Adjoining Basins Research Articles

Morphometric evidences of neotectonic block movement in Yamuna Tear Zone of Outer Himalaya, India

The Himalayan Foreland fold-thrust belt have developed small to large basins all along its marginal part, which have evolved during the thrust sheet movement. These basins are bound by thrusts in the Outer Himalayan Belt (Siwalik Terrane) and are laterally restricted by a number of thrust splays, which appear as transverse faults on the surface. The present study is related to block movement in Sukh Rao basin which occupies a NW-SE trending synclinal trough south of Paonta Sahib in Sirmaur district of Himachal Pradesh, India. Sukh Rao is a tributary stream of Yamuna River and has a parallel disposition with other tributaries like Bata and Giri rivers, located in the north. All these streams, occupying intermontaine valleys, initially flow longitudinally from NW to SE and take a sharp bend towards south before joining the trunk stream. The southern water divide of Sukh Rao basin is marked by sharp crested Upper Siwalik rocks, which are dominantly conglomeratic in nature. The southern face of this water divide is drained by NE-SW trending Nimbuwala Khala and Chikan Khol transverse streams, which have encroached the adjoining Sukh Rao basin in response to the block movement and tilting. Interpretation of satellite imagery, supported by morphometric analysis, indicates that the tectonic blocks covering the area have moved, tilted and skewed sinistrally forcing the SE flowing Giri, Bata and Sukh Rao streams to take sharp southward trend along the segments of Yamuna Tear. The NE-SW trending syngenetic transverse faults (thrust splays) have induced stream piracy through fast erosion. The Nimbuwala Khala has completely pirated the upper part of Sukh Rao basin while the Chikan Khol has only nibbled part of the basin. With the present rate of erosion (dissection index 0.37), it is likely that Chikan Khol will follow suit of its predecessor Nimbuwala Khala.

Climatic versus halokinetic control on sedimentation in a dryland fluvial succession

AbstractFluvial systems and their preserved stratigraphic expression as the fill of evolving basins are controlled by multiple factors, which can vary both spatially and temporally, including prevailing climate, sediment provenance, localized changes in the rates of creation and infill of accommodation in response to subsidence, and diversion by surface topographic features. In basins that develop in response to halokinesis, mobilized salt tends to be displaced by sediment loading to create a series of rapidly subsiding mini‐basins, each separated by growing salt walls. The style and pattern of fluvial sedimentation governs the rate at which accommodation becomes filled, whereas the rate of growth of basin‐bounding salt walls governs whether an emergent surface topography will develop that has the potential to divert and modify fluvial drainage pathways and thereby dictate the resultant fluvial stratigraphic architecture. Discerning the relative roles played by halokinesis and other factors, such as climate‐driven variations in the rate and style of sediment supply, is far from straightforward. Diverse stratigraphic architectures present in temporally equivalent, neighbouring salt‐walled mini‐basins demonstrate the effectiveness of topographically elevated salt walls as agents that partition and guide fluvial pathways, and thereby control the loci of accumulation of fluvial successions in evolving mini‐basins: drainage pathways can be focused into a single mini‐basin to preserve a sand‐prone fill style, whilst leaving adjoining basins relatively sand‐starved. By contrast, over the evolutionary history of a suite of salt‐walled mini‐basins, region‐wide changes in fluvial style can be shown to have been driven by changes in palaeoclimate and sediment‐delivery style. The Triassic Moenkopi Formation of the south‐western USA represents the preserved expression of a dryland fluvial system that accumulated across a broad, low‐relief alluvial plain, in a regressive continental to paralic setting. Within south‐eastern Utah, the Moenkopi Formation accumulated in a series of actively subsiding salt‐walled mini‐basins, ongoing evolution of which exerted a significant control on the style of drainage and resultant pattern of stratigraphic accumulation. Drainage pathways developed axial (parallel) to salt walls, resulting in compartmentalized accumulation of strata whereby neighbouring mini‐basins record significant variations in sedimentary style at the same stratigraphic level. Despite the complexities created by halokinetic controls, the signature of climate‐driven sediment delivery can be deciphered from the preserved succession by comparison with the stratigraphic expression of part of the system that accumulated beyond the influence of halokinesis, and this approach can be used to demonstrate regional variations in climate‐controlled styles of sediment delivery.

