Pliocene Basin Research Articles

Research on Water Quality Indicators at the Rovinari Power Plant

Abstract Indicators of: pH, temperature, conductivity, filtered residue at 105°C, suspended matter, ammonium, chemical oxygen consumption-CCOCr, chlorides, biochemical oxygen consumption - CBO5, sulfates, extractable substances with organic solvents, petroleum products, total iron, calcium, magnesium, sulfides and hydrogen sulfide. The excesses recorded in the sulfate and ammonium indicators in the phreatic waters within the unit premises and in the area of the slag and ash deposits are mainly due to natural causes and to a small extent to anthropogenic action. In accordance with the specialized literature, but also with the studies and research carried out, it is found that the exceedances recorded in the Oltenia area of the specified indicators are due to:- for ammonium (NH4+) - the primary conditions in the Pliocene basin for the formation of aquifer sand deposits; - for sulfates (SO42-) - washing by underground waters of lignite layers in which sulfides frequently appear, especially in the form of pyrite.

УСЛОВИЯ ФОРМИРОВАНИЯ КЛИНОФОРМ В СРЕДНЕ- И ЮЖНО-КАСПИЙСКОМ МЕГАБАССЕЙНЕ

The paper considers sedimentation process and objects of lateral development in deep-water uncompensated and shallow-water – epicontinental paleobasins developed at various evolution stages of South- Caspian and Middle-Caspian basins. The South Caspian megabasin is a great tectonic crustal element and a highly prospective sedimentary basin in the central segment of the Alpine-Himalayan mobile belt. The role of boundary structures of Scythian-Turan platform in the Middle Caspian (such as South-Caspian land and Karaboghaz arc) and avalanche sedimentation on the continental shelf in development of sedimentation units and specific shape objects of lateral development in many kilometers long sedimentary cover of South-Caspian basin has been shown. According to interpretation of seismo-stratigraphic data the inflow of paleodeltaic, avandelatic and turbidite objects of lateral development for infill of the Early Pliocene basin has been proved. Seismo-stratigraphic analysis, using other analyses (e.g. study of morphostructure of palaeorelief and thicknesses of the units and formations) and GSW, enabled the genesis of deposits in the underlying PS formations to be clarified from a new perspective and the favou- rable zones of formation of large lithological and stratigraphic traps for oil and gas accumulations to be identified.

Gravity contribution to the Mejerda foreland basin, Northwestern region of Tunisia

The Mejerda basin in northwestern Tunisia is located between the Tell and Atlas Mountains and contains structures related to the complicated tectonic history of the study region. The Mejerda contains compressional structures related to the Cenozoic collision between Europe and Africa, and strike-slip faults related to extensional tectonics. As a result of the varied tectonic history, there has been numerous models of the basin formation ranging from simple grabens, pull-apart basins and foreland basins. In order to constrain the subsurface structure of the basin, a gravity analysis consisting of the construction of residual gravity anomaly maps, estimated depths from upward continuation and Euler deconvolution, and detailed two-dimensional forward models. The gravity analysis was constrained by a seismic reflection profile and a deep well. The map analysis indicated two separate basins, one called the Quaternary basin and another called the Pliocene basin. Based on the gravity depth analyses and the gravity forward modeling, and the residual gravity anomaly map, these basins were between 2.5 and 3 km thick, and separated by gravity maxima probably due to uplift of Triassic and Cretaceous sediments related to compressional tectonics and evaporitic movement. The Euler deconvolution analysis imaged a number of lineaments, interpreted to be faults, that trend in the NE and NW directions and these faults basically delineate the basins. Results confirm that the Mejerda basin is a wedge-top basin located in the foreland side of the Tellian thrust belt and consists of two separate basins whose origin was mostly determined by thin-skin compressional tectonics.

