Lower Cambrian Sequence Research Articles

The Lower Cambrian sequence in Skåne, Sweden

The Lower Cambrian sequence in Skåne, Sweden

Microfossils and small shelly fossils from the Lower CambrianHyolithesLimestone at Nuneaton, English Midlands

AbstractThe Lower Cambrian sequence at Nuneaton is outlined, paying particular attention to the 2 m thick Home Farm Member (including theHyolithesLimestone) and its faunal succession at the type locality, Woodlands Quarry, Hartshill. There follows the first modern description and illustration of microfossils and small shelly fossils from this member. Of thirty-two species covered here, twenty are described and illustrated from Nuneaton for the first time and eight of these are new records. The varied fauna includes phosphatic and calcareous microproblematica (especiallyColeoloides typicalis), protoconodonts, agglutinated foraminifera, cap-shaped molluscs, primitive bivalves, hyoliths, inarticulate brachiopods and sponges. The fauna has affinity with fossils in the top Tommotian to lower Atdabanian rocks from Siberia and China, from the Baltic area and the belt from southeast Newfoundland to Massachusetts.

Lower Cambrian trilobites from southern Swedish Lapland

Abstract Lower Cambrian trilobites from the Caledonian margin in the County of Vasterbotten (Vasterbottens lan), southern Swedish Lapland, are described and/or figured. Species of the orders Olenellida and Ptychopariida are recognized. Probably all of the trilobites are from strata that correlate with the middle to upper Lower Cambrian Holmia kjerulfi-group Zone. Holmia lapponica n.sp. is described. The autochthonous Upper Proterozoic—Lower Cambrian sequence in southern Swedish Lapland is briefly described.

Radiations and extinctions of plankton in the late Proterozoic and early Cambrian

The intrinsic palaeobiological importance of planktonic algal microfossils of Proterozoic and early Cambrian age has been widely documented1–8. The evidence supporting the biostrati-graphical significance of planktonic microfossils in the correlation of Upper Proterozoic and Lower Cambrian sequences has also been assessed1,4–8. We contend here that both within-flora (α) and total (γ) taxonomic diversity trends for late Proterozoic planktonic microfossils indicate that a distinct radiation of presumed cyst-forming eukaryotic plankters occurred during late Riphean and early Vendian (used here in the sense introduced in refs 1, 8). Following this, a mid- to late Vendian extinction episode reduced observable plankton diversity by some 70%, extirpating most morphologically complex, pre-existing taxa. A second radiation restored high plankton diversity levels, but not until well into the early Cambrian.

Precambrian rocks of the Ross Sea region

Abstract Precambrian rocks of at least two orogenic cycles form the basement of the Transantarctic Mountains between the Ross and Weddell Seas. Precambrian basement rocks also outcrop in Marie Byrd Land and in the intervening Ross Sea depression. In the central Transantarctic Mountains, the Beardmore Group comprises folded metagreywackes overlying shallow-water calcareous and quartzitic metasediments. In the Queen Maud and Thiel Mountains, similar metagreywacke terrains underlie and are intruded by silicic ignimbrite and quartz porphyry. Folded metagreywacke associations in northern Victoria Land and in Marie Byrd Land are tentatively correlated on the basis of late Proterozoic acritarch assemblages. The Beardmore Group and southern equivalents were deformed, metamorphosed and intruded by granites before the deposition of shallow-water Lower Cambrian carbonate and clastic sequences. Precambrian metamorphic complexes in the Transantarctic Mountains have undergone polyphase deformation and metamorphism. Mig...

Cambrian stratigraphy in Peary Land, eastern North Greenland

Cambrian strata in southern Peary Land occur in a continuous Outerop from J. P. Koch Fjord and Adams Gletscher in the west to lndependence Fjord in the eas! (fig. 15), forming a conspicuous rampart on the northern side of Wandal Dal. The Lower Cambrian sequence around Jørgen Brønlund Fjord has previously been described by TroeIsen (1949), Jepsen (1971) and Christie & Peel (1977), who recorded possible Cambrian dolomites of the Portfjeld Formation succeded by the clastic Buen Formation and the dolomitic Brønlund Fjord Formation, both of Early Cambrian age. Troelsen (1956) and Christie & Ineson (1979) have discussed a similar sequence which occurs near G.B. Schley Fjord in eastern Peary Land (fig. 1).

