Lower Cambrian Strata Research Articles

Lapworthellids and other skeletonised microfossils from the Cambrian Stage 3 of the northern Montagne Noire, southern France

The Montagne Noire (southern France) possesses one of the most complete Cambrian successions in the western peri-Gondwana margin and might provide a good stratigraphic reference for both regional charts and international correlations. However, to date, the lower Cambrian succession of the northern Montagne Noire has been supposed to be devoid of biostratigraphically significant fossils. The complex tectonostratigraphic framework of the area (a range divided into Axial Zone, northern and southern Montagne Noire) exacerbated problems related to regional correlations and palaeogeographic reconstructions. As a result, the chronostratigraphic context of the lower Cambrian of northern Montagne Noire is still uncertain and stratigraphic reports have broadly relied on putative lithostratigraphic correlations with the southern Montagne Noire. The purpose of this study is to characterise, for the first time, the fossil record of carbonate beds and lenses of the northern Montagne Noire occurring at the top of the siliciclastic-dominated Marcory Formation, in order to provide regional bio- and chronostratigraphic constraints on lower Cambrian strata. Moreover, this study is aimed at improving international chronostratigraphic correlation. Carbonate beds and lenses cropping out along the Orque Cliff, in the Mélagues thrust slice, were investigated. They yielded a faunal assemblage constituted of molluscs (Igorella cf. ungulata and Igorella moncereti n. sp.), hyoliths (Conotheca brevica), chancelloriids (Archiasterella cf. pentactina and Allonnia sp.) and tommotiids (Lapworthella rete). L. rete is recorded in upper Meishucunian (Cambrian Stage 3) strata of the Yangtze Platform (South China) where it is used as index fossil of the Cambrian Stage 3 Sinosachites flabelliformis–Tannuolina zhangwentangi Assemblage Zone. Therefore, the presence of this tommotiid provides evidence that the studied carbonate beds and lenses are Cambrian Age 3 (Atdabanian according to the Siberian chart). The upper part of the Marcory Formation in the Mélagues slice, dated as Cambrian Stage 3, might represent a lateral equivalent of the mixed (carbonate-siliciclastic) Pardailhan Formation defined in the southern Montagne Noire.

The Ediacaran–Early Cambrian detrital zircon record of NW Iberia: possible sources and paleogeographic constraints

Ediacaran and Early Cambrian sedimentary rocks from NW Iberia have been investigated for detrital zircon U–Pb ages. A total of 1,161 concordant U–Pb ages were obtained in zircons separated from four Ediacaran samples (3 from the Cantabrian Zone and one from the Central Iberian zone) and two Lower Cambrian samples (one from the Cantabrian Zone and one from the Central Iberian Zone). Major and trace elements including REE and Sm–Nd isotopes were also analyzed on the same set of samples. The stratigraphically older Ediacaran sequence in the Cantabrian Zone has a maximum sedimentation age of ca. 600 Ma based on detrital zircon content and is intruded by ca. 590–580 Ma granitoids constraining the deposition of this part of the sequence between ca. 600 and 580 Ma. The stratigraphically younger Ediacaran sequence in the Cantabrian Zone has a maximum sedimentation age of ca. 553 Ma. The Ediacaran sample from the Central Iberian Zone has an identical within error maximum sedimentation age of ca. 555 Ma. The detrital zircon U–Pb age patterns are very similar in all the Ediacaran samples from both zones including the main age groups ca. 0.55–0.75 Ga, ca. 0.85–1.15 Ga and minor Paleoproterozoic (ca. 1.9–2.1 Ga) and Archean (ca. 2.4–2.6 Ga) populations. Kolmogorov–Smirnov statistical tests performed on this set of samples indicate that they all were derived from the same parent population (i.e., same source area). The same can be said on the basis of Nd isotopes, REE patterns and trace element concentrations. The two Cambrian samples, however, show contrasting signatures: The sample from the Cantabrian Zone lacks the ca. 0.85–1.15 Ga population and has a high proportion of Paleoproterozoic and Archean zircons (>60 %) and a more negative eNd and higher TDM values than the Ediacaran samples. The Early Cambrian sample from the Central Iberian Zone has the same U–Pb detrital zircon age distribution (based on KS tests) as all the Ediacaran samples but has a significantly more negative eNd value. These data suggest apparently continuous sedimentation in the NW Iberian realm of northern Gondwana between ca. 600 and 550 Ma and changes in the detrital influx around the Ediacaran–Cambrian boundary. The nature and origin of these changes cannot be determined with available data, but they must involve tectonic activity on the margin as evidenced by the angular unconformity separating the Ediacaran and Lower Cambrian strata in the Cantabrian Zone. The absence of this unconformity and the apparent continuity of detrital zircon age distribution between Ediacaran and Cambrian rocks in the Central Iberian Zone suggest that the margin became segmented with significant transport and sedimentation flux changes in relatively short distances. As to the paleoposition of NW Iberia in Ediacaran–Early Cambrian times, comparison of the data presented herein with a wealth of relevant data from the literature both on the European peri-Gondwanan terranes and on the terranes of northern Africa suggests that NW Iberia may have lain closer to the present-day Egypt–Israel–Jordan area and that the potential source of the hitherto enigmatic Tonian–Stenian zircons could be traced to exposed segments of arc terranes such as that described in the Sinai Peninsula (Be’eri-Shlevin et al. in Geology 40:403–406, 2012).

