Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times

The Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin.     

The geodynamic evolution of the South-Tethyan,margin in Zanskar,NW-Himalaya,as revealed by the Spongtang ophiolitic melanges

Abstract

— The composite nappe of the Spongtang ophiolite is thrust over Mesozoic and Cenozoic sediments of the North-Indian margin and shelf. The ophiolitic peridotiles tectonic-ally overlie a sedimentary melange, the detailed stratigraphy of which reveals the evolution of the South-Tethyan margin from its opening to its closure. The matrix of the melange is dated as Upper Campanian to Lower Eocene. Volcano-sedimentary olistoliths indicate carbonate platform sedimentation associated with alkaline lavas in the Permian, followed by more pelagic sedimentation of Upper Triassic and mid- Cretaceous age. They derived from external platforms near to the Indian shelf, but separated from it. Composite olistoliths of mid to late Cretaceous age, containing Permian elements, are found in the upper Cretaceous to lower Eocene wildflysch. Primary contacts of melange upon serpentinites indicates that the deeply eroded oceanic crust served partly as a substratum for the melange.     

Stratigraphy of Upper Cretaceous and Cenozoic deposits of the Bakchar iron ore deposit (southwestern Siberia): New data

The results of complex palynological and microfaunistic studies of Upper Cretaceous and Cenozoic deposits of the Bakchar iron ore deposit are presented. Geochronologically, the age of the deposits varies from Campanian to Quaternary. It was established that the Slavgorod, Gan’kino, and Jurki (?) formations contain four biostratons in the rank of beds with dinocysts and three biostratons in the rank of beds with spores and pollen. The Cenozoic continental deposits contain four biostratons in the rank of beds, containing spores and pollen. As a result of the study, a large stratigraphic gap in the Cretaceous–Paleogene boundary deposits, covering a significant part of the Maastrichtian, Paleocene, Ypresian, and Lutetian stages of the Eocene, was established. The remnants of a new morphotype of heteromorphic ammonites of genus Baculites were first described in deposits of the Slavgorod Formation (preliminarily, upper Campanian). The distribution features of the different palynomorph groups in the Upper Cretaceous–Cenozoic deposits in the area of study due to transgressive-regressive cycles and climate fluctuations were revealed.     

Importance of active tectonics during karst formation. A Middle Eocene to Pleistocene example of the Lina Moutains (Irian Jaya,Indonesia)

Abstract

The Lina Moutains show a typical example of karst formation associated to recent and active tectonics. The limestone samples were collected from giant potholes present beneath the heavy rainforest, during speleological expeditions to the Bird’s Head of Irian-Jaya. Micropalaeontological data allow us to give a Middle Pleistocene age for the most recent karst formation. A detailed stratigraphy between the Upper Lutetian and the Middle Pleistocene was recorded, with tectonic events during the Oligocene and Pleistocene. The edge of the resurgence layer was also dated. We also conclude the probable existence of a subterraneous network downhill of the karst within the most recent levels of the Kais Limestone formation. We replace this formation within the tectonic evolution of this area between the Eocene and the Middle Pleistocene, in conjunction with the oblique convergence of the Pacific plate carrying volcanic arc fragments and the Australian margin, which resulted in folding, normal faulting associated with local extension, and wrench motion, which are settings capable of creating uplift of the carbonated platform. © Elsevier, Paris     

Polyphase wrench tectonics in the southern french Massif Central: kinematic inferences from pre- and syntectonic granitoids