Archaeocyatha from New Jersey: Evidence for an intra-Cambrian unconformity in the north-central Appalachians

Research Article| December 01, 1976 Archaeocyatha from New Jersey: Evidence for an intra-Cambrian unconformity in the north-central Appalachians Allison R. Palmer; Allison R. Palmer 1Department of Earth and Space Sciences, State University of New York, Stony Brook, New York 11794 Search for other works by this author on: GSW Google Scholar Alexei Yu. Rozanov Alexei Yu. Rozanov 2Geological Institute, Academy of Sciences, Moscow, USSR Search for other works by this author on: GSW Google Scholar Author and Article Information Allison R. Palmer 1Department of Earth and Space Sciences, State University of New York, Stony Brook, New York 11794 Alexei Yu. Rozanov 2Geological Institute, Academy of Sciences, Moscow, USSR Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1976) 4 (12): 773–774. https://doi.org/10.1130/0091-7613(1976)4<773:AFNJEF>2.0.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 Allison R. Palmer, Alexei Yu. Rozanov; Archaeocyatha from New Jersey: Evidence for an intra-Cambrian unconformity in the north-central Appalachians. Geology 1976;; 4 (12): 773–774. doi: https://doi.org/10.1130/0091-7613(1976)4<773:AFNJEF>2.0.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 Archaeocyathids from the lower few metres of the Leithsville Formation in New Jersey correlate with faunas of the Forteau Formation of early Bonnia-Olenellus zone age [ Lenian (=Botomian) or early Elankian ] in Labrador and Newfoundland. The absence of younger Lower Cambrian regressive clastics known throughout most of the Appalachian region strongly suggests the existence of a previously unsuspected major unconformity within the Leithsville and equivalent carbonates of the thin Lower Cambrian sequences from eastern Pennsylvania to northern Massachusetts. 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.

Extension of the Cordilleran Miogeosynclinal Belt to the San Andreas Fault, Southern California

Correlations of marine sedimentary rocks in the San Bernardino Mountains and western Mojave Desert area with known uppermost Precambrian and some Paleozoic rocks of the southern Great Basin suggest that a nearly complete succession of Cordilleran miogeosynclinal rocks extends into southern California. Pre-Mesozoic rocks in the San Bernardino Mountains consist of (1) gneiss and schist of Precambrian age (in part older than 1,750 m.y.); (2) the Saragossa Quartzite, here considered to be latest Precambrian and Early Cambrian in age; and (3) the Furnace Limestone, the upper part of which is locally dated by megafossils as Mississippian and possibly Pennsylvanian or Permian but considered here to contain strata ranging in age from Early Cambrian to Permian(?). The Saragossa Quartzite contains distinct units that can be lithologically correlated confidently with parts of the uppermost Precambrian and Lower Cambrian sequence containing the Johnnie, Stirling, Wood Canyon, and Zabriskie Formations of the eastern Mojave Desert and the southern Great Basin. Some rock units on Quartzite Mountain in the western Mojave Desert are lithologically correlated with the uppermost Precambrian and Cambrian Wood Canyon, Zabriskie, Carrara, and Bonanza King Formations of the eastern Mojave Desert and southern Great Basin. The Cordilleran miogeosynclinal belt is obliquely truncated by the San Andreas fault in southern California; a displaced segment may occur in the Salinian block 450 km to the northwest. Cordilleran miogeosynclinal rocks also occur in northwestern Mexico east of the San Andreas fault, indicating a major change in trend of the geosyncline between the Great Basin and Mexico.

The sandstone sequence at Listarum—A contribution to the stratigraphy of the Lower Cambrian in Skåne, southern Sweden

Abstract The stratigraphy of the Lower Cambrian in SE. Skane, based partly on the results from five drill-holes made around the Listarum Quarry, and partly on the observations made in the Quarry, is presented. The results in general are in close agreement with those from the Simrishamn area. However there seems to be no justification for dividing the Lower Cambrian sequence in SE. Skane into various formations as done by some previous workers. It is suggested that in accordance with the lithostratigraphical scheme these “formations” must be considered as various members of a clastic sandstone-siltstone formation, which may be designated “Simrishamn Formation”. Fragments of olenellid trilobites have been recorded in the Norretorp Sandstone and there is evidence of a brachiopod fauna in the Brantevik Sandstone.