Ediacara-type fossils from Lower Cambrian strata in Qingzhen County, Guizhou Province, South China

INTRODUCTION The Ediacara fauna, generally believed to contain the oldest metazoan fossils, has been described from about 25 localities around the world (Hofmann et al., 1990). It was commonly considered that this fauna was restricted to Late Neoproterozoic (Glaessner, 1984). These were suggested to be mostly nonlocomotory quasi-autotrophs that were wiped out during the mass extinction at the Neoproterozoic– Cambrian boundary (Seilacher, 1984). The oldest Ediacara-type body fossils were discovered below Proterozoic glacial deposits (Hofmann et al., 1990), but mainly restricted to Late Neoproterozoic (Glaessner, 1984). However, some elements of this fauna were continually discovered in Cambrian strata (Hagadom and Waggoner, 2000; Hagadom et al., 2000; Jensen et al., 1998; Crimes et al., 1995; Narbonne et al., 1991). In Qingzhen County, Guizhou Province, South China, there is a well exposed stratigraphic succession spanning the Neoproterozoic–Cambrian boundary. Here, an Ediacara fauna, including Tirasiana

A section of Vendian in the east of West Siberian Plate ( based on data from the Borehole Vostok 3)

The Borehole Vostok 3 drilled in the east of the West Siberian Plate (Tomsk Region) revealed a Vendian section in the depth range 5002–3870 m, which was subdivided into the Poiga, Kotodzha, and Raiga Formations based on geological, geophysical, and paleontological data. In the Kotodzha and Raiga Formations, typical Upper Vendian fossils of Cloudina hartmanae and Namacalathus sp. were found along with diverse Platysolenites, which are commonly considered to be of zonal significance in Lower Cambrian strata. Hence, the stratigraphic interval with abundant diverse Platysolenites has a wider stratigraphic range than it was believed earlier and seems to cover the Upper Vendian and Lower Cambrian deposits. The Borehole Vostok 3 is the first Siberian occurrence of the fossils Namacalathus, the world's fourth occurrence of the Cloudina-Namacalathus association, and the first site where coexisting Platysolenites and typical Vendian organisms have been found. Therefore, the borehole provides one of the most informative (in paleontological context) Upper Vendian sections.

A Walcottella-like bradoriid (Arthropoda) from the lower Cambrian of Sweden

A probable new bradoriid genus and species, represented by a single specimen, is described tentatively as Walcottella? aff. apicalis Ulrich & Bassler from lower Cambrian strata of Sweden. The specimen comes from the Bergmyrhobben section west of Storuman in Västerbotten County, northern Sweden. It was found in mudstone in the lower part of the Grammajukku Formation, co-occurring with a rich acritarch assemblage of the Skiagia ornata-Fimbriaglomerella membranacea acritarch Zone that corresponds to the Schmidtiellus trilobite Zone. The specimen represents one of the oldest bradoriids known from the paleocontinent Baltica. Characteristics of the specimen are a dorsomedian to mid-dorsal acuminate nod and a flattened shell border along the free margin, the latter feature unknown from other bradoriid taxa. The specimen occurs at the same level where the first trilobites were found in the investigated section. The biogeographic affinities of the Baltic bradoriid genera to the bradoriid fauna of Avalonia, western Gondwana and Laurentia are reviewed and discussed.

