South American Data Research Articles

The Palaeogeographical Evolution of the South Atlantic: An Integrated Regional Study Based on South American, African and Antarctic Data: ABSTRACT

The Palaeogeographical Evolution of the South Atlantic: An Integrated Regional Study Based on South American, African and Antarctic Data: ABSTRACT

Lithospheric magnetic property contrasts within the South American plate derived from damped least-squares inversion of satellite magnetic data

A ridge regression (or damped least-squares) method has been used in a large-scale equivalent source inversion of South American MAGSAT data. The optimum damping parameter is selected based on percent increase in the sum of squared residual of the observed and the calculated anomaly and on the variance and the range of the solution for a series of damping parameters. Solutions obtained by the damping parameter selected in this manner are numerically stable and geologically meaningful. Consequently, these solutions are used in various applications such as transformation into effective magnetic susceptibility variation, altitude normalization, differential reduction-to-pole, and downward continuation of the data set. The spacing of equivalent sources and the source-observation distance are shown to introduce significant errors in the estimation of the physical property variation from equivalent source solutions for the large source spacing (> 1°) commonly in use. The correction for these geometric factors is essential in estimating the physical property variation from the equivalent source solutions. A continental and an oceanic profile have been analyzed from the South American maps derived from the above techniques. The continental profile transects a variety of geologic/tectonic features, including shields, aulacogens, basins and fold belts, near the north coast of South America. Along the profile, there is a good correlation between the radially polarized MAGSAT magnetic anomalies and other available geologic and geophysical information. In addition, the variation in effective susceptibility obtained from the damped equivalent source inversion is consistent with our present knowledge of continental lithospheric susceptibilities expected from the geologic/tectonic provinces along the profile. The oceanic profile extends from the trailing margin of South America through the Cretaceous normal polarity rocks of the South Atlantic Ocean. The variations in the magnetic properties along this profile can be broadly correlated with the depth anomaly variation, indicating a possible genetic relationship. Two conceptual models requiring undepleted mantle intrusions under the oceanic uplifts appear possible. In the first model, the high magnetization can be accounted for by a (weakly) magnetic upper mantle below the uplifts; in the second model, very highly magnetic rocks are required in the crust of these uplifted regions to account for the observed anomaly values.

Impaction surface coatings intercomparison and measurements with cascade impactors

Intercomparison tests of aerosol particle sampling using single-orifice cascade impactors of the Battelle design have been made with different impaction surface coatings. Results from two runs in Tallahassee, Florida and data representative of 40 South American runs show that Vaseline is the preferred coating to use for cascade impactors and elemental analysis by proton induced X-ray emission (PIXE) analysis. Uncoated and paraffin coated impaction surfaces were 25–45% and 50–75%, respectively, as effective in particle retention as Apiezon L grease and Vaseline from tests run in Tallahassee. The South American and Tallahassee data show that the aerosol particle sources and relative humidity are important factors in determining the efficiency of particle collection and retention in cascade impactors. For optimal sampling results, sample loading in cascade impactors should be kept to a minimum.

The interpretation of surface equatorial magnetic daily variations on disturbed days

Reference is made to the results of an analysis of magnetic data from the lowlatitude station M'Bour—published in the Annls Géophys., 1970 No. 4—from which it is apparent that the contribution of non-ionospheric currents to surface magnetic daily variations is considerable on all days other than magnetically Q days. It is shown that correction for the symmetric ring current using Sugiura's D st values does not completely account for the difference between Q and D days and it is suggested that the discrepancy arises from the asymmetric part of the ring current. On disturbed days at equatorial stations, it is found, from examination of South American IGY data, that in addition to the contributions of the symmetric and asymmetric ring currents, there are superimposed fluctuations in the H component of duration 1–2 hr. These are enhanced around local noon and at the dip equator. In the Z component, there are corresponding fluctuations which appear to be enhanced near the edges of the electrojet region. Possible sources of these fluctuations are suggested.

A palaeomagnetic survey of South American rock formations - A palaeomagnetic survey of South American rock formations: General introduction

The results of this survey are presented in five papers which follow this introductory paper. Experimental methods, statistical treatment, conventions and abbreviations used in the work as a whole are described here. A list of references to published work in English on South American geology and also of South American palaeomagnetic data is appended.

THE DEVELOPMENT OF THE SOUTH AMERICAN DATUM 1969

The Pan American Institute on Geography and History (PAIGH) adopted a new South American Datum (SAD 69) at the XIth Pan American Consultation on Cartography in Washington, D.C., June 1969. The questions may arise, what has been used before, why is it important to change, and what are the characteristics of the new datum?

