Association Round Table 297 Recent Deep Sea Drilling Project (DSDP) coring along U.S. Geologi- cal Survey (USGS) multichannel seismic lines 25 and 35 provides direct sampling of the depositional sequences that constitute the lower continen- tal slope and upper continental rise of New Jersey. The sedimentary record from four core sites, integrated with a closely spaced grid of multi- channel seismic profiles, reveals 12 depositional sequences in the upper Campanian to Quaternary section that are bounded by erosional uncon- formities. Equivalent unconformity-bound depositional sequences are present on the contiguous continental shelf and upper slope; most sequences have counterparts in the Vail depositional model. Of particular interest is a complicated, stacked series of buried erosional channels dra- matically displayed on seismic lines paralleling the depositional strike of the upper continental rise. The channels, which cut the upper surface of nearly every depositional sequence, probably formed during periods of low sea level. Channels on the lower Eocene surface display the greatest physiographic relief. Integration of seismic and bore-hole data suggests alternative correlations for several stratigraphically significant regional reflectors, such as A*, A', and A". POL, JAMES C , ARCO Exploration Co., Denver, CO Early Diagenetic History of Late Pennsylvanian Calclithite Beds, Hueco Mountains, El Paso County, Texas Calclithite beds exposed on the western escarpment of the Hueco Mountains were deposited in a fan-delta system featuring fluvial chan- nels, marine bars or beach sands, shallow-marine shale and limestone, and tidal flats and lagoons. Two distinct calclithite types occur. One is a coarse, poorly sorted gravelly sand with angular to subrounded grains. This type occurs in discontinuous or channel-shaped beds. Sedimentary structures include fining-upward sets, imbrication, and trough cross- bedding. These characteristics indicate sporadic unidirectional flow, as would be expected in ephemeral streams. The second calclithite type is fine to medium-grained well-sorted sand with very well-rounded grains. This type crops out as thin, relatively continuous units. Sedimentary structures include ripples, small-scale cross-beds, low-angle and horizon- tal or planar bedding. The early diagenetic history of the calclithites reflects their depositional environment. The coarse calclithite was deposited in undersaturated freshwater conditions, shown by the absence of early cement. Early com- paction of the coarse calclithite, indicated by intergranular microstyloliti- zation and shale-clast deformation, is the most commonly observed texture. The fine-grained calclithite exhibits a markedly different diagen- etic history. The first recognizable "diagenetic" event is micritization of marine-derived fossils and calclithite grains. Early cementation in the marine phreatic environment resulted in isopachous rims of fibrous arag- onite and bladed Mg-calcite cement. Pore centers contain a later equant calcite cement. Little or no early compaction occurred in the fine cal- clithite. Freshwater flushing is indicated by the replacement of former aragonite cement rims by finely crystalline equant calcite. POL, JAMES C , and PAUL K. MESCHER, ARCO Exploration Co., Denver, CO Environmental Significance of Evaporitic Textures of Mississippian Mis- sion Canyon Formation, Williston Basin, North Dakota The Mission Canyon evaporite wedge, the Frobisher-Alida interval, has commonly been interpreted as typical nodular or "chicken-wire" anhydrite from a sabkha depositional setting. Upon examination of over 190 cores from North Dakota and Montana, we identified a variety of evaporite textures and interpreted several distinct origins for them. The following evaporite textures were recognized: (A) precipitative or pri- mary, (B) intraclastic, (C) evaporite cement, (D) replacement, and (E) dissolution-stage. Depositional evaporites (A, B) form by direct precipitation in supersat- urated solutions (primary texture) or by reworking of primary evaporite (intraclastic texture). Primary texture forms by direct precipitation from a supersaturated brine occurring in shallow lagoons or tidal ponds (sub- aqueous evaporite) or within the sediment (nodular anhydrite). Three types of subaqueous textures were identified: (1) isolated laths, (2) rosettes or clusters of