The importance of Planolites in the Cambrian substrate revolution

Early Cambrian subtidal shelf substrates were characterized by low water content and steep chemical gradients, conditions likely facilitated by the presence of microbial mats as reflected by an abundance of microbially-mediated sedimentary structures in Lower Cambrian strata. Such substrate conditions would have been unfavourable for burrowing by benthic metazoans. A combination of environmental restrictions and a lack of adaptations to vertical burrowing likely prevented most benthic metazoans from burrowing infaunally in Early Cambrian subtidal shelf substrates. The eventual acquisition of burrowing adaptations by benthic metazoans later in the Cambrian promoted an increase in the depth and intensity of bioturbation and initiated a transition toward well-hydrated substrates in which extensive infaunal activity was possible. Siliciclastic units of the Lower Cambrian succession in the White–Inyo Mountains, eastern California, contain abundant horizontal bioturbation on bedding planes, as documented by bedding plane bioturbation indices, but little vertical bioturbation, as shown by ichnofabric indices and x-radiography. Planolites, a simple horizontal trace fossil, represents the dominant type of bioturbation in these units. Planolites is found in a range of diameters, indicating that more than one species of tracemaker likely produced this type of trace. Although these Planolites do not have a vertical component, their abundance on bedding planes indicates that the activities of Planolites tracemakers had a significant impact on subtidal shelf substrates, represented by Lower Cambrian units in the White–Inyo Mountains, early in the Cambrian substrate revolution.

Taphonomy and palaeoecology of the emuellid trilobite Balcoracania dailyi (early Cambrian, South Australia)

Monospecific assemblages of the trilobite Balcoracania dailyi occur in lower Cambrian strata within the Adelaide Geosyncline in South Australia. Biostratinomic data from single bedding plane assemblages within the Warragee and Coads Hill Members of the Billy Creek Formation and White Point Conglomerate reveal a range of taphonomic signatures from census to within-habitat, time-averaged assemblages. These assemblages are interpreted as having inhabited protected, shallow, marginal marine environments. Size–frequency distributions, coupled with taphonomic data, show that the Warragee Member census assemblage represents a living population in a physically stressful environment within a tidally-influenced lagoon, while the original population structure of the Coads Hill Member and White Point Conglomerate assemblages has been lost due to varying degrees of taphonomic overprinting. Integration of taphonomic, stratigraphic and sedimentological data supports the interpretation of B. dailyi as representing an opportunistic species. A preserved body cluster from the Warragee Member assemblage is considered to characterise a congregation formed for the purpose of synchronous reproduction and ecdysis, representing one of the oldest examples of gregarious behaviour in the arthropod fossil record. Furthermore, by analogy with modern horseshoe crabs, the high number of juveniles (i.e., protaspides and early meraspides) within the same assemblage are believed to be constituents of a nursery within the intertidal zone, with adults migrating into the shallows to copulate and spawn. Preserved moult ensembles from the Coads Hill Member and White Point Conglomerate have enabled the description of exuviation techniques for B. dailyi.

Trace- and rare-earth element geochemistry and Pb–Pb dating of black shales and intercalated Ni–Mo–PGE–Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb–Pb isotope dating for the Ni–Mo–PGE–Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni–Mo–PGE–Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb–Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni–Mo–PGE–Au sulfide ores, and two Pb–Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni–Mo–PGE–Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.

