Pliocene Sedimentary Rocks Research Articles

Source of Oligocene to Pliocene sedimentary rocks in the Linxia basin in northeastern Tibet from Nd isotopes: Implications for tectonic forcing of climate

We used Nd isotopes and trace element data to determine the provenance of sedimentary rocks in the Linxia basin, northeastern Tibet, whose Oligocene through Pliocene sedimentation history has been interpreted to refl ect deposition in a fl exural basin associated with contractional deformation along the northeastern margin of the Tibetan Plateau. Paleozoic‐early Mesozoic metasedimentary source rocks from the KunlunQaidam and Songpan-Ganzi terranes have e Nd values between −11.8 and −16.1, whereas Paleozoic and Mesozoic plutonic source rocks that intrude the metasedimentary rocks have more positive e Nd values between −3.6 and −11.2. Cretaceous sedimentary source rocks display e Nd values of −9.7 and ‐9.9 in the Maxian Shan, north of the Linxia basin, and ‐15.3 in the plateau margin south of the basin. With e Nd values that range between −8.4 and −10.4 before ca. 15 Ma, and −6.2 and −11.8 after ca. 14 Ma, sedimentary rocks of the Linxia basin are less negative than metasedimentary rocks, which are dominant source rocks within the margin of the Tibetan Plateau today. The relatively positive e Nd values of Linxia basin sedimentary rocks could refl ect several possible sources, including (1) a mixture of plutonic and metasedimentary rocks within the northeastern margin of Tibet, (2) Cretaceous sedimentary rocks derived from the north, or (3) loess derived from central Asian deserts. A mass balance calculation indicates that plutonic rocks are not volumetrically signifi cant enough to generate the e Nd values observed in Linxia basin sedimentary rocks through mixing of plutonic and metasedimentary sources. Rare earth element patterns suggest that Cretaceous rocks were not a dominant source of sediment. The Nd isotopic composition and rare earth element pattern of Quaternary loess are similar to older deposits in the Linxia basin and refl ect loess deposited elsewhere in the Loess plateau and the North Pacifi c (e Nd = −8.6 to ‐10.5). In addition, the modern Daxia River, which drains the margin of the plateau today, transports clay and silt with e Nd values of ‐10.5 to ‐10.8 despite the river’s source in more negative metasedimentary rocks of the Kunlun-Qaidam and Songpan-Ganzi terranes, which indicates that the modern fi ne-grained sedimentary budget is dominated by recent loess deposits. Considering the slow sedimentation rates in the Linxia basin, it is likely that loess sources have contributed a signifi cant volume of fi grained sediment to this basin throughout its history. An increase in the range of e Nd values at ca. 14 Ma in the Linxia basin may refl ect increased unroofi ng of the northeastern margin of Tibet, which slightly preceded a change in climate between ca. 13 and 12 Ma in the Linxia basin. A 1.5‰ increase in baseline δ 18 O values of lacustrine carbonates has been interpreted as the result of reorganization of atmospheric circulation and an increase in aridity on the northeastern margin of the Tibetan Plateau, perhaps associated with the plateau having achieved an elevation suffi cient to block moisture from the Indian Ocean and/or Pacifi c Ocean. Similar timing of exhumation and climate change suggests that northeastward and eastward propagation of the plateau margin was responsible for the middle Miocene climate change observed in the Linxia basin.

Tectonic implications of fault-scarp–derived volcaniclastic deposits on Macquarie Island: Sedimentation at a fossil ridge-transform intersection?

Upper Miocene to lower Pliocene sedimentary rocks on Macquarie Island are dominantly volcaniclastic breccia, sandstone, and siltstone produced by the physical disintegration and tectonic abrasion of oceanic crust in fault zones and mass wasting of these tectonic features. They represent small debris fans and small-scale turbidites deposited at the base of active fault scarps, related to Late Miocene to Early Pliocene seafloor spreading. Most of the sediment is derived from basalts, but diabase and gabbro clasts in some sedimentary rocks indicate that middle and lower oceanic crust was exposed to erosion on the sea floor. A lack of exotic clasts and a low degree of clast roundness are consistent with a local source for the sediment and no input from continental rocks. Spatial relationships between sedimentary rocks and major faults associated with seafloor spreading on the island and correlation between sedimentary clast and adjacent up-thrown block compositions allow us to infer paleotectonic relief for Macquarie Island crust during deposition. Our data support a model involving the deposition of these rocks at the inside corner of a ridge-transform intersection. Furthermore, a tectonic reconstruction of the Australian-Pacific plate boundary for the approximate time that Macquarie Island crust formed (10.9 Ma) also shows that Macquarie Island crust most likely formed near a ridge-transform intersection. This paper describes sedimentation associated with active faulting at a ridge-transform intersection that has been uplifted in situ above sea level along with the surrounding oceanic crust, and demonstrates that high-angle faults have the most pronounced influence, compared with low-angle faults, on sedimentation in this tectonic environment.

