Foreland Uplift Research Articles

Microstructural characterization of natural fractures and faults in the Opalinus Clay: insights from a deep drilling campaign across central northern Switzerland

The Middle-Jurassic Opalinus Clay is the foreseen host rock for radioactive waste disposal in central northern Switzerland. An extensive drilling campaign aiming to characterize the argillaceous formation resulted in a comprehensive drill core data set. The rheologically weak Opalinus Clay is only mildly deformed compared to the over- and underlying rock units but shows a variety of natural fractures. While these structures are hydraulically indistinguishable from macroscopically non-deformed Opalinus Clay today, their analysis allows for a better understanding of the deformation behaviour in the geological past. Here, we present an overview of the different fracture and fault types recorded in the Opalinus Clay and a detailed microstructural characterization of veins—natural dilational fractures healed by secondary calcite and celestite mineralizations. Macroscopic drill core analysis revealed five different natural fracture types that encompass tension gashes of various orientations with respect to bedding and small-scale faults with displacements typically not exceeding the drill core diameter. The occurrence of different fault types generally fits well with the local tectonic setting of the different drilling sites and with respect to the neighbouring regional fault zones. The microstructural investigations of the various vein types revealed their often polyphase character. Fibrous bedding-parallel veins of presumable early age were found to be overprinted by secondary slickenfibres. The polyphase nature of fibrous bedding parallel veins and slickenfibres is supported by differing elemental compositions, pointing towards repeated fracturing and mineralization events. Direct dating of vein calcites with U–Pb was unsuccessful. Nevertheless, age constraints can be inferred from structural orientations and fault slip kinematics. Accordingly, some of the veins already formed during sediment compaction in Mesozoic times, others possibly relate to Early Cenozoic foreland uplift. The youngest veins are most likely related to Late Cenozoic regional tectonic events, such as the Jura fold-and-thrust belt to the south and the Hegau-Lake Constance Graben to the northeast of the study area. During these latest tectonic events, previously formed veins acted as rheologically stiff discontinuities in the otherwise comparably weak Opalinus Clay along which deformation of the rock formation was re-localized.

Petrography of quartz sandstone in Nanggulan formation at Sermo area, Kulon Progo Regency, Daerah Istimewa Yogyakarta, Indonesia: implications on provenance and basin origin

Provenance can be used to determine how the sedimentary rock formed, as reflected in the mineral composition of lithology as the composition of sedimentary minerals. The Research area is located in the Hargowilis area, Kokap district, Kulon Progo Regency, Daerah Istimewa Yogyakarta Province. This Study uses a surface geological mapping method supported by laboratory analysis in the form of petrographic analysis. Based on the analysis of the sandstone provenance in the study area, the results show the research area is included in the Recycled orogenic provenance zone, foreland uplift sub-zone to continental block provenance with a dominant quartz percentage (92%). The tectonic setting in the research area was controlled by an orogenous process during the Eocene showing that the analysis is very relevant to the provenance in the research area which shows the source of recycled rock due to the orogenous process which is then deposited in the basins formed as a result of the process.

Formation of overpressure system and its relationship with the distribution of large gas fields in typical foreland basins in central and western China

Based on the data of measured formation pressure, drilling fluid density of key exploration wells and calculated pressure by well logging, combined with the analysis of natural gas geological conditions, the characteristics and formation mechanisms of formation fluid overpressure systems in different foreland basins and the relationship between overpressure systems and large-scale gas accumulation are discussed. (1) The formation mechanisms of formation overpressure in different foreland basins are different. The formation mechanism of overpressure in the Kuqa foreland basin is mainly the overpressure sealing of plastic salt gypsum layer and hydrocarbon generation pressurization in deep–ultra-deep layers, that in the southern Junggar foreland basin is mainly hydrocarbon generation pressurization and under-compaction sealing, and that in the western Sichuan foreland basin is mainly hydrocarbon generation pressurization and paleo-fluid overpressure residual. (2) There are three common characteristics in foreland basins, i.e. superimposed development of multi-type overpressure and multi-layer overpressure, strong–extremely strong overpressure developed in a closed foreland thrust belt, and strong–extremely strong overpressure developed in a deep foreland uplift area. (3) There are four regional overpressure sealing and storage mechanisms, which play an important role in controlling large gas fields, such as the overpressure of plastic salt gypsum layer, the overpressure formed by hydrocarbon generation pressurization, the residual overpressure after Himalayan uplift and denudation, and the under-compaction overpressure. (4) Regional overpressure is an important guarantee for forming large gas fields, the sufficient gas source, large-scale reservoir and trap development in overpressure system are the basic conditions for forming large gas fields, and the overpressure system is conducive to forming deep to ultra-deep large gas fields.

