Depression Zone Research Articles

Palaeogeomorphology and its control on the development of sequence stratigraphy and depositional systems of the Early Silurian in the Tarim Basin

The Silurian in the Tarim Basin was deposited on the basement deformed by the Caledonian tectonic movements at the end of the Late Ordovician. The development and distribution of sedimentary sequences of the Early Silurian have been clearly controlled by the palaeogeomorphology of the Late Ordovician. Based on unconformity characteristics and distribution of erosion, several zones can be differentiated including a high uplifted erosion zone, a transitional slope zone and a depression zone. The central and west Tabei Uplift zones show high angular unconformity and intense erosion. The Tarim Basin in the late Ordovician shows characteristics of higher in the west, lower in the east while higher in the south, lower in the north. The Early Silurian mainly developed transgressive and highstand systems tracts on the whole, while the lowstand systems tract only developed partly below the slope break. The palaeogeomorphology controlled the clastic source supply and deposit distribution. Braided delta system and tidal flat-estuary system were deposited. The duration of uplifting of the Tazhong paleouplift was longer than that of the Tabei paleo-uplift, and deposition was later. This led to the lower and middle members of the Kepingtage Formation missing in that area. As a large-scale transgression occurred during the deposition period of the upper member of the Kepingtage Formation, sediment from the west of the basin was transported and deposited by tides and waves, forming tidal-marine debris systems above the uplift. Proximal alluvial fan and fan delta coarse clastic deposits developed in proximal uplift zone in the east and southeast of the basin, and braided delta put forward to the transitional zone between the edge of uplift and the sea. Large-scale tidal channel, sub-distributary channel and mouth bar of the delta front can form favorable reservoirs, and they are primary targets for oil and gas exploration. This research on sequence-depositional systems development and distribution controlled by palaeogeomorphology is significant in guiding the prediction of reservoir sandstones.

Relationship between earthquake swarm, rifting history, magmatism and pore pressure diffusion — an example from South Andaman Sea, India

An extraordinarily strong and persistent earthquake swarm (Andaman swarm 2005) originated in the Andaman back-arc following the aftershock sequences of the 26 December 2004 Sumatra earthquake. The swarm (n = 651, mb max = 5.9) came mainly in two phases: January 26-31 and Feb. - Aug. 2005, in an area of size 90 x 40 km 2 , at the centre of which lies a broad bathymetric depression and high gravity zone. The swarm demonstrates a complex faulting series, initially the strike-slip motion followed by normal faulting in repetitive sequences, whose representative fault planes orient at high angle to the regional faults. The swarm character as well as the distribution of stress-axes and their correlation to tectonic features lends speculation for formation of a nascent rift segment in NW-SE direction at the doorstep of the Sewell Seamount. The swarm has given rise to 21 episodes of rifting activities of variable time extent within 26 -31 January 2005. The r-t plots corresponding to the swarm data, modelled with variable hydraulic diffusivity (D) values 4, 6, 8 and 10 m 2 /s, suggest for excess pressure front from ascending magmatic fluid. This eventually heralded the rifting; causing pore pressure perturbations that propagated in accordance with known diffusion parabolic equations.

Genetic suppositions of oil and gas formation and conditions of hydrocarbon deposits in Mesozoic-Cenozoic sediments in the Caspian Sea shelf

Source rocks are present in all the stratigraphic units of the Mesozoic-Cenozoic deposits of the Turkmen shelf in the Caspian Sea. The highest source rock potential is characteristic of I terrigenous and carbonate-terrigenous rocks of Middle Jurassic age, and the Aptian, Paleogene, Neogene and Apsheron stages of the Quaternary system. To reveal the formation conditions of hydrocarbon deposits within Southwestern Turkmenistan, the principle of chemical thermodynamics is primarily used via the calculation of the free energy of gaseous hydrocarbons. This showed that hydrocarbon deposits within the topmost depositional complex (the red-colored strata of the Middle Miocene at the Akchagyl and Apsheron stages) are syngenetic; their formation was due to lateral migration from even-aged deposits from depression zones neighboring the uplifts.

