A Paleomagnetic Reversal in the Osler Volcanic Group, Northern Lake Superior

1974 ◽  
Vol 11 (9) ◽  
pp. 1200-1207 ◽  
Author(s):  
H. C. Halls
Keyword(s):  
Volcanic Activity ◽  
Lake Superior ◽  
Aeromagnetic Data ◽  
Magnetic Reversal ◽  
Geological Evidence ◽  
Late Precambrian ◽  
Quiescent Period ◽  
Clastic Sediments ◽  
Paleomagnetic Study ◽  
Reversed Polarity

A geological and paleomagnetic study in the Nipigon Strait area, northern Lake Superior, has confirmed previous conclusions drawn from aeromagnetic data, that an unconformity occurs within the Late Precambrian Keweenawan Osler volcanics and separates normally magnetized lavas from older ones with reversed polarity. The new data, together with other paleomagnetic and geological evidence from Keweenawan rocks, suggest that the magnetic reversal occurred when there was a temporary halt or decline in volcanic activity throughout the Lake Superior region. During the quiescent period, coarse clastic sediments were deposited by marginal erosion of the subsiding Keweenawan basin; sinking of the basin with corresponding uplift of the margins may have been greater in the south where the thickest sections of conglomerate and sandstone are preserved.

Magnetic Studies in Northern Lake Superior

1972 ◽  
Vol 9 (11) ◽  
pp. 1349-1367 ◽  
Author(s):  
H. C. Halls
Keyword(s):  
Lake Superior ◽  
Magnetic Polarity ◽  
Magnetic Data ◽  
Aeromagnetic Data ◽  
Total Field ◽  
Magnetic Studies ◽  
Late Precambrian ◽  
Thunder Bay ◽  
Basement Ridge ◽  
Volcanic Series

Analysis of total field magnetic data, together with other geophysical evidence has led to the following conclusions concerning the structure and stratigraphy of late Precambrian Keweenawan rocks that underlie and border the northern part of Lake Superior:(1) The uppermost few hundred feet of the Osler Volcanic Series has a normal remanent magnetization. The normally magnetized mafic flows are separated from older, reversely magnetized ones which form the bulk of the Osler Series, by a thin zone of felsic igneous rocks with unknown magnetic polarity. The upper mafic unit appears from aeromagnetic data to outcrop on some of the outer islands at the mouth of Nipigon Strait, and represents the lowest part of a normally magnetized volcanic sequence that lies offshore, beneath the waters of Lake Superior.(2) The contact between the upper mafic unit and older rocks of the Osler Series is a stratigraphic rather than a faulted one. Aeromagnetic data show that mafic volcanics above and below this contact have the same strike, except toward the Thunder Bay and Schreiber regions. In these areas there is a convergence in strike between the two mafic units which may indicate an unconformity between them or a thinning of flows in the older unit. Ultimately the older, reversely magnetized unit appears to pinch out beneath the younger one to both the east and west.(3) The younger volcanics and overlying sediments occur in a large basin centered about 30 mi (50 km) WSW of the Slate Islands. Whether the older, reversely magnetized volcanics accumulated in this basin or in a smaller more northerly one is not entirely clear. The eastern margin of the main basin appears to be formed by a basement ridge extending from the Slate Islands southward to Superior Shoal, over which volcanics and younger sediments are relatively thin.

Stable isotope geochemistry and palynology of the late Precambrian to Early Cambrian sequence in Newfoundland

1992 ◽  
Vol 29 (8) ◽  
pp. 1662-1673 ◽  
Author(s):  
Harald Strauss ◽  
Stefan Bengtson ◽  
Paul M. Myrow ◽  
Gonzalo Vidal
Keyword(s):  
Stable Isotope ◽  
Organic Carbon ◽  
Isotope Geochemistry ◽  
Depositional Environments ◽  
Early Cambrian ◽  
Bacterial Sulfate Reduction ◽  
Stable Isotope Geochemistry ◽  
Forming Process ◽  
Late Precambrian ◽  
Clastic Sediments

A sequence of clastic sediments in southeastern Newfoundland straddling the Precambrian–Cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid-resistant organic-walled microfossils. A detailed study of the Chapel Island Formation, which includes the boundary interval, has revealed fluctuations in the isotopic composition of organic carbon. These are largely interpreted as caused by differences in the depositional environments. Highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite-forming process, sometimes under sulfate-limited conditions. Palynological results are quite limited with respect to diagnostic microfossils.