The Equatorial F‐layer Irregularity Extent as Observed From Huancayo, Peru

Simultaneous observations of propagation paths to two synchronous satellites transmitting at 137 MHz have revealed distinctive characteristics of the equatorial irregularity structure. Data were taken between July 1967 and February 1969. The abrupt onset of scintillations on a particular path within minutes led to the concept that a sharp boundary of about 10 km exists between quiet non‐scintillating regions and regions of irregularities. Once the scintillation has started, a region over 5000 km wide from east to west may contain irregularities. Within such a region there is strong localized control of irregularities. Comparison of scintillation onset on two paths spaced 1 to 2 hours apart at their subionospheric points reveals that, in the mean, scintillation onset is a function of local time. However, many days show nearly simultaneous onset on two paths that are 1 hour apart in local time. Other days show onset of scintillations on the westerly satellite path before onset at the eastern intersection; this variability is clearly a negation of the diurnal pattern. Maximum occurrence of scintillation has been observed in September, October, and November. A somewhat lower occurrence of high‐amplitude scintillation is noted in the December–January solstice period. A secondary maximum exists in March, according to other South American data. A very low occurrence of scintillation is observed in May, June, and July. The scintillation phenomenon is correlated in the mean with the downward motion of the F layer after 2100 local time at Huancayo. A hypothesis is advanced that after 2100 the westerly F‐layer maximum is higher in altitude and has a greater electron density than the easterly maximum. This west‐east gradient of electron density produces (either through electrodynamic forces or diffusion) the irregularities that show an apparent eastward drift. The diurnal pattern, with its nighttime maximum of scintillation occurrence, is a westward motion, but the irregularity drifts noted are clearly eastward in the direction of lower electron density profiles.

South American Foragers: A Case Study in Cultural Devolution1

Contemporary evolutionary typologies characterize band society largely on the basis of patrilocal residence and/or patrilineal descent patterns. The South American data challenge the adequacy and universal applicability of these models with a high incidence of matriliny and matrilocality and with forms of political integration that extend far beyond the local residential group. Furthermore, when viewed in a diachronic perspective, these hunters and gatherers have undergone a process of simplification from early contact to modern times. Contemporary band societies appear to represent degenerated structures formerly characterized by larger population concentrations, corporate unilineal descent groups, and heterogeneous political communities.

P.T.C. thresholds, blood factors, colour vision and fingerprints of Jivaro Indians in Eastern Ecuador.

AbstractAmong the Jivaro Indians of Eastern Ecuador, very low non‐taster frequencies were found, a situation in accord with most of the other, through few sets of P. T. C. data available for South American Indians. The Jivaro have maximal frequencies (1.000) of the alleles I° and D, typical of most South American Indian groups. The colour blindness frequency of males (7.1%) is seemingly higher than North American Indian figures and is similar to European frequencies. Jivaro dermatoglyphic data are in broad general agreement with data available for Amerindian groups generally, and for many Asian mongoloids, with high pattern intensity indices for males and females, mainly the result of a very high whorl incidence. The digital distribution of the pattern types for the greater part accords with the generalisations of Cummins and Midlo ('61). There are marked sex differences in the data, females having a lower mean pattern intensity index, a higher value for Dankmeijer's Index and a lower value for Furuhata's Index. Unfortunately there are few other sets of South American Indian data available for comparative purposes.

The Primary Mental Abilities Of South American Students : A Second Comparative Study Of The Generality Of A Cognitive Factor Structure.

In an earlier study, the Primary Mental Abilities (PMAs) of Chinese students studying in American Universities was compared with those of American college students. In the present study, the PMAs of South American college students are compared with the PMAs of the Chinese students. Thirty- one tests (twenty with English instructions and eleven with Spanish instructions) were administered to 92 South American students who were participating in the English Language Institute of the University of Michigan. After treating the South American data by Ahmavaara's transformation analysis, seven factors were matched between the South American and Chinese studies; the congruence indices for the two sets of factors ranged between .953 and .780.

BASAL METABOLISM AND RESPIRATION IN MEN LIVING AT 5,800 M (19,000 FT).

Respiratory determinations were carried out on eight members of the Himalayan Scientific and Mountaineering Expedition 1960—1961 and three Sherpas during a prolonged stay at 5,800 m (19,000 ft). Ventilation and oxygen uptake were similar in both groups, although the Sherpas were smaller men. The Sherpas had lower alveolar ventilation, higher PaCOCO2 and lower PaOO2 values than the scientists. Among six of the scientists mean basal metabolic rate was 10% above the mean value predicted from sea-level standards. There was no increase in the two others, who did not acclimatize. The mean basal metabolic rate in the three Sherpas was +21%. The findings were not explained by the extra O2 cost of increased breathing, changes in body composition, or exposure to cold, although this may have been a factor in the Sherpas. The results were similar to recent South American data on residents at 4,540 m (14,900 ft). It was concluded that acclimatization to great altitudes in man is associated with increase in basal metabolism, but there is insufficient evidence as to whether this is a response to hypoxia or other environmental factors. basal respiration; acclimatized men; high altitude (5,800 m) Submitted on March 30, 1964