Cambrian Ordovician Research Articles

Review of trilobite biofacies distributions at the Cambrian–Ordovician Boundary

AbstractDetailed analysis of trilobite assemblages at the Cambrian–Tremadoc transition reveals the presence of four, possibly five, biogeographic provinces: Baltic, North China, Southeast China, North American, and possibly Siberian. One or more discrete biofacies characterize the transition in each province. When plotted palaeogeographically these appear to be largely temperature controlled. Interdigitation of provincialized trilobite biofacies is recognized by the representation of dominant types of trilobite, olenaceans, ceratopygaceans, remopleuridaceans, dikelocephalaceans and leio-stegiaceans in particular, on key boundary sections. These sections, at Nochixtlán, Mexico; Batyrbay, southern Kazakhstan; Broken Skull River, District of Mackenzie, Canada; and Jiangshan–Chang-shan, western Zhejiang, China, permit the correlation of biogeographic provinces globally. As a result of the application of trilobite biostratigraphy relatively few problems prevent the maintenance of a Cambrian–Ordovician Boundary stratotype section in its traditional Baltic biogeographic setting.

Introduction to papers on the Cambrian–Ordovician Boundary

AbstractThe Working Group has the responsibility of recommending a specific level within a suitable stratigraphic section to serve as the global stratotype for the Cambrian–Ordovician Boundary. Commencing in 1974, comprehensive studies culminated in a plenary session in Calgary in 1985 resulting in decisions on the ‘golden-spike’ principle of selecting the boundary at a horizon just below the first influx of nematophorous graptolites. Conodonts are to be used as the primary guide for the selection of the specific horizon and the global stratotype section must have potential for studies using paleomagnetism, geochemistry and other non-biological correlation tools. The specific horizon will correspond approximately to the base of the Tremadoc Series of Wales and slightly higher than the base of Canadian Series as used in western North America.The Calgary meeting considered the Broom Point and Green Point sections in Newfoundland, Canada, and the Xiaoyangqiao section at Dayangcha, China, as prime candidates to serve as the global stratotype. A delegation from the Working Group inspected the Dayangcha sections in 1986. For this visit, comprehensive documentation and description of the sequence were prepared and published and are briefly summarized in the present issue.Specific uncertainties remain to be resolved for the Dayangcha and Newfoundland stratigraphic sections before the Working Group will be ready to recommend selection of a global stratotype.

Batyrbay Section, South Kazakhstan, U.S.S.R. – potential stratotype for the Cambrian–Ordovician Boundary

AbstractThe base of the Cordylodus proavus conodont Zone is the most appropriate horizon for the Cambrian–Ordovician Boundary. At Batyrbay the horizon reflects a significant global eustatic event that is marked by distinctive geochemical changes and by drastic changes in the trilobite and conodont faunas. The palaeomagnetic polarities change from reversal to normal just below this horizon.

The Nærsnes section, Oslo Region, Norway: trilobite, graptolite and conodont fossils reviewed

AbstractNew collections of trilobites, graptolites and conodonts, the latter figured for the first time, have been made from an unbroken, uniform sedimentary succession across the Cambrian–Ordovician Boundary. The zonal conodont Cordylodus proavus first appears in undoubted pre-Tremadoc strata. Additional conodonts show that the base of the Tremadoc lies within beds correlative with the Symphysurina Zone of North America and at a level above the base of the Hirsutodontus simplex subzone of the C. proavus Zone. Cordylodus lindstromi and Iapetognathus preaengensis first appear at the base of the Tremadoc. The olenid trilobite Jujuyaspis occurs in the same lower Tremadoc interval and has great potential for interregional correlation.

Taconic deformation and metasomatism in Proterozoic rocks of the easternmost Adirondacks

Proterozoic gneiss exposed in readcuts between Fort Ann and Whitehall, New York, is close to the Precambrian/Paleozoic unconformity. It exhibits several features not previously described in Adirondack rocks. These (features include (1) extensive slickensides (azimuth 120°–150°, plunge 0°–30°, southeast-over-northwest sense of movement) on preexisting foliation surfaces; (2) coexistence of calcite marbles that contain granulite facies mineral assemblages with dolomite marbles that contain dolomite, quartz, microcline, and serpentine in unreacted mutual contact; (3) ferroan dolomite that fills veins, faults, and fractures and occurs in thin, foliation-parallel lamellae in gneiss; and (4) minerals of probable low-temperature origin (adularia, celadonite, and cherty silica) that fill veins and interstitial spaces in gneiss and marbles. We suggest that these features can best be explained by minor rotational shear deformation during the Taconic orogeny, accompanied by local metasomatism caused by Mg-rich connate brines expelled from Cambrian–Ordovician sedimentary rocks by overriding Taconic thrust slices.

