Gravity interpretation of nonoutcropping sedimentary basins in which the density contrast decreases parabolically with depth

The decrease in density contrast of sedimentary rocks with depth in many sedimentary basins can be approximated by a parabolic density function. Analytical gravity expression of an outcropping two-dimensional vertical step along which the density contrast decreases parabolically with depth is derived in the space domain. A modification ofBott's (1960) method of gravity interpretation is proposed by considering two outcropping vertical steps on either side of the first and last observation points in addition toN outcropping vertical prisms in order to interpret the gravity anomalies of nonoutcropping basins. The thicknesses of the two outcropping vertical steps are made equal to the thicknesses of the two outcropping vertical prisms placed below the first and last observation points. The initial depth estimates of the sedimentary basin are calculated by the infinite slab formula ofVisweswara Rao et al. (1993). The gravity effects of theN outcropping prisms and the two outcropping vertical steps are calculated at each anomaly point and the depth to the floor of the basin are adjusted based on the differences between the observed and calculated anomalies. A gravity anomaly profile of Los Angeles basin, California is interpreted.     

Gravity contributions to the understanding of salt tectonics from the Jebel Cheid area (dome zone, Northern Tunisia)

Detailed gravity measurements integrated with geological data were computed to constrain the mechanisms that were active during the emplacement of the Triassic evaporite-bearing folds of Jebel Cheid from the salt-dome zone in the Atlassic region. The gravity analysis consists in mapping the contrasting gravity responses: complete Bouguer anomaly, residual anomaly and derivative maps; the main results display a positive amplitude gravity anomaly as the response of Triassic evaporite bodies and important NE–SW-trending features at the boundaries between the Triassic outcrops and their enveloping strata. In contrast with gravity calculations of a salt dome structure usually resulting in negative gravity anomaly models, the Jebel Cheid clearly expresses a positive gravity anomaly; furthermore, this result is supported by synthetic gravity interpretation.     

Structural Setting of Northern Tunisia Insights from Gravity Data Analysis Jendouba Case Study

Detailed gravity data in conjunction with available surface geology are analyzed to infer the organization of the underlying structures in Jendouba area. Gravity data analysis benefits from the gravity Bouguer anomaly, upward continuations, residual distribution, derivatives and Euler deconvolved maps. The main results display a positive amplitude gravity anomaly as the response of Triassic evaporitic bodies and important NE trending features at the boundaries between the Triassic outcrops and their enveloping strata. Integration of gravity, geological and structural maps let to the identification of major structural directions and trends of the study area. It confirms some structural elements gathered from outcrops. It defines also new ones.     

Stratigraphy of the mid‐ to upper‐Cretaceous System in the Aridagawa area,Wakayama, Southwest Japan

The litho‐ and biostratigraphy of the mid‐ to upper‐Cretaceous System around the Yagumaike Pond in the Aridagawa area, Wakayama, Southwest Japan, were investigated. Many Middle to Late Albian megafossils were found in the strata of a block bounded by faults. It was also revealed that the Upper Cretaceous System of other blocks ranges from the Middle Turonian to Santonian. The Albian megafossil assemblage contains few benthic organisms, in contrast with the abundance of nektons found (e.g. cephalopods). Sedimentological observations of the mudstone profiles also indicate that scarcely or weakly bioturbated, well‐laminated mudstone is dominant among the Albian deposits. These results suggest deposition of the Albian mudstone under a dysaerobic to anoxic environment. It is comparable to the extended oceanic anoxia (OAEs) in mid‐Cretaceous time. Albian deposits with similar characteristics are also known to exist in Shikoku, Southwest Japan. A wide sedimentary basin that was directly affected by global environmental events, such as OAEs, seemed to be formed on the Chichibu Belt in the Albian. The Upper Cretaceous strata in the study area are extremely thin, similar to the coeval deposits on the Chichibu Belt in Shikoku. It is suggested that the sedimentation rate in the sedimentary basin on the Chichibu Belt was extremely low during early Late Cretaceous time.     