PETROGRAFI KARAKTERISTIK BATUPASIR FORMASI GAMPING WUNGKAL IMPLIKASI UNTUK PROVENAN, DIAGENESIS, DAN PROSES PENGENDAPAN, FORMASI GAMPING WUNGKAL, KECAMATAN BAYAT, KABUPATEN KLATEN, PROVINSI JAWA TENGAH

Gamping Wungkal Formation, middle Eocene to Upper Eocene, which consists of sandstones, sandy marl, claystone and limestone which are the problems of provenance rock, diagenesis and its deposition process. Retrieval of stratigraphic data to determine the deposition process which is divided into several facies and determine its depositional environment, petrographic observations to determine the type of rock, provenance, tectonic settings. Interpretation of tectonic settings of sandstones Gamping Wungkal Formations on QFL diagram plots include recycled orogens, foreland uplift sub-zones while the plot in the QmFLt diagram of the provenance rock is the same as the QFL diagram, which is recycled orogen, sub-zone foreland uplift, rock model from recycled orogen foreland uplift sub-zone. The sandstone diagenesis of the Gamping Wungkal Formation in the study area is included in the mesodiagenesis stage where the compaction or burial process still dominates, the depositional environment in the study area is an area formed in the transitional environment or intertidal flat (Middle tidal flat) and subtidal (Lower tidal flat).

Chronology of deposition and unconformity development across the Cretaceous–Paleogene boundary, Magallanes-Austral Basin, Patagonian Andes

The Magallanes-Austral foreland basin preserves an important record of orogenesis and landscape evolution in the Patagonian Andes of Chile and Argentina. Throughout the retroarc foreland basin, a regional disconformity with little to no angular discordance separates Upper Cretaceous–lower Paleocene strata from overlying deposits of diachronous Eocene to Miocene age. Here we report detrital zircon U-Pb geochronological results for 11 sandstone samples, and vitrinite reflectance data for 6 samples of organic matter from a fossiliferous dinosaur-bearing mixed nonmarine and marine clastic succession in the Río de las Chinas valley (50–51°S) of central-southern Patagonia to: (1) determine the timing and duration of the unconformity using U-Pb maximum depositional age constraints, (2) reconstruct sediment provenance and dispersal patterns, (3) assess possible temporal variations in arc magmatism, (4) evaluate the amount of sedimentary overburden removed during unconformity development, and (5) confirm the presence of a fossiliferous southern hemisphere Cretaceous–Paleogene (K/Pg) boundary site. Samples from the Dorotea Formation yield maximum depositional ages spanning Maastrichtian to Danian time (with ages as young as ∼65–63 Ma), confirming preservation of the K/Pg boundary in a section with recently discovered fossils of dinosaurs, other terrestrial vertebrates, and plants. Samples from directly above the unconformity in the Man Aike Formation, yield middle Eocene maximum depositional ages (with a prominent 45–40 Ma age cluster), indicating a long-lived ∼20 Myr hiatus representative of nondeposition or erosion. Analyses of organic matter preserved in multiple coal horizons of the uppermost Dorotea Formation show consistently low vitrinite reflectance values, requiring limited sedimentary burial, consistent with nondeposition or sediment bypass rather than deposition and later erosional removal of a previously proposed thick package of Paleocene to middle Eocene clastic material. On the basis of regional trends in the age and geometry of the unconformity, timing of arc magmatism, and temporal variations in sediment provenance, we consider a range of potential mechanisms for unconformity genesis, including (1) shortening-related uplift of the frontal fold-thrust belt, (2) cratonward advance of a flexural forebulge, (3) accommodation changes driven by regional or eustatic variations in sea level, (4) ridge collision and slab-window genesis, (5) isostatic rebound during tectonic quiescence (or minor extension), or (6) regional foreland uplift during flat-slab subduction.

