Oligocene Middle Miocene Research Articles

3D sedimentary evolution of a canyon fill (Lower Miocene-age) from the Mandorove Formation, offshore Gabon

Seismic and well data are integrated through 3D modelling and used to examine the sedimentary evolution of the Baliste-Crécerelle canyon, offshore Gabon. The canyon fill (4 km wide, 400 m thick) forms part of the Mandarove Formation (Upper Oligocene–Middle Miocene age) and was fed by a major delta system of the Ogooué River. Salt diapirism influenced the position of the canyon and had a local impact on the filling. Two major fining-upwards stratigraphic cycles are recognised within the canyon. The deposits of sinuous gravity flow channels (100–300 m wide) which show a wide range of planform geometries dominate the canyon fill. The width, amplitude and wavelength of channels recognised within the two stratigraphic cycles are notably different. Canyon filling results from phases of erosional bypass and aggradational filling at the scale of a single turbidite channel story and at the scale of the canyon itself.

Seismically active fracture zones and distribution of large accumulations of metals in the central part of Andean South America

The analysis of the geometry of distribution of earthquake foci in the central part of Andean South America between 18° and 34°S made the delineation of several seismically active fracture zones in the continental wedge overlying the subducting Nazca plate possible. Correlation of their position with the distribution of hypogene accumulations of metals revealed that the majority of large mineral deposits and mining districts are situated in the outcrops of these fracture zones. We present geometrical documentation (map of epicentres, vertical and longitudinal cross sections) of the most important fracture zones and data on mineralogical composition, genetic type and available radiometric ages of mineral deposits. Sixteen mining districts in Chile, and 24 in Argentina, were attributed to the seismically active fracture zones. Major mining districts and individual large mineral deposits occur in six seismically active fracture zones roughly parallel to the axis of the Peru-Chile trench (Carachas-Portillo, Choquelimpie, Iquique, Domeyko, Rio Blanco-Los Bayos and Farellones F.Z.), in six fracture zones roughly perpendicular to the trench (El Salvador, Maricunga, Jaroma, Ujina, Tumbaya and Incahuasi-Leon Muerto F.Z.) and in two fracture zones oriented at an angle of about 45° in relation to the direction of the presently active Andean subduction (Aconcagua and Sierra del Volcan F.Z.). The occurrences of large mineral deposits of different ages show that these fracture zones were also active in the geological past and represent sites of permanent re-opening of paths allowing ore-bearing solutions and long-term accumulation of large amounts of metals to occur in relatively restricted domains of the Earth's crust. The mining districts with dated mineral deposits are arranged into four periods of hypogene mineralization: Upper Miocene-Pliocene, Upper Oligocene-Middle Miocene, Upper Eocene-Middle Oligocene, Lower Paleocene-Upper Eocene. These periods of metallogenic activity correlate well with four supposed Andean subduction cycles active in the Tertiary. The occurrence of mineral deposits of different ages in recently active fracture zones can be used as an important evidence in favour of long-term spatial permanence and activity of these zones and as a guide for the discovery of further mineral deposits hidden under young sedimentary and volcanic cover in the fracture zones.

Backarc deformation along the eastern Japan Sea margin, offshore northern Honshu

The structural evolution of the eastern Japan Sea margin offshore northern Honshu, is discussed on the basis of single-channel seismic profiles. Backarc structures evolved in response to late Oligocene–Middle Miocene extension, which was generated at high angles to the arc/trench system. The evolution of a Late Miocene–Recent compressional plate-tectonic regime resulted in widespread basement inversion. The eastern Japan Sea margin is characterized by variable inverted half graben systems, which are obliquely oriented to the island arc. The area is underlain by three major structural blocks, which are separated by a NW- and a WNW-trending structural discontinuity. These blocks experienced a northward increase in extension. The two southern blocks contain NNE–NE oriented reverse faults, while the northern block is underlain by N–NNW trending reverse faults. The orientation and geometry of basement faults compares well with faults mapped onshore Honshu. The evaluation of the eastern Japan Sea margin can be explained by Early Miocene ESE-directed extension followed by a Middle Miocene SSE-directed extension. Pliocene–Recent east-dipping reverse faults extend along the base of the continental slope and form a discontinuous thrust front, which is characterized by minor fault offsets. These reverse faults are locally associated with small active arc volcanoes.