Gravity field and tectonic features of Block L2 in the Lamu basin,Kenya

A gravity survey on the scale of 1: 250 000 was carried out in Block L2 located in the Lamu basin of south‐east Kenya in order to study tectonic features and find out favourable petroleum prospects in the block. This paper, through data processing and synthetic interpretation of the measured gravity data in the block, discusses characteristics of the gravity field and their geological implications, determines the fault system and the basement depth, analyses features of the main strata, divides structure units and predicts favourable petroleum zones. In the block, the regional gravity anomaly is mainly caused by the inclined Moho surface that rises in the east and subsides in the west topographically and the Bouguer gravity anomaly primarily reflects the superimposition of the gravity effect derived from the Moho surface and the basement relief. Two groups of faults extending NW (NWW) and NE (NEE) respectively are dominant in the block and their activities resulted in the framework of east‐west zoning and south‐north blocking. The basement depth greatly changes in an alternative high and low pattern. The Permian‐Triassic, Jurassic and Tertiary strata are extensively developed, while the Cretaceous is only developed in the east of the block. Structurally, the block can be divided into five units, of which the Tana sag shows excellent source‐reservoir‐seal associations and is a favourable target for future petroleum exploration.     

Delineating depth to bedrock beneath shallow unconfined aquifers: a gravity transect across the Palmer River Basin

In view of the increasing demand on ground water supplies in the northeastern United States, it is imperative to develop appropriate methods to geophysically characterize the most widely used sources of ground water in the region: shallow unconfined aquifers consisting of well-sorted, stratified glacial deposits laid down in bedrock valleys and channels. The gravity method, despite its proven value in delineating buried bedrock valleys elsewhere, is seldom used by geophysical contractors in this region. To demonstrate the method's effectiveness for evaluating such aquifers, a pilot study was undertaken in the Palmer River Basin in southeastern Massachusetts. Because bedrock is so shallow beneath this aquifer (maximum depth is 30 m), the depth-integrated mass deficiency of the overlying unconsolidated material was small, so that the observed gravity anomaly was on the order of 1 milligal (mGal) or less. Thus data uncertainties were significant. Moreover, unlike previous gravity studies elsewhere, we had no a priori information on the density of the sediment. Under such circumstances, it is essential to include model constraints and weighted least-squares in the inversion procedure. Among the model constraints were water table configuration, bedrock outcrops, and depth to bedrock from five water wells. Our procedure allowed us to delineate depth to bedrock along a 3.5 km profile with a confidence interval of 1.8 m at a nominal depth of 17 m. Moreover, we obtained a porosity estimate in the range of 39% to 44%. Thus the gravity method, with appropriate refinements, is an effective tool for the reconnaissance of shallow unconfined aquifers.     

Palaeomagnetism and palaeogeography of Mongolia from the Carboniferous to the Cretaceous—final report

The present study summarizes the results of palaeomagnetic investigations of Carboniferous to Cretaceous rocks with respect to global-tectonic interpretations of Eurasia. Normal and reverse directions of stable remanence components were found for the Carboniferous to Cretaceous rocks within single outcrops, sometimes even within individual samples. Triassic, Permian and Carboniferous pole positions for Mongolia are strikingly different from those of the Siberian platform. The conclusion about the different palaeogeographical development of Mongolia with respect to the Siberian platform is well seen from differences in palaeolatitudes (up to 50°) and palaeorotations (up to 150°). The apparent polar wander paths for Mongolia and the north China block are almost identical since the Carboniferous. This way, palaeomagnetic and palaeogeographical data are contributing to the global-tectonics model of the regions under study. During the Carboniferous, Permian and Triassic, the regions of Mongolia investigated were not part of Eurasia. Together with the north China block, they show a palaeogeographical affinity with the Pacific Plate.     

Calcareous nannofossil biostratigraphic study of forearc basin sediments: Lower to Upper Cretaceous Budden Canyon Formation (Great Valley Group), northern California,USA

The results of a calcareous nannofossil biostratigraphic investigation of the North Fork Cottonwood Creek section of the Budden Canyon Formation (BCF; Hauterivian–Turonian) in northern California are summarized using the Boreal – cosmopolitan Boreal Nannofossil Biostratigraphy (BC) – Upper Cretaceous Nannofossil Biostratigraphy (UC) nannofossil zonal schemes of Bown et al. and Burnett et al. Sixteen intervals, ranging from the BC15 to UC8 zones, were established in the section. Combined biostratigraphic and magnetostratigraphic studies suggest a Hauterivian to mid‐Turonian age for the studied sequence. The Hauterivian–Barremian, Barremian–Aptian, Aptian–Albian, Albian–Cenomanian, and Cenomanian–Turonian stage boundaries were delineated near the top of the Ogo Member, below the Huling Sandstone Member, within the upper Chickabally Member, in the upper portion of the Bald Hills Member and within the Gas Point Member, respectively. Unconformities probably exist at the base of the Huling Sandstone Member and the upper part of the upper Chickabally Member. The nannofossil assemblage in the North Fork Cottonwood Creek suggests that the study area was under the influence of cold‐water conditions during the Barremian to Lower Aptian interval, shifting to tropical/warm‐water conditions during the Albian to Turonian interval as a result of the mid‐Cretaceous global warming. Although oceanic anoxic events have not yet been reported in the BCF, preliminary total organic carbon, along with nannofossil data, suggest the presence of the global Cenomanian–Turonian boundary oceanic anoxic event 2.     