The Anglo-Brabant Massif: Persistent but enigmatic palaeo-relief at the heart of western Europe

The surface geology of central England and Belgium obscures a large ‘basement’ massif with a complex history and stronger crust and lithosphere than surrounding regions. The nucleus was forged by subduction-related magmatism at the Gondwana margin in Ediacaran time. Partitioning into a platform, in the English Midlands, and a basin stretching to Belgium, in the east, was already evident in Cambrian/earliest Ordovician time. The accretion of the Monian Composite Terrane during the Penobscotian deformation phase preceded late Tremadocian rifting, and Floian separation, of the Avalonia Terrane from the Gondwana margin. Late Ordovician magmatism in a belt from the Lake District to Belgium records subduction beneath Avalonia of part of the Tornquist Sea. This ‘Western Pacific-style’ oceanic basin closed in latest Ordovician time, uniting Avalonia and Baltica. Closure of the Iapetus Ocean in early Silurian time was soon followed by closure of the Rheic Ocean, recorded by subduction along the southern margin of the massif. The causes of late Caledonian deformation are poorly understood and controversial. Partitioned behaviour of the massif persisted into late Palaeozoic time. Late Devonian and Carboniferous sequences show strong onlap onto the massif, which was little affected by crustal extension. Compressional deformation during the Variscan Orogeny also appears slight, and was focussed in the west where a wedge-shaped mountain foreland uplift was driven by orogenic indentation, splitting the massif from the Welsh Massif along the reactivated Malvern Line. Permian to Mesozoic sequences exhibit persistent but variable degrees of onlap onto the massif.

Foreland uplift during flat subduction: Insights from the Peruvian Andes and Fitzcarrald Arch

Foreland deformation has long been associated with flat-slab subduction, but the precise mechanism linking these two processes remains unclear. One example of foreland deformation corresponding in space and time to flat subduction is the Fitzcarrald Arch, a broad NE-SW trending topographically high feature covering an area of >4 × 105 km2 in the Peruvian Andean foreland. Recent imaging of the southern segment of Peruvian flat slab shows that the shallowest part of the slab, which corresponds to the subducted Nazca Ridge northeast of the present intersection of the ridge and the Peruvian trench, extends up to and partly under the southwestern edge of the arch. Here, we evaluate models for the formation of this foreland arch and find that a basal-shear model is most consistent with observations. We calculate that ~5 km of lower crustal thickening would be sufficient to generate the arch's uplift since the late Miocene. This magnitude is consistent with prior observations of unusually thickened crust in the Andes immediately south of the subducted ridge that may also have been induced by flat subduction. This suggests that the Fitzcarrald Arch's formation by the Nazca Ridge may be one of the clearest examples of upper plate deformation induced through basal shear observed in a flat-slab subduction setting. We then explore the more general implications of our results for understanding deformation above flat slabs in the geologic past.

Tectonic control on deltaic sediment dispersal in the middle to upper Turonian Western Cordilleran Foreland Basin, USA

AbstractTectonic forcing of delta progradation is increasingly being invoked to explain stratal stacking patterns in foreland basins. Nonetheless, the recognition of different types of tectonic forcing and their consequences for the spatial and temporal distribution of accommodation often rely on incomplete data sets and indirect sequence stratigraphic criteria. Previous work has concluded that the Cenomanian–Turonian Frontier Formation of northern Utah, north‐west Colorado and south‐west Wyoming (‘Vernal Delta’) owes its origin largely to tectonic overprinting of depositional patterns, although the lack of a comprehensive sequence stratigraphic framework for the unit has hampered evaluation of this claim. This study provides detailed facies and sequence stratigraphic analyses based on outcrop sections and wireline log suites from the Uinta, Piceance and Green River basins. Four genetically related intervals were defined and mapped by using regionally traceable stratigraphic horizons (flooding surfaces and sequence boundaries). Internally, intervals are composed of distal and proximal delta front lithologies, and coastal plain facies. Overall, Intervals 1 to 4 form a major basinward projection of coarse clastic strata generated in response to four separate, high‐frequency regressions. Furthermore, a change through time from southward projection of elongate lobes (Intervals 1 and 2) to eastward dispersal and development of a broad, arcuate planform (Intervals 3 and 4) can be explained in terms of changes in prevailing tectonic forcing mechanisms. North–south trending Sevier Orogeny forebulge structures controlled Intervals 1 and 2. West–east progradation (Intervals 3 and 4) was probably controlled by Proterozoic basement lineament reactivation due to Laramide foreland uplifts. Therefore, this study provides direct geological evidence for the initiation of local Laramide deformation as early as 90 Ma. These findings contribute to a more complete understanding of tectonic forcing of coastal to shallow marine successions in foreland basins and the tectonic evolution of the western USA.

