The Double Mer Formation and the Lake Melville rift system, eastern Labrador

1986 ◽  
Vol 23 (3) ◽  
pp. 359-368 ◽  
Author(s):  
Charles F. Gower ◽  
Philippe Erdmer ◽  
Richard J. Wardle
Keyword(s):  
Lower Cambrian ◽  
Structural Model ◽  
Rift System ◽  
Early Cambrian ◽  
Crustal Extension ◽  
Grenville Province ◽  
Mafic Dike ◽  
Iapetus Ocean ◽  
Half Graben ◽  
Arkosic Sandstone

The Double Mer Formation is a sequence of redbed arkosic sandstone, conglomerate, siltstone, and shale in the Grenville Province of eastern Labrador. The formation is closely associated with a rift system extending inland for at least 300 km from the Labrador coast. Substantial thicknesses of strata of Double Mer Formation are confined to two basins, the Lake Melville graben and the Double Mer half graben. Strata correlated with the Double Mer Formation are found elsewhere in southeast Labrador; one isolated outcrop occurs within the Sandwich Bay graben, a separate, smaller basin 100 km to the southeast that trends parallel to the Lake Melville graben.The only definite age constraint on the Double Mer Formation is that it postdates Grenvillian deformation. Previously, the formation was assigned a latest Precambrian to Early Cambrian age based on lithological similarity with the Lower Cambrian Bradore Formation of the southeast coast of Labrador. On the basis of a structural model proposed here that suggests a link between graben configuration and latest Precambrian – Early Cambrian mafic dike trends, we concur with this viewpoint. The Double Mer Formation thus preserves the basin fill presumed to have accompanied graben formation, which, together with emplacement of mafic dikes and anorogenic plutons, documents latest Precambrian to Early Cambrian crustal extension that eventually led to the opening of the Iapetus Ocean.

Sedimentation in an intracratonic extensional basin: the Karoo of the Central Morondava Basin, Madagascar

1989 ◽  
Vol 126 (4) ◽  
pp. 339-354 ◽  
Author(s):  
G. J. Nichols ◽  
M. C. Daly
Keyword(s):  
Structural Control ◽  
Rift System ◽  
Crustal Extension ◽  
Erosion And Deposition ◽  
Base Level ◽  
Clastic Sediments ◽  
Metamorphic Basement ◽  
Half Graben ◽  
River Deposits ◽  
East West

AbstractThe late Carboniferous to Triassic Karoo Supergroup of Madagascar is a sequence of predominantly continental clastic sediments deposited during a long period of regional crustal extension. In the Morondava Basin of western Madagascar the lower two divisions of the Karoo sediments – the Sakoa and the Sakamena – are deposits of fluvial and lacustrine sedimentation systems supplied from the Precambrian metamorphic basement terrain to the east. East–west crustal extension produced a series of graben and half-graben structures after the Sakoa period which were reactivated after the Sakamena. The position and orientation of these half graben, which were marginal to a larger rift system to the west, were partly controlled by the steep NNE–SSW mylonitic fabric in the metamorphic basement. Palaeocurrents in the braided river deposits of the Sakoa and Lower Sakamena indicate flow to the southwest and west in both sequences. The rivers followed a regional palaeoslope to the southwest/west and were apparently not significantly influenced by the local structural trends which were oriented perpendicular to this slope. The absence of local structural control is attributed to extensive erosional events which followed each tectonic episode and preceded the onset of further sedimentation which took place on an essentially peneplained surface. The tectonic episodes brought about changes in base level which caused this part of the basin to fluctuate between erosion and deposition.

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

1981 ◽  
Vol 18 (6) ◽  
pp. 1012-1017 ◽  
Author(s):  
M. J. McLeod ◽  
S. R. McCutcheon
Keyword(s):  
New Brunswick ◽  
Lower Cambrian ◽  
Volcanic Belt ◽  
Basal Part ◽  
Early Cambrian ◽  
Iapetus Ocean ◽  
Saint John

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.

