ADVANCES IN DETERMINING GEOMETRIES OF SEDIMENTARY BODIES, FROM 1.5 TO 3 DIMENSIONS

Thirty years ago, sedimentary bodies were usually were usually accurately measured only in the vertical dimension. Lateral facies changes were usually accurately depicted but not accurately located. Today, new tools allow three-dimensional subsurface delineation of volumes of facies and sediment bodies. For many of us the result of this revolution has been very like looking a picture showing a field of colored dots and suddenly seeing the picture of a mans face hidden inside all along.

Although new geophysical and computer applications provide images of volumes, the key elements are conceptual changes that improved our understanding of stratigraphic correlation and how facies are correlated. One key conceptual change was appreciating of the importance of bounding surfaces in defining sedimentary bodies. At the smallest scale, hierarchies of bounding surfaces revealed the internal structures of channels and barforms. At the largest scale, stratigraphic sequences redefined regional and global correlation. Panoramic photomosaics of outcrops when overlain with bounding surfaces provided accurate two-dimensional delineation of sedimentary bodies.

Within the last few years, three-dimensional seismic data, and ground penetrating radar volumes have expanded accurate representation to the third-dimension for subsurface bodies. New techniques of accurate outcrop mapping, using global positioning surveys allow projection of some outcrops into the third dimension. New three dimensional imaging programs allow scientists to literally walk through sedimentary rock bodies. Finally, using GIS and similar programs has allowed us to integrate divergent data and draw new conclusions.