Northern Basin Margin Research Articles

Fluvial architecture variations linked to changes in accommodation space: Río Chico Formation (Late Paleocene), Golfo San Jorge basin, Argentina

The Upper Paleocene Río Chico Formation is a 50–180m thick fluvial succession developed in a passive-margin setting, Golfo San Jorge basin, Central Patagonia, Argentina. A detailed description and interpretation of outcrops was carried out, analyzing exposures from the northern basin margin to the most complete successions at the southern depocenter. The unit is characterized by a regional fluvial system that flowed to the south-east. Five main lithofacies associations were defined: (I) active fluvial channels, with three sub-types: braided, meandering and low-sinuosity, (II) sheet-flood deposits, (III) proximal floodplain (natural levee and crevasse-splay), (IV) distal floodplain, and (V) abandoned channels.Lateral/vertical changes in fluvial architecture of the Río Chico Formation were recognized by variations in preserved thickness, fluvial styles, geometry of fluvial channels, regional paleoflow directions, and channel/floodplain ratios. Close to the northern basin margin, the fluvial succession is 50–60m thick, composed of braided channels, sheet-flow deposits, and high channel/floodplain ratio. In a basinward direction, the alluvial succession increases to 180m in thickness, the dominant fluvial styles change to low-sinuosity and meandering channels and channel/floodplain ratio reduces.The fluvial architecture of the Río Chico Formation shows two main depositional trends that resulted from changes in accommodation space across the basin. The interpreted break-point coincides with the underlying Cretaceous basin-boundary, thus the synsedimentary extensional reactivation of the pre-existing tectonic lineament generated differential subsidence, delimiting two different accommodation settings.

Comparison of the Quaternary travertine sites in the Denizli extensional basin based on their depositional and geochemical data

In the Denizli Basin (Turkey), located in the western Anatolian extensional province, travertine and tufa deposition has been an ongoing process for at least 600,000years. Travertine bodies, which are 30 to 75m thick and each covers areas of 1 to 34km2, are up to 1km3 in volume.Today, spring waters in this area have temperatures of 19 to 57°C, are of the Ca–Mg–HCO3–SO4 type in the Pamukkale, Kelkaya and Pınarbaşı areas and the Ca–Mg–SO4–HCO3 type at Çukurbağ. Thermal waters along the northern margin of the basin are generally hotter than those in the east–southeast and south. The δ18O and δD values of the spring waters indicate a meteoric origin. The average temperatures of the hydrothermal systems in the Denizli Basin appear to have decreased from Pleistocene to Holocene.Travertine, which formed from the hotter water, is more widespread than the tufa that formed in the cooler spring waters. Deposition of the travertine, which formed largely on slopes, in depressions, and along fissure ridges (mostly on northern basin margins), was controlled by the interplay between various intrinsic and extrinsic parameters. The travertines are formed largely of calcite with only minor amounts of aragonite in some of the vertically banded, crystalline crust, raft and pisoid travertines found in some of the northern sites. The aragonitic samples, rich in Sr, are typically found around the spring orifices and along the central axis of the fissure ridges.The stable isotope values of the travertine found in the northwest and southeast parts of the basin are different. The δ13C values of the northern travertine deposits are more positive (3.7 to 11.7‰ VPBD) than those found in the south–southeast areas (−4 to 5.8‰ VPDB). In contrast, the travertine and tufa in the southeastern areas have higher δ18O values (−15.2 to −7.8‰ VPDB) than those of the northern areas (−16.6 to −4.8‰ VPDB). Available evidence indicates that spring activity and associated travertine precipitation in the Denizli Basin were controlled largely by tectonic activity rather than by climatic conditions.

Transition from extensional to compressional magnetic fabrics in the Cretaceous Cabuérniga basin (North Spain)

The transition between extensional and compressional-driven magnetic fabrics in sedimentary rocks is explored in this paper through the study of an example of the Basque–Cantabrian basin. In the area where extensional structures prevail and no superimposed deformation is observed, except for gentle large-scale folds, the magnetic fabric is interpreted as extensional, in consistency with mesostructural (tension gashes) and macrostructural (large-scale faults) data. Compressional tectonic fabrics are unequivocally interpreted in the area with cleavage development related to the buttressing of the syn-rift sequence against faults located near the northern basin margin. In this area, kmax is oriented according either to the intersection lineation or the dip direction of cleavage planes. In the area located in-between, where no macroscopic evidence of either compression or extension exist, there is a transitional fabric between compressional (resulting from the modification during inversion of a previous sedimentary or extensional fabric) and extensional (inherited from the extensional stage) magnetic fabrics that correlate with subtle evidences at the microscopic scale (pressure shadows, deformation and re-orientation of nodules). Therefore, the magnetic fabric is revealed as an exceptionally sensitive marker of deformation in sedimentary rocks. This transition in the magnetic fabric occurs within a length of 6.25 km along the cross-section that correlates with a thickness of 200 m of the stratigraphic pile. These results indicate that even in the absence of clear structural markers of compressional deformation, extensional magnetic fabrics can be only interpreted when there is a minimum separation (in the vertical or the horizontal) to the cleavage front.