Initial Deposits in the Cordilleran Geosyncline: Evidence of a Late Precambrian (&lt;850 m.y.) Continental Separation

Upper Precambrian and Lower Cambrian strata in western North America are exposed in a narrow slightly sinuous belt extending from Alaska and northern Canada to northern Mexico, a distance of 2,500 mi. Within this belt, the strata thicken from 0 ft on the east to 15,000 to 25,000 ft in areas 100 to 300 mi to the west. The basal unit of this sequence is a diamictite (conglomeratic mudstone) which is widely distributed but discontinuous and is generally considered to be of glacial origin. Overlying sedimentary rocks consist predominantly of siltstone, shale, argillite, quartzite, and conglomerate. Tholeiitic basalt forms thick and widespread units near the base of the sequence but is sparse higher in the section. The distribution pattern and lithologic characteristics of the upper Precambrian and Lower Cambrian sequence fit the recently developed concept that thick sedimentary sequences accumulate along stable continental margins subsequent to a time of continental separation. The depositional pattern of the sequence is unlike that of underlying rocks, a relation consistent with the idea of a continental separation cutting across the grain of previous structures. The pattern is, on the other hand, similar to that of overlying lower and middle Paleozoic rocks, suggesting that the diamictite and post-diamictite rocks were the initial deposits in the Cordilleran geosyncline. Thick units of volcanic rock near the bottom of the sedimentary sequence indicate volcanic activity related to the thinning and rifting of the crust during the continental separation.

Diapiric Structures and Upper Proterozoic to Lower Cambrian Sedimentation in the Flinders Ranges, South Australia: ABSTRACT

During deposition of the Adelaide System (Upper Proterozoic) and Lower Cambrian Series, which together exceed 50,000 feet in thickness, an incompetent dolomite-silstone sequence (Callanna beds) formed piercement structures which influenced sedimentation. More than thirty discrete diapiric structures occur along fairly well-defined trends which are regarded as a basement fault system. Surface diameters of the eroded cores of the domes range up to several miles but the injection of carbonate-siltstone breccia has caused complication of some folds and resulted in irregular bodies with dike-like tongues. End_Page 337------------------------------ The main period of folding in the early Paleozoic has resulted in cross-sectional exposures of several diapirs. Bald cap structures and interdigitation of conglomerates with basin sediments along the flanks of the domes indicate repeated phases of diapir movement. Adjacent diapirs show evidence of uplift at widely different times from the glacial phase of the Late Proterozoic to the Early Cambrian. Boulder trains derived from the core of one diapir (Enorama) successively onlap along the flank of the structure and the unconformity may be traced for several miles. The same stratigraphic units (Umberatana Group) on the opposite flank, are truncated by subsequent movements of the core. An example of a structure of irregular form is the Arkaba diapir, which shows control over facies and thickness from the top of the Umberatana Group through the Wilpena Group to the Lower Cambrian. Other structures (Frome and Wirrealpa diapirs) exist on an important hinge zone which controlled Lower Cambrian deposition. The Frome diapir shows repeated intervals of erosion near the Adelaide System-Cambrian boundary and offers exposures of both diapiric and depositional contacts. The Wirrealpa diapir and associated faults separate a Lower Cambrian sequence to the south, comprising two formations (2,000 feet in thickness) from an equivalent section to the north, of seven distinct units totalling 10,000 feet in thickness. The diapir core was eroded during this interval. Exposed is a cross section of a graben which developed during the early Cambrian above a diapir (Oraparinna), the bounding faults of which controlled the development of an Archaeocyatha biohermal bank which intertongues with basinal facies. Diapiric structures which affected late Proterozoic and early Paleozoic deposition have been recorded 750 miles to the northwest of this province from the Amadeus Basin in central Australia. Evaporitic deposits there are reported within the Bitter Springs Limestone which occurs below a late Proterozoic glacial unit. End_of_Article - Last_Page 338------------

