Search

A model has been developed for the daily variation in soil temperature at 5 cm depth, for use where both the minimum and maximum temperatures are known or can be estimated. The model is based on data from three Australian sites with minute-by-minute data over 3-7 years. The model uses two sine curves; one for the increase from minimum to maximum and another for the relatively rapid decrease in temperature immediately after the maximum. An exponential decay function is used for the slower decrease in temperature until the minimum is reached. The time of the minimum soil temperature is primarily determined by the time of sunrise and therefore varies depending on the day of the year, whereas the time of the maximum temperature is influenced primarily by the time of the middle of the day (midpoint between sunrise and sunset). The time of the transition point between the maximum and the next minimum is related to the time of sunset. Therefore, the model uses latitude, longitude, and the day of the year to determine the time of sunrise and sunset to adjust the shape of the temperature profile throughout the day. The model has been validated using 3-hourly soil temperature data for 35 other sites in Australia, with a correlation of 0.993 between actual 3-hourly temperatures and those predicted. Its use for degree-day calculations has been validated using hourly data from a site in Victoria, where the model's estimates of degree-days differ Additional keywords: daily temperature profile, air temperature., Introduction The development of plants (He et al. 2010), insects (Dallwitz 1984), and soil microbes (Uchida et al. 2010) is temperature-dependent and is often calculated using degree-days or similar units [...]

Soil temperatures are related to air temperature and rainfall on the current day and preceding days, and this can be expressed in a non-linear relationship to provide a weighted value for the effect of air temperature or rainfall based on days lag and soil depth. The weighted minimum and maximum air temperatures and weighted rainfall can then be combined with latitude and a seasonal function to estimate soil temperature at any depth in the range 5-100 cm. The model had a root mean square deviation of 1.21-1.85°C for minimum, average, and maximum soil temperature for all weather stations in Australia (mainland and Tasmania), except for maximum soil temperature at 5 and 10 cm, where the model was less precise (3.39° and 2.52°, respectively). Data for this analysis were obtained from 3240 Bureau of Meteorology weather stations throughout Australia and the proposed model was validated using 5-fold cross-validation., Introduction Soil temperature influences the rate of activity of biological processes, including plant growth (Hanson and Baker 1993), development of insects in the soil (Dallwitz and Wardhaugh 1984), microbial activity [...]

[1] Sedimentologic, provenance, oxygen isotope, and [.sup.40]Ar/[.sup.39]Ar results provide insights into late Cenozoic evolution of an extensional hinterland basin in the Peruvian Andes. The 5-6.5 km Cordillera Blanca composes the glaciated footwall of a low-angle normal fault parallel to active contractional structures in the Andean fold-thrust belt. The -200 km long, WSW dipping (19[degrees]-36[degrees]) Cordillera Blanca detachment fault accommodated > 12-15 km of dip-slip displacement, inducing subsidence of the hanging-wall supradetachment basin, which is filled by ~1300 m of conglomerate, sandstone, siltstone, and limited carbonate of the upper Miocene-Pliocene Lloclla Formation. Lithofacies associations are attributed to lacustrine fan-delta to proximal, stream-dominated alluvial fan sedimentation. Provenance data record footwall unroofing of Jurassic through Miocene volcanic and sedimentary rocks during NW directed, axial dispersal of sediment. Provenance data record the appearance of footwall-derived granite clasts from the upper Miocene Cordillera Blanca batholith and a change to transverse, WSW directed transport. Variations in the character and preservation of basin fill suggest along-strike propagation of the fault through time. Initial extension and subsidence is constrained to the latest Miocene by an 4[degrees]Ar/39Ar biotite age of 5.4 [+ or -] 0.1 Ma for a basal tuff in the Lloclla Formation. Estimation of paleolake water composition shows very negative [delta][sup.18](VSMOW) values (-13.6%0 to-18.2%o), indicating that high elevations comparable to modern were already attained in the Cordillera Blanca during earliest normal faulting and basin evolution. These results lend support to models suggesting that substantial shortening, crustal thickening, and surface uplift were necessary precursor conditions for the generation of the Cordillera Blanca detachment fault. Citation: Giovanni, M. K., B. K. Horton, C. N. Garzione, B. McNulty, and M. Grove (2010), Extensional basin evolution in the Cordillera Blanca, Peru: Stratigraphic and isotopic records of detachment faulting and orogenic collapse in the Andean hinterland, Tectonics, 29, TC6007, doi: 10.1029/2010TC002666.

