Fossil Assemblage Zones Research Articles

Correlation and stratigraphic implications of the lowermost Cambrian small shelly fossils from new sites of South China

Early Cambrian small shelly fossils (SSFs) represent some of the earliest biomineralized examples of metazoans and are often extremely abundant and diverse, so can be useful for regional and intercontinental correlation in pre-trilobitic carbonate or phosphorite deposits. New SSF assemblages chemically extracted from the Cambrian Yangjiagou Member carbonates in the Fucheng area, southern Shaanxi Province, China. The SSFs include anabaritids, protoconodonts, hyolitheminths, maikhanellids, Quadrapyrgites , Archaeooides , Olivooides and Siphogonuchites . The recovered SSFs represent two previously identified SSF assemblage zones: the Anabarites trisulcatus – Protohertzina anabarica assemblage zone and the succeeding Paragloborilus subglobosa – Purella squamulosa assemblage zone. The early Cambrian fossil assemblage zones described from this locality are correlated on a regional scale across the Yangtze Platform from eastern Yunnan, the Three Gorge region of western Hubei, northern Sichuan, the Ningqiang and Xixiang regions of southern Shaanxi and the Nemakit–Daldynian Stages of Siberia. The results reveal that the Yangjiagou Member is provisionally equivalent to the Zhongyicun Member of Yunnan, the Yanjiahe Formation of Hubei, the Maidiping Formation of Sichuan and the Kuanchuanpu Formation of Shaanxi. This paper offers new evidence and fossil data for the location of the Precambrian–Cambrian boundary in the Micangshan area of South China.

New Small Shelly Fossils (AcanthocassisandXinlispinaGen. Nov.) from the Fortunian Stage (Early Cambrian) in Southern China

AbstractWe describe new material of three‐dimensionally phosphatized small shelly fossilsAcanthocassisandXinlispinagen. nov. from the Fortunian Stage (early Cambrian) of southern Shaanxi and northern Sichuan Provinces. The new materials allow description of the delicate morphology of these skeletons, and also their skeletogenesis.AcanthocassisandXinlispinahave comparable morphological features: a main branch and radially arranged sub‐branches. They differ from each other in many details, e.g., the presence of a single central branch only inXinlispina, and the presence of small nodes only inAcanthocassis. Acanthocassiscannot be a naked anthopolyp or hydropolyp because of the more‐or‐less stiffened cuticle and the absence of a mouth.AcanthocassisandXinlispinadiffer from coeval sponge spicules and chancelloriid sclerites and rosettes of crossed pedicellariae of echinoderms, and might be cuticular ornaments of animals of unclear affinities. They occur in the first small shelly fossil assemblage zone, and could be adopted as auxiliary fossils for biostratigraphic correlation in southern China.

Turonian-Santonian echinoids from Wadi Qena, Eastern Desert, Egypt; a new arrangement of apical disc plating in spatangoids

Eighteen echinoid species (seven regular and eleven irregular) belonging to twelve genera have been described from the Turonian-Santonian succession of two sections located in the northern part of Wadi Qena, Eastern Desert. The diversity of the recorded species is low in the Turonian (six species), but comparatively high in the Coniacian-Santonian (twelve species). Of the recorded species, Most of these species (72%) are recorded for the first time from Wadi Qena area, one left in open nomenclature, Mecaster sp., represents a new species, and two, Phymosoma microtuberculatum and Thylechinus (T.) said, represent new records for Egypt. The taxonomic rank of Parapygus sudrensis has been changed. Phymosoma microtuberculatum which is known from the ‘Senonian’ of southwest Europe is recorded herein in the lower Turonian. Two echinoid assemblage zones are recognizable in each of the studied two sections. They are correlated with other fossil assemblage zones in Egypt. Faunal affinity and paleobiogeography of the species are discussed. A new arrangement of apical disc plating in spatangoids is described and discussed.