Improved salt imaging in a basin context by high resolution potential field data: Nordkapp Basin,Barents Sea

The seismic imaging of salt diapirs in the Nordkapp Basin gave rise to considerable problems in defining their shape and volume. Independent information was added by integrating the interpretation with high resolution gravity and magnetic data. We developed a novel, iterative workflow, separated into sub‐categories: sediments, salt structures, basement and Moho. Distinctions between the sources of the anomalies from different depths was achieved by utilizing the different decay characteristics of gravity, gravity gradiometry and high resolution magnetic anomalies. The workflow was applied to the southern part of the Nordkapp Basin. It started with the sedimentary model derived from seismics, populated with measured densities and magnetic susceptibilities and a starting model for the base salt. The residual after the removal of this model was interpreted in terms of a crustal model, including flexural isostatic calculations for the Moho with the sedimentary load. The residual after the removal of crustal and early sedimentary model was used to tune the salt model. As these major and minor modelling steps depend on each other, an iterative process was applied to stepwise improve the density and magnetic susceptibility model. The first vertical gradient of gravity and the magnetic field were found to give most information about the cap rock of the diapirs. The improvement in salt imaging, integrated with results from controlled‐source electromagnetic and magneto‐telluric modelling is shown for the salt diapir Uranus, where a well, terminated in the salt, constrains the minimum of the depth to base salt.     

Age of radiolarian-chert blocks from the Senonian Ophiolitic Mélange (Ankara, Turkey)

Abstract The Senonian Ophiolitic Mélange of the Ankara Mélange Supergroup includes numerous blocks of radiolarian cherts. These blocks contain various radiolarian assemblages from the Albian to the Turonian ( Pseudodictyomitra pseudomacrocephala, Thanarla tieneta) , the Lower Cretaceous ( Thanarla conica, Alievium helenae, Pseudodictyomitra carpatica) , the Kimmeridgian-Tithonian ( Ristola altissima, Sethocapsa cetia, Podocapsa umphitreptera) and the lower Jurassic ( Parahsuum simplum). Upper Norian radiolarians were obtained from two of these blocks. The assemblage is represented by Betraccium deweveri Pessagno and Blome, Ferresium triquetrum Carter, Pylostephanidium ankaraense n. sp. (Genus Pylostephanidizi was formerly unknown in the upper Triassic) and other taxa. Thus, upper Norian fauna of Turkey exhibits close similarity to the radiolarian assemblages of western North America, Eastern Russia, Japan and the Philippines. This provides further evidence for the correlation of Mediterranean and Pacific Triassic sequences. These data allow for the conclusion that the sedimentation of radiolarian cherts was common in this part of Tethys during the Late Triassic and the Jurassic.     

Composition,environment, and economic value of the Permian to Cretaceous coated grains from Zagros and the Persian Gulf

Ooid grainstone/packstone carbonate facies of the Dalan, Kangan, and Arab formations are the main hydrocarbon reservoirs in the Persian Gulf. Based on detailed petrographic and petrophysical analyses,sedimentological and mineralogical features of the Permian to Late Cretaceous carbonate and iron-rich coated grains from Zagros and the Persian Gulf were investigated. Frequent ooids in these formations indicate a high-energy environment and a wave-dominated shallow carbonate platform. Because of wi...     

