Isobath Maps Research Articles

Holocene Evolution of the Pearl River Delta: Mapping Integral Isobaths and Delta Progradation

The Pearl River Delta (PRD, China) has undergone complex geological development within a multi-island faulted basin, shaped by the interplay of regional tectonic movements, Quaternary sea-level fluctuations, and fluvial-marine interactions. Despite a great number of studies on the Holocene sedimentary sequences and spatial differences of lithofacies and environments, scant attention has been paid to the overarching human influence on deltaic evolution and coastline modifications since the Neolithic epoch. To further elucidate the spatial variation in Holocene sedimentation and its underlying basement topography shaped during the Last Glacial Maximum (LGM), we compiled a comprehensive dataset incorporating borehole data from over 2800 cores (the maximum depth can reach 92.5 m) within the PRD. Subsequently, high-resolution isobath maps of Quaternary deltaic deposits were generated, offering unprecedented insights into sediment distribution. This dataset facilitated a nuanced reconstruction of pre-Holocene topography, revealing a zone characterized by elongated, deep-incised valleys governed by NW-SE fault orientations. Further, we delineated coastline shifts since the period of maximum Holocene transgression (~7000 years BP), contributing to an enhanced understanding of the formation and evolutionary patterns of the delta and river network oscillations. Our findings illuminate an increasing anthropogenic impact on the rate of fluvial sedimentation and land growth, particularly accentuated over the last two millennia, favoring deltaic accretion.

Комплексные археологические и геофизические исследования в портовой части Херсонеса Таврического

The best results of researching archaeological sites in the coastal zone come from integrated interdisciplinary approach involving modern geophysical methods. The analysis of the archaeological material obtained during excavations of the “diamond-shaped tower” in the water area near the port quarters of Chersonese suggests that the structure was constructed in the ninth and tenth centuries AD. The results of research on this site show that from the ninth and tenth to the period from the late eleventh to the first half of the thirteenth centuries the sea level in Karantinnaia Bay rose by ca 1 meter. The data obtained by continuous seismoacoustic profiling were used to identify continuous changes of the coastline in result of transgression and accumulation of the bottom sediments in the section of the water area near the port district of Chersonese. The analysis of the built-up seismogeological sections and isobath map enabled the research group to identify 3 terraces and associated morphological elements indicating the location of ancient coastlines in different historical periods. A spatial relationship has been established between the archaeological objects found at the sea bottom and the position of the underwater terraces. A reconstruction of the ninth- and tenth-century coastline has been suggested according to the archaeological data. The location of the “diamond-shaped tower” and the construction remains discovered in 2019 on the same terrace suggests that the structures existed approximately at the same time. Electrical prospecting research using bottom electrotomography explored the sediment structure of marine terraces to a depth of 10 m. The research results have determined bottom anomalies corresponding to various stages of development of the coast of Karantinnaia Bay. An extended linear anomaly, located 40–50 m from the modern coast and hidden by a layer of bottom soil up to 3 m thick, most likely corresponds to the early period of the ancient city. The sea in this area is ca 2–3 m deep.

Neogene-Quaternary structuring of the Kalaa Khesba Graben, northwestern Tunisia: A push-up inversion structure

Interpretation of lithostratigraphic, seismic and gravity data from Kalaa Khesba Graben shows (i) lateral and in-depth variation of the lithostratigraphic series, (ii) complex structuring of faulting. Reverse faults affected Paleocene to Quaternary horizons with a duplication of Eocene-Paleocene series occurred at subsurface evidenced within well W6. Isochron, isovelocity and isobath maps, combined with gravity data, show subsurface structures oriented predominantly NW-SE to NS and NE-SW to EW. Faults and horizons on the seismic lines, superimposed to gravity lineaments, reveal negative anomalies occurring at shallow depth. Such features may reflect the existence of low density Neogene-Quaternary series, strike-slips and thrust faults within Kalaa Khesba Graben. Depths deduced from Euler deconvolution solutions vary from 0.5 to 4 km. At subsurface, well log data located in the center of the graben, ensured the presence of Triassic bodies. A model of initiation of Kalaa Khesba Graben through a N160° σ1 transpression is proposed.