Laser ablation--inductively coupled plasma--mass spectrometry (LA-ICP-MS) analyses of 29 samples from the Eastern Cordillera of Colombia reveal the origin of northern Andean basement and patterns of sedimentation during Paleozoic subsidence, Jurassic--Early Cretaceous extension, Late Cretaceous postrift subsidence, and Cenozoic shortening and foreland-basin evolution. U-Pb geochronological results indicate that presumed Precambrian basement is mainly a product of early Paleozoic magmatism (520-420 Ma) potentially linked to subduction and possible collision. Inherited zircons provide evidence for Mesoproterozoic tectonomagmatic events at 1200-1000 Ma during Grenville-age orogenesis. Detrital zircon U-Pb ages for Paleozoic strata show derivation from Andean basement, syndepositional magmatic sources (420-380 Ma), and distal sources of chiefly Mesoproterozoic basement (1650-900 Ma) in the Amazonian craton (Guyana shield) to the east or in possible continental terranes along the western margin of South America. Sedimentation during Jurassic--Early Cretaceous rifting is expressed in detrital zircon age spectra as Andean basement sources, recycled Paleozoic contributions, and igneous sources of Carboniferous--Permian (310-250 Ma) and Late Triassic--Early Jurassic (220-180 Ma) origin. Detrital zircon provenance during continued Cretaceous extension and postrift thermal subsidence recorded the elimination of Andean basement sources and increased influence of craton-derived drainage systems providing mainly Paleoproterozoic and Mesoproterozoic (2050-950 Ma) grains. By Eocene time, zircons from the Guyana shield (1850-1350 Ma) dominated the detrital signal in the easternmost Eastern Cordillera. In contrast, coeval Eocene deposits in the axial Eastern Cordillera contain Late Cretaceous--Paleocene (90-55 Ma), Jurassic (190-150 Ma), and limited Permian--Triassic (280-220 Ma) zircons recording initial uplift and exhumation of principally Mesozoic magmatic-arc rocks to the west in the Central Cordillera. Oligocene--Miocene sandstones of the proximal Llanos foreland basin document uplift-induced exhumation of the Eastern Cordillera fold-thrust belt and recycling of the Paleogene cover succession rich in both arc-derived detritus (dominantly 180-40 Ma) and shield-derived sediments (mostly 1850-950 Ma). Late Miocene--Pliocene erosion into the underlying Cretaceous section is evidenced by elimination of Mesozoic--Cenozoic zircons and increased proportions of 1650-900 Ma zircons emblematic of Cretaceous strata. doi: 10.1130/B30118.1

The upper Oligocene to lower Miocene Penas and Aranjuez formations are exposed in north-northwest--trending outcrop belts of the central Andean backthrust belt situated within the central Andean plateau along the boundary between the northern Altiplano and the Eastern Cordillera of Bolivia. Sedimentary lithofacies analyses indicate that these coarse-grained siliciclastic formations were deposited primarily in alluvial fan to braided fluvial environments. An upsection change from principally fine-grained sandstone to cobble conglomerate is consistent with increased proximity to the sediment source with time. Paleocurrent analyses reveal that flow was predominantly directed toward the west-southwest away from Cordillera Real, the elevated core of the Eastern Cordillera. Provenance data from conglomerate clast compositions and sandstone petrofacies suggest derivation from recycled quartz-rich metasedimentary and sedimentary rocks from the Paleozoic section in the Eastern Cordillera. The paleoflow orientations, sediment provenance, and increased proximity of the sediment source suggest that deposition of the Penas and Aranjuez formations was related to surface uplift of the Eastern Cordillera relative to the Altiplano. Growth strata observed in the Aranjuez Formarion further indicate that shortening was synchronous with deposition, probably in a hinterland basin. New [sup.40]Ar/[sup.39]Ar ages from a lowermost exposed igneous unit and interbedded ash-fall tuff beds in the Aranjuez and Penas formations show that synorogenic sedimentation and fold-thrust deformation in the frontal (west-southwestern) zone of the central Andean backthrust belt was concentrated during late Oligocene--early Miocene time. These age results are consistent with previous studies of east-derived sedimentation in the Altiplano and indicate regional uplift of the Eastern Cordillera at this time. Upsection trends in provenance data further suggest a progressively greater contribution from younger Paleozoic strata, possibly due to activation of new thrust faults during west-southwestward propagation of the backthrust belt toward the Altiplano. Such a progression of late Oligocene--early Miocene shortening along the Altiplano--Eastern Cordillera boundary likely reflects significant crustal thickening, potential isostatic uplift, and initial topographic expression of the eastern margin of the central Andean plateau. doi: 10.1130/B30129.1