Stratigraphy of the Danek Bonebed (Upper Cretaceous Horseshoe Canyon Formation, central Alberta) and correlations with strata in the Drumheller and Grande Prairie regions

Although considerable work has been conducted on the stratigraphy and dinosaur assemblages of the Horseshoe Canyon Formation of southern Alberta, equivalent strata and assemblages in central Alberta remain poorly understood. Data from the Danek Bonebed (Edmonton, Alberta) are beginning to fill this gap. The bonebed occurs 4 m above the #9 Big Island Coal Seam. This stratigraphic position lies just below the middle of the Horseshoe Canyon Formation in the Edmonton region, and also lies below a thick, stratigraphically significant non-coaly interval that is expressed throughout central and southern Alberta. The stratigraphic position of the Danek Bonebed equates best with the uppermost Horsethief Member of the Horseshoe Canyon Formation in the Drumheller region and the upper part of Unit 4 of the Wapiti Formation in the Grande Prairie region. In both Drumheller and Grande Prairie, the correlated position of the bonebed underlies a zone of marine transgression (Drumheller Marine Tongue), which, in turn, includes the Campanian–Maastrichtian boundary. In the context of Geologic Time Scale 2004, we infer a late Campanian age of 71.0–71.3 Ma for the bonebed. The Danek’s dinosaurian assemblage is limited taxonomically, but compares well with the Edmontosaurus regalis – Pachyrhinosaurus canadensis fossil assemblage zone in the Drumheller region. We propose that a mega-herbivore faunal assemblage, characterized by Edmontosaurus and Pachyrhinosaurus, extended continuously across the climatically wet coastal plain of latest Campanian southern and central Alberta, and likely extended northwest into the North Slope of Alaska, where it persisted into the early Maastrichtian.

Late Cretaceous palynology and paleoclimate change: Evidence from the SK1 (South) core, Songliao Basin, NE China

Cretaceous climate was warmer than today. The Songliao Basin contains one of the most important Late Cretaceous non-marine deposits in China for the research of the paleoenvironment and paleoclimate. This research is based on core samples from the SK1(S) borehole. The strata sampled are the upper part of the Quantou Formation to member 2 of the Nenjiang Formation, where spores, pollen, dinoflagellates, and other microfossils are abundantly preserved. Based on analysis of the spores and pollen fossils from the core samples, the following six fossil assemblage zones have been recognized in ascending order: The Cicatricosisporites-Cyathidites-Pinuspollenites, Schizaeoisporites-Cyathidites-Classopollis, Cyathidites-Schizaeoisporites, Schizaeoisporites-Cyathidites-Proteacidites, Proteacidites-Cyathidites-Dictyotriletes, and the Lythraites-Callistipollenites-Schizaeoisporites zones. The six fossil zones range from the late Cenomanian to early Campanian. The Late Cretaceous dinoflagellate cysts in the Songliao Basin are of high abundance and low diversity. Specific phytoplankton types reflect salinity changes of the Songliao Lake. Paleoecology of the dinoflagellates suggests that sediments of members 2 and 3 of the Yaojia Formation (K2 y 2+3) were deposited in a freshwater environment, whereas members 2 and 3 of the Qingshankou Formation (K2 q 2+3) and members 1 and 2 of the Nenjiang Formation (K2 n 1+2) were deposited in freshwater to brackish water environments. Combined with the paleoecology of dinoflagellates and the palynomorph biozones, valuable information of the paleoclimate was provided. The quantitative analyses of spores and pollen fossils, such as vegetation type, climate type, and humidity type, diversity and dominance, indicate a relatively sub-humid, mid-subtropical paleoclimate, with slight climatic fluctuation and/or temporal change.

