Nonmarine Basins Research Articles

Offshore Northwest Java (ONWJ) 1000 Wells Later: Application to Exploration in Non-Marine Rift Basins

Offshore Northwest Java (ONWJ) 1000 Wells Later: Application to Exploration in Non-Marine Rift Basins

The origin of Upper Palaeozoic sedimentary basins in Northern Ireland and relationships with the Canadian Maritime Provinces

Abstract The evolution of Carboniferous and early Permian sedimentary basins in Northern Ireland is related to a rapidly changing pattern of tectonic episodes. Characteristic sedimentary assemblages and facies changes are associated with discrete phases of basin formation and were related to tectonic events that can be correlated with events in a wide zone of dextral strike-slip in the Canadian Maritime Provinces. Small, localized non-marine basins developed during late Asbian-early Brigantian and Westphalian B times. These data support the extension of the Canadian Maritime transform fault system into Northern Ireland in late Silesian times.

Tertiary paleomagnetism of regions around the South China Sea

Paleomagnetic data from the Philippine Sea Plate (PSP) reveal a history of plate-wide clockwise (CW) rotation and northerly translation since the late Eocene about a nearby pole to the east. The motion has generated left lateral oblique convergence between the Philippine Sea Plate and S.E. Asia. Paleomagnetic data from Luzon in the northern Philippines show early Miocene CCW rotation followed by late Miocene CW rotation. In contrast, the Southern and Central Philippines display early Miocene CW rotation and unrotated late Miocene directions. These results define two different paleomagnetic domains with distinct post early Miocene histories. Pre-Miocene CCW rotation is suggested by data from Zambales, the Visayas and the Celebes Sea. In Borneo, a history of Tertiary CCW rotation has been found in Sarawak, and Sabah. Conflicting results have been reported from Kalimantan, some show no rotation with respect to Eurasia, while others give CCW rotations. In the Malaysian peninsula, the Segamat basalts and Kuantan dykes, of probable late Cretaceous early Tertiary age show CCW rotations similar to those seen in Sarawak. To the north peninsular Thailand, CW rotations have been found in two Miocene non-marine basins. Late Tertiary basalts from Northern and Central Thailand yield similar CW rotations while coeval flows on the Khorat plateau in Eastern Thailand are unrotated. The tectonic implications of the results remain problematical. In particular, the relative importance of true plate rotations and localized rotation of upper crustal blocks in distributed shear zones is unclear. The substantial region of CCW rotation in Borneo, the Celebes Sea and the Philippines is consistent with the broad features of the Holloway model, although the timing of the rotations precludes simple coherent rotation. The model must also be modified to include the effect of the left lateral oblique convergence between the PSP and Eurasia. The CW rotations seen in peninsular Thailand and Malaysia are consistent with the propagating extrusion tectonic model, but we cannot yet preclude a local transtensional origin for these rotations. The lack of Tertiary rocks in the peninsula has hampered attempts to relate these late Tertiary CW rotations to the late Mesozoic and Tertiary CCW rotations seen in Malaysia and Borneo.

Characteristics of the biomarkers from nonmarine crude oils in China — A review

The present paper deals with the biomarker characteristics of crude oils and source rocks from different environments (fresh, fresh-brackish and salt waters) of nonmarine depositional basins of different ages in China. Their characters are summarized as follows: 1 ) Source rocks and crude oils derived from fresh-water lacustrine facies have an odd / even predominance of n-alkanes and high pristane / phytane ratios. Oils from the fresh-water lacustrine fecies differ from typical marine oils in the relative contents of total steranes and terpanes, the concentrations of hopanes and organic sulphur compounds and the values of methylphenanthrene indices and C, H, S stable isotopes. 2) The source rocks and crude oils derived from saline lacustrine fecies possess an even / odd predominance of n-alkanes and high phytane / pristane ratios. There are also some differences between saline lacustrine oils and freshwater lacustrine oils in the concentrations of steranes, tricyclic terpanes and organic sulphur compounds, as well as in the values of methylphenanthrene indices and C, H, S stable isotopes. 3) Oils derived from fresh-brackish water lake facies differ from oils from fresh-water lacustrine or saline lacustrine environments in respect of some biomarkers. According to the various distributions of these biomarkers, a number of geochemical parameters can be applied synthetically to differentiating and identifying the nature of original depositional environments of crude oils and source rocks and that of organisms — primary source materials present in those environments.