Disturbances of the topside ionosphere caused by typhoons

The measurements on board the Cosmos-1809 satellite of various parameters of the topside ionosphere plasma during more than ten typhoons in various regions are analyzed. It is shown that specific zones of increased pressure of the electron gas, electric field, and intense ion oscillations are formed during the intensification stage. In some cases the “typhoon eye” is formed over the tropical depression zone in the ionosphere, that is, the region with sharply decreased plasma density and pressure is observed a day and more prior to the moment when it happens in the atmosphere.

Late Quaternary history of paleoseismic activity along the Hohhot Segmentof the Daqingshan piedmont faultin Hetao depression zone, North China

The Daqingshan Piedmont Fault (DPF) is one of the major active normal faults in the Hetao depression zone in the northern part of Ordos Block, North China. It extends in NEE direction along the Daqingshan piedmont zone in the eastern part of the depression, dipping to the south, for a length of 223 km. The fault formed in the Eocene and underwent strong movement during the Cenozoic time. Its vertical displacement amplitude has exceeded 2400 m since the Quaternary. The fault can be divided into 5 active segments. Paleoseismological studies were concentrated on its western part from Baotou to Tumdzuoqi whereas the Hohhot Segment to the east was scarcely studied. To fill this gap of knowlegde, the authors carried out in-depth study on the Daqingshan piedmont fault during recent years. Excavation of trenches at Kuisu, Ulanblang, and Bakouzi sites on the Hohhot Segment of the Daqingshan piedmont fault and study of geomorphic surfaces allow us to identify and date paleoearthquakes and to evaluate the completeness of paleoseismic activity history. This was done both for the individual sites and for the entire segment since the Late Quaternary using the «method for displacement confining» along the fault and «method for correlation between multiple trenches». In this paper we present the geological loggings of two trenches at Kuisu site, provide the evidence for 6 events since 19 ka BP and the cumulative displacement amount produced by them is around 7 m. But the cumulative displacement amount obtained from difference in heights of geomorphic surfaces is 5.??.5.5 m. Results of tests using the method of displacement confining show that the event sequence revealed at this site can be considered complete. The data supplemented with information obtained in the Ulanblang and Bakouzi trenches show that 7 paleoseismic events occurred on the Hohhot Fault Segment since 19 ka BP, i.e. they occurred at 18.75 ± 0.75 ka, 16.97 ± ± 0.96 ka, 14.65 ± 0.67 ka, 11.82 ± 0.69 ka, 9.45 ± 0.26 ka, 6.83 ± 0.26 ka, and 4.50 ± 0.23 ka BP, respectively, and the average recurrence interval is 2.375 ± 0.432 ka. These results basically reflects the history of paleoseismic activity on the fault segment in this period of time.

September 2005 mega‐dike emplacement in the Manda‐Harraro nascent oceanic rift (Afar depression)

Local and regional seismic data constrain the space‐time history of deformation and likely magma sources for the September 2005 diking episode in the Manda‐Harraro rift zone of the Afar depression. The results distinguish three centers from which subhorizontal dike propagation progressed: two distinct sources around the Dabbahu‐Gab'ho Volcanic Complex (DVC) and the third at the Ado'Ale Volcanic Complex (AVC). The temporal development of seismicity shows that the majority of the dike volume is fed from beneath AVC and migrated laterally with an average rate of 15–30 cm/sec. This dike emplacement at a divergent plate boundary is unusual due to the rapid intrusion of a large volume of magma and the large amount of seismic moment release. We interpret this volcano‐tectonic crisis as a complex interaction of multiple magma plumbing sources and lithosphere at a plate boundary under extension. Such repeated episodes will eventually shape the incipient oceanic rift morphology.

