This study focuses on the interpretation of seismic reflection lines, gravity, and well data in the Estancia Basin, which is located along the eastern margin of the Rio Grande rift in central New Mexico. Major new data introduced are seven seismic reflection lines provided by the Mobil Exploration and Production Company. The basin began to form during Late Mississippian and Early Pennsylvanian uplift of the Ancestral Rocky Mountains. Laramide-age thrusting and folding occurred west of the basin and may have caused strike-slip movements in the basin. Limited packages of Tertiary rocks occur in local outcrops, and small normal faults associated with the Rio Grande rift are the latest structural features in the basin. An integrated interpretation of the seismic reflection data and other geophysical and geological data make the following observations and interpretations possible: (1) the Pennsylvanian basin is a narrow, fault-bounded trough with a north-south trend; (2) the eastern boundary of this trough is a strike-slip fault that was probably active during formation of the basin; (3) this strike-slip fault was also probably active in the Laramide and possibly active in the Precambrian; (4) there are many prominent dipping reflectors in the Precambrian basement that may represent ductile shear zones, and (5) the effects of the Rio Grande rifting in the area were minor.

In the Galisteo drainage basin south of Santa Fe, a fold and several faults related to the Rio Grande rift deform late Eocene–Oligocene dikes, laccoliths, and the Espinaso Formation. The largest rift-related feature, a northerly plunging syncline, comprises the south end of the Santa Fe embayment of the Española Basin and the northern end of the Estancia Basin. The east limb of the syncline is cut by northerly trending, graben-forming, normal faults of the Agua Fria fault system in the Santa Fe embayment. East of the Tijeras-Cañoncito fault system, the east limb of the Estancia Basin is disrupted by down-to-the-west, normal faults of the Glorieta Mesa boundary fault and the Hub Mesa fault system. The fold is offset by down-to-the-northwest movement, and a small component of right slip, on the Tijeras-Cañoncito fault system, which separates the two basins. The above-mentioned rift-related fold and north-trending faults are superimposed across the southeastern margin of the San Luis uplift and the younger Galisteo Basin. Geologic maps and drill data reveal four, and possibly five, phases of Laramide deformation associated with recurrent movement along the Tijeras-Cañoncito fault system: (1) a possible Late Cretaceous, cryptic phase of strike slip associated with elevation of the highest portions of the Santa Fe Range uplift to the north-northeast; (2) the early Paleocene San Luis uplift that formed a southwest plunging, V-shaped anticlinal nose whose southeast limb is the Lamy monocline, which extends 25 km southwest from Precambrian basement at the margin of the Santa Fe Range at Cañoncito to the Cretaceous Menefee Formation; (3) following erosional beveling, the collapse of the southern shoulder of the San Luis uplift, forming a portion of the north-northeast–trending, latest Paleocene–Eocene Diamond Tail subbasin, the axial portion of which lies along the trend of the Tijeras-Cañoncito fault zone; (4) minor Eocene uplift which interrupted deposition in the basin; and (5) Eocene subsidence across the broader Galisteo subbasin and deposition of the Galisteo Formation and latest Eocene–Oligocene Espinaso Formation. Late Eocene–Oligocene intrusions in Los Cerrillos and the Ortiz Mountains deformed the Cretaceous and Tertiary host rocks. Across the Tijeras-Cañoncito fault system, the northwest-trending erosional edge of the Campanian Point Lookout Sandstone displays 400 m of pre–Diamond Tail Formation, right-lateral separation, and the Diamond Tail Formation shows no lateral offset between the overlapping San Lazarus and Los Angeles faults. Although the axis of the Galisteo Basin parallels the fault system, and the basin has been proposed to have formed in a releasing bend of a strike-slip fault along the Tijeras-Cañoncito fault system, any major Laramide strike-slip movement pre-dates the deposition of the Diamond Tail Formation and the formation of the Lamy monocline. The faulted core of the pre–Diamond Tail Lamy monocline, initially up ~800 m on the northwest, was reactivated during rift development and downdropped on the northwest by ~250 m of dip slip. An earlier period of movement (either early Laramide or older strike slip or down-to-the southeast Pennsylvanian movement) is suggested by contrasting thicknesses of Paleozoic formations across the fault zone.