The Cretaceous deposits of the Iullemmeden Basin of Niger, central West Africa

The Cretaceous sediments of the Iullemmeden Basin represent two major biosedimentary episodes. The first, during the “Neocomian” to Cenomanian, is dominated by deposition in a nonmarine basin characterized by braided river and meandering shallow river, floodplain systems. The Upper Cretaceous, from Cenomanian to top Maastrichtian is characterized by an alternation of shallow marine, coastal plain deposits. During this episode the basin forms, albeit intermittently, the central region of the trans-Saharan seaway, which connected waters of the opening Atlantic with those of Tethys. Migration routes for both marine and nonmarine faunas existed throughout the Cretaceous period across the Iullemmeden region.

The geology of the western part of the Fintona Block, Northern Ireland: evolution of Carboniferous basins

AbstractThe western part of the Fintona Block is divided into four fault-bounded segments that contain red-bed sediments formerly assigned to the Lower Old Red Sandstone.Dating by miospores indicates the presence of deposits of early Devonian age in the Irvinestown Segment, late Viséan–early Silesian age in the Tempo–Lisbellaw Segment, and late Viséan–early Silesian and late Silesian ages in the Milltown Segment. Northward migration of the early Carboniferous marine transgression in the northern part of Ireland coincided with the sequential propagation of back-stepping faults and resulted in the development of diachronous facies belts between late Courceyan and Arundian times. Tectonic uplift, of a possible southwesterly extension of the Tyrone Igneous Complex, gave rise to the deposition of Asbian to Pendleian red-beds to the south of a massif. An interface between these red-beds and contemporaneous marine sediments farther to the south is recognized and dated. A new non-marine basin, containing Brigantian and Pendleian red-beds, also developed to the north of the massif A waterlogged floodplain that developed during Westphalian A times may be coeval with more widespread coal-bearing sequences elsewhere in Ireland. Alluvial fans prograded southwards over this plain during Westphalian B times when faults bordering a northern landmass were reactivated.

Late Cenozoic Paleomagnetism and Chronology of Andean Basins of Bolivia: Evidence for Possible Oroclinal Bending

New paleomagnetic and radioisotopic data are reported from two late Tertiary high-elevation, non-marine basins in the eastern Cordillera of Bolivia. (1) Quebrada Honda, located at 22° S lat., consists of a 300 m thick section containing abundant Santacrucian or Friasian (middle Miocene) fossil mammals. This locality is constrained by mean $^{40}K/^{40}Ar$ ages of 12.83 ± 0.11 Ma and 11.96 ± 0.11 Ma, and the local magnetostratigraphy is correlated to chrons C5AA through C5A on the Magnetic Polarity Time Scale (MPTS). The fossil mammals from Quebrada Honda have an extrapolated age of about 13.0 to 12.7 Ma. (2) Micana, located at 17° S lat., consists of a 205 m thick section containing late Miocene fossil mammals, including a megatheriid sloth and the tiny mesothere Microtypotherium cf. M. choquecotense. This locality is constrained by a fission-track age determination of 6.9 ± 1.1 Ma, and the local magnetostratigraphy is correlated to Chron 7 on the MPTS. The fossil mammals from this section have an extrapo...

Coarse-grained deltaic sedimentation in the Miocene Cuyama strike-slip basin, California Coast Ranges

