Clastic Sequence Research Articles

The heart of China revisited, I. Proterozoic tectonics of the Qin mountains in the core of supercontinent Rodinia

The Qinling‐Dabie orogenic collage, central China, constitutes the geographic, geologic, and cultural heart of China; it plays a key role in understanding the amalgamation and breakup of the Rodinia supercontinent and the subduction and exhumation of continental crust under ultrahigh‐pressure conditions. Herein, we investigate the Proterozoic evolution of the Qinling‐Dabie orogenic collage and surrounding segments of the bounding South China craton (SCC) and North China craton (NCC), employing published and new U/Th–Pb geochronology. The Kongling, Hong'an‐Dabie, and Douling‐Foping complexes constitute the nucleus of the Yangtze block, recording a common ~2.0 Ga orogenic event that integrated the Yangtze block into the supercontinent Columbia. The ~1.10–0.95 Ga Miaowan “ophiolite”‐Shennongjia arc association of the Huangling dome‐Shennongjia massif seems to have split and reassembled that nucleus. It formed earlier than or contemporaneously with the Sibao orogeny along the southeastern margin of the Yangtze block. The ~0.95–0.80 Ga Mian‐Lue complex comprises an oceanic accretionary wedge that formed outboard of an associated fore‐arc‐arc system represented by the Bikou‐Hannan‐Micangshan massifs along the north(western) margin of the Yangtze block. The Qinling complex, currently sandwiched between the SCC and NCC, lacks pre‐Mesoproterozoic cratonal basement, and its igneous rocks intruded a ~1.7–1.0 Ga old clastic wedge that incorporates meta‐basites; it might have been part of the extended passive margin of East Antarctica and/or Australia. Neoproterozoic Qinling‐complex magmatism spanned ~260 Myr and evolved from partial melting of the thick clastic sequence over an arc to a rift setting; most Qinling‐complex paragneisses are erosional products of these igneous rocks. The ~1.0–0.85 Ga Qinling‐complex magmatism formed independently from that along the north(west)ern Yangtze‐block margin, but its ~0.8–0.7 Ga magmatism, peaking at ~750 Ma, is widespread throughout the Yangtze block; this suggests post‐ ~ 825 Ma accretion of the Qinling complex to the Yangtze block. The Daba and Wudang Shan, Douling, and Hong'an‐Dabie areas of the northern Yangtze block are dominated by ~0.8–0.6 Ga bimodal continental‐rift igneous rocks; in accordance with similar ages in the Qinling complex and the entire SCC, continental rifting appears to have been most active at ~750 Ma. Our Rodinia scenario suggests that the Qinling‐Dabie orogenic collage records the final stages of the assemblage of the core of Rodinia, and this was completed not earlier than ~825 Ma, and its breakup, which was most active at ~750 Ma.

Earliest Cretaceous Pacificward offset of the Klamath Mountains salient, NW California–SW Oregon

Although Late Triassic igneous rocks are present, the Sierra Nevada–Klamath calc-alkaline arc began massive construction along the continental margin at ca. 170 Ma during oblique underflow of paleo-Pacific oceanic lithosphere; intense activity continued throughout the volcanic-plutonic belt until at least ca. 140 Ma. This volcanic-plutonic arc supplied detritus to the Mariposa-Galice proximal clastic sequence starting by ca. 165–160 Ma. After onset of uppermost Jurassic Myrtle overlap sedimentation on the western flank of the Klamath Mountains, but before Hornbrook and Valanginian Great Valley Group overlap deposition on the eastern and southeastern sides, the Klamath Mountains salient was displaced ∼200 km westward relative to the igneous arc. The orogen thus moved off the deep-seated magmagenic zone underlying the arc and did not participate in the massive Sierra Nevada igneous flare-up between ca. 125 and ca. 85 Ma. I suggest that, beginning at ca. 140 Ma, underflow of a young, thin oceanic slab beneath the Klamath Mountains slid beneath the gently east-dipping stack of thrust sheets without disturbing their inclinations. Subduction and collision of much thicker oceanic lithosphere on both the north and south caused contraction, eastward relative displacement of the continental margin arc, and ductility-enhanced rotation of the superjacent stack of allochthons into near-vertical dips. After a magmatic lull, heightened igneous activity in the Sierra Nevada recommenced at ca. 125 Ma. The earliest Cretaceous oceanward plate junction rollback lay directly offshore the Klamath imbricate orogen, but to the south trapped the ca. 165 Ma Coast Range ophiolite on the North American side of the suture. After ca. 140 Ma, first-cycle arc detritus began to accumulate on the mafic igneous basement flooring the Great Valley forearc, and turbiditic clastic material also was carried oceanward across the forearc into the coeval Franciscan trench.