Tectonosedimentary framework of Upper Cretaceous –Neogene series in the Gulf of Tunis inferred from subsurface data: implications for petroleum exploration

Abstract The objective and the main contribution of this issue are dedicated to using subsurface data to delineate a basin beneath the Gulf of Tunis and its neighbouring areas, and to investigate the potential of this area in terms of hydrocarbon resources. Available well data provided information about the subsurface geology beneath the Gulf of Tunis. 2D seismic data allowed delineation of the basin shape, strata geometries, and some potential promising subsurface structures in terms of hydrocarbon accumulation. Together with lithostratigraphic data obtained from drilled wells, seismic data permitted the construction of isochron and isobath maps of Upper Cretaceous-Neogene strata. Structural and lithostratigraphic interpretations indicate that the area is tectonically complex, and they highlight the tectonic control of strata deposition during the Cretaceous and Neogene. Tectonic activity related to the geodynamic evolution of the northern African margin appears to have been responsible for several thickness and facies variations, and to have played a significant role in the establishment and evolution of petroleum systems in northeastern Tunisia. As for petroleum systems in the basin, the Cretaceous series of the Bahloul, Mouelha and Fahdene formations are acknowledged to be the main source rocks. In addition, potential reservoirs (Fractured Abiod and Bou Dabbous carbonated formations) sealed by shaly and marly formations (Haria and Souar formations respectively) show favourable geometries of trap structures (anticlines, tilted blocks, unconformities, etc.) which make this area adequate for hydrocarbon accumulations.

Determining Aquifers and Bedrock of Qaen Plain by the Resistance Measurement Method

The aim of this study is to determine aquifers and bedrock of Qaen plain by the resistance measurement method. Using symmetrical Schlumberger electrode array, the most common method to detect underground water, Qaen plain was located in the west of Khanik village situated in the North East of drainage basinto the West of Aliabad village situated in the West of drainage basinat 159 electric sounding stations along 13 profiles under the geoelectrical operation. Profiles were along the south East-North West. At most, the half of the Electrode distance was 500 meters in the Schlumberger array. Interpretation of geoelectric sounding was done using the Partial and computer compliancemethod (using ipi2win Software). The obtained results of the Geoelectrical operation were interpreted and drawn by resistivity section, resistivity profiles, the apparent resistivity maps of the different flow lines (AB including 200, 600, and 1000 meters), and isobath map of the rock.

Tordera River Delta system build up (NE Iberian Peninsula): sedimentary sequences and offshore correlation

The Tordera River Delta is made up of coarse sand bodies which were formed during the last sea level rise. Marine and land seismic profiles and wells show three depositional Holocene sequences corresponding to a) the transgressive base level, b) the progradant intermediate unit and c) the progradant unit which onlaps the Plio-Pleistocene sequence seawards and the granitic basement on the present delta plain and northern coast. The morphology of the sedimentary bodies, isobath maps and marine geophysical data enabled us to gain fresh insights into the evolution of the delta and its prodelta and into the various relict sand bodies on the inner shelf. The evolution of the coastline can be followed during the prograding process of the lower units from the successive coastal and internal lagoons. These coastal lagoons were conditioned by river changes and basement morphology. Once the sea level maximum was attained, the prograding units covered these morphologies, resulting in the present delta configuration.