Structural Geology of Central Northern Egan Range, Nevada

Approximately 32,700 feet of Late Precambrian through Permian strata are exposed in the central northern Egan Range, Nevada. The lower 12,500 feet are a quartzose and argillaceous sequence including seven Precambrian formations and the Cambrian Prospect Mountain Quartzite and Pioche Shale. There follows 16,100 feet of strata composed predominantly of carbonates with minor shale and quartzite units, ranging from the Cambrian Eldorado Limestone through the Devonian Guilmette Formation. The exposed upper 4,100 feet of the Paleozoic include shales, siltstones, sandstones, and limestones; this sequence begins with the Upper Devonian and Mississippian Pilot Shale and ends within the Arcturus Formation of Permian age. Tertiary limestone conglomerate and volcanic rocks occur locally along the west margin of the range; these units are not involved in the internal structural complexities of the Egan Range. Regional low-grade metamorphism of Precambrian rocks produced metasiltstones, slates, phyllites, and metaquartzites prior to thrusting. Later local static thermal metamorphism associated with a quartz monzonite intrusion at Heusser Mountain created hornfelsic rock in a contact aureole in Precambrian strata. Mesozoic thrusting, displacing strata of Precambrian through Permian age, generally has moved younger over older rocks, and locally older over younger. Associated minor overturned folds indicate yielding to the east. Four major structural plates are separated by thrust faults. A major thrust above the Precambrian and Lower Cambrian clastic sequence may be part of a regional shearing-off or decollement plane. Higher major thrusts separate different facies of Paleozoic rocks. High-angle Cenozoic faults, characterized by small stratigraphic displacement and little topographic expression, occur within the range and displace thrusts. A later stage of basin-range deformation has converted the central northern Egan Range in part into a horst and in part into a tilted fault block.

Taconic Stratigraphy in Northern Washington County, New York

A lithostratigraphic sequence consisting of Lower and Upper Cambrian and Lower and Middle Ordovician clastic rocks has been mapped within the Taconic sequence in northern Washington County, New York, and an adjacent part of Rutland County, Vermont. The several lithostratigraphic units are dated by fossils collected from 28 localities, 20 of which are new. There are two Lower Cambrian formations. The lower, the Bull Formation, consists of two members: the Bomoseen Graywacke, dominantly of olive-green graywacke, and the overlying Mettawee Slate, dominantly of purple and green slates containing limestone conglomerates correlated with the type Schodack south of Schodack Landing, New York, and locally bearing the Elliptocephala asaphoides fauna. The overlying Lower Cambrian formation, now named West Castleton Formation but earlier named Schodack, consists essentially of black shales and limestone conglomerates locally bearing the Elliptocephala asaphoides fauna and, at one locality, an overlying Paedeumias-Bonnia fauna. Subdivision of this Lower Cambrian sequence into chronostratigraphic units is not possible at present because (1) there are lateral lithofacies gradations, (2) the first appearance of Lower Cambrian fossils is determined by the occurrence of a calcareous biotope within the time-span of the fauna, and (3) lack of evidence prohibits subdividing the Elliptocephala asaphoides fauna into upper and lower faunules. The fact that the Lower Cambrian faunas are mixed, including typical Atlantic province, Pacific province, and endemic genera, is not incompatible with a Taconic klippe hypothesis; the Taconic rocks could have been deposited anywhere between their present location and the nearest known occurrence of a typical Atlantic province fauna in eastern Massachusetts. Black shales with associated rotten-weathering bluish-gray sandstones, named the Hatch Hill Formation, overlie the West Castleton Formation unconformably. The Hatch Hill Formation contains a probable latest Cambrian graptolite fauna. The overlying Poultney Slate is divided into three members: (1) the A member, consisting of black shales with local interbedded limestone conglomerates and thin sublithographic limestones, overlain by (2) the B member, dominantly of bluish-gray argillites with thin beds of orange dolomitic quartzite locally in its lower part, and (3) the C member of dark-gray to black siliceous argillite, partly coeval with the B member in the northern part of the area mapped. The A member and, locally, the B member are lithologically identical with part of the Schaghticoke Shale at its type locality in the gorge of the Hoosick River at Schaghticoke, New York. The Poultney Slate contains Early Canadian (Late Tremadoc) graptolites in the lower part of the B member and Normanskill graptolites in its upper part. It passes conformably into the Indian River Slate of red and bluish-green slates. The Indian River Slate is overlain unconformably by the Pawlet Formation of graywackes and dark-gray or black shales with Normanskill graptolites. The Taconic rocks in northern Washington County occur in several approximately north-south-trending overturned folds whose axial planes dip eastward. The westward margin of the area is an overthrust from the east, which probably has a displacement of at least 20 miles.