The problematic fossil Triplicatella from the Early Cambrian of Greenland, Canada, and Siberia

2004 ◽  
Vol 41 (11) ◽  
pp. 1273-1283 ◽  
Author(s):  
Christian B Skovsted ◽  
John S Peel ◽  
Christian J Atkins
Keyword(s):  
New Species ◽  
Functional Morphology ◽  
Lower Cambrian ◽  
Early Cambrian ◽  
Taxonomic Affinity ◽  
East Greenland ◽  
North East ◽  
Close Proximity ◽  
Two New Species

The cap-shaped Early Cambrian fossil Triplicatella, previously known only from Australia, is reported from the upper Lower Cambrian of North and North-East Greenland, western Newfoundland, and Siberia. The occurrence of Triplicatella in Laurentia strengthens faunal ties between Laurentia and the Australian margin of Gondwana in late Early Cambrian times and supports hypotheses advocating the close proximity for the two palaeocontinents. Two new species, Triplicatella sinuosa n. sp., and T. peltata n. sp. are described, morphological details of which help elucidate the functional morphology and taxonomic affinity of the group. Three opercular types attributable to Triplicatella are left in open taxonomy. The postulated affinity of Triplicatella to hyoliths is confirmed, although the genus can not be placed within either of the two orders of hyoliths currently recognized.

Distribution of crustal extension and regional basin architecture of the Albertine rift system, East Africa

2000 ◽  
Vol 17 (10) ◽  
pp. 1131-1150 ◽  
Author(s):  
G.D. Karner ◽  
B.R. Byamungu ◽  
C.J. Ebinger ◽  
A.B. Kampunzu ◽  
R.K. Mukasa ◽  
...  
Keyword(s):  
East Africa ◽  
Rift System ◽  
Crustal Extension ◽  
Albertine Rift

Lower Cambrian (Branchian) trilobites and biostratigraphy of the Hanford Brook Formation, southern New Brunswick

2000 ◽  
Vol 74 (5) ◽  
pp. 858-878 ◽  
Author(s):  
Stephen R. Westrop ◽  
Ed Landing
Keyword(s):  
New Species ◽  
Nova Scotia ◽  
North America ◽  
New Brunswick ◽  
Lower Cambrian ◽  
Early Cambrian ◽  
The West ◽  
Middle Cambrian ◽  
Sequence Stratigraphic ◽  
Two New Species

The Hanford Brook Formation, one of the classic Cambrian units of Avalonian North America, contains at least eight species of endemic trilobites, including Berabichia milleri Westrop n. sp., that are assigned to seven genera. The vertical succession of faunas is far more complex than has been recognized previously, with each member containing a lithofacies-specific assemblage. These are, in ascending order: a bradoriid-linguloid Association without trilobites in the nearshore St. Martin's Member, a Protolenus Association in dysaerobic siltstones and sandstones of the Somerset Street Member, and a Kingaspidoides-Berabichia Association in hummocky cross-stratified sandstones of the Long Island Member that overlie a parasequence boundary at Hanford Brook. Due to the breakdown of biogeographic barriers in the late Early Cambrian, two new species-based zones, the Protolenus elegans and Kingaspidoides cf. obliquoculatus zones, share trilobite genera with the Tissafinian Stage of Morocco. This generic similarity has been the basis for correlation of this upper Lower Cambrian interval on the Avalon continent with the West Gondwanan lowest Middle Cambrian. However, the clear facies control on the occurrence of genera in the Hanford Brook Formation and the presence of an abrupt faunal break and unconformity at the base of the Tissafinian in Morocco makes this correlation questionable. The Hanford Brook Formation may represent a late Early Cambrian interval unknown in Gondwana. Sequence-stratigraphic criteria even raise the possibility that the Protolenus Association is the biofacies equivalent of Callavia broeggeri Zone faunas of the Brigus Formation of Newfoundland, Nova Scotia and Massachusetts.

scholarly journals Taxonomic diversity and faunal turnover in the Early Cambrian: Did the most severe mass extinction of the Phanerozoic occur in the Botomian stage?