Plio-Pleistocene foraminiferal biostratigraphy of the eastern Kendeng Zone (Java, Indonesia): The Marmoyo and Sumberingin Sections

The Plio-Pleistocene of the eastern Kendeng Zone (Java, Indonesia) consists of a >1250 m thick series, passing upwards from diatomaceous laminated mudstones to blue clays and deltaic sandstones. The fine-grained marine beds have received little attention from researchers. Age assumptions are based on correlations with better-studied sections in the western Kendeng Zone. In contrast, the deltaic sandstones at the top of the series have received ample attention. These beds are renowned for their fossil vertebrate fauna, including Homo erectus. Lately, doubts have arisen concerning the age and stratigraphic position of the fossiliferous sandstones. The aim of this study is to establish a detailed biostratigraphy of the fine-grained marine beds, which may also provide new age indications for the overlying fossil-bearing sandstones.We selected the Marmoyo and Sumberingin Sections as suitable representatives for the local marine stratigraphy. Both sections were logged and sampled and the samples were analysed for their foraminifera content. The sections provide sufficient biostratigraphic markers to allow for a reasonable age control. We found that the diatomaceous facies is older than previously thought: it dates from the Early Pliocene and corresponds in age with bathyal, foraminifera-rich mudstones of the western Kendeng Zone. It implies the existence of two bio-geographic zones in the Early Pliocene basin, with eutrophic, oxygen-depleted conditions in the east and normal oxygen conditions in the west. The diatomaceous mudstones change upwards into foraminifera-rich mudstones, marking a return to normal oxygen conditions later in the Early Pliocene, and eventually into blue clays, representing a shift from bathyal to outer shelf conditions in the Late Pliocene. Higher up in the blue clays, changes in the planktonic foraminifera assemblage indicate cooler water conditions, which we relate to the beginning of the Pleistocene.Although generally regarded as a continuous regressive series, our work revealed the existence of an unconformity within the blue clays. The blue clays above this unconformity represent a shallow marine, deltaic setting. It is this second blue clay series that passes conformably into the overlying deltaic sandstones. The presence of reworked planktonic foraminifera in the upper clay-series hampers adequate biostratigraphic dating, but the stratigraphic break within the clays suggests that this second sequence is younger than previously assumed.

LATERAL GROWTH OBJECTS IN SEDIMENTARY COVER OF SOUTH CASPIAN BASIN

In this paper sedimentation process and lateral growth objects in deepwater uncompensated and shallow water epicontinental-paleo basins developed at various evolution stages of South Caspian and Middle Caspian basins are being considered. The role of boundary structures of Scythian-Turan platform in the Middle Caspian and avalanche sedimentation on the continental shelf in development of sedimentation units and specific shape objects of lateral growth in many kilometers long sedimentary cover of South-Caspian basin has been shown. According to the interpretation of seismo-stratigraphic data the inflow of paleodeltaic, avandeltaic and turbidite objects of lateral development for infill of the Early Pliocene basin has been proved

Age of a Pliocene basin fill along the Sevier River, southwestern Utah, U.S.A., based on fossil rodents

Age of a Pliocene basin fill along the Sevier River, southwestern Utah, U.S.A., based on fossil rodents

A brief review on 7 papers from the special issue of “The environmental significance of soft-sediment deformation” of the Sedimentary Geology 344 (2016)