Major unconformities, tectonostratigraphic frameword, and evolution of the superimposed Tarim basin, Northwest China

The Tarim basin experienced a complex tectonic evolutionary history from Sinian to Cenozoic. Eight large-scale and more than 20 subordinate unconformities defining tectonosequences of different protobasins formed in various tectonic settings have been identified within the Phanerozoic in the Tarim basin, their distribution determining the general characteristics of sequence stratigraphic framework of the basin. Tectonostratigraphic unit I (magasequence) consists mainly of the Sinian System, which formed in a rift or aulacogen setting and can been subdivided into two subordinate stratigraphic units (supersequences). Unconformity (Tg9) between Sinian and Cambrian with surface karstification is regarded as a post-rift unconformity. Tectonostratigraphic unit II comprises the Cambrian and the Ordovician and can be divided into six subordinate tectonostratigraphic units, recording the tectonogeographic evolution of the prototype basins from Cambrian to Early Ordovician passive carbonate continental margin or cratonic depression and the Late Ordovician submarine to neritic retroarc foreland and cratonic depressions. The tectonic uplift related to the formation of the unconformity Tg5-2 resulted in the remarkable change in basin tectonic setting from a passive divergent to an active convergent, with the development of the Tazhong (塔中) uplift, the Tangguzibasi (塘古孜巴斯), and the northern depression at the end of the Middle to the early Late Ordovician. The widespread angular unconformity Tg5 formed by a relatively strong compressive deformation, which caused an abrupt tectonogeographic change of the basin from abyssal to a neritic setting in response to the collision and associated tectonic deformation of the North Kunlun (昆仑) orogenesis during the Late Ordovician to the Early Silurian. Tectonostratigraphic unit III is composed of the Silurian and the Lower to Middle Devonian and characterized by the development of fluvial or deltaic and clastic littoral and neritic deposits. Large-scale terrigenous clastic depositional wedges progradated from the north to south in the southeastern slope of the basin indicate the continuously shallowing and uplifting along the northern basin margin. Tectonostratigraphic unit IV includes the Upper Devonian, Carboniferous, and Permian and can be classified into two subordinate tectonostratigraphic sequences. The angular unconformity (Tg3) at the base of the unit is the most widespread unconformity and the strong compression and uplift of the basin during this period has been suggested to be related to the collision of the Tianshan (天山) orogenesis and resulted in fundamental change in tectonic geomorphology with higher to the northeast and lower to the southwest. Tectonostratigraphic unit IV records another tectonic cycle from weak extension to compression in basin setting and is composed mainly of nearshore clastic deposits of embayment basin fills. From the Triassic, the Tarim basin evolved into a period characteristic of development of intracontinental depressions and marginal foreland basins and experienced several cycles from rapid subsidence to strong uplift and deformation, resulting in superimposition and reformation of differently orientated protobasins filled with a series of regional depositional cycles bounded by major unconformities and consisting of extremely thick alluvial and lacustrine deposits. The Kuqa foreland depression in the northwestern basin margin developed since the Triassic and deposited a clastic wedge of the Mesozoic to Cenozoic more than 100 000 m in thickness, which progradated and thin towards the southern Tabei (塔北) forebulge. The large-scale sedimentary cycles from alluvial, fluvial to lacustrine, and finally fluvial deposits are attributed to the results of foreland tectonisim from active to relatively quiet stages. The foreland tectonisim was active during the Triassic, relatively quiet during the Jurassic, and active again from the Late Jurassic to the Cretaceous. To the Eogene, the depression subsided again and the compression intermittently increased, resulting in a series of faulted and folded structural belts.

Iodine-129, 87Sr/86Sr, and trace elemental geochemistry of northern Appalachian Basin brines: Evidence for basinal-scale fluid migration and clay mineral diagenesis

Evidence for basin scale brine migration and clay mineral diagenesis in the northern Appalachian Basin was investigated using elemental and isotope (129I/I, 87Sr/86Sr) geochemistry of formation waters collected from the Middle to Upper Devonian section of the northern basin margin in western New York, northwest Pennsylvania, and eastern Kentucky. One sample from each of the Mississippian Berea sandstone and the Silurian Medina sandstone were analyzed for comparison. Measured iodine ratios range between 28 to 1,890 × 10−15 and are anomalously high compared to cosmogenic iodine sourced from Devonian age organic matter. Iodine-129 in the waters was largely derived from fissiogenic sources, the spontaneous fission of 238U to produce 129I, with estimated 129I/I values up to 270 × 10−15, which occur locally in the organic-rich shales. There are three water samples that have values of 490 × 10−15, 860 × 10−15, and 1,890 × 10−15, which are above the range for local fissiogenic 129I and may be accounted for by topographically driven, basin scale fluid flow through a regionally high fissiogenic source. Relatively large uranium occurrences lie along the structural front of the Appalachian Basin in the Blue Ridge Province and are situated within hypothesized flow paths parallel to the main compressional direction of the Alleghanian orogeny. Estimated 129I/I values for these uranium occurrences are in excess of 55,000 × 10−15. The strontium isotope composition and Sr concentration of brines display a mixing trend between a highly radiogenic end-member (0.7210) with low Sr (51 mg/L) and a non-radiogenic (0.7100), high Sr (4789 mg/L) end-member. Potassium and boron concentrations are notably depleted relative to evaporated Paleozoic seawater, the hypothesized source of Appalachian Basin brines. The K/Rb values of formation waters are depleted relative to seawater values, but in some cases are well above values indicative of water-rock reactions. The Sr isotopic composition, K and B depletion, and intermediate K/Rb ratios are consistent with smectite diagenesis and paleo-temperatures that are likely greater than approximately 150 °C. These temperatures may be high given the burial history of the study area and support the flow of formation waters from deeper within the basin. The combined isotopic and elemental results of formation waters provide compelling evidence for basin scale fluid migration in the northern Appalachian Basin and are consistent with previously published evidence documented from the rock record, including clay mineral diagenesis and ore deposition.

