Conglomeratic Sediments Research Articles

Submarine volcanic activity and giant amygdale formation along the Panama island arc as a precursor to 6000-year-old agate exploitation on Pedro González Island

AbstractAn extensive deposit of agate occurs in Pedro González Island in the Gulf of Panama. Previous archaeological research showed that the agate was exploited between 6200 and 5600 cal BP to make stone tools found at the oldest known Preceramic human settlement in the Pearl Island archipelago. We constrain here the origin and geological context of the agate through a geological and geochemical study of the island. We show that it includes primary volcanic breccias, lavas, and tuffaceous marine deposits with sedimentary conglomerates and debris flow deposits, which we define as the Pedro González Formation. This formation records submarine to subaerial volcanic activity along an island arc during the Oligo-Miocene, confirming previous regional models that favour progressive emergence of the isthmus in the early Miocene. The igneous rocks have an extreme tholeiitic character that is interpreted to reflect magmatic cessation in eastern Panama during the early Miocene. The agate is hosted in andesitic lavas in unusually large amygdales up to 20–40 cm in diameter, as well as small amygdales (0.1–1.0 cm) in a bimodal distribution, and in veins. The large size of the agates made them suitable for tool manufacture. Field evidence suggests that the formation of large amygdales resulted from subaqueous lava–sediment interaction, in which water released from unconsolidated tuffaceous deposits at the base of lava flows rose through the lavas, coalesced, and accumulated below the chilled lava top, with subsequent hydrothermal mineralization. These amygdales could therefore be regarded as an unusual result of combined peperitic and hydrothermal processes.

Utilizing borehole electrical image and conventional logs to characterize petrology of mixed volcanic and sedimentary rocks in Jiamuhe Formation at JL2 Wellfield, Zhongguai Uplift, Junggar Basin, NW China

Lower Permian Jiamuhe Formation of JL2 Wellfield, Zhongguai Uplift, Junggar Basin, was constituted by mixed volcanic and sedimentary rocks. The rock types were various, and it is difficult to characterize the petrology just relying on limited cores in oil-bearing intervals. Based on core photos, petrological characteristics were synthetically interpreted using borehole electrical image and conventional logs in this paper. Six types of common volcanic rocks (rhyolite, dacite, andesite, basalt, tuff, and breccia) and three types of clastic sedimentary rocks (conglomerate, sand, and silt-clay) were represented by borehole electrical image log and conventional natural gamma ray (GR), resistivity (RT), neutron (CNL), and bulk density (DEN) logs. Two special volcanic textures, pillow structure and natural fracture, were also described in electrical images. Serial cross-plots in pairs of four conventional logs were formed to distinguish typical rocks, and the distinction between volcanic breccias and sedimentary conglomerates was analyzed in electrical images. Borehole electrical image and conventional logs can be efficiently used to supplement coring and petrological information, which provides important insights on the paleogeology of mixed volcanic and sedimentary rocks in Jiamuhe Formation at JL2 Wellfield.

Ries impact crater sedimentary conglomerates: Sedimentary particle 'impact pre-processing', transport distances and provenance, and implications for Gale crater conglomerates, Mars