Jujuyaspis borealisand associated trilobites and conodonts from the Lower Ordovician of Texas and Utah

Jujuyaspis borealisis reported from earliest Ordovician (North American usage) limestones in central Texas and western Utah, the first time this species has been recognized in the United States.Jujuyaspisis a widespread olenid trilobite that occurs near the base of the Tremadoc Series in a variety of lithologies in North and South America, Europe, and Asia. When international agreement is reached on the exact horizon at or near the base of the Tremadoc Series that is to be used as the Cambrian–Ordovician boundary,Jujuyaspiswill likely prove to be a very useful taxon for recognition of the boundary interval.

Metallogeny and tectonic development of the Tasman Fold Belt System in New South Wales

The northwestern corner of New South Wales consists of the paratectonic Late Proterozoic to Early Cambrian Adelaide Fold Belt and older rocks, which represent basement inliers in this fold belt. The rest of the state is built by the composite Late Proterozoic to Triassic Tasman Fold Belt System or Tasmanides. In New South Wales the Tasman Fold Belt System includes three fold belts: (1) the Late Proterozoic to Early Palaeozoic Kanmantoo Fold Belt; (2) the Early to Middle Palaeozoic Lachlan Fold Belt; and (3) the Early Palaeozoic to Triassic New England Fold Belt. The Late Palaeozoic to Triassic Sydney—Bowen Basin represents the foredeep of the New England Fold Belt. The Tasmanides developed in an active plate margin setting through the interaction of East Gondwanaland with the Ur-(Precambrian) and Palaeo-Pacific plates. The Tasmanides are characterized by a polyphase terrane accretion history: during the Late Proterozoic to Triassic the Tasmanides experienced three major episodes of terrane dispersal (Late Proterozoic—Cambrian, Silurian—Devonian, and Late Carboniferous—Permian) and six terrane accretionary events (Cambrian—Ordovician, Late Ordovician—Early Silurian, Middle Devonian, Carboniferous, Middle-Late Permian, and Triassic). The individual fold belts resulted from one or more accretionary events. The Kanmantoo Fold Belt has a very restricted range of mineralization and is characterized by stratabound copper deposits, whereas the Lachlan and New England Fold Belts have a great variety of metallogenic environments associated with both accretionary and dispersive tectonic episodes. The earliest deposits in the Lachlan Fold Belt are stratabound Cu and Mn deposits of Cambro-Ordovician age. In the Ordovician Cu deposits were formed in a volcanic are. In the Silurian porphyry CuAu deposits were formed during the late stages of development of the same volcanic are. Post-accretionary porphyry CuAu deposits were emplaced in the Early Devonian on the sites of the accreted volcanic arc. In the Middle to Late Silurian and Early Devonian a large number of base metal deposits originated as a result of rifting and felsic volcanism. In the Silurian and Early Devonian numerous SnW, Mo and base metal—Au granitoid related deposits were formed. A younger group of MoW and Sn deposits resulted from Early—Middle Carboniferous granitic plutonism in the eastern part of the Lachlan Fold Belt. In the Middle Devonian epithermal Au was associated with rifting and bimodal volcanism in the extreme eastern part of the Lachlan Fold Belt. In the New England Fold Belt pre-accretionary deposits comprise stratabound Cu and Mn deposits (pre-Early Devonian): stratabound Cu and Mn and ?exhalite Au deposits (Late Devonian to Early Carboniferous); and stratabound Cu, exhalite Au, and quartz—magnetite (?Late Carboniferous). S-type magmatism in the Late Carboniferous—Early Permian was responsible for vein Sn and possibly AuAsAgSb deposits. Volcanogenic base metals, when compared with the Lachlan Fold Belt, are only poorly represented, and were formed in the Early Permian. The metallogenesis of the New England Fold Belt is dominated by granitoid-related mineralization of Middle Permian to Triassic age, including SnW, MoW, and AuAgAs Sb deposits. Also in the Middle Permian epithermal AuAg mineralization was developed. During the above period of post-orogenic magmatism sizeable metahydrothermal SbAu(W) and Au deposits were emplaced in major fracture and shear zones in central and eastern New England. The occurrence of antimony provides an additional distinguishing factor between the New England and Lachlan Fold Belts. In the New England Fold Belt antimony deposits are abundant whereas they are rare in the Lachlan Fold Belt. This may suggest fundamental crustal differences.