Coupling Basin and Reservoir Simulators for an Improved CO2 Injection Flow Model

Abstract The goal of this work is to model the present basin-scale groundwater flow of the Paris basin with a basin modelling approach and to use it to initialise a reservoir model for CO 2 injection. It is part of the ULTimateCO2 FP7 European funded project which aims to significantly enhance our knowledge of specific processes that may affect the long-term fate of geologically stored CO 2 . Basin models simulate the history of sedimentary basins through time by coupling geological events such as deposition, erosion, compaction, structural deformation and subsurface flow simulation. In order to construct the basin model of the Paris Basin in IFPEN basin software TemisFlow®, several types of data were gathered. The current surface topography and 11 horizons representing the top of selected main geological layers (from basement to surface) were constructed from outcrop boundaries, wells and isobath maps. Seven erosion maps for the main unconformities recorded in the Paris Basin were also constructed to complete the burial history of the sedimentary basin. TemisFlow® computes pressure, temperature and salinity fields over the basin history up to the present-day. The final state of the basin simulation is then used as initial state of the reservoir numerical model (Coores TM ). The latter is used to simulate the injection of CO 2 and its effects on the pressure field for instance.

The paleo-Etel River incised valley on the Southern Brittany inner shelf (Atlantic coast, France): Preservation of Holocene transgression within the remnant of a middle Pleistocene incision?

The study of a dense and regular grid of 59 High Resolution seismic profiles supplemented by 23 superficial vibro-cores has led to propose a three-dimensional detailed sedimentary model of the paleo-Etel River buried valley located on the inner shelf of South Brittany (Atlantic Coast, France).This fluvial valley (S2) lies at a mean depth of −37m below mean sea level above Paleozoic meta-sediments (U1) and middle to late Eocene formations (U2). No fluvial deposits seem to have been preserved. Its sedimentary record reflects the retrogradation of estuarine environments (tidal flats (U3), Tidal Ravinement Surface (S3), and intra to pro-estuarine sand bars (U4/S4/U5)) during the Holocene transgression (ca. 9000 to 7500calyr BP). Open marine environments seal up this estuary with the onset of a flat Wave Ravinement Surface (S5) overlain by thin muddy-sands deposits (U6-F2) interpreted as low-energy open marine conditions (4250 to 1800calyr BP). Shoreface sands, made up of coarse sands bodies migrating landwards (U6-F3, F4), cover this sedimentary sequence since 1800calyr BP.A numerical interpolation of the picked seimic horizons was proceed to produce seismic isopach maps of sedimentary units and isobath maps of their boundary surfaces. Furthermore, the isobath map of the basal channel topography has enabled us to calculate some geomorphological features (W/D ratio, mean slope, sinuosity index) that characterized the type of channel pattern. The Etel River geomorphological indexes correspond to a straight channel that involves bed-load transportation processes, potentially associated to braided deposits if the sediment load is sufficient. Compared to the Vilaine River, which braided regime is dated at middle Pleistocene in several zones, we assume a possible mainly climatic control for river incisions in Southern Brittany linked to drastical changes in climate regimes occurring during the “Middle Pleistocene Transition”.

Geophysics Contribution for the Determination of Aquifers with a Case Study

The determination and monitoring of aquifer formations on the eastern border of Moroccan Gharb basin are very difficult because of their spatial and temporal variation. To delimit these formations, a geophysical survey of 52 geoelectric soundings was performed with a mesh of 500 m and electrodes distance between 1000 m and 3000 m. Geoelectric sections and resistivity maps show a horst and graben structure. The correlation of existing oil drillings shows that the Jurassic and Neogene formations are both affected by normal faults causing Jurassic deposits collapse with local thickening of the Miocene deposits, and reverse faults delimiting tectonic slices due to tension caused by prerifaine nappe advance. This fact confirms the generated structure by the resistivity method. The isobath map of resistant formations's roof show average depths extending from 400 to 800 m for calcareous sandstone that are potential aquifers while oil drillings indicate over 1000 m depths.

The first printed isobath map

Detailed sea depth data and hydrological observations for the first printed isobath map were collected by Marsigli in the Gulf of Lion three hundred years ago. This map, an annex to his large and comprehensive volume on the seas, has been considered one of the forerunners of thematic maps. Although the cartographic and oceanographic literature often refers to Marsigli’s map, several authors have misinterpreted the data and information contained in the map. This paper re-examines the map legend and the drawing of the map, compares the first isobath map with a modern map of the area, and finally evaluates Marsigli’s contribution to earth sciences.