Abstract Possible future petroleum provinces in southwestern New Mexico and southern Arizona are: (1) Tularosa Valley and Jornada del Muerto basins, where they include parts of the late Paleozoic Orogrande basin in western Otero, eastern Dona Ana, and eastern Sierra Counties; (2) Paleozoic Pedregosa basin of southern Hidalgo and southeastern Cochise Counties (and adjacent parts of Chihuahua in Mexico); (3) Estancia basin in central Torrance County; (4) south flanks of the Zuni Mountains in Valencia, northwestern Socorro, and northern Catron Counties; and (5) small buried Pennsylvanian basins, such as the Lucero basin in eastern Valencia and northwestern Socorro Counties and the San Mateo basin in southwestern Socorro County. Paleozoic beds with petroleum potential that were deposited in the Pedregosa basin area in southeast Arizona and southwest New Mexico consisted of more than 4,800 cu mi (20,000 cu km); the original Paleozoic section in the Orogrande basin consisted of about 7,200 cu mi (30,000 cu km) of marine carbonate rocks and sandstone-shale beds. Shoreline and nearshore sandstone lenses, algal reef mounds, and shelf-edge bioclastic carbonate banks of Pennsylvanian and Early Permian age, associated with nearby black, organic-rich basinal facies, are primary petroleum targets of the late Paleozoic basin areas, such as the Pedregosa and Orogrande basins, which are similar to the petroliferous Permian basin. Porous dolomite in Leonardian and younger Permian carbonate rocks offers porosity traps in sequences rich in organic materials. The thick Lower Cretaceous sequence in the Pedregosa region contains sandstone wedges, coralline reefs, and bioclastic banks which all are possible reservoirs. Ordovician and Silurian dolomite beds, especially where overlain by truncating black, shaly Devonian strata, are possible stratigraphic-trap reservoirs, as are the locally porous, biohermal, "crinoidal-hash" limestone beds of the Mississippian.

Abstract Pennsylvanian strata in southwestern New Mexico and southeastern Arizona range from Morrowan? to Virgilian in age, are disconformable to angularly unconformable above Precambrian to upper Missis-sippian rocks, and are as much as 4,000 feet thick, although in most localities they range from 1,000 to 2,000 feet in thickness. The Pennsylvanian-Permian contact in many areas appears gradational, and the boundary is drawn within a zone of indeterminate age between Virgilian and Wolfcampian fossil-bearing beds. Permian rocks at some localities, as well as Cretaceous and Tertiary rocks in other places, are erosionally unconformable on the Pennsylvanian System, and in the southern Hueco Mountains and the Florida Mountains all the Pennsylvanian beds were removed by erosion during early Permian time. Pennsylvanian rocks in southeastern Arizona are mapped as the Horquilla formation and lower part of the Earp formation of the Naco group, and in south-central Arizona as the Naco formation and lower part of the Supai red beds. In southwesternmost New Mexico, the upper part of the Horquilla formation is younger than in Arizona and includes Wolfcampian beds. Pennsylvanian strata in central and southwestern New Mexico generally have been referred to the Sandia and Madera formations of the Magdalena group by the U. S. Geological Survey or to the faunal equivalents of the Morrowan, Derryan (Atokan), Desmoinesian, Missourian, and Virgilian Series, which have been subdivided by Thompson (1942) into groups and formations. Lithic units have been named from outcrops in isolated mountain ranges, such as the Gobbler, Beeman, and Holder formations in the Sacramento Mountains; the Red House, Nakaye, and Bar B formations in the Caballo Mountains; and the Panther Seep formation in the San Andres Mountains. Clastic sediments were derived chiefly from the Pennsylvanian Pedernal mountains to the east, and locally from the Florida, Joyita, Zuni-Defiance, and Kaibab positive-tending areas, which at times during the Pennsylvanian were emergent, and during other epochs were covered by shallow seas. Five troughs or basins, where thick sections were deposited, stand out on the isopach map (1) the Estancia trough, in which Pennsylvanian sediments approach 4,000 feet in thickness; (2) the Orogrande basin, which contained as much as 3,000 feet of Pennsylvanian rocks, of which more than two-thirds was deposited in late Pennsylvanian time; (3) the Pedregosa basin, in which Pennsylvanian strata are almost 2,500 feet thick; (4) the Lucero basin, with as much as 2,700 feet; and (5) the San Mateo basin, with almost 2,700 feet of Pennsylvanian strata. The Orogrande, San Mateo, and Lucero basins are aligned along a north-south trend that probably marks a channelway northward across the Cabezon sag to the Paradox basin; the Pedregosa and Orogrande basins probably connected eastward, in northern Chihuahua and westernmost Texas, with the Marfa and Delaware basins. Over a large area from Clifton, Arizona, southeastward to the Florida Mountains in New Mexico, Pennsylvanian rocks are absent, and Permian or Cretaceous strata rest upon pre-Pennsylvanian rocks. The Pennsylvanian sequence is a limestone lithofacies (clastic ratio less than 0.25) throughout most of the southern part of the area. Northward it grades into lime-shale and then into shale-lime lithofacies of interbedded red beds and nodular limestone on the Mogollon Rim, but of interbedded grayish calcareous shale and fossiliferous limestone west of the Pedernal landmass. Deposits in the Pedregosa basin are chiefly of limestone and lime-shale; those in the Orogrande basin are shale-lime at the south and sand-lime lithofacies on the north; whereas the Pennsylvanian beds in the Estancia trough are of shale-lime lithofacies that intertongue eastward toward the Pedernal mountains, with a sand-shale lithofacies. In small areas near the Joyita Hills and Florida Mountains, lime-sand and sand-lime lithofacies dominate; the Joyita Hills are on the east side of the Lucero basin, which shows a westward gradation from sand-lime to lime-sand to lime-shale, and toward the Zuni positive area, to shale-lime. The thick San Mateo sections are of lime-shale lithofacies. Pennsylvanian strata are potential sources of oil and gas in at least the northern and eastern parts of the region, on the southern edge of the Colorado Plateau, and in the Estancia Valley, Acoma embay-ment, Chupadera Mesa, Jornada del Muerto, and the Tularosa Valley. Even the basin-and-range country and Datil-Mogollon volcanic plateau are underlain by possibly productive Pennsylvanian (and Permian) beds. Large-scale use of the various Pennsylvanian rocks as industrial minerals and rocks is hampered by the long distances to populous areas, the limestones, shale, and gypsum having been used only locally for building stone and crushed rock, in agriculture, and to make bricks, tile, cement, and lime products.