Paleogene clockwise tectonic rotation of the Xining‐Lanzhou region, northeastern Tibetan Plateau

To help understand the deformational history of the northeastern Tibetan Plateau, paleomagnetic samples were collected from 177 sites and two magnetostratigraphic sections at 16 localities distributed among Upper Jurassic‐Lower Cretaceous to Pliocene sedimentary and subordinate volcanic rocks within the Xining‐Lanzhou region (34–37°N, 101–105°E). A total of 127 sites at 12 localities yielded primary magnetizations confirmed by fold, reversal, and conglomerate tests. Age control on sedimentary rocks is provided by regional synthesis of chronostratigraphic data and our own biostratigraphic and magnetostratigraphic analysis presented in the companion paper by Horton et al. [2004]. Analysis of paleomagnetic declination combined with results from previous studies yield a remarkably consistent trend of vertical axis tectonic rotations across the studied region. Whereas 19.0 ± 7.2° to 37.8 ± 10.6° clockwise rotations are recorded consistently in all paleomagnetic localities in Lower Cretaceous to Eocene rocks, all paleomagnetic localities in Oligocene to Pliocene rocks have recorded minor to insignificant rotations, indicating that the Xining‐Lanzhou region has undergone a wholesale regional clockwise rotation during late Paleogene time. Consistent with regional chronostratigraphic and thermochronologic results, this late Paleogene tectonic rotation confirms that deformation reached regions of the northern Tibetan Plateau shortly after the initial collision of India with Asia. When compared to rotational paleomagnetic results from adjacent regions, several mechanisms can be proposed to explain the clockwise rotation. On the basis of consistency with geologic data we prefer a model involving clockwise rotation of the Xining‐Lanzhou region through right‐lateral shear, and associated shortening, related to northward indentation of the Qaidam basin.

Middle Miocene–early Pliocene paleo-oceanic environment of Japan Sea deduced from geochemical features of sedimentary rocks

Chemical and isotopic compositions (Sr isotopic ratio, major elements, trace elements, rare earth elements, total carbon, nitrogen, and sulfur contents) of rock samples collected from middle Miocene to early Pliocene sedimentary rocks on the Oga Peninsula, northern Japan, were analyzed to elucidate the paleo-oceanic environment of the Japan Sea. The rocks studied were shales from the Nishikurosawa, Onnagawa and Funakawa formations in stratigraphically ascending order. The Onnagawa sedimentary rocks in the lower (ca. 12.6–11.4 Ma), middle (ca. 10.6–9.0 Ma) and upper (ca. 8.3–7.0 Ma) horizons have high Mo/Al, Ni/Al, and Ba/Al ratios and high total organic carbon as well as high K/Ti and 87Sr/ 86Sr ratios and a positive Eu anomaly. These geochemical variations imply high primary productivity, and reducing conditions indicative of a deep paleo-ocean. The formation of petroleum source rocks on these horizons is attributed to increasing of nutrient delivery from the terrigenous system, which may have been induced by strong wind from Asian continent related to the uplift of Himalayan and Tibetan regions.

堆積岩の化学組成及び同位体組成より推定した古日本海海洋環境

Chemical and isotopic analyses (Sr isotopic ratio, major element, trace element, rare earth element, total carbon, nitrogen, and sulfur contents) of rock samples collected from middle Miocene to early Pliocene sedimentary rocks, Oga Peninsula, northern Japan were performed to elucidate the paleoceanographic environment of Japan Sea. The rocks studied include shale from Nishikurosawa, Onnagawa, and Funakawa formations in stratigraphically ascending order. The Onnagawa sedimentary rocks in the lower (ca. 12.6-11.4 Ma), middle (ca. 10.5-9.0 Ma), and upper (ca. 8.3-7.0 Ma) horizons are characterized by high Mo/Al, P/Al, and Ba/Al ratios and total organic carbon content. Positive Eu anomaly, K/Ti ratio and 87Sr/86Sr ratio are also high in the same horizons. These geochemical variations imply that high primary productivity, and reducing condition of deep paleoocean, and formation of petroleum source rocks were caused by an upwelling of deep seawater. The upwelling of deep seawater is considered to have been influenced by strong winds from the Asian continent, which was related to the uplift of Himalayan and Tibetan regions.