南海重力异常的沉积层密度改正及其对区域构造特征分析的意义

南海位于太平洋板块、印澳板块和欧亚板块交汇处,自晚中生代以来历经张裂作用、海底扩张以及印藏碰撞、菲律宾海板块西向运动等构造事件的叠加改造,不仅形成了复杂多样的构造格局,而且堆积了厚薄不均的沉积层.为了考察沉积层密度改正对利用重力资料分析南海不同尺度构造特征的影响,本文利用南海各区域不同深度沉积层的地震波速度及钻孔密度等数据,建立了沉积层与沉积基底密度差随深度变化的二次函数关系式,并基于该关系式,计算了南海沉积层相对基底密度低而产生的重力异常值.结果显示,南海沉积层的重力异常值在海盆区介于-40~-60 mGal,而在堆积巨厚沉积物的莺歌海盆地可达到-135 mGal;相对于空间重力异常、布格重力异常,经沉积层重力异常改正后的地壳布格重力异常更能突出深部不同尺度的密度结构和莫霍面的起伏特征,其总水平导数模更突显了南海西北部红河断裂带的海上延伸;利用谱分析技术估算岩石圈强度时,经沉积层重力异常改正的地壳布格重力异常数据获得的岩石圈有效弹性厚度值更为符合地质实际,特别是在长条形的巨厚沉积区如莺歌海盆地和马来盆地.分析表明,重力异常的沉积层密度改正对揭示南海构造特征具有重要的意义.     

Tethyan ophiolites and Pangea break-up

Abstract The break‐up of Pangea began during the Triassic and was preceded by a generalized Permo‐Triassic formation of continental rifts along the future margins between Africa and Europe, between Africa and North America, and between North and South America. During the Middle–Late Triassic, an ocean basin cutting the eastern equatorial portion of the Pangea opened as a prograding branch of the Paleotethys or as a new ocean (the Eastern Tethys); westwards, continental rift basins developed. The Western Tethys and Central Atlantic began to open only during the Middle Jurassic. The timing of the break‐up can be hypothesized from data from the oceanic remnants of the peri‐Mediterranean and peri‐Caribbean regions (the Mesozoic ophiolites) and from the Atlantic ocean crust. In the Eastern Tethys, Middle–Late Triassic mid‐oceanic ridge basalt (MORB) ophiolites, Middle–Upper Jurassic MORB, island arc tholeiite (IAT) supra‐subduction ophiolites and Middle–Upper Jurassic metamorphic soles occur, suggesting that the ocean drifting was active from the Triassic to the Middle Jurassic. The compressive phases, as early as during the Middle Jurassic, were when the drifting was still active and caused the ocean closure at the Jurassic–Cretaceous boundary and, successively, the formation of the orogenic belts. The present scattering of the ophiolites is a consequence of the orogenesis: once the tectonic disturbances are removed, the Eastern Tethys ophiolites constitute a single alignment. In the Western Tethys only Middle–Upper Jurassic MORB ophiolites are present – this was the drifting time. The closure began during the Late Cretaceous and was completed during the Eocene. Along the area linking the Western Tethys to the Central Atlantic, the break‐up was realized through left lateral wrench movements. In the Central Atlantic – the link between the Western Tethys and the Caribbean Tethys – the drifting began at the same time and is still continuing. The Caribbean Tethys opened probably during the Late Jurassic–Early Cretaceous. The general picture rising from the previous data suggest a Pangea break‐up rejuvenating from east to west, from the Middle–Late Triassic to the Late Jurassic–Early Cretaceous.     

Metallogenesis on a Mesozoic passive continental margin,Antalya Complex,southwest Turkey

A variety of Fe, Mn and trace-metal-enriched Mesozoic pelagic sediments are associated with the tectonically emplaced Antalya Complex in southwestern Turkey. Palaeotectonic settings represented within the complex comprise a continental platform, passing laterally through a Mesozoic passive margin into a zone of marginal oceanic crust, formed during the early stages of continental separation. The origins of the metalliferous sediments are elucidated using mineralogical, major, trace element and REE data, and comparisons with oceanic and ophiolite-related sediments.Late Triassic deposition during the initial continental separation was mostly terrigenous, including detrital carbonate derived from adjacent reef complexes. During the Jurassic and Early Cretaceous the passive margin underwent accumulation of fine-grained terrigenous matter and biogenic silica in deep water below the carbonate compensation depth. Argillaceous mudstones deposited during a regional hiatus at the end of the Upper Triassic show unusual Fe and trace metal enrichment, together with a marked positive Ce anomaly, indicative of slow hydrogenous accumulation.The marginal oceanic crustal zone also shows dominantly terrigenous and siliceous biogenic deposition but with the addition of an important hydrothermal component represented by Fe-Mn deposits. These occur within and immediately above the Upper Triassic lavas of the oceanic crust and as intercalations in the overlying Lower Cretaceous radiolarian chert sequence. Most of these sediments show strong Fe-Mn fractionation; several show a negative Ce anomaly implying rapid incorporation of the REEs from seawater.The Upper Triassic Fe-Mn deposits associated with the lavas are relatively trace-element-depleted and record rapid localised precipitation from relatively high-temperature hydrothermal solutions. By contrast, the more manganiferous and trace-element-enriched metalliferous horizons in the Jurassic to Lower Cretaceous chert sequences represent more dilute low-temperature hydrothermal discharge. Regional comparisons suggest that dominantly manganiferous deposits free of sulphides are characteristic of the early formed Mesozoic ocean crust compared with well established spreading axes like the Troodos Massif, Cyprus.     

