Projection of dip data in conical folds onto a cross-section plane

The projection of dip data onto a section plane can be a source of errors in the relative and absolute position of data depending on the choice of projection vectors. To properly transfer data in conical folds onto a plane of section, a best-fitting cone must be defined for the fold. Dip data must be projected along the best-fit cone generatrices, which are defined individually for each dip measurement according to its orientation. For individual dip measurements on bedding in a conical fold, their corresponding generatrix can be defined as the line of tangency between bedding and the conical fold. Dip measurements on bedding not fitting an ideal conical geometry must be corrected before a valid generatrix can be calculated. Graphical procedures to obtain generatrices for individual dip data are discussed, and a new analytical method is proposed to calculate generatrices for dip measurements on bedding not fitting an ideal conical geometry. The maximum projection distance within conical folds is discussed, and a way to estimate the natural extent of conical folds is defined. The proposed methods are illustrated with data from a conical syncline in NE Spain.