laths, and (3) large "swallowtails." Intraclastic tex- ture results from the reworking of previously precipitated evaporite. It is recognized by angularity of the clasts, size sorting, and association with carbonate inlraclasts. Depositional environment of this texture is inter- preted as evaporitic shallow-water lagoons, punctuated by occasional storm events. Diagenetic textures include cementation, replacement, and evaporite dissolution. Cementauon by evaporite was found primarily in carbonate grainslones and is usually poikilotopic. Replacement textures may develop early or late in the diagenetic history of the rocks. Early replace- ment was found in primary restricted carbonate facies. Original texture (algal laminations, bioturbation, carbonate grains) were usually pre- served after replacement. Late-stage replacement was observed in more marine facies, with the original texture not preserved. Isolated nodules of fibrous anhydrite result. PORTER, LORNA A., Porter Geological Corp., Golden, CO, and FRED S. REID, ES.R. Assocs., Englewood, CO Exploration Applications of a Transgressive Tidal-Flats Model to Missis- sippian Midale Carbonates, Eastern Williston Basin Midale (Mississippian) production was first indicated in 1953 in Sas- katchewan, Canada. The unit was initially defined in the subsurface as the carbonate interval between the top of the Frobisher Anhydrite and the base of the Midale Anhydrite. This same nomenclature is used in this paper. In 1953, Midale production was found on the United States side of the Williston basin in Bottineau County, North Dakota. Later explora- tion extended Midale production westward into Burke County, North Dakota, in 1955. Cumulative production from the Midale is approxi- mately 660 million bbl with 640 million from the Canadian side of the Williston basin. Initially, hydrocarbon entrapment in the Midale was believed to be con- trolled by the Mississippian subcrop, with the Burke County production controlled by low-reUef structural closure. Petrographic examination of cores and cuttings from the Midale in both Saskatchewan, Canada, and Burke and Bottineau Counties, North Dakota, indicates that production is controlled by facies changes within the unit. Stratigraphic traps are formed by the lateral and vertical changes from grain-supported facies deposited in tidal-channel, subtidal-bar, or beach settings; seals are formed by mud-rich sediments. Use of a transgressive carbonate tidal- flats model best explains current production patterns and indicates sub- stantial potential for additional production in eastern North Dakota and South Dakota. POSEY, HARRY H., Univ. North Carolina, Chapel Hill, NC, STEPHEN D. HURST, Conoco Oil Co., Ponca City, OK, J. RICHARD KYLE, Univ. Texas at Austin, Austin, TX, PETER E. PRICE, Mara- thon Oil Co., Denver, CO, and ARNOLD R. TAYLOR, Conoco Oil Co., Ponca City, OK Provincial Variations in Cap Rock Source Materials of Gulf Coast Salt Domes Isotopes of strontium, carbon, and oxygen are used to model hydro- carbon, brine, and meteoric fluid interactions during cap rock evolution. Provincial isolopic variations occur between older salt domes of the east Texas (ETx) and northern Louisiana (NLa) basins and the younger domes of the Texas-Lotiisiana (Tx-La) coastal basin. ETx and NLa cap rocks exhibit normal, mid-Jurassic seawater values ("Sr/^'Sr = 0.7068 to 0.7076), very wide 6' ' c ranges ( - 5 to - 49 per mil PDB) and 6 " 0 val- ues ( - 6 to -11 per mil PDB) that are slightly lighter than Tx-La ( - 4 to - 1 0 per mil). Tx-La domes yield remarkably high *^Sr/*'Sr ratios (0.7073 to 0.7100), and their S'^C values ( - 8 to - 41 per mil) have means which are 5 to 15 per mil heavier than ETx and NLa domes. Detailed studies of the Hockley dome (Tx-La basin) reveal chemical diversity not recognized in domes farther inland. Anhydrite from the salt stock (mid-Jurassic Louann evaporites) mixed with two separate stron- tium sources during calcite formation. Calcites near the dome's center formed from an intermediate Sr ratio fluid (*'Sr/*'Sr = 0.7090), which, based on heavier than average S'^C values, was enriched in COj relative to CH 4; peripheral calcites evolved from a high Sr ratio fluid ( Sr/^*Sr = 0.7105) with a lower CO2/CH4 ratio. High * Sr/**Sr ratios in other Tx-La anhydrite cap rocks compared with normal mid-Jurassic type values in ETx and NLa cap rocks suggest