1992 ◽  
Vol 6 ◽  
pp. 272-272 ◽  
Author(s):  
Philip W. Signor
Keyword(s):  
Lower Cambrian ◽  
Substantial Reduction ◽  
Taxonomic Diversity ◽  
Early Cambrian ◽  
Shelf Area ◽  
Extinction Rate ◽  
Mass Extinctions ◽  
High Turnover ◽  
Faunal Turnover ◽  
Global Correlation

A handful of mass extinctions, scattered through the Phanerozoic, forever changed the course of life on Earth, eliminating large numbers of clades from the evolutionary race and allowing the survivors to diversify following the extinction. These ecological-evolutionary upheavals extirpated whole communities and eliminated otherwise successful clades from the evolutionary race. While the mechanism(s) responsible for most mass extinctions remain to be identified, their impact on the biosphere is self-evident. Thus, recognition of a previously overlooked, severe extinction early in the Phanerozoic provides important new insights and perspectives on the history of lifeIn the course of research on the biogeographic distribution of Early Cambrian metazoan taxa, I compiled a database on the geographic and stratigraphic distribution of metazoan genera. The data are derived from the primary literature on the paleogeographic and stratigraphic distributions and systematics of Early Cambrian fossils. The Russian zonation scheme for the Siberian Platform (incorporating four stages, in ascending order: Tommotian, Atabanian, Botomian, and Toyonian) was employed for biostratigraphic correlations. Correlations of other regions to the Siberian stages were based upon work by F. Debrenne and her colleagues on archaeocyathans and upon M. D. Brasier's correlations from small shelly fossils. While there is no accepted global correlation scheme for Lower Cambrian strata, this approach yields results that are useful at the four-stage level of resolution. The data base currently includes more than 850 genera.Examination of the aggregate data reveals a substantial reduction (>60%) in the global total of genera extant in the Toyonian, in comparison to the Botomian stage. The extinction rate of genera at the end of the Botomian exceeds 80 percent. By comparison, the end-Permian extinction eliminated slightly more than 60 percent of the extant genera.In addition to the general reduction in generic diversity, Brasier (1982) has documented a fall in sea level and reduction in the shelf area. Associated with this regression was a loss of reef-forming archaeocyathan genera. While a small number of archaeocyathan genera persisted into the Toyonian (and a few genera have been reported from Late Cambrian strata in Antarctica), the bulk of archaeocyath diversity was lost in the Botomian. The losses in diversity, extermination of reef-forming organisms, and high turnover in conjunction with a marine regression matches the pattern observed at most other mass extinctions.It is remarkable that this relatively severe extinction has gone mostly unnoticed by paleobiologists. Much of the data is relatively new, a product of intense international study of early metazoan faunas. Most likely, the mass of data produced by Lower Cambrian specialists over the past ten years has yet to reach the treatises and monographs where it can be easily summarized. Also, resolution of patterns within the Early Cambrian has waited on the development of correlations and a satisfactory zonation. Indeed, detailed study of the Botomian extinction will await more accurate correlations.

New evidence that the Lower Cambrian Leny Limestone at Callander, Perthshire, belongs to the Dalradian Supergroup, and a reassessment of the ‘exotic’ status of the Highland Border Complex

1995 ◽  
Vol 132 (5) ◽  
pp. 473-483 ◽  
Author(s):  
P. W. G. Tanner
Keyword(s):  
Lower Cambrian ◽  
Alternative Hypothesis ◽  
Structural Relationship ◽  
Early Cambrian ◽  
Minimum Age ◽  
Entire Sequence ◽  
New Evidence ◽  
Critical Sections ◽  
Radiometric Data

AbstractThe Lower Cambrian Leny Limestone at Callander in Scotland lies within a sequence of palecoloured grits and dark slates (here named the Keltie Water Grit Formation (KWGF)) which has lithological similarities with members of the Highland Border Complex (HBC) (Ordovician) seen elsewhere along the Highland Border. The Keltie Water Grit Formation has a transitional boundary with a grit-slate sequence of undoubted Dalradian parentage; as the ‘Leny Grits’ of previous workers include both the KWGF and part of the Dalradian sequence, this term is now rendered invalid. The entire sequence youngs upwards from the Dalradian to the top of the overlying Keltie Water Grit Formation, shares the same structural sequence and geometry, and has the same facing and vergence direction on the main cleavage. All field and petrographic data are consistent with a minimum age of post-early Cambrian for the Grampian event, the main orogenic event to affect the Dalradian. Examination of critical sections elsewhere across the Highland Border shows that there is an apparently consistent stratigraphical and structural relationship between the Highland Border Complex and the Dalradian which, as suggested by some previous workers, would require the Grampian event to be post-Arenig in age. However, we are faced with a so-far unresolved paradox that there are certain palaeontological and radiometric data which are in conflict with this conclusion, and support the alternative hypothesis that the Highland Border Complex docked with the Dalradian in post-Ordovician times.