Distributions and phylogeographic data of rheophilic freshwater fishes provide evidences on the geographic extension of a central-brazilian amazonian palaeoplateau in the area of the present day Pantanal Wetland

The analysis of the distribution patterns presented by examples of freshwater fishes restricted to headwater habitat: the anostomid Leporinus octomaculatus, the characins Jubiaba acanthogaster, Oligosarcus perdido, Moenkhausia cosmops, Knodus chapadae, Planaltina sp., the loricariid Hypostomus cochliodon, and the auchenipterid Centromochlus sp. provided evidences of a relatively recent shared history between the highlands of the upper rio Paraguay and adjoining upland drainage basins. Restricted to headwater of the uplands in the upper rio Paraguay and adjoining basins, these species provide biological evidence of the former extension of the central Brazilian plateau before the origin of the Pantanal Wetland. Disjunction took place due to an ecological barrier to these rheophilic taxa represented tectonic subsidence related to the origin of the Pantanal Wetland. Molecular analysis of Jubiaba acanthogaster revealed that the sample from the upper rio Xingu basin are the sister-group of a clade that includes samples from the upper rio Arinos (upper rio Tapajós) plus the upper rio Paraguay basin, supporting the assumption that the origin of the upper rio Paraguay basin causing vicariance between this basin and the upper rio Tapajós is the least vicariant event in the evolutionary history of the group.

Provenances of late Pliocene rare-metal-titanium placers in the Tamansky Peninsula

The comprehensive mineralogical analysis of the Taman nearshore Ti-Zr placers and their provenances in the adjoining late Pliocene sedimentation basin is presented. Taking into account paleogeographic reconstructions and contemporary mineral potential of sediments in the Sea of Azov, a contribution of specific feeding sources of terrigenous minerals to the formation of the late Pliocene placers have been estimated. These sources are crystalline and sedimentary rocks of the Caucasus, the southern Russian Plate, and the southeastern Ukrainian Shield (listed in the order of their contribution). The Miocene placers of the Stavropol Arch and Adygea Prominence, as well as the Cretaceous and younger placers of the Ukrainian Shield and the Voronezh Anteclise are suggested to be transitional reservoirs. Economic deposits are forecasted in the zone of paleostraits.

Upper Permian reef complex in the basinal facies of the Zechstein Limestone (Ca1), western Poland

Stromatolite and bryozoan build‐ups from the Werra Cycle (Zechstein) of the Southern Permian Basin of Europe meet all definitions given by various authors for reefs and they commonly occur at the shelf edge. In a few places, including western Poland, they are also recorded in the basinal facies. The main part of the reef is formed by fragmented bryozoan zoaria. The reef biota are a typical bryonoderm association indicating cool‐water and cold‐water environments. A characteristic feature is a large amount of fragmented skeletal remains lacking rigidity. The main part of the reefs is built of rudstones, and only stromatolitic crusts form massive constructions. Remarkable is the mechanism of the origin of clearly morphologically separated reef constructions from the remains of a relatively low potential of fossilization. Zones built of crushed remains dominate over parts representing massive constructions. The colonization of the substrate began very early, as indicated by the interbedding of breccia and bioclastic carbonates in the lowermost part of the Zechstein Limestone in some reef sections. The Zechstein Limestone reefs of western Poland abound in the hemispheroid (botryoid) aragonitic cement that is otherwise common for the Zechstein reefs. The abundance of the cement recorded in Permian reefs is interpreted as the result of an unusually high saturation state of surface seawater because of a number of factors, including prolific carbonate precipitation due to the occasional upwelling of warmer saline waters on shelf environments in the stratified Zechstein Basin. The pervasive carbonate precipitation in the reef area contrasts with a restricted carbonate precipitation in the adjoining basin where very thin sequences have accumulated. Copyright © 2012 John Wiley & Sons, Ltd.

