Descriptions of turbidite deposits in the 1960s were based almost wholly on the Bouma (1962) sequence and its variations (Figs. 3-7 and 7-18). Very thick-bedded, massive sandstone and conglomerate lacking the ordered divisions of the Bouma sequence were termed fluxoturbidites (Dzulynsky et al., 1959), grain-flow deposits (Stauffer, 1967) and various other names. These deposits were little understood and their relation to turbidites that are organized into the Bouma sequence was very uncertain. Basin analyses were made chiefly by paleo-current, petrographic, and Bouma-sequence analysis.
The initial deposits of a turbidity current on a basin floor were thought to result in a bed that contained the complete (Ta−e) Bouma sequence (Figs. 3-7, 7-14, and 8-1). As the turbidity current flows basinward, the turbidite deposit becomes progressively finer, thinner, and progressively composed of the higher divisions of the Bouma sequence. The basic nature of this gradual transition has been proven by a number of laboratory experiments (Fig. 3-8). Walker (1967), based on these considerations as well as field experience with ancient turbidite systems, developed the ABC or Proximality Index for basin analysis of turbidite systems (Fig. 8-2). By comparing the percentage of beds beginning with the Bouma T division to the percentage of beds beginning with the Bouma Tb division, it was thought that proximal-distal relations for a group of turbidites or given basin could be determined. Walker (1967) also compared in tabular form the chief characteristics of proximal and distal turbiditedepos (Fig. 8-3).
However, the increasing recognition of major channels on modern