Separating human and climatic impacts on Mediterranean forests: a combined dynamic modeling/palynological approach

In the present study, we investigate the Mediterranean–Paratethys connection during the late Miocene in Strymon Basin (North Aegean, northeastern Mediterranean) and compare this onshore sequence with the adjacent offshore Prinos-Nestos sequence, before, during, and after the Messinian Salinity Crisis (MSC). Strymon Basin was a peripheral shallow-water basin during the first MSC stage. The Akropotamos sections expose a clastic sequence with gypsum intercalations, which is dated in the Messinian based on the ostracod and calcareous nannofossil assemblages. This sequence records the Primary Lower Gypsum deposition in a shallow marine environment and its passage via the Messinian erosional surface to a brackish environment with changing salinity conditions similar to the Paratethyan depositional environments. The sequence is capped by a travertine marker horizon observed across the entire Strymon Basin indicating freshwater environment. The Miocene–Pliocene transition is characterized by salinity changes caused by the interaction between Atlantic-Mediterranean and Paratethyan waters, predating the marine reflooding at the end of the MSC, which is attested by the overlying Pliocene open marine deposits. The offshore Prinos-Nestos basin incorporates the Nestos intermediate basin and the Prinos intermediate-deep basin. Borehole and seismic profile data from the offshore Prinos-Nestos oil field reflect a thick clastic sequence, topped by turbidites, and followed by an evaporitic unit deposited during the Messinian. In the Nestos slope area, the evaporite unit consists of anhydrite-shale alternations. Toward the basin's depocenter (Prinos Basin), anhydrite is replaced by halite. The sequence is overlain by Pliocene–Holocene deltaic prograding deposits. Sedimentologic and biostratigraphic data show that the thick halite-shale couplets in the deepest part of the offshore Prinos-Nestos Basin were deposited under permanent marine conditions, suggesting no desiccation before, during, and after the MSC. Conclusively, the present results indicate that a connection between the Mediterranean and the Paratethys was occasionally established before the Pliocene reflooding and favor the non-desiccation MSC model for the deep marine evaporite deposition.

Soil-gas survey of liquefaction and collapsed caves during the Emilia seismic sequence

<p>The epicentral area of the Emilia seismic sequence is located in the Emilia-Romagna Region (northern Italy), 45 km from the city of Modena (Figure 1). This area is sited within thrust-related folds of the Ferrara Arc, which represent the most external part of the northern Apennines. This sector is considered as having been active during late Pliocene to early Pleistocene times [Scrocca et al. 2007] and encompasses also the Mirandola and Ferrara seismogenic sources [e.g., Burrato et al. 2003, Boccaletti et al. 2004, Basili et al. 2008]. The main sedimentary infilling of the Po Plain is represented by Pliocene–Pleistocene alluvial deposits (alternating fluvial sands and clays) that overlie a foredeep clastic sequence, with a total average thickness of 2 km to 4 km [e.g., Carminati et al. 2010]. Soon after the mainshock, several liquefaction phenomena coupled to ground fractures were observed in the epicentral area (e.g., San Carlo, Ferrara). Soil liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. […] Collapsed caves reported in the literature and/or local press [e.g., Febo 1999, Martelli 2002] in the epicentral area were previously investigated by our research group in 2008, with several soil measurements of CO2 and CH4 fluxes. Immediately after the May 20, 2012, mainshock and during the Emilia seismic sequence, the collapsed caves were sampled again to determine any variations in these CO2 and CH4 fluxes. In this survey, newly formed collapsed caves were also found and measured (especially in the northern part of investigated area). […]</p>

Stratigraphic and palaeoenvironmental framework of the Early Permian sequence in the Salt Range, Pakistan