Terrestrial impact cratering events produce anomalous rock fragmentation and alteration, and form sedimentary basins that are out of equilibrium with the local geomorphological environment. Assessement of their initial deposits, crater erosion and infilling, lacustrine environments and biology can provide important insights into similar features on Mars. Here we report on fluviodeltaic conglomerates associated with the 26 km diameter Miocene Ries impact structure (target: sediments overlying crystalline basement) with respect to shock features, grain size distribution, roundness, and potential parent rocks (provenance). The poorly sorted conglomerates form coarsening-upwards cycles associated with a delta-mouth bar system, with subangular to subrounded pebbles derived from crystalline rock impact breccia deposits. Pebbles comprise a wide range of lithologies and states ranging from fresh and solid to intensively impact-fractured, friable crystalline rocks, including shatter cones. Shocked quartz grains, however, are restricted to the sand fraction. The latter observation points to suevite as an additional, but subordinate source of the conglomerates. Granulometric analysis indicates that, in contrast to being derived from weathering of bedrock, impact brecciation of the parent crystalline rocks generated the initial grain size distribution of the conglomerates (i.e., preprocessing). This concept of “impact preprocessing” helped to defne the provenance, the post-impact sedimentologic history and the sediment transport distances of the conglomerates. Post-impact fluvial transport leads to the outwash of fine fractions into the prodelta subenvironment, and an increase in roundness and mean diameter in the residual conglomerates (i.e. hydraulic sorting). On the basis of the characteristics of the ejecta deposits and the present-day locations and occurrences of crystalline rock impact breccias and blocks in the northwestern Ries crater segment analyzed, a transport distance of less than 3.5 km is derived for these impact-preprocessed conglomerates. Reconstruction of the initial distribution and composition of the primary ejecta layer indicates that the conglomerates composed solely of crystalline rock had a maximum transport distance less than 6.5 km, i.e., within the closed basin of the Ries impact structure. In contrast to traditional interpretations of conglomerates, requiring long transport distances from bedrock source regions to deposition to ensure sufficient rounding and sorting, the rounding and sorting associated with these short transport distances are explained by preprocessing of parent rocks by impact brecciation and enhanced susceptibility to abrasion. Consequently, transport distances of conglomeratic fragments associated with impact craters, such as Gale crater on Mars, are likely to have been only a few kilometers, and derived from nearby ejecta, most likely from the inner crater walls. This Ries crater-based preprocessing and transport model implies that the unusual Gale crater conglomeratic fragments are likely to represent the immediate target material excavated by the Gale cratering event, rather than fragments transported laterally from greater distances outside the crater.

19 瀬戸内および山陰中新統の礫質堆積物からみた中期中新世古地理(地域地質)

19 瀬戸内および山陰中新統の礫質堆積物からみた中期中新世古地理(地域地質)

A-Differential Synthetic Aperture Radar Interferometry analysis of a Deep Seated Gravitational Slope Deformation occurring at Bisaccia (Italy)

This paper presents the results of an investigation on a Deep Seated Gravitational Slope Deformation (DSGSD), previously only hypothesized by some authors, affecting Bisaccia, a small town located in Campania region, Italy. The study was conducted through the integration of conventional methods (geological-geomorphological field survey, air-photo interpretation) and an Advanced-Differential Interferometry Synthetic Aperture Radar (A-DInSAR) technique. The DSGSD involves a brittle lithotype (conglomerates of the Ariano Irpino Supersynthem) resting over a Structurally Complex Formation (Varycoloured Clays of Calaggio Formation). At Bisaccia, probably as a consequence of post-cyclic recompression phenomena triggered by reiterated seismic actions, the rigid plate made up of conglomeratic sediments resulted to be split in five portions, showing different rates of displacements, whose deformations are in the order of some centimeter/year, thus inducing severe damage to the urban settlement.A-DInSAR techniques confirmed to be a reliable tool in monitoring slow-moving landslides. In this case 96 ENVIronmental SATellite-Advanced Synthetic Aperture Radar (ENVISAT-ASAR) images, in ascending and descending orbits, have been processed using SUBSOFT software, developed by the Remote Sensing Laboratory (RSLab) group from the Universitat Politècnica de Catalunya (UPC). The DInSAR results, coupled with field survey, supported the analysis of the instability mechanism and confirmed the historical record of the movements already available for the town.

Martian Fluvial Conglomerates at Gale Crater

Observations by the Mars Science Laboratory Mast Camera (Mastcam) in Gale crater reveal isolated outcrops of cemented pebbles (2 to 40 millimeters in diameter) and sand grains with textures typical of fluvial sedimentary conglomerates. Rounded pebbles in the conglomerates indicate substantial fluvial abrasion. ChemCam emission spectra at one outcrop show a predominantly feldspathic composition, consistent with minimal aqueous alteration of sediments. Sediment was mobilized in ancient water flows that likely exceeded the threshold conditions (depth 0.03 to 0.9 meter, average velocity 0.20 to 0.75 meter per second) required to transport the pebbles. Climate conditions at the time sediment was transported must have differed substantially from the cold, hyper-arid modern environment to permit aqueous flows across several kilometers.

Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory

The Mars Science Laboratory spacecraft, containing the Curiosity rover, was launched to Mars on 26 November 2011, and for most of the 253-day, 560-million-kilometer cruise to Mars, the Radiation Assessment Detector made detailed measurements of the energetic particle radiation environment inside the spacecraft. These data provide insights into the radiation hazards that would be associated with a human mission to Mars. We report measurements of the radiation dose, dose equivalent, and linear energy transfer spectra. The dose equivalent for even the shortest round-trip with current propulsion systems and comparable shielding is found to be 0.66 ± 0.12 sievert.

Luminescence of diamonds from metamorphic rocks

This study explores the effects of metamorphism on luminescence of diamond. Four diamond suites extracted from metamorphic rocks were characterized using optical cathodoluminescence, FTIR spectroscopy, photoluminescence at the liquid nitrogen temperature, and cathodoluminescence spectroscopy. The studied diamonds are from sedimentary conglomerate and lamprophyric breccia metamorphosed to the greenschist facies (Wawa, Canada), and from the ultrahigh-pressure (UHP) terranes of Kokchetav (Kazakhstan) and Erzgebirge (Germany). The majority of studied diamonds that experienced metamorphism have distinct cathodoluminescence and photoluminescence when compared to diamonds from unmetamorphosed rocks, i.e., kimberlites or placers. Diamonds in metamorphic rocks do not show the prevalent blue cathodoluminescence emittance at 415–440 and 480–490 nm typical of common kimberlite and placer diamonds. Ultrahigh-pressure diamonds are mostly non-luminescent, whereas diamonds from greenschists display green, yellow, orange, and red cathodoluminescent colors emitting light at 520 and 576 nm, and between 586 and 664 nm. The shift of cathodoluminescence in octahedrally grown Type Ia diamonds metamorphosed in the greenschist facies results from the presence of optical centers with zero-phonon lines at 575 and 637 nm detected via photoluminescence spectroscopy. The centers may have formed due to irradiation of diamonds in the upper crust followed by annealing at T > 500 °C. This process creates vacancies that diffuse through the diamond lattice and get trapped at N sites, creating NV o and NV − optical centers. The distinct luminescence of metamorphosed diamonds can persist for billions of years in the crust, but is annealed in the mantle.

Phreatomagmatic boulder conglomerates at the tip of the ca 2772 Ma Black Range dolerite dyke, Pilbara Craton, Western Australia

Unusual volcanic conglomerates with a mixture of well-rounded granitic boulders (to 1.2 m diameter) derived from adjacent basement rocks, and smaller (1 – 10 cm) subspherical basaltic droplets with chilled margins occupy a linear zone along strike of the northern end of the Late Archaean Black Range dolerite dyke in the Pilbara Craton, Western Australia. The matrix of the volcanic conglomerates becomes more angular with decreasing grainsize and grades to rock flour, a trend opposite to that in sedimentary conglomerates. In other places, the matrix consists of chlorite that cuts through, and resorbs, granitic clasts, indicating an origin as volcanic melt. The volcanic conglomerates have peperitic contacts with immediately adjacent flows of the Mt Roe Basalt of the Fortescue Group. A welded volcanic tuff at the peperitic contact is dated at 2767 ± 3 Ma, within error of the 2772 ± 2 Ma Black Range dolerite dyke and the Mt Roe Basalt (2775 ± 10 Ma), confirming the contemporaneity of formation of these geological elements. Subsequent normal faulting has juxtaposed the higher level conglomerates down into their present exposure level along strike of the Black Range dolerite dyke. The linear zone of volcanic conglomerates is interpreted to represent a phreatomagmatic pebble dyke that formed immediately above, and as a result of intrusion of, the Black Range dolerite dyke. Interaction of magma with groundwater caused phreatomagmatic brecciation of the country rock, in situ milling of granitic boulders, incorporation of basaltic melt droplets, and the formation of a mixed matrix of devitrified volcanic glass and granitic material. This process was accompanied by along-strike epithermal Cu – Hg – Au mineralisation.