The assembly of Gondwana 800-550 Ma : Meert J.G. & Van der Voo R., Journal of Geodynamics, 1997, 23/3–4 (223–235)

Southeastward subduction of oceanic lithosphere in front of the rifted continental block of southern China under an emergent oceanic basement in the eastern part of Sabah controlled the development of an elongate basin trending NE-SW. This basin became the site for the deposition of Middle Eocene-Early Miocene sediments. Active opening of the South China Sea Basin in NW-SE and N-S directions during the Middle Oligocene-Middle Miocene caused further subduction and narrowing of the basin. As a result the Middle Eocene-Early Miocene sediments were compressed into a fold-thrust belt trending approximately NE-SW in the western part of Sabah and NW-SE in the northern and eastern part of Sabah. The subduction was accompanied by volcanic activity in the eastern part of Sabah during the Early-Middle Miocene. The deformed sedimentary pile and underlying oceanic basement were then subjected to a NW-SE extension related to the opening of the Sulu Sea Basin during the Early-Middle Miocene. This resulted in the development of extensive chaotic deposits in the eastern and central part of Sabah. This extension also controlled the development of several circular basins for the deposition of the thick, Early-Late Miocene sediments. Continued extension in this region resulted in further southeastward subduction in southeastern Sabah producing the Late Miocene-Quaternary volcanics.

Paleomagnetic evidence for Neogene tectonic rotations in the northern Apennines, Italy

Paleomagnetic analysis was carried out in the northern Apennines on Eocene to Pliocene Epiligurian units. Five Early Miocene and two Middle Miocene sites yielded dual polarity site-mean directions which show signs of clustering after correction for bedding tilt. These likely primary magnetizations, in conjunction with data from the literature, give an overall mean Late Oligocene–Middle Miocene paleomagnetic pole which shows a large and significant counterclockwise rotation of 52° (±≈8°) with respect to the Africa reference paleopoles (or a similar amount of rotation with respect to the coeval Europe reference paleopole). However, this paleopole falls close to the roughly coeval paleopole for Corsica–Sardinia, which is here calculated by averaging data from the literature. Three additional Early Miocene sites from an area west of Parma affected by Pliocene tectonics yielded site-mean directions which pass the fold test and are rotated counterclockwise by a lesser amount than the rest of the Miocene sites. Most of the remaining sites bear paleomagnetic directions acquired after tilting during a recent phase of remagnetization. We suggest that the large-scale rotation observed in the northern Apennines was associated with the motion of the Corsica–Sardinia block within the general context of the Africa–Europe relative motions. A compilation of published data from the central Apennines also shows a differential rotation of the northern relative to the southern Umbria belt which occurred after the motion of Corsica–Sardinia and may have been due to pivoting of the northern Umbria belt against a deep-seated lineament during the non-rotational opening of the Tyrrhenian Sea.

Cartes paléogéographiques-palinspastiques du bassin molassique suisse (Oligocène inférieur - Miocène moyen)

Cartes paléogéographiques-palinspastiques du bassin molassique suisse (Oligocène inférieur - Miocène moyen)

The significance of tectonic-related tertiary remagnetization along the margins of the Valencia trough

The paleomagnetic data from the margins of the Valencia Trough are derived from Mesozoic and Tertiary rocks from the Balearic Islands, Catalan Coastal Ranges and Eastern Iberian Chain. These rocks are affected by a complex structural evolution consisting of an initial compressive stage followed by one of extension. Cenozoic paleomagnetic data indicate that rotations occurred during the Paleogene compression and before the extension started (Lower Miocene) in the Catalan Coastal Ranges. In contrast, in the Balearic Islands the rotations are synchronous to both compressional (Late Oligocene-Middle Miocene) and extensional tectonics (post-Middle Miocene). In both areas the Mesozoic limestones are remagnetized. In the Catalan Coastal Ranges they display the same direction as the Paleogene syn-compressive deposits whereas in the Balearic Islands they conform with Lower Miocene (Burdigalian) syncompressive rocks. It is concluded that the processes of remagnetization that affected eastern Iberia are related to a compressive rather than an extensional tectonics regime