The Early Permian Gondwana regime succession of the Nilawahan Group is exposed only in the Salt Range of Pakistan. After a prolonged episode of non-deposition that spanned much of the Palaeozoic, the 350 m thick predominantly clastic sequence of the Nilawahan Group records a late glacial and post-glacial episode in which a range of glacio-fluvial, marine and fluvial environments evolved and accumulated. The Early Permian succession of the Salt Range has been classified into four formations, which together indicates a changing climatic regime during the Early Permian in the Salt Range region. The lower-most, Tobra Formation unconformably overlies a Cambrian sequence and is composed of tillite, diamictite and fresh water facies, which contain a floral assemblage (Gangamopteris and Glossopteris) that confirms an Asselian age. The Tobra Formation is overlain by marginal marine deposits of the Dandot Formation (Sakmarian), which contain an abundant brachiopods assemblage (Eurydesma and Conularia). Accumulation of the Dandot Formation was terminated by a regional sea-level fall and a change to the deposition of the fluvial deposits of the Warchha Sandstone (Artinskian). The Warchha Sandstone was deposited by high sinuosity meandering, avulsion prone river with well developed floodplains. This episode of fluvial sedimentation was terminated by a widespread marine transgression, as represented by the abrupt upward transition to the overlying shallow marine Sardhai Formation (Kungurian). The Early Permian Gondwana sequence represented by the Nilawahan Group is capped by predominantly shallow shelf carbonate deposits of the Tethyan realm. The sedimentologic and stratigraphic relationship of these four lithostratigraphic units in the Salt Range reveals a complex stratigraphic history for the Early Permian, which is mainly controlled by eustatic sea-level change due to climatic variation associated with climatic amelioration at the end of the major Gondwana glacial episode, and the gradual regional northward drift to a lower latitude of the Indian plate.

From arc-continent collision to continuous convergence, clues from Paleogene conglomerates along the southern Caribbean–South America plate boundary

A Paleogene conglomeratic-sandy succession preserves the complex record of arc-continent collision, orogen collapse and basin opening, followed by inversion related to renewed oblique convergence. This record is unique because both arc and continental margin are now severely fragmented and only partially exposed along the southern Caribbean–South American boundary in northern Colombia. We studied these clastic sequences in the San Jacinto deformed belt using an integrated provenance study that includes conglomerate clast counting, geochemistry and U–Pb and Hf isotopic analysis in magmatic clasts, together with sandstone petrography, heavy mineral analysis and detrital zircon U–Pb geochronology. The record of events extracted from these coarse clastic rocks includes the formation and approach of an allochthonous Upper Cretaceous intra-oceanic arc active from 88Ma until 73Ma. This arc collides against the upper Paleozoic to Triassic continental margin after 73Ma, but before late Paleocene times. Poorly exposed remnants of serpentinized peridotites and middle pressure metamorphic detritus are related to closure of an intervening oceanic basin between the continent and the colliding arc. This orogen was emerged in late Maastrichtian–early Paleocene, and then collapsed as recorded by the thick upper Paleocene and younger succession of the San Jacinto deformed belt where the coarse clastics, subject of this study, are exposed.Orogenic collapse may have been the result of subduction zone flip, with incipient subduction of the buoyant Caribbean Plate under South America.

Siliciclastic Ordovician to Silurian units of the Argentine Precordillera: Constraints on provenance and tectonic setting in the proto-Andean margin of Gondwana

Abstract A combination of petrography, geochemistry, Sm–Nd, Pb–Pb and U–Pb detrital zircon dating provide constraints to the provenance of Middle Ordovician to Early Silurian clastic sequences of the Precordillera s.s. as a part of the Cuyania terrane in western-central Argentina. The uniformity shown by the provenance proxies indicate that there were no important changes in the provenance within these units. A dominant upper crustal component is evident as well as a subordinate mafic input. Nd isotopes indicate e Nd of −5.4, ƒ Sm/Nd −0.34 and T DM 1.57 Ga in average for all the units studied. Pb-isotope ratios display average values for 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb of 19.37, 15.86 and 39.43 respectively. Detrital zircon dating further constraints the input as being dominantly of Mesoproterozoic age (51–83%), but with contributions from Neoproterozoic–Lower Cambrian (9–31%), Middle Cambrian to Ordovician grains (recorded up to 7%), and Palaeoproterozoic (2–7%) sources. The combination of the different provenance approaches applied indicates that the Mesoproterozoic Cuyania terrane basement, and partially the Pampia terrane were the main sources. The new information provided for the Ordovician to Silurian clastic sequences permitted enhanced the known geochemical and isotopic dataset to constrain the tectonic evolution of the Cuyania terrane. The interpretation of the obtained data supports that the terrane accretion to the proto-Andean margin of Gondwana probably occurred during Middle to early Upper Ordovician.