[1] Apatite and zircon (U-Th)/He cooling ages are used to quantify the timing of exhumation associated with thrust faulting in the High Zagros fold-thrust belt. Single-grain cooling age data were collected from (1) Cambrian sandstone in various thrust sheets, (2) sandstone and basement clasts derived from structurally controlled salt plugs or fault-bounded slices, and (3) syntectonic Neogene siliciclastics strata. In the northwestern (Kuhrang) and central (Kuh-e Lajin) High Zagros, apatite (U-Th)/He (AHe) ages range from ~26.7 to ~0.38 Ma. Most cooling and exhumation occurred in the early to middle Miocene, constrained by AHe ages ~19-15 Ma from the High Zagros thrust sheet, localized faults, and reset cooling ages from Bakhtiyari deposits. In the southeastern High Zagros (Kuh-e Dinar), cooling occurred later with AHe ages ranging from ~16.5 to ~0.79 Ma. Here most cooling and exhumation occurred in the late Miocene, constrained by AHe ages ~12-8 Ma from the High Zagros fault, and exhumed Paleozoic clasts in synorogenic strata. Zircon (U-Th)/He (ZHe) ages from bedrock samples across the High Zagros are reflective of the precollisional thermal history. The preservation of precollisional ZHe ages limits the pre-Miocene maximum burial temperature of the exhumed strata to < 180 [degrees]C, and indicate < 7-9 km of maximum exhumation in the central Zagros. This study shows that thrust activity in the High Zagros and continental suturing along the Zagros suture was underway by at least 19 Ma, and initiated no later than latest Oligocene to early Miocene time (~23 Ma). Citation: Gavillot, Y., G. J. Axen, D. F. Stockli, B. K. Horton, and M. D. Fakhari (2010), Timing of thrust activity in the High Zagros fold-thrust belt, Iran, from (U-Th)/He thermochronometry, Tectonics, 29, TC4025, doi: 10.1029/2009TC002484.

The shortening history of the Andes is important for understanding retroarc deformation along convergent margins and forcing mechanisms of Cenozoic climate. However, the timing of uplift in the northern Andes is poorly constrained, with estimates ranging from Cretaceous to Pliocene. Detrital zircon U-Pb ages from the Middle Magdalena Valley Basin in Colombia reveal two provenance shifts during Cenozoic time. The first shift occurs between early and late Paleocene strata, where U-Pb results show a switch from Proterozoic-dominated to Phanerozoic-dominated age spectra. We attribute this change to uplift-related exhumation of the Central Cordillera. The second shift occurs between middle-late Eocene and late Oligocene strata, where increased Grenville ages and diminished Mesozoic ages can be linked to uplift of the Eastern Cordillera. Our results show that significant pre-Neogene deformation affected the northern Andes, underscoring the potential importance of Andean uplift on the dynamics of Paleogene climate. doi: 10.1130/G30775.1