Electron microscope studies of fossil bacteria and the search for biogenic structures in precambrian rocks

Most studies of presumed biological cells in Precambrain rocks have been based on thin section analysis of the rocks, although quite a few studies have also used both scanning and transmission electron microscope methods. Owing to the small size of most bacteria (generally < 2 ~tm), the electron microscope offers the best means of observing the micro-organisms. Many of the Precambrian "biogenic" structures are embedded in cherts and it is believed that they were entrapped in situ in a sedimentary environment in silica gel (Pflug, 1967; Barghoorn, 1971). Phanerozoic examples of silicified bacteria are rare but Monty et al. (1991) discovered some extremely wellpreserved, silicified bacteria from deep sea sediments (Uppermost Oligocene-Middle Miocene age) with the SEM and TEM. The fossilbearing, siliceous Precambrian rocks, in contrast, are highly indurated. One of the problems in studying them is that most preparational techniques used can lead to contamination of the samples; the best method of undisturbed observation is in (ultra) thin section. With the aim of studying the silicification of bacteria and, especially, their aspect in ultra thin section (TEM), bacteria and other microorganisms (including fungi) were experimentally silicified for periods up to 4 months. The experiments were undertaken under both atmospheric pressures and at moderate pressures of 500 atm (the process is accelerated under moderate pressures). In this experiment, the fossilised samples were impegnated in resin and cut with a microtome for TEM observation. In this way, the appearance of small, silicified bacetria in section could be studied as an aid to the identification of such structures in the Precambrian rocks (Westall et al., 1995) This method has also been used for the study of other bacteria-containing rocks (phosphorites, carbonates, siderites, silicates) with varying degrees of success. However, the more indurated siliceous samples are difficult to section with the microtome (e.g. the micro-organisms silieified under pressure for 4 months). At present ionic thinning of thin sections is being undertaken to try to obtain better sections for TEM study.

Are the Oligocene-Middle Miocene Global Stages Depositional Sequences? A Correlation Study from the Pannonian Basin, Hungary: ABSTRACT

Are the Oligocene-Middle Miocene Global Stages Depositional Sequences? A Correlation Study from the Pannonian Basin, Hungary: ABSTRACT

Late oligocene and miocene faulting and sedimentation, and evolution of the southern Rio Grande rift, New Mexico, USA

The distribution of nonmarine lithofacies, paleocurrents, and provenance data are used to define the evolution of late Oligocene and Miocene basins and complementary uplifts in the southern Rio Grande rift in the vicinity of Hatch, New Mexico, USA. The late Oligocene-middle Miocene Hayner Ranch Formation, which consists of a maximum of 1000 m of alluvial-fan, alluvial-flat, and lacustrine-carbonate lithofacies, was deposited in a narrow (12 km), northwest-trending, northeast-tilted half graben, whose footwall was the Caballo Mountains block. Stratigraphic separation on the border faults of the Caballo Mountains block was approximately 1615 m. An additional 854 m of stratigraphic separation along the Caballo Mountains border faults occurred during deposition of the middle-late Miocene Rincon Valley Formation, which is composed of up to 610 m of alluvial-fan, alluvial-flat, braided-fluvial, and gypsiferous playa lithofacies. Two new, north-trending fault blocks (Sierra de las Uvas and Dona Ana Mountains) and complementary west-northwest-tilted half graben also developed during Rincon Valley time, with approximately 549 m of stratigraphic separation along the border fault of the Sierra de las Uvas block. In latest Miocene and early Pliocene time, following deposition of the Rincon Valley Formation, movement continued along the border faults of the Caballo Mountains, Dona Ana Mountains, and Sierra de las Uvas blocks, and large parts of the Hayner Ranch and Rincon Valley basins were segmented into smaller fault blocks and basins by movement along new, largely north-trending faults. Analysis of the Hayner Ranch and Rincon Valley Formations, along with previous studies of the early Oligocene Bell Top Formation and late Pliocene-early Pleistocene Camp Rice Formation, indicate that the traditional two-stage model for development of the southern Rio Grande rift should be abandoned in favor of at least four episodes of block faulting beginning 35 Ma ago. With the exception of two northwest-trending border faults of the Caballo Mountains block that may be reactivated along Eocene compressional structures, the majority of border faults and complementary basins throughout the history of the southern Rio Grande rift were north-trending, which challenges the conventional idea of a clockwise change in stress through time.