From the viewpoint of origins of soft-sediment deformation structures (SSDS), 7 papers (Ito et al., 2016; Jiang et al., 2016; Lunina and Gladkov, 2016; Moretti et al., 2016; Rana et al., 2016; Rodríguez-Pascua et al., 2016; Wheatley et al., 2016) selected from the special issue of “The environmental significance of soft-sediment deformation” of the Sedimentary Geology 344 (2016) were reviewed. (1) The first paper (according to the published order) by Moretti et al. is a general review and introduction of this special issue. This special issue has made an important contribution to the study of sedimentary environments. (2) The fourth paper by Rodríguez-Pascua et al. is an excellent case study. All evidence of earthquake in this paper is reliable. The old Roman City (adjacent to Madrid, the capital of Spain) was definitely destroyed by an earthquake. This paper solved the problem that the archaeologists have not solved yet. (3) The 19th paper by Rana et al. is another excellent case study. It demonstrated that SSDS in the youngest modern sediments in the seismically active area, i.e., the Alaknanda Valley, Garhwal Himalaya, India, are of non-seismic origin, but with typically sedimentary origin. All evidence of sedimentary origin of SSDS in the study area is reliable. (4) The second paper by Lunina and Gladkov stated that SSDS (mainly clastic dikes) in epicentral areas of the recent earthquakes in southern Siberia were originated by earthquakes and that the clastic dikes are the most reliable indicators in the epicentral areas of earthquakes. This conclusion is right. However, it is not accurate to consider all clastic injections as “in-situ earthquake structures” in anywhere, because the clastic injections are with multiple origins. (5) The third paper by Wheatley et al. comprehensively stated the clastic pipes of the Jurassic in the Colorado Plateau, USA. However, the principal origin of the clastic pipes (columns) was possibly not originated by “palaeoseismic controls”, but by “tectonic controls” or “tectonic uplifts”. (6) The 10th paper by Jiang et al. proposed that 6 types of SSDS of the Lixian Section in eastern Tibetan Plateau, i.e., in a tectonically and seismically active area, were originated by earthquakes. However, the evidence of seismic origin is not sufficient. Therefore, the origins of SSDS in the Lixian Section are worthy to be further discussed. (7) The “injectites” and “extrudites” in a Late Pliocene basin on the Boso Peninsula, Japan, from the 24th paper by Ito et al., are non-SSDS and their origin is unreliable.The above viewpoints may be inappropriate. Criticisms and corrections are welcome.This paper is not only the author's brief review on 7 papers selected from the special issue of the Sedimentary Geology 344 (2016), but also an invitation to geologists worldwide to write papers for a new special issue of “The origins of SSDS” of the Journal of Palaeogeography which is planned to be published in 2018.

Application of the authigenic 10Be/9Be dating method to Late Miocene–Pliocene sequences in the northern Danube Basin (Pannonian Basin System): Confirmation of heterochronous evolution of sedimentary environments

Authigenic 10Be/9Be dating method was applied to lacustrine, deltaic and alluvial sequences of the northern Danube Basin (Pannonian Basin System), to bridge the insufficiency of geochronological data for the Late Miocene to Pliocene period. The measurements of 51 samples (both lacustrine and floodplain), ranging from 11.6 to 0.95Ma are consistent with the existing magnetostratigraphic and biostratigraphic data standing mainly on the evolution degree of endemic mollusk fauna, mammals and dinocysts. This agreement confirms our assumption that the incoming beryllium fluxes remained constant over the studied time period and thus that the two initial 10Be/9Be ratios determined in actual Holocene/Late Pleistocene sediments (lacustrine and floodplain) are valid for these environments.The obtained ages indicate gradual progradation of the deltaic depositional systems across the Danube Basin with a clear time-transgressional character, replacing basin floor and shelfal environments. Deltaic sedimentation occurred firstly in the north at foothills of the Western Carpathians from 11.0Ma, and changed to the alluvial environment after 10.5Ma. At the same time (~10.5Ma), the paleo-Danube deltaic system draining the Eastern Alps entered the study area from the Vienna Basin situated on the West. Later, the deltaic systems were merged in the central part of the basin and reached its southeastern margin at ~9.4Ma. Regression of the Lake Pannon from the southernmost part of the study area is evidenced after 8.7Ma. Alluvial deposition of meandering rivers lasting until 6.0–5.0Ma followed and was interrupted by the early Pliocene basin inversion. Sedimentation of braided streams took place during the late Pliocene and Pleistocene, reflecting uplift of mountains surrounding the basin margins.This study documents the powerful potential of the authigenic 10Be/9Be dating method and its reliability in a basin with complicated tectonic and sedimentary history. It demonstrates that this method can effectively be applied to lacustrine and floodplain deposits and to samples from outcrops as well as boreholes.