Geological evolution and structural style of the Palaeozoic Tafilalt sub‐basin, eastern Anti‐Atlas (Morocco, North Africa)

AbstractThe Tafilalt is one of a number of generally unexplored sub‐basins in the eastern Anti‐Atlas of Morocco, all of which probably underwent a similar tectono‐stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000 km of 2‐D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi‐phase deformation history for the Palaeozoic‐aged Tafilalt sub‐basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic‐aged strata, producing a structural style characteristic of thin‐skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault‐propagation folding related to the thrust imbricates that ramp up‐section from the décollement. Copyright © 2007 John Wiley & Sons, Ltd.

Contribution à l'étude d'une partie du bassin d'Essaouira (Maroc) par sismique réflexion

Abstract A large number of seismic reflection lines and boreholes have been carried out in the Essaouira Basin by the oil industry. The present study concentrates on the reinterpretation of these data in the restricted area of Khemis Meskala, in order to better characterise the structure of the Cretaceous aquiferous system. The reflector corresponding to the bottom of the Vraconian formation has been identified on the different seismic sections. This horizon, which marks the base of the aquiferous system, was first digitised on time migration sections and then converted to depth sections using a suitable linear velocity law. The isobath map of the bottom of the Vraconian resulting from this study images the 3D geometrical structure of this horizon and shows that it is slightly folded in domes and basins. This document will be useful for rationalising the future hydrogeological researches that will be undertaken in the Khemis Meskala area. To cite this article: M. Jaffal et al., C. R. Geoscience 334 (2002) 229–234.

Accuracy of the spatial representation of the seafloor with bathymetric sidescan sonars

When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.

Handil Field, East Kalimantan, Indonesia: ABSTRACT

Handil field is located in the swamp area of the present delta of the Mahakam River in East Kalimantan, Indonesia, in the central part of the Tertiary Kutei basin. The anticlinal feature was found by seismic work in 1973, the discovery well being drilled in April 1974. An east-west fault perpendicular to the axis of the anticline (10.5 km long, 4.5 km wide) divides the field into two blocks of equivalent area. Areal closure is 35 sq km. Vertical closure increases with depth through the hydrocarbon-bearing section. Most of the 120 reservoir sands between 500 and 2,900 m are tidal to fluvial delta-plain sediments (middle to late Miocene). Most of them are oil bearing with a gas cap. Their types of deposition can be identified as channel fills, offshore bars, etc. A high pressure zone is encountered below 2,900 m, where deeper prospects remain for investigation. More than 50 significant markers (lignite, carbonate streaks) are used to correlate the sand bodies. Vertically, the field has been divided into six zones corresponding to End_Page 545------------------------------ changes in environmental conditions and/or oil characteristics. Isobath maps show a displacement to the southwest (approximately 2.5 km) of the top of the anticline from deeper horizons to surface. In the upper and shallow zones, hydrocarbons are found in the south block only, divided into smaller blocks by an east-west fault pattern. Daily production is 160,000 bbl. Cumulative production is 125 million STB (October 1978). End_of_Article - Last_Page 546------------

Structure of the Barents Sea from seismic refraction

The Barents Sea is underlain by a thick (up to 5 km) sedimentary basin. Seismic refraction has outlined four main velocity discontinuities which have been correlated with geological units on the basis of the geological history of the region. The basin is underlain by a crystalline basement, the nature of which cannot be determined on the basis of seismic velocity alone. Metamorphosed Paleozoic units (velocities around 5–4 km/sec) lie over this basement. Their thickness is not well established but appears to reach 1 or 2 km in some cases. A very distinct and thick (up to 2.5 km) layer (4.1 km/sec) is found almost everywhere and is thought to correspond to a major discontinuity at the end ot the Paleozoic. This discontinuity is followed by a variable velocity layer (2.4–4 km/sec, up to 1.2 km thick) which includes Mesozoic and Cenozoic sediments and is limited to the south of the Barents Sea. The absence of thick Tertiary deposits support the idea that the Barents shelf was emergent at that time. Recent low-velocity sediments are found close to the shelf edge. Gravity anomaly trends reflect a series of depressions of the 5.4-km/sec layer isobath map and suggest that the deeper part of the basin is made of a succession of faulted blocks or intense folds.