Distribution and erosion of the Paleozoic tectonic unconformities in the Tarim Basin, Northwest China: Significance for the evolution of paleo-uplifts and tectonic geography during deformation

The distribution and erosional features of the Paleozoic major tectonic unconformities in the Tarim Basin, and their genetic relation to the development of paleo-uplifts as well as the evolution of geodynamic settings, are documented in this paper based on the integral analysis of seismic, drilling, and outcrop data. During the Paleozoic, the Tarim Basin underwent three major tectonic deformation stages, which resulted in three angular unconformities and in significant changes in basin geomorphology and paleogeography. The tectonic deformation at the end of the Middle Ordovician was characterized by development of the southern central paleo-uplift, the northern depression, and the southeastern Tangguzibasi depression in the basin. The thickest denudation belts of the unconformity (Tg5-2) are distributed mainly along the thrust structural highs. A stronger deformation event took place at the end of the Late Ordovician and formed a huge uplift along the southwestern and southeastern basin margins and the western part of the Tabei uplift along the northern basin margin, producing an extensive angular unconformity (Tg5) with maximum erosion thickness of 1500–2000m. This tectonic event resulted in an abrupt change in overall geography of the basin, from a deepwater marine environment at the late stages of the Late Ordovician to a littoral and neritic basin in the Early Silurian. The deformation that occurred at the end of the Middle Devonian was the strongest in the Paleozoic. It generated the most widespread angular unconformity (Tg3) within the basin and led to extensive erosion, with maximum denudation thickness of 3000–5000m in the northern and northeastern parts of the basin. The topography of the basin during the late Devonian was characterized by a high in the northeast and a low in the southwest, forming an embayment basin opening to the southwest during the Early Devonian to Carboniferous. The transgression in general from southwest to northeast deposited extensive coastal sandstones onlapping the erosion-leveled unconformity (Tg3). Comparative analysis of uplifting in the basin with the regional tectonic setting shows that deformation that took place during the three periods was related to the evolution of the paleo-oceanic plates and the orogenesis around the basin. The closure of the North Kunlun Ocean and subsequent collision is suggested to be the main cause for the development of the central paleo-uplift at the end of the Middle Ordovician and the strong uplift and erosion of the southwestern and southeastern basin margin at the end of the Late Ordovician. The large-scale uplift and denudation of the northern part of the basin, including the Tabei–Kongquehe uplift belt, as well as the folding and hinging of the Manjiaer depression, was coeval with, and more related to, the subduction and collision of the South Tianshan orogenic belt and the Altyn trench-arc-basin system at the end of the Middle Devonian.

Basin width control of faulting in the Naryn Basin, south‐central Kyrgyzstan

In Central Asia's Tien Shan, deformation is distributed across the wide orogen, a characteristic of intracontinental mountain building. Active faults are commonly found within intramontane basins that separate its constituent ranges. In order to explore the controls on this intramontane basin deformation, we study the Naryn Basin of south‐central Kyrgyzstan. A series of five balanced cross‐sections reveals a transition in patterns of faulting from faults confined to basin margins to faults focused within the basin center. The 20‐km‐wide eastern Naryn Basin displays deformation attributed to low‐angle splays of the northern, basin‐bounding fault. In the 40‐km‐wide western Naryn Basin, the pattern of deformation linked to the northern range remains, but is accompanied by steeper faults that dip both south and north without being directly linked to the basin‐bounding fault. We compare these cross‐sections to synthetic aperture radar interferometry (InSAR) measurements of surface deformation. Profiles of InSAR‐derived surface deformation rates across the Naryn Basin reveal that in the west, deformation is distributed across the broad basin interior, whereas in the east, rapid uplift is concentrated at the margin of the narrower basin. From the geodetic and structural data, we infer that in the western Naryn Basin, deformation has migrated away from the northern basin margin and into the interior. Deformation of the eastern basin interior, however, remains linked to the basin‐bounding fault. A simple mechanical model demonstrates that basin width may control basin deformation whereby basin‐interior faulting in the narrow, eastern Naryn Basin is inhibited by the overburden of adjacent ranges.

