REMANENT MAGNETISM AS A CONTRIBUTOR TO SOME AEROMAGNETIC ANOMALIES

Geophysics ◽  
1962 ◽  
Vol 27 (3) ◽  
pp. 359-375 ◽  
Author(s):  
Kenneth G. Books
Keyword(s):  
Remanent Magnetization ◽  
Volcanic Rocks ◽  
Horizontal Direction ◽  
Dominant Factor ◽  
Rock Body ◽  
North Central ◽  
Remanent Magnetism ◽  
Aeromagnetic Anomalies ◽  
Intrusive Rocks ◽  
Central Montana

An investigation of some aeromagnetic anomalies in north‐central Montana shows that remanent magnetization is the dominant factor in anomalies over some rocks and a contributing factor in anomalies over others. In volcanic rocks, remanence is commonly south‐seeking down and has an intensity approximately ten times the induced intensity of magnetization. Remanence is shown to be the dominating factor in anomalies over volcanic rocks by the agreement between the profiles of an observed anomaly over a volcanic rock body and an anomaly calculated from remanence data for the same body. In intrusive rocks, the remanence is north‐seeking down and comparable in intensity to the induced intensity of magnetization. That remanence also contributes to the anomalies over some intrusive rocks is shown by the agreement between the profiles of an observed anomaly over an intrusive body and an anomaly calculated from the resultant of induced and remanent magnetizations. A consistent relationship between the axis of the anomaly, or direction between the anomaly high and low, and the horizontal direction of magnetization suggests that the direction of the anomaly axis can be used to indicate the horizontal direction of magnetization in this area.

Density and magnetic susceptibility measurements in southeastern New Brunswick

1977 ◽  
Vol 14 (1) ◽  
pp. 128-132
Author(s):  
V. K. Gupta ◽  
K. B. S. Burke
Keyword(s):  
Magnetic Susceptibility ◽  
New Brunswick ◽  
Volcanic Rocks ◽  
Considerable Variability ◽  
Aeromagnetic Anomalies ◽  
Rock Types ◽  
Flow Units ◽  
Intrusive Rocks ◽  
Density Values

The results of over 200 density and 400 (at 37 sites) in-situ magnetic susceptibility measurements from southeastern New Brunswick are presented. Intrusive rocks were found to be homogeneous in density and to have values similar to those reported from adjacent areas of the Northern Appalachians. However, most of the Coldbrook volcanic rocks show considerable variability in density values even within individual rock types. As expected, rocks containing higher proportions of ferromagnesian minerals (i.e., basalt, diorite, and gabbro) generally gave higher magnetic susceptibility values. The lack of aeromagnetic anomalies over mafic volcanic rocks in the central Caledonia Highlands may possibly be explained in terms of thin and flat-lying flow units.

New Insights into Interpretation of Aeromagnetic Data for Distribution of Igneous Rocks in Central Iran

2021 ◽  
Author(s):  
M. Mohammadzadeh Moghaddam ◽  
S. Mirzaei ◽  
M. Abedi
Keyword(s):  
Magnetic Susceptibility ◽  
Volcanic Rocks ◽  
Igneous Rocks ◽  
Aeromagnetic Data ◽  
3D Inversion ◽  
Aeromagnetic Anomalies ◽  
Susceptibility Data ◽  
Lut Block ◽  
Wide Range ◽  
Intrusive Rocks

Abstract —New insights in the aeromagnetic data over the Central Iranian Microcontinent (CIM) have revealed interesting results for future studies and exploration. This work presents the interpretation of different magnetic analyses and the calculated 3D inversion model to provide important insights into the distribution of igneous rocks in the area that may be traced under significant cover. By analyzing several hundred magnetic susceptibility data points and aeromagnetic anomalies of known igneous rocks over the area, it was determined that mafic–ultramafic intrusive rocks generally have a high magnetic susceptibility and produce a strong magnetic response. Intermediate–felsic intrusive rocks have a low magnetic susceptibility and show a smooth gradient variation and commonly regular shape. Volcanic rocks show a wide range of magnetic susceptibility; therefore, the aeromagnetic anomalies are often random or show strong amplitude with high frequency signals and are rapidly eliminated when an upward continuation is applied. Based on the results of analysis of different magnetic maps and 3D inversion of data, and combining this information with known outcropped of igneous rocks, we revealed 1215 concealed intrusive rocks and 528 volcanic rocks in the area. We also renewed the boundaries of tens outcropped igneous rocks. The known and new mapped igneous rocks can be identified as 12 regions (or zones) for intrusive rocks and 4 regions for volcanic rocks. The results indicate that the mafic–ultramafic rocks are mainly located in the Sistan suture zone of eastern Iran along the Nehbandan fault zone. They also show that the many parts of the Lut block as the main structure of CIM have been under magmatic events, so that most of concealed igneous rocks are distributed in the middle and southern part of the Lut block. Volcanic rocks are widespread in the southeastern and northern parts of the area such as the Urumieh-Dokhtar Magmatic Arc, North Lut, and Bam region.

Dwarf Shrew (Sorex nanus) in North-Central Montana

1977 ◽  
Vol 58 (2) ◽  
pp. 248-250 ◽  
Author(s):  
L. S. Thompson
Keyword(s):  
North Central ◽  
Central Montana

Evidence for Picea pungens in north-central Montana and its significance

1978 ◽  
Vol 56 (9) ◽  
pp. 1118-1121 ◽  
Author(s):  
W. L. Strong
Keyword(s):  
Native Species ◽  
The State ◽  
Geographical Range ◽  
North Central ◽  
Picea Pungens ◽  
Central Montana

The analysis of Picea cone scales from the Sweetgrass Hills of Montana substantiates the existence of Picea pungens Engelm. in north-central Montana. These results extend the geographical range of P. pungens and identify a new native species within the state of Montana.

Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana

Paleobiology ◽  
2017 ◽  
Vol 43 (2) ◽  
pp. 248-273 ◽  
Author(s):  
Raymond R. Rogers ◽  
Matthew T. Carrano ◽  
Kristina A. Curry Rogers ◽  
Magaly Perez ◽  
Anik K. Regan
Keyword(s):  
Upper Cretaceous ◽  
Statistical Tests ◽  
Sampling Strategies ◽  
North Central ◽  
Wetland Ecosystems ◽  
Future Studies ◽  
Size And Shape ◽  
Definition Of ◽  
Central Montana ◽  
Judith River Formation

AbstractVertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

scholarly journals Assessment of undiscovered oil and gas resources in the North-Central Montana Province, 2017

Fact Sheet ◽  
2018 ◽  
Author(s):  
Christopher J. Schenk ◽  
Tracey J. Mercier ◽  
Michael E. Brownfield ◽  
Marilyn E. Tennyson ◽  
Cheryl A. Woodall ◽  
...  
Keyword(s):  
Oil And Gas ◽  
North Central ◽  
The North ◽  
Oil And Gas Resources ◽  
Central Montana
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