Subsidence, extension and thermal history of the West African margin in Senegal

The subsidence of the Atlantic margin in Senegal clearly shows two rapid stages related to the formation of (1) the Central Atlantic during the early Jurassic (around 200 Ma), and (2) the Equatorial Atlantic during the Cretaceous (100 Ma). A simple model of extension is used to interpret the subsidence history and to derive the thermal evolution of this basin. The present-day gravity, bathymetry, bottom hole temperatures (BHT) in oil exploration boreholes and heat flow density are used to control the validity of the model. Two cross sections from the outcropping basement to oceanic crust are used, one in Casamance and the other one at the south to latitude of Dakar. The model can fully explain the first-order subsidence history as well as the present-day observations, and therefore can provide valuable information about the thermal evolution of sediments and about the structure of the continental crust along the margin. Comparisons with the opposite margin in North America (Blake Plateau and Carolina trough) indicate a rather different evolution (the North American margin did not undergo the second stage of rifting) and a different crustal structure (crustal thinning is less important on the African margin).     

苏鲁地区剪切波速度结构研究及与地震关系探讨

利用S波纯波形拟合法以及T函数法反演了苏鲁地区壳幔剪切波速度结构,并利用长周期P波T函数反演得到了连云港和莱阳台下方800km深度的速度结构。结果显示:(1)苏鲁地区大部分台站地壳表层及上地壳浅部速度偏高,分别对应高压、超高压物质和古老基底出露地区;(2)沿郯庐断裂带分布的台站均显示明显低速层,并具有北浅南深的特点;(3)连云港和莱阳台超深度反演结果显示两台均在150km深度下出现高速层,反映扬子板块的俯冲深度为100km以下,俯冲板片厚度在100km以上;板片拆离下沉深度甚至达到300km或者更深;(4)地震深度分布与低速层关系密切,沿郯庐断裂和烟台—五莲断裂的中小地震震源深度都比较深,有的甚至达到地壳的底部,反映这两条断裂目前切割深度都比较大,而且地幔物质相对比较活跃。     

Morphology and sedimentology of a microtidal beach with beachrocks: Vatera,Lesbos, NE Mediterranean

The present contribution considers the dynamics of beaches occupied by outcropping/buried beachrocks, i.e. hard coastal formations consisting of beach material lithified by in situ precipitated carbonate cements. The dynamics of a Greek microtidal beach with beachrocks (Vatera, Lesbos) are examined through the collection and analysis of morphological and sedimentary field data, a 2-D nearshore hydrodynamic model and a specially constructed 1-D morphodynamic model. The results showed that the beachrock-occupied part of the beach is characterised by distinctive morphodynamics as: (i) its beachface is associated with large slopes; (ii) there is a good spatial correlation between the sub-aerial and shallow submerged mean beach profile and the buried/outcropping upper beachrock surface; and (iii) the seaward margins of the submerged beachrock outcrops are always associated with a ‘scour step’ i.e. a submerged cliff. The results also showed that beachrock outcrops can bias cross-shore sediment exchanges by impeding onshore transport due to the presence of the scour step. In this sense, beachrock outcrops may be considered as offshore transport ‘conduits’ for the beach sediments. A conceptual model of beach sediment transport, based on the field data and the hydrodynamic modelling is proposed. According to this model, fresh beach material from adjacent terrestrial sources is transported alongshore, towards the central part of the embayment, where a littoral transport convergence zone occurs under most wave conditions. There, the laterally supplied sediments are lost offshore.     

