Paleomagnetism of the Devonian Catskill Red Beds: Evidence for Motion of the Coastal New England-Canadian Maritime Region Relative to Cratonic North America

The natural remanent magnetizations of reddish clay stones, siltstones, and sandstones from the nearly flat lying Middle to Upper Devonian Catskill sequence of southeastern New York were analyzed with thermal, alternating field, and chemical demagnetization techniques. After removal of a low blocking temperature component along the present geomagnetic field direction a characteristic direction of magnetization was isolated: D = 172.3°, I = 1.0°, k = 116, and α_95 = 4.7° for N = 9 sites (43 samples), giving a paleomagnetic north pole at 46.8°N, 116.7°E, dp = 2.4°, and dm = 4.7°. The combined demagnetization analyses show this to be the only stable component of magnetization present in these rocks. The derived pole position agrees well with the poles reported for some Devonian limestones in Ohio, all falling near the Permian poles for North America, but disagrees with Devonian results from eastern Maine-New Brunswick and eastern Massachusetts which give poles at lower latitudes. A similar geographical grouping with similar directions is also apparent for Lower Carboniferous (Mississippian) paleomagnetic poles for North America. We interpret these and other late Paleozoic paleomagnetic data to show that the coastal Canadian Maritime-New England region was not an integral part of cratonic North America until about the Late Carboniferous. Geological considerations suggest that the Carboniferous relative motion was along transcurrent shear zones

Multicomponent magnetizations from the Mississippian Mauch Chunk Formation of the central Appalachians and their tectonic implications

Previous paleomagnetic study of Mississippian red beds of the Mauch Chunk Formation from the central Appalachians reported shallow inclination directions. A positive fold test was obtained after thermal demagnetization, typically to only 550°C. The near-equatorial position for North America indicated by these results has been used to support the idea of a circa 15° latitudinal tectonic offset of the Acadia displaced terrain in the northern Appalachians. The present study of 153 samples from 29 sites occupied in the Mauch Chunk Formation of eastern and southern Pennsylvania reveals multicomponent magnetizations. A characteristic component (Declination (D) = 161.0°, Inclination (I)=27.8°, alpha95 (a95)=7.9°) with unblocking temperatures usually concentrated above 650°C and with dual polarity (10 sites normal, 13 sites reversed) is isolated in 23 sites and passes a fold test at the 99% confidence level. It is interpreted as an early acquired hematitic (detrital or chemical) magnetization of pre-Alleghanian orogeny and pre-Kiaman Reverse Polarity Interval age; a southern hemisphere paleolatitude of 15° for the sampling area is indicated. Another component has generally lower unblocking temperatures which, however, can extend up to 650°C or more and therefore is also likely to be carried by hematite. This secondary magnetization (D=170.6°, I=-5.3°, a95=5.0°) isolated in 25 sites is of uniform reverse polarity, and application of fold tests suggests that it is of synfolding origin; a near-equatorial paleolatitude (3°N) at the time of acquisition is obtained, consistent with Permo-Carboniferous Kiaman directions from North America. Incomplete removal of the secondary component can explain the previous results from the Mauch Chunk. Comparison of the present paleomagnetic results with those from similar age rocks in the Canadian Maritimes does not support a latitudinal offset of Acadia with respect to interior North America in the Early Carboniferous. In fact, according to these and other paleomagnetic data thought to be representative of this age, the Atlantic-bordering continents already were near to a Pangea configuration. The Alleghanian and particularly the Hercynian orogenies therefore may not be associated with the closure of a large (latitudinal) ocean later in the Carboniferous and Permian. Alleghanian deformation, however may have resulted in the partial bending of the Pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

The Early Carboniferous paleomagnetic field of North America and its bearing on tectonics of the Northern Appalachians