Provenance of the northern part of the Kahramanmaraş Peripheral Foreland Basin (Miocene, S Turkey)

The Miocene Kahramanmaraş Peripheral Foreland Basin (KPFB) resemble to classic foreland basin model, with small differences. In the classic model, both the accretionary wedge and foredeep extend lengthways parallel to the plate margin. In addition, accretionary wedge includes wedge top basin or piggy back basin that extends parallel to foredeep. However, the accretionary wedge of the KPFB contains small half-graben type basins that obliquely intersect the plate margin between the Arabian Plate and the Anatolide–Taurides Platform (due to the irregular shape of the plate boundary). Tectonic lineaments controlled the shape and orientation of these basins and larger main depocentre of the KFPB, which were predominantly filled with deep-sea sediments. This paper focuses on the provenance of features of the KFPB, predominantly was fed from the northern basin margin, while also aiming to resolve the complex basin evolution that occurred during the Miocene. Clasts of Palaeozoic and Mesozoic limestone and ophiolites are common components of the confined deep-water clastic systems, which evolved as elongated trenches in the north-western sector of the KPFB during the Early-Middle Miocene. During the Middle Miocene, continuous thrusting of the northern basin margin to south caused depocentre migration to south-east, through the basin interior. At that time, the north-east and central depocentres of the KPFB were filled primarily by clasts of ophiolite and metamorphic units. The tectonic control on basin fill architecture can be observed anywhere in the KFPB. The principal tectonic features controlled the geometry and orientation of the canyon, the channel geometry of the deep-water slope on the northern basin margin, the frequency and distribution of slump-slide-debris flows and the overall pattern of sedimentation cycles in the stratigraphy of the slope and the central basin floor. Some basin sectors have continuously reactivated and as a result, different sediment entry points with substantial local accumulation of sediment and deformation have evolved on the slope and basin floor. Three scales of provenance were used to investigate the source rock: (a) field-based observation and analysis of conglomerate clasts, (b) modal analysis of sandstone facies and (c) geochemical analysis, all of which were in agreement.

An early Campanian rocky shore at Ivö Klack, southern Sweden

Well-exposed, ancient rocky shores are rare and the associated shelly faunas are normally strongly worn and fragmented due to erosion during both sea-level rise and fall. An early Campanian rocky shore with a rich fauna is preserved at Ivö Klack in the Kristianstad Basin, southern Sweden. Ivö Klack is situated on the small, hilly island of Ivö situated in lake Ivösjön with a lake level about 6 m above present-day sea level. The rocky shore was formed during a major late early Campanian transgression caused by a sea-level rise up to about 100 m above present sea level. An archipelago was formed along the northern basin margin during the transgression with numerous small islands and peninsulas. The steep palaeo-coast at Ivö Klack consists of gneiss overlain in the lower part by more than 30 m of kaolin in places containing large boulders of gneiss with a kaolinized outer crust. The kaolin wedges out upslope and is absent above 30–35 m above lake level. The kaolin is overlain by up to 5 m of muddy quartz sand with highly angular grains, representing a residue of the kaolin formed during transgressive wave and current reworking. The steep gneiss coast was rapidly transgressed by the sea in the latest early Campanian and at least 25 m of onlapping coarse-grained skeletal sand, gravel and whole fossils were deposited on the clean gneiss surface during the Belemnellocamax mammilatus belemnite biozone. Large boulders of gneiss are common in the carbonates and formed distinct boulder beds at some levels but these are now quarried away. The top 6 m of the preserved carbonate succession are free of boulders. The rocky surface is fairly even on a large scale, but highly irregular in detail with numerous metre-sized hummocks and boulders formed during terrestrial weathering and kaolinization. The lowest part of the shore is developed as a bench, topped by a sub-horizontal irregular platform, 20–30 m wide, with large hummocks and rounded boulders. The platform passes upwards into a steep boulder-strewn slope. A well-developed glauconitized hardground with Thalassinoides burrows and several incipient hardgrounds occur in the carbonates draping the bench and lower part of the platform. They dip gently outwards and probably represent a kind of beach rock. A highly diverse benthic fauna with more than 200 shell-bearing species lived between, below and on the hummocks and boulders. It comprises bivalves, brachiopods, polychaetes, gastropods, echinoids, asteroids, bryozoans and is dominated by large oysters and includes the northernmost Late Cretaceous rudists and hermatypic corals. The remaining benthic invertebrate groups are represented by only a few species each. The non-benthic invertebrate fauna comprises four belemnite species and one rare ammonite species. The lower Campanian carbonates of the small basin have yielded an unusually diverse vertebrate fauna totalling more than 60 species, including mosasaurs, plesiosaurs, crocodiles, turtles, birds, and as many as 44 species of sharks and rays. Ivö Klack thus provides information on virtually all trophic levels in the rocky shore ecosystem and represents the most diverse rocky shore fauna known from the geological record. This paper aims at providing the framework for a series of papers on the palaeoecology of the main benthic faunal groups.