In the Variscan French Massif Central, the South Limousin area consists of low- to medium-grade metamorphic rocks intruded by two granitic bodies. The structural and textural analyses of these plutons undertaken in parallel with the structural analysis of their host rocks allow us to characterize and to date different stages in the tectonic evolution of this area. This study shows that the South Limousin area experienced successivelly two strike-slip events along two geographically distinct shear zones, from north to south the left-lateral Estivaux and the right-lateral South Limousin strike-slip faults, respectively. These ductile faults subdivide the South Limousin into three structural units, from north to south they are the Upper Gneiss unit, Thiviers-Payzac unit .and Génis unit. The two granitic bodies intrude the Thiviers-Payzac unit only. The younger Estivaux granite is a syntectonic pluton which emplaced during left-lateral wrenching. ⁴⁰Ar/³⁹Ar dates from biotites indicate an Early Carboniferous age (346 ± 3 Ma). The older granite is a pretectonic body. It is the Ordovician Saut du Saumon augen orthogneiss in which detailed structural analyses show the polyphase nature of the solid-state deformation. Our microtectonic data indicate that the right-lateral motions overprint the left-lateral ones and produce apparently symmetrical fabrics.     

The Devonian units of the Marimanya massif and their relationship with the Pyrenean Devonian facies areas

Abstract

The metasedimentary materials of the Marimanya Massif are chiefly made up of Devonian deposits, classically attributed to the Cambro-Ordovician. Their stratigraphic succession has been reconstructed from geological mapping, structural analysis and the study of the limestone conodont content, and subsequently divided into four Devonian units.

The lower part consists of the Moredo-Salau carbonatic unit (braided alternation, crinoidal carbonates, parallel alternation and Campaus limestones). Its age ranges from the Upper Silurian to Lower Emsian. This unit is overlain by lutites with limestone and fine sandstone intercalations from the Beret series (Lower Emsian-Lower Frasnian).

The two units are correlated in the east with the Salau carbonate series and the “Shales Bleutes”, and in the Vielha synclinal with the “Calcaire Basal” and the Entecada, Auba, Sa Fusta and Mont Corbisum units.

The Upper part of the succession is formed by the Montgarri and Can Cabau Detrital units, which are lithologically correlated with the Sa Cal and Riu Nere units in the Vall d’Aran and, in the west, with the Agudes-Cap de Pales and Sia series.

Thus the Devonian Central facies area stretches eastwards to the Pyrenees ariégeoises and westwards to the Vielha syncline, Les Agudes, Sia, Sagette and Laruns.

The new biostratigraphic succession established in the Marimanya Massif represents, to date, the most complete within the Central facies area. The new data obtained enable the correlation between the Devonian units in this facies area with the units in the remaining Devonian facies area in the Pyrenees.     

Cenozoic tectonics and landform evolution in the Qilian Mountains and adjacent areas

ABSTRACT

The formation of the Qilian mountains and the evolution of adjacent basins were controlled by the uplift and northeastward growth of the Tibetan Plateau. In a field survey conducted on the main Cenozoic basin sediments in the Qilian Mountains and adjacent areas, fission track age data of apatite obtained previously were analyzed. Cenozoic tectonics and landform evolution in the area where the Qilian Mountains now stand and its response to the uplift of the Tibetan Plateau were studied. In the Oligocene Epoch, the Tibetan Plateau was initially uplifted and extended northeastward, forming the Guide-Xining-Lanzhou-Linxia foreland basin on the northern margin of the western Qinling Mountains, and the foreland basin in the area where the Qilian Mountains now stand received widespread sediments. In the Miocene, influenced by the enhanced uplift and northeastward thrust of the Tibetan Plateau, a stage of intracontinental squeezing orogeny and foreland basin splitting began in the area where the Qilian Mountains now stand. In the Pliocene Epoch, the Qilian Mountains were continuously uplifted, the basins shrank, large lake basins disappeared gradually, and large-area red-clay-type aeolian sediments appeared. During the Quaternary Period, the uplift of the Tibetan Plateau accelerated, causing a rapid rise in the altitude of the Qilian Mountains. Global climate change occurred and mountain glaciers began to develop. Quaternary moraine deposits appeared for the first time in the area, and very thick loess sediments appeared in the Longzhong area, east of the area where the Qilian Mountains now stand, forming the famous Loess Plateau.     