Certain Caddo Sites on Stone Chimney Creek, Cherokee County, Texas

Limited archaeological investigations coupled with private landowner’s surface collections on Stone Chimney Creek in northwestern Cherokee County, Texas has resulted in the recording of nine new Caddo sites, several of which appear to have been occupied after ca. A.D. 1650 in the Allen phase. The landowner had collected artifacts on his farm and contacted the Texas Historical Commission (THC) about getting information about them, who in turn contacted the author, a member of the Texas Archeological Stewardship Network. The landowner was interested in learning more about the native inhabitants who had once called this portion of Stone Chimney Creek home. Stone Chimney Creek originates in northern Cherokee County and flows in a southerly direction before joining the Neches River under present day Lake Palestine. The study area is some 4.8 km north of the confluence of Stone Chimney Creek and the Neches River. Stone Chimney Creek, in the study area, is deeply entrenched with a narrow floodplain and steep valley walls. Therefore, in the study area, there are no good alluvial settings for archaeological sites. Rather, archaeological sites are located on upland slopes or on top of upland landforms paralleling Stone Chimney Creek. Some of the site settings are unusual, being at the head of dry drainages and gullies, as they are in the adjoining Flat Creek basin and long distances (in terms of easy access to water) from Stone Chimney Creek proper. The soils in the study area are of the Nacogdoches series, which are the principal red soils in the Redlands section of East Texas. The iron and red pigments in these soils permeate everything: skin, clothing, the outside of houses, even artifacts. Depending on the degree of slope, soil layers and fertility vary across the study area; the steeper slopes are heavily eroded. Parent material is greensand marl or glauconitic sandy clay and clay. Certain locations in the study area have been mined of soil for construction purposes. There is evidence of old farming activities, such as farming terraces, but currently large portions of the study area have been cleared and developed for pasture. This land clearing and mining provided good surface visibility at certain sites, resulting in some large surface collections from those areas. Shovel tests were conducted at six of the recorded sites and a 1 x 1 m test unit was placed in a midden deposit at 41CE426. This article characterizes the work to date on these Stone Chimney Creek sites, focusing mainly on five sites with the largest surface collections. The article concludes with a discussion of the broader character and cultural affiliation of these sites with respect to the recently defined Upper Neches River cluster of Historic Caddo sites.

The Clovis Occupation of the Dietz Site (35LK1529), Lake County, Oregon, and its Bearing on the Adaptive Diversity of Clovis Foragers

Archaeological models of Clovis adaptations are divided between those that argue for a single hunting adaptation characterized by high residential mobility without fixed territories and those that argue for a diversity of environment-specific adaptations and settlement systems. The Dietz site (35LK1529), the largest Clovis site in the Pacific Northwest, is composed of many overlapping, spatially coherent artifact clusters from which 75 whole and fragmentary fluted points have been recovered. The artifact assemblage is inconsistent with use of the site as a kill, camp, or quarry site. Geoarchaeological data show that the site area during the Clovis occupation was a sparsely vegetated, seasonal playa that is unlikely to have supported large herds of game animals. However, the site sits astride what was probably a major transportation corridor linking highly productive ecosystems in the adjoining basins, and Clovis foragers appear to have camped at Dietz repeatedly while traveling between these nearby basins. The systematic and redundant use of a geographically small landscape by Clovis foragers is inconsistent with expectations based on a model of residentially mobile foragers occupying new territories.

Tsunami Simulations for Regional Sources in the South China and Adjoining Seas

We present 14 scenarios of potential tsunamis in the South China Sea and its adjoining basins, the Sulu and Sulawezi Seas. The sources consist of earthquake dislocations inspired by the the study of historical events, either recorded (since 1900) or described in historical documents going back to 1604. We consider worst-case scenarios, where the size of the earthquake is not limited by the largest known event, but merely by the dimension of the basin over which a coherent fault may propagate. While such scenarios are arguably improbable, they may not be impossible, and as such must be examined. For each scenario, we present a simulation of the tsunami’s propagation in the marine basin, exclusive of its interaction with the coastline. Our results show that the South China, Sulu and Sulawezi Seas make up three largely independent basins where tsunamis generated in one basin do not leak into another. Similarly, the Sunda arc provides an efficient barrier to tsunamis originating in the Indian Ocean. Furthermore, the shallow continental shelves in the Java Sea, the Gulf of Thailand and the western part of the South China Sea significantly dampen the amplitude of the waves. The eastern shores of the Malay Peninsula are threatened only by the greatest—and most improbable—of our sources, a mega-earthquake rupturing all of the Luzon Trench. We also consider two models of underwater landslides (which can be triggered by smaller events, even in an intraplate setting). These sources, for which there is both historical and geological evidence, could pose a significant threat to all shorelines in the region, including the Malay Peninsula.