Whole-rock geochemistry and Sr–Nd isotopic composition of the pre-rift sequence of the Camamu Basin, northeastern Brazil

Abstract Whole-rock geochemistry, combined with Sr–Nd isotopic composition of pelitic sedimentary rocks, have been considered to be useful parameters to estimate not only their provenance but also to make inferences about their depositional environment as well as the weathering processes they have been through. The basal sedimentary units of the basins of the northeastern Brazilian continental margin, particularly those of the pre-rift sequence, have been subject of interest of studies based on chemical and isotopic data, since they lack fossil content to establish their age and, therefore, stratigraphic correlations are difficult. The major and trace element contents as well as Sr–Nd isotopic compositions of whole-rock shale samples from five outcrops attributed to the pre-rift supersequence of the Camamu Basin were analyzed with the purpose of characterizing and obtaining further information that would allow a better correlation between the sites studied. The geochemical data suggest that the rocks exposed in the studied outcrops are part of the same sedimentary unit and that they might be correlated to the Capianga Member of the Alianca Formation of the Reconcavo Basin, exposed to the north of the Camamu Basin. The chemical index of alteration (CIA) suggests conditions associated with a humid tropical/subtropical climate at the time of deposition. Nd isotopic compositions indicate provenance from the Paleoproterozoic rocks of the Sao Francisco craton. The results presented here, therefore, show that the combined use of chemical and isotopic analyses may be of great interest to characterize and correlate lithologically homogeneous clastic sedimentary sequences.

Exploration for Cretaceous stratigraphic traps in the Gulf of Guinea, West Africa and the discovery of the Jubilee Field: a play opening discovery in the Tano Basin, Offshore Ghana

Abstract The discovery of the Jubilee Oil Field in 2007 in the Tano Basin of Ghana is a primary example of the potential for Late Cretaceous deep-water stratigraphic traps in basins previously overlooked by the exploration industry. The Tano Basin forms the eastern extension of the Deep Ivorian Basin, which resulted from Aptian–Albian trans-tension associated with the opening of the Atlantic between the St Paul and Romanche fracture zones and the subsequent post-rift subsidence. The basin was the focus for deposition of a thick Upper Cretaceous, deep-water clastic sequence, which, in combination with a modest Tertiary section, provided sufficient thickness to mature a Cretaceous source rock in the central part of the Tano Basin. This well-defined reservoir and charge fairway forms the play, which, when draped over a large plunging nose (the South Tano high), resulted in the formation of a stratigraphic–structural combination trapping geometry that is characteristic of the Jubilee Field and subsequent discoveries in this play.

High-resolution ultrasonic measurements as proxies to resolve clastic reservoir heterogeneity in a salt-cemented gas reservoir

Petrophysical properties and their heterogeneity within sandstone bodies are key parameters in the evaluation of hydrocarbon and geothermal reservoirs. However, common tools applied to constrain the porosity distribution pattern in borehole cores are commonly time consuming and destructive, or suffer from a resolution limited to the meter to decimeter scale. We examine the applicability of nondestructive high-resolution sonic (HRS) logging of well core sections in the ultrasonic frequency range as a method providing porosity proxy data at the centimeter scale in a clastic sedimentary sequence. The middle Solling Sandstone Member, a gas-bearing reservoir offshore from the Netherlands, is used as a test sample. It consists almost entirely of clean, cross-bedded to massive eolian dune and dry sand-flat deposits that are salt plugged to variable degrees. Plots of HRS logging data versus core-plug porosity values show a positive linear relationship that develops the highest coefficient of determination (R2 = 0.86) in structureless eolian dune sands, most probably caused by the lack of bedding-related anisotropies there. Once calibrated for a particular facies type, this correlation enables the calculation of porosity proxy data from sonic transit time values, acquired at centimetric steps. High-resolution sonic logging thus contributes a reliable and time-efficient, highly spatially resolving quantification of reservoir heterogeneities at centimeter scale and turns out to be a suitable tool for the nondestructive in-situ detection of high-porosity zones in otherwise uniform sandstone successions. Moreover, plots of closely spaced HRS logging–derived porosity proxy data significantly improve interpolation between single, wider spaced core-plug porosity data points.