Biogenic origin of coastal honeycomb weathering

Honeycomb weathering occurs in two environments in Late Cretaceous and Eocene sandstone outcrops along the coastlines of south‐west Oregon and north‐west Washington, USA, and south‐west British Columbia, Canada. At these sites honeycomb weathering is found on subhorizontal rock surfaces in the intertidal zone, and on steep faces in the salt spray zone above the mean high tide level. In both environments, cavity development is initiated by salt weathering. In the intertidal zone, cavity shapes and sizes are primarily controlled by wetting/drying cycles, and the rate of development greatly diminishes when cavities reach a critical size where the amount of seawater left by receding tides is so great that evaporation no longer produces saturated solutions. Encrustations of algae or barnacles may also inhibit cavity enlargement. In the supratidal spray zone, honeycomb weathering results from a dynamic balance between the corrosive action of salt and the protective effects of endolithic microbes. Subtle environmental shifts may cause honeycomb cavity patterns to continue to develop, to become stable, or to coalesce to produce a barren surface. Cavity patterns produced by complex interactions between inorganic processes and biologic activity provide a geological model of ‘self‐organization’. Surface hardening is not a factor in honeycomb formation at these study sites. Salt weathering in coastal environments is an intermittently active process that requires particular wind and tidal conditions to provide a supply of salt water, and temperature and humidity conditions that cause evaporation. Under these conditions, salt residues may be detectable in honeycomb‐weathered rock, but absent at other times. Honeycomb weathering can form in only a few decades, but erosion rates are retarded in areas of the rock that contain cavity patterns relative to adjacent non‐honeycombed surfaces. Copyright © 2010 John Wiley & Sons, Ltd.     

Detrital zircon multi‐chronology,provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex,eastern Shikoku,Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone

Detrital zircon multi‐chronology combined with provenance and low‐grade metamorphism analyses enables the reinterpretation of the tectonic evolution of the Cretaceous Shimanto accretionary complex in Southwest Japan. Detrital zircon U–Pb ages and provenance analysis defines the depositional age of trench‐fill turbidites associated with igneous activity in provenance. Periods of low igneous activity are recorded by youngest single grain zircon U–Pb ages (YSG) that approximate or are older than the depositional ages obtained from radiolarian fossil‐bearing mudstone. Periods of intensive igneous activity recorded by youngest cluster U–Pb ages (YC1σ) that correspond to the younger limits of radiolarian ages. The YC1σ U–Pb ages obtained from sandstones within mélange units provide more accurate younger depositional ages than radiolarian ages derived from mudstone. Determining true depositional ages requires a combination of fossil data, detrital zircon ages, and provenance information. Fission‐track ages using zircons estimated YC1σ U–Pb ages are useful for assessing depositional and annealing ages for the low‐grade metamorphosed accretionary complex. These new dating presented here indicates the following tectonic history of the accretionary wedge. Evolution of the Shimanto accretionary complex from the Albian to the Turonian was caused by the subduction of the Izanagi plate, a process that supplied sediments via the erosion of Permian and Triassic to Early Jurassic granitic rocks and the eruption of minor amounts of Early Cretaceous intermediate volcanic rocks. The complex subsequently underwent intensive igneous activity from the Coniacian to the early Paleocene as a result of the subduction of a hot and young oceanic slab, such as the Kula–Pacific plate. Finally, the major out‐of‐sequence thrusts of the Fukase Fault and the Aki Tectonic Line formed after the middle Eocene, and this reactivation of the Shimanto accretionary complex as a result of the subduction of the Pacific plate.     

Use of Nested Flow Models and Interpolation Techniques for Science‐Based Management of the Sheyenne National Grassland,North Dakota,USA

Noxious weeds threaten the Sheyenne National Grassland (SNG) ecosystem and therefore herbicides have been used for control. To protect groundwater quality, the herbicide application is restricted to areas where the water table is less than 10 feet (3.05 m) below the ground surface in highly permeable soils, or less than 6 feet (1.83 m) below the ground surface in low permeable soils. A local MODFLOW model was extracted from a regional GFLOW analytic element model and used to develop depth‐to‐groundwater maps in the SNG that are representative for the particular time frame of herbicide applications. These maps are based on a modeled groundwater table and a digital elevation model (DEM). The accuracy of these depth‐to‐groundwater maps is enhanced by an artificial neural networks (ANNs) interpolation scheme that reduces residuals at 48 monitoring wells. The combination of groundwater modeling and ANN improved depth‐to‐groundwater maps, which in turn provided more informed decisions about where herbicides can or cannot be safely applied.