Jurassic and Cretaceous (Yanshannian) tectonics,magmatism and metallogenesis in South China: preface

ABSTRACT

South China is famous for its poly-metal deposits, with more than 50% of global W and Sb reserves, 20% of global Sn reserves, as well as abundant Cu-Mo-Pb-Zn-Au-Ag, Ta, Nb, REE and U deposits. This special issue consists of 21 papers, reporting recent progress on Yanshannian tectonic evolution, magmatism and ore deposits in South China, aiming at better understandings on the Mesozoic large-scale magmatism and mineralization events.     

Evolution of the Academician Ridge Accommodation Zone in the central part of the Baikal Rift, from high-resolution reflection seismic profiling and geological field investigations

 New high-resolution seismic reflection data from the central part of Lake Baikal provide new insight into the structure and stratigraphy of Academician Ridge, a large intra-rift accommodation zone separating the Central and North Baikal basins. Four seismic packages are distinguished above the basement: a thin top-of-basement unit; seismic-stratigraphic unit X; seismic-stratigraphic unit A; and seismic-stratigraphic unit B. Units A and B were cored on selected key locations. The four packages are correlated with a series of deposits exposed on the nearby western shores: the Ularyar Sequence (Oligocene); the Tagay Sequence (Lower to Middle Miocene); the Sasa Sequence (Upper Miocene to Lower Pliocene); the Kharantsy Sequence (Upper Pliocene); and the Nyurga Sequence (Lower Pleistocene). Based on stratal relationships, sedimentary geometries, distribution patterns and principal morphostructural elements – both onshore and offshore – we propose a new palaeogeographic evolution model for the area. In this model progressive tectonic subsidence of the Baikal basins and successive pulses of uplift of various segments of the rift margins lead to: (a) formation of the ridge as a structural and morphological feature separating the Central and North Baikal basins during the Middle to Late Miocene; (b) gradual flooding of the main parts of the ridge and establishment of a lacustrine connection between the two rift basins during the Late Miocene; and (c) total submergence of the top parts of the crest of the ridge during the latest Pleistocene. This new model helps to better constrain numerous phases in the structural evolution of the Baikal Rift, in which the Academician Ridge as an accommodation zone plays a crucial role. Received: 26 November 1999 / Accepted: 12 March 2000     

The Byers Basin: Jurassic-Cretaceous tectonic and depositional evolution of the forearc deposits of the South Shetland Islands and its implications for the northern Antarctic Peninsula

ABSTRACT

This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as ⁴⁰Ar/³⁹Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin.     

Thrust tectonics and paleogene syntectonic sedimentation in the Empordà area,southeastern Pyrenees

Abstract

The structure of the southern Pyrenees, east of the Albanyà fault (Empordà area), consists of several Alpine thrust sheets. From bottom upwards three main structural units can be distinguished : the Roc de Frausa, the Biure-Bac Grillera and the Figueres units. The former involves basement and Paleogene cover rocks. This unit is deformed by E-W trending kilometric-scale folds, its north dipping floor thrust represents the sole thrust in this area. The middle unit is formed by an incomplete Mesozoic succession overlain by Garumnian and Eocene sediments. Mesozoic rocks internal structure consists of an imbricate stack. The floor thrust dips to the south and climbs up section southwards. The upper unit exibits the most complete Mesozoic sequence. Its floor thrust is subhorizontal. The lower and middle units thrust in a piggy-back sequence. The upper unit was emplaced out of sequence.

Lower Eocene sedimentation in the Biure-Bac Grillera unit was controlled by emergent imbricate thrusts and synchronic extensional faults. One of these faults (La Salut fault) represents the boundary between a platform domain in the footwall and a subsident trough in the hangingwall. Southward thrust propagation produces the inversion of these faults and the development of cleavage-related folds in their hangingwalls (buttressing effect). This inversion is also recorded by syntectonic deposits, which have been grouped in four depositional sequences. The lower sequences represent the filling on the hangingwall trough and the upper sequences the spreading of clastics to the south once the extensional movement ends.     