Provenance of the Lower Ocoee Supergroup, eastern Great Smoky Mountains

Provenance and tectonic setting of clastic rocks of the Neoproterozoic Ocoee Supergroup were assessed using modes of detrital framework minerals, detrital feldspar chemistry, whole-rock geochemistry, heavy mineral assemblages and chemistry, and detrital zircon U-Pb geochronology. Putative source rocks comprising locally exposed Grenville basement were analyzed for comparison. Samples studied are primarily arkosic to subarkosic siltstones, sandstones, and minor conglomerate. Ternary tectonic discrimination diagrams indicate a continental basement uplift setting, although the mineralogically most mature Longarm quartzite indicates a continental interior setting. The range of detrital feldspar compositions among Ocoee units is comparable to feldspar in basement rocks. Orthoclase-rich detrital alkali feldspar predominates over detrital albitic plagioclase. Whole-rock normative Qz-Or-Pl values and trace-element abundances closely match those of local basement. Snowbird Group siltstones and sandstones contain high abundances of zircon, apatite, titanite, ilmenite, and epidote, which locally occur as concentrations of heavy minerals in discrete laminae. Zircon-tourmaline-rutile indices and titanite compositions are most consistent with a granitic source for these sediments. The majority of detrital zircon U-Pb ages are late Mesoproterozoic, with scattered late Neoproterozoic and Paleoproterozoic grains. All but one of the ∼1200 detrital zircons (at ca. 2000 Ma) can be accounted for by a local Blue Ridge basement magmatic source terrane. Archean detrital zircon ages are absent from the Ocoee detrital zircon age population. This absence is consistent with the general paucity of Archean grains in other Neoproterozoic Southern Appalachian clastic sequences. All data are consistent with a lithologically and geochronologically restricted, proximal, flank source for sediment filling a marginal continental rift. The Ocoee represents the first pulse of sediment dominated by Grenville-age zircon on the eastern Laurentian margin and serves as a major source of recycled zircon for Paleozoic clastic sequences in eastern Laurentia. The youngest detrital zircon age obtained from the basal Ocoee Wading Branch Formation (639 ± 8 Ma) provides a maximum depositional age for the Ocoee Supergroup and onset of rift-filling sedimentation in the intracontinental Ocoee basin.

Tectonic Deformation and Fluid Flow: Implications for the Formation of Unconformity-Related Uranium Deposits

Numerical experiments were carried out to investigate the fluid flow in typical Proterozoic basins that host unconformity-related uranium deposits. We have constructed a simplified conceptual model by integrating important features shared by the Athabasca, Thelon, and Kombolgie Basins. Based on this conceptual model, various numerical scenarios were designed to explore the interaction between fluid flow, heat transport, topographic relief, and tectonic deformation. Our modeling suggests that thermally driven free convection may develop in the thick sandstone sequence at a geothermal gradient of between 25° and 35°C/km during periods of tectonic quiescence, with a maximum velocity of about 1.0 m/yr. However, reactivation of preexisting basement structures and the generation of new faults suppressed free convection and led to deformation-dominated fluid flow or mixed convection, depending on strain rates. During compressive deformation, reduced brines in the basement may flow out along fractured zones and encounter uranium-bearing fluids in the clastic sequence to form sandstone-hosted deposits. In contrast, basement-hosted deposits are likely to form during extension, when oxidized basinal brines flow into faulted structures to interact with reduced minerals or fluids in the basement. Maximum flow rates are estimated to be up to ~7 and ~2.5 m/yr in the relatively high permeability fracture zone for compressive and extensional deformation, respectively, given a strain rate of 10 −13 s −1 and a geothermal gradient of 30°C/km. In addition, the rate of pressure accumulation and dissipation is different in various geologic units depending on their hydrological properties and strain rates.

Source rock potential of Lower to Middle Jurassic black clastic sequences of the Intermontane belt1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia.

Lower to Middle Jurassic clastic sequences are widespread within the interior of the Canadian Cordillera. These successions cap waning Jurassic volcanism in many Cordilleran arc terranes and are succeeded by clastic sequences of the Intermontane basins. Fine-grained, carbonaceous lithologies, which locally contain elevated levels of organic carbon, characterize these clastic successions. These include sections of the Spatsizi Formation (Abou Member) and Smithers Formation in northern and western Bowser basin, respectively, Ashcroft Formation and equivalent strata in central Quesnellia, and Last Creek Formation and Junction Creek rocks below the Tyaughton–Methow basin. These rocks locally contain metre-thick sections with total organic carbon (TOC) levels >5 wt.% and others have thicknesses approaching 100 m with TOC between 3 and 5 wt.%. Thermal maturation levels are high in many sections, suggesting original organic contents were greater and that these rocks may have been excellent source beds. Associated bitumen in these successions, together with Mesozoic oil in some overlying Intermontane clastic rocks, also suggests these sequences may have been effective oil source rocks. TOC levels, thermal maturity, and thickness of some sections are comparable with shale gas sequences being exploited elsewhere in North America. TOC concentrations within these rocks, together with other elemental abundances, indicate anoxic conditions during deposition. The age of these clastic rocks brackets the global Toarcian anoxic event and that of other organic-rich sequences in North America. Elemental abundances suggest predominantly volcanic-arc complexes as source terranes, although continental signatures are suggested by rocks in western Quesnellia.