Very high resolution seismic investigation of the sedimentary infill of the Leucate lagoon (Aude and Pyrénées-Orientales – SE France)

Abstract A very high resolution seismic investigation has for the first time allowed the imaging of the sedimentary infill of a Mediterranean lagoon. The Leucate lagoon is part of a lagoon system located along the shore of the western Gulf of Lions, from the Rhone delta to the Spanish border. These lagoons are separated and protected from the sea by sandy barriers, also called lidos, which are the result of a process of shore regularization by waves. The seismic data, obtained by using a boomer-Seistec, coupled with lithological and radiocarbon data [Martin, 1978] previously collected from cores, have revealed three main sedimentary formations : The basal formation represents the substratum of the lagoon and the middle and upper formations its infill. The basal formation displays a very uniform seismic facies with reflectors almost constantly dipping towards the sea. It comprises conglomeratic sediments and is interpreted as a progradating fluvio-deltaïc formation. Its upper surface is erosional and is locally deeply incised. In the shallowest parts of the lagoon, where the basal formation almost emerges, its upper part is reworked by modern processes into multiple cut-and-fill structures. The middle formation overlaps the basal formation, and constitutes the main depositional unit of the lagoon fill (up to 20 ms twtt thick). The seismic facies are variable and correspond to sand and clay sediments deposited under fluvio-lagoonal to lagoonal and marine conditions. The upper formation represents the upper part of the infill. It rests above the middle formation through a conformable surface, locally slightly erosional, and overlaps the basal formation along the western rim and in the shallowest parts of the basin. The thickness of this upper formation does not exceed 3mst wtt. It mainly consists of clay sediments of lagoonal origin. The main characteristic of this upper formation is a thin sole of very dense sand at the base. This bed is also a remarkable seismic reflector, and is interpreted as resulting from the maximum marine flooding of the system. This occurs before the beginning of the barrier construction, and the progressive closure of the lagoon. Another remarkable aspect of the upper formation is the simultaneity of its basal part with the lido construction. In this upper unit, the seismic data allow the imaging of the lateral passing between the planar bedded sediments of the infill, with the sigmoidal beds representing washover fans that construct the lagoonal side of the lido. The uppermost part of the formation represents the final and present-day stage of the lagoonal infill since the final closure by the barrier. Dating, performed on cored sediments, allow the sediments of the basal formation to be assigned to the Middle Pleistocene (with no more precision). The erosion of the top of the basal formation is interpreted as fluvial incision during the last sea level fall. The lagoon infilling is of Holocene age and comprises two stages : the first and main stage corresponds to fluvio- to marino-lagoonal sedimentation, and occurred before 6,000 B.P. The second corresponds to the recent to modern infilling that began around 4,000 B.P. with the construction of the lido and the closure of the lagoon. The two stages are clearly separated by a period of maximum marine flooding. The thickness of the lagoon fill is relatively limited, probably no more than 20 m.

Stratigraphy of the Fungurume Group - evolving foreland basin succession in the Lufilian fold-thrust belt, Neoproterozoic-Lower Palaeozoic, Democratic Republic of Congo