A note on the biostratigraphic application of Permian plant fossils of the Normandien Formation (Beaufort Group, Northeastern Main Karoo Basin), South Africa

Two new assemblages (farms Christina and Moorfield) of plant fossils belonging to the Glossopterid flora are described from the northeastern part of the Main Karoo basin, within the Late Permian Normandien Formation, Beaufort Group, Karoo Supergroup. The Normandien Formation comprises three sandstone members (lower Frankfort, Rooinek, upper Schoondraai) each overlain by an argillaceous interval. Two informal plant fossil assemblage zones are distinguished in the field: a “Christina assemblage zone” defined by Morphotype Pnc1, Morphotype Pnc2, Morphotype Pnc3 and Morphotype Pnc7, between the Frankfort and Rooinek sandstones; a younger “Moorfield assemblage zone” between the Rooinek and Schoondraai sandstones, defined by Morphotype Pnm1 , Morphotype Pnm2, Morphotype Pnm3, Rigbya arberioides and Sphenophyllum speciosum. These two proposed plant fossil assemblage zones enable subdivision of the Dicynodon therapod assemblage zone coincident with the Normandien Formation, and the two plant fossil zones have been successfully mapped out over a large area.

Yangtzedonta and the early evolution of shelled molluscs

The holotype ofYangtzedonta Yu, 1985 and its type species,Y. primitiva Yu, 1985, is an incomplete specimen ofXianfengella prima He et Yang, 1982. Therefore, based on the principle of priority, the namesYangtzedonta and Y.primitiva Yu (1985) should be abandoned. The fact that ven-tral valve ofXianfengella is bilaterally symmetrical indicates that they are not the left valve of a bivalved mollusc, as originally proposed by Yu. At present, the oldest certain bi-valve isXianfengoconcha elliptica Zhang, which occurs in the Early Cambrian Qiongzhusi Stage in China. The oldest known rostroconch isHeraultipegma yunnanensis He et Yang, which first occurs in the third small shelly fossil assemblage zone of the Early Cambrian Meishucunian Stage. The oldest known monoplacophoran,Maikhanella pristinis (Jiang), first occurs in the first small shelly fossil assemblage zone (Me-ishucunian Stage). Evidence derived from analyses of shell morphology, mode of growth, histology, and stratigraphic occurrence suggests that bivalves evolved from a branch of rostroconchs, and that rostroconchs in turn evolved from a branch of monoplacophorans. The hypothesis that these three groups originated simultaneously and independently at the beginning of the Cambrian and subsequently evolved in parallel, probably is incorrect.

Discovery of Trace Fossils from the Sinian—Cambrian Boundary Beds in Eastern Yunnan and Their Significance for Global Correlation1

Abstract There are abundant and highly varied trace fossils in the Sinian—Cambrian boundary beds in eastern Yunnan. Collections from 27 sections and their study give altogether 45 ichnogenera and 87 ichnospecies. Among them, 2 ichnogenera and 7 ichnospecies are new, and 31 known ichnogenera and 38 known ichnospecies first found in the region. According to their order of appearance in the boundary beds and their assemblage features, the trace fossils in the Sinian—Cambrian boundary beds in the region may fall into 4 trace fossil assemblage zones in ascending order. In the paper they are correlated with those in the equivalent horizons abroad and their geological significance is discussed preliminarily.

Microfossils from the Chert in the Lower Cambrian Shuijingtuo Formation at Miaohe, Zigui, Hubei Province1

Abstract This paper reports for the first time on the microfossils discovered in the black cherts of the basal part of the Lower Cambrian Shuijingtuo Formation at Miaohe village, Zigui County, Hubei Province, all of which were observed in thin sections. Nine genera, 9 species and 3 indeterminate species (including a new species) are described. According to these microfossils, the conclusion is made that the microfossil zone may be equivalent to the small shelly fossil assemblage zones 2‐3 of the Meishucun stage. They have provided another important line of evidence for the correlation of the Sinian‐Cambrian boundary strata with those of the adjacent areas.