Kinematic evolution of the Patagonian retroarc fold-and-thrust belt and Magallanes foreland basin, Chile and Argentina, 51 30'S

The kinematic evolution of the Patagonian fold-and-thrust belt and cogenetic Magallanes retroarc foreland basin is reconstructed using new geologic mapping, two-dimensional (2-D) seismic-reflection data, and zircon U/Pb geochronology. Results span an ~160-km-wide transect of the thrust belt and Magallanes Basin near 51°30′S and highlight the influence of inherited extensional structures on basin paleogeography, syntectonic sedimentation, and Late Cretaceous–Neogene foreland shortening. South of 50°S, the Patagonian fold-and-thrust belt developed on oceanic and attenuated crust of the predecessor Late Jurassic Rocas Verdes rift basin, resulting in a collisional nature to early fold-and-thrust belt development and foreland sedimentation atop rifted South American crust. We identify six principal stages of development between Late Cretaceous and Neogene time. A palinspastic restoration indicates ~32–40 km (~19%–23%) of retroarc shortening following closure of the Rocas Verdes Basin and incipient growth of the thrust belt. More than half of the estimated crustal shortening occurred synchronously with the deep-water phase of Late Cretaceous foreland basin sedimentation. Subsequent deformation migrated into the foreland, accounting for ~12 km of shortening across the Cretaceous–early Miocene basin fill. Thick-skinned thrust faulting along multiple detachment levels in Paleozoic metamorphic basement resulted in –5 km of foreland uplift and exposure of preforeland basin deposits. The final phase of early Miocene deformation ca. 21–18 Ma may reflect enhanced coupling between the continental and oceanic lithospheres, causing foreland basement uplifts as the Chile Ridge spreading ridge approached the trench. We speculate that Neogene foreland shortening was accommodated by reactivation of Mesozoic normal faults zones and accounts for broad uplift of the Patagonian fold-and-thrust belt.

Accumulation Models of the Natural Gas in the Foreland Basins of China and their Physical Simulation Experiment

The paper chooses foreland basin as its research object. after summarizing the accumulation characteristics of the different phases and different parts of them, the common models of the whole foreland basin are given and the physical simulation experiments are carried out. It shows that the foreland basins experience three phases of evolution. Phase 1 is the period that the source rock and structure oil and gas traps form. Phase 2 is the period that multi-cycle reservoir and lithologic oil and gas pool form. phase 3 is the period that foreland uplift belt and fault anticline pool form. Then a foreland basins has three different belts including of thrust belt, foredeep and foreland slope belt, foreland uplift belt, and the belts have different accumulation models. With regard to the hydrocarbon accumulation period of the foreland basin, the thrust belt have precedence to other belt. foredeep and foreland slope belt forms the secondary pools. Foreland uplift belt accumulates hydrocarbon very quickly.

Quaternary history of the piedmont reach of Río Diamante, Argentina

The Río Diamante is located in a segment of the southern Central Andes that is transitional in terms of morphology and foreland tectonics (33–37°S). The piedmont reach of the river flows eastwards between the main mountain front and the San Rafael Block (the southernmost foreland uplift to the east of the southern Central Andes). Unlike adjacent rivers, the Río Diamante has incised into pre-Quaternary bedrock to form a deep canyon across the piedmont. Five fill and strath terraces were mapped, correlated, and surveyed along the ∼35 km piedmont reach to determine their paleo-long profiles. Chronological data for the terraces were provided by geochemical correlation of interbedded tephras to a previously dated ignimbrite, as well as by eight cosmogenic 10Be ages, and suggest a synchronous relationship between fill terrace deposition and glaciation upstream. Terraces are tentatively correlated with oxygen isotope stages 16 (Qt1), 12 (Qt2), 4 (Qt3) and 2 (Qt4 and Qt5). Minor spatial variation in incision along the reach is apparent from the long profile of the Qt2 strath (∼450 ka), which shows low-amplitude folding. The long-term reach average rate of bedrock incision is estimated to be ∼0.1–0.5 m/kyr and the recent shorter term (post-OIS 2) rate is estimated at ∼2 m/kyr. Mid and late Quaternary uplift of the piedmont area is a likely cause for the incision; however, other possible explanations include a delayed response to pre-mid Quaternary uplift, or a response to changes in climate and sediment supply on a tectonically stable portion of the piedmont flanked by subsiding basins. Base-level fall due to subsidence on the eastern side of the San Rafael Block creating a westward migrating knickzone may have contributed to the incision, but the depth of incision is greater than the observed subsidence and no major knickzone is present in the modern river profile of the study reach. Studies such as this on piedmont geomorphic processes are important for understanding the topographic and tectonic transitions that characterise the southern Central Andes.