The Lufilian arc (Neoproterozoic-Lower Palaeozoic) is a Pan-African orogen that lies between the Kalahari Craton in the south and the Congo Craton in the north. North vergent thrusting of its Katangan metasedimentary succession formed a fold-thrust belt in the northern sector of the arc. The belt contains prominent bodies of fragmental rocks including thrust sheets and megablocks of older Katangan strata, some of which contain Cu-Co mineralisation. These fragmental rocks were traditionally considered as tectonic friction breccias formed underneath the advancing Katangan nappes. This paper presents the stratigraphic implications of a recent reinterpretation of these breccias as sedimentary conglomerates in the fold-thrust belt of the Lufilian arc. The Katangan succession in Zambia and the Democratic Republic of Congo (DRC) is traditionally subdivided into four main lithostratigraphic units: Roan, Mwashya, Lower Kundelungu and Upper Kundelungu. It has been considered that that the Roan, Mwashya and Lower Kundelungu strata were deposited in a progressively opening rift basin, then folded and thrust northwards during Upper Kundelungu times. No syntectonic sedimentation associated with this orogenesis was previously recognised. Megabreccias within the Kundelungu succession in the northern part of the fold-thrust belt are interpreted here to be sedimentary complexes of synorogenic conglomerates derived from the orogenic front advancing from the south and deposited in a newly recognised foreland basin to the north. The sedimentary origin means that the ‘megabreccias’ should be classified as new lithostratigraphic units of the Katangan succession. The Fungurume Group (new unit), which unconformably overlies older strata, represents foreland basin fill and is subdivided into three formations. The Mutoshi Formation is characterised by continental red beds, previously called RAT. A facies association of hematite-rich, marginal marine, mixed clastic and carbonate rocks constitutes the Dipeta Formation. The Kambove Formation comprises olistostromes deposited by subaqueous sediment-gravity flows. The Mutoshi and Dipeta Formations were previously correlated with the rift-related Roan Group of Zambia. The Cu-Co-bearing Roan-derived strata, traditionally called the Mines Group, occur only as allochthonous blocks embedded in any of the above formations. Therefore, the Mines Group does not form a legitimate lithostratigraphic unit, and it is excluded herein from the revised stratigraphy of the Katanga Supergroup. The undeformed continental molasse of the Plateau Group fills the youngest foreland basin, extending ahead of the fold-thrust belt.

Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China

The continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that overlie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 814 ±12 Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Formation. This age is younger than previously reported values of 921–933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: (1) Lower Neoproterozoic strata (814–1000 Ma) are missing in the studied area; (2) the Nanhua rift system was initiated at about 820 Ma; and (3) an age of ∼820 Ma may be taken as the lower boundary timing of the Nanhua System (even Neoproterozoic) in South China.

Taking the roof off a suture zone: basin setting and provenance of conglomerates in the ORS Dingle Basin of SW Ireland

Abstract The Late Silurian to Mid-Devonian Dingle Basin occupies a central position within the Iapetus Suture Zone of SW Ireland. The basin is believed to have formed from late Silurian times onwards as a product of sinistral transpression along several major faults within this suture zone. Conglomeratic sediments were deposited by moderately large gravelly fans shed into the basin from the NW (Glashabeg Formation) and the SE (Trabeg Conglomerate Formation). The systems fed into a large apparently through-going sandy, axial river (Slea Head Formation) that flowed towards the NE. The lateral, basin-margin systems were sourced from two disparate source terranes. To the NW lay a basic volcanic hinterland with some intermediate volcanic rocks and limestones, mudstones, sandstones and chert. During the Early Devonian time the SE drainage basin was underlain by sandstones, quartzites, phyllites and limestones probably intruded by a granite. Some of these lithologies can be found in outcrop in the pre-Dingle Group of the peninsula. Others need to be correlated with rocks of the oceanic terranes in the northern part of the suture zone. The southerly derived clasts have corollaries in the rocks of the Avalonian Leinster Terrane south of the suture. Following partial inversion of the Dingle Basin, the southerly hinterland was apparently further unroofed during mid-Devonian time, when the Inch Conglomerate Formation was deposited by alluvial fans shed northwards from a source area formed along the Dingle Bay Lineament. The Inch conglomerates are characterized by distinctive clasts of schist, gneiss, mylonite, tourmalinite and granite. The general picture of the Early Devonian deformation, intrusion by granite and unroofing of terranes currently partially exposed in central and southern Ireland within the Iapetus Suture Zone is largely consistent with clast lithotypes. However, some exploratory isotopic data indicate at least two possible vagaries in the interpretation. First, model ND T DM ages of Trabeg sedimentary clasts yield several results older than typical southern Iapetean or Avalonian crustal material. This suggests a complex history of sedimentary mixing of material across the developing Iapetus Ocean. Second, two of three Rb-Sr muscovite-whole-rock dates of Inch metamorphic clasts indicate Silurian ages. These data similar to Rb-Sr dates derived from the Carnsore and Saltees granites in the Rosslare Terrane, perhaps extending the geographical spread of this Silurian deformation.