Lower Ovetian (Lower Cambrian) trilobites and biostratigraphy of the Pedroche Formation (Sierra de Córdoba, southern Spain)

The low Lower Cambrian rocks from the Sierra de Córdoba, which consist of well exposed mixed facies and abundant fossil assemblages showing long stratigraphic ranges throughout the Pedroche Formation, represent one of the best successions of this age in Europe. The fossil assemblages include diverse Ovetian archaeocyaths, trilobites, small shelly fossils, calcimicrobia, trace fossils and stromatolites. Trilobites are still poorly known, and thus they are the main objective of this work. The trilobites studied originate from three sections. At the Arroyo de Pedroche 1 section, cf. Bigotinella and Bigotina bivallata are replaced towards the top by Lemdadella linaresae, Lemdadella perejoni sp. nov. and, finally, by Eoredlichia cf. ovetensis. At the Arroyo de Pedroche 2 section, Lemdadella linaresae is replaced by Lemdadella perejoni sp. nov. and Eoredlichia cf. ovetensis, while at the Puente de Hierro section Lemdadella linaresae, L. aff. linaresae and Serrania verae occur together. These new biostratigraphic data confirm that the Pedroche Formation, originally defined as a repetitive sequence of four members, contains only two members. The new trilobite discoveries permit the first tentative correlation between the Ovetian of southern Spain and Lower Cambrian strata from the High Atlas (Morocco), Siberia, Antarctica and Carteret (France).

New species of Yochelcionella (Mollusca: Helcionelloida) from the Lower Cambrian of North Greenland

Two new species of the helcionelloid mollusc genus Yochelcionella Runnegar & Pojeta, 1974 are described from Lower Cambrian strata within the Brønlund Fjord Group of central North Greenland. Yochelcionella greenlandica n. sp. is also tentatively identified from continental slope deposits of the Browns Pond Formation of New York and the ‘Anse Maranda Formation’ of Québec. The internal mould of the almost orthoconic Yochelcionella gracilis n.sp. shows a pegma-like fissure between the apex and the snorkel, a feature ortherwise only reported in Y. fissurata Hinz-Schallreuter, 1997 from the Middle Cambrian of Bornholm.

Early Cambrian Salterella and Volborthella (Phylum Agmata) re‐evaluated

The genus Volborthella is removed from synonymy under Salterella and placed in the extinct phylum Agmata. Volborthella is more restricted geographically and occurs in older Lower Cambrian strata than Salterella, but distinguishing younger specimens of that genus from poorly preserved Salterella is difficult. Vologinella is not related to Volborthella or other Agmata. Other genera assigned to the phylum by various workers are discussed, but their assignment to this phylum is either enigmatic or rejected. The published concept that specimens of Volborthella and Salterella are agglutinated sclerites or spines on a larger soft-bodied organism is discussed. The material on which this notion is based is re-illustrated and the notion rejected in favor of the view that these conical forms are the hard parts of discrete organisms.

Early Cambrian phytoplankton diversification and appearance of trilobites in the Swedish Caledonides with implications for coupled evolutionary events between primary producers and consumers

The newly examined Lower Cambrian strata in the Laisvall-Storuman area, central Swedish Caledonides, yield diverse and stratigraphically significant phytoplanktic organic-walled microfossils (acritarchs) associated with the olenellid trilobites of Holmia sp. that appear to be at the lowermost horizon ever recorded in the Caledonides. The acritarchs, recovered throughout the Grammajukku Formation, are taxonomically reviewed in the context of regional and global trends of phytoplankton diversity. The assemblages are assigned to acritarch zones Skiagia ornata-Fimbriaglomerella membranacea and Heliosphaeridium dissimilare-Skiagia ciliosa, corresponding to the Schmidtiellus mickwitzi and Holmia kjerulfi trilobite zones. The records of acritarch radiations and appearances of trilobites and other faunas in Baltica, and on a more interregional scale, are biochronologically correlated, revealing tightly coupled evolutionary events among primary producers and consumers. The timing of early diversifications of trilobites in various faunal provinces is discussed and the relative age of the oldest known non-mineralized arthropods from the Zawiszyn Formation in Poland is estimated.

Occurrence ofByronia Matthew andSphenothallus Hall in the Lower Cambrian of China

Rare phosphatic tubular fossils from the Lower-Middle Cambrian Kaili Formation of Guizhou Province, southern China were originally identified as non-calcified algae or ‘worms’ (ScoleciellusLiu). Re-examination of these fossils indicates that specimens identified as non-calcified algae areSphenothallus taijiangensis n. sp., while specimens identified asScoleciellus belong toByronia natus (Liu).Sphenothallus taijiangensis andByronia natus from Lower Cambrian strata in the Kaili Formation are the oldest known representatives of their genera. In addition,B. natus (Liu) is the only known species ofByronia with the exception ofB. annulataMatthew (Middle Cambrian, British Columbia).