Distinguishing fault reactivation from flexural deformation in the distal stratigraphy of the Peripheral Blountian Foreland Basin, southern Appalachians, USA

AbstractReactivation of intraplate structures and weak zones within the foreland lithosphere disrupt the modelled geometry and pattern of migration of the flexural wave in foreland basins. In the southern Appalachians (USA), the Middle Ordovician unconformity, irregular Middle Ordovician distal foreland deposition and backstepping of Middle–lower Upper Ordovician carbonate strata have been related to migration of the flexural wave. However, integration of stratigraphy, tectonic subsidence history and composition of palinspastically restored distal foreland strata, using a map of subsurface basement structures as reference, allows us to distinguish an early event of inversion from two events of flexural migration. Sections restoring at very short distances outside the boundaries of a former basement graben have the youngest passive‐margin strata preserved beneath Middle Ordovician (∼466 Ma) peritidal to deep lagoonal carbonates with gravel‐size chert clasts. In contrast, sections restoring inside the graben record >470 m of truncation of pre‐Middle Ordovician passive‐margin strata, late onset of deposition (∼456 Ma), and subaerial features in carbonate and siliciclastic strata. The lacuna geometry and early patterns of distal foreland uplift and carbonate deposition indicate that inversion of a basement graben in response to Middle Ordovician convergence, rather than a migrating or semi‐fixed forebulge, was the primary control on the early evolution of the distal foreland. Drowning of the carbonate platform in more proximal settings, northeastward onset of deposition on upthrown blocks, and thick accumulation of carbonates in downthrown blocks record northwestward and northeastward flexural wave migration at the Middle–Late Ordovician boundary. In early Late Ordovician, the overall shoaling of carbonate and siliciclastic depocentres and the rise of tectonic subsidence curves indicate hinterlandward migration of flexural uplift. Both events of flexural migration were accompanied by influx of volcanic ash and synorogenic sediments.

ABSTRACT: Subduction Geometry and Volcanic Activity in the Andes: Key to Understanding Thick-skinned Foreland Uplifts and Changes in Foreland Basin Sequence Stratigraphy

ABSTRACT: Subduction Geometry and Volcanic Activity in the Andes: Key to Understanding Thick-skinned Foreland Uplifts and Changes in Foreland Basin Sequence Stratigraphy

Stratigraphic base level and fluvial architecture: Ericson Sandstone (Campanian), Rock Springs Uplift, SW Wyoming, USA

The concept of stratigraphic base level, or the ratio between accommodation and sediment supply (A/S ratio), has been used to analyse the Rusty and Canyon Creek Members of the Campanian Ericson Sandstone in the Rock Springs Uplift, SW Wyoming, USA. The Ericson Sandstone was deposited under fluvial to estuarine conditions in a foreland basin setting influenced both by Sevier‐style (thrust belt) tectonism and by more local, Laramide‐style, foreland uplifts. The depositional setting was situated several tens to a few hundred kilometres from the nearest shoreline. Therefore, sea level change at the contemporaneous shoreline probably had little, if any, influence on the development of the sedimentary architecture.The Rusty Member shows an alternation between incised valleys filled by multi‐storey estuarine channel sandstones showing palaeoflow to the south and delta plain sediments with single‐storey channels with no evidence of tidal influence, which show palaeoflow to the east. This cyclicity is interpreted as recording repeated uplift of the Wind River Range to the north, causing valley incision and reduction of the A/S ratio. During quiescent periods, the A/S ratio increased allowing the valleys to fill and delta plain conditions to be subsequently re‐established because of increased sediment supply from the thrust belt in the west.A regional unconformity at the base of the Canyon Creek Member truncates the Rusty Member, and represents a significant reduction of the A/S ratio caused by Laramide tectonic uplift. The Canyon Creek Member is a multi‐storey, multi‐lateral fluvial channel sandstone, where channel preservation and thickness increase upwards, suggesting an increase of the A/S ratio. The Canyon Creek Member channels are interpreted to have been sinuous, meandering channels from the observed sedimentary structures and fill patterns, despite their sand‐rich nature. It is argued that grain size is a poor indicator of channel planform, and that there was very low preservation potential for fine material because of a relatively low A/S ratio.The top of the Canyon Creek Member is a regionally correlative surface marking an abrupt increase of the A/S ratio. This surface is termed an expansion surface, denoting an abrupt increase in accommodation. The overlying Almond Formation shows a single‐storey alluvial architecture with a very high preservation of fine‐grained material. An assumed correspondence in time of the Late Absaroka thrust phase in the Sevier belt to the west and the formation of the sharp top of the Canyon Creek Member suggests that the thrust phase caused a basin‐wide abrupt increase of subsidence that changed the alluvial architecture.As an alternative to sequence stratigraphic nomenclature defined for strata controlled by shoreline movements, a scheme relating systems tracts and surfaces to changes in stratigraphic base level is proposed. Such a scheme is useful where correlations to shoreline strata are ambiguous or cannot be made, or where tectonics and climate are important controls.