方解石含有率に着目した大深度堆積れき岩の物性に関する検討

方解石含有率に着目した大深度堆積れき岩の物性に関する検討

供試体を用いた大深度堆積れき岩物性の分類の試み

供試体を用いた大深度堆積れき岩物性の分類の試み

Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming

The Harebell Formation is a syntectonic sequence of conglomeratic sediments deposited in a narrow, rapidly subsiding trough that formed in the latest Cretaceous along the eastern margin of the ancestral uplift of what are today the Teton and Gros Ventre Mountains of northwestern Wyoming. On at least two occasions subsidence temporarily exceeded the rate of sediment supply and the area was flooded by a brackish or marine incursion from the Western Interior Seaway that lay to the east. The age of the Harebell Formation is Maastrichtian, corroborated by 4 0K/ 4 0Ar isotopic ages, vertebrate and palynomorph biostratigraphy, and a preliminary magnetostratigraphic analysis which correlates it to the geomagnetic reversal time scale from the upper part of C31R to the base of C30N. Sandstone slabs collected from the lower Whetstone Falls Member contain nine partial and complete footprints attributable to a theropod (Dinosauria: Saurischia). The footprints were formed as surface tracks in the tabular-bedded sandstone by dinosaurs that roamed the burrowed and leaf-littered sand flats and shallow waters along the margins of a low-energy, brackish-water embayment. Eight of the nine footprints represent a hitherto unknown ichnogenus, representing a four-toed pedal morphology for a theropod dinosaur which is unprecedented in the Late Cretaceous. The theropod nature of the tracks is implied by the length and narrowness of the digits and the sharp claw impressions. The tracks have clearly defined impressions of four toes, none of which appears to be a hallux in the traditional theropod sense of a small, retroverted hallux. The metapodial impression is also unlike that of other known theropod tracks: greater in relief than the digits but quite small in area. The tracks represent at least two individuals, although no clear trackways are available. Exallopus lovei, gen. et sp. nov., represents a type of theropod not currently recognized from body fossils.

Sedimentology of two fan-delta systems in the Pliocene-Pleistocene of the Mesaoria Basin, Cyprus

Two fan-delta systems have been recognised in the Pliocene-Pleistocene deposits of the Mesaoria Basin, an asymmetrical half-graben located on the northern side of the Troodos ophiolite, Cyprus. The older fan-delta system, the Pliocene Nicosia Formation, was deposited when the Mesaoria Basin was actively subsiding. It comprises a number of small, isolated fan deltas which built across a narrow ( < 5 km), steep, fault-controlled, largely submerged basin margin. The preserved marine facies of this fan-delta system are confined to channels cut into the basin margin, and are dominated by marine conglomeratic, mass-flow deposits. In contrast, the much thinner ( < 20 m), younger (Late Pliocene-Pleistocene) fan-delta system of the Kakkaristra Formation was deposited when basin subsidence had virtually ceased and the Mesaoria seaway had filled to become a shallow, sandy platform. This renewed fan-delta sedimentation was initiated by uplift of the Troodos ophiolitic massif. In response to uplift, alluvial systems built northwards and coalesced at the coastline, giving rise to a large shelf fan delta that prograded into the basin. Conglomeratic sediments were largely trapped in subaerial and coastal areas, and were deposited by both mass-flow and traction-current processes. In addition, some gravel was redistributed along the shoreline by wave action. Coastal fan-delta deposition was terminated by renewed uplift of the Troodos Massif, initiating deposition of the Pleistocene fanglomerate unit.