A biota of Ediacaran aspect from lower Cambrian strata on the Digermul Peninsula, Arctic Norway

Three elements of the ‘Ediacara fauna’ are described from lower Cambrian strata on the Digermul Peninsula, Norway. Nimbia occlusa Fedonkin, 1980 and Tirasiana sp. occur approximately 80 m above the base of the Lower Breivik Member, which approximately coincides with the Neoproterozoic–Cambrian boundary. A specimen of Cyclomedusa sp. has also been found in the Lower Duolbasgaissa Member about 600 m above the boundary, in rocks of trilobite-bearing age.These discoveries add to a growing body of evidence that some elements of the dominantly Neoproterozoic Ediacara fauna continue into the Phanerozoic, thereby diminishing the scope of a possible late Neoproterozoic mass-extinction event.The taxa described here, particularly Nimbia and Cyclomedusa, also occur at many other localities within Neoproterozoic strata and, in common with other elements of the Ediacara fauna, display remarkable morphological variation. Some of this diversity in form is probably caused by environmental and preservational factors. The possibility that it may, at least in part, reflect an inability of these early life forms to replicate faithfully their genes during reproduction should, however, not be overlooked.

The Citronen Fjord massive sulphide deposit, Peary Land, North Greenland: discovery, stratigraphy, mineralization and structural setting

The Citronen Fjord massive sulphide deposit in the Lower Palaeozoic of North Greenland is the world's most northerly base metal mineralization. Since discovery in 1993, it has been intensively investigated by geological and geophysical surveys, and by drilling. The deposit is generally flat lying with a thickness up to 50 m; it extends from outcrop level to depths of 300 m.
 Three main stratiform sulphide sheets occur within a 200 m thick stratigraphic sequence; these are composed of massive and bedded pyrite with variable amounts of sphalerite and minor galena. The proven mineralization is continuous over a strike length of at least 3 km with a maximum width of 500 m; an additional 5 km of mineralization along the same trend is suggested by geological mapping and gravity surveys. The total tonnage of sulphides is estimated to exceed 350 million tons. The overall base metal resource is estimated at 20 million tons of 7 per cent zinc, with a higher grade core of 7 million tons containing 9 per cent zinc and 1 per cent lead.
 The Citronen Fjord deposit is located at the eastern end of the Palaeozoic Franklinian Basin that extends through the Arctic Islands of Canada and across northern Greenland. Its discovery is an example of a successful exploration strategy based on regional evaluation, sparse but telltale surface mineralization observations and low-cost logistics: a skidoo-sledge expedition. The stratiform mineralization is hosted in the dark argillaceous rocks of the Amundsen Land Group of latest Ordovician to Early Silurian age that comprises a starved basin sequence of cherts and shales with siltstones and mudstones, punctuated by carbonate debris flow conglomerates derived from the nearby southern carbonate shelf. The Lower Palaeozoic strata at Citronen Fjord are part of the southern margin of the North Greenland Fold Belt characterized by southerly-facing folds and thrust faults.
 A new geological map of the Citronen Fjord area is presented featuring Cambrian, Ordovician and Silurian strata, with two north-south cross-sections illustrating the main structure. Twelve informally-named lithostratigraphic units are recognized and comments given on correlation to the regional stratigraphy. Tectonic contacts separate Lower Cambrian strata from the Ordovician-Silurian part of the succession. It is concluded that the Citronen Fjord stratigraphy could be of local development in a sub-basin controlled by syn-genetic faults.
 The lead-zinc deposit is interpreted to be of sedimentary-exhalative origin formed by the precipitation of sulphides from metal-bearing fluids introduced onto the sea-floor through underlying fractures. The significant components of this deposition model include the existence of a tensional tectonic regime, deep-seated fractures and a restricted sub-basin morphology. Massive to dendritic-textured pyrite is interpreted to represent vent-facies deposition while the bedded sulphides are taken to be the corresponding distal facies. The precise tectonic control of the fractures is debatable, as is the role of the so-called Navarana Fjord Escarpment - a palaeo-topographic feature marking the junction between shelf and trough that is assumed to lie immediately to the south of the Citronen Fjord.