Geochemical Signature of the Kizildere Geothermal Field, Western Anatolia, Turkey

The Kizildere thermal waters are located in the northern part of the Büyük Menderes rift zone. The Paleozoic metamorphic rocks form the basement of the studied area and are discordantly overlain by Pliocene clastic sediments. The thermal waters are associated with NE-SW- and NW-SE- oriented faults, representing a compressional event that followed extensional formation of the rift zone. The hydrothermal alteration includes phyllic, argillic, silicic, hematitized, and carbonatized alteration zones. Precambrian to Cambrian metamorphic and Pliocene sedimentary rocks are distinguished from one another by enrichment patterns for Hg, Sb, As, Tl, Ag, and Au, and depletion patterns for alkaline and alkaline-earth elements in connection with degree of hydrothermal alteration. The thermal waters have surface temperatures of up to 100°C and reservoir temperatures from 148 to 198°C in the Sazak formation and from 200 to 212°C in the Igdecik formation. Hydrogeochemically, Kizildere thermal waters are of the Na-HCO3-(SO4) type. Metalloids of As and Sb and some trace elements (e.g., B and F, indicating high-temperature water-rock interaction), are found in high concentrations. Isotopic data reveal that Kizildere thermal waters do not contain measurable 3H. Conversely, some nearby thermal springs with temperatures of up to 88°C contain atmospheric and anthropogenic 3H (up to 6.5 TU). Therefore, there is evidence for a mixing process between the fresh groundwater and deep thermal water. The Kizildere thermal waters are of meteoric origin. Stable isotope values of σD and σ18O show that the mixed groundwater-thermal water systems lie along the meteoric water line, whereas high-temperature, deep groundwater systems deviate from the meteoric water line in showing a water-rock interaction at high-temperature conditions. These data agree well with the results of hydrogeochemical analyses indicating intensive water-rock interaction and reactions with silicates. Due to the deep circulation, the water is heated by recent subvolcanic activity. Overprinting by reactions with crystalline rocks was intensified by outgassing of magmatic CO2 and H2S, proven by isotope analyses of σ13C, σ34S, and σ11B. Although intense geochemical near-surface reactions occur, the geochemical features of high-temperature, water-rock interaction dominate the chemical and isotopic characteristics of the studied waters.

Tectonic rotation about the termination of a major strike‐slip fault, Marlborough Fault System, New Zealand

The Marlborough fault system comprises a series of major right‐lateral strike‐slip faults that link the Alpine fault to the Hikurangi subduction zone in the Pacific/Australia plate boundary zone in New Zealand. All of the major active faults of the Marlborough fault system have continuous traces except for the Clarence fault which terminates abruptly near the Ward syncline. Paleomagnetic data from upper Miocene and lower Pliocene sedimentary rocks between the Marlborough faults indicate a consistent post‐early Pliocene regional clockwise rotation of about 20°. An additional rotation of about 10° is evident at many localities near the termination of the Clarence fault. It is proposed that the additional rotation, relative to the rest of the region, is caused by a velocity gradient that likely exists between the active Awatere fault and the termination of the Clarence fault. The existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one‐third of the displacement in the Marlborough fault system occurs between the Awatere and Clarence faults. The kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the Clarence fault. The block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data.

The Campania, southern Italy, earthquakes of 1962 August 21

Summary Two earthquakes that occurred on 1962 August 21 in southern Italy, approximately 50 km NW of the destructive Campania-Basilicata event of 1980 November 23 have been studied in order to investigate their geometry of faulting. Both events involved normal faulting; preferred focal mechanisms have one nodal plane that strikes NW parallel to the trend of the Apennines, and dips to the NE (strike 310°, dip 65°, rake – 130° for 18:09 event, and strike 310°, dip 65°, rake – 110° for 18:19 event). The 1962 events, like that of 1980, occurred at around 10 km depth beneath an intra-Apennine sedimentary basin. A normal fault with the same orientation as the NE dipping nodal plane of the focal mechanisms has been observed on a commercial seismic reflection profile crossing this basin. It is suggested that this is the fault that moved in these events, and that repeated motion on this fault is responsible for the development of the basin and for the subsequent folding of Pliocene sedimentary rocks that outcrop in the area. Repetition of earthquakes in these areas suggests that intra-Apennine sedimentary basins should be regarded as areas of high seismic hazard relative to surrounding localities.