The tidal and wind induced hydrodynamics of the composite system Adriatic Sea/Lagoon of Venice

A shallow water hydrostatic 2D hydrodynamic numerical model, based on the boundary conforming coordinate system, was used to simulate aspects of both general and small scale oceanic features occurring in the composite system constituted by the Adriatic Sea and the Lagoon of Venice (Italy), under the influence of tide and realistic atmospheric forcing. Due to a specific technique for the treatment of movable lateral boundaries, the model is able to simulate efficiently dry up and flooding processes within the lagoon. Firstly, a model calibration was performed by comparing the results of the model, forced using tides and ECMWF atmospheric pressure and wind fields, with observations collected for a set of 33 mareographic stations uniformly distributed in the Adriatic Sea and in the Lagoon of Venice. A second numerical experiment was then carried out by considering only the tidal forcing. Through a comparison between the results obtained in the two experiments it was possible to assess the reliability of the estimated parameter through the composite forcing. Model results were then verified by comparing simulated amplitude and phase of each tidal constituent as well as tidal velocities simulated at the inlets of the lagoon and in the Northern Adriatic Sea with the corresponding observed values. The model accurately reproduces the observed harmonics: mean amplitude differences rarely exceed 1 cm, while phase errors are commonly confined below 15°. Semidiurnal and diurnal currents were correctly reproduced in the northern basin and a good agreement was obtained with measurements carried out at the lagoon inlets. On this basis, the outcomes of the hydrodynamic model were analyzed in order to investigate: (i) small-scale coastal circulation features observed at the interface between the adjoining basins, which consist often of vortical dipoles connected with the tidal flow of Adriatic water entering and leaving the Lagoon of Venice and with along-shore current fields connected with specific wind patterns; (ii) residual oscillations, which are often connected to meteorological forcing over the basin. In particular, it emerges that small-scale vortical features generated near the lagoon inlet can be efficiently transported toward the open sea, thus contributing to the water exchange between the two marine regions, and a realistic representation of observed residual oscillations in the area would require a very detailed knowledge of atmospheric as well as remote oceanic forcing.

Can footwall unloading explain late Cenozoic uplift of the Sierra Nevada crest?

Globally, normal-fault displacement bends and warps rift flanks upwards, as adjoining basins drop downwards. Perhaps the most evident manifestations are the flanks of the East African Rift, which cuts across the otherwise minimally deformed continent. Flank uplift was explained by Vening Meinesz (1950, Institut Royal Colonial Belge, Bulletin des Séances, v. 21, p. 539–552), who recognized that isostasy should cause uplift of a normal-faulted footwall and subsidence of its hanging wall. Uplift occurs because slip on a dipping normal fault creates a broader root of less-dense material beneath the footwall, and a narrowed one beneath the hanging wall. In this paper, we investigate the potential influence of this process on the latest stages of Sierra Nevada uplift. Through theoretical calculations and 3D finite element modelling, we find that cumulative slip of about 4 km on range-front faults would have produced about 1.3 km peak isostatic uplift at the ridge crest. Numerical models suggest that the zone of uplift is narrow, with the width controlled by bending resistance of the seismogenic crust. We conclude that footwall unloading cannot account for the entire elevation of the Sierran crest above sea level, but if range-front faulting initiated in an already elevated plateau like the adjacent Basin and Range Province, then a hybrid model of pre-existing regional uplift and localized footwall unloading can account for the older and newer uplift phases suggested by the geologic record.

