S.B. Kroonenberg

The wandering of the Volga delta: a response to rapid Caspian sea-level change

Due to its very low gradient and absence of tide and surf, the Volga delta is an even more extreme example of the fluvially dominated type than the Mississippi delta. However, it differs from all other large delta systems in that it borders a closed basin, the Caspian Sea, now at -26 m below global sea-level. Caspian sea-level is much more dynamic than that of the world oceans, and rises at present about 1.5 cm/yr, a hundred time the eustatic rate. Within the Quatemary, sea-level oscillations of at least 5 orders of magnitudes have been distinguished, which seem grossly out of phase with eustatic sea-level. Between the Weichselian Early Khvalyn highstand of +50 m and the Early Holocene Mangyshlak lowstand at -80 m the apex of the Volga delta has wandered over 700 km alongstream. The present-day Volga delta is not a highstand deposit but probably represents a minor transgression in a major regressional stage. The delta does not show a coarsening-upwards sedimentary sequence, but consists of a Weichselian transgressional fining-upwards sequence topped by eolian deposits, in which the delta distributary channels have been incised. Present-day sedimentation is limited to a narrow fringe along the delta front, and to deeper waters over 200 km offshore. Sea-level changes outpaced aggradation to such an extent, that Volga sediment is spread over the whole North Caspian Plain. Sequence-stratigraphical principles are difficult to apply because sea-level cycles of five orders of magnitude are superimposed, and because there is not enough sediment loading or tectonic subsidence to create sufficient accommodation space.

Process-Response Modeling of Wave-Dominated Coastal Systems: Simulating Evolution and Stratigraphy on Geological Timescales

ABSTRACT Numerical modeling on a geological timescale is a rapidly expanding tool to investigate controls on formation of the stratigraphic record. Modeling enables us to test existing ideas, but verification of model results is commonly difficult. Many models are based on geometric or diffusion rules, yet neither type of model has much relevance with actual processes that control sedimentary systems. Here we describe a process-response approach to model the evolution and stratigraphy of wave-dominated coastal systems in two dimensions, based on simple approximations of cross-shore erosion and sedimentation. Separating erosion and deposition functions enables us to simulate coastal evolution, stratigraphy, erosion surfaces, and transport of multiple-grain-size classes. The simulated stratigraphic record contains detailed information on grain size and stratal geometry. We calibrated the model with data sets on coastal transgression in the Caspian Sea, Dagestan, and on grain-size distributions at the island of Terschelling, The Netherlands. Furthermore, hypothetical examples are presented to show the effect of changes in sea level and sediment supply, substrate slope, and sediment size distribution. These tests show that the model is capable of reproducing widely accepted conceptual models of coastal evolution on geological timescales (progradation, aggradation, and various modes of retrogradation).

SMALL-SCALE STRATIGRAPHY IN A LARGE RAMP DELTA: RECENT AND HOLOCENE SEDIMENTATION IN THE VOLGA DELTA, CASPIAN SEA

The Volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient (f5 cm/km) and by being affected by the rapid sea-level changes of the Caspian Sea, at rates up to a hundred times the global sealevel rise. This paper reports (1) the morphological and facies development of part of the lower delta during the last full sealevel cycle between 1929 and 1995, as monitored using remote sensing and field mapping, and (2) the Holocene development of the delta from outcrop data and augered transects. During a sea-level fall of 3 m between 1929 and 1977, rapid progradation of levees, composed of fine sand, took place along over 800 distributary channels along the delta front. Smaller distributaries became filled with clay and organics. During the 3-m sea-level rise from 1977 to 1995, aggradation occurred, leading to deposition of silt and clay on the levees and minor filling of the flood basins. Sedimentation rates as established with 137 Cs dating are up to 2–5 cm/year. Total thickness of Holocene deposits in the lower delta plain is 4–10 m.

A method to evaluate the capability of Landsat-5 TM band 6 data for sub-pixel coal fire detection

On the basis of the method of converting the radiance from thermal remote sensing data into radiant temperature, this paper presents a method to evaluate the capability of Landsat TM thermal data for the detection of sub-pixel coal fires with respect to their sizes and temperatures. This method can also be used for the temperature estimation of coal fire areas of sub-pixel size, with the knowledge of the fire size being provided by airborne thermal scanner data or field survey data.

Micromorphological analysis of effects of alternating phases of landscape stability and instability on two soil profiles in Galicia, N.W. Spain

Abstract Two complex profiles in slope deposits in Galicia, Spain, were examined both in the field and in the laboratory. One profile consists of humous colluvium on solifluction material overlying gabbro, the other shows various layers of humous collovium on granite. The micromorphology and soil chemistry revealed an oscillation in environmental conditions — periods of landscape stability and soil formation, alternating with periods of erosion and deposition — which was not readily evident from field studies. The shortcomings of existing systems of soil horizon nomenclatures and classification schemes of slope deposits became very evident.

Imaging spectrometry data correlated to hydrocarbon microseepage

Modular Airborne Imaging Spectrometer (MAIS) data were used to map hydrocarbon microseepages in the Weibei Depression, Peoples Republic of China, as an aid to petroleum exploration. To convert the radiance data to reflectance, the Empirical Line Method was used and the resulting data were similar to the field spectra. After first delineating the wheat fields, three bands (at 719.75nm, 739nm and 758.25nm) were used to map the pixels that had a red shift. A neighbourhood summation function was applied to evaluate which pixels were more likely to be anomalies. The non-systematic geometric distortions were corrected with the aid of linear features in the image and subsequently the systematic geometric distortions were corrected using ground control points. Ethane concentrations of 217 soil samples were used to assess the mapping result. It appears that high ethane concentrations in the map area are positively correlated to red-edge shift, which suggests that a high ethane concentration in soil may cause red-edge shift in wheat spectra. However, sub-surface structure and stratigraphy must be considered as well when analysing MAIS data.