Sedimentación y paleogeografía del Cretacico y Cenozoico del Litoral Pacifico de Costa Rica

The systematic stratigraphy of the Pacific littoral of Costa Rica has been reorganized in three supergroups: 1. Papagayo: mafic and ultramafic oceanic basements and volcanicaIly or tectonically associated sediments. 2. Garza: oceanic sedimentary cover including pelagics (Sabana Grande Group) and slope deposits (Samara Group). 3. Mal Pais: neritic sedimentary cover, subdivided into 5 epochs. A major, upper Santonian tectonic event divides the geologic history into two phases: 1. The Nicoya Complex with its Bathonian/Callovian Santonian (BAUMGARTNER 1984) oceanic sedimentary cover and the Santa Elena Peridotite form together a nappe edifice with a southern vergence (BOURa15— et al. in press). 2. Since the Campanian, this structure is part of the stable isthmic crust, the substrate of the studied upper Senonian-Cenozoic sedimentary sequen ces, affected by open folding and normal faulting only. No accretionary struc-tures related to subduction along the Middle-American Trench, effective since ttat latest Senonian, have been observed. Ocean floor continued te form during the latest Senonian-early Paleocene in a primitive island arc environment (Que-pos, Osa). Campanian-middle Eocene pelagic (and background) sedimentation followed the paleooceanographic trends observed in the Pacific, amplified by local (equatorial, eastern ocean margin) high fertility. A shallow CCD is reflected by Santonian-lower Campanian and upper Paleocen-middle Eocene radiolarian-rich siliceous deposits. In the late Campanian-Maestrichtian a drastic drop of the CCD overruled subsidence and resulted in deposition of foraminifer-rich pelagic limestones. Thick Maestrichtian-Paleocene turbidite and mass flow sequences were deposited in YW-SE trending elongate basins and document the erosion of an emerged andesitic volcanic are, che product of active subduction, surrounded by narrow carbonate and silicic/astio shelves, set aboye steep, unstable slopes. A tectonic event at the middleilate ocene boundary caused mayor gravitative s/iding and slumping of the upper part of the oceanic sequence, subsequent uplift and a regional, unconformable onset of shallow carbonate deposition, while turbiditc sedimentation persisted in some arcas (Santa Elena, Quepos). An inferred thickened oceanic crust in isostatic equilibrium should form a sea floor at subphotie depths. However, tectonie uplift has repeatdly brought the substrate te shallow depth and allowed the deposition of unconformable, thin, shortlived, neritic sequences, forffied during five succesive epochs: Epoch 1. Campanian-Maestriehtian: The structurally highest parts of the upper Santonian orogen were uplifted te subaerial and shallow photic depths where rudis-tid limestones developed. Epoch 2. Paleocene-early Encone: Voleanic activity related tu subduction gave rise tu an island are surrounded by shallow platforms NE of the study area, only known from reworked carbonate elasts in slope deposits (Samara, Quepos). Epoch 3. Middle-late Eoeene: Tectonic uplift brought most of the area tu shallow photic depth which led tu the formation uf the widespread largor foramini-fer - red algal limestones. Epoch 4. Oligocene-early Miocene: Most of the central area was emerged and only near the trench (Nosara-Mal Pais) thin shallow clastic sequences developed, while turbidite basins persisted in the NW and SE (Dept. Rivas, Nicaragua, Fila Costena). Epoch 5. Late Miocene-Pleistocene: Littoral deposits are concentrated around the south of Nieoya, in areas of recent uplift (FISCHER 1980).

The Kappa model of probability and higher-order rock sequences

In any depositional environment, the sequence of sediments follows specific high- and low-frequency patterns of rock occurrences or events. The occurrence of a rock in a spatial location is conditional to a prior rock event at a distant location. Subsequently, a third rock occurs between the two locations. This third event is conditional to both prior events and is driven by a third-order conditional probability P(C ∣ (A ∩ B)). Such probability has to be characterized beyond the classic conditional independence model, and this research has found that exact computation requires a third-order co-cumulant term. The co-cumulants provide the higher-order redundancy among multiple indicator variables. A Bayesian analysis has been performed with “known” numerical co-cumulants yielding a novel model of conditional probability that is called the “Kappa model.” This model was applied to three-point variables, and the concept has been extended for multiple events P(G ∣ A ∩ B ∩ C ∩ D... ∩ N), allowing the reproduction of complex transitions of rocks in sequence stratigraphy. The Kappa model and co-cumulants have been illustrated with simple numerical examples for clastic rock sequences. In addition, the co-cumulant has been used to discover an extension of the variogram called the indicator cumulogram. In this way, multiple prior events are no longer ignored for evaluating the probability of a posterior event with higher-order co-cumulant considerations.