The Cuyama basin, located in the southern Coast Ranges of California southwest of the San Andreas fault, developed early in the history of the San Andreas transform system. The Miocene marine basin formed in a transtensional setting along a dextral strike-slip fault of the transform system following Oligocene non-marine basin formation in an extensional setting. The lower and middle Miocene Vaqueros Formation in the northwestern part of the basin, which represents the first of two transgressive-regressive cycles, is described here in terms of nine facies in two broad facies groups. The 400-m-thick Soda Lake Shale Member (of the Vaqueros) comprises deep-basin and starved-basin facies. A thin transgressive facies occurs locally at the base of the formation. The overlying Painted Rock Sandstone Member (of the Vaqueros), which is more than 2200 m thick and consists mostly of coarse-grained sandstone and pebbly sandstone, constitutes a delta complex of prodelta, slope channel, delta front, tide-influenced distributary channel, interdistributary bay, and fluvial channel facies. The basinal depositional system consisted of turbidite mud and sand, and hemipelagic and pelagic sediments of the basinal facies deposited in a rapidly subsiding basin. The delta depositional system consisted of the delta complex facies that prograded into the deep basin and had a steep prodelta slope that extended to bathyal depths. The delta is inferred to be a mixed fluvial-wave-dominated fan delta, analogous in its delta-front morphology and processes to a fjord delta, in which coarse sediment delivered to the delta front by braided streams was transported down the prodelta slope into deep water by sediment gravity flows. Transgression and rapid deepening of the basin in the early Miocene coincided with rapid tectonic subsidence. Deepening culminated with deposition of a starved-basin facies or condensed section at the time of maximum transgression, which was followed by the beginning of a regression and basin shallowing. The overall basin history and geometry of the northwestern Cuyama basin are typical of strike-slip basins. The initial rapid subsidence to bathyal depths at rates of more than 500 m/m.y. in the early Miocene is interpreted to be a result of extension at the releasing bend of a dextral strike-slip fault.

Coarse-Grained Deltaic Sedimentation in the Miocene Cuyama Strike-Slip Basin, California Coast Ranges: ABSTRACT

The Cuyama basin, located in the southern Coast Ranges southwest of the San Andreas fault developed early in the history of the San Andreas transform system. The Miocene marine basin formed in a transtensional setting along a dextral strike-slip fault of the transform system, the San Juan-Chimineas fault following Oligocene nonmarine basin formation in an extensional setting. The lower and middle Miocene Vaqueros Formation in the northwestern part of the basin, which represents the first of two transgressive-regressive cycles, consists of eight facies making up two depositional systems. The 400-m-thick Soda Lake Shale Member constitutes a basinal system consisting of deep-basin and starved-basin facies. The overlying 2,200-m-thick Painted Rock Sandstone Member consists mostly of coarse-grained, pebbly sandstone and constitutes a deltaic depositional system of prodelta, slope channel, delta front, tidal channel, interdistributary bay, and fluvial channel facies. The basinal depositional system consists of turbidite sand and mud, and hemipelagic and pelagic sediments that were deposited in a rapidly subsiding basin. The deltaic depositional system prograded into the deep basin and had a steep prodelta slope that extended to bathyal depths. The delta is inferred to be a river-dominated fan delta in which coarse sediment was transported down the prodelta slopemore » into deep water by sediment gravity flows. The overall basin history and geometry of the northwestern Cuyama basin are typical of strike-slip basins. The initial rapid subsidence to bathyal depths at rates of more than 500 m/m.y. in the early Miocene is interpreted to be a result of extension at the releasing bend of a dextral strike-slip fault.« less

Late Cenozoic tectonics of the northwestern San Bernardino Mountains, southern California

The late Cenozoic structural and stratigraphic history of the northwestern San Bernardino Mountains supports two distinct episodes of uplift, in late Miocene to earliest Pliocene and Quaternary time, that we hypothesize are related to movements on low-angle structures beneath the range. In this paper, we document the nature, distribution, and timing of late Cenozoic deformation and deposition in the northwestern San Bernardino Mountains, and we illustrate the neotectonic evolution of the area in a series of interpretive paleotectonic block diagrams. In the first episode of deformation, late Miocene to earliest Pliocene motion on the south-southwest-directed Squaw Peak thrust system disrupted drainage in pre-existing Miocene nonmarine basins and uplifted the western third of the present range to form the ancestral San Bernardino Mountains. Crystalline rocks of the San Bernardino Mountains were thrust southward across the present site of the San Andreas fault between 9.5 and 4.1 Ma, at a time when the San Gabriel fault was the active strand of the San Andreas transform system. We speculate that the Liebre Mountain crystalline block at the northern margin of the Ridge Basin may be the missing upper plate of the Squaw Peak thrust, now offset along the San Andreas fault. The second episode of deformation began with uplift of the northern plateau of the modern San Bernardino Mountains on north-directed, range-front thrusts in early Pleistocene time, between 2.0 and 1.5 Ma. Synchronous uplift of the northern plateau, recorded in early Pleistocene fanglomerates on the northwestern margin of the range, is interpreted to be the result of movement of a relatively coherent crustal block northward up a south-dipping detachment ramp beneath the central range. In middle Pleistocene time, activity on the northern range front began to wane, and the locus of uplift shifted to a narrow zone of arching and northward tilting adjacent to the San Andreas fault, which subsequently migrated rapidly northwestward along the San Andreas fault from the western San Bernardino Mountains into the northeastern San Gabriel Mountains. We attribute this pattern of deformation to the passage of a bulge or strike-slip ramp attached to the southwest side of the San Andreas fault at depth.