Geology and Mineral Deposits of the New World District, Park County, Montana

ABSTRACT Five gold-copper-silver deposits have been identified in the New World mining district, located near Cooke City in Park County, Montana (Figs. 1,3). The Como, Fisher Mountain, McLaren, Miller Creek, and Homestake deposits formed largely by replacement of Cambrian limestone adjacent to Tertiary intrusive complexes and within a breccia pipe. In total these deposits contain more than 12 million tons of geologic reserves that have average grades of 0.222 ounces per ton (opt) Au, 0.87 opt Ag, and 0.75 pet Cu. The New World district, is a major intrusive center of Eocene age. It is compositionally and temporally related to the Absaroka-Gallatin volcanic field of northwestern Wyoming and south-central Montana (Chadwick, 1970). The area is located within the Beartooth block, a large foreland uplift of Archean granitic gneisses in south-central Montana and northwestern Wyoming. The Cooke City area is one of several intrusive centers along the Cooke City zone, a prominent northwest-trending lineament and structural low (Foose et al., 1961) within the Beartooth uplift Other intrusive centers, each of which have associated historic mining districts, along the Cooke City zone are the Sunlight Mining Region in Wyoming and the Horseshoe Mountain, Independence (Cowles), and Mill Creek-Emigrant areas in Montana.

Marathon Foreland Uplifts and Flexure of Adjacent Basinal Areas, Permian Basin, Texas and New Mexico

Marathon Foreland Uplifts and Flexure of Adjacent Basinal Areas, Permian Basin, Texas and New Mexico

Thrust belt development in the central Apennines (Italy): Northward polarity of thrusting and out‐of‐sequence deformations in the Gran Sasso Chain

The Lazio‐Abruzzi carbonate platform overrides the outermost sectors of the foreland fold and thrust belt of the central Apennines of Italy along an arcuate thrust front, which swings from E‐W to NNW‐SSE orientation. The E‐W striking, north verging thrust faults of the Gran Sasso cut in their footwall the N‐S oriented, east verging imbricates of the Marche thrust belt and the adjacent Adriatic foredeep. Our field mapping of the Gran Sasso imbricate system shows an array of six major thrust faults crosscutting each other in such a way that oblique propagation of higher thrust faults across the preexisting thrust sheets causes rethrusting of earlier imbricated units, decapitation of previous folds, and superposition of younger on older beds. Deformation in the Gran Sasso thrust belt mainly occurred between Messinian and middle Pliocene times and is partly synchronous with the development of the Marche thrust belt, thus implying that shortening resulted from a complex combination of northward and eastward propagating thrust systems. Increasing west to east shortening along the Gran Sasso thrust front indicates large, differential anticlockwise rotation by decoupling along a N‐S transpressive right‐lateral shear zone. This mechanism could have been induced by the Maiella foreland uplift, acting as a buttress against which the Lazio‐Abruzzi carbonate platform was stacked and forced to rotate anticlockwise, with consequent shortening by out‐of‐sequence thrust propagation.

