Evolution of the southern Taiwan–Sinzi Folded Zone and opening of the southern Okinawa trough

Recent interpretation of seismic sections and free-air gravity anomalies in offshore northern Taiwan reveals that the southern Taiwan–Sinzi Folded Zone began to form in late Middle Miocene, though it was mainly constructed in the Late Pliocene with strong reverse faulting and folding. Two westward progradational sequences were deposited in the shelf basin with sediments supplied from the southern Taiwan–Sinzi Folded Zone and the southern Ryukyu Arc. These two structures are displaced by several northwest-striking dextral strike–slip faults that were active in the early Quaternary when the clockwise-rotated southern Ryukyu Arc and the folded southern Taiwan–Sinzi Folded Zone were broken. It is believed that recent extension in the southern Okinawa Trough started in the early Quaternary because uplift on the southern Taiwan–Sinzi Folded Zone continued to latest Pliocene–early Quaternary. Paleogene–Miocene sediments of the East China Sea Shelf in the western part of the southern Okinawa Trough Basin are interpreted to indicate that the East China Sea Shelf Basin extended to the east of the southern Taiwan–Sinzi Folded Zone.     

Metal contamination in southern Brazil vineyard soils

The viticulture is a rapidly developing agricultural branch in the Rio Grande do Sul State (southern Brazil). Situated in a region with a humid temperate climate, Brazilian vine-growing areas are dampest in the world (annual precipitation close to 2000 mm…     

The Mesolithic–Neolithic transition in southern Iberia

New data and a review of historiographic information from Neolithic sites of the Malaga and Algarve coasts (southern Iberian Peninsula) and from the Maghreb (North Africa) reveal the existence of a Neolithic settlement at least from 7.5 cal ka BP. The agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the Mesolithic populations. The timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems, including upwelling intensity, sea-level changes and increased aridity in the Sahara and along the Iberian coast. These changes likely impacted the subsistence strategies of the Mesolithic populations along the Iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the Mesolithic–Neolithic transition. The rapid expansion and area of dispersal of the early Neolithic traits suggest the use of marine technology. Different evidences for a Maghrebian origin for the first colonists have been summarized. The recognition of an early North-African Neolithic influence in Southern Iberia and the Maghreb is vital for understanding the appearance and development of the Neolithic in Western Europe. Our review suggests links between climate change, resource allocation, and population turnover.     

The Palomares brittle—ductile Shear Zone of southern Spain

The Palomares Shear Zone is a major Neogene-Quaternary strike—slip zone which transects the crust of the Betic Cordillera in SE Spain. The shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology. It is emphasized that the formation of the Palomares Shear Zone was not an isolated tectonic event, but part of a complex Neogene tectonic history. The Neogene evolution of the Betic-Rif orogen and its central Alboran Basin is characterised by the following events: (1) emplacement of the Alboran Diapir with resulting nappe-shedding from the overlying crust between 25 and 20 Ma ago; (2) onset of the subsidence of the Alboran Basin between 20 and 15 Ma ago due to cooling of the Alboran Diapir and the overlying crust; (3) formation of the Cabo de Gata Volcanic Chain between 15 and 8 Ma ago; and (4) refolding of the nappe sheets in the Betic-Rif orogen into a basin and range structure about 7 Ma ago. Continuous activity of the Crevillente Fault of southern Spain may have occured over a period from 20 Ma ago up to the present. The interrelated Palomare Fault in SE Spain was probably formed between 15 and 8 Ma ago and seem to be active still. The Palomares Shear Zone affects a rock volume 44 km wide, at least 80 km long and 30 km deep. A shear strain—distance diagram constructed across the Palomares Shear Zone and its axial Palomares Fault involves a new method to estimate or constrain the shear strain magnitude along brittle-ductile shears. The typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the Palomares Fault are of the order 10⁻¹³–10⁻¹⁴ s⁻¹. The tensor shear strain rate along the Palomares Fault itself is of the order 10⁻¹²s⁻¹ and the time averaged relative displacement rate of its walls is about 2 mm a⁻¹. The range of strain rates within the Palomares Shear Zone are interpreted to be due to a combination of various flow-softening mechanisms: geometric, structural, thermal and strain-rate softening. These softening mechanisms might explain the difference in vertically averaged viscosities of 10²⁰ Pa s and 10²⁵ Pa s or lower suggested for the crustal rocks in the Palomares Fault proper and that of the relatively rigid boundaries of the Palomares Shear Zone, respectively.     