The Alpine evolution of the Southern Alps around the Giudicarie faults: A Late Cretaceous to Early Eocene transfer zone

Data supporting relevant Late Cretaceous–Early Eocene sinistral displacement along the Giudicarie fault zone and a minor Neogene dextral displacement along the Periadriatic lineament are discussed. The pre-Adamello structural belt is present only in the internal Lombardy zone, located W of the Adamello massif. This belt is unknown in the Dolomites and surrounding areas located to the E of the Giudicarie lineament. Upper Cretaceous–Early Eocene thick syntectonic Flysch deposits of Lombardy and Giudicarie are well preserved along the southern and eastern border of the pre-Adamello belt (S-vergent Alpine orogen). Towards the E, in the Dolomites and in the Carnic Alps and external Dinarides, only incomplete remnants of Flysch deposits, Aptian–Albian and Turonian–Maastrichtian in age, are present. They can be considered as equivalent to those of Lombardy and Giudicarie formerly in connection to each other along the N-Giudicarie corridor. To the S, the syntectonic Flysch deposits are laterally replaced by the calcareous red pelagites of the Scaglia Rossa and by the carbonate shelf deposits of the Friuli (to the E) and Bagnolo (to the S) carbonate platforms. The different location in the southern structural accretion of the eastern and western opposite blocks (the Dolomites versus the pre-Adamello belt) can be related to the Cretaceous–Eocene convergence. In this frame, the N-Giudicarie fault has been considered as part of a former transfer zone, which produced the sinistral lateral displacement of the Southern Alps front for an amount of some 50 km. During the Late Eocene to Early Oligocene the transfer zone was mostly sealed by the Paleogene Adamello batholith. Oligocene to Neogene compressional evolution inverted the N-Giudicarie fault into a backthrust of the Austroalpine units over the South-Alpine chain.     

On the role of the Hercynian and Alpine thrusts in the Upper Paleozoic rocks of the Central and Eastern Pyrenees

Abstract

The structure of the Pyrenean pre-Hercynian rocks involved in the “Axial Zone” antiformal stack, results from the association of Hercynian cleavage-related folds and Hercynian and Alpine thrusts. Some of these Alpine and Hercynian thrusts separate thrust sheets in which Upper Paleozoic rocks, Devonian and pre-Hercynian Carboniferous, exhibit different lithostratigraphy and internal structure.

In order to know both, the original Devonian facies distribution and the structural characteristics, the effects of the Alpine and the Hercynian thrusts must be considered. If a conceptual restored cross-section is constructed taking into account both the Alpine and Hercynian thrusts, a different Devonian facies distribution is achieved. Devonian carbonatic successions were originally located in a northernmost position, whereas sequences made by alternations of slates and limestones lie in southernmost areas. Moreover, a N-S variation of the Hercynian structural style appears. In the northern units thrusts are synchronous to folding development and they are the most conspicuous structures. In the intermediate units, thrust postdate cleavage-related folds, and in the southernmost units several folding episodes, previous to the thrusts, are well developed.

We present some examples which enable us to discuss the importance of the Hercynian and Alpine thrusts in the reconstruction of the Pyrenean pre-Alpine geology.     

