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The classical questions are: "Do reefs create recognizable gravity anomalies?" "If and when they do, then what causes these anomalies?" To find the answers to these questions, first a study of the case histories was made. It indicated that deeply buried, "isolated" organic reefs frequently create recognizable but "mysterious" gravity anomalies, and that there is no evident direct relation between the reef mass and the gravity anomaly. To find out the causes of these anomalies, the field of investigation proved to be so large that this paper could be entitled "a tentative density analysis of the sedimentary subsurface."
The reef mechanism and the depositional processes are such that there is a concentration of sand in the over-reef section. Densities in clay and sand mixtures were investigated in terms of composition and depth of burial. The sand concentration alone is capable of creating shallow positive and deep negative density contrasts sufficient to account for the major part of the gravity anomaly. The gravity effect of a hypothetical reef was calculated. The result was very much like those actually observed. The gravity anomaly depends mainly on what has happened after the reef was buried, and not on the contrast at the reef level.
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