Features and effects of some acid-saline groundwaters of southern Australia

Many salt lakes have formed in southern Australia where regional saline groundwaters form discharge zones. Some of these groundwaters are characterized by acidity and high salinity. These are commonly found where underlying Tertiary sediments are sulfide-…     

Climate prediction experiences in southern Africa 1990–2005 and key outcomes

This paper reviews long-range climate prediction with a focus on experiences in southern Africa from 1990 to 2005 and statistical techniques based on historical replication. The initial growth and use of climate predictions in southern Africa created an understanding of tropical Atlantic and Indian Ocean coupling with Pacific El Niño and the African monsoon, and fostered extensions of the global observing system as a key outcome. An intercomparison of forecast errors highlights optimal scales for model aggregation. Cases of forecast development are analyzed and a tendency for neutral messages is found. South African maize yield exhibits an uptrend (+0.26 T ha^?1/year) since 1992 that may be related to the increased use of Internet and uptake of long-range forecasts.     

Biostratigraphy of a Paleocene–Eocene Foreland Basin boundary in southern Tibet

This study of the Paleocene–Eocene boundary within a foreland basin of southern Tibet, which was dominated by a carbonate ramp depositional environment, documents more complex environmental conditions than can be derived from studies of the deep oceanic environment. Extinction rates for larger foraminiferal species in the Zongpu-1 Section apply to up to 46% of the larger foraminiferal taxa. The extinction rate in southern Tibet is similar to rates elsewhere in the world, but it shows that the Paleocene fauna disappeared stepwise through the Late Paleocene, with Eocene taxa appearing abruptly above the boundary. A foraminifera turnover was identified between Members 3 and 4 of the Zongpu Formation—from the Miscellanea–Daviesina assemblage to an Orbitolites–Alveolina assemblage. The Paleocene and Eocene boundary is between the SBZ 4 and SBZ 5, where it is marked by the extinction of Miscellanea miscella and the first appearance of Alveolina ellipsodalis and a large number of Orbitolites. Chemostratigraphically, the δ13C values from both the Zongpu-1 and Zongpu-2 Sections show three negative excursions in the transitional strata, one in Late Paleocene, one at the boundary, and one in the early Eocene. The second negative excursion of δ13C, which is located at the P–E boundary, coincides with larger foraminifera overturn. These faunal changes and the observed δ13C negative excursions provide new evidence on environmental changes across the Paleocene–Eocene boundary in Tibet.     

Karstification at Beşkonak dam site and reservoir area,southern Turkey

Bekonak dam and hydroelectric power plant are planned to be constructed on the Köprüçay river, 40 km east of the Antalya city. In the dam site and reservoir area, Köprüçay Conglomerates of Miocene age and the Bekonak Formation (sandstone-claystone) alternating with each other crop out vertically. Köprüçay conglomerates, with the components of limestone fragments and carbonate texture, are karstic and permeable, whereas the Bekonak Formation is impermeable. At the northern edge of the reservoir area, the Olukköprü karst springs discharge at a minimum of 30 m³/s. These springs discharge mainly through vertical and subvertical joint systems. Intensive superficial karstification developed along the joint systems and the terrane reveals columns of rocks, called fairy chimneys. Olukköprü springs represent the discharge point for a large and continuous system of underground solution cavities. In the Köprüçay basin, there are numerous karstic features within the conglomerates. Within the reservoir area, Kuruköprü cave, with a length of 530 m, is an example of these caves developed within the conglomerates. In some parts of the reservoir area, where the groundwater level is lower than the surface-river elevation, a highly developed karstification zone is present within the fluctuation range of groundwater between depths of 40 and 50 m. The above-mentioned Kuruköprü cave is an active cave developed in the dam site and its vicinity. The solution conduits developed along the system of mostly vertical fractures and joints are interconnected, thus giving rise to a three-dimensional conduit network. On the other hand, a majority of these conduits have clay and calcite filling materials. Karstification in the dam site varies with depth exponentially. Data suggest that karstification has a vertical extention as deep as –220 m.     