The India and South China cratons at the margin of Rodinia — Synchronous Neoproterozoic magmatism revealed by LA-ICP-MS zircon analyses

The palaeogeographic position of South China in relation to India in the Neoproterozoic is controversial. Resolution of this controversy constrains the reconstruction of Rodinia during its breakup and contributes to our understanding of Snowball Earth. This work compares the Neoproterozoic histories of the Lesser Himalaya in northern India and the Yangtze block in southern China. We present U–Pb LA-ICP-MS ages of detrital zircon grains from six Indian and three Chinese siliciclastic sedimentary rocks, such as sandstones or diamictites/tillites. In total, 1148 grains were analysed from which 833 measurements gave ages with a degree of concordance between 90 and 110%. The correlation of the Indian and the Chinese sections is possible using the tillites of both areas purportedly deposited during the Snowball Earth time interval: the Blaini tillite from India and the Nantuo tillite from China. The U–Pb ages confirm the Marinoan age of the Chinese Liantuo tillite. Although the youngest zircon age for the Indian Blaini tillite is about 678 Ma, the Marinoan age is indicated by the presence of a typical Marinoan white to bright yellowish overlying cap carbonate. In addition to the tillites, representative detrital zircon ages from over- and underlying clastic rocks were determined. The Chinese samples are dominated by zircons with Neoproterozoic ages with a main peak between ca. 750 Ma and ca. 950 Ma and are characterised by the absence of Archaean ages. The Indian samples contain abundant Neoproterozoic zircon grains, but also contain Mesoproterozoic to Archaean zircons. For all samples, a local source area that provided the Neoproterozoic zircons is likely. A synchronous Neoproterozoic magmatic event in both cratons probably reflects the breakup of the supercontinent Rodinia and therefore the same tectono-magmatic event. Our results indicate a similar history for India and South China which both underwent at least one synchronous episode of crustal growth during the Neoproterozoic. In addition, our data set shows that both passive margin clastic sequences had the same source area for all zircons older than Neoproterozoic. Therefore we infer that India and South China were close to each other and along the same passive margin during the breakup of Rodinia in the Late Neoproterozoic.

Chapter 57 Glaciogenic rocks of the Neoproterozoic Smalfjord and Mortensnes formations, Vestertana Group, E. Finnmark, Norway

Abstract The Vestertana Group in East Finnmark, North Norway, contains two Neoproterozoic glaciogenic sequences, the Smalfjord and Mortensnes formations, preserved on the northern edge of Baltica. The former comprises up to 420 m of aeolian, fluvioglacial and glaciomarine sediments and terrestrial diamictite. The latter consists of up to 50 m of predominantly diamictite. The Smalfjord Formation (Fm.) is underlain by dolostones (Grasdalen Fm., Tanafjorden Group), only locally preserved due to the sub-Smalfjord Fm. unconformity, which cuts down-section through a c. 2.5 km dominantly clastic sequence to rest on Baltic Shield gneisses. The two glaciogenic successions are separated by c. 350 m of mostly clastic sediments (Nyborg Fm.), with thin dolostones at the base and towards the top. The latter are generally absent due to the sub-Mortensnes Fm. unconformity, which also cuts down southwards through the Nyborg and Smalfjord formations to the Baltic Shield. No robust isotopic age constraints are available for the succession. δ 13 C data, together with cap dolostone characteristics, offer paradigmic correlations with other areas (Smalfjord ≡ Marinoan; Mortensnes ≡ Gaskiers). A limited Ediacaran fauna, including Aspidella , give only broad age constraints. Palaeomagnetic data are ambiguous; some suggest Baltica lay at equatorial (15°S) to mid-latitudes (50°S) for the period 750–550 Ma, respectively, while other interpretations place it at either 30°N or S at c. 550 Ma.