Diapir-Like Ridges and Possible Hydrocarbon Occurrence, Northern California Continental Margin: ABSTRACT

The Eel River basin of northern California contains a relatively thick (> 4 km) section of Miocene, Pliocene, and Quaternary fine-grained sedimentary rocks that extends more than 200 km northward from Eureka along the shelf and adjacent Klamath plateau. The east margin of the basin is a fault contact with the coastal belt Franciscan assemblage; the west margin is defined by a zone of uplift along the outer plateau-upper slope. This uplifted zone is characterized by a series of north-south trending ridges that rise as much as 200 m above the adjacent seafloor and against which Quaternary sediments thin. Seismic reflection profiling and coring studies of these ridges have shown them to be diapiric. Quaternary sediments thin against the eastern flanks and are generally absent on the upper flanks and crests of the ridges. Many of the ridges are bounded by one or more faults showing large vertical separation. Seismic reflection records show internal structure of ridges to be homogenous and acoustically opaque, or to consist of faulted and deformed strata. Ridge crests are irregular in surface topography and are presumed to be highly deformed. Shallow cores from ridge crests contain stiff clayey silts of Pliocene age. A 2-m core from ponded sediments on the crest of one of the diapir-like ridges contained significant amounts of gasoline-range hydrocarbons as well as anomalously high quantities of gas in the methane to butane range. We infer that these hydrocarbons are derived from sediments deeper in the Neogene sedimentary section and are being released through fractures in the ridges. Deformation of young surface sediments in ridge areas indicates that uplift is presently occurring along the 200-km long lineament defined by the ridges. These diapir-like ridges may prove useful targets for evaluating the hydrocarbon potential of the offshore Eel River basin. End_of_Article - Last_Page 706------------

THE EROSION SURFACE OF THE NORTHERN AWAJI ISLAND, JAPAN INLAND SEA

In Japan most of the coastal plains are originated from the sedimentary basin of the Neogene formations. Three types of formation process have been reported to explain the accordant level of the hills around the coastal plain; Type A: When the terrace surface of the soft rocks around the coastal plain is cut controled by the next, slightly lower baselevel, the undulating surface is made as a state of dynamic equilibrium of the unconsolidated materials. Type B: At the thinner soft rocks around the sedimentary basin, the basement of the soft rocks reappears as undulating surface without any baselevel control. Type C: The undulating surface emerged in early Pleistocene and subjected to erosion under the baselevel control till the formation of the Higher Terrace. The types A and P have been reported by the author with the examples in the Kitakami valley plain, Tohoku, and in the Muroto peninsula, Shikoku. The type C has been reported by others to explain the so-called “Setouchi Surface” along the Japan inland sea. The erosion surface of the northern Awaji island reported in this paper is correlated with the “Setouchi Surface”. The undulating surface on the horst corresponds to the basement of Miocene and Upper Pliocene sedimentary rocks on the granite bedrock. Judging from the development of paleo red soil with 10R hue, it becomes clear that this erosion surface had been formed before the Higher Terrace stage. The surface had not been covered with any sea level during the Higher Terrace stage nor with the Lower Pleistocene member of the Osaka Group. So-called “Setouchi Surface” may have various origins and formation processes in each tectonic location. The type E is also suggestive for the explanation of the lower peneplain in the Chugoku mountains.

Age and Rate of Movement of the Northern Part of the Death Valley-Furnace Creek Fault Zone, California

Large right-lateral displacements along the Death Valley-Furnace Creek fault zone have probably taken place since Middle Jurassic time. Matching of Middle Jurassic granitic rocks (160 m.y. old by K-Ar dating) on either side of the fault zone suggests displacement on the order of 30 miles. The distribution of Pliocene sedimentary rocks (3.5 m.y. old by K-Ar dating) in the same region suggests the possibility of approximately 3000 feet of right-lateral movement since Pliocene time. The calculated rate of displacement since the Middle Jurassic is similar to the tentative rate since the late Pliocene:

Etude stratigraphique et hydrogeologique de l'extremite meridionale de la Hamada du Guir

Abstract The Miocene and lower Pliocene sandstone and overlying limestone, and the upper Pliocene and Quaternary sedimentary rocks and detrital deposits of the southern portion of the Hamada du Guir (Algeria) rest upon the eroded surface of deformed Paleozoic basement rocks. Significant amounts of ground water in the upper Tertiary sandstones are indicated by four wells in the area west and northwest of Beni-Abbes. Solution pockets and channels, travertine, and other vestiges of ground water are widespread in Quaternary deposits.

Manganese on Punta Concepcion, Baja California, Mexico

On Punta Concepcion in Baja California, a group of volcanic rocks of Miocene age is intruded by igneous rocks of the same age, and both are overlain unconformably by lower Pliocene sedimentary rocks of non-marine and marine origin. Veins of pyrolusite and other minerals are abundant in some basalts of the volcanic series and also cut the intrusives and the lowermost lower Pliocene rocks but form detrital grains in other members of the lower Pliocene series. The veins of almost pure pyrolusite are very narrow but very rich and locally abundant. They provided a small supply of chemical grade ore during World War II. The veins are believed to be of primary hydrothermal origin.