四国，石鎚山第三系久万層群の凝灰岩のフィッション・トラック年代

Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U‐Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U‐Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10–20% of the 40Ar/ 39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short‐lived and early in the prism history (210–190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200–100 Ma) at 265–290°C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210°C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low‐grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny.

Tracking crustal processes by FT thermochronology in a forearc high (Hikurangi margin, New Zealand) involving Cretaceous subduction termination and mid-Cenozoic subduction initiation

To determine how local geological events contributed to the evolution of accretionary complexes and eventual exposure of rocks with different structural levels, geochronological mapping was carried out using fission track (FT) analysis at the Kii Peninsula, southwest Japan. At this site, the original zonal structure of Cretaceous accretionary complexes parallel to the subduction zone is disturbed by the northward projection of the Shimanto accretionary complex. Twenty‐six zircon FT ages were obtained from an area of ∼12 km in an east–west direction and ∼15 km in a north–south direction, and classified into three groups: (i) ages ∼15 Ma (range ∼10–20 Ma), which are distributed along the northwest–southeast valley; (ii) ages of ∼50 Ma in the northwest of the study area; and (iii) ages older than those in Groups 1 and 2. Based on results from eight zircon FT length distributions, the Miocene ages appear to be the result of spatial variations in heat influx and cooling after the regional exhumation of the area, as recorded by FT ages of ∼50 Ma.

The cooling history of Silurian to Cretaceous alkaline ring complexes, south Eastern Desert, Egypt, as revealed by fission-track analysis

Within the north‐eastern part of the Palawan Continental Terrane, which forms the south‐western part of the Philippine archipelago, several metamorphic complexes are exposed that are considered to be rifted parts of the Asian margin in South‐East China. The protolith age(s) and correlations of these complexes are contentious. The largest metamorphic complex of the Palawan Continental Terrane comprises the Mindoro Metamorphics. The north‐eastern part of this metamorphic complex has recently been found to be composed of protoliths of Late Carboniferous to Late Permian protolith age. However, meta‐sediments exposed at the westernmost tip and close to the southern boundary of the exposure of the Mindoro Metamorphics contain detrital zircons and with U–Pb ages, determined by LA–ICP–MS, in the range 22–56 Ma. In addition, zircons as young as 112 Ma were found in a sample of the Romblon Metamorphics in Tablas. As the youngest detrital zircons provide an upper age limit for the time of deposition in meta‐sediments, these results suggest that the Mindoro and Romblon Metamorphics comprise protoliths of variable age: Late Carboniferous to Late Permian in NE Mindoro; Eocene or later in NW Mindoro; Miocene at the southern margin of the Mindoro metamorphics; and Cretaceous or later on Tablas. The presence of non‐metamorphic sediments of Late Eocene to Early Oligocene age in Mindoro (Lasala Formation), which are older than the youngest metasediments, suggests that metamorphism of the young meta‐sediments of Mindoro is the result of the collision of the Palawan Continental terrane with the Philippine Mobile Belt in Late Miocene. Similarities of the age spectra of zircons from the Eocene to Miocene metamorphics with the Eocene to Early Miocene Lasala Formation suggest that the protoliths of the young metamorphics may be equivalents of the Lasala Formation or were recycled from the Lasala Formation.