Geodynamic Significance of the Early Triassic Karaburun Granitoid (Western Turkey) for the Opening History of Neo-Tethys

The Karaburun Peninsula, which is considered part of the Anatolide-Tauride Block of Turkey, contains clastic and carbonate sequences deposited on the northern margin of Gondwana. The Palaeozoic clastic sequence, which is intruded by the Early Triassic granitoid and tectonically overlies a Mesozoic mélange sequence, can be divided into three subunits: a lower clastic subunit consisting of a sandstone-shale alternation, an upper clastic subunit consisting of black chert-bearing shales, sandstone and conglomerate, and a Permo-Carboniferous carbonate subunit. The lower Triassic Karaburun I-type granitoid has a high initial ^8^7Sr/^8^6Sr ratio (0.709021-0.709168), and low ^1^4^3Nd/^1^4^4Nd ratio (0.512004-0.512023) and \epsilonNd (-5.34 to -5.70) isotopic values. Geochronological data indicate a crystallization (intrusion) age of 247.1±2.0 Ma (Scythian). Geochemically, the acidic magmatism reflects a subduction-related continental-arc basin tectonic setting, which can be linked to the opening of the northern branch of Neo-Tethys as a continental back-arc rifting basin on the northern margin of Gondwana. This can be related to the closure through southward subduction of the Palaeotethys Ocean beneath Gondwana.

Neogene–Quaternary tectonic stratigraphy of the eastern Southern Alps, NE Italy

In order to reconstruct the Neogene–Quaternary Tectonic Stratigraphy of the eastern Southern Alps, the late Tortonian-lower Pleistocene foredeep clastic sequences, cropping out in the Veneto and Friuli piedmont areas have been extensively investigated focusing on the contractional features observed in the frequent conglomerate layers (pitted pebbles). The eastern Southern Alps is the result of a typical polyphase tectonic activity initiated in Late Oligocene, characterised by the occurrence of several non-coaxial stress regimes. Based on careful analyses of the pebbles’ surfaces (shape and orientation of the indented features) and following a systematic and statistical approach, the mean orientation of the maximum compressive stress axis (σ 1) has been obtained for more than 30 sites of measurements along the ca. 120 km-long investigated piedmont area. The affected lithostratigraphic units and the orientation (pre- versus post-tilting) of the stereonets density peaks make it possible to recognize four distinct deformational events and characterize them in terms of mean σ 1 direction and timing: late Tortonian ( σ 1 = 313°/00°), late Messinian-Early Pliocene (338°/04°), Late Pliocene (314°/03°), and Early-Middle Pleistocene (160°/03°). The Tectonic Stratigraphy of the eastern Southern Alps during the last ca. 10 Ma shows the occurrence of several variations of the stress field characterized by a repeated oscillation of the σ 1 axis between an NNW-SSE and NW-SE directions (Twist Tectonics). Taking also into account literature data about older deformational events (Chattian–Burdigalian and Serravallian-Tortonian), we analyse the Neogene–Quaternary tectonic evolution in the frame of the central Mediterranean realm and compare it with the convergence direction between the Adria–Africa and Europe lithospheric plates. We show that compressional directions within the eastern Southern Alps are basically governed by the remote plate convergence, though since late Messinian, the approaching Northern Apennines started to play a crucial role within the investigated area. Alternating short-lived phases (1–2 Ma) of coupling and decoupling along the basal detachment of the Apennines accretionary wedge probably caused temporary perturbations of the ‘local’ stress field and complex accommodation structures in this region of ongoing crustal collision.

Provenance of Ordovician clastic sequences of the San Rafael Block (Central Argentina), with emphasis on the Ponón Trehué Formation

The Ordovician Ponón Trehué Formation is the only early Palaeozoic sedimentary sequence known to record a primary contact with the Grenvillian-age basement of the Argentinean Cuyania terrane, in its southwards extension named the San Rafael block. Petrographic and geochemical data indicate contributions from a dominantly upper continental crustal component and a subordinated depleted component. Nd isotopes indicate ε Nd of − 4.6, ƒ Sm/Nd − 0.36 and T DM 1.47 Ga in average. Pb-isotope ratios display average values for 206Pb/ 204Pb, 207Pb/ 204Pb, and 208Pb/ 204Pb of 19.15, 15.69 and 38.94 respectively. U–Pb detrital zircon ages from the Ponón Trehué Formation cluster around values of 1.2 Ga, indicating a main derivation from a local basement source (Cerro La Ventana Formation). The Upper Ordovician Pavón Formation records a younger episode of clastic sedimentation within the San Rafael block, and it shows a more complex detrital zircon age population (peaks at 1.1 and 1.4 Ga as well as Palaeoproterozoic and Neoproterozoic detrital grains). Detailed comparison between the two Ordovician clastic units indicates a shift with time in provenance from localized basement to more regional sources. Middle to early Upper Ordovician age is inferred for accretion of the Cuyania terrane to the proto-Andean margin of Gondwana.