The Citronen Fjord massive sulphide deposit, Peary Land, North Greenland: discovery, stratigraphy, mineralization and structural setting

The Citronen Fjord massive sulphide deposit in the Lower Palaeozoic of North Greenland is the world's most northerly base metal mineralization. Since discovery in 1993, it has been intensively investigated by geological and geophysical surveys, and by drilling. The deposit is generally flat lying with a thickness up to 50 m; it extends from outcrop level to depths of 300 m.
 Three main stratiform sulphide sheets occur within a 200 m thick stratigraphic sequence; these are composed of massive and bedded pyrite with variable amounts of sphalerite and minor galena. The proven mineralization is continuous over a strike length of at least 3 km with a maximum width of 500 m; an additional 5 km of mineralization along the same trend is suggested by geological mapping and gravity surveys. The total tonnage of sulphides is estimated to exceed 350 million tons. The overall base metal resource is estimated at 20 million tons of 7 per cent zinc, with a higher grade core of 7 million tons containing 9 per cent zinc and 1 per cent lead.
 The Citronen Fjord deposit is located at the eastern end of the Palaeozoic Franklinian Basin that extends through the Arctic Islands of Canada and across northern Greenland. Its discovery is an example of a successful exploration strategy based on regional evaluation, sparse but telltale surface mineralization observations and low-cost logistics: a skidoo-sledge expedition. The stratiform mineralization is hosted in the dark argillaceous rocks of the Amundsen Land Group of latest Ordovician to Early Silurian age that comprises a starved basin sequence of cherts and shales with siltstones and mudstones, punctuated by carbonate debris flow conglomerates derived from the nearby southern carbonate shelf. The Lower Palaeozoic strata at Citronen Fjord are part of the southern margin of the North Greenland Fold Belt characterized by southerly-facing folds and thrust faults.
 A new geological map of the Citronen Fjord area is presented featuring Cambrian, Ordovician and Silurian strata, with two north-south cross-sections illustrating the main structure. Twelve informally-named lithostratigraphic units are recognized and comments given on correlation to the regional stratigraphy. Tectonic contacts separate Lower Cambrian strata from the Ordovician-Silurian part of the succession. It is concluded that the Citronen Fjord stratigraphy could be of local development in a sub-basin controlled by syn-genetic faults.
 The lead-zinc deposit is interpreted to be of sedimentary-exhalative origin formed by the precipitation of sulphides from metal-bearing fluids introduced onto the sea-floor through underlying fractures. The significant components of this deposition model include the existence of a tensional tectonic regime, deep-seated fractures and a restricted sub-basin morphology. Massive to dendritic-textured pyrite is interpreted to represent vent-facies deposition while the bedded sulphides are taken to be the corresponding distal facies. The precise tectonic control of the fractures is debatable, as is the role of the so-called Navarana Fjord Escarpment - a palaeo-topographic feature marking the junction between shelf and trough that is assumed to lie immediately to the south of the Citronen Fjord.

Esmeraldina rowei and associated Lower Cambrian trilobites (1f fauna) at the base of Walcott's Waucoban series, southern Great Basin, U.S.A.

Walcott described the If fauna from Silver Peak Range, Nevada in 1910 as consisting of Nevadia weeksi n. sp. and gen. and Holmia rowei n. sp. (herein recognized as Esmeraldina rowei). Being the oldest trilobite fauna known at the time, it played an important roll in Walcott's locating the base of his Lower Cambrian Waucoban Series. The original If collection is reviewed, as is more material collected near the type locality, “Nevadella” Zone, Montenegro Member of the Campeto Formation. Additional trilobite taxa herein recognized in the If collection are Esmeraldina? cometes n. sp., Esmeraldina lidensis n. sp., Palmettaspis consorta n. gen. and sp., and Palmettaspis parallela n. sp. A close similarity between E. rowei and the type species for Holmia in Baltica led Walcott to a controversial Laurentia–Baltica correlation. His incorporation of three trilobite taxa among his syntypes for Holmia rowei also posed a problem. Overriding these faults was Walcott's foresight in using the 1f fauna in his Waucoban concept. Even today, after the 1992 international agreement to lower the base of the Cambrian to a pre-trilobite horizon, the Waucoban is being applied in Canada to upper Lower Cambrian strata.