Origin and Geography of the Fish Fauna of the Laurentian Great Lakes Basin

1981 ◽  
Vol 38 (12) ◽  
pp. 1539-1561 ◽  
Author(s):  
Reeve M. Bailey ◽  
Gerald R. Smith
Keyword(s):  
Great Lakes ◽  
Lake Trout ◽  
Lake Superior ◽  
Fish Fauna ◽  
Secondary Contact ◽  
Species Differentiation ◽  
Stizostedion Vitreum ◽  
Great Lakes Basin ◽  
Geological Evidence ◽  
The Past

The native fishes of the Great Lakes basin consist of 153 species, 64 genera, and 25 families. The total ichthyofaunal lists for the several lakes and (in parentheses) their tributary basins are as follows: Nipigon (and tributaries), 40; Superior, 53 (82); Michigan, 91 (135); Huron, 90 (112); St. Clair and Detroit River 108; Erie, 106 (125); Ontario, 95 (125). (These totals include 21 introduced species, most named species of ciscoes and chubs, and the blue pike (Stizostedion vitreum glaucum).)Several areas show notable within-species differentiation. Tributaries to Lake Ontario are part of a zone of secondary contact of a few small, nonmanaged, subspecies that entered the basin from both eastern and western glacial refugia. In the Great Lakes themselves, stocks of lake trout (Salvelinus namaycush), ciscoes, walleyes (Stizostedion vitreum vitreum), and a few nonmanaged species stem from differentiation within the basin or reflect interglacial events that occurred in Mississippi refugia.Species distribution patterns suggest colonization of the Great Lakes by 122 kinds solely from Mississippi basin refugia, 14 kinds only from Atlantic drainage refugia, and dual refugia for at least 18 kinds. Geological evidence provides some support for this interpretation. It is unlikely that any species colonized the Great Lakes from an Alaskan refuge in the past 14 000 yr.The ciscoes and chubs of the genus Coregonus include numerous genetically differentiated stocks, some of which may predate the opening of the Great Lakes in the past 14 000 yr. This conclusion is based on the occurrence in Lake Nipigon and Lake Superior of several forms that must have colonized prior to 9000 yr ago when the last access existed from Lake Superior to Lake Nipigon. At least four and perhaps up to eight forms of Great Lakes coregonines probably survived (or differentiated during) the last glaciation south of the ice in proglacial waters at the heads of major river systems. There is no evidence to support the hypothesized post-Wisconsinan dispersal of any of these forms from a northwestern refugium or their Pleistocene derivation by introgression with a Eurasian species.Despite the evidence for some long-standing genetic differentiation within Coregonus, morphological and biochemical characters fail to support the unequivocal recognition within the Great Lakes of more than one to four current biological species (apart from clupeaformis). The presently recognized species are groups of stocks whose position in the classification system is problematical. The named groups (two of which are extinct) included numerous stocks that were (or are) isolated by homing behavior specific to time and place. The lack of intrinsic reproductive isolation among forms increases their vulnerability to extinction because rare forms apparently hybridize with common forms spawning at adjacent times or places.Key words: biogeography, Coregonus, fish, Great Lakes, introduced fishes, Pleistocene, species, subspecies

scholarly journals Paleomagnetism and cycle stratigraphy of the Triassic Fleming Fjord and Gipsdalen Formations of East Greenland

1996 ◽  
Vol 42 ◽  
pp. 121-136
Author(s):  
D.V. Kent ◽  
L.B. Clemmensen
Keyword(s):  
Late Triassic ◽  
Eastern North America ◽  
Stability Characteristic ◽  
East Greenland ◽  
Paleomagnetic Study ◽  
The Mean ◽  
Reversed Polarity ◽  
Formation Section ◽  
Milankovitch Orbital ◽  
Newark Basin