We have obtained additional evidence for the Early Carboniferous paleomagnetic field for cratonic North America from study of the Barnett Formation of central Texas. A characteristic magnetization of this unit was isolated after thermal demagnetization at four sites (36 samples) out of eight sites (65 samples) collected. The mean direction of declination = 156.3°, inclination = 5.8° (N = 4 ,k = 905 , α95 = 3.0°), corresponds to a paleomagnetic pole position at lat. = 49.1°N,long. = 119.3°E (dp = 1.5° , dm = 3.0°). Field evidence suggests that characteristic magnetization was acquired very early in the history of the rock unit whereas the rejected sites are comprised of weakly magnetized limestones dominated by secondary components near the present-day field direction. Comparison of the Barnett pole with other Early Carboniferous (Mississippian) paleopoles from North America shows that it lies close to the apparent polar wander path for stable North America and that the divergence of paleopoles from the Northern Appalachians noted previously for the Devonian persisted into the Early Carboniferous. We interpret this difference in paleopoles as further evidence for the Northern Appalachian displaced terrain which we refer to here as Acadia, and the apparent coherence of Late Carboniferous paleopoles as indicating a large (∼1500 km) motion of Acadia with respect to stable North America over a rather short time interval in the Carboniferou

Climate Change in the North Pacific Using Ice-Rafted Detritus as a Climatic Indicator

The variations in weight percent of the grain size fraction greater than 250 μ in nine cores from the North Pacific were determined using sampling intervals of 5 to 20 cm. Material in this size fraction is interpreted as transported by icebergs, and fluctuations are attributed to the waxing and waning of glaciers on the surrounding continents. At least eleven periods of increased ice rafting are detected in the cores during the time from 1.2 m.y. ago to the present, whereas only about four are identified from 1.2 m.y. to 2.5 m.y. B.P. The dating and time correlations are based on the magnetic stratigraphy, ash falls, and faunal extinctions. The ice-rafted detritus indicates a cooling beginning about 1.2 m.y. ago and becoming very intense between the Jaramillo event and the Brunhes-Matuyama boundary. This time may correspond to the initiation of mid-latitude glaciations of Europe and North America. At least six zones of ice-rafted sediment are present in the Brunhes normal polarity series. The correlations between these and the carbonate fluctuations of the central Pacific are good. Evidence for a marked interglacial ranging from about 460,000 to 530,000 yrs B.P. occurs within these cores. This interglacial may be worldwide in extent

Details of magnetic polarity transitions recorded in a high deposition rate deep-sea core

Measurements of the NRM of a 26 m long deep-sea core from the southern Indian Ocean indicated the presence of three transitions of magnetic polarity which have been identified as the upper and lower Jaramillo and the upper Olduvai on the basis of micropaleontological criteria. Detailed studies of the magnetic reversals were made in view of the high deposition rates (~9 cm/10^3 yr) present over sections of the core. The NRM was found stable against alternating fields. Magnetic mineralogy studies indicated the presence of titanomagnetite and magnetite which probably have not undergone any significant low-temperature oxidation. The three polarity changes had the following features in common: (1) presence of intermediate directions of magnetization; (2) a pronounced drop in the intensity of magnetization; (3) the drop in intensity of magnetization was coincident with the large directional fluctuations. Measurements of saturation isothermal and anhysteretic remanence, and bulk susceptibility, show that the decrease in NRM intensity associated with each polarity change is not due to a low concentration of the magnetic minerals. The best estimate for the duration of a polarity transition is approximately 4600 yr. There is evidence for both eastward and westward drift of the non-dipole field, which appears to be dominant during the polarity transition interval. The data presented here support a model of a reversing field in which the main dipole field decays to a low value and then builds up in the opposite direction

A synthesis of magnetostratigraphic results from Pliocene-Pleistocene sediments cored using the hydraulic piston corer