Evidence for Late Ordovician glaciation of Al Kufrah Basin, Libya

Fieldwork at the flanks of Al Kufrah Basin, Libya, reveals that Late Ordovician ice sheets were present in the eastern Sahara and that they extended northeastward toward Egypt. Evidence for grounded ice sheets is preserved at the both the southeastern (Jabal Azbah) and northern (Jabal az-Zalmah) basin margins. Characteristic soft-sediment deformation structures, including soft-sediment folds, small-scale faults and striated pavements indicate subglacial shearing and the formation of glacial erosion surfaces. These findings support the presence of a Late Ordovician ice margin in the eastern Sahara and add vital new constraints to reconstructions of the morphology of North African grounded ice sheets. Prior to our study, there existed two plausible models on ice sheet geometry. The first was that separate ice sheets – namely a north and west African ice sheet and an Arabian ice sheet – extended over this part of western North Gondwana. The second was that ice cover was continuous. The presence of a suite of subglacially-generated deformation structures adds considerable credence to the latter interpretation.

The Monagas Fold–Thrust belt of Eastern Venezuela. Part II: Structural and palaeo-geographic controls on the turbidite reservoir potential of the middle Miocene foreland sequence

This paper presents a new structural-stratigraphic approach to constrain the reservoir potential of the middle Miocene turbidite systems within the Monagas Fold–Thrust Belt (MFTB) and Maturín Sub-Basin (MSB) of eastern Venezuela. In the frontal anticline structures of the MFTB (Amarilis Area) light hydrocarbons have been produced from these turbidite systems which were deposited in a foreland basin with a complex tectonostratigraphic evolution. In order to predict the location of other analogous reservoirs we used the structural model presented in Part I ( Parra et al., 2010) to developed a palaeo-topographic reconstruction at early-middle Miocene. We have then used this reconstruction to constrain the palaeogeography of the middle Miocene foredeep where the turbidites were deposited. The area considered has 5000 km 2. By middle Miocene four regions are identified: 1) The southern basin margin dipped 1.5–2.5° north; 2) The foredeep axis had a southwest–northeast orientation. Within the foredeep the proto-structures of the MFTB created submerged highs that control the distribution of sediments; 3) The northern basin margin dipped 3–4° south; the coastline was controlled by the Pirital thrust sheet; 4) The main source of sediments was located towards the northwest on the Pirital thrust sheet and Serranía del Interior. Variations in shortening across the strike of the Pirital thrust were accommodated by a lateral ramp which controlled the location of a valley that acted as the main sediment pathway for the sediments that fed the turbidite system. This relationship between the thrust belt geomorphology and the location of turbidite sediment within the foredeep must be considered in order to assess the distribution of the Miocene turbidite reservoirs.

Glaciation and deglaciation of the Libyan Desert: The Late Ordovician record

Detailed outcrop studies at the flanks of Al Kufrah Basin, Libya, reveal the nature of glacially-related sedimentation and post-depositional deformation styles produced in association with the Late Ordovician glaciation, during which ice sheets expanded northward over North Africa to deposit the Mamuniyat Formation. At the SE basin flank (Jabal Azbah), the Mamuniyat Formation is sand-dominated, and incises interfingering braidplain and shallow marine deposits of the Hawaz Formation. The glacially-related sediments include intercalations of mud-chip bearing tabular sandstones and intraformational conglomerates, which are interpreted as turbidite and debrite facies respectively. These record aggradation of an extensive sediment wedge in front of a stable former ice margin. An increase in mudstone content northward is accompanied by the occurrence of more evolved turbidites. A widespread surface, bearing streamlined NW–SE striking ridges and grooves, punctuates this succession. The structures on the surface are interpreted to have formed during a regional north-westward ice advance. Above, siltstones bearing Arthrophycus burrows, and Orthocone-bearing sandstones beneath tidal bars testify to glaciomarine conditions for deposition of the underflow deposits beneath. By contrast, the northern basin margin (Jabal az-Zalmah) is appreciably different in recording shallower water/paralic sedimentation styles and major glaciotectonic deformation features, although facies analysis also reveals northward deepening. Here, a siltstone wedging from 8 to 50 m toward the north was deposited (lower delta plain), succeeded by climbing ripple cross-laminated sandstones up to 60 m in thickness (distal through proximal delta mouth bar deposits) with occasional diamictite interbeds. These rocks are deformed by thrusts and > 50 m amplitude fault-propagation folds, the deformation locally sealed by a diamictite then overlain by conglomeratic lag during ultimate deglaciation. Integrating observations from both basin margins, a model of fluvial-dominated delta systems feeding a pulsed debrite and turbidite fan system in a shallow proglacial shelf is proposed.

Multidisciplinary approach to an extensional syncline model for the Mesozoic Cameros Basin (N Spain)

In this paper we explore the possibility of reconstructing the initial geometry of inverted basins using combined geophysical and geological methods: seismic reflection profiles, paleomagnetism, analogue modelling and 3D geometrical analysis. These techniques allow for some unknowns in the geometry and evolution of extensional sedimentary basins (mainly the normal drag–reverse drag geometrical problem) to be solved. The example chosen for checking these techniques is the Cameros Basin (northern Iberian Chain), formed during the Late Jurassic–Early Cretaceous, and inverted during the Tertiary compressional stage. According to the reconstruction proposed, the Cameros Basin can be characterised as a lens-shaped, syncline basin with maximum thickness of deposits of about 8000 m in its depocenter, gradually diminishing toward the North and South. The extensional geometry of the Cameros Basin is defined by: 1) a large-scale growth syncline over the major basement fault, with southward-dipping beds in the northern basin margin, forming a southward-opening sedimentary wedge, with upward-decreasing dip values (large-scale normal drag geometry); 2) roll-over anticlines at the contact between the pre-rift series against the normal fault limiting the basin (smaller-scale reverse drag geometry). The combined syncline–anticline syn-extensional structures were characterised by means of paleomagnetic analysis of a remagnetization acquired at the time of extension. Analogue models indicate that the development of syncline basin geometries in extensional settings, as the one interpreted for the Cameros Basin, is closely related to the presence of a detachment level in the pre-rift sequence above the main basement faults.