Miocene biostratigraphy and biochronology of the Dove Spring Formation, Mojave Desert, California, and characterization of the Clarendonian mammal age (late Miocene) in California

i ng on other continents (Savage and Russell, 1983). The characterization of the NMLMA has undergone continuous revision since 1941, but the The Dove Spring Formation (DSF) is an 1,800-m-thick succes- first comprehensive redefinition was recently completed after a 12-year sion of fluvial, lacustrine, and volcanic rocks that contains a nearly effort (Woodburne, 1987). Detailed studies of local successions, such as continuous sequence of diverse vertebrate fossil assemblages. When the Dove Spring Formation (DSF), provide the data needed for further the North American provincial mammalian ages were originally de- refinement of the North American terrestrial biochronologic system, fined in 1941, the fossil fauna of the DSF (now part of the Ricardo Due to rapid rates of speciation in fossil mammals during Cenozoic Group) was one of four fossil assemblages named as principal correla- time, it is possible to construct detailed biostratigraphic histories that often tives of the Clarendonian mammal age. Early radiometric work depict complex evolutionary patterns. Terrestrial vertebrates are influ- yielded a maximum age of 10.0 Ma for this fossil assemblage, and by enced by tectonic barriers and local environmental factors, however, and correlation to the Great Plains of the United States, this date was these animals become isolated into regional zoogeographic provincial as- considered representative of Clarendonian time. s ociations. The significance of biostratigraphies developed in localized ba- Detailed geologic mapping and precise stratigraphic control of sins thus cannot be fully evaluated in the absence of independent fossils collected in the DSF permit the development of a biostratig- chronological control. raphy consisting of four mammalian fossil assemblage zones. The ; Radiometric-dating techniques provide a powerful tool for establish- biologic characterization of the Clarendonian mammal age in Califor- ing the desired age control. Radioisotopic dates (Evernden and others, nia is expanded on the basis of this succession of assemblage zones. 1964) have yielded valuable insights into timing of evolutionary events, Radiometric and paleomagnetic results provide a detailed chron- but these dates could only be applied to a limited number of fossil-bearing ologic framework that indicates a time span from at least 13.5 Ma to sequences, most found in the far-western United States. More recently, 7.3 Ma for the fossils of the DSF. Furthermore, the new sequence of studies utilizing magnetic polarity stratigraphy, often in conjunction with assemblage zones helps to fill faunal gaps that appear to exist at the radiometric dating, have been successfully applied to terrestrial sediments

中〜後期更新世における古植物相 東北地方を中心として

Middle-Upper Pleistocene strata yielding abundant macroscopic plant and pollen fossils are distributed here and there in the coastal plain and inland basin areas in Northeast Honshu, Japan. Among them, those in the southern part of Tohoku district are investigated in full detail. On the basis of stratigraphical distribution of the taxa of woody plants obtained from these strata, the local assemblage zones are recognized as shown in Table 1, namely, TODERA 1-2, TODERA 3, TODERA 4, TODERA 5-6, TODERA 7, TODERA 8, LIG, LG III, LG II and LG I fossil assemblage zones, in ascending order. LIG and LG I fossil assemblage zones can be subdivided into two subzones: the former is subdivided into LIGa and LIGb fossil assemblage subzones, and the latter into LG Ia and LG Ib subzones.The LG I fossil assemblage zone is assigned to the later cold time (about 35, 000-10, 000y.B.P. based on radiocarbon dating); the LG II fossil assemblage zone may be from the middle temperate time (about 50, 000-35, 000y.B.P. based partly on radiocarbon dating), and the LG III fossil assemblage zone may be the early cold time of the period corresponding to the Last Glacial Age in the glaciated areas. The LIG fossil assemblage zone is assigned to the Last Interglacial Age. Moreover, the fossil assemblage zones of TODERA 8, TODERA 7, TODERA 5-6, TODERA 4, TODERA 3 and TODERA 1-2 may date from the middle to early ages of the Middle Pleistocene.The fossil assemblages belonging to the LG II, TODERA 7 and TODERA 1-2 zones and LIGb subzone chiefly consist of the taxa commonly found in the temperate deciduous broadleaf forest in the Japanese Islands. On the other hand, the fossil assemblages belonging to the LG Ia subzone and TODERA 8 zone are chiefly composed of the taxa distributed in the subalpine to montane or the subarctic to boreal mixed conifer and deciduous broadleaf forests in the Japanese Islands, Kurile Islands and Sakhalin. The fossil assemblages belonging to the TODERA 5-6, TODERA 4, TODERA 3 and LG III zones and to the LIGa and LG Ib subzones consist of a mixture of the taxa in the temperate deciduous broadleaf forest and the taxa of needleleaf and broadleaf trees which are distributed in the subalpine to montane or the subarctic to boreal mixed conifer and deciduous broadleaf forests in Japan. The fossil assemblages belonging to the TODERA 4 zone and LIGa subzone include more taxa distributed in the temperate deciduous broadleaf forest than those in the subalpine to montane or in the subarctic to boreal mixed conifer and deciduous broadleaf forest. The fossil assemblages belonging to the TODERA 3, TODERA 5-6 and LG III zones and LG Ib subzone are composed of taxa consisting in opposite ratitos to those belonging to the TODERA 4 zone and the LIGa subzone.Although stratigraphcal gaps are often found in the Middle to Upper Pleistocene strata in Northeast Honshu, it is clearly recognized that the plant fossil assemblage composition periodically changed through the Middle to Late Pleistocene. In Northeast Honshu, the periodic oscillation of vegetation, which shifted between two forests represented by the present ones in the Japanese Islands, the temperate deciduous broadleaf forest and the boreal mixed conifer and deciduous broadleaf forest, became more remarkable with time during the Middle to Late Pleistocene.