New reef targets for oil and gas exploration in Fiji, Southwest Pacific

Fiji forms part of the Southwest Pacific island arc system which marks the boundary between the Indo-Australia and Pacific plates_ The territorial waters cover almost 1.3 million km2 and contain two shallow water Tertiary sedimentary basins_ Bligh Water Basin, covering some 9500 km2, has sediment thicknesses in excess of 5 km and has excellent potential for hydrocarbons_ Bau Waters Basin is also prospective, having a shallow water area of about 1600 km2, with sediment thicknesses up to 4 km_ Fiji lies on the same regional play trend of Miocene reefs which produce oil in Irian Jaya, Indonesia and gas/condensate in offshore Papua New Guinea. Indeed Fiji's basins have many similarities with the oil and gas producing, arc-related basins of Southeast Asia. Source rocks of Oligocene, Miocene and Pliocene age are exposed onshore in Fiji and have been encountered by drilling in the offshore basins. An oil seep in Bligh Water Basin and oil and gas shows in wells provide evidence that hydrocarbons have been generated in the basins. Modelling studies indicate peak oil generation to be at about 2.6 km below sea floor. Miocene and Pliocene reefal limestones form spectacular outcrops in Fiji and represent the best potential reservoirs. Reefs of the same age have been identified on seismic data from the offshore basins and represent attractive targets for exploration. Common forms are reefal mounds and prograded platforms. Over twenty structural reefal traps have been identified on seismic lines in the Late Miocene and Pliocene sequences, mostly in Bligh Water Basin. Estimates of potential unrisked recoverable reserves are 270 million barrels of oil per structure. If structural-stratigraphic trapping occurs, recoverable reserves could increase to over 1 billion barrels of oil per structure. There is considerable scope for more reefal structures in the deeper Oligocene-Middle Miocene interval which cannot be resolved on the existing seismic data, and in areas where seismic coverage is sparse. Limestone turbidite lobes have also been identified on seismic data. These constitute a secondary play and may contain estimated recoverable reserves of 100-200 million barrels of oil per structure. There are no exploration or production licences at present. Fiji has comprehensive petroleum legislation and the Government seeks to encourage exploration investment by oil companies. All reports and data are available in the Fiji Petroleum Data Package which may be ordered from the SOPAC Petroleum Data Bank, Canberra.

Ceratodus diutinus, a new ceratodont from Cretaceous and Late Oligocene–Medial Miocene deposits in Australia

Ceratodus diutinus, a new species of ceratodont lungfish similar to but not identical withCeratodus kaupiAgassiz, 1838–1844, is described from the Lower Cretaceous Griman Creek Formation at Grawan and Lightning Ridge in northern New South Wales, Australia, and the Toolebuc Formation at Canary Station near Boulia in western Queensland. The species also occurred in one Late Oligocene–Middle Miocene deposit at North Prospect, Lake Pinpa, South Australia (Namba Formation). This is the first record from Australia of a species ofCeratodussimilar to the Triassic ceratodonts of Europe. The Australian species lasted much longer than the related European species,C. kaupi, which is restricted to Triassic deposits.