Abstract Hyperpycnal flow deposits and associated facies in upper Cretaceous res-ervoirs of the Magallanes Formation in the Campo Boleadoras-Estancia Agua Fresca-Puesto Peter area of southern Patagonia, Argentina, are docu-mented based on subsurface data. The study represents one of the first ichnologic characterizations of a deltaic system dominated by hyperpycnal processes. The fluvial-deltaic system was sourced from uplifted areas located in Central Patagonia and the Río Chico High and prograded toward the south and southeast. In-tegration of sedimentologic and ichnologic data allows establishing proximal-distal trends within a sediment transport system. The bulk of sandy hyperpycnal lobe deposits consists of coarse- to fine-grained sandstones that are either structureless or display a subtle parallel lamination that is commonly delineated by abundant plant remains. Vertical grain-size changes reflect flow fluctuations, with coarsening- and fining-upward intervals indicating waxing and waning flows, respectively. The concentration of plant remains indicates phytodetrital pulses in connection with direct fluvial discharges. These deposits are unburrowed to sparsely bioturbated, containing the Thalassinoides ichnofabric, which records opportunistic colonization during times of decreased sedimentation rate. However, the pervasive laminated fill of the burrows may reflect relatively high sedimentation rates, most likely because of suspension fallout of fine-grained material. The extreme compaction suggests burrow emplacement in a water-saturated soft substrate that underwent compaction subsequent to the bioturbation event. Associated heterolithic intervals contain the Planolites-Teichichnus ichnofabric, which characterizes marginal areas with respect to the hyperpycnal sand-rich lobes and times of quiescence between flows. During times of reduced sediment supply, material was reworked by wave processes, and hypopycnal conditions were dominant. The Thalassinoides-Teichichnus ichnofabric records colonization of these wave-reworked sandstone units, whereas the Terebellina-Phycosiphon ichnofabric reflects stable conditions that allowed intense bioturbation and the establishment of a moderately diverse benthic fauna. Fully marine offshore deposits are characterized by the Teichichnus-Phycosiphon ichnofabric, which display total biogenic reworking, high ichnodiversity, and a complex tiering structure.

Abstract Marine shales and marls of the Valanginian–Hauterivian Agrio Formation have been studied at five localities in order to assess lateral variations over a 100 km S–N, shelf to basin transition. The two main organic-rich intervals at the base of the Pilmatue Member (Valanginian) and the base of Agua de la Mula Member (late early Hauterivian) have been characterized using a combination of bulk organic chemistry and palynofacies. Except for the former at the southern end of the transect, both intervals have mean total organic carbon (TOC) contents of 2–3% and are dominated by marine amorphous organic matter, suggesting a similar dysoxic genetic organic facies. The mean hydrogen indices determined from the slope of S2 v. TOC are 174 in the Pilmatue Member, but 387 in the basal part of the Agua de la Mula Member, a difference that mainly reflects the range in thermal maturity (late v. early oil window, respectively). Significant lateral variation occurs in the Pilmatue Member, with dark organic-rich intervals being rare in the south but dominant at the northern (distal) end of the transect; this trend is matched by a progressive increase in the peak or mean carbonate-free TOC and hydrogen indices, the latter reaching 6% and 297, respectively, near Estancia Pampa Tril. The bulk of the Agua de la Mula Member in the south is developed in organic-poor oxic facies, with a predominance of terrestrial phytoclasts and type IV kerogen, but dysoxic–anoxic conditions apparently predominate in the northern area. Valanginian–Hauterivian black shale facies appear generally rare on a global basis, but their occurrence can be related to the combination of the progressive rise in sea level during the Early Cretaceous and locally more restricted conditions.