Acoustic Detection of the Causative Fault of 1969 Ms7.4 Earthquake in Bohai Sea

AbstractThe Ms7.4 earthquake of 18 July, 1969 is the only strong earthquake in the Bohai Sea that has been recorded by seismometers. Arguments about this large earthquake are focused on its causative fault. To tackle this problem, three cruises in the epicenter region from 2005 to 2008 were executed and 3 kinds of acoustic data with high‐resolution, including shallow penetrated single channel seismic data, sidescan sonar data and CHIRP data were collected. This paper presents the results based on these new acoustic data. A small depression zone 2~3 m beneath the seabed is first found in the Holocene sediments in the epicenter region. The zone with an NE30‐ strike is 20 km long and 3 km wide. CHIRP data reveal that depositional border formed at about 5000 a B.P. has a throw of 1.5 m in the zone. The good match of the locations of the depression zone and the BZ28 fault and aftershocks distribution of the 1969 earthquake suggests that the depression zone is the result of tectonic activities of the BZ28 fault and the bottom deformation of sequence A which was formed since 150 a B.P. is caused by 1969 earthquake. The BZ28 fault with a NE30° strike, a branch fault of the Tan‐Lu Fault Zone, is the causative fault of the Ms7.4 earthquake. CHIRP data show that the latest faulting age is the late Holocene. Based on the forming age of stratigraphic sequences and vertical displacement of the fault, the vertical slip rate of the BZ28 fault since late Pleistocene is calculated. The results show that the rate during the Holocene is 0.3 mm/a, which is larger than 0.05 mm/a during the late Pleistocene‐Holocene, reflecting a trend of aggrandizement.

Correlations between shortening rate, uplift rate, and inversion rate in central inversion zone of Xihu depression, East China Sea basin

Late Miocene shortening rate, uplift rate, and inversion rate in the central inversion zone of the Xihu (西湖) depression, East China Sea basin, were independently determined from a large number of 2D reflection seismic data and methods. Shortening rate was estimated from the 2DMOVE balanced cross-section technology, uplift rate was calculated after absolute erosions were determined from seismic data during the uplifting time, and inversion rate was measured using the improved calculation method by Song (1997). The cross correlations among shortening rate, uplift rate, and inversion rate show a good positive relationship, with some differences existing in local areas. This article analyzes the cross correlation between these structural rates and discusses the dynamics of mechanisms for basin inversion and their influence on hydrocarbon accumulation.

Evolution of the Girilambone regolith landscape, central-western New South Wales

A model of regolith and landscape evolution for the Girilambone region is derived from regolith–landform mapping and interpretation of drillhole information, the latter being underpinned by detailed petrography and Portable Infrared Mineral Analyser (PIMA) characterisation. The model is partly constrained by the interpretation of palynological, paleomagnetic, apatite fission-track, and airborne magnetic data. The model interprets the architecture of the three main sediment sequences and explains their derivation: a possible Late Jurassic fluvial sequence, an Early Cretaceous estuarine–shallow-marine and fluviolacustrine sequence (both sequences being part of the Surat Basin), and a Late Pliocene to Holocene colluvial–alluvial sequence. Implications of this model are that much, if not all, of the Cobar Uplands was covered by a shallow sea in the Early Cretaceous, and that neotectonic reactivation of north-trending Paleozoic faults caused the formation of the north-plunging depressed zone that contains the Mulga–Tindarey Paleovalley System.

LITHOLOGY AND DATING OF THE MIDDLE-UPPER EOCENE DEPOSITS IN THE JUNCTION ZONE OF THE DNIEPER-DONETS DEPRESSION AND THE DONETS BASIN

A lithologic and biostratigraphic study of the Kiev and Obukhov regional stages in the junction zone of the Dnieper-Donets Depression, Voronezh anteclise and northwest margin of the Donets Basin has confirmed two-component structure of the Kiev regional stage, with chertification being typical of the upper part of the Kiev and lower part of the Obukhov regional stages. Foraminiferal layers with Acarinina kiewensis and layers with Pseudoclavulina subbotinae-Robulus dimorphus, nannoplankton Zone NP16, dinocyst Zone DP9 and diatom layers with Stictodiscus kossutii have been recognized in the lower carbonaceous part of Kiev deposits. Layers with agglutinated foraminifers, dinocyst Zone DP10 and the diatom Cristodiscus succinctus Zone have been recognized in the non-carbonate part of Kiev deposits. Diatomes of the Plagiogramma paleоgena Zone have been identified in the lower part of Obukhov deposits. According to the identified microfossil assemblages, the Kiev and Obukhov regional stages in the region under study are dated to be Bartonian and Priabonian, respectively. This study reveals difficulties connected with the recognition of standard oceanic zones in epicontinental basins and points to the necessity of creating regional biostratigraphic schemes.

