Geology topics

Richard R. Doell

Publications and source records attributed to Richard R. Doell.

23 records · Page 2Linked to original sources

USGS1961

Paleomagnetism

This chapter highlights the ways in which rocks become magnetized. It also interprets paleomagnetic results in terms of the theories of polar wandering, continental drift, and an expanding Earth. The chapter describes the salient characteristics and trends of the geomagnetic field during the period of direct observation. Several questions are posed concerning the extension of these properties back to earlier times. Some of these questions can now be answered from the results of paleomagnetic research. The intensity of the main dipole component of the geomagnetic field appears to have been decreasing since well before the period of direct observation. Furthermore, two important properties of the geomagnetic field have been established by spherical harmonic analysis. First, the field is derivable from a potential and, hence, contributions to the total field from currents flowing across the Earth–air interface are negligibly small. Secondly, 2–5% of the field is of external origin and is because of movements of charged particles in the space around the Earth.

Advances in Geophysics↗

USGS1961

Palæomagnetic evidence relevant to a change in the earth's radius

INTEREST in the hypothesis that the Earth's radius has increased during geological history has been renewed in recent years because of several sets of independent observations and interpretations. From studies of the deformation of mountain ranges and the distribution of faults and oceans, Carey 1 proposes an increase in the Earth's area of 45 per cent since the Palæozoic era. Heezen 2 similarly interprets submarine topography as indicating that the oceans may be immense rift valleys formed by a pulling apart of the continents as the Earth expanded. Using a different approach, Egyed 3,4 infers a rate of increase of the Earth's radius of 0.4–0.8 mm. per year. This calculation is based on a decrease in the total amount of continental area covered by oceans during the past 400 million years, as determined palæographically. Egyed 4 has also pointed out the desirability of using palæomagnetic data to test this hypothesis.

Nature↗

USGS1961

Palæomagnetic evidence relevant to a change in the Earth's radius

IT is important to note that if, during an expansion of the Earth, each point on the surface were to move radially outward, then all sampling areas would have the same relative geographical co-ordinates before and after expansion. Palæomagnetic results could not be used to detect an expansion of this type. However, an alternative model of expansion is that in which most or all of the increase in area is reflected by an increase in the area of the ocean basins. We considered Prof. Carey's model of Earth expansion to be of this general type, since he concludes 1 that the Atlantic, Indian and Pacific Ocean basins formed by dilatation attendant on expansion. If the ocean basins formed in this way, the method we used would show an increase in the Earth's radius, even if the continents had also grown a lesser amount.

Nature↗

USGS1961

Palæomagnetism of Hawaiian lava flows

PALÆOMAGNETIC investigations of volcanic rocks extruded in various parts of the world during the past several million years have generally revealed a younger sequence of lava flows magnetized nearly parallel to the field of a theoretical geocentric axial dipole, underlain by a sequence of older flows with exactly the opposite direction of remanent magnetization. A 180-degree reversal of the geomagnetic field, occurring near the middle of the Pleistocene epoch, has been inferred by many workers from such results 1–3 . This is a preliminary report of an investigation of 755 oriented samples collected from 152 lava flows on the island of Hawaii, selected to represent as many stratigraphic horizons as possible. (Sampling details are indicated in Table 1.) This work was undertaken because Hawaii's numerous thick sequences of lava flows, previously mapped as Pliocene to Historic by Stearns and Macdonald 4 , and afterwards assigned ages ranging from later Tertiary to Recent, by Macdonald and Davis 5 , appeared to offer an ideal opportunity to examine the most recent reversal of Earth's field.

Nature↗

USGS1960

Review of paleomagnetism

This review is an attempt to bring together and discuss relevant information concerning the magnetization of rocks, especially that having paleomagnetic significance. All paleomagnetic measurements available to the authors are here compiled and evaluated, with a key to the summary table and illustrations in English and Russian. The principles upon which the evaluation of paleomagnetic measurements is based are summarized, with special emphasis on statistical methods and on the evidence and tests for magnetic stability and paleomagnetic applicability. Evaluation of the data summarized leads to the following general conclusions: (1) The earth's average magnetic field, throughout Oligocene to Recent time, has very closely approximated that due to a dipole at the center of the earth oriented parallel to the present axis of rotation. (2) Paleomagnetic results for the Mesozoic and early Tertiary might be explained more plausibly by a relatively rapidly changing magnetic field, with or without wandering of the rotational pole, than by large-scale continental drift. (3) The Carboniferous and especially the Permian magnetic fields were relatively very “steady” and were vastly different from the present configuration of the field. (4) The Precambrian magnetic field was different from the present field configuration and, considering the time spanned, was remarkably consistent for all continents.

GSA Bulletin↗