The BMR regional seismic line across the Amadeus Basin, central Australia: implications for the tectonics of the Basin and for hydrocarbon exploration

In 1985 the Bureau of Mineral Resources undertook deep seismic reflection and refraction profiling experiments across the Early Proterozoic to Late Palaeozoic Amadeus Basin and Arunta Block in central Australia. The experiments were designed to test various models of intracratonic basin formation which involved tectonic interaction with the surrounding basement. The seismic reflection results show the thrust belt at the northern margin of the Amadeus Basin to be dominated by a major, south-directed, basement thrust feature, the Redbank Thrust Zone, which was imaged to mantle depths. Other, more southerly, basement-cored thrusts appear to splay southwards from the Redbank Thrust Zone towards the Amadeus Basin. The seismic reflection results support a 'thick-skinned' Laramide or Wind River style of overthrusting for the final compressive Late Devonian-Carboniferous event, the Alice Springs Orogeny. It was the accumulation of thick, synorogenic conglomeratic sediments in a foreland-like setting at the time of thrusting that appears to have been the dominant control on maturation of the underlying Early Ordovician source rocks. In contrast to the northern margin, in the central and southern parts of the Amadeus Basin, the seismic reflection results indicate north-directed, 'thin-skinned' overthrusting on shallow detachments that were accompanied by Jura-style box folding. The detachments sole out in a salt horizon near the base of the succession. Major repetition of part of the succession has occurred, particularly at the leading northern edge of the overthrust region. Basement involvement at the southern basin margin is enigmatic, but appears to involve both Late Proterozoic and Devonian-Carboniferous tectonism.

The origins of marine conglomerates in the Pindus foreland basin, Greece

Conglomeratic sediments in the Pindus foreland basin of western Greece record major sedimentary events and give important clues to aid the interpretation of the basin dynamics. The principal source of detritus lay to the southeast and east, in the adjacent Pindus thrust belt, although minor amounts of sediment were derived from a carbonate platform in the west. The topography of the basin floor was controlled by movement on thrusts propagating westward in advance of the mountain front. Locally, thrusts broke up-section to produce limestone-cored thrust culminations emergent above the basin-floor sediments. The topography over these structures locally formed intrabasinal sediment sources. Three major process-related classes of conglomerate are recognised in the basin: (a) clast-supported, polymict conglomerates interpreted as high-density turbidity current deposits with a similar source to widespread sandy turbidite deposits; (b) muddy, matrix-supported, polymict conglomerates representing resedimented material from the mountain front; (c) oligomict, clast-supported conglomerates derived locally from topographic highs within the basin. The debris flows and turbidites were triggered on the mountain front but followed different flow paths into the basin. The features described here are thought to be characteristic of gravity flow-dominated sedimentation in an active foreland basin.

Tectogenic Sedimentary Fill and Subsidence History of Hanna Basin, Southeastern Wyoming: ABSTRACT

The Hanna basin in southeastern Wyoming if unique because of its small size, and great depth, and extremely thick upper Cretaceous through Tertiary tectogenic sedimentary fill. The basin filled from the north, where proximal conglomeratic sediments were shed by the rising Sweetwater arch, and from the southwest, where more distal sandy sediments prograded into the basin. At the same time, vast coal deposits were accumulating in the center of the basin. Subsidence analysis, together with detailed stratigraphic and structural studies along the northern basin margin, show that the Hanna basin did not form as a flexural response to tectonic loading by the Shirley thrust. Constraints on potential mechanisms for Hanna basin evolution include (1) approximately 43,000 ft of basement offset adjacent to the Shirley thrust, (2) nearly 25,000 ft of basement relief adjacent to Simpson Ridge, (3) deposition of about 30,000 ft of Late Cretaceous through Tertiary tectogenic sedimentary fill, and (4) a pre-Shirley fault source for feldspathic sediments from the north. Their current modeling suggests that the present basin configuration is the result of at least three evolutionary phases: (1) initial uplift of the Sweetwater arch and associated downwarping of the adjacent syncline to the south, (2) breakup andmore » deepening of the synclinal depression, possibly by basement-block rotation and associated extension, and (3) post-early Eocene compression that activated the Shirley thrust and molded the present structural configuration of the Hanna basin.« less