The floating astronomical time scale for the terrestrial Late Cretaceous Qingshankou Formation from the Songliao Basin of Northeast China and its stratigraphic and paleoclimate implications

The Upper Cretaceous Qingshankou Formation (K 2qn) in the Songliao Basin (SLB) of Northeast China consists of up to 550 m thick, lacustrine mudstone and shale that constitute one of the most important source rocks of the Daqing oil field. A high-resolution cyclostratigraphic analysis of the natural gamma-ray logging from 10 wells of the Qingshankou Formation (K 2qn) reveals orbital cycles of precession (20 ka), obliquity (40 ka) and eccentricity (100 ka and 405 ka), providing strong evidence for astronomically driven climate changes in the Late Cretaceous terrestrial environments. Floating astronomical time scales (ATS) are established for all sections, which demonstrate variable durations of K 2qn across the basin (1.09 Ma–5.20 Ma) and strong diachroneity of the lacustrine strata. Four periods of high depositional rates can be identified in the central parts of the basin, possibly recording deposition during times of sustained wet climate and high chemical weathering. An ATS established from well M206 in the central depression zone of the basin, where the most complete and stable Milankovitch cycles are present, suggests that the maximum duration of the K 2qn is 5.20 Ma (from 94.27 Ma to 89.07 Ma; Late Cenomanian to Early Coniacian). The lacustrine anoxic event 1 (LAE1) at the Cenomanian–Turonian boundary lasted ~ 210–310 ka, during which the most prolific petroleum source rocks in SLB were deposited. The onset (~ 94.21–94.18 Ma) and duration (~ 210–310 Ka) of LAE1 in SLB are comparable to those of the oceanic anoxic event 2 (OAE2; onset at 94.21 Ma and duration of ~ 320–900 ka), suggesting that the same trigger mechanism, such as increased atmospheric CO 2 from large-scale igneous activity, may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems.

An Examination of Morphometric Variations in a Neotropical Toad Population (Proceratophrys cristiceps, Amphibia, Anura, Cycloramphidae)

The species Proceratophrys cristiceps belongs to the genus Proceratophrys within the family Cycloramphidae. These amphibians are found exclusively in South America in the morphoclimatic domain of the semi-arid depression zones in northeastern Brazil known as the Caatinga. We examined intrapopulational variation using univariate and multivariate statistics with traditional and geometric morphometrics, which supported the existence of two morphotypes of this species. Our results indicated significant degrees of variation in skeletal characteristics between some natural populations of this species. Careful analyses of variability levels are fundamental to avoid taxonomic errors, principally in populations that demonstrate characteristics intimately associated with their area of occurrence, as is the case of Proceratophrys cristiceps.

ベトナム北部Sam Nua Depression Zoneにおける堆積岩及び火成岩の地球化学

ベトナム北部Sam Nua Depression Zoneにおける堆積岩及び火成岩の地球化学

Constructing a 3D structural block diagram of the Central Basin in Marmara Sea by means of bathymetric and seismic data

In this study we made a comparative interpretation of multibeam bathymetric and seismic reflection data with different resolutions and penetration properties collected in the Central Basin of the Marmara Sea. Our main objectives were (i) to investigate and compare the active tectonic deformation observed on the sea bottom and within the uppermost sedimentary layers to that of the deep-seated deformation within the limits of resolution and penetration of the available geophysical data and (ii) to build a three-dimensional (3D) block diagram of the active tectonic and buried features by means of a sliced mapping technique. In this approach, we produced slice maps of the active and buried structural features at selected depths and then combined them to form a 3D structural block diagram. Motivation for our work was to produce a 3D structural diagram to derive a more detailed image of the structural features in the Central Basin where there is no available 3D seismic data. The observations from the bathymetry and seismic data and developed 3D diagram support the presence of a through-going strike-slip fault that forms a rotational depression zone against a right-stepping strike-slip faulting causing a pull-apart basin in the Central Depression zone.

Modèles d'astroblèmes d'après le déplacement des masses rocheuses : Charlevoix et le Ries

One can determine the movement of rock masses in the formation of an astrobleme by ascertaining the displacements of stratigraphic reference levels before and during the impact. