basin are Palmer (1960a, 1960b, 1962) presented a with Dunderbergia variagranula, Dy- listed in Table 4. The 13 trilobite taxa number of Dresbachian sections from the tremacephalus granulosus, Cheilocephalus assigned to the succeeding Dicanthopyge Great Basin, indicated that the Eureka, brevilobus, and Angulotreta triangularis. Zone are listed in Table 5. Of the 23 species Nevada, section is incomplete for the late These ranges and associations indicate that Dresbachian Stage, and showed the position the faunule of Palmer's post-Aphelaspis TABLE 4. TRILOBITES ASSIGNED TO APHELASPIS ZONE, of the Crepicephalus, Aphelaspis, Zone of Texr.s certainly is NOT GREAT BASIN, BY PALMER (1965) post-Aphelaspis, that it is only slightly Dunderbergia, and Elvinia Zones in these Aphelaspis buttsi sections. He recognized (1960a) an upper younger than the faunule assigned to the Aphelaspis haguei Aphelaspis brachyphasis and a lower subzone in both the Aphelaspis Aphelaspis Zone in Texas by Palmer, and Aphelaspis subdita and the Dunderbergia Zones. that it represents the same time span as the Aphelaspis longispina Olenaapella separata In June 1965, Rasetti published an faunule of the middle subzone and possibly Olenaspella regularis Cheilocephalus brevilobus analysis of the Upper Cambrian trilobite the base of the upper subzone of the Glaphyraspis orncta faunas of northeastern Tennessee. Very Aphelaspis Zone of Tennessee (see Table 9). Terranovella brevis Blountia bristolensis detailed collecting was done through the Consequently, in all my recent papers Listroa toxoura Cedaria faunules in the upper Maryville (Lochman-Balk, 1970, 1971, 1972), I have Hardyoides minor Limestone and basal Nolichucky Forma- considered that only faunules of the tion, and through the Crepicephalus and Aphelaspis Zone time span are present in the TABLE 5. TRILOBITES ASSIGNED TO DICAHTHOPiGE ZONE, Aphelaspis faunules in the upper Texas sections. The faunules "spanning the GREAT BASIN, BY PALMER (1965) Nolichucky Formation to the highest median level of the Dunderbergia biozone" Aphelaspis subdita fossiliferous beds. Aphelaspis occurs in all (Lochman-Balk and Wilson, 1958, p. 333), Tumicephalus depressus Dicanthopyge quadrata faunules overlying the Crepicephalus as- as developed in Nevada, are all absent from Dicanthopyge convergens Dicanthopyge reaucta semblage, and Rasetti placed all the faunules central Texas; the disconformity between Olenaspella regt.laris in the Aphelaspis Zone (see Table 3). Rasetti the Lion Mountain Sandstone member and Olenaspella paucisegmenta Listroa toxoura divided the zone into lower, middle, and the Welge Sandstone Member occupies the Dunderbergia brcvispina time span of at least the upper half of the late Cheilocephalus crranulosus upper subzones, discussed in detail the Bromella Veritas association and appearance of the various Dresbachian (see Table 9, col. 6). Hardyoides mimiom Prehousia prima species in each subzone (1965, p. 30—37) Palmer (1965) described the late Dres- and indicated the range of each species bachian faunas of the Great Basin as the (1965, Fig. 1, p. 36). These faunules are very trilobites of the Pterocephaliid biomere. occurring in these two faunules, Olenaspella These are the faunules that he had assigned paucisegmenta and Bromella Veritas range

TABLE 3. TRILOBITES ASSIGNED TO APHELASPIS ZONE, to the Aphelaspis, Dunderbergia, and into the succeeding Prehousia Zone, and NORTHEASTERN TENNESSEE, BY RASETTI (1965) Elvinia Zones in earlier publications. He Cheilocephalus granulosus continues higher (1965) recognized (in ascending order) five into the Dunderbergia Zone. Three species Upper Subzone Aphelaspis tarda zones, Aphelaspis, Dicanthopyge, Pre- occur in both faunules, and Listroa, Aphelaspie punctata housia, Dunderbergia, and Elvinia; he Hardyoides, and Aphelaspis are restricted to Dytremacephalus angulatuB Dytremacephalus sulcifrons considered (1965, p. 6, Fig. 3) the Great the two zones. Tumicephalus depressus, a Dunderbergia tennesseensis Basin Aphelaspis, Dicanthopyge, and common species in the Dicanthopyge Zone, Cheilocephalus brachyops Middle Subzone Prehousia Zones to be the equivalent of his represents the same genus as Aphelaspis Aphelaspis washbumensis Aphelaspis Zone in Texas and the tumifrons (Palmer, 1965, p. 90; Rasetti, Aphelaspis cajtrivo Dunderbergia Zone to be equivalent to his 1965, p. 37), which Rasetti finds in the Aphelaspis laxa Aphelaspis quadrata post-Aphelaspis Zone in Texas. Palmer did middle Aphelaspis Zone of Tennessee. In Aphelaspis rotundata Aphelaspis palmeri not indicate (1965, p. 6, Fig. 3) the Nevada, species of Dunderbergia first Aphelaspis arses relationship of his new zones to the appear in the upper Dicanthopyge Zone. Aphelaspis inermis Aphelaspis arsoidee Dunderbergia and Aphelaspis Zones as used The faunules of the two zones show a Aphelaspis tumifrons Aphelaspidella macropyge in his earlier publications. The position of significant relationship. The presence of Paraphelaspis vigilans the Dunderbergia-Aphelaspis Zone bound- Aphelaspis in both, as well as their Dytremacephalus angulatuB Dytremacephalus striotus ary (Palmer, 1960a), with reference to resemblance to the faunules of the Dunderbergia longifvons thickness and lithology, was shown on Aphelaspis Zone of Tennessee, leads me to Cheilocephalus sp. undet. Glaphyraspis declivis measured sections from Snake Range, Deep conclude that they comprise a single Glaphyraspis oderi Pseudagnostus cormturds Creek, and Cherry Creek. Comparison of faunizone assemblage best known as the Lower Subzone these sections with the correlation chart Aphelaspis Zone. Aphelaspis buttsi (Palmer, 1965, p. 14, Fig. 9) indicates thai: Aphelaspis lata Dimderbergia Zone Aphelaspis transversa Palmer (1960a) was placing the boundary Aphelaspis minor between the Dunderbergia and Aphelaspis Aphelaspis walcotti Palmer (1965) recognized a small faunule Cheilocephalus brevilobus Zones in the Great Basin at the base of his as the Prehousia Zone, succeeding the Coosella perplexa Tricrepicephalus sp. undet. 1965 Dunderbergia Zone. Dicanthopyge Zone. The nine trilobite taxa Glaphyraspis parva Glaphyraspis omata Palmer (1965) presented the detailed of this zone are listed in Table 6'. The first Glaphyraspis declivis four species are restricted to this faunule, Glaphyraspis oderi biostratigraphy of the late Dresbachian Blountia bristolensis faunules. I believe that this faunal succession although both Cerntiolimbus and Prehousia Blountia mimula represents an unbroken sequence through continue up into the Dunderbergia Zone,

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and Cheilocephalus bracbyops and trilobite taxa (Table 8). Because of the survival to maturity of so many variants in Dunderbergia calculosa range into the number of genera and species that range each population was possible only because Elvinia Zone and the upper Dunderbergia upward from the Dunderbergia faunizone, numerous trilobite habitats were unoc- Zone, respectively. The small Prehousia authors usually have determined the base of cupied and now available in the infralittoral faunule is a transition faunule between the the Elvinia Zone as the first appearance of zone, as the species of the Crepicephalus distinctive older faunules of the Aphelaspis Elvinia. assemblage, unable to adapt to the lower Zone and the distinctive younger faunules of water temperature, died out. Thus, the Palmer's 1965 Dunderbergia Zone. As ORIGINS OF THE LATE Aphelaspis faunules described from the shelf Aphelaspis has apparently become extinct DRESBACHIAN TRILOBITES and miogeoclinal sites are composed largely and as Cernuolimbus, Cheilocephalus The relatively sudden appearance of of genera and species evolving from brachyops, and Dunderbergia calculosa that Aphelaspis in shelf and miogeoclinal sites of Aphelaspis in response to these environmen- first appear in the Prehousia faunule, as well both eastern and western North America tal opportunities. The genera and species did as Prehousia, range well up into the marks the base of the Aphelaspis Zone and not exist prior to the appearance ofthe three Dunderbergia Zone, I conclude that the the beginning of the late Dresbachian Stage. ancestral species of Aphelaspis. Prehousia faunule should be placed as the The simultaneous extinction of the estab- The faunal assemblage that lived in the basal faunule of the Dunderbergia Zone lished C repicephalus Zone assemblage cool waters of the circalittoral to epibathyal faunal assemblage. without evidence of a physical break in the depths of the open ocean and that was sections suggests that the faunal change was contemporaneous with the earlier TABLE 6. TRILOBITES ASSIGNED TO PREHOUSIA ZONE, GREAT BASIN, BY PALMER (1965) caused by a relatively rapid change in one or Cedaria-Crepicephalus assemblage of the more physical factors of the marine infralittoral sites had a different composi- Prehousia indentata environment. At this critical horizon, the tion. It was composed of the three early Prehousia impolita Prehousia alata large and varied fauna of the Crepicephalus species of Aphelaspis, Olenaspella separata, Cernuolimbus laevifrons Cheilocephalus brachyops Zone is suddenly replaced by a small and one or two species of Eugonocare and Cheilocephalus granulosus assemblage composed primarily of Nericia. Palmer (1962, p. F32) placed all Dunderbergia calculosa Bromella Veritas Aphelaspis and Cheilocephalus representing four genera in his Aphelaspidinae, but he Olenaspella paucisegmenta two new and independent stocks. The stated that "it may be preferable to remove lithostratigraphy of the sections indicates these genera [the latter three] to a separate Palmer (1965) recorded 61 trilobite taxa that during this time the sedimentation rate subfamily." The similarity of Olenaspella for the Dunderbergia Zone of the Great over the shelves and most of the miogeo- and Nericia to the Olenidae has been noted Basin (see Table 7). Of the 24 genera, 19 clines was extremely slow so that no record by several authors (Wilson, 1954, 1956; make their first appearance in this of the dying out of the older assemblage was Henningsmoen, 1957; Palmer, 1962, p. 32). faunizone. From this large assemblage, only preserved in most areas. In Texas and Other elements of this open-ocean assem- Cheilocephalus granulosus, C. brachyops, Tennessee, however, partial records are blage were Olenus in the Acado-Baltic and Dunderbergia calculosa occur in beds known from the geologically short time span province and possibly one or two other below the base of Palmer's Dunderbergia during which the environmental change genera of the Olenidae, Cheilocephalus Zone, and the two latter species first appear took place; one species each of (Cheilocephalidae), several genera refer- in Palmer's upper Prehousia Zone. Six Tricrepicephalus, Coosia, Coosina, able to the Erixaniidae, Nasocephalus genera are restricted to the Dunderbergia Coosella, Blountia, and Llanoaspis (as well (Marjumiidae), Cedaria (Cedariidae), Zone: Minupeltis, Strigambitus, Erixanium, as the longer ranging Glaphyraspis) is found Meteoraspis (s.l.) and Tricrepicephalus (s. Morosa, Taenora, and Elburgia. Twelve associated with the earliest species of 1.) of the Tricrepicephalidae, Crepicephalus genera and twelve species continue into the Aphelaspis (see Table 9). borealis Lermontova 1940 (which Palmer Elvinia Zone. Of these, Dunderbergia I believe that the environmental change [1965, p. 64] considered an unnamed genus nitida, D. variagranula, Iddingsia inter- was a rapid cooling of the ocean waters; the closely related to Olenaspella and media, Pterocephalia sanctisabae, Sig- cooling occurred over a relatively short span Eugonocare), and a number of agnostid mocheilus flabellifer, Housia ovata, and of geologic time, comparable to that genera including Pseudagnostus, Elviniella laevis are common. The large and recorded for Pleistocene temperature Glyptagnostus, and Homagnostus. The distinctive assemblage of the Dunderbergia changes. Cheilocephalus, Aphelaspis, and nature of this assemblage is indicated by the Zone of the Great Basin sections in Nevada Olenaspella were genera which lived in the faunules described by Palmer (1962) from occupies "a position spanning the median cool waters of the open ocean. They may Alabama; by Wilson (1954, 1956) from level of the Dunderbergia biozone" have been benthonic forms living at boulders in the Woods Hollow Shale, (Lochman-Balk and Wilson, 1958). This circalittoral to epibathyal depths, or they Marathon uplift, Texas; and by Opik (1963, assemblage, with the inclusion of the may have been nektonic. Of these genera, 1967) from northwest Queensland, Aus- Prehousia Zone faunule at the base, should however, only Aphelaspis possessed the tralia. Elements of the assemblage evolved comprise the faunizone assemblage of the potential to fully exploit the cooling waters slowly through the time span of latest Dunderbergia Zone. over the infralittoral depths of the shelves Middle Cambrian, all of the Dresbachian and miogeoclines. Aphelaspis is the ances- Age, and through Elvinia Zone time. By the Elvinia Zone tral stock of most of the genera assigned to end of early Franconian time, the composi- Faunules of the Elvinia Zone faunal the Aphelaspididae as well as of Prehousia, tion of the assemblage had changed assemblage have been recognized and Dytremacephalus, Dunderbergia, and sufficiently for a new assemblage, the described from many localities in the Pterocephalia. The oldest species that Hungaia fauna, to be recognized in the eastern, central, and western United States. moved from the open ocean into the open-ocean sites for the remainder of the The faunules known from the shelf sites of miogeoclinal and shelf areas were probably Franconian Age. the craton are much more diversified than Aphelaspis brachyphasis, A. buttsi, and A. Although I regard Aphelaspis as the the faunules from the miogeoclinal sites of walcotti. Thousands of individuals of these ancestor of most of the genera of the the Great Basin. From the Nevada sections species comprised populations charac- "Pterocephaliid biomere," I do not think ofthe GreatBasin, Palmer (1965) records 37 terized by wide phenotypic variability. The that each particular genus and species

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TABLE 7. TRILOBITES ASSIGNED TO DUNDERBERGIA ZONE, GREAT BASIN, BY PALMER (1965)

Apachia butlerensis* Iddingsia intermedia Apachia prima Litooephalus bilcbatus Anechocephalus trigranulatus Litocephalus granulomarginatus Aphelotoxon acuminata Litooephalus venuculapeza Aphelotoxon granulosus Morosa brevispina Aphelotoxon limbata Morosa extensa Aphelotoxon marginata Morosa longispinc. Aphelotoxon punctata Minupeltis conservator Aphelotoxon spinosus Minupeltis definita Cernuolimbus depressile Oligometopus breviceps* Cernuolimbus granulosus Oligometopus contractus Cernuolimbus orygmatos Parahousia subeqvalis Cernuolimbus semigranulosus Prehousia diverte. Cheilocephalus braohyops Prehousia semicircularis Cheilocephalus granulosus Pterocephalia? pinctata Dunderbergia? anyta Pterocephalia coricava Dunderbergia bigranulosa Pterocephalia elongata Dunderbergia oaloulosa Pterocephalia sanctisabae* Dunderbergia nitida Pseudosaratogia leptogranulata* Dunderbergia variagranula Sigmocheilus flabellifer Dunderbergia polybothra Sigmocheilus grata Dytremacephalus asperaxis Sigmocheilus notha Dytremacephalus granulosus Sigmocheilus pogonipensis* Elburgia granulosa Strigambitus bilobus Elburgia intermedia Striganibitus? bU'-pharina Elburgia quirmensis Strigambitus transversus Elviniella laevis Strigambitus utdhensis Erixanium carinatum Simulolenus grannlatus Erixanium multisegmentus Simulolenus wilsoni Erixanium? brachyaxis Taenora expansa Housia ovata*

*As shown on range chart (PI. 21) but not in text. Palmer (1965).

evolved from its ancestor at exactly the same slightly different phenotypes were favored species present at each particular time would time in all the seaways on both the eastern by each of the different niches. Full respond in identical manner in all places so and western sides of the continent. adaptation to a particular niche would lead as to give rise to the synchronous develop- Evolutionary development of different taxa to reproductive isolation and the establish- ment of a genus and (or) species at all sites. results from the interaction of genetic ment of a species. I cannot accept the Dunderbergia was the earliest genus to variability of a population with the concept that identical habitats would be evolve from Apbelaspis, and it appeared in variations in the physical environment. As encountered at essentially instantaneous southern coastal waters in early Apbelaspis particular variants became adapted to the times all around the continent and that the Zone time. Palmer (1955) recognized a numerous vacant habitats and niches, genetic composition of the Apbelaspis single highly variable species named D.

TABLE 8. TRILOBITES ASSIGNED ~0 ELVINIA Z0>IE, GREAT BASIN, BY PALMER (1965)

Elvinia roemeri Bynumia globosa Elvinia granulata Kindbladia affinis Cheilocephalus brachyops Dokimocephalus pernasutus Dunderbergia variagranula Pseudosaratogia abnorrnis Dunderbergia nitida. Litocephalus magnus Iddingsia intermedia Pseudokingstonia exotica Iddingsia robusta Irvingella flohri Iddingsia utahensis Irvingella angustilimbatus Iddingsia similis Irvingella transversa Elviniella laevis Irvingella major Pterocephalia sanctisabae Stenanibon megagranulus Aphelotoxon marginata Stenambon paucigranulus Sigmocheilus pogonipensis Xenocheilos granulosus Sigmocheilus flabellifer Aciculolenus pecularis Housia ovata Anechocephalus spinosus Housia varrò Comanchia minus Oligometopus contractus Dellea? punctata Parahousia subequalis Simulolenus quadrisulaatus Parahousia constricta

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TABLE 9. NOMENCLATURE AND RELATION OF LATE DRESBACHIAN FAUNIZONES s Central Texas* Nevada and , Great Basin Northeastern Great Basin** Central Texas++ North America central Texas Tennessee#

Elvinia Zone Elvinia Zone Elvinia Zone Unknown Elvinia Zone Elvinia Zone Elvinia Zone

Hiatus? Hiatus?

post-Aphelaspis Dunderbergia Dunderbergia Unknown Dunderbergia Hiatus Dunderbergia Zone Zone Zone Zone Zone

Prehousia Zone

Aphelaspis Aphelaspis Aphelaspis Aphe laspis Dicanthopyge pos t-Aphelaspis Zone Zone Zone Zone Zone Zone Aphelaspis Zone

Aphelaspis Aphelaspis Zone Zone

*Palmer (1955) in Palmer (1965). **Palmer (1965). f Lochman-Balk and Wilson (1958). fiLochman-Balk (1970, 1971). §Palmer (1960a, 1960b, 1962). §§Lochman-Balk (1970, 1971, 1972, this rept.). #Rasetti (1965).

variagranula that occurs in his Aphelaspis Dytremacephalus was the second genus to maximum regression and early in the and post-Aphelaspis Zones. He illustrated develop from Aphelaspis, and its origin was ensuing transgression, it had moved west- several cranidia showing extremes ir. also in the southern coastal waters. D. ward; and P. concava is the earliest variation. In Tennessee, Rasetti recognized strictus appears near the base of the middle Pterocephalia species in the Great Basin, two more narrowly defined species, D. Aphelaspis Zone in Tennessee and is appearing in the upper half of the lower longifrons in his middle Aphelaspis Zone followed by D. angulatus and D. sulcifrons, Dunderbergia Zone. NOTE: Two correc- and D. tennesseensis high in the upper which survive into the highest beds of the tions should be made on Figure 10, Loch- subzone. Both species are derivable from the upper Aphelaspis Zone. In Texas, two man-Balk, 1970—the range of Ptero- Texas D. variagranula. In northeast Utah, species D. laevis and D. granulosus are cephalia should be extended into the cranidia of an unnamed species of associated with Aphelaspis walcotti in upper Aphelaspis Zone, and Tumicephalus Dunderbergia, resembling the cranidium Palmer's Aphelaspis Zone, and D. should be placed in the Aphelaspididae. shown by Palmer (1955, PI. 89, fig. 1), are granulosus continues into the highest beds The varying geographic and temporal associated with species of Aphelaspis in the preserved, probably correlative in time with distribution of these genera indicates that upper beds of the Nounan Formation. D. the base of the upper Aphelaspis Zone in each genus, at the time of its origin, still brevispina, the first species to appear in the Tennessee. D. granulosus is the earliest possessed a highly variable gene pool and Nevada assemblages, is associated with species recorded in the Nevada sections and throughout late Dresbachian time remained Tumicephalus depressus near the top of the appears in the middle third of the lower capable of giving rise to younger species Aphelaspis Zone (Palmer's upper Dunderbergia Zone. Palmer (1965, p. 85) adapting to the different habitats the genus Dicanthopyge Zone). D. brevispina belongs mentioned a possible earlier species from the encountered. The presence of Dunderbergia to a different and distinct lineage of variants, base of the Dunderbergia Zone (Palmer's does not automatically place the associated that were shown by Palmer (1955, PI. 88, fig. Prehousia Zone). faunule in the Dunderbergia Zone. The 7) as one of the extremes. Cranidia of this Pterocephalia was the third genus to biozone of the genus extends from the lineage in the Nevada sections were develop, and its origin was apparently in the middle of the Aphelaspis Zone to very near identified by Palmer (1965) as D. calculosa Texas coastal waters. P. concava appears in the top of the Elvinia Zone. The total from the base of the Dunderbergia Zone the highest beds preserved in the Aphelaspis composition of each associated faunule (Palmer's Prehousia Zone) and as D. variag- Zone of Texas (Palmer's post-Aphelaspis must be carefully considered before its ranula, ranging from the upper Zone). It is not known whether the genus correct temporal position can be deter- Dunderbergia Zone into the Elvinia Zone. ever moved eastward; but during the time of mined.

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REFERENCES CITED Interscience P jbs., Inc., p. 79-167. Great Basin: U.S. Gesl. Survey Prof. Paper 1972, Cambrian of the Rocky Mountain 400B, p. 289-290. Drewes, H., and Palmer, A. R., 1957, Cambrian region, in Geologic atlas of the Rocky 1960c, Trilobites of the Upper Cambrian rocks of southern Snake Range, Nevada: Mountain region: Rocky Mtn. Assoc. Dunderberg Shale, Eureka district, Nevada: Am. Assoc. Petroleum Geologists Bull., v. Petroleum Geologists, p. 60-75. U.S. Geol. Survey Prof. Paper 334—C, p. 41, p. 104-120. Lochman-Balk, C , and Wilson, J. L., 1958, 53-107. Freeman, Tom, 1969, Cement-composition dis- Cambrian jiostratigraphy in North 1962, Glyptagnostus and associated trilo- continuity in the Cambrian of Texas and its America: Jour. Paleontology, v. 32, p. bites in the United St ites: U.S. Geol. Survey stratigraphic implications: Geol. Soc. 312-350. Prof. Paper 374-F, 49 p. America Bull., v. 80, p. 2095-2096. Nolan, T. B., Mer-iam, C. W., and Williams, J. 1965, Trilobites of the Late Cambrian • Henningsmoen, G., 1957, The trilobite family S., 1956, The stratigraphic section in the Pterocephaliid biomi re in the Great Basin, Olenidae; with description of Norwegian vicinity of Eureka, Nevada: U.S. Geol. United States: U.S. Geol. Survey Prof. Paper material and remarks on the Olenid Survey Prof. I'aper 276, 77 p. 493,101 p. and Tremadocian series: Norske Opik, A. A., 1963. Early upper Cambrian fossils 1971, Upper Cambr.an faunai patterns on Vidensk.-Akad. Oslo Skr., Mat.-Naturv. from Queensland: Australia Bur. Mineral the craton: Discussion: Geol. Soc. America Kl., no. 1,304 p. Resources, Geology and Geophysics Bull. Bull., v. 82, p. 927-930. Howell and others, 1944, Correlation of the 64,133 p. Rasetti, Franco, 1965, Upper Cambrian trilobite Cambrian formations of North America: 1967, The Mindyallan fauna of northwest- faunas of northeastern Tennessee: Smithso- Geol. Soc. America Bull., v. 55, p. ern Queensland: Australia Bur. Mineral nian Misc. Colin., v. 148, no. 3,127 p. 993-1003. Resources, Geology and Geophysics Bull. Wilson, J. L., 1954, Late Cambrian and early Kurtz, V. E., 1971, Upper Cambrian Acrotretidae 74, v. 1,404 p.; v. 2,167 p. Ordovician trilobites from the Marathon from Missouri: Jour. Paleontology, v. 45, p. Palmer, A. R., 1955 (1954), The faunas of the Uplift, Texas: Jour. Paleontology, v. 28, p. 470^76. Riley Formation in central Texas: Jour. 249-285. Lochman, Christina, 1938, Upper Cambrian Paleontology, v. 28, p. 709-786. 1956, Revisions in nomenclature and new faunas of the Cap Mountain Formation of 1960a, Some aspects of the early Upper species of Cambro-Ordovician trilobites Texas: Jour. Paleontology, v. 12, p. 72-85. Cambrian stratigraphy of White Pine from the Marathon Uplift, West Texas: Lochman-Balk, C., 1970, Upper Cambrian faunal County, Nevada and vicinity, in Geology of Jour. Paleontology, v. 30, p. 1341-1349. patterns on the craton: Geol. Soc. America east central Nevada: Intermnt. Assoc. Pe- Bull, v. 81, p. 3197-3224. troleum Geologists Guidebook 11th Ann. 1971, The Cambrian of the craton of the Field Conf., [960, p. 53-58. MANUSCRIPT RECEIVED BY THE SOCIETY, APRIL United States, in Holland, C. H., ed., 1960b, Identification of the Dunderberg 20,1973 Cambrian of the New World: New York, Shale of Late Cambrian age in the western REVISED MANUSCRIPT RECEIVED JULY 9,1973

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