Entertainment was modeled as a nested temporal process using ecological momentary assessments. In natural viewing conditions, participants watched a Super Bowl game on television and answered a brief questionnaire via the Internet at the beginning of commercial breaks. Multilevel data analytic techniques were employed to analyze the longitudinal data from these assessments. After controlling for individual differences, such as gender, fandom, and team support, affect played a critical role. Average positive affect, averaged over the course of the game, and situational positive affect during specific moments in the game had a significant impact on entertainment, suggesting a baseline level of entertainment that is associated with the ritual of watching the event and added situational entertainment that is tied to the events in the game. Interestingly, situational negative affect was also significant and seemed to work in concert with positive affect. Keywords: entertainment: audience response, affect: sports television; ecological momentary assessments; longitudinal analysis; multilevel analysis

[1] Oligocene-Miocene strata preserved in synclinal outcrop belts of the western Alborz Mountains record the onset of Arabia-Eurasia collision-related deformation in northern Iran. Two stratigraphic intervals, informally named the Gand Ab and Narijan units, represent a former basin system that existed in the Alborz. The Gand Ab unit is composed of marine lagoonal mudstones, fluvial and alluvial-fan clastic rocks, fossiliferous Rupelian to Burdigalian marine carbonates, and basalt flows yielding [sup.40]Ar/[39.sup.Ar] ages of 32.7 [+ or -] 0.3 and 32.9 [+ or -] 0.2 Ma. The Gand Ab unit is correlated with the Oligocene-lower Miocene Qom Formation of central Iran and is considered a product of thermal subsidence following Eocene extension. The Narijan unit unconformably overlies the Gand Ab unit and is composed of fluvial-lacustrine and alluvial fan sediments exhibiting contractional growth strata. We correlate the Narijan unit with the middle to upper Miocene Upper Red Formation of central Iran on the basis of lithofacies similarities, stratigraphic position, and an 8.74 [+ or -] 0.15 Ma microdiorite dike ([sup.40]Ar/[39.sup.Ar]) that intruded the basal strata. Deformation timing is constrained by crosscutting relationships and independent thermochronological data. The Parachan thrust system along the eastern edge of the ancestral Taleghan-Alamut basin is cut by dikes dated at 8.74 [+ or -] 0.15 Ma to 6.68 [+ or -] 0.07 Ma ([sup.40]Ar/[39.sup.Ar]). Subhorizontal gravels that unconformably overlie tightly folded and faulted Narijan strata are capped by 2.86 [+ or -] 0.83 Ma ([sup.40]Ar/[39.sup.Ar]) andesitic lava flows. These relationships suggest that Alborz deformation had migrated southward into the Taleghan-Alamut basin by late Miocene time and shifted to its present location along the active range front by late Pliocene time. Data presented here demonstrate that shortening in the western Alborz Mountains had started by late middle Miocene time. This estimate is consistent with recent thermochronological results that place the onset of rapid exhumation in the western Alborz at ~12 Ma. Moreover, nearly synchronous Miocene contraction in the Alborz, Zagros Mountains, Turkish-Iranian plateau, and Anatolia suggests that the Arabia-Eurasia collision affected a large region simultaneously, without a systematic outward progression of mountain building away from the collision zone. doi: 10.1029/2006TC002091.

[1] Structural mapping, [sup.40]Ar/[sup.39]Ar and fission track thermochronology, U-Pb geochronology, and basin analysis reveal rapid cooling during middle Eocene-late Oligocene and late Miocene--Pliocene exhumation in the central Andean plateau of Bolivia. In the 4-6 km high Cordillera Real, numerous granites and SW directed fold-thrust structures define the central Andean backthrust belt along the Altiplano--Eastern Cordillera boundary. U-Pb zircon analyses indicate Permo-Triassic granitic magmatism, with less extensive magmatism of late Oligocene age. Mapping reveals low magnitudes of slip (5 km depth. The ~26 Ma Quimsa Cruz granite postdated most thrust structures, suggesting that upper crustal shortening in the Cordillera Real had largely ceased by late Oligocene time. Results of [sup.40]Ar/[sup.39]Ar and fission track modeling help constrain the moderate to low-temperature (