Kinematic history of a foreland uplift from Paleocene synorogenic conglomerate, Beartooth Range, Wyoming and Montana

An integrated structural, sedimentological, and provenance study of the upper Paleocene Beartooth Conglomerate along the eastern flank of the Beartooth Range in Montana and Wyoming yields new information about Laramide tectonics in the northern Rocky Mountain foreland and has implications for models of fault-propagation folding and the development of synorogenic basins in thrust-faulted terranes. During the Laramide orogeny, the Beartooth Conglomerate was deposited by alluvial fans and a coarse braided fluvial system along the eastern flank of the range in response to displacement on the Beartooth fault, a 30°-35° west-dipping thrust fault that places Precambrian rocks on Paleozoic and Mesozoic cover rocks. Displacement along the Beartooth fault produced a large fault-propagation fold (Berg's fold-thrust) that eventually was transected by the fault along the entire eastern flank of the range. Lithologic provenance modeling indicates that the Beartooth Conglomerate was produced by unroofing of the Upper Cretaceous through Precambrian section of the eastern Beartooth Range. The model results indicate that source-area relief during deposition of the lower part of the Beartooth Conglomerate was relatively low (∼600 m) while the soft, mudstone-dominated Upper Cretaceous part of the source section was being eroded from the crest of the uplift. Coarse, alluvial-fan accumulation commenced when resistant Paleozoic carbonate and quartz-arenitic rocks were exposed and source-area relief increased to ∼1,400 m. Relief steadily diminished thenceforth to ∼600-800 m, as the upper part of the source section was eroded from the Beartooth Range, leaving only a resistant carapace of Paleozoic carbonate rocks and Precambrian crystalline rocks. Source-area relief was controlled both by bedrock composition of the source terrane and by individual episodes of uplift. Like many thrust-derived conglomerates, the Beartooth Conglomerate contains intraformational, syndepositional folds, faults, and angular unconformities that can be used with provenance modeling to define the kinematics of uplift during conglomerate deposition. By utilizing the results of our provenance modeling and the orientations of the basal and intraformational angular unconformities, we have been able to retrodeform stepwise an area-balanced cross section through the eastern Beartooth uplift. Retrodeformation of the cross section indicates that 3.8 km of uplift occurred before deposition of the oldest part of the proximal Beartooth Conglomerate. Further uplift of ∼1.7 km and total horizontal shortening of ∼3.7 km accompanied ∼1.3 km of displacement on the Beartooth fault. Cross sections indicate that additional uplift of ∼1 km and horizontal shortening of ∼2 km accompanied displacement on the Line Creek fault. Our data indicate that during the early stages of uplift by fault-propagation folding, sediment derived from the uplift bypassed the proximal realm and was deposited in distal settings. Bypassing occurred because the eventual footwall of the Beartooth fault was uplifted during fault-propagation folding. Viewed from this perspective, the early fine-grained fills of many Laramide basins may owe their existence to a combination of fine-grained source material and sediment bypassing during the early stages of Laramide uplifts.

Seismic and Structural Expression of Rocky Mountain Foreland Uplift Overhangs Incorporating New Data from 1980's Drilling Activity.: ABSTRACT

Seismic and Structural Expression of Rocky Mountain Foreland Uplift Overhangs Incorporating New Data from 1980's Drilling Activity.: ABSTRACT

Geometry and Kinematics of Thrust System Within Central Snowcrest Range: A Major Rocky Mountain Foreland Uplift and Exploration Target in Southwest Montana: ABSTRACT

The Snowcrest Range forms the southeastern limb of the Late Cretaceous, northeast-trending, southeast-verging Blacktail-Snowcrest uplift. Field mapping and regional balanced cross sections indicate the Snowcrest thrust system consists of two master thrust faults (Snowcrest and sub-Snowcrest thrusts), each involving a system of subsidiary thrust imbricates, splays, and shear zones. East of the Snowcrest Range, the Gravelly Range thrusts are attributed to this system as regional splays. The Snowcrest thrust dips approximately 39/degrees/NW and forms the western boundary of large-scale, uprift, and overturned folds within Phanerozoic rocks above the sub-Snowcrest (Greenhorn) thrust. The sub-Snowcrest thrust is buried beneath or within the synorogenic deposit of the Beaverhead group and is inferred to merge with the Snowcrest thrust in Precambrian basement rocks at depth. Small-scale structures indicate a significant component of right-lateral oblique slip occurred on the sub-Snowcrest thrust system along the central and southern portions of the range. Preliminary strain data indicate that the principal shortening was directed east-southeast.