A 210 m section of Late Triassic Fleming Fjord Formation (the Malmros Klint Member and the lowermost 80m of the overlying Carlsberg Fjord beds of the Ørsted Dal Member) in the Tait Bjerg area of the Jameson Land Basin, East Greenland, was sampled for paleomagnetic study and measured for cycle stratigraphie analysis. Paleomagnetic samples were also taken from the underlying Gipsdalen Formation in the Gipsdalen area. A high stability characteristic magnetization carried by hematite was successfully isolated in 63 sampling levels in the Fleming Fjord Formation and 9 sampling sites in the Gipsdalen Formation using progressive thermal demagnetization. The mean characteristic directions for the Herning Fjord and the Gipsdalen Formations may be be biased by sedimentary inclination error but are consistent with a northward drift of East Greenland of about 10° from the arid (ca. 25° N) to semihumid (ca. 35° N) paleoclimatic belts in the Middle to Late Triassic. Seven normal and reversed polarity intervals are clearly delineated in the Fleming Fjord Formation section. A preferred correlation of the magnetostratigraphy to a cyclostratigraphically calibrated reference polarity sequence recently derived from drill cores in the Newark Basin of eastern North America suggests that the sampled interval represents about a 3.5 m.y. interval of the late Norian. The Malmros Klint Member and the overlying Carlsberg Fjord beds have composite sedimentary cycles that vary in thickness from 25 m to about 1 m and seem to match Milankovitch orbital climatic cyclicity with periods of ~400ky, ~100ky, ~40ky, and ~20ky. The composition and thickness ratio of the cycles suggest that the measured section of the Malmros Klint Member and the Carlsberg Fjord beds represents lacustrine accumulation over about 4 m.y., a duration consistent with the magnetostratigraphic correlations.

scholarly journals Chronological implications of the paleomagnetic record of the Late Cenozoic volcanic activity along the Moravia-Silesia border (NE Bohemian Massif)

2012 ◽  
Vol 63 (5) ◽  
pp. 423-435 ◽  
Author(s):  
Vladimír Cajz ◽  
Petr Schnabl ◽  
Zoltan Pécskay ◽  
Zuzana Skácelová ◽  
Daniela Venhodová ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Multidisciplinary Approach ◽  
Field Survey ◽  
Volcanic Field ◽  
Late Cenozoic ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Scoria Cones ◽  
Age Determinations

Abstract This paper presents the results of a paleomagnetic study carried out on Plio-Pleistocene Cenozoic basalts from the NE part of the Bohemian Massif. Paleomagnetic data were supplemented by 27 newly obtained K/Ar age determinations. Lavas and volcaniclastics from 6 volcanoes were sampled. The declination and inclination values of paleomagnetic vectors vary in the ranges of 130 to 174 and -85 to -68° for reversed polarity (Pleistocene); or 345 to 350° and around 62° for normal polarity (Pliocene). Volcanological evaluation and compilation of older geophysical data from field survey served as the basis for the interpretation of these results. The Pleistocene volcanic stage consists of two volcanic phases, fairly closely spaced in time. Four volcanoes constitute the Bruntál Volcanic Field; two others are located 20 km to the E and 65 km to the NW, respectively. The volcanoes are defined as monogenetic ones, producing scoria cones and lavas. Exceptionally, the largest volcano shows a possibility of remobilization during the youngest volcanic phase, suggested by paleomagnetic properties. The oldest one (4.3-3.3 Ma), Břidličná Volcano, was simultaneously active with the Lutynia Volcano (Poland) which produced the Zálesí lava relic (normal polarity). Three other volcanoes of the volcanic field are younger and reversely polarized. The Velký Roudný Volcano was active during the Gelasian (2.6-2.1 Ma) and possibly could have been reactivated during the youngest (Calabrian, 1.8-1.1 Ma) phase which gave birth to the Venušina sopka and Uhlířský vrch volcanoes. The reliability of all available K-Ar data was evaluated using a multidisciplinary approach.