Climate controls on marine ecosystems and fish populations

This paper discusses large-scale climate variability for several marine ecosystems and suggests types of ecosystem responses to climate change. Our analysis of observations and model results for the Pacific and Atlantic Oceans concludes that most climate variability is accounted for by the combination of intermittent 1–2 year duration events, e.g. the cumulative effect of monthly weather anomalies or the more organized El Niño/La Niña, plus broad-band “red noise” intrinsic variability operating at decadal and longer timescales. While ocean processes such as heat storage and lags due to ocean circulation provide some multi-year memory to the climate system, basic understanding of the mechanisms resulting in observed large decadal variability is lacking and forces the adoption of a “stochastic or red noise” conceptual model of low frequency variability at the present time. Thus we conclude that decadal events with rapid shifts and major departures from climatic means will occur, but their timing cannot be forecast. The responses to climate by biological systems are diverse in character because intervening processes introduce a variety of amplifications, time lags, feedbacks, and non-linearities. Decadal ecosystem variability can involve a variety of climate to ecosystem transfer functions. These can be expected to convert red noise of the physical system to redder (lower frequency) noise of the biological response, but can also convert climatic red noise to more abrupt and discontinuous biological shifts, transient climatic disturbance to prolonged ecosystem recovery, and perhaps transient disturbance to sustained ecosystem regimes. All of these ecosystem response characteristics are likely to be active for at least some locations and time periods, leading to a mix of slow fluctuations, prolonged trends, and step-like changes in ecosystems and fish populations in response to climate change. Climate variables such as temperatures and winds can have strong teleconnections (large spatial covariability) within individual ocean basins, but between-basin teleconnections, and potential climate-driven biological synchrony over several decades, are usually much weaker and a highly intermittent function of the conditions prevailing at the time within the adjoining basins. As noted in the recent IPCC 4th Assessment Report, a warming trend of ocean surface layers and loss of regional sea ice is likely before 2030, due to addition of greenhouse gases. Combined with large continuing natural climate variability, this will stress ecosystems in ways that they have not encountered for at least 100s of years.

Rainfall and Water Resources Variability in Sub-Saharan Africa during the Twentieth Century

Abstract River basin rainfall series and extensive river flow records are used to characterize and improve understanding of spatial and temporal variability in sub-Saharan African water resources during the last century. Nine major international river basins were chosen for examination primarily for their extensive, good quality flow records. A range of statistical descriptors highlight the substantial variability in rainfall and river flows [e.g., differences in rainfall (flows) of up to −14% (−51%) between 1931–60 and 1961–90 in West Africa], the marked regional differences, and the modest intraregional differences. On decadal time scales, sub-Saharan Africa exhibits drying across the Sahel after the early 1970s, relative stability punctuated by extreme wet years in East Africa, and periodic behavior underlying high interannual variability in southern Africa. Central Africa shows very modest decadal variability, with some similarities to the Sahel in the adjoining basins. No consistent signals in rainfall and river flows emerge across the whole of the region. An analysis of rainfall–runoff relationships reveals varying behavior including strong but nonstationary relationships (particularly in West Africa); many basins with marked variations (temporal and spatial) in strength; weak, almost random behavior (particularly in southern Africa); and very few strong, temporally stable relationships. Twenty-year running correlations between rainfall and river flow tend to be higher during periods of greater rainfall station density; however, there are situations in which weak (strong) relationships exist even with reasonable (poor) station coverage. The authors conclude for sub-Saharan Africa that robust identification and attribution of hydrological change is severely limited by data availability, conflicting behavior across basins/regions, low signal-to-noise ratios, sometimes weak rainfall–runoff relationships, and limited quantification of the magnitude and effects of land use change.

Improved Reservoir Operation Using Hybrid Genetic Algorithm and Neurofuzzy Computing