ETUDE DES DIAPIRS EN ALSACE ET BADEN‐WURTEMBERG PAR LA METHODE DU RECTANGLE DE RESISTIVITE*

AbstractThe study of tectonics of salt and of diapirs in particular is an important problem in the mining field as well as in that of petroleum exploration. This paper describes surveys that were carried out, using the method of the rectangle of resistivities.After stating the principle of the method, the way it is carried out and its advantages, three examples are discussed: two in the Alsace plain (Hettenschlag‐Oberentzen and Blodelsheim), the third in Baden‐Wurtemberg (Weinstetten‐Heitersheim). Geological conditions are practically the same (resistive alluvia, very conductive marls and resistive salt series); the depth at which the top of the salt was found varied from 100 meters to more than 1000 meters. Maps of resistivities (with current electrode spacing of 6000 meters) and graphs of a few electrical soundings are presented, together with the results obtained under the form of isobath maps of the top of the salt series.The surveys lasted 26 months and covered 171 square kilometers. The work presented corresponds to three sections totalling 93 square kilometers and was chosen because of the diversity of the tectonics. Four drill holes have been carried out since then and have confirmed the results quite well.The method may be extended to the survey of the tectonics of a salt series or of a resistive substratum, for instance a limestone formation, that are deeper than the above cases (2000 meters or more), using current electrode spacing of 20 kilometers. Surveys of this type have already been realized in the field.

The Southern Extremity of the "Clinton" Gas Pools in Ohio

Published in Petroleum Transactions, AIME, Volume 57, 1917, pages 984–988. The Cleveland (O.) gas pool described by Frank R. Van Horn,' is the northern extremity of the great "Clinton" sand gas development in Ohio. Numerous gas pools have been developed in this formation, which are now more or less connected, link by link, forming an almost continuous gas pool, starting at Cleveland, and running thence southward through Cuyahoga, Medina, Wayne, Ashland, Richland, Knox, Licking, Fairfield, Hocking, and Vinton counties. The present southern extremity of these connected pools is in Richland Township, Vinton County (Fig. 1). The writer offers his analysis of the Richland Township development which may serve to compare the northern and southern extremities. Geology The geologist is greatly handicapped by the lack of a suitable key- horizon, inasmuch as the outcropping rocks are members of the "Big Injun" series of the Logan Group (Mississippian). The underlying shales (Waverly shales) show that considerable erosion took place before the deposition of the "Big Injun," which accounts for the presence of an erosion plane between these two formations, further complicating the study of the geological structure from surface outcrops. A reliable structural map of the "Clinton" is obtainable only by spirit-level elevations at the mouth of the various wells drilled, and the elevation of the sand calculated from the logs of the wells. The accompanying isobath map has been prepared in this manner (Fig. 2). Since the completion of this map, numerous wells have been drilled in the town- ship, which, if taken into consideration, might cause a slight variation in the appearance of the contour lines. The monotonous monoclinal structure of the "Clinton" sand is evident from this map. The thickness of the Berea is variable from place to place without any regularity; but in the other formations cited, the smaller measurements are met with in the western part of the township, the thickening taking place toward the east (Fig. 3). The Berea lies at an elevation of about 250 ft. above sea level at the western line, and is close to sea level at the eastern line of the township. The average dip for the Berea is about 35 ft. per mile. This compares with an average dip of 80 ft. per mile for the "Clinton" in the same territory. The difference in dip is due to the lateral variation of the intervening strata. T.P. 057–48