Kaolinite, illite, and mixed-layer montmorillonite-illite are present in interlaminated sandstones and shales from the Eocene Wilcox Formation of the Texas Gulf Coast at depths of 2,000 to 4,000 m. Ratios of kaolinite to discrete illite are higher in the sandstones than in the interlaminated shales. Mixed-layer clays in the sandstones are 5 to 20% more expansible and less ordered than those in interlaminated shales. These mineralogic differences are interpreted to reflect a significant difference in the solution chemistry of pore waters in the sandstones from that of pore waters in the interlaminated shales. At the relatively shallow depth of 2,000 m, mixed-layer montmorillonite-illite from the shales is roughly 30% expansible; this figure is significantly less than the 7 % expansibility reported by J. Hower et al for Miocene age mixed-layer clays at similar depths. Assuming similar source and geothermal gradient for the two sets of samples, two explanations may account for these differences. The most plausible explanation is that the expansibility of the mixed-layer clay is controlled by the montmorillonite-to-illite transformation rate. Because the Eocene sediments have had an additional 25 m.y. to react, the montmorillonite-to-illite transformation is more complete in these samples. An alternative explanation is that the chemistry of pore waters in the Wilcox Formation is significantly different from that of pore waters in sediments studied by Hower. End_of_Article - Last_Page 469------------

Tertiary shorelines, Texas coastal plain

Un nouveau mastodonte zygolophodonte ( Proboscidea, Mammalia) dans le Miocène inférieur d'Afrique orientale: Systématique et paléoenvironnement

The present study deals with the biostratigraphy of the Aquitanian -Lower Early Langhian successions age in Kor Mor well No.3 at Kirkuk area. The studied section includes six formations with a total thickness of about (430) meters.These are: Ibrahim, Azkand, Anah, Euphrates, Dhiban and Jeribe formations. Eighteen species and subspecies of planktonic foraminifera and twenty one species and subspecies of benthonic foraminifera are recognized. Also some forams of benthonic foraminifera to the genus level are identified. Fragments of mullosca shell, echinoderm, green and red algae were recognized from the studied succession.They permit an identification of five biostratigraphic zones and are from younger to older: Borelis melo curdica Total Taxon - Range Zone. Miogypsina globulina Total Taxon - Range Zone. Miogypsinoides complanatus Total Taxon - Range Zone. Catapsydrax dissimilis Partial - Range Zone (N.5). Globigerinoides primordius Partial - Range Zone (N.4). The first two zones are withen Ibrahim Formation, of Early Miocene (Early Aquitanian) age.Whereas, the third zone affilated to Azkand and Anah formations of Early Miocene (Late Aquitanian) age,The fourth zone is related to Euphrates and Dhiban formations of Early Miocene (Late Burdigalian) age. The last zone represent Jeribe Formation of Middle Miocene (Lower Early Langhian).

Sixteen mafic and intermediate lava flows of Eocene to Pleistocene age from the northwestern Great Basin have initial Sr 87 /Sr 86 ratios of from 0.7029 to 0.7047. Seven upper Miocene mafic and intermediate lava flows have initial ratios of from 0.7037 to 0.7041, suggesting a common source for the Steens Basalt and contemporaneous rocks of the northwestern Great Basin. Values of 0.7047 and 0.7033 obtained on olivine basalts of early Miocene and Quaternary ages, respectively, suggest that these lavas were derived from different source materials than were the late Miocene rocks. Unusually low values of 0.7029 obtained on two specimens of andesite from the Eocene Cedarville Series of Russell (1928) suggest that these lava flows were derived from still another source material. Ten silicic volcanic rocks, most from widespread and voluminous ash-flow sheets and lava complexes, have initial ratios of approximately 0.7023 to 0.7057. Some of the more radiogenic values, obtained on very highly differentiated and strontium-poor rock units, provide only an upper limit for the initial Sr 87 /Sr 86 ratios of the parent magmas. The close similiarity of the strontium isotopic composition of the silicic rocks to those of spatially and temporally associated intermediate lavas supports the concept that the widespread Miocene silicic volcanic rocks of the northwestern Great Basin were produced by the fractional crystallization of enormous volumes of mantle-derived mafic magma. The data also provide indirect support for the interpretation that the relatively radiogenic character of many salic volcanic rocks from other parts of the Great Basin largely reflects the presence of an unusually radiogenic mantle rather than the involvement of crustal material.

