6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



Elsewhere in New Mexico, where the Coloradoan sediments are 

 more uniform (Mancos Shale of most authors), the distribution of 

 members of the L. lugubris group is not as well established. Lopha 

 hellaplicata novamexicana occurs in the middle Mancos, in the zone 

 of Collignoniceras hyatti (late Middle Turonian). The range and 

 position of L. hellaplicata hellaplicata is not precisely known, except 

 that it occurs in the middle Mancos below the Juana Lopez calcarenites. 

 L. luguhris occurs widely in the middle and basal upper Mancos, in 

 calcarenites equivalent to the Juana Lopez Member, Here it is 

 associated with Prionocyclus wyomingensis Wyoming ensis Meek, P. 

 macombi Meek, and Scaphites warreni Meek and Hayden, a Juana 

 Lopez assemblage. It has also been reported from slightly younger 

 beds (zone of P. wyomingensis elegans Haas : middle Late Turonian) . 



Stratigraphic conclusions. — Comparison of the Texas, northeastern 

 New Mexico, and south-central to southeastern Colorado Turonian 

 sediments reveals a marked similarity in the sequence of ostreids, 

 ammonites, sediment types (in part), and in the position of the 

 Middle-Upper Turonian boundary, in many places marked by a 

 disconformity. In these areas dark clay shale, locally sandy, silty, 

 and containing lensing siltstones, silty limestones, and sandstones 

 (upper Eagle Ford Shale ; Codell Sandstone in many places) underlies 

 this boundary. This unit contains L. hellaplicata hellaplicata and 

 species of Collignoniceras (C. hyatti, C. sp.) in all areas and is locally 

 underlain by sediments carrying L. hellaplicata novamexicana. Brown 

 to rusty, sandy calcarenites and calcareous sandstones, locally con- 

 taining fish tooth, bone, and phosphate pebble conglomerates overlie 

 the boundary, especially where it is marked by a disconformity 

 (Juana Lopez Member; "reworked Eagle Ford" zone), at many 

 localities. This unit contains L. luguhris and species of Prionocyclus 

 (P. wyomingensis wyomingensis, P. macomhi, P. sp.) in the great 

 majority of localities where it is found. In both Colorado (question- 

 able occurrence) and Texas, L. luguhris is found rarely in the upper- 

 most part of the lower unit (upper Eagle Ford equivalents), partially 

 overlapping the range of L. hellaplicata hellaplicata. 



I propose that the two sequences are correlative in the manner 

 shown on figure 1, and that they may be correlated on the basis of 

 lophid oysters as well as ammonites. Based on lithologic and faunal 

 relationships, I suggest that the thin calcarenite locally present above 

 the Middle-Upper Turonian boundary and disconformity in Texas 

 should not be assigned to the Austin but rather to the Eagle Ford, 

 forming the highest zone of that formation (zone of Lopha luguhris). 