Application of detrital zircon U-Pb geochronology to surface and subsurface correlations of provenance, paleodrainage, and tectonics of the Middle Magdalena Valley Basin of Colombia

Detrital zircon U-Pb geochronology has been used extensively to develop provenance histories for surface outcrops of key stratigraphic localities within sedimentary basins. However, many basins lack sufficiently continuous and widespread exposures of complete successions to evaluate proposed long-term tectonic histories, stratigraphic correlations, and paleodrainage patterns within individual basins. Here, we demonstrate the utility of subsurface detrital zircon U-Pb analysis by integrating ages from three key wells (21 subsurface samples) with previously reported data from six exposed intervals (90 surface samples) within a single basin. Samples from the 5-10-km-thick clastic successions span several structural blocks over an similar to 300 x 50 km swath of the Middle Magdalena Valley Basin, a north-trending intermontane basin in the northern Andes of Colombia. Available U-Pb age distributions for modern rivers highlight the distinctive signatures of several competing sediment sources, including two major contiguous ranges (Central Cordillera and Eastern Cordillera) and two localized block uplifts (Santander Massif and San Lucas range). U-Pb results from Jurassic through Neogene stratigraphic units spanning the nine surface and subsurface sites, including several type localities, enable comparisons of provenance shifts at specific sites and spatial variations among key stratigraphic intervals across multiple sites. Distinctive age populations for the Andean magmatic arc, retroarc fold-thrust belt, and South American craton facilitate correlation of stratigraphic units and reconstruction of the long-term provenance and tectonic evolution of the Middle Magdalena Valley Basin. Nearly all surface and subsurface localities show up-section changes in age spectra consistent with (1) Jurassic growth of extensional subbasins fed by local igneous sources, (2) Cretaceous deposition in an extensive postrift setting, and (3) protracted Cenozoic growth of basin-bounding ranges during Andean crustal shortening. Subsurface samples augment surface samples, highlighting their utility in developing regional source-to-sink relationships, the timing of paleodrainage integration, and tectonic reconstructions. Provenance shifts of mid-Paleocene and latest Eocene-earliest Oligocene age are consistent with incipient uplift of the flanking Central Cordillera and Eastern Cordillera, respectively. However, a well-documented phase of latest Paleocene-middle Eocene beveling of basement uplifts in the Middle Magdalena Valley Basin appears to be largely aliased in the detrital record. Moreover, despite the proximity of the magmatic arc, there is insufficient syndepositional evidence for a proposed Paleogene pulse of magmatism and, in this case, limited utility of U-Pb ages in pinpointing precise depositional (stratigraphic) ages. U-Pb age spectra for Oligocene through Pliocene basin fill underscore complex along-strike (north-south) and cross-strike (east-west) variations reflective of compartmentalized transverse deposystems demarcated by point-source contributions from the Central Cordillera and Eastern Cordillera. The late Miocene appearance of 100-0 Ma grains and a regional switch to broad, multimodal age distributions suggest the initial integration of the longitudinal proto-Magdalena River, linking the Middle Magdalena Valley Basin with southern headwaters in the Upper Magdalena Valley and likely driving increased sedimentation rates farther north in the offshore Magdalena submarine fan of the southern Caribbean margin.

A sequence stratigraphic model for the Upper Miocene–Pliocene basin fill of the Pannonian Basin, eastern Hungary

Interpretations of subsurface data and computer simulations of basin-fill history in the late Neogene Pannonian Basin of eastern Hungary established a regional stratigraphic model presented in this paper. Three fluvial systems overfilled the basin: a large system from the NE, another from the NW and a third smaller system transported sediments from the territory of Romania, from the SE. Large part of the basin had been filled by Messinian time (late Miocene); the remaining lake was located in southeastern Hungary and neighboring countries. In the Tortonian stage, the three fluvial systems advanced concomitantly (with small-scale, high-frequency cycles), toward the basin center. A significant relative lake-level drop occurred in the Messinian, which induced large-scale erosion and fluvial incision and generated an unconformity surface that provides a major division in the Pannonian strata; it appears as a significant stratigraphic divide that separates two different stages in the history of the Pannonian Basin. In the upper Messinian-Pliocene stage, the basin underwent a tectonic inversion; the shallow lake was filled up rapidly by lowstand turbidites and prograding delta-slope sediments. The inversion continues up to the present day. Turbidites and lowstand prograding wedges associated with the Messinian event may be targets for hydrocarbon exploration. Four main stages can be identified in the Upper Miocene–Pliocene basin fill history: (1) Tortonian highstand regression with several low-rank relative lake-level cycles; (2) Messinian lake-level drop, accompanied by the formation of the “Messinian unconformity” and the deposition of a falling-stage systems tract (FST). The “Messinian unconformity” is a composite surface, represented by a subaerial unconformity at the margins, and a basal surface of forced regression in the depocenters; (3) relative rise of lake level, when the FST turned to a lowstand systems tract (LST); (4) tectonic inversion (basinward tilt and marginal uplift) during or at the beginning of the LST.