STRATIGRAPHY, PALEONTOLOGY, AND PALEOGEOGRAPHY OF THE ELLIPTOCEPHALA ASAPHOIDES STRATA IN CAMBRIDGE AND HOOSICK QUADRANGLES, NEW YORK

An Elliptocephala asaphoides fauna from rocks of the “Taconic sequence” of eastern New York is a characteristic “Schodack” faunule comparable in age and composition to those described by Ford from the vicinity of Troy, New York, and by Walcott from northern Washington County. Several new species and a revision of described species show that this fauna is a transitional assemblage composed of some typical Atlantic province genera, some typical Pacific province genera, and several unique genera. Eleven trilobite genera are present, of which the two belonging to Dorypygidae are new. Two new trilobite and one new molluscan species are described. A detailed population study of Calodiscus lobatus (Hall) was possible on the large number of specimens. One limestone pebble with a diagnostic Middle Cambrian fossil and several with Tremadocian fossils were found in Prindle's collection. Outcrops in the Cambridge-Hoosick quadrangles give a limited stratigraphic section; but on the basis of distribution of several trilobite species two faunules of stratigraphic significance can be distinguished within the Elliptocephala asaphoides fauna. Lack of appreciation of the concept of lateral gradation of lithofacies has caused considerable stratigraphic confusion in the Slate Belt; yet this principle was emphasized by Dale and has been reaffirmed by all recent studies. Fossils and careful attention to details of the lithofacies units in this region show three consecutive Lower Cambrian phases or times of deposition during which one or several major lithofacies units were deposited. When the lithologic units were given formational names by Ruedemann a time-stratigraphic significance was incorrectly attached to them, and the sequences from Rensselaer County and from the Slate Belt were erroneously correlated. The position of first appearance of the lower Elliptocephala asaphoides faunule is the only significant datum level for age correlation in this Lower Cambrian sequence, indicating as it does the approximate age equivalence of all beds at this position and above, regardless of their particular lithofacies expression. The mixed composition of the Elliptocephala asaphoides fauna demands a revision of paleogeographic concepts. To account for mixing, the enclosing beds must have been deposited in essentially the same geographic relationship they now hold to the Lower Cambrian rocks of adjoining areas. The faunal assemblage also indicates that the major barrier between Atlantic province faunas and Pacific province faunas was a fundamental difference in environment and not, as previously assumed, a continuous land barrier. The Pacific province genera were normal inhabitants of an environment, a shallow submerged coastal shelf, which bounded the western, northern, and eastern shores of the old North American continent, Laurentia. The outer edge of this environment was the landward boundary of the Atlantic province environment, and the intermingling of faunal elements observed in the Elliptocephala asaphoides fauna could have occurred only in such a boundary area. It is postulated that in eastern New York and adjoining parts of Vermont one or more deeply downwarped basins developed on the shallow coastal shelf and that these basins had narrow connections eastward and southward with the Atlantic Ocean. The benthonic environment of these basins was similar to that of the open ocean and contrasted sharply with the biofacies of the surrounding shallow coastal shelf. Consequently, it would be inhabited by an assemblage primarily adjusted to ocean temperatures, pressures, and salinity and showing affinities to Atlantic province faunas dwelling to the south and east. Few normal benthonic species of the coastal shelf could establish themselves in such an alien environment, although, because of the geographic proximity of the two areas, sporadically drifted individuals might be found.