Paleogeographic and paleotectonic setting of Laramide sedimentary basins in the central Rocky Mountain region

In the Rocky Mountain region between central Montana and central New Mexico, sedimentologically isolated nonmarine basins were produced by basement deformation during the Laramide orogeny within the area formerly occupied by a broad Late Cretaceous foreland basin in which laterally continuous marine facies had accumulated previously. Laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere. Laramide basins include perimeter basins along the cratonic periphery of the arcuate Laramide province, axial basins along a north-south intramontane trend, and ponded basins located farther west closer to the overthrust belt. Twelve specific stratigraphic and sedimentologic criteria for the onset, duration, and termination of Laramide deformation allow the chronology of basin development to be inferred independently for each basin. Maastrichtian initiation of Laramide deformation was approximately synchronous throughout the Laramide province, but termination of Laramide deformation was systematically diachronous from north to south between early and late Eocene time. Widespread Eocene erosion surfaces truncate syntectonic Laramide sequences and are overlain by largely volcanic and volcaniclastic post-Laramide strata of Eocene age in the north and Oligocene age in the south. Fluvial depositional systems draining toward the Great Plains were dominant in perimeter and axial basins, but ponded basins were occupied at times by large lakes that served as regional sediment traps. Paleocene drainages from ponded basins also led eastward toward the continental interior, but partly interconnected lakes that developed within several ponded basins by mid-Eocene time were either closed hydrologically, or else they drained westward into the Tyee paleoriver of the Pacific Northwest.

Paleogeographic evolution of the United States Pacific Northwest during Paleogene time

Paleogeographic reconstructions for Oregon and Washington during Paleogene time illustrate a major transition from a dominantly compressional (prior to middle Eocene time) to an extensional tectonic regime. This transition resulted in the development of three phases of Paleogene basin evolution in the United States Pacific Northwest. During the initial phase, basins formed along the continental margin during collision of oceanic islands. Sediments in these basins were derived from nearby orogenic highlands. The second phase of basin development began in middle Eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region. Nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting. Rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from Cretaceous plutonic sources far to the east. The final stage of basin development was the modification of previous basin configurations by the growth of the Cascade volcanic arc, which was initiated in early Oligocene time. The rising Cascade Range diverted streams carrying eastern-derived material, thereby reducing overall sedimentation rates in the coastal basins and providing a local source of volcanic detritus.

Gondwana coal basins of Australia and South Africa: tectonic setting, depositional systems and resources