A hybrid genetic and neurofuzzy computing algorithm was developed to enhance efficiency of water management for a multipurpose reservoir system. The genetic algorithm was applied to search for the optimal input combination of a neurofuzzy system. The optimal model structure is modified using the selection index (SI) criterion expressed as the weighted combination of normalized values of root mean square error (RMSE) and maximum absolute percentage of error (MAPE). The hybrid learning algorithm combines the gradient descent and the least-square methods to train the genetic-based neurofuzzy network by adjusting the parameters of the neurofuzzy system. The applicability of this modeling approach is demonstrated through an operational study of the Pasak Jolasid Reservoir in Pasak River Basin, Thailand. The optimal reservoir releases are determined based on the reservoir inflow, storage stage, sideflow, diversion flow from the adjoining basin, and the water demand. Reliability, vulnerability and resiliency are used as indicators to evaluate the model performance in meeting objectives of satisfying water demand and maximizing flood prevention. Results of the performance evaluation indicate that the releases predicted by the genetic-based neurofuzzy model gave higher reliability for water supply and flood protection compared to the actual operation, the releases based on simulation following the current rule curve, and the predicted releases based on other approaches such as the fuzzy rule-based model and the neurofuzzy model. Also the predicted releases based on the newly developed approach result in the lowest amount of deficit and spill indicating that the developed modeling approach would assist in improved operation of Pasak Jolasid Reservoir.

Identification of ‘extinct’ freshwater mussel species using DNA barcoding

Freshwater mollusks are highly imperiled, with 70% of the North American species extinct, endangered, or at risk of extinction. Impoundments and other human impacts on the Coosa River of Alabama, Georgia and Tennessee of the southeastern USA alone are believed to have caused 50 mollusk species extinctions, but uncertainty over boundaries among several putatively closely related species makes this number preliminary. Our examination of freshwater mussels collected during an extensive survey of the upper-drainage basin, DNA barcoding and molecular phylogenetic analyses confirm the rediscovery of four morphospecies in the genus Pleurobema (Unionidae) previously thought to be extinct from the upper Coosa basin. A fifth 'extinct' form was found in an adjoining basin. Molecular data show that the Coosa morphologies represent at least three species-level taxa: Pleurobema decisum, P. hanleyianum and P. stabile. Endemism is higher than currently recognized, both at the species level and for multispecies clades. Prompt conservation efforts may preserve some of these taxa and their ecosystem.

Upper crustal structure of the Tamworth Belt, New South Wales: constraints from new gravity data

New gravity data along five profiles across the western side of the southern New England Fold Belt and the adjoining Gunnedah Basin show the Namoi Gravity High over the Tamworth Belt and the Meandarra Gravity Ridge over the Gunnedah Basin. Forward modelling of gravity anomalies, combined with previous geological mapping and a seismic-reflection transect acquired by Geoscience Australia, has led to iterative testing of models of the crustal structure of the southern New England Fold Belt, which indicates that the gravity anomalies can generally be explained using the densities of the presently exposed rock units. The Namoi Gravity High over the Tamworth Belt results from the high density of the rocks of this belt that reflects the mafic volcanic source of the older sedimentary rocks in the Tamworth Belt, the burial metamorphism of the pre-Permian units and the presence of some mafic volcanic units. Modelling shows that the Woolomin Association, present immediately east of the Peel Fault and constituting the most western part of the Tablelands Complex, also has a relatively high density of 2.72 – 2.75 t/m3, and this unit also contributes to the Namoi Gravity High. The Tamworth Belt can be modelled with a configuration where the Tablelands Complex has been thrust over the Tamworth Belt along the Peel Fault that dips steeply to the east. The Tamworth Belt is thrust westward over the Sydney – Gunnedah Basin for 15 – 30 km on the Mooki Fault, which has a shallow dip (∼25°) to the east. The Meandarra Gravity Ridge in the Gunnedah Basin was modelled as a high-density volcanic rock unit with a density contrast of 0.25 t/m3 relative to the underlying rocks of the Lachlan Fold Belt. The modelled volcanic rock unit has a steep western margin, a gently tapering eastern margin and a thickness range of 4.5 – 6 km. These volcanic rocks are assumed to be Lower Permian and to be the western extension of the Permian Werrie Basalts that outcrop on the western edge of the Tamworth Belt and which have been argued to have formed in an extensional basin. Blind granitic plutons are inferred to occur near the Peel Fault along the central and the southern profiles.