Is there a Messinian unconformity in the Central Paratethys?

Since the conception of the Mediterranean Messinian Salinity Crisis model in the 1970s, regional unconformities as candidates for indicators of a correlative base level drop have been sought in the neighbouring Paratethyan basins. Some authors have suggested that seismic sections and borehole profiles from the Late Miocene to Pliocene lacustrine to fluvial succession of the Central Paratethyan Pannonian Basin include such unconformities. We argue that none of these unconformities evidence a significant drop in water-levels. One type of such unconformities is marked by the onlap of seismic reflections onto the lower portion of the shelf-edge clinoforms, a feature repeatedly observed in the eastern Hungarian part of the basin. This geometry, however, resulted from strike variability of the sediment feeder system, thus it is a local phenomenon which does not necessarily justify general base level drops. The only regional unconformity was observed on the shelf, not on the slope. It separates originally flat-lying Messinian deltaic-fluvial deposits from the overlying Pliocene fluvial-terrestrial sediments. This surface can be traced along the entire length of the northern basin margin both in seismic and borehole data. The unconformity is angular and thus has a tectonic origin. It is tilted together with the underlying sediments toward the basin proper, indicating the onset of basin inversion in the latest Miocene or earliest Pliocene. Thus, the seismic and borehole data published so far from the Pannonian Basin do not evidence that thewater level of the Central Paratethys was directly influenced by the drawdown of the Mediterranean or the Eastern Paratethys.

High-resolution seismic analysis of the coastal Mecklenburg Bay (North German Basin): the pre-Alpine evolution

The pre-Alpine structural and geological evolution in the northern part of the North German Basin have been revealed on the basis of a very dense reflection seismic profile grid. The study area is situated in the coastal Mecklenburg Bay (Germany), part of the southwestern Baltic Sea. From the central part of the North German Basin to the northern basin margin in the Grimmen High area a series of high-resolution maps show the evolution from the base Zechstein to the Lower Jurassic. We present a map of basement faults affecting the pre-Zechstein. The pre-Alpine structural evolution of the region has been determined from digital mapping of post-Permian key horizons traced on the processed seismic time sections. The geological evolution of the North German Basin can be separated into four distinct periods in the Rerik study area. During Late Permian and Early Triassic evaporites and clastics were deposited. Salt movement was initiated after the deposition of the Middle Triassic Muschelkalk. Salt pillows, which were previously unmapped in the study area, are responsible for the creation of smaller subsidence centers and angular unconformities in the Late Triassic Keuper, especially in the vicinity of the fault-bounded Grimmen High. In this area, partly Lower Jurassic sediments overlie the Keuper unconformably. The change from extension to compression in the regional stress field remobilized the salt, leading to a major unconformity marked at the base of the Late Cretaceous.

40Ar/39Ar ages of detrital white mica constrain the Cenozoic development of the intracontinental Qaidam Basin, China

Ar/ 39 Ar dating of detrital white mica from Cenozoic sediments from the nonmarine Qaidam Basin in western China yields several age groups. These include (1) ca. 350– 450 Ma, (2) 220–280 Ma, subordinate clusters with (3) 122–140 Ma, and (4) a minor group ca. 500 Ma. Ages between 350 and 450 Ma are the most common and dominating in the analyzed samples. Detrital mica in the western Qaidam Basin can be of a northern (Altyn Mountains) and/ or a southern (Qimantagh–Kunlun Mountains) provenance. The main age group of 350–450 Ma is well known from intrusions in the Altyn Mountains, whereas the young ages (120–126 Ma) have been found within shear zones along the Central Kunlun and Altyn Tagh faults. However, hinterland sectors beyond the Altyn Tagh and Central Kunlun faults must be considered as potential source areas, because the imbalance between the amount of basin fi ll to eroded basement material requires additional sources. Early Paleozoic ages (ca. 500 Ma) have been documented so far only in the Hongliugou suture zone north of the Altyn Tagh fault. This suggests late or slow continuous uplift of the southern Altyn Range, and because of sinistral slip along the Altyn Tagh fault, further units of the same age are now exposed farther westward. The age group of 220–280 Ma has been documented only from the northern basin margin. This age group may indicate recycling from Triassic–Jurassic cover sequences of the Altyn Mountains or provenance from Permian–Triassic granite bodies that possibly originated in the Qilian Mountains.