Detrital-zircon U-Pb evidence precludes paleo–Colorado River sediment in the exposed Muddy Creek Formation of the Virgin River depression

Only since 5–6 Ma has the Colorado River flowed through the western Grand Canyon into the Grand Wash Trough at the eastern end of Lake Mead. Before then, the river may have flowed through a paleocanyon transiting the Kaibab uplift at a stratigraphic level above the present eastern Grand Canyon to cross the Shivwits Plateau north of the western Grand Canyon and enter the Virgin River drainage, which exits the Colorado Plateau into the Virgin River depression north of Lake Mead. U-Pb age spectra of detrital zircons from Miocene–Pliocene basin fill of the Muddy Creek Formation in the Virgin River depression preclude any paleo–Colorado River sand in Muddy Creek exposures but fail to show that a Miocene paleo–Colorado River never flowed into the Virgin River depression, because all exposed Muddy Creek horizons sampled for detrital zircons postdate ca. 6 Ma. Detrital-zircon populations from available surface collections cannot test for the presence of Colorado River sediment within unexposed lower Muddy Creek or sub–Muddy Creek strata in the subsurface of the Virgin River depression. Alternate scenarios include rejection of paleo–Colorado flow into the Virgin River drainage at any time, or exit of the pre–6 Ma paleo–Colorado River from the upper Virgin paleodrainage toward the northwest into the eastern Great Basin without flowing southwest into the Virgin River depression through the Virgin River gorge, which may be younger than ca. 6 Ma.

Oligocene to Lower Pliocene deposits of the Norwegian continental shelf, Norwegian Sea, Svalbard, Denmark and their relation to the uplift of Fennoscandia: A synthesis

This study provides the results of the first integrated study of Oligocene–Pliocene basins around Norway.Within the study area, three main depocentres have been identified where sandy sediments accumulated throughout the Oligocene to Early Pliocene period. The depocentre in the Norwegian–Danish Basin received sediments from the southern Scandes Mountains, with a general progradation from north to south during the studied period. The depocentre in the basinal areas of the UK and Norwegian sectors of the North Sea north of 58°N received sediments from the Scotland–Shetland area. Because of the sedimentary infilling there was a gradual shallowing of the northern North Sea basin in the Oligocene and Miocene. A smaller depocentre is identified offshore northern Nordland between Ranafjorden (approximately 66°N) and Vesterålen (approximately 68°N) where the northern Scandes Mountains were the source of the Oligocene to Early Pliocene sediments. In other local depocentres along the west coast of Norway, sandy sedimentation occurred in only parts of the period. Shifts in local depocentres are indicative of changes in the paleogeography in the source areas.In the Barents Sea and south to approximately 68°N, the Oligocene to Early Pliocene section is eroded except for distal fine-grained and biogenic deposits along the western margin and on the oceanic crust. This margin was undergoing deformation in a strike-slip regime until the Eocene–Oligocene transition. The Early Oligocene sediments dated in the Vestbakken Volcanic Province and the Forlandssundet Basin represent the termination of this strike-slip regime.The change in the plate tectonic regime at the Eocene–Oligocene transition affected mainly the northern part of the study area, and was followed by a quiet tectonic period until the Middle Miocene, when large compressional dome and basin structures were formed in the Norwegian Sea. The Middle Miocene event is correlated with a relative fall in sea level in the main depocentres in the North Sea, formation of a large delta in the Viking Graben (Frigg area) and uplift of the North and South Scandes domes. In the Norwegian–Danish Basin, the Sorgenfrei-Tornquist Zone was reactivated in the Early Miocene, possibly causing a shift in the deltaic progradation towards the east. A Late Pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2.7 Ma when the Scandes Mountains were strongly eroded and became a major source of sediments for the Norwegian shelf, whilst the Frigg delta prograded farther to the northeast.