Field mapping, geochronological analyses, and cross section construction reveal a protracted deformation history and a minimum of 61 km of Cenozoic NE-SW shortening (in present coordinates) across the Yushu-Nangqian thrust belt in northern Tibet. Cenozoic contraction started prior to 51 Ma and was followed first by northwest-striking right-slip faulting and later by northwest-striking left-slip faulting. Renewed NE-SW contraction is expressed by folding of Neogene strata and thrusting, which again was followed by northwest-striking left-slip faults. Late Neogene deformation is expressed by local north-striking normal faults. Shortening across the Yushu-Nangqian belt appears to be accommodated by thin-skinned thrusting, which raises the question of how the deformation was accommodated in the lower crustal levels. To resolve this problem, we perform geochemical analysis of igneous rocks dated as 51-49 and 38-37 Ma. The rocks exhibit geochemical signatures characteristic of subduction, which implies that coeval crustal thickening in northeastern Tibet was most likely induced by continental subduction. Keywords: Asia, China, Tibetan Plateau, thrust belts, strike-slip faults, syncollisional magmatism.

Newly released reflection seismic and borehole data, combined with sedimentological, provenance, and biostratigraphic data from Upper Cretaceous-Paleocene strata in the proximal part of the Cordilleran foreland-basin system in Utah, establish the nature of tectonic controls on stratigraphic sequences in the proximal to distal foreland basin. During Campanian time, coarse-grained sand and gravel were derived from the internally shortening Charleston-Nebo salient of the Sevier thrust belt. A rapid, regional Campanian progradational event in the distal foreland basin (>200 km from the thrust belt in Keywords: sequence stratigraphy, foreland basins, fold and thrust belts, progradation, Book Cliffs, Utah.

A >2.5.km-thick succession of Tertiary strata in the Eastern Cordillera of southern central Bolivia consists of predominantly fluvial and lacustrine deposits. The age of the base of the succession is middle Paleocene, and its upper part (which is erosionally truncated) is probably late Oligocene-early Miocene. The lower 50-130 m of the succession consists of interbedded fluvial sandstone and mudstone (including minor paleosols) of the Santa Lucia Formation. These strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the Santa Lucia Formation and lower part of the Impora Formation that may represent much of late Paleocene--Eocene time. Above the paleosol zone is a thin zone (~10 m) of lacustrine carbonate and clastic rocks in the uppermost Impora Formation, and this in turn is overlain by a >2000-m-thick, upward-coarsening succession of clastic fluvial deposits in the Cayara, Camargo, and Suticollo Formations. Paleocurrent data indicate that fluvial channels that deposited the Santa Lucia, Impora, and Cayara Formations flowed mainly westward, whereas channels responsible for the Camargo and Suticollo Formations flowed generally eastward. Modal sandstone petrographic data show a long-term evolution from subarkosic (during Santa Lucia deposition) to quartzarenitic (during Impora and Cayara deposition) to sublitharenitic (during Camargo and Suticolio deposition) compositions. We argue that the lithofacies and sediment-accumulation history of this succession are most consistent with deposition in an eastward-migrating foreland basin system. Critical to this interpretation is the zone of extreme stratigraphic condensation in the lower Impora Formation, the inferred upper Paleocene-Eocene part of the succession. The abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous, postrift thermal subsidence resulted in a gradual, continuous decay of early Tertiary sediment-accumulation rates. Stratigraphic condensation is, however, consistent with passage of the forebulge through the region, an interpretation that also can be reconciled with the record of foreland basin development in the Altiplano to the west and gross sediment accumulation patterns in the Subandean zone and modern foreland basin to the east. Simple flexural modeling and palinspastic reconstruction of the complete Cenozoic migration history of the foreland basin system suggest that ~1000 km of foreland lithosphere has been underthrust westward beneath the Andean orogenic belt at the latitude of southern Bolivia. The amount of middle and lower crust that would have been added to the Andean infrastructure is sufficient to explain the present crustal thicknesses in Bolivia. Keywords: Andes, foreland basins, foldthrust belts, Tertiary, sedimentology, sedimentary petrology.