Abstract Upper Carboniferous and Permian coals of eastern Australia (Bowen, Sydney, Cooper, Galilee and satellite basins) and southern Africa (Karoo Basin) resemble one another in their general composition and associated clastic facies. The Australian examples, however, show more petrographic and geometric variability than their southern African Gondwana counterparts. Critical controls on the distribution and quality of coal in both regions appear to have been (1) a near-polar location with accompanying periglacial conditions, (2) Permian through early Triassic warming independent of any significant change in palaeolatitude, (3) associated floral changes from tundra vegetation to swamps and deciduous Glossopteris forests, (4) variable subsidence and sedimentation rates in foredeep, rift, and epicratonic basin settings, (5) local palaeotopographic effects, (6) eustatically induced changes in base level and marine transgression, and (7) a range of depositional systems from proximal conglomeratic alluvial fans through fluvial, delta-plain, lake-margin, back-barrier, and blanket peat mires in sediment-starved basins. In most cases, palaeotopography and depositional environment were the most important factors in determining coal seam geometry, and had considerable influence on coal quality, specifically its maceral content. Most of the commercial seams are contained in fluvial and delta-plain sequences, with thick, dip-elongate interchannel seams and really extensive coals typically overlying abandoned delta lobes. However, some important seams are juxtaposed with conglomerates of wet alluvial-fan origin or are associated with quartzose barrier sandstones; others originated in clastic-starved systems bordering shallow lakes or in blanket swamps that received moisture from groundwater discharge or direct rainfall. Some seams display characteristics that were primarily controlled by other more regional factors such as rapid tectonic subsidence, changes in groundwater regime, or gradual marine transgression. While influencing the thickness and areal extent of seams, these factors were even more important in determining microlithotypes, maceral content, and inorganic composition of the coals. Not only is coal mining crucial to the economies of both Australia and S Africa, with further expansion likely in the coming decades, but coal and dispersed coal particles have generated billions of barrels of commercial oil reserves along with large volumes of gas. Australian petroleum reserves are predominantly of land-plant origin, and source-reservoir relationships provide important analogues for exploring other non-marine basins.

Cenozoic Stratigraphy and Basin Tectonics of the Andes Mountains, 20ø-28ø South Latitude

Clastic sedimentary basins have evolved during the past 40 m.y. in the central Andes (lat. 20°-28°S) in response to shifting patterns of magmatism and deformation. The distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the North American Rocky Mountains during the Late Cretaceous and early Cenozoic. Petroleum exploration has focused on zones underlying the upper Cenozoic strata along the eastern margin of the Andes mountain belt. Between about 40 and 25 Ma, a nonmarine basin extended across the region that is now the Andes Mountains. Between about 25 and 10 Ma, the western part of the former basin became the site of a volcanic arc; sediment accumulation continued in the east, where marine intercalations demonstrate the low elevation of the basin. After 10 Ma, the volcanic arc remained active and locally widened, and crustal shortening caused regionally important thrust and reverse faulted ranges. During the past 10 m.y., up to 4,000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains; meanwhile in the interior of the mountains, over 4,000 m of fine-grained strata and evaporites accumulated in local depocenters.

COMPARISON OF SELECTED NON-MARINE PETROLEUM-BEARING BASINS IN AUSTRALIA AND CHINA

This paper summarises the geology and hydrocarbon potential of two Chinese and two Australian basins (Ordos, Northern Jiangsu, Eromanga, and Surat basins) in order to compare factors affecting the generation, migration, and entrapment of hydrocarbons. In all four basins, hydrocarbons are generated from nonmarine source rocks of lacustrine and fluvial-overbank origin. While the Chinese and Australian basins contain a similar range of sedimentary facies, from alluvial fan to lacustrine, the arrangement and relative thicknesses of these facies vary considerably as a result of different tectonic and palaeoclimatic settings.During the Triassic, the Ordos Basin was dominated by retroarc foredeep subsidence and the development of deep, fresh-water lakes with anoxic bottom waters. This non-bioturbated substrate, with Type I and II kerogen precursors, provided an excellent oil source for adjacent fan-delta, deltaic, and fluvial reservoirs, and for the unconformably overlying Jurassic fluvial valley-fill sandstone reservoirs.The Northern Jiangsu Basin was initiated by back-arc extension and underwent very rapid half-graben subsidence in the Eocene. Alluvial fan, shoreline, and fluvial facies aggraded in a relatively narrow zone along the active, faulted margin, and merged laterally into organic-rich shales which provided a local source for oil.By comparison, the Eromanga/Surat basins developed in response to gentle downwarp and reactivation of older structural trends. Reservoirs are largely restricted to craton-derived quartzose facies such as in the Hutton, Precipice, and Namur sandstones. There is probably a dual source for oil, from the underlying Permian (which may be the dominant source in the Surat Basin), and from shales deposited in shallow, partly oxygenated lakes and overbank facies of Jurassic age (important in the Eromanga, and possibly subordinate in the Surat Basin). Deep lacustrine facies, typical of the Chinese basins, did not develop. The greater abundance of oil in the Chinese nonmarine basins is explained in terms of tectonic and palaeoclimatic factors which yielded thicker and better quality source rocks, more rapid maturation, and a better juxtaposition of source rocks and good-quality reservoirs, thus providing short, highly efficient migration routes.