Paleozoic Unconformities Favorable for Uranium Concentration in Northern Appalachian Basin: ABSTRACT

Unconformities can redistribute uranium from protore rock as ground water moves through poorly consolidated strata beneath the erosion surface, or later moves along the unconformity. Groundwater could migrate farther than in present-day lithified Paleozoic strata in the Appalachian basin, now locally deformed by the Taconic and Allegheny orogenies. Several paleoaquifer systems could have developed uranium geochemical cells. Sandstone mineralogy, occurrences of fluvial strata, and reduzate facies are important factors. Other possibilities include silcrete developed during desert exposure, and uranium concentrated in paleokarst. Thirteen unconformities are evaluated to determine favorable areas for uranium concentration. Cambrian Potsdam sandstone (New York) contains arkoses and possible silcretes just above crystalline basement. Unconformities involving beveled sandstones and possible fluvial strata include Cambrian Hardyston sandstone (New Jersey), Cambrian Potsdam Sandstone (New York), Ordovician Oswego and Juniata formations (Pennsylvania and New York), Silurian Medina Group (New York), and Silurian Vernon, High Falls, and Longwood formations (New York and New Jersey). Devonian Catskill Formation is beveled by Pennsylvanian strata (New York and Pennsylvania). The pre-Pennsylvanian unconformity also bevels Lower Mississippian Pocono, Knapp, and Waverly strata (Pennsylvania, New York, and Ohio), truncates Upper Mississippian Mauch Chunk Formation (Pennsylvania), and forms paleokarst on Mississippian Loyalhanna Limestone (Pennsylvania) and Maxville Limestonemore » (Ohio). Strata associated with these unconformities contain several reports of uranium. Unconformities unfavorable for uranium concentration occur beneath the Middle Ordovician (New York), Middle Devonian (Ohio and New York), and Upper Devonian (Ohio and New York); these involve marine strata overlying marine strata and probably much submarine erosion.« less

A newly recognized sequence of possible Early Cambrian age in southern New Brunswick: evidence for major southward-directed thrusting

Several previously unidentified occurrences of possible Lower Cambrian strata have been discovered recently in the Eastern Volcanic Belt (Avalon zone) of southern New Brunswick. The basal part of the sequence is lithologically similar to the Lower Cambrian parastratotype on Hanford Brook near Saint John, New Brunswick. Some of the newly recognized Cambrian rocks crop out beneath major northeast-trending and north-dipping thrusts, and rest unconformably on subaqueous Upper Precambrian equivalents of the Coldbrook Group. The presence of these Cambrian rocks in the Eastern Volcanic Belt indicates that the Cambrian–Ordovician Iapetus Ocean transgressed across the entire Avalon zone of southern New Brunswick.

Correlation of Cambrian–Ordovician boundary between Europe and North America: new data from western Newfoundland

The Cow Head Group in western Newfoundland includes a record of continuous graptolite evolution across the Cambrian–Ordovician boundary. In sections at Broom Point, interbedded breccias contain blocks with rich platform trilobite faunas which give a complete succession of North American zones. The stratigraphic relationship between graptolites and trilobites clearly establishes that the base of the type Tremadoc Series lies above that of the Missisquoia Zone. The sequence of earliest planktonic graptolites is the most complete known and serves to remove objections to the selection of Dictyonema flabelliforme, or one of its subspecies, as an index for the base of the Ordovician System.