Contrasting red bed diagenesis: the southern and northern margin of the Central European Basin

We compare the diagenetic evolution of deeply buried Rotliegend (Permian) red bed sandstones at the southern and northern margin of the Central European Basin (CEB) in Germany. Main target is to evaluate the influence of maturation products from hydrocarbon (HC) source rocks during red bed diagenesis. At the southern margin of the CEB, thick coal-bearing Carboniferous source rocks are omnipresent beneath the Rotliegend. They contain dominantly gas-prone terrigenous organic material and some oil source rocks. Hydrocarbons were generated from Late Carboniferous onwards throughout most of basin subsidence. At the northern margin of the CEB, source rocks are almost absent due to deep erosion of Carboniferous rocks and a low TOC of local Lower Carboniferous relics. Early diagenetic processes are comparable at both basin margins. Significant differences in burial diagenetic evolution are spatially correlated to the occurrence of hydrocarbon source rocks. Burial diagenesis at the southern margin of the CEB is characterized especially by bleaching of red beds, major dissolution events, pervasive illite formation, impregnation of pore surfaces with bitumen, and formation of late Fe-rich cements. Almost none of these features were detected at the northern basin margin. Instead, relatively early cements are preserved down to maximum burial depths. This suggests that major diagenetic mineral reactions in deeply buried red bed sandstones are controlled by the presence or absence of maturing hydrocarbon source rocks.

Record of palaeoenvironmental changes in a Lower Permian organic-rich lacustrine succession: Integrated sedimentological and geochemical study of the Rudník member, Krkonoše Piedmont Basin, Czech Republic

This study presents an integrated sedimentological and geochemical analysis of the Lower Permian Rudník member — the most extensive lacustrine deposits in the Krkonoše Piedmont Basin. Grey to black and variegated lacustrine mudstones, laminites and carbonates of the Rudník member have a lateral extent of more than 400 km 2. In the studied sections four facies associations were recognised: A) anoxic offshore, B) suboxic to oxic offshore, C) nearshore and mudflat, and D) slope deposits. In the northern part of the E–W elongated basin, anoxic to suboxic organic-rich offshore lacustrine facies dominate and form a succession up to 130 m thick. Fan-delta and turbidite facies occur locally along the faulted northern basin margin. The central part of the basin is occupied by anoxic to oxic offshore facies interfingering with nearshore carbonate and mudflat facies of the low-gradient lacustrine margin. In the central part of the basin, the thickness of the lacustrine deposits of the Rudník member reaches up to 60–70 m. In the southern part of the basin fluvial and alluvial plain facies dominate and alternate with minor lacustrine nearshore facies. The lateral facies distribution indicates that subsidence along the northern basin fault was the main mechanism generating the asymmetric infill geometry in the basin's half-graben setting. The δ 1 8O values of primary and early diagenetic calcite range between − 11.0‰ and + 1.3‰ (V-PDB) and δ 1 3C values between − 5.1‰ and + 3.7‰; most of the data fall within the range of freshwater limestones. Coarser-grained pure microspar laminae show more positive δ 1 3C values in comparison to clayey organic-rich micrite laminae, and are interpreted as a record of bioinduced precipitation during seasonal eutrophication. The obtained δ 1 3C TOC values range from − 29.0‰ to − 24.0‰, the total organic carbon (TOC) content from 0.26% to 23%. Maceral analysis and Rock-Eval pyrolysis indicate that most of the samples contain a mixture of aquatic and terrestrial organic matter, but two minor, distinctive groups of samples with algally-dominated and terrestrially-dominated organic matter composition, respectively, were also found. The study of vertical changes in boron content in the clay fraction of the lacustrine mudstones shows that high lake level stages were periods of lower salinity with the lowest boron contents (from 73 to 268 ppm), and periods of falling lake level were followed by significant increases in salinity with much higher boron values (293–603 ppm). Lake-level fluctuations of the Rudník lacustrine system, which are recorded by shallowing-up units of sedimentary facies within most of the sections throughout the basin, can also be traced within the monotonous black shale dominated sections, where no sedimentological evidence of these lake level changes exists. Good indicators for such changes seem to be the δ 1 8O and δ 1 3C values of primary calcite, δ 1 3C TOC and HI. These lake level fluctuations are interpreted as driven by climatic oscillations in the order of tens of thousands years, which could reflect climatic changes connected with the last glaciation event of Gondwana.

Sedimentology and provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains, Alaska: Bearings on the accretionary tectonic history of the Wrangellia composite terrane