Latest Oligocene to Earliest Pliocene Benthic Foraminiferal Biofacies of the Northeastern Gulf of Mexico

We examined uppermost Oligocene to lowermost Pliocene sections from four northeastern Gulf of Mexico boreholes for quantitative benthic foraminiferal faunal changes, stratigraphic ranges, paleobathymetry, organic carbon content, and planktonic foraminiferal relative abundances. The Eureka boreholes provide a depth transect in the De Soto Canyon area from the upper to lower bathyal zone: E68-136 (557m present depth, -600m paleodepth), E66-73 (857m present depth, 860-lOOOm paleodepth), E68-151A (1326m present depth, -1300m paleodepth), and E68-14 1A (1599m present depth, -1600m paleodepth). A number of taxa last appeared in the late Oligocene to early Miocene (Biochrons P22-N5) at E68-136; several of these disappearances constitute global last occurrences. A global benthic foraminiferal taxonomic turnover that began in the latest early Miocene in other parts of the ocean was restricted to the middle Miocene at E68-136 (Biochrons N9-N12), although faunal abundance changes began in late early Miocene Biochron N8. At middle bathyal borehole E66-73, ten taxa last occurred in Biochrons N8-N10, which is consistent with the timing of the taxonomic turnover in the Pacific and Atlantic. Depth-related faunal trends are examined and compared with previously published distributional data, resulting in revised paleobathymetric ranges of 12 taxa. Detailed age-paleodepth reconstructions reveal several stratigraphically and bathymetrically significant predominance biofacies in the northeast Gulf of Mexico: 1) Uvigerina pigmea dominated the middle-upper bathyal late Neogene; 2) Lenticulina spp. dominated the late Oligocenemiddle Miocene bathyal zone; 3) Oridorsalis spp., Gyroidinoides spp., and Globocassidulina subglobosa dominated the late Neogene lower bathyal zone; and 4) Uvigerina proboscidea was important in the late Neogene in the middle to upper bathyal zones. Four distinct bathymetric migrations are mapped, and 34 additional taxa are shown to have distinct paleobathymetric distributions. Planktonic foraminiferal biostratigraphic control allows us to evaluate the stratigraphic usefulness of benthic foraminiferal ranges. We revise the stratigraphic ranges of 12 bathyal benthic foraminiferal taxa, requiring re-correlation of the benthic foraminiferal zonal boundaries of Berggren and Miller (1989). INTRODUCTION Previous studies have shown that one of the largest benthic foraminiferal faunal changes of the Cenozoic occurred throughout the deep sea (>200m) in the late early to middle Miocene (Berggren 1972; Schnitker 1979, 1986; Woodruff and Douglas 1981; Boersma 1986; Thomas 1985, 1986a, 1886b, 1989, 1992; Woodruff 1985; Kurihara and Kennett 1986; Miller and Katz 1987; Thomas and Vincent 1987; Woodruff and Savin 1989; Miller et al. 1992; Thomas 1992; for an alternative view, see Boltovskoy and Boltovskoy 1988; Boltovskoy et al. 1992). These authors documented that major changes in taxonomic composition, percentages, and absolute abundances of benthic foraminifera began in the late early Miocene and culminated in the middle Miocene. Although this event has been well documented at open ocean locations, it remains poorly documented in marginal seas such as the Gulf of Mexico. The Eureka boreholes examined in this study (northeast Gulf of Mexico) yield faunal abundance changes and stratigraphic ranges that reflect this global middle Miocene benthic foraminiferal event. Benthic foraminiferal faunas have been recognized for their potential to assess paleobathymetry (e.g. Natland 1933; Bandy 1960). While Bandy (1960) promoted the concept that benthic foraminifera have distinct upper and lower depth limits, Streeter (1973) and Schnitker (1974) established that deep-water (>200m; bathyal-abyssal) benthic foraminifera are correlated to water mass properties that may vary independently of depth. Numerous subsequent studies have documented that deep-water benthic foraminiferal distributions are associated with physiochemical properties other than depth, and that depth alone does not control the vertical distribution of benthic foraminifera. For example, vertical distributions are correlated with water masses (e.g. Lohmann 1978; Corliss 1979; Schnitker 1979; Murray 1984; for Gulf of Mexico examples, see Pflum and 88? 86? 84? TEXT-FIGURE 1 Eureka bo ehole location map in the Gulf of Mexico. Contours are in meters. micropaleontology, vol. 39, no. 4, pp.367-403, plates 1-6, text-figures 1-32, tables 1-5, 1993 367 This content downloaded from 157.55.39.152 on Sat, 26 Nov 2016 04:11:28 UTC All use subject to http://about.jstor.org/terms M. E. Katz and K. G. Miller: Latest Oligocene to Earliest Pliocene benthicforaminiferal biofacies of the northeastern Gulf of Mexico TABLE 1 Age model parameters Datum Age (Ma) Depth (feet below sea level) E68-136 E66-73 E68-151 FO C. acutus & 5.