阿武くま山地中央部における第四系と植物化石群 最終氷期における東北南部の植生変遷の一例

The Quaternary strata in the environs of Takine town in the central part of the Abukuma Mountains can be classified as shown in Table 1 and Figure 3. The Saru-uchi I Formation and the Saru-uchi II Formation are considered assignable to the Last Glacial Age on the basis of radiocarbon dates, regional tephra, paleomagnetic data and plant fossil assemblages (macroscopic and pollen fossils), and the Ishigami Formation to Early Holocene in age on the basis of radiocarbon date and plant fossil assemblages (macroscopic and pollen fossils).The Saru-uchi I Formation can be represented by a plant fossil assemblage zone Sr-1 of local significance. The Saru-uchi II Formation is classified into three local plant fossil assemblage zones, Sr-2, Sr-3 and Sr-4, in ascending order. The plant fossil assemblages characterizing the Sr-1 and Sr-4 zones seem to represent stadial floras and the one characterizing the Sr-2 zone an interstadial flora, all during the Last Glacial Age in the southern Tohoku District. And, the plant fossil assemblages characterizing the Sr-3 zone may represent a flora with intermediate characters between the stadial and interstadial floras. The Sr-2 zone is nearly suited to the Ts-b magnetozone containing an excursion, and assigned to ages of about 34, 000 to 30, 000 years B.P. as the results of radiocarbon dating.The plant fossil assemblages in the zones of Sr-1 and Sr-4 may represent the vegetation closely resembling to that of the subalpine zone in the central Honshu, and those in the zone of Sr-2 may represent a vegetation composed of taxas of the subalpine and montane zones in the central Honshu of Japan. The plant fossil assemblages in the zone of Sr-3 may represent the vegetation which contains the elements of the subalpine zone more abundantly than those of the montane zone.Finally, the characters of flora and vegetation in the southern Tohoku District during the Last Glacial Age are tentatively considered, based on the plant fossil assemblages from some areas.

NUMERICAL METHODS IN QUATERNARY PALAEOECOLOGY I. ZONATION OF POLLEN DIAGRAMS

SummaryThe concept of the pollen zone as a fossil assemblage zone is discussed, and the advantages of numerical approaches to the recognition and delimitation of such zones are considered. Existing procedures are reviewed, and original constrained agglomerative and divisive procedures are advanced. The results of these procedures are discussed in relation to existing zonation schemes for three sets of data, and the limitations and potentialities of the procedures are considered. The initial zonations suggested by visual inspection are, in general, confirmed by the numerical procedures. The application of these procedures to the subdivision of both pollen and macro‐fossil data in the same stratigraphical sequence is also discussed. Details are given of the computer time and storage required for the analyses.