Research Article| May 01, 2005 Sedimentology and provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains, Alaska: Bearings on the accretionary tectonic history of the Wrangellia composite terrane Jeffrey M. Tropaff; Jeffrey M. Tropaff 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Search for other works by this author on: GSW Google Scholar Darren A. Szuch; Darren A. Szuch 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Search for other works by this author on: GSW Google Scholar Matthew Rioux; Matthew Rioux 2Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Robert B. Blodgett Robert B. Blodgett 3U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Jeffrey M. Tropaff 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Darren A. Szuch 1Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA Matthew Rioux 2Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA Robert B. Blodgett 3U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508, USA Publisher: Geological Society of America Received: 24 Jan 2004 Revision Received: 30 Jun 2004 Accepted: 10 Sep 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2005) 117 (5-6): 570–588. https://doi.org/10.1130/B25575.1 Article history Received: 24 Jan 2004 Revision Received: 30 Jun 2004 Accepted: 10 Sep 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey M. Tropaff, Darren A. Szuch, Matthew Rioux, Robert B. Blodgett; Sedimentology and provenance of the Upper Jurassic Naknek Formation, Talkeetna Mountains, Alaska: Bearings on the accretionary tectonic history of the Wrangellia composite terrane. GSA Bulletin 2005;; 117 (5-6): 570–588. doi: https://doi.org/10.1130/B25575.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Analysis of the Upper Jurassic Naknek Formation in the Talkeetna Mountains, Alaska, documents synorogenic sedimentation in a forearc basin along the outboard (southern) margin of the allochthonous Peninsular terrane during accretion to the western North American continental margin. New geochronologic, sedimentologic, and compositional data define a two-part stratigraphy for the Naknek Formation. Microfossil, megafossil, and U-Pb clast ages document early Oxfordian to early Kimmeridgian deposition of the lower 690 m of the Naknek Formation and early Kimmeridgian to early Tithonian deposition of the upper 225 m of the Naknek Formation. Lithofacies and paleocurrent data from the lower Naknek Formation demonstrate initial deposition on a high-gradient, southward-dipping basin floor. Submarine mass flows deposited poorly sorted, cobbl-boulder conglomerate in proximal fan-delta environments. Gravelly mass flows transformed downslope into sandy turbidity currents on a muddy pro-delta slope. During early Kimmeridgian to early Tithonian time, fan-delta environments were replaced by lower gradient marine shelf environments characterized by deposition of cross-stratified sandstone and bioturbated mudstone. Sourc-diagnostic clasts, feldspathic sandstone compositions, southward-directed paleocurrent indicators, and U-Pb zircon ages of plutonic clasts (167.6 ± 0.3 Ma; 166.5 ± 0.2 Ma, 164–159 Ma, 156.2 ± 0.4 Ma) indicate that the Naknek Formation was derived primarily from volcanic and plutonic source terranes exposed along the northern basin margin in the southern Talkeetna Mountains. Geologic mapping documents the Little Oshetna fault, a newly identified northward-dipping reverse fault that bounds the northern margin of the Naknek Formation in the Talkeetna Mountains. The concentration of boulder-rich mass-flow deposits in the foot-wall of the fault in combination with geochronologic and compositional data suggest that sedimentation was coeval with Late Jurassic shortening along the fault and exhumation of plutonic source terranes exposed in the hanging wall of the fault. From a regional perspective, coars-grained forearc sedimentation and pluton exhumation along the outboard (southern) segment of the Peninsular terrane were coeval with crustal-scale shortening and synorogenic sedimentation in retroarc basins along the inboard (northern) margin of the Wrangellia terrane (Kahiltna, Nutzotin, and Wrangell Mountains basins). We interpret the regional and synchronous nature of Late Jurassic crustal-scale deformation and synorogenic sedimentation in south-central Alaska as reflecting either initial collision of the Wrangellia and Peninsular terranes with the former continental margin of western North America or amalgamation of the two terranes prior to collision. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Uppermost Cretaceous–Lower Tertiary Ulukışla Basin, south-central Turkey: sedimentary evolution of part of a unified basin complex within an evolving Neotethyan suture zone

The Ulukışla Basin, the southerly and best exposed of the Lower Tertiary Central Anatolian Basins, sheds light on one of the outstanding problems of the tectonic assembly of suture zones: how large deep-water basins can form within a zone of regional plate convergence. The oldest Ulukışla Basin sediments, of Maastrichtian age, transgressively overlie mélange and ophiolitic rocks that were emplaced southwards onto the Tauride microcontinent during the latest Cretaceous time. The Niğde-Kirşehir Massif forming the northern basin margin probably represents another rifted continental fragment that was surrounded by oceanic crust during Mesozoic time. The stratigraphic succession of the Ulukışla Basin begins with the deposition of shallow-marine carbonates of Maastrichtian–Early Palaeocene age, then passes upwards into slope-facies carbonates, with localised sedimentary breccias and channelised units, followed by deep-water clastic turbidites of Middle Palaeocene–Early Eocene age. This was followed by the extrusion of c. 2000 m of basic volcanic rocks during Early to Mid Eocene time. After volcanism ended, coral-bearing neritic carbonates and nummulitic shelf sediments accumulated along the northern and southern margins of the basin, respectively. Deposition of the Ulukışla Basin ended with gypsum deposits including turbidites, debris flows, and sabkhas, followed by a regional Oligocene unconformity. The Ulukışla Basin is interpreted as the result of extension (or transtension) coupled with subsidence and basic volcanism. After post-volcanic subsidence, the basin was terminated by regional convergence, culminating in thrusting and folding in Late Eocene time. Comparisons of the Ulukışla Basin with the adjacent central Anatolian basins (e.g. Tuzgölü, Sivas and Şarkişla) support the view that these basins formed parts of a regional transtensional (to extensional) basin system. In our preferred hypothesis, the Ulukışla Basin developed during an intermediate stage of continental collision, after steady-state subduction of oceanic crust had more or less ended (“soft collision”), but before the opposing Tauride and Eurasian continental units forcefully collided (“hard collision”). Late Eocene forceful collision terminated the basinal evolution and initiated uplift of the Taurus Mountains.