Late Precambrian glacial climate and the Earth's obliquity

1975 ◽  
Vol 112 (5) ◽  
pp. 441-465 ◽  
Author(s):  
G. E. Williams
Keyword(s):  
Ice Sheets ◽  
Warm Water ◽  
Secular Change ◽  
Substantial Evidence ◽  
Geological Evidence ◽  
Late Precambrian ◽  
Middle Latitudes ◽  
Water Origin ◽  
Iron Formations ◽  
Glacial Climate

SummaryLate Precambrian (∼ 750±200 Ma) glaciogenic sequences exhibit substantial evidence for marked climatic inequability of seasonal and longer periodicity (10° to ∼ 106yrs): (1) tillites are closely associated with dolomites, limestones and evaporites apparently of warm-water origin; (2) tillites occur with red beds and iron-formations whose iron probably was derived ultimately from lateritic weathering; (3) glacial dropstones occur locally within carbonates and iron-formations; (4) laminae, interpreted asvarvesby many workers, are common in argillites, carbonates and iron-formations; and (5) permafrost structures attributable to repeated seasonal changes of temperature are locally abundant. Such climatic, particularlyseasonalinequability apparently conflicts however with the probable low (≲30°) palaeolatitudes of deposition of numerous late Precambrian glaciogenic sequences.The contradictions presented by such sequences may be resolved by postulating a considerably increased obliquity of the ecliptic (ε) in late Precambrian time. Substantial increase in e would: (1) greatly amplify global seasonality; (2) weaken climatic zonation, thus allowing warm-water sedimentation and lateritic weathering over wide latitudes; and (3) increase the ratio of radiation received annually at either pole to that received at the equator, so when 54° < ε < 126° low and middle latitudes (≤ 43°) would be glaciated in preference to the poles. Ice sheets and permafrost thus can be envisaged principally in low and middle latitudes with contiguous warm-water and iron-rich facies under a markedly seasonal climate. The concept of secular change of e is supported by other geological evidence.

scholarly journals Palynostratigraphy of the Lower Tertiary volcanics and marine clastic sediments in the southern part of the West Greenland Basin: implications for the timing and duration of the volcanism

1992 ◽  
Vol 154 ◽  
pp. 13-31
Author(s):  
S Piasecki ◽  
L.M Larsen ◽  
A.K Pedersen ◽  
G.K Pedersen
Keyword(s):  
Volcanic Activity ◽  
Volcanic Rocks ◽  
Dinoflagellate Cysts ◽  
East Greenland ◽  
West Greenland ◽  
Second Stage ◽  
The Third ◽  
The North ◽  
Clastic Sediments ◽  
Third Stage

Volcanic rocks, forming hyaloclastites and subaqueous lava flows, were deposited intercalated with clastic sediments in a water-filled basin in West Greenland in the Early Tertiary. Three main stages of basin infilling occurred in the Disko-Nuussuaq area. The distribution of dinoflagellate cysts in the sediments shows that the basin was marine in the first stage and non-marine in the second stage of infilling. In the third stage the basin was displaced towards the south and was marginally marine. The dinoflagellate cysts form a typical mid-Paleocene assemblage which may be correlated with the calcareous nannoplankton (NP) zonation. The stratigraphically lowest investigated localities are coeval with the uppermost part of nannoplankton zone NP4, whereas the overlying localities within the marine basin (first stage) may be correlated with NP5-6. The localities from the non-marine second stage cannot be correlated with the NP zonation because they do not contain dinoflagellate cysts. Localities from the third stage are coeval with NP7-8. Younger volcanics are subaerially deposited. The total known range of the volcanics now falls within the NP3 to NP8 interval, giving a minimum duration for the main plateau-building stage of the volcanism of 4–6 million years. The subaerial basalts have previously been found to be mainly reversely magnetised, with one normally magnetised sequence which can now be stratigraphically correlated with NP4, and thereby identified as anomaly 27. The basalts in East Greenland started erupting during the NP9 zone, so that the volcanic activity in East Greenland largely succeeded that in West Greenland. In relation to the postulated mantle plume in the North Atlantic this means that the volcanic activity started in the peripheral part of the plume and only later switched to the central part.

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