Late Cretaceous – Early Tertiary sedimentation and tectonic inversion in the southern Netherlands

Analysis of the Upper Cretaceous stratigraphy of the Peel Block reveals the basin development of the block to have been influenced by both the inversion of the Roer Valley Graben and Central Netherlands Basin, and the overall Late Cretaceous transgression. Sediments of Santonian to Danian age were deposited on the block. These sediments are compared with the detailed lithostratigraphy of southern Limburg, where Late Cretaceous strata are exposed. Four successions can be recognised in southern Limburg. The two oldest successions, the Santonian Oploo Formation (new name, proposed in the present contribution) and the mainly Early Campanian Vaals Formation, are restricted to the central and northern parts of the block. These siliciclastic formations were deposited under the influence of inversion of the Roer Valley Graben and the Central Netherlands Basin, as well as under the influence of a rising sea level. Towards the north, sands of the Oploo Formation grade into marls and chalks of the Ommelanden Formation. The two youngest successions comprise the largely Late Campanian to Maastrichtian Gulpen and Maastricht Formations and the Danian Houthem Formation. These chalk formations were deposited under the influence of regional subsidence during a sea-level highstand. Subsequent to deposition of the Houthem Formation, a regional regression triggered a change from shallow-marine carbonate to paralic siliciclastic deposition.     

Kaveri crater – An impact structure in the Precambrian terrain of southern India

The region to the east of Palghat gap is of low elevation and nearly circular in shape. It forms a part of the Kaveri river basin. The predominantly gneissic terrain is surrounded by the charnockitic hill ranges, prominent among which are Nilgiris and Biligirirangan to the north; and Anaimalai and Kodaikanal to the south. The charnockite massifs have a steep slope facing the circular feature and a gentler slope in the opposite direction. Fractures/faults/shear zones are noticed in many parts. The Bouguer anomaly in the gneissic terrain is elliptical in shape and positive, relative to the surrounding elevated region. The magnetic contours are also elliptical and the magnetic basement is deeper by about one km compared to regions in the periphery. The shallow seismic velocity picture from Chennimalai to Palani indicates a graben structure. The velocity structure also depicts a 4–5 km Moho upwarp near Chennimalai. Junction between the gneissic and charnockitic terrain and even beyond, is marked by the presence of pseudotachylites and breccia. Field and petrographic studies indicate presence of suevite, Planar Deformation Features (PDF), Planar Fractures, diaplectic glass of quartz and plagioclase and spherical inclusion in suevite. These evidences taken together point to an extra-terrestrial impact which created a crater of approximately 120 km in diameter. Several lines of indirect evidences point to Neoproterozoic age for the impact. Kaveri Crater is the fourth largest crater on the surface of the Earth; other larger craters being Vredefort (160 km), Chicxulub (150 km) and Sudbury (130 km).     

Early Tertiary deformation of the Zhongba–Gyangze Thrust in central southern Tibet

As the boundary thrust between India and Asia in southern Tibet, the Zhongba–Gyangze Thrust (ZGT) emplaced the Yarlung Zangbo Suture Zone (YZSZ) units in the hanging wall southward onto Tethyan Himalaya sequences (THS) of the northern Indian continental margin in the footwall. Detailed field investigation, electron backscatter diffraction (EBSD) analysis, detrital zircon U–Pb geochronology and ⁴⁰Ar–³⁹Ar thermochronology were conducted to understand the evolution of the ZGT in Sangsang area, central southern Tibet. The shear zone of ZGT is located within the sedimentary-matrix mélange of YZSZ that is mainly composed of matrix of blueschist with meta pelagic–hemipelagic siliceous and siliciclastic rocks and blocks of basalt, limestone and sandstone. Penetrative F1 foliation and kink band structure were recorded within the matrix both on outcrop and under microscope. Strong lattice preferred orientation (LPO) fabric initiated by the low-temperature (350−450 °C) (010)[001] slip system was detected by EBSD in the sodic amphiboles of the blueschist. The ⁴⁰Ar–³⁹Ar ages of the phengites from blueschist and sericites from the phyllite in the shear zone indicate that the activity of ZGT occurred between 71 and 60 Ma. In the THS, a newly documented younger unit preserving detrital zircons from the southern Asian margin lies above the Triassic–Cretaceous sequences that carries only detrital zircons from the Indian continent. This unit is dated to be ~ 61 Ma by the detrital zircon ages, similar to the Sangdanlin Formation and representing the Yarlung Zangbo Foreland Basin (YZFB) system. The ZGT had probably been active due to the initial India–Asia collision and acted as the frontal thrust controlling the development of YZFB.     