Sedimentologic, stratigraphic, compositional, and structural data from four elongate basins (30 km long) in the Nangqian-Yushu region of east-central Tibet (near the headwaters of the Mekong and Yangtze Rivers) indicate non-marine sedimentation synchronous with Paleocene-Eocene northeast-southwest shortening. Sedimentation in the Nangqian, Niuguoda, Xialaxiu, and Shanglaxiu basins involved (1) mud and carbonate accumulation in offshore to nearshore lacustrine environments and (2) gravel and sand deposition in fan-delta to alluvial-fan environments localized near basin margins. Growth strata in both fine- and coarse--grained deposits, primarily in upper levels of basin fill, provide evidence for sedimentation contemporaneous with motion on fold-thrust structures. Provenance data collected from 25 measured stratigraphic sections, including >1500 paleocurrent measurements and >150 conglomerate compositional analyses, show that each basin was fed sediment from several directions by proximal source areas composed of Carboniferous-Triassic rocks. The source-area proximity and a stratigraphic variability among the basins suggest that each basin evolved independently and was filled by sediment derived from relatively small drainage networks ( Keywords: Asia, basin, China, fold-thrust belts, plateaus, Tibet.

A large volume of Tertiary synorogenic sediment accumulated on top of the Eastern Cordillera of southern Bolivia as the Andean orogenic wedge was shortened, thickened, and uplifted. Oligocene to upper Miocene strata were deposited in five basins that were separated by active, north-trending, fold-thrust structures of the then-frontal part of the orogenic wedge. These coarse-grained deposits recorded accumulation in the most proximal sector of the Andean foreland basin system, the wedge-top depozone. Analyses of depositional systems, sediment dispersal patterns, and clast provenance of 0.6-2.3-km-thick, Oligocene to upper Miocene wedge-top successions demonstrate that fault-propagation and fault-bend folds commonly isolated individual basins while serving as primary sediment sources. Growth strata which formed by progressive fold-limb rotation indicate thrust-fault displacement and related folding concurrent with deposition. Alluvial fans defined most basin margins, whereas braided streams or small lakes occupied basin axes. Diagnostic stratigraphic units confined to individual basins suggest that streams were rarely able to cut across growing folds to connect adjacent basins. Growth strata and crosscutting and onlapping relationships between contractional structures and wedge-top strata delineate the chronology of fold-thrust deformation in the Eastern Cordillera. Five new 40Ar/39Ar dates and previously published K-Ar dates, ranging from 30 to 8 Ma, define an Oligocene phase of west-vergent backthrusting followed by primarily east-vergent thrusting during Miocene time. Timing of displacement on two east-vergent thrusts is determined by 40Ar/39Ar ages of tuffs within adjacent growth strata sequences of the Tupiza Formation conglomerate (16.14 [+ or -] 0.06 Ma) and Oploca Formation (13.33 [+ or -] 0.15 Ma, 15.7 [+ or -] 2.4 Ma). These ages, combined with basin depositional histories, demonstrate synchronous and out-of-sequence thrust displacement during Miocene shortening. Upper-crustal contractional deformation and wedge-top deposition terminated in the Eastern Cordillera during late Miocene time as the thrust front propagated eastward into the Subandean Zone. Continued thrust-front migration produced the present-day configuration in which Eastern Cordillera wedge-top basins, originally developed above the toe of the orogenic wedge at relatively low elevations, are now >250 km west of the active thrust front and at [approximately]3 km elevation. The modern wedge-top depozone overlies the active frontal part of the orogenic wedge and consists of strata in thrust-bounded, Subandean Zone basins and sediment overlying blind structures beneath the westernmost Chaco Plain. In general, wedge-top deposits become highly susceptible to erosional recycling as the orogenic wedge propagates forward and the wedge surface is uplifted. Nevertheless, Eastern Cordillera wedge-top deposits have been preserved for [approximately]10-30 m.y. in southern Bolivia. Such long-term preservation may reflect the inability of drainage systems to remove sediment mass from this low-precipitation region of the central Andes. Retention of sediment mass within the orogenic belt may promote critical thrust-wedge conditions in which propagation of the thrust front is favored.