The Albin and La Grange areas in southeastern Wyoming are two adjoining different hydrologic areas. Since ground water is the only source of water for irrigation in the Albin area, 34 irrigation wells have been drilled since 1968 and developed in conjunction mostly with center-pivot sprinkler systems that in 1974 irrigated about 6,980 acres. Most irrigation wells are developed in channel deposits of the Ogallala Formation of late Miocene. Water levels in parts of these channel deposits have declined about 4 to 7 feet since pumping began in 1968. In the La Grange area, lands are irrigated by surface water, ground water or a combination of both. The best producing wells are those completed in both the Brule Formation of Oligocene age and the alluvium. Secondary porosity was located and elevated in the Brule using caliper logs, an Acoustic Borehole Televiewer and geophysical logs. From the spring of 1970 to the spring of 1974, hydrographs of wells in parts of the La Grange area show water-level rises of about 5 feet resulting from the net effect of surface-water recharge and groundwater pumpage. Throughout the La Grange area no significant annual water-table declines have occurred. It is unlikely that irrigation wells pumping near Horse Creek have caused significant direct streamflow depletion. (Woodard-USGS)

Lithologic and stratigraphic data from rocks dredged from the continental shelf off Onslow Bay, North Carolina, provide surface control for seismic studies of the southeastern United States continental margin and help to explain the distribution of potentially economic phosphate-rich sediments on this shelf. Outcropping Miocene rocks in this area indicate that the region has long been a positive geologic feature and has received relatively little Pliocene and Pleistocene sedimentation. Leached, molluscan-moldic calcareous quartz sandstones of late Oligocene to early Miocene age (Belgrade Formation) and middle to late Miocene age (Pungo River Formation) crop out in southwestern and northeastern Onslow Bay, respectively. These two areas border a band of highly phosphatic su ficial sediments probably derived from unlithified, phosphatic units of the Pungo River Formation. Lower Pleistocene calcarenites that correlate with the Waccamaw Formation crop out on the sea floor near Cape Fear, which bounds Onslow Bay on the south. A core on Frying Pan Shoals off Cape Fear, after passing through Pleistocene coquina, calcareous quartz sandstone, and oolitic sand, penetrated upper Pliocene calcarenites of the Bear Bluff Formation and middle Miocene phosphatic argillaceous sandstones of the Pungo River Formation. Samples from this core hole show that phosphate increases toward the top of the unindurated Pungo River Formation section, indicating that this formation is probably the source of the high phosphate concentrations in the surficial sediments near Cape Fear, wher the Bear Bluff calcarenites also crop out. Upper Pleistocene units include oolitic limestones adjacent to the outer shelf, calcareous quartz sandstones around Cape Fear, and molluscan coquinas near Cape Lookout which bounds Onslow Bay on the north. The outer shelf is blanketed by submarine lithified algal limestones and sandstones of Holocene age.