Carbonate Depocenters and Facies Distribution on Passive Cambrian Shelf and Middle Ordovician Foreland Basin, Appalachian Orogene, Virginia: ABSTRACT

Depocenters in the southern and central Appalachians in Virginia appear to have been a major influence on thickness and carbonate facies distribution on the passive Cambrian-Ordovician shelf and in the Middle Ordovician foreland basin. The Upper Cambrian Nolichucky Formation illustrates sedimentation patterns associated with a shelf embayment (located above the southern Appalachian depocenter) on the passive Cambrian shelf. The Noli-chucky Formation is an onlap-offlap, shallow ramp to deep shelf sequence that consists of peritidal stromatolitic carbonate rocks, ooid grainstones, deeper ramp ribbon carbonate rocks, and embayment plain shale/siltstone/flat-pebble conglomerate facies. Facies bands are normal to the regional shelf edge and parallel the outline of the shelf embayment. The Middle Ordovician sequence illustrates the influence of depocenters on foreland basin evolution during a time of profound tectonism, when the shelf edge was uplifted, deformed, and subjected to erosion. The Middle Ordovician ramp-to-basin sequence is an onlap-of-flap package, that consists of peritidal fenestral lime mudstones, shallow subtidal cherty wackestones, ramp and downslope skeletal buildups, deeper ramp shaly skeletal wackestones, and basinal black limestones and shales. Widespread ramp and basin deposition commenced in southwest Virginia during south to north transgression from the southern depocenter. Widespread downwarping extended the basin into northern Virginia. Rapid clastic influx coupled with progradation of the carbonate ramp caused the southern basin to fill. Recognition of depocenters associated with carbonate sequences in orogenic belts is important if controls on direction of transgression, facies distributions, and thicknesses of units are to be better understood. Furthermore, the carbonate depocenters appear to localize development of subsequent clastic wedges. End_of_Article - Last_Page 770------------

Appalachian Orogen in Canada

The Appalachian Orogen is divided into five broad zones based on stratigraphic and structural contrasts between Cambrian–Ordovician and older rocks. From west to east, these are the Humber, Dunnage, Gander, Avalon, and Meguma Zones.The westerly three zones fit present models for the development of the orogen through the generation and destruction of a late Precambrian – Early Paleozoic Iapetus Ocean. Thus, the Humber Zone records the development and destruction on an Atlantic-type continental margin, i.e., the ancient continental margin of Eastern North America that lay to the west of Iapetus; the Dunnage Zone represents vestiges of Iapetus with island arc sequences and mélanges built upon oceanic crust; and the Gander Zone records the development and destruction of a continental margin, at least in places of Andean type, that lay to the east of Iapetus.The Precambrian development of the Avalon Zone relates either to rifting and the initiation of Iapetus or to subduction and a cycle that preceded the opening of Iapetus. During the Cambrian Period, the Avalon Zone was a stable platform or marine shelf.Cambrian–Ordovician rocks of the Meguma Zone represent either a remnant of the continental embankment of ancient Northwest Africa or the marine fill of a graben developed within the Avalon Zone.Silurian and younger rocks of the Appalachian Orogen are mixed marine and terrestrial deposits that are unrelated to the earlier Paleozoic zonation of the system. Silurian and later development of the orogen is viewed as the history of deposition and deformation in successor basins that formed across the already destroyed margins and oceanic tract of Iapetus.

The geologic setting of the Southeast Missouri lead district; regional geologic history, structure and stratigraphy

The Viburnum mineralized area lies near the southern edge of the central stable region of the North American craton. Erosion of the Precambrian preceded establishment of basins and uplifts in early Paleozoic time. Shelf deposition prevailed in the Late Cambrian and Early Ordovician, followed by emergence and erosion resulting in the post-Knox unconformity. Silurian and Devonian deposition were followed by severe erosion, and Lower Mississippian strata were laid down on a rough karst surface. Emergence since Pennsylvanian time has exposed the Ozarks and surrounding areas to continous erosion, and the region has been stable. Block faulting surrounds the core of the uplifted St. Francois Mountains; farther west, long faults and joints trend northwest and northeast.The Upper Cambrian series in southeast Missouri comprises six formations, which are, in ascending order: Lamotte Sandstone, Bonneterre Formation, Davis Formation and Derby-Doerun Dolomite (Elvins Group), Potosi Dolomite, and Eminence Dolomite. These rocks are dominantly carbonates with varying amounts of detrital material, except for the basal Paleozoic sandstone, the Lamotte. In Late Cambrian time, clastic sedimentation was dominant in the Upper Mississippi Valley, with a progressive increase in carbonates southward to the Ozarks. Although hindered by considerable distance and a paucity of subsurface data, correlations between the two regions are presented with reasonable confidence.