Synopsis of strontium isotope variations in groundwater at Äspö, southern Sweden

Strontium isotope ratios are used to identify end-member ground-water compositions at Äspö in southeastern Sweden where the Hard Rock Laboratory (HRL) has been constructed to evaluate the suitability of crystalline rock for the geologic disposal of nuclear waste. The Hard Rock Laboratory is a decline (tunnel) constructed in 1.8 Ga-old granitic rock that forms islands in an archipelago along the Swedish coast. Ground-water samples were obtained for isotopic analyses from boreholes drilled from the surface and from side boreholes drilled within the HRL. Infiltration at Äspö occurs primarily through fractures zones in the granitic bedrock beneath thin soils throughout the area. Because of extremely low Sr concentrations, rain and snow are not important contributors to the Sr isotope budget of the ground-water system. At shallow levels, water percolating downward along fractures and fracture zones acquires a δ⁸⁷Sr between +9.5 and +10.0‰ and maintains this value downward while Sr concentrations increase by two orders of magnitude. Ground-water samples from both boreholes and from in the HRL show the effects of mixing with saline waters containing as much as 59 mg/L Sr and δ⁸⁷Sr values as large as +13.9‰. Baltic Sea water is a potential component of the groundwater system with δ⁸⁷Sr values only slightly larger than modern marine values (+0.3‰) but with much lower concentrations (1.5 mg/L) than ocean water (8 mg/L). However, because of large Sr concentration differences between the saline groundwater (59 mg/L) and Baltic Sea water (1.5 mg/L), δ⁸⁷Sr values are not particularly sensitive indicators of sea-water intrusion even though their δ⁸⁷Sr values differ substantially.     

“Source-Diagenesis-Accumulation” enrichment and accumulation regularity of marine shale gas in southern China

After the breakthrough of shale gas exploration and development in the Ordovician Wufeng Formation (Fm.) and Silurian Longmaxi Fm. of Chongqing Jiaoshiba area, Changning-Weiyuan area, etc. in Sichuan basin, a series of discovery and breakthrough were obtained by China Geological Survey in the Cambrian Niutitang Fm. and Sinian Doushantuo Fm. shale of the areas with complicated structure outside Sichuan basin. Based on the understanding of the law of shale gas enrichment in Longmaxi Fm. in the basin, this paper puts forward three elements of the formation and enrichment of shale gas, which are the “Source”, the “Diagenesis” and the “Accumulation”, after deeply studying the law shale gas enrichment and accumulation in Sinian-Cambrian reservoir of the complex structure area outside the basin. The “Source” means the sedimentary environment and petrological characteristics of organic shale. The “Diagenesis” means the basin tectonic subsidence and hydrocarbon generation and expulsion process of organic matter. The “Accumulation” means the tectonic uplift and shale gas preservation. It is proposed that the Sinian-Cambrian and Ordovician-Silurian black shale series in the middle and upper Yangtze region of southern China were both formed in the deep-water shelf environment of rift trough and foreland basin respectively. The dessert intervals were formed in the strong reduction environment under transgressive system tract. The shale lithology belongs to calcium-siliceous and charcoal-siliceous respectively. Based on the summary of structural evolution in Yangtze area, the correlation of structural burial depth with shale diagenesis and the coupling evolution of organic matter with pore structure are discussed. Combining with structural styles, the preservation conditions of shale gas are discussed. Five types of shale gas reservoir control models are further described. Two types of future exploration directions, which are reverse fault syncline and paleo-uplift margin in complex structural area outside the basin, are proposed.     