Tertiary volcanism of the Galatia province, north-west Central Anatolia, Turkey

Determination of how much production contribution from individual zones in amulti-layer environment is very critical in optimizing initial commingled completions and subsequent workovers. The conventional Individual Zone Production Testing (IZT) method to determine the maximum well productivity is very inefficient due to unnecessary repetitions in workovers resulting in higher operation cost. The possible maximum production rate of each layer can be estimated by calculating its productivity index and applying the maximum allowable pressure drawdown. Data to calculate the productivity index for each layer is not always available. Production logging (PLT) or IZT, the source of data is not run in every well. These common problems could be addressed by instituting a production zone allocation system. This paper reports a practical approach to estimate absolute horizontal permeability and the specific productivity index (SPI) by correlating to density porosity (d) and Volume Shale of Gamma Ray Index (VshGR) for Sihapas formation in Minas Field. The d and VshGR are calculated from open hole log data, which is usually available. The correlation is principally generated by using the permeability - density porosity transform, relative permeability curve and Darcy's law for radial flow in porous media. The calculated SPI is a fairly good match with actual field data obtained from PLT and IZT. In some conditions the calculated SPI is under estimate compared to actual data. Thisslight disagreement will also be reviewed in this paper. The method to generate this practical correlation can also be applied to data from other fields. Introduction Estimation of formation fluid or oil production from each layer is a fundamental common problem in the multi-layer oil production system, such as Minas Field. Inter layer communication behind cement, and water cross-flow through channels in the cement between casing and formation can even make it worst. Production allocation system can be expected to ease the problem in the reservoir management. However, it is very complicated to generate the system due to reservoir heterogeneity and complexities with very limited data available. Minas is a major oil field in Indonesia located about 33 KM northern Pekanbaru, the capital city of Riau Province. This field, operated by PT. Caltex Pacific Indonesia with a Production Sharing Contract (PSC) system, is agently dipping anticline which is 28 km in length and 7 to 13 km in width. Original oil-in-place is estimated to be 9.0 billion STB. Minas field was discovered in 1944, and the first oil well was initially completed and put on production in 1952. The initial field development was 214acres spacing. To enhance the natural aquifer pressure support, peripheral water injection was started in 1970. A closer well spacing of 71 acres field development was begun in 1978. In order to increase oil recovery, 23.7 acrespacing of Phase 1 inverted seven spot waterflood has been implemented in high graded areas of the field since late 1993. The ultimate oil recovery of the waterflood project is expected to be 51 % of the original oil-in-place. The average recent field production is around 250,000 BOPD and 94.9 % watercut from commingling of several layers of Sihapas formation. The Minas fluid production is artificially lifted by Electric Submersible Pumps (ESP) from 679active wells, that will increase significantly in the near future when the planned tertiary oil recovery processes with a closer well spacing is implemented. Sihapas formation of early Miocene age is overlain by the Telisa formation of the Middle Miocene age, and underlain by Pematang formation of the Paleoceneage. The Reservoir sands of Sihapas are divided into six major units referred to as A1, A2, B1, B2, D and S sands separated by five major shales. P. 183^

Fossil otariid pinnipeds of the extinct genera Prototaria Takeyama and Ozawa, 1984, and Neotherium Kellogg, 1931, known from Middle Miocene deposits bordering the North Pacific Ocean, are small, primitive pinnipeds in the subfamily Imagotariinae. They have a small supraorbital process of the frontal or have lost it entirely, a three‐rooted first molar, small paroccipital process, and ear morphology indicating that they belong in the subfamily Imagotariinae. Their unique derived characters include extreme intertemporal constriction and highly modified cheek teeth, the premolars having become molarized by the addition of protocones and lingual cingula. Prototaria Takeyama and Ozawa, 1984, the most primitive known imagotariine genus, contains two species, P. primigena Takeyama and Ozawa, 1984, and P. planicephala Kohno, 1994, both of early Middle Miocene age from Japan. Prototaria has a few derived characters, including a large antorbital process, narrow intertemporal region, and large orbit, but its primitive characters apparently were inherited from enaliarctine ancestors. The long enigmatic Neotherium mirum Kellogg, 1931, of Middle Miocene age from California, USA, is related to Prototaria, but differs by having an elongate skull, very slender zygomatic arch, ventrally exposed median lacerate foramen, and smaller but more molarized premolars. A more primitive new genus and species, Proneotherium repenningi Barnes, related to N. mirum, is from the early Middle Miocene Astoria Formation, coastal Oregon, USA. It shares some derived characters with Prototaria, and shares many other important derived characters with N. mirum. Imagotariines probably arose from some species of Early Miocene enaliarctines, became diverse in Middle and Late Miocene time, and are only known from the North Pacific realm. Although they might include the ancestors of true walruses of the subfamily Odobeninae, no known imagotariines appear to have been adapted for mollusk feeding as are the highly evolved modern walruses. Instead, imagotariines appear to have retained a primitive piscivorous diet, as did the fur seals and sea lions of the subfamily Otariinae.