Anatomy and emplacement mechanism of a large submarine slide within a Miocene foredeep in the northern Apennines, Italy: A field perspective

The Casaglia Monte della Colonna (CMC) body, from the middle Miocene Marnoso-arenacea Formation of the Northern Apennines, covering more than 350 square kilometers, provides a rare opportunity to study the geometry and the internal deformation of a large, basin-wide submarine landslide. Although the head zone of the landslide has not been preserved, the body has a transitional zone, a contractional ramp cutting off more than 200 meters of the footwall stratigraphic succession, and a very wide lobe spilling over onto the adjoining basin plain deposits. The extent of the body, the depth of the ramp cut-off and the widening of the lobe are comparable with the largest present-day submarine landslides, not often observed in fossil examples. Internal deformation structures are distributed differently in the ramp and lobe zones. The ramp zone has antiformal stacking of duplexes and steeply inclined folds. The lobe has a well-defined strain partition: the upper part of the body is affected by extensional structures such as listric normal faults and extensional duplexes; the lower part is deformed by recumbent folds, boudinage and stacking of blocks, which are compatible with flow-induced, heterogeneous simple shear. This distribution is consistent with a kinematic model of extrusion-spreading, implying rear compression in the ramp zone with thickening and shortening of the body, and spreading in the lobe with thinning and stretching. The localized buckling present in the distal part of the lobe may be related to the onset of lateral confinement, due to local topographic features of the basin plain (synsedimentary intrabasinal high). The various degrees and styles of stratal disruption in the mass wasting body depend on the different combination of progressive simple shear, layer-parallel extension and shortening. Different structural associations occur in well-defined parts of the body due to kinematics of emplacement (spreading, flow and buckling). These associations may be diagnostic of gravitational mass wasting processes rather than shallow-level tectonic deformation.

Mixed Clastic–Carbonate Cycles and Sequences: Quaternary of Egypt and Carboniferous of England

There are various types of mixed clastic–carbonate sequences andparasequences in the geological record and sea-level change is oneof the major controls on their development, as well as the obviousavailability of terrigenous material. Mixed-lithology sequences areespecially well-developed in icehouse times, as in the Permo–Carboniferous and Quaternary. The two major types, lower carbonate – upper clastic and lower clastic – upper carbonate sequences, reflect the rates of sea-level change and the source of clastic sediment – whether itis brought across the carbonate platform from the adjacent landmassor supplied axially to the basin. Two examples of carbonate–clastichigh-frequency sequences are discussed: 1) from the Red Sea coastof Egypt, Quaternary transgressive/highstand shallow-water carbonatesand late highstand/falling-stage/lowstand clastics deposited inincised-valley fills and fan deltas, and 2) from northern England,mid-Carboniferous ‘Yoredale’ cycles of transgressive shelf carbonatespassing up into highstand coarsening-up deltaic and shoreline clastics,capped by palaeosoils and coal. Locally, falling-stage incised-valleyssupplied sediments to the adjoining basin. One significant differencebetween these two examples is the palaeoclimate: arid in the Red Sealeading to the episodic supply of sand and gravel, and humid in theCarboniferous resulting in the more continuous supply of mud andsand, each having a different effect on carbonate deposition.

Extension and compression in the Northern Apennines (Italy) hinterland: Evidence from the late Miocene‐Pliocene Siena‐Radicofani Basin and relations with basement structures