Covariance of structural and stratigraphic trends: Evidence for anticlockwise rotation within the Walker Lane belt Death Valley region, California and Nevada

Large‐magnitude relative rotations of range‐scale structural blocks are inferred to be products of crustal extension in the Death Valley region, in California and Nevada. Reconstructions of the extended terrain restore pre‐Tertiary contractile structures with currently diverse trends into a relatively simple, north‐northeast trending thrust belt. We interpret trends of major contractile structures throughout the Death Valley region as characteristically discordant to, and thus geometrically independent from, stratigraphic trends. We compare trends of pre‐Tertiary contractile structures with paleoflow orientations in Lower Cambrian strata throughout the extended terrain. Significant differences between mean paleoflow orientations are consistent in magnitude and sense with differences observed in the structural trends. Available evidence does not support interpretation of paleoflow data from apparently rotated areas as representing an original paleogeography distinct from that of adjacent areas. Facies variations are present within the contractile structures. We interpret the strong covariance throughout the study area between structural and paleoflow trends of diverse orientations as evidence for vertical axis rotations. Combined rotation estimates from these data indicate clockwise rotations of 85° ± 12° for Bare Mountain and 73° ± 24° for the Striped Hills but anticlockwise rotations of 30° ± 35° and 87° ± 29°, respectively, for the northern and southern Grapevine Mountains. Such large rotations of opposite sense may be related to north‐south shortening accommodated by conjugate strike‐slip faults during large‐magnitude extension in the Death Valley region but are difficult to explain as products of regional dextral shear within the southern Walker Lane belt.

New constraint on the division of Cambrian time

A U-Pb zircon age of 530.7 ±0.9 Ma for a volcanic ash in the lower Placentian Series of the Avalonian terrane in southern New Brunswick provides a precise point for calibration of Early Cambrian biologic evolution. The ash is from the middle Rusophycus avalonensis Zone in Saint John, New Brunswick. This date is on subtrilobitic, Lower Cambrian strata that may be approximately correlative with the sub-Tommotian Manykaian Stage of Siberia and the lowest Meishucunian Stage of the South China platform. This age, when combined with published geochronologic data from the Cambrian, suggests that the Manykaian Stage may have lasted approximately 13 m.y. and that the Tommotian may have been considerably shorter.

New and extraordinary Early Cambrian sponge spicule assemblage from China

Research Article| January 01, 1994 New and extraordinary Early Cambrian sponge spicule assemblage from China Xi-guang Zhang; Xi-guang Zhang 1Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0, Canada Search for other works by this author on: GSW Google Scholar Brian R. Pratt Brian R. Pratt 1Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0, Canada Search for other works by this author on: GSW Google Scholar Geology (1994) 22 (1): 43–46. https://doi.org/10.1130/0091-7613(1994)022<0043:NAEECS>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Xi-guang Zhang, Brian R. Pratt; New and extraordinary Early Cambrian sponge spicule assemblage from China. Geology 1994;; 22 (1): 43–46. doi: https://doi.org/10.1130/0091-7613(1994)022<0043:NAEECS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The fossil record of siliceous sponges, compared with that of other skeleton- secreting Metazoa, is poorly known, based as it is on disarticulated spicules and sporadically preserved body fossils. Abundant spicules recovered from Lower Cambrian strata in Shaanxi, China, essentially double the known morphological diversity of siliceous sponges for that interval of geologic time. These fossils, along with a comparable coeval fauna from South Australia, have a remarkably modern aspect, thereby demonstrating that the principal siliceous sponge groups and styles of body architecture were established quickly in the earliest Phanerozoic as part of the Cambrian "explosion" and that they inhabited a variety of low-energy, relatively deep water settings. The similarity of spicule shape and variation to that of younger assemblages reflects a conservative architecture for the siliceous sponges. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.