Interior Provinces in Alaska: ABSTRACT

The U.S. Geological Survey is using a multidisciplinary approach to assess the petroleum potential of the interior provinces of Alaska. Geophysical parameters, petroleum geochemistry, thermal maturation, paleontology, and petrography are some of the disciplines being used to evaluate the basins as well as to compare them geologically with other explored basins. Three types of interior provinces have been tested by exploratory drilling for their petroleum potential: three Tertiary nonmarine basins, two Jurassic and Cretaceous flysch and fold belts, and a Paleozoic thrust belt. Although the presence of hydrocarbons has not yet been demonstrated, the present data base is too limited to make a definitive assessment of hydrocarbon potential. During the 1983-84 field seasons, we acquired new gravity data and collected rock samples in and adjacent to the Yukon flats and the Nenana basins. These basins contain upper Tertiary, primarily nonmarine, sedimentary rock in extensional graben and half-graben complexes that are superimposed across preexisting terrane boundaries. The location and development of the basins result from strike-slip motion along the Tintina and Denali fault systems. Adjacent to the basins and within the fault systems are thick sections of nonmarine lower Tertiary coal-bearing rocks in deformed basin remnants. If these lower Tertiary rocks are present beneath the upper Tertiary fill, their greater depth and advanced maturation could enhance the hydrocarbon generative potential. Gravity modeling suggests th Tertiary fill is at least 3 km thick in the deeper parts of the basins and may be significantly thicker. End_of_Article - Last_Page 667------------

Active intra-basinal highs and palaeodrainage reversals in the late orogenic hominoid-bearing Siwalik basin

The Himalayan mountain chain is a product of the continent-to-continent collision of India with Asia. Major mountain building activity in the Himalaya was followed by the shedding of sediments which were deposited in extensive non-marine basins on the Indian craton. The late orogenic hominoid-bearing Siwalik basin, comprising alluvial deposits, occurs along the northern margin of the Indian plate and has itself been uplifted. Major Siwalik palaeodrainages are believed to have originated in the Himalaya. We now report bed by bed measurement of palaeocurrent data of the Upper Siwalik rocks from the outermost Foothills Belt which suggest that active intra-basinal highs have locally caused palaeodrainage reversals. Discontinuity in apparently continuous stratigraphical sequences is recognized as the composite aggradation of alternating depositional events related to drainages controlled by basin margin and intra-basinal structural highs. The period of repeated uplift of these structures is estimated to be 1 to 5 × 105 yr.

Neogene stratigraphy of the Avawatz Mountains between the Garlock and Death Valley fault zones, southern Death Valley, California: Implications as to late Cenozoic tectonism

Syntectonic continental strata of the Avawatz Mountains near Death Valley, California, record a minimum of 1000 m uplift and possibly 20 km dextral offset of the range since latest Tertiary time. The bedrock of the Avawatz Mountains is primarily diorite and metavolcanic rock. Uppermost Miocene and Pliocene fluvial and lacustrine strata overlying it, contain granitic and subordinant carbonate detritus but only minor amounts of sediment derived from bedrock of the Avawatz Mountains. The strata include both basin and basin-margin facies with multiple unconformities and growth structures. Associated paleocurrents emanate from the east and south. Facies studies of the strata show that during the late Tertiary, a nonmarine basin lay at the site of the present Avawatz Mountains. This basin received sediment first from the east and later from the south. Provenance analyses suggest that the Tertiary sediment was derived not from bedrock of the Avawatz Mountains but rather from the Halloran Hills and to a lesser extent, from the Soda Mountains. The Soda Mountains are presently located 10 km south of the Avawatz Mountains, while the Halloran Hills are 20 km southeast. These factors suggest that during the late Tertiary, the ancestral Halloran Hills were situated due east of the Avawatz Mountains depocenter, and have since been faulted apart. Such offset is possible if the Death Valley fault zone continues a minimum of 20 km southward of its presently-accepted terminous in the Avawatz Mountains. Quaternary fan complexes unconformably overlying the Tertiary strata are derived exclusively from bedrock of the Avawatz Mountains. Containing numerous unconformities, they were also deformed during deposition. On the north side of the range, they are prograding into the course of the Amargosa River. Their locally derived provenance indicates that the Avawatz Mountains uplifted during the latest Tertiary and were supplying large volumes of detritus for the first time. As the bedrock surface was only barely emergent during the latest Miocene and Pliocene, and it now stands 1000 m higher than Tertiary strata overlying its sides, it is proposed that the bedrock has uplifted a minimum of 1000 m since the Pliocene. Prograding alluvial fans and east-directed faulting of the range over Quaternary alluvial fans suggest that the uplift may be ongoing.

