| Popis: |
Data concerning the composition of sands from modern continental margins has enabled an actualistic scheme of provenances to be formulated. In order to avoid secondary controls of detrital modes some of the variables have been standardized. This means that optical-microscope analyses can be interpreted in terms of provenance only when (1) they are conducted according to the Gazzi-Dickinson method and in such detail as to include secondary parameters, (2) they deal with terrigenous, texturally immature and medium- to fine-grained sands, and (3) they are obtained from deep-sea deposits which have not been subjected to diagenetic modifications. Source-area types have been identified on the scale of large plate features and named First Order Provenances (FOP); the same size-scale should be considered when using such provenances for paleogeographic reconstructions. |