The role of rifting in the evolution of the continental margin of Eastern Asia: Geophysical evidence

The role of rift processes is analysed in the structural evolution of the continental margins of Eastern Asia including the Indo-China Peninsula and North China plain. Paleoreconstructions were made for the Indo-China Peninsula to characterize individual stages of rifting covering the Late Cretaceous-Eocene, Oligocene-Middle Miocene and Late Pliocene-Early Quaternary epochs. The rifting of continental margins occurred synchronously with spreading processes in marginal seas, whereas the formation of rift structures in the North China plain was concurrent with the formation of a deep-water basin of the Philippine Sea. The development of asthenospheric diapire led to crustal extension and was responsible for the formation of rift structures in marginal seas and continental margins.

Neogene arc-continent collision in Sabah, Northern Borneo (Malaysia)—Reply

Abstract The Neogene evolution of Sabah can be interpreted in terms of an arc-continent collision initiated during early Middle Miocene time and followed by intraplate shortening, the latter being active in this area at the present day. The volcanic arc of Late Oligocene-Middle Miocene age is imbricated with melanges and thrust northwestward on a polyphase-deformed turbiditic sequence of Late Cretaceous-Middle Miocene age (Crocker Range). Intraplate shortening is seen in the thrusting and folding offshore Sabah along the Palawan-North Borneo Trench, and also by broad open folds and strike-slip faulting in the previously sutured terranes. This collision can either be interpreted as the final stage of southward subduction of the hypothetical Proto-South China Sea, or the result of back thrusting of the Sulu volcanic arc resulting from the subduction of the Celebes Sea toward the north.

Tectonic evolution of Sabah, Malaysia

Southeastward subduction of oceanic lithosphere in front of the rifted continental block of southern China under an emergent oceanic basement in the eastern part of Sabah controlled the development of an elongate basin trending NE-SW. This basin became the site for the deposition of Middle Eocene-Early Miocene sediments. Active opening of the South China Sea Basin in NW-SE and N-S directions during the Middle Oligocene-Middle Miocene caused further subduction and narrowing of the basin. As a result the Middle Eocene-Early Miocene sediments were compressed into a fold-thrust belt trending approximately NE-SW in the western part of Sabah and NW-SE in the northern and eastern part of Sabah. The subduction was accompanied by volcanic activity in the eastern part of Sabah during the Early-Middle Miocene. The deformed sedimentary pile and underlying oceanic basement were then subjected to a NW-SE extension related to the opening of the Sulu Sea Basin during the Early-Middle Miocene. This resulted in the development of extensive chaotic deposits in the eastern and central part of Sabah. This extension also controlled the development of several circular basins for the deposition of the thick, Early-Late Miocene sediments. Continued extension in this region resulted in further southeastward subduction in southeastern Sabah producing the Late Miocene-Quaternary volcanics.