We present a summary evaluation of the distribution and qualitative ranking of the Plio-Pleistocene magnetostratigraphic results obtained to date from Deep Sea Drilling Project and Ocean Drilling Program piston-cored sites. A review of the published magnetostratigraphic records provides insights into the important extrinsic and intrinsic factors which affect the quality of the paleomagnetic records. The extrinsic factors originate with drilling processes, such as core barrel remagnetization, and steps can be taken to reduce these effects and improve the data quality. The distribution of the high-quality records correlates well both with areas of terrigenous sediment input as well as regions of moderate biological productivity. This suggests that important intrinsic factors include the origin of the original magnetic carrier in the sediment (lithogenic or biogenic) and the degree to which the magnetic carrier has been affected by reduction diagenesis

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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95549/1/eost11864.pd

Paleomagnetism and Magnetic Properties of Igneous Rock Samples—Leg 38

Basaltic rock was recovered from nine sites on Leg 38. Initially, one to three partially oriented specimens in the form of right-circular cylinders, 2.5 cm in diameter and 2.5 cm high, were obtained from each of these sites for preliminary magnetic studies. The studies included measurement of intensity and direction of remanent magnetism, susceptibility, stability of remanence against alternating fields, and thermomagnetic characteristics. Additional samples were taken subsequently from cores some of the sites in order to resolve some discrepancies apparent in our initial observations, particularly at Site 336, as well as between these and measurements on the same rocks made by Russian workers. Results from the additional samples are incorporated in this report

Paleomagnetism of Siluro-Devonian rocks from eastern Maine

A diverse suite of rocks was collected for paleomagnetic study from two formations in the Eastport area of northeastern Maine: 18 sites (103 samples) from redbeds and diabase sills of the Hersey Formation (uppermost Silurian to Lower Devonian) and 14 sites (74 samples) from lavas, redbeds, and calcareous nodules of the Eastport Formation (Lower Devonian; Rb/Sr age 412 Ma). Characteristic magnetizations based on AF and thermal demagnetization analyses give mean directions, after simple correction for bedding tilt, of D = 163.6°, I = 41.3°, α_95 = 6.3°, for N = 16 sites in the Hersey, and D = 179.3°, I = 38.0°, α_95 = 9.4°, for N = 14 sites in the Eastport Formation. Baked contact relations, the presence of opposite polarities, and the similarity in directions over different rock types and magnetic carriers point to an acquisition of magnetization near to the time of rock formation. The mean directions correspond to (south) paleopole positions at 19.8°S lat., 308.8°E long. (δp, δm = 4.7°, 7.7°) for the Hersey and 23.7°S lat., 293.7°E long. (δp, δm = 6.6°, 11.1°) for the Eastport Formation. These paleopoles are removed from the Upper Silurian Bloomsburg Formation pole, but are in reasonable agreement with similar age results from central Newfoundland, suggesting that the Acadia displaced terrain encompassed these areas. Siluro-Devonian paleopoles from intrusive rocks in northeastern North America are generally widely divergent and these may not be providing an accurate record of paleomagnetic field in all cases

Widespread late Mesozoic to Recent remagnetization of Paleozoic and lower Triassic sedimentary rocks from South China

Paleomagnetic results are described from eighteen formations sampled in the Nanjing (Jiangsu Province) and Yichang (Hubei Province) areas of South China. The marine platform carbonates and elastics range in age from early Cambrian to early Triassic. Progressive alternating field and/or thermal demagnetization analyses reveal predominantly single component magnetizations, sometimes of both normal and reverse polarity. These magnetizations, isolated in 457 of the 549 samples studied, typically have directions in geographic coordinates coincident with late Mesozoic to Recent fields. A secondary origin for the magnetizations is supported by negative fold tests in several units. A lower Carboniferous and possibly a lower Triassic limestone may have escaped the pervasive remagnetization; if the remanences isolated are indeed prefolding, a large counterclockwise tectonic rotation of the Nanjing area is implied by comparison with available Carboniferous and Triassic paleopoles reported from elsewhere in South China. This rotation may have been associated with Mesozoic left-lateral motion on the Tancheng-Lujiang fault zone