The Northern Apennines (NA) hinterland area is characterized by a complex Neogene‐Quaternary tectonics where both crustal extension, associated with the Tyrrhenian Basin opening, and crustal shortening in the onshore area took part in the deformation. Analysis of synorogenic deposits preserved in the NNW trending Siena‐Radicofani Basin (SRB), extending along a large part of the NA hinterland, documents the evolution of deformation of this sector during the last 9 Ma. Information from subsurface geology (deep seismic lines, commercial seismic lines, and deep wells), surface geology (mapping and structural analysis), and from analogue modeling was integrated and used to infer the tectono‐sedimentary history of the SRB and its relation with structures in the substratum, as well as the possible implications for the evolution of the NA hinterland. The results we obtain indicate that the SRB and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation. Seismic lines across the SRB display various examples of compressional structures affecting the basin fill and the substratum, such as thrust anticlines and reverse faults. Notably, these basin‐scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop‐scale compressional structures. The thrust anticlines bounding the basins are often cored by Triassic evaporites (Burano Formation), suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution. In this circumstance, three series of scaled brittle‐ductile physical models have been used to investigate the development of a basement cover system, with a décollement ductile layer at the base of the sedimentary cover. These models simulate the evolution of the Northern Apennines hinterland, where the basement is involved in the thrusting, and the sedimentary cover is shortened above a basal ductile layer given by the Burano Formation. Longitudinal models cross sections display similar deformation patterns to those observed in the NA hinterland, such as characteristic wavelength of both basement and cover structures, as well as detachment and fault propagation folding in the cover. Extensional tectonics is instead found to control sedimentation in the southern part of the SRB (at ∼8 Ma) or representing recent deformation. The older extensional event is here related to the forelandward propagation of Tyrrhenian‐related extension that could reactivate suitably oriented basement thrusts. Transfer zones produced a differential propagation of extension, such that along‐strike sectors of the hinterland were eventually deformed by different stress fields. Analysis of the SRB and of other adjoining basins reveals that the NA hinterland experienced alternated periods of forward and backward migration of the compression‐extension transition. In our interpretation, the competition between extension and compression in the hinterland is related to the NNW directed Africa (Pelagian) indentation responsible for the lateral extrusion of the NA and the contemporaneous opening of the Tyrrhenian Basin in the inner zone. Increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well.

Improving a regional model using reduced complexity and parameter estimation.

The availability of powerful desktop computers and graphical user interfaces for ground water flow models makes possible the construction of ever more complex models. A proposed copper-zinc sulfide mine in northern Wisconsin offers a unique case in which the same hydrologic system has been modeled using a variety of techniques covering a wide range of sophistication and complexity. Early in the permitting process, simple numerical models were used to evaluate the necessary amount of water to be pumped from the mine, reductions in streamflow, and the drawdowns in the regional aquifer. More complex models have subsequently been used in an attempt to refine the predictions. Even after so much modeling effort, questions regarding the accuracy and reliability of the predictions remain. We have performed a new analysis of the proposed mine using the two-dimensional analytic element code GFLOW coupled with the nonlinear parameter estimation code UCODE. The new model is parsimonious, containing fewer than 10 parameters, and covers a region several times larger in areal extent than any of the previous models. The model demonstrates the suitability of analytic element codes for use with parameter estimation codes. The simplified model results are similar to the more complex models; predicted mine inflows and UCODE-derived 95% confidence intervals are consistent with the previous predictions. More important, the large areal extent of the model allowed us to examine hydrological features not included in the previous models, resulting in new insights about the effects that far-field boundary conditions can have on near-field model calibration and parameterization. In this case, the addition of surface water runoff into a lake in the headwaters of a stream while holding recharge constant moved a regional ground watershed divide and resulted in some of the added water being captured by the adjoining basin. Finally, a simple analytical solution was used to clarify the GFLOW model's prediction that, for a model that is properly calibrated for heads, regional drawdowns are relatively unaffected by the choice of aquifer properties, but that mine inflows are strongly affected. Paradoxically, by reducing model complexity, we have increased the understanding gained from the modeling effort.

A REGRESSION-BASED APPROACH TO UNDERSTAND BASELINE TOTAL NITROGEN LOADING FOR TMDL PLANNING

Requirements under Section 303(d) of the Clean Water Act have led North Carolina environmental officials to prepare a total nitrogen (TN) total maximum daily load (TMDL) plan for the entire Neuse River Basin. The SPARROW (SPAtially Referenced Regression On Watershed attributes) watershed model was used to develop baseline estimates of TN inputs and delivery and a TN budget for the Neuse River Basin and two adjoining basins, the Cape Fear and Tar-Pamlico. The model explained 94% of the variability in log-transformed stream TN flux. Estimates of stream yield typically were within 25% of the observed values at the 44 monitoring stations used to calibrate the model. The model indicates that landscape factors, such as soil drainage characteristics, and channel transport factors, such as aquatic processes in streams and reservoirs, both exert a large influence on the transport of TN at both the reach and whole-basin scale. TN losses associated with in-stream processes occurred at a rate of about 5% per kilometer in streams with a mean annual discharge less than 1.04 cubic meters per second; losses in larger streams occurred at a rate of 0.2% per kilometer.