Anatomy of a Cambrian suture in Gondwana: Pacific-type orogeny in southern India?

Southern India occupies a central position in the Late Neoproterozoic–Cambrian Gondwana supercontinent assembly. The Proterozoic mosaic of southern India comprises a collage of crustal blocks dissected by Late Neoproterozoic–Cambrian crust-scale shear/suture zones. Among these, the Palghat–Cauvery Suture Zone (PCSZ) has been identified as the trace of the Cambrian suture representing Mozambique Ocean closure during the final phase of amalgamation of the Gondwana supercontinent. Here we propose a model involving Pacific-type orogeny to explain the Neoproterozoic evolution of southern India and its final amalgamation within the Gondwana assembly. Our model envisages an early rifting stage which gave birth to the Mozambique Ocean, followed by the initiation of southward subduction of the oceanic plate beneath a thick tectosphere-bearing Archean Dharwar Craton. Slices of the ocean floor carrying dunite–pyroxenite–gabbro sequence intruded by mafic dykes representing a probable ophiolite suite and invaded by plagiogranite are exposed at Manamedu along the southern part the PCSZ. Evidence for the southward subduction and subsequent northward extrusion are preserved in the PCSZ where the orogenic core carries high-pressure and ultrahigh-temperature metamorphic assemblages with ages corresponding to the Cambrian collisional orogeny. Typical eclogites facies rocks with garnet + omphacite + quartz and diagnostic ultrahigh-temperature assemblages with sapphirine + quartz, spinel + quartz and high alumina orthopyroxene + sillimanite + quartz indicate extreme metamorphism during the subduction–collision process. Eclogites and UHT granulites in the orogenic core define P–T maxima of 1000 °C and up to 20 kbar. The close association of eclogites with ultramafic rocks having abyssal signatures together with linear belts of iron formation and metachert in several localities within the PCSZ probably represents subduction–accretion setting. Fragments of the mantle wedge were brought up through extrusion tectonics within the orogenic core, which now occur as suprasubduction zone/arc assemblages including chromitites, highly depleted dunites, and pyroxene bearing ultramafic assemblages around Salem. Extensive CO₂ metasomatism of the ultramafic units generated magnesite deposits such as those around Salem. High temperature ocean floor hydrothermal alteration is also indicated by the occurrence of diopsidite dykes with calcite veining. Thermal metamorphism from the top resulted in the dehydration of the passive margin sediments trapped beneath the orogenic core, releasing copious hydrous fluids which moved upward and caused widespread hydration, as commonly preserved in the Barrovian amphibolite facies units in the PCSZ. The crustal flower structure mapped from PCSZ supports the extrusion model, and the large scale north verging thrusts towards the north of the orogenic core may represent a fold-thrust belt. Towards the south of the PCSZ is the Madurai Block where evidence for extensive magmatism occurs, represented by a number of granitic plutons and igneous charnockite massifs of possible tonalite–trondhjemite–granodiorite (TTG) setting, with ages ranging from ca. 750–560 Ma suggesting a long-lived Neoproterozoic magmatic arc within a > 200 km wide belt. All these magmatic units were subsequently metamorphosed, when the Pacific-type orogeny switched over to collision-type in the Cambrian during the final phase of assembly of the Gondwana supercontinent. One of the most notable aspects is the occurrence of arc magmatic rocks together with high P/T rocks, representing the deeply eroded zone of subduction. The juxtaposition of these contrasting rock units may suggest the root of an evolved Andean-type margin, as in many arc environments the roots of the arc comprise ultramafic/mafic cumulates and the felsic rocks represent the core of the arc. The final phase of the orogeny witnessed the closure of an extensive ocean — the Mozambique Ocean — and the collisional assembly of continental fragments within the Gondwana supercontinent amalgam. The tectonic history of southern India represents a progressive sequence from Pacific-type to collision-type orogeny which finally gave rise to a Himalayan-type Cambrian orogen with characteristic magmatic, metasomatic and metamorphic factories operating in subduction–collision setting.