Abstract The Upper Mississippian Brockie Lake Conglomerate (BLC) of the Pioneer Mountains of south-central Idaho ( Figure 1 ) forms a ~650-m (~2132-ft)-thick conglomeratic unit deposited in the Mississippian Antler foreland basin. It was derived from erosion of the Antler highlands to the west and was bounded by a cratonic carbonate platform to the east. Rapid rates of subsidence and sedimentation characterize the basin. The unit appears to form the lower lowstand portion of a second-order, technically driven sequence that grades upward into transgressive and highstand shoreface deposits of the overlying Iron Bog Creek Member. The BLC was originally interpreted as the proximal channelized part of a larger, coarse-grained, submarine-fan complex ( Nilsen, 1977 ). More recent interpretations suggest that the upper part of the BLC may represent a deep-water fan-delta succession that accumulated during the late history of the foreland basin that was dominated by a second episode of flexural subsidence marked by structural segmentation of the basin ( Link et al., 1996 ). The Brockie Lake Conglomerate Member is part of the Copper Basin Group. The Copper Basin Group is divided by Link et al. (1996) into three 1-20 m.y. sequences thought to have formed in response to tectonic effects. The lower two are of Early Mississippian age and the upper one is of Late Mississippian age. The upper sequence includes the BLC and Iron Bog Creek Members of the Argosy Creek Formation. This sequence is Meramecian and chesterian in age (20-30 m.y. duration), and consists of lowstand turbidites and fan-delta deposits of the BLC overlain by transgressive

Abstract 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 T b 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