Petrology and provenance of the Toro Negro Formation (Neogene) of the Vinchina broken-foreland basin (Central Andes of Argentina)

Detrital modes of sandstones and conglomerates of the Toro Negro Formation (Late Miocene-early Pliocene) were used to analyze the evolution of the broken-foreland stage of the Vinchina Basin (28°30′–29°00′ S and 68°30′–68°20′ W) of NW Argentina. This basin located in the Western Sierras Pampeanas is bounded to the west by the Precordillera and to the east by the Famatina System. Three sandstone petrofacies: plutonic-metamorphic, volcanic and mixed petrofacies and three conglomerate lithic associations: basement, sedimentary and volcanic lithic associations were recognized, allowing to establish three source areas: Western Sierras Pampeanas (Toro Negro and Umango Ranges), Cordillera Frontal and Precordillera.During the Late Miocene, the Toro Negro Range (to the north) together with the Cordillera Frontal and Precordillera (to the west) were the main sources for depositional sequences I and II (lower member of the Toro Negro Formation). On the contrary, during the latest Miocene-early Pliocene, Depositional Sequence III (upper member) exhibited a progressive increase in the supply from the eastern Precordillera (to the west) with additional material from the Umango Range to the south. Besides, evidence of synchronic volcanism is recorded in the upper part of Depositional Sequence II and the lower part of Depositional Sequence III.The coexistence of the three source areas and the changing distribution patterns due to re-accommodation of sediment dispersal routes demonstrate that the evolution of this type of basin is much more complex than previously envisaged. Therefore, an integrated analysis using different tools (sedimentary facies, paleocurrent measurements, sandstone petrography and conglomerate composition) is needed for a clearer understanding of broken-foreland basins.     

Réflexions sur la « révolution danienne » dans les Pyrénées

This work disproves the magmatic (ophitic rises) and sedimentological (submarine trans-Pyrenean trough filled with breccias and hemipelagites) arguments presented in favour of a Danian distension step following a major Upper to Late Cretaceous Pyrenean compression phase. In the western Pyrenees (Bearn area) the tholeiitic magmatism is really Triassic or Lowermost Liassic in age. The ophites cross mechanically the Jurassic and Cretaceous enclosing sedimentary beds without any contact metamorphism, which could give proof of a Palaeocene age for the magmatic emplacement. As for the supposed submarine breccias rich in planktonic foraminifera, they really correspond to diapiric Early Cretaceous breccias, to Cretaceous or Tertiary tectono-karstic breccias or to Quaternary colluvial deposits. The Danian/Selandian trough does not exist. The proposed interpretation assigns that the Palaeocene interval must be included within the long compression (transpression) period, which begins in the Upper Cretaceous times and increases during the Early Cenozoic, leading to the main structural step of the Pyrenean cycle, towards the Middle–Upper Eocene. To cite this article: J. Canérot, C. R. Geoscience 338 (2006).     

The Tanlu Fault Zone and Gold Ore Metallogenesis in Eastern China

The Tanlu Fault Zone (TFZ) is a large NE-trending fault system in eastern China that is the locus of several significant gold deposits. At different periods of its evolution and in different zones along its length, the TFZ has distinct geological features that control gold mineralization. In the northeastern part of the TFZ, early-stage faulting activity (from the Jurassic to Cretaceous) is associated with abundant calc-alkaline volcanic rocks, reflecting the compressive structural setting in the Jurassic and Cretaceous. However, activities in the late stage (Cenozoic) produced alkali basalts, indicating a mainly extensional tectonic regime. In the middle and southern segments of the TFZ, early-stage (Jurassic) activity was characterized by calc-alkalic granite intrusions, followed later (Cretaceous) by partial alkalic and alkalic volcanic-intrusive complexes, and in the latest stage (Cenozoic) by alkalic volcanic eruptions.

The TFZ system controls the distribution of gold metallogenic provinces in eastern China, and periods of mineralization of gold ore deposits coincide with the major stages of faulting. Gold ore deposits in eastern China are products of the evolution of the TFZ. During the early evolution of the TFZ, gold ore deposits related to calc-alkalic granite intrusions were formed—e.g., of the quartz-vein and altered-rock types. Gold deposits of the interlayer–sliding fault breccia type were formed along the margin of the extensional basin during the middle period of TFZ evolution. Finally, epithermal gold deposits related to alkalic magmatism were formed during the latest stage of TFZ evolution.     