Growth Faults in Cambrian and Lower Ordovician Rocks of Western Pennsylvania

A Cambrian basin lies beneath the Appalachian Plateau of western Pennsylvania; it trends northeast-southwest between shelf sediments of northwestern Pennsylvania, where most of the Cambrian wells are drilled, and the overthrust outcrop belt of central Pennsylvania. The western edge of the basin is believed to be bounded by growth faults which restrict to the basin a thick sandstone herein named the Olin Sandstone. Evidence for growth faults is derived from many changes in regional stratigraphy of deep wells in Potter and Armstrong Counties, Pennsylvania, and Marshall County, West Virginia. The presence of growth faults also is postulated in Lower Ordovician rocks east of the faulting in the Cambrian strata. By projecting the Cambrian and Early Ordovician growth faults to he Precambrian structural contour map of Beck and Mattick, a Precambrian basin is indicated with structural relief of several thousand feet (about 1,200 m).

Notes on cystoids

SUMMARY“Strobilocystites? kearsargensis Stauffer,” a supposed rhombiferan cystoid from the Kennett Formation, Kearsarge, California, is a diploporite cystoid tentatively assigned to Revalocystis Jaekel. This extends the stratigraphic range of the Dactylocystidae into the Silurian and is the first reported occurrence of Dactylocystidae from North America. An unusual specimen of Glansicystis baccata (Forbes) with IL1 represented by two small pentagonal plates is described. Glansicystis had four short ambulacra: I and IV have only one brachiole; II and V may have one to three brachioles.An isolated echinoderm plate with structures which may represent pectinirhombs is described from the Whipple Cave Formation, Near Lund, Nevada. The structures differ from typical pectinirhombs and are older (Uppermost Cambrian or Basal Ordovician) than any previously described pectinirhombs.

Paleozoic History of Southeastern Colorado

Southeastern Colorado was first covered by Paleozoic seas in Late Cambrian time, when coarse clastics (Lamotte sandstone) derived mainly from the north were deposited in front of a low landmass that extended from New Mexico northwestward to the vicinity of Canon City. The seas gradually encroached on this landmass, depositing additional Upper Cambrian (Bonneterre dolomite) and Lower Ordovician (Arbuckle group) rocks farther southwest. Near the close of Early Ordovician time, gentle upwarping raised the central part of southeastern Colorado above sea-level. During Middle and Late Ordovician time, seas lapped upon the eastern and western slopes of this upwarp, depositing the sediments of the Simpson group and the Viola limestone. After the close of Ordovician time, upliftin , probably with some faulting, along the present trend of the Front Range, Wet Mountains, and Apishapa-Sierra Grande uplift, permitted the removal by erosion of most of the Cambrian and Ordovician rocks from that area. In Mississippian time the seas advanced from the Anadarko basin, lapping on the gently sloping landmass. During Meramec time the seas probably completely covered the landmass and at the end of Meramec time began a withdrawal into the Anadarko basin. During Chester time the seas appear to have been restricted to the Hugoton embayment in the southeasternmost part of Colorado. At the beginning of Pennsylvanian time, the seas advanced upon the flanks of the low landmass of eastern Colorado, bringing clastic material from the southeast. Near the end of Morrow time major uplifting accompanied by faulting elevated the Apishapa-Sierra Grande uplift, the Wet Mountains, and the Front Range, which supplied clastic material to transgressing seas during the remainder of Pennsylvanian time. A cross flexure marking the earliest beginnings of the Las Animas arch seems to have developed near the end of Missouri time. During early Permian time the seas gradually covered the Apishapa-Sierra Grande landmass, and during late Permian time the shore line remained fairly stable, until the seas receded at the close of the period.

CAMBRIAN AND EARLY ORDOVICIAN STRATIGRAPHY OF THE LOWER ST. LAWRENCE VALLEY

CAMBRIAN AND EARLY ORDOVICIAN STRATIGRAPHY OF THE LOWER ST. LAWRENCE VALLEY