This paper discusses almost exclusively the use of the so-called smaller Foraminifera in stratigraphical correlation. The abundance of these microfossils, notably in certain Tertiary deposits, together with the limited vertical distribution of a number of the species, particularly favour their use in problems related to petroleum geology. As a basis for correlation in a given area it is considered important that a reliable type section be sampled at regular intervals and studied in detail. The technique in the preparation of samples is briefly discussed. It- is emphasised that a close definition of the foraminiferal species is essential to the successful application of micropalaeontology in stratigraphy. A slide suitable for mounting or separating Foraminifera is described. Attention is drawn to the influence of facies on microfaunas, in particular with regard to geological correlation and the faunal changes which may occur both laterally and vertically. Reasons are advanced for concluding that the micropaheontology of each Tertiary basin of deposition has to be considered as a distinct problem. As an example of the use of Foraminifera in stratigraphy a table is given showing the distribution of the more characteristic forms in the Tampico Embayment of Mexico.
During recent years the practical value of micropalmontology in petroleum geology has become increasingly recognised. In regions where foraminiferal strata exist, as is not uncommon in the marine Tertiary, conditions are often found suitable for application of micro-palaeontology. After making detailed studies of smaller Foraminifera and their relation to stratigraphy, various workers have shown that these organisms are frequently valuable as horizon markers. In this paper the author has attempted to indicate the scope and limitations of the subject, and to describe briefly certain working methods which in the course of several years have been found of value in economic work. This paper has been published.by published. by permission of the Bataafsche Petroleum Maatschappij. The writer is indebted to members of the Company's Geological Staff for suggestions herein incorporated.
The selection of a reliable standard or type section is of utmost importance. It is improbable that a single unbroken section of the whole sequence will anywhere be present. However, in areas without serious tectonic disturbance parts of the stratigraphical column are present, either at the surface or in wells. The entire stratigraphical column for a certain embayment or country has nearly always to be pieced together from overlapping partial sections.