Paleogene tectono-sedimentary evolution of the Alicante Trough (External Betic Zone,SE Spain) and its bearing on the timing of the deformation of the South-Iberian Margin

The Paleogene Alicante Trough of the South-Iberian Margin (External Betic Zone) consists of a narrow sedimentary basin that has active margins located to the north-northwest (active mainly during the Eocene) and to the south-southeast (active during the Oligocene). Both margins, consisting of shallow unstable platforms, were the source areas for the external-platform slope (in the opposite margins) and deepbasin (in the middle) depositional realms. The southern margin, lost under the Mediterranean Sea, is recognized only by the reconstructed Oligocene slope sediments.

The eight successions studied, on opposites external-platform-slope margins and the deep within the central part of the basin, lead us to divide the basin into two depositional realms: the subsident Western Depositional Area (WDA) and the not subsident Eastern Depositional Area (EDA). This study has also enabled us to divide the infilling of the basin into two depositional sequences: Eocene p.p. (EDS) and Oligocene p.p. (ODS) in age, respectively, bound by two sequence boundaries (unconformities) at the Early Eocene (P6 zone) and Early Oligocene (P19 zone). The EDS and ODS are comprised of turbiditic and olisthostromic deposits and frequently slumps, evidencing an active tectonic in the margin-basin system.

The correlation of the Paleogene sedimentary reconstructed in the Alicante Trough with other four synthetic successions throughout the External (three in the Subbetic Domain) and one in the Internal Betic Zone indicate a Paleogene generalised deformational framework. In addition, this evolution is contemporaneous to the Pyrenean, Iberian and the Nevado-Filabride Alpine deformation. The Paleogene tectonic recognised in the External Betic Zone is younger since the main orogenic deformation took place in the late Burdigalian to early Tortonian. The origin of these early tectonics is discussed in relation to the Nevado-Filabride Alpine deformation.     

Sedimentological characteristics and new detrital zircon SHRIMP U–Pb ages of the Babulu Formation in the Fohorem area,Timor-Leste

Sedimentological characteristics and zircon provenance dating of the Babulu Formation in the Fohorem area, Timor-Leste, provide new insights into depositional process, detailed sedimentary environment and the distribution of source rocks in the provenance. Detrital zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages range from Neoarchean to Triassic, with the main age pulses being Paleozoic to Triassic. In addition, the maximum deposition ages based on the youngest major age peak (ca 256–238 Ma) of zircon grains indicate that the basal sedimentation of the Babulu Formation occurred after the early Upper Triassic. The formation consists predominantly of mudstone with minor sandstone, limestone and conglomerate that were deposited in a deep marine environment. These deposits are composed of six lithofacies that can be grouped into three facies associations (FAs) based on the constituent lithofacies and bedding features: basin plain deposits (FA I), distal fringe lobe deposits (FA II) and medial to distal lobe deposits (FA III). The predominance of mudstone (FA I) together with intervening thin-bedded sandstones (FA II) suggest that the paleodepositional environment was a low energy setting with slightly basin-ward input of the distal part of the depositional lobes. Discrete and abrupt occurrences of thick-bedded sandstone (FA III) within the FA I mudstone suggests that sandstone originated from a collapse of upslope sediments rather than a progressive progradation of deltaic turbidites. This combined petrological and geochronological study demonstrates that the Babulu Formation in the Fohorem area of the Timor-Leste was initiated as a submarine lobe system in a relatively deep marine environment during the Upper Triassic and represents the extension of the Gondwana Sequence at the Australian margin.     

新疆东天山康古尔金矿控矿构造特征

作者通过构造控矿分析发现,康古尔金矿是受一韧性挤压带控制的中低温岩浆-变质热液型金矿床。成矿作用与控矿韧性挤压带从韧性向脆、韧性变形演化密切相关。本文具体分析了控矿构造类型和构造演化对矿化的控制程序以及矿体定位机制,建立了构造成矿模式指出了找矿方向。