Late Miocene to present-day exhumation and uplift of the Internal Zone of the Rif chain: Insights from low temperature thermochronometry and basin analysis

Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (40Ar/39Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60–100°C/Ma between 22.5 and 19Ma, then cooled to temperatures around 40°C between 19 and 18Ma. They were re-heated at around 110°C between 18 and 15Ma then rapidly cooled and exhumed to reach the surface temperature at around 13Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13Ma the cooling resumed at a rate of 50°C/Ma indicating an exhumation rate of 0.8mm/y considering an average 40°C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8Ma. The whole coastal area was uplifted at slow average rates (0.01–0.03mm/y) in relation with a northeastward tilting of 0.2–0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.

Snapshot of a lower Pliocene Dendropoma reef from Sant Onofre (Baix Ebre Basin, Tarragona, NE Spain)

We study a vermetid–coralline algal buildup from the lower Pliocene deposits of the Baix Ebre Basin (Sant Onofre, NE Spain). The bioconstruction framework is made up by the intergrowth of Dendropoma and encrusting coralline algae, mostly Spongites fruticulosus with rare Neogoniolithon brassica-florida. Thus, it can be considered a fossil analog of the present-day Mediterranean Dendropoma reefs. The bioconstruction developed on top of a flat palaeotopographic high formed by pre-Pliocene substrate in a sheltered embayment. Submarine cliff sediments, consisting of big blocks and boulders, were deposited along the margin of the palaeohigh. Crusts of coralline algae, intergrowing with serpulids and vermetids, extend from the flat top downwards along the talus. Gray-bluish marl, yellowish silt and fine-grained sand, were deposited in the surrounding low areas. A rich and diverse dweller assemblage occurs in the buildup: bivalves (pectinids, venerids, Lithophaga), gastropods (muricids, nassarids, olivids, cancellarids), ahermatypic coral Cladocora ?, barnacles of the family Pyrgomatidae, Balanus trigonus and regular echinoids. In the talus deposits, clusters of Neopycnodonte cochlear, Hinnites ercolanianus and Balanus sp. dominate the faunal assemblage. Further, the blocks of the talus are densely bored, showing Gastrochaenolites, Entobia, Maeandropolydora and Caulostrepsis. Faunal and boring assemblages indicate that the buildup settled and developed in very shallow conditions (most likely less than 10m water depth). The whole fossil assemblage, framework and dweller community, are preserved in situ, maintaining their original growth positions. Development in a protected setting, together with rapid burial due to progradation of siliciclastics on top of the palaeotopographic high, accounts for this exceptional preservation in such a shallow environment.The vermetid bioconstruction of Sant Onofre represents the only carbonate deposits found in the lower Pliocene basins of NE Spain. Sequence stratigraphic architecture indicates that these carbonates represent the maximum flooding deposits. Thus, maximum carbonate production took place due to sediment starvation in the palaeohigh while terrigenous deposits were formed in the surrounded low areas.

Provenances of late Pliocene rare-metal-titanium placers in the Tamansky Peninsula

The comprehensive mineralogical analysis of the Taman nearshore Ti-Zr placers and their provenances in the adjoining late Pliocene sedimentation basin is presented. Taking into account paleogeographic reconstructions and contemporary mineral potential of sediments in the Sea of Azov, a contribution of specific feeding sources of terrigenous minerals to the formation of the late Pliocene placers have been estimated. These sources are crystalline and sedimentary rocks of the Caucasus, the southern Russian Plate, and the southeastern Ukrainian Shield (listed in the order of their contribution). The Miocene placers of the Stavropol Arch and Adygea Prominence, as well as the Cretaceous and younger placers of the Ukrainian Shield and the Voronezh Anteclise are suggested to be transitional reservoirs. Economic deposits are forecasted in the zone of paleostraits.

Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance model

Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance modelThe development of the Turiec Basin and landscape evolution in its catchment has been reconstructed by methods of geological research (structural geology, sedimentology, paleoecology, and geochronological data) as well as by geophysics and geomorphology. The basin and its surrounding mountains were a subject of a mass balance study during periods of tectonic activity, accompanied by considerable altitudinal differentiation of relief and also during quiet periods, characterized by a development of planation surfaces in the mountains. The coarse clastic alluvial fans deposited beneath the offshore pelitic sediments document the rapid Middle Miocene uplift of mountains on the margin of the Turiec Basin. The Late Miocene finegrained sedimentation represents the main fill of this basin and its origin was associated with the formation of planation surfaces in the surrounding mountains. The rapid uplift of the western and northern parts of the catchment area during the latest Miocene and Early Pliocene times further generated the deposition of coarse-grained alluvial fans. The Late Pliocene basin inversion, due to uplift of the whole Western Carpathians mountain chain, was associated with the formation of the Early Quaternary pediment and ultimately with the formation of the Turiec river terrace systems.

Late Miocene stratigraphy, palaeoecology and palaeogeography of the Tabriz Basin (NW Iran, Eastern Paratethys)

The Tabriz Basin is located in NW Iran within the collision zone of the Arabian and Eurasian plates. Its Upper Miocene and ?Pliocene basin fill, termed Lignite Beds and Fish Beds, can provide detailed insights into the Neogene environments and processes during a time of intense tectonics and volcanism. However, a modern re-evaluation of the Lignite Beds and Fish Beds is lacking. Here we present fission track (FT) data from the northern hinterland of the Tabriz Basin (Upper Red Formation) and from the Fish Beds, which support previous age assumptions for the Upper Red Formation, but, together with the new biostratigraphic data, point to an older stratigraphic age for the Lignite and Fish Beds than previously thought (Lignite Beds: 11.6–10.0 Ma; Fish Beds: 10.0–7.5 Ma). Furthermore, we describe for the first time the fossil fish and ostracod fauna and the diatom assemblages from both the Lignite Beds and Fish Beds. All fossil groups are characterized by the occurrence of freshwater and brackish forms; additional marine–euryhaline taxa appear among the fishes and diatoms. It can be assumed that the Lignite and Fish Beds represent deposits of a lacustrine to euryhaline Late Miocene Lake Urmia during the initial state of the Tabriz Basin subsidence, and that the ancient lake was located farther to the east and in a higher altitude than the present-day Lake Urmia. The fossil assemblages indicate a new palaeogeography for the Late Miocene of the study area, with temporary connections between the Tabriz Basin and the southern Caspian Sea, perhaps via an ancient Araks River passage.

Tectonic evolution and origin of the Golfo Dulce gold placers in southern Costa Rica

A new model of the geologic evolution of the Golfo Dulce gold placers is presented. It is shown that the placers were formed on or about an Early Miocene to Late Pleistocene island, prior to its tectonic break-up between Late Pleistonce and Recent times. The island had its origin in a post-Cretaceous swelling or anticlinal doming of the deep oceanic crust, from the crest of which the older pelagic sedimentary cover (Golfito Formation) was removed by submarine erosion, and was preserved only on its flanks. Younger pelagic sediments (Salsipuedes-Pavones Formation) were depostied directly over the older crust in the central part of the structure; and over the Golfito Formation on the flanks. Simultaneously, gold-bearing basaltic intrusive and extrusive activity took place in the tensionally weakened central part of the structure, giving rise to a younger Basement Complex or crust. By Early Miocene, this basement rose above sea level, and formed the island. Later it began subsiding, allowing the Charco Azul Formation to gradually encroach upon it -if not actually cover it-by Late Pliocene time. The first concentrations of gold were formed in the basal strata of this formation. Thereafter, a period of stanstill or possible slight uplift followed, allowing the erosion of the Charco Azul strata in certain parts of the island, and the depositionof the Armuelles Formation in a brackish/near-shore to neritic enviroment. Second cycle gold concentrations were formed in its basal strata. Post-Armuelles tectonic movements caused third-cyclegold concentrations. The structurally high younger basement was thrust over the strata of its own detritic sedimentary cover by the Osa Overthrust; and the older basement was thrust over the same sediments in the area of Golfo Dulce; and over younger basement rocks in the area of the isthmus. This later faulting was brought about by the Golfo Dulce Oriental Fault and associated structures to the northwest. Therefore, no pull-apart Pliocene basins exist in the Golfo Dulce are, nor do certain right-lateral-strike-slip faults related to he Panama Fracture Zone.