An analysis of the Miocene Horse Camp basin in the central Basin and Range province demonstrates that individual components of an extensional basin system may undergo initial subsidence and subsequent uplift and exhumation during extension. The Horse Camp basin developed during Miocene time above a westdipping detachment fault and between two east-striking accommodation faults. Growth strata indicate that the west-dipping detachment was active throughout basin filling. Lateral facies variations in alluvial-fan, fan-delta, and lacustrine deposits indicate that the eaststriking accommodation faults along the northern and southern basin margins bounded primary sediment source areas. During late Miocene time, the hanging-wall block of the detachment system was broken by the westdipping Railroad Valley normal fault, thereby inducing development of an extensional basin, Railroad Valley, in the newly formed hanging wall and uplift and exhumation of the older Horse Camp basin in the footwall. The total amount of exhumation during Neogene extension is calculated for a single range block, the northern Grant Range. Early exhumation is recorded by the detrital compositions of middle-late Miocene strata in the southern part of the Horse Camp basin. Provenance modeling indicates that approximately 1600 m of Mississippian to Silurian section was exhumed in the range during middle-late Miocene Horse Camp deposition. From late Miocene to Holocene time, both the northern Grant Range and Horse Camp basin were exhumed in the footwall of the Railroad Valley fault. A comparison between the currently exposed bedrock geology and calculated late Miocene exposure levels from the provenance model indicates that 1000-2000 m of Cambrian-Ordovician section must have been exposed in the range after late Miocene deposition in the Horse Camp basin. Modern alluvial fans in eastern Railroad Valley have drainage networks that contain exposures of the fill of the Horse Camp basin, indicating that older basin fill is being recycled into the modern extensional basin. Extensional basin systems having similar basinward shifts of the major fault system are particularly susceptible to uplift, exhumation, and erosional recycling, not unlike the structurally dismembered margins of foreland basin systems.

[1] Investigation of Cenozoic deformation, sediment accumulation, and provenance in the Eastern Cordillera of Bolivia at 17-21[degrees]S indicates major shortening (60-140 km) and foredeep development followed by limited internal shortening and intermontane basin development. Contrasting histories of shortening, deposition, sediment dispersal, and detrital composition distinguish a formerly extensive Paleogene foredeep exposed along an eastern belt of synclines from a zone of principally Neogene intermontane basins in the central Eastern Cordillera. New [sup.40]Ar/[sup.39]Ar ages of 25-17 Ma for interbedded tufts reveal latest Oligocene--early Miocene accumulation in intermontane basins at rates

Late Cretaceous large-volume pluton emplacement and accompanying volcanism within the evolving western Montana thrust wedge may have played important roles in determining the geometric and kinematic development of the thrust wedge, thereby influencing patterns of sediment dispersal and subsidence in the adjacent foreland basin. Intrusion of the Upper Cretaceous Boulder batholith and coeval eruption of the Elkhorn Mountains Volcanics were focused mainly at the trailing margin of the Lombard-Eldorado allochthon. The resultant thick (16-17 km) igneous culmination evolved over a relatively short interval (80-70 Ma), thickening the orogenic wedge to the point of supercritical taper and facilitating continued motion along the Lombard-Eldorado thrust system, thrust imbrication at the wedge toe, and forelandward translation of the Helena salient. Delivery of eroded volcaniclastic detritus from the thickened thrust wedge and accelerated basin subsidence due to thrust loading resulted in accumulation of a thick (4-5 km) sequence of Campanian-Maastrichtian volcaniclastic strata in the foreland basin (Livingston Group). The structural and sedimentological effects of this structural-magmatic culmination are similar to those of basement-cored culminations elsewhere in the Sevier orogen and to the Neogene central Andean orogenic wedge. Keywords: batholiths, plutons, Sevier orogenic belt, Montana, Andes.

The dynamic interplay of tectonics and climate has forced for advances in basin research. A study on Tibetan and Altiplano Puna plateaus by Edward Sobel and colleagues found that an arid climate and internal drainage could be necessary conditions for plateau growth. The different applications with regards to sedimentary research are discussed.

The hypothesis that the change in orogen width and variations in thrust belt geometry and kinematics in the central Andes are controlled by long-term erosional processes, is examined. A progressive eastward migration of thrusting in the thrust belt south of the bend, is interpreted to be due to long-term critical thrust-wedge conditions resulting from extremely low rates of denudation since mid-Miocene.