TECTONOSTRATIGRAPHY AND POTENTIAL SOURCE ROCKS OF THE BASS BASIN

2005 ◽  
Vol 45 (1) ◽  
pp. 601 ◽  
Author(s):  
J.E. Blevin ◽  
K.R. Trigg ◽  
A.D. Partridge ◽  
C.J. Boreham ◽  
S.C. Lang
Keyword(s):  
Seismic Data ◽  
Middle Eocene ◽  
Liquid Hydrocarbon ◽  
Source Rocks ◽  
Rift System ◽  
Complex Nature ◽  
Hydrocarbon Generation ◽  
Crustal Extension ◽  
Principal Source ◽  
Seismic Sequence Stratigraphy

A study of the Bass Basin using a basin-wide integration of seismic data, well logs, biostratigraphy and seismic/sequence stratigraphy has resulted in the identification of six basin phases and related megasequences/ supersequences. These sequences correlate to three periods of extension and three subsidence phases. The complex nature of facies relationships across the basin is attributed to the mostly terrestrial setting of the basin until the Middle Eocene, multiple phases of extension, strong compartmentalisation of the basin due to underlying basement fabric, and differential subsidence during extension and early subsidence phases. The Bass Basin formed through upper crustal extension associated with three main regional events:rifting in the Southern Margin Rift System;rifting associated with the formation of the Tasman Basin; and,prolonged separation, fragmentation and clearance between the Australian and Antarctic plates along the western margin of Tasmania.The final stage of extension was the result of far-field stresses that were likely to be oblique in orientation. The late Early Eocene to Middle Eocene was a time of rifttransition and early subsidence as the effects of intra-plate stresses progressively waned from east to west. Most of the coaly source rocks now typed to liquid hydrocarbon generation were deposited during this rift-transition phase. Biostratigraphic studies have identified three major lacustrine episodes during the Late Cretaceous to Middle Eocene. The lacustrine shales are likely to be more important as seal facies, while coals deposited fringing the lakes are the principal source rocks in the basin.

scholarly journals Caught in the act: priapulid burrowers in early Cambrian substrates

2019 ◽  
Vol 286 (1894) ◽  
pp. 20182505 ◽  
Author(s):  
Giannis Kesidis ◽  
Ben J. Slater ◽  
Sören Jensen ◽  
Graham E. Budd
Keyword(s):  
Comparative Analysis ◽  
Lower Cambrian ◽  
Trace Fossil ◽  
Considerable Importance ◽  
Cambrian Explosion ◽  
Early Cambrian ◽  
Southern Sweden ◽  
Stage 4 ◽  
Organic Remains

The fossilized traces of burrowing worms have taken on a considerable importance in studies of the Cambrian explosion, partly because of their use in defining the base of the Cambrian. Foremost among these are the treptichnids, a group of relatively large open probing burrows that have sometimes been assigned to the activities of priapulid scalidophoran worms. Nevertheless, most Cambrian burrows have an uncertain progenitor. Here we report a suite of exceptionally preserved trace and body fossils from sandstones of the lower Cambrian (Stage 4) File Haidar Formation of southern Sweden that can unequivocally be assigned to a scalidophoran producer. We further present the first burrow casts produced via actualistic experiments on living priapulids, and demonstrate the remarkable morphological parallels between these modern and Cambrian fossil equivalents. In addition, co-occurrence of scalidophoran-derived cuticular remains permits a unique synthesis of evidence from trace fossil, body and organic remains. Comparative analysis of these exceptionally preserved fossils supports a scalidophoran producer for treptichnids and by extension suggests a latest Ediacaran origin of the ecdysozoan clade.

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