Pericollisional Strike-Slip Basins in Western Cordillera, Canada: ABSTRACT

The late Mesozoic-Paleogene evolution of the Canadian Cordillera was dominated by accretion of elongate crustal blocks against the North American craton. Geologic and paleomagnetic evidence suggest that these exotic terranes dispersed from volcanic arcs and oceanic platforms and approached North America along anastomosing right-lateral faults with great cumulative displacement. Obduction of oceanic allochthons was followed by transpressive thickening and regional metamorphism of the cratonic margin in the mid-Jurassic. Strike-slip motion and emplacement of plutonic rocks continued near relict sutures and reactivated deep faults. Sedimentary basins related to strike-slip faults formed by elongation of accreted terranes (Stikinia and Wrangellia) and by shear within the eformed cratonic margin zone (Rocky Mountain Trench). Subsidence is reflected by northwest-southeast stretching along pull-apart structures, and by massive influx of turbidites from incipient collision zones and relict arc relief. It was interrupted and outlived by rotation of blocks, folding of basin sediments, and vigorous progradation of deltaic-fluvial clastics from rising collision belts. Transition from predominant transtension to prevailing transpression is diachronous from basin to basin. Near the Stikine-Wrangellia collision zone (Bowser basin), it occurred in the Late Jurassic; along the Stikine-Wrangellia border it occurred in the mid to Late Cretaceous. Only small nonmarine basins developed in the Rocky Mountain Trench system, which, in its southernmost part, was closed com letely during Paleogene thrust faulting. The strike-slip basins of the western Canadian Cordillera were subject to high regional heat flow and also suffered from widespread intrusion of Paleogene granitoids. Therefore, they are generally poor oil and gas prospects. End_of_Article - Last_Page 473------------

Eocene Strike-Slip Faulting and Basin Formation in Washington: ABSTRACT

Eocene right-lateral displacements occurred on several fault zones in western and central Washington, including the Straight Creek fault (90-190 km or 56-118 mi of offset), the Entiat-Leavenworth fault system (amount of offset unknown), and possibly a major unnamed north-south trending fault through the Puget lowland. Within this framework, nonmarine sediments accumulated in several rapidly subsiding basins to form some of the thickest (more than 5,800 m or 19,000 ft) nonmarine sequences in North America. Two types of sedimentary basins are recognized. The Chiwaukum and Foss River grabens are small pull-apart basins that formed along the major faults. The Chuckanut, Swauk, and Puget(?) basins are much larger (up to 100 km or 62 mi wide) and formed between the major faults To varying degree, these larger basins display the characteristics of idealized smaller pull-apart basins: (1) high sediment accumulation rates; (2) rapid facies changes; (3) abrupt stratigraphic thickening and thinning; (4) partly internal drainage patterns; (5) irregular basin margins characterized by dip-slip faults and unconformities; (6) predicted deformational patterns; (7) rapid changes between extensional and compressional tectonics; and (8) interbedded and intrusive relationships with extension-generated(?) volcanic rocks. The difference in size and mode of occurrence between these basin types emphasizes the regional as well as local control that strike-slip faulting has on basin formation. This extensional-basin province formed in a forearc setting between an obliquely subducting oceanic plate to the west, and the broad, diffuse Challis volcanic arc to the east. Eocene nonmarine basins in Washington should therefore be considered as end-member types of forearc basins. End_of_Article - Last_Page 493------------