Selective alteration of arkose framework in Oligo-Miocene turbidites of the Northern Apennines foreland: impact on sedimentary provenance analysis

Abstract Upper Oligocene-Middle Miocene turbidites of the Macigno and Cervarola Formations fill post-collisional elongate basins of the Northern Apennines foreland; they crop out axially for distances up to 300 km and reach a total thickness of 4000 m. Sandstones are arkosic with quartzose grains averaging 50% and fine-grained lithic clasts from 5 to 25%; K-feldspar and plagioclase abundances are similar, and rock fragments are dominated by igneous and metamorphic types. The Macigno sandstones reach a much higher diagenetic grade than the younger Cervarola sandstones. The latter (mature stage of diagenesis), have a clay mineral assemblage with ordered I/S interlayers and illite crystallinity (I.K.) averaging from 8.0 to 10.1, while in the Lower Unit of the Macigno Formation clay crystallinity averages 3.8 (Kübler’s epizone). The evolution of diagenetic processes is unusual because of the abundance of unstable grains. Physical compaction is the main cause of pore reduction. Post-depositional mineralogical changes are relevant in both formations; ignoring authigenic overgrowths and late calcite replacements, they commonly affect 10–20% of the framework grains. Several mineralogical-textural changes influence provenance determinations, including: dissolution processes, which almost totally eliminate unstable species, such as amphibole and pyroxene, originally dominating the heavy mineral population; replacement processes, mainly represented by albite after plagioclase, and by clay or mica materials after unstable grains; intense deformation plus replacement of ductile or brittle grains with the authigenesis of chlorite, white mica and pseudomatrix.

Neogene arc-continent collision in Sabah, Northern Borneo (Malaysia)

The Neogene evolution of Sabah can be interpreted in terms of an arc-continent collision initiated during early Middle Miocene time and followed by intraplate shortening, the latter being active in this area at the present day. The volcanic arc of Late Oligocene-Middle Miocene age is imbricated with melanges and thrust northwestward on a polyphase-deformed turbiditic sequence of Late Cretaceous-Middle Miocene age (Crocker Range). Intraplate shortening is seen in the thrusting and folding offshore Sabah along the Palawan-North Borneo Trench, and also by broad open folds and strike-slip faulting in the previously sutured terranes. This collision can either be interpreted as the final stage of southward subduction of the hypothetical Proto-South China Sea, or the result of back thrusting of the Sulu volcanic arc resulting from the subduction of the Celebes Sea toward the north.

Tectonic evolution of the gulf of Aqaba-Dead Sea transform fault system

Neogene tectonic phases related to stresses which created the Gulf of Aqaba-Dead Sea transform fault system were recorded from evidence in the central part of the Wadi Araba. The chronological sequence of deformation stages is as follows: 1. (1) Epeirogeny (latest late Eocene-Oligocene). 2. (2) Faulting and warping (?Oligocene-Middle Miocene). 3. (3) Folding striking between north-northeast and northeast, E-W trending and N-S shear faulting, and NW-SE normal faulting (Miocene). 4. (4) Uplift and faulting (Pliocene-Pleistocene). 5. (5) Faulting with volcanic activity (Pleistocene). 6. (6) Sinistral movement along the major shear fault in the Wadi Araba. Indications are that this phase is still active (Pleistocene-Recent). The re-strain phases recognised are clues for the investigated area and the entire region to the understanding of the tectonic evolution of the Gulf of Aqaba-Dead Sea transform. Structural features contributing to evidence of strike-slip movement are: drag folds, reverse and normal flower structures, alternation of the downthrown side along the fault trace, gently waved vertical fault planes, horizontal slickensides, transpressive and transtensional pressure ridges and rhombs, linear fault traces without marked vertical throw, and fault plane ridges. A sinistral offset of 40 km along the N-S Al Quweira Fault was deduced from the displacement of distinctive andesitic rocks found on both sides of the fault. For the E-W Salawan Fault, a dextral movement of at least 7 km was determined from the offset of formation boundaries. North-northeast-striking deformed belts containing monoclinal to recumbent en-echelon folds can be seen in the Gulf of Aqaba-Dead Sea transform fault zone. The axial planes of the folds dip southeast and face northwest. These structural elements indicate local SE-NW compressional stress.

Oligocene-Middle Miocene Evolution of the Southeastern San Joaquin Basin, CA: ABSTRACT

Oligocene-Middle Miocene Evolution of the Southeastern San Joaquin Basin, CA: ABSTRACT