Geological map of the Pliocene succession of the Northern Siena Basin (Tuscany, Italy)

Please click here to download the map associated with this article. The late Miocene-Pliocene sedimentary fill of the Siena Basin (Tuscany, Italy) consists dominantly of clastics and has internal architecture that reflects the interplay of tectonics, relative sea-level changes and climate variations. Pliocene sediments are extensively exposed and overlay both late Miocene deposits and pre-Neogene bedrock. Specifically, Pliocene basin margin sediments consist largely of sand with gravel and mud intercalations, deposited mainly in nearshore settings with minor fluvial depositional episodes. They grade basinward to dominantly offshore fines with intervening turbiditic sand bodies. New fieldwork revealed that basin margin deposits, notwithstanding lithologically rather homogeneous, are made of a variety of sedimentary facies and bear several unconformities. They have been traditionally described and mapped using lithostratigraphic criteria, that have proven to be unfit to represent such complex stratigraphic architectures. The aim of this paper is to describe the allostratigraphic architecture of the Pliocene deposits exposed in a marginal key-area (45 km) of the northern Siena Basin by means of a 1:10,000 scale geological map. The recognized succession of allostratigraphic units and their bounding discontinuities, along with new biostratigraphic data from calcareous plankton, provides new insights into the geological history of the Siena Basin and represents valuable constraints for long-distance correlation.

Volcanic Framework of the Pliocene El Dorado Low-Sulfidation Epithermal Gold District, El Salvador

The Pliocene El Dorado low-sulfidation epithermal Au-Ag vein system, located within an 84-km2 district in north-central El Salvador, is hosted by volcanic rocks formed along the Caribbean plate margin in response to the subduction of the Cocos plate during the Tertiary. The principal volcanic host rocks to epithermal veins, and effective basement in the district, consist of a >400-m-thick sequence of basaltic to andesitic lava flows and volcanogenic sedimentary rocks. Locally, porphyritic basaltic to andesitic domes and dikes intruded this sequence during the late Miocene (10.7 ± 1.9 Ma). The mineralized volcanic basement rocks, outcropping mainly in north and central El Dorado, represent different parts of a complex volcanic sequence composed of multiple superimposed volcanic centers. Vein formation in the district occurred in the Pliocene between 4.7 ± 0.2 Ma and 4.06 ± 0.29 Ma, based on K-Ar and 40Ar-39Ar plateau ages on vein adularia. Vein formation overlapped with Pliocene felsic volcanism (3.94 ± 0.29 Ma to 3.36 ± 0.49 Ma), based on field relationships and 40Ar-39Ar geochronology. Pliocene felsic volcanic rock sequences crop out widely in southern El Dorado at lower elevations relative to central and northern El Dorado. The felsic rocks have sinters intercalated with pyroclastic and sedimentary rocks at the base of the sequence that define the paleosurface of the epithermal vein system, at least in this part of the district. The depth of erosion in central and northern El Dorado, the primary Au-Ag resource, is below the paleosurface, as only the low sulfidation–style epithermal veins are present. Field relationships and geochronology suggest that the onset of extensive felsic volcanism marks the waning stage of hydrothermal activity associated with vein formation and mineralization. From north to south, the El Dorado district represents an oblique cross section through the volcanic and epithermal vein system formed during east-west extension. Northern and central El Dorado, dominated by mineralized mafic to intermediate volcanic basement rocks, represent the deeper parts of the volcanic and hydrothermal system. Southern El Dorado is the shallow level of the volcanic field and epithermal vein system, preserving the surface and shallow subsurface environments, including the sinters and contemporaneous to postmineral felsic volcanic rocks. Although we cannot preclude that the distribution of volcanic rocks represents lateral facies changes in a Pliocene felsic dome field or that the variations in depth within the low-sulfidation epithermal system represent simply lateral flow driven by topography in the geothermal system, the preponderance of evidence suggests that the oblique section is principally due to postmineral deformation associated with formation of large Pliocene and Pleistocene Rio Titihuappa basin lying to the immediate south.