Zircon age constraints on sediment provenance in the Caspian region

Sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages for detrital zircons from the Caspian region reveal the age ranges of basement terrains that supplied the sediment. One sample from the modern Volga river has groupings at c. 340–370 Ma, c. 900–1300 Ma and c. 1450–1800 Ma, with a small number of older zircons. This is consistent with derivation from the Precambrian basement of the East European Craton, and Palaeozoic arcs in the Urals. Mid- and Late Proterozoic components may be derived from beyond the present Volga drainage basin, such as the Sveconorwegian orogen. A Bajocian sandstone from the Greater Caucasus has 73% zircons that post-date 350 Ma. Ages cluster at c. 165–185 Ma, c. 220–260 Ma, c. 280–360 Ma and c. 440–460 Ma. This pattern suggests derivation from Palaeozoic basement of the Greater Caucasus itself and/or the Scythian Platform, and igneous rocks generated at a Jurassic arc in the Lesser Caucasus. Four samples from the Lower Pliocene Productive Series of the South Caspian Basin have common Phanerozoic grains, and groups between c. 900–1300 Ma and 1500–2000 Ma. Each sample contains zircons dated to c. 2700 Ma. The overall age patterns in the Productive Series samples suggest a combination of East European Craton and Greater Caucasus source components.

Reconstructions of deltaic environments from Holocene palynological records in the Volga delta, northern Caspian Sea

New palynological and ostracod data are presented from the Holocene Volga delta, obtained from short cores and surface samples collected in the Damchik region, near Astrakhan, Russian Federation in the northern Caspian Sea. Four phases of delta deposition are recognized and constrained by accelerated mass spectrometry (AMS) radiocarbon ages. Palynological records show that erosive channels, dunes (Baer hills) and inter-dune lakes were present during the period 11,500–8900 cal. BP at the time of the Mangyshlak Caspian lowstand. The period 8900–3770 cal. BP was characterized regionally by extensive steppe vegetation, with forest present at times with warmer, more humid climates, and with halophytic and xerophytic vegetation present at times of drought. The period 3770–2080 cal. BP was a time of active delta deposition, with forest or woodland close to the delta, indicating relatively warm and humid climates and variable Caspian Sea levels. From 2080 cal. BP to the present-day, aquatic pollen is frequent in highstand intervals and herbaceous pollen and fungal hyphae frequent in lowstand intervals. Soils and incised valley sediments are associated with the regional Derbent regression and may be time-equivalent with the ‘Medieval Warm Period’. Fungal spores are an indicator of erosional or aeolian processes, whereas fungal hyphae are associated with soil formation. Freshwater algae, ostracods and dinocysts indicate mainly freshwater conditions during the Holocene with minor brackish influences. Dinocysts present include Spiniferites cruciformis, Caspidinium rugosum, Impagidinium caspienense and Pterocysta cruciformis, the latter a new record for the Caspian Sea. The Holocene Volga delta is a partial analogue for the much larger oil and gas bearing Mio-Pliocene palaeo-Volga delta.

Modelling Holocene stratigraphy and depocentre migration of the Volga delta due to Caspian Sea-level change

The Volga system is sensitive to allogenic control due to its low on- and offshore gradient (similar to 5 cm/km). In sequence stratigraphy, little attention has been paid to the effects of sea-level change in these ramp-margin fluvio-deltaic settings. The high-frequency sea-level changes of the Caspian basin have considerable amplitude (up to 18 m) over the Holocene time-span, which is usually considered as the lower boundary of fifth-order cycles. A process-response model, AQUATELLUS, has been used to investigate fluvio-deltaic response to sea-level fluctuation. Calibration of the model with measured data over the last century, comprising a full 3-m sea-level cycle, showed plausible progradation and sedimentation rates. The numerical modelling showed that sea-level changes forced the Holocene Volga delta to migrate similar to 200 km over the Caspian plain, leaving only thin laterally extensive deposits. The frequent depocentre shifts add a whole new perspective to the ongoing discussion about the impact of sea-level changes along the longitudinal profile. The periods during which significant deposition occurred coincide with the times that migration distances were relatively low. Thicker progradational wedges have been deposited at these time intervals, at similar to 9000-8000, similar to 7400-6700, similar to 5200-3700 and similar to 2400-900 years BP. C-14 dated deposits in the lower delta plain area corroborate the model output. Remarkably, this is both in highstand and lowstand conditions. The low gradient makes wave effects insignificant and tides are nonexistent, so that the fluvial deposits are hardly reworked and no shoreface facies or maximum flooding surface develop. The Volga delta response indicates that sequence-stratigraphic concepts are not scale-independent in low-gradient settings and that short-term high-frequency sea-level changes have a far-reaching impact on the stratigraphy

The Impact of Rapid Sea Level Changes on Recent Azerbaijan Beach Ridges

Abstract A ground-penetrating radar survey of a newly formed series of beach ridges along the southern Azerbaijan coast, Caspian Sea, illustrates rapid coastal response to the most recent sea level fall of 0.8 m in the Caspian Sea between 1995 and 1999. Effects of seasonal sea level fluctuations as well as individual storm occurrences can be linked to depositional beds on the ground-penetrating radar profiles. The beach ridge system is swash built and formed primarily under fair weather conditions. Ridge and swale topography can be related to seasonal sea level change. The rapid sea level change in the Caspian Sea combined with surface and subsurface data on coastal beach ridges provides a unique opportunity to observe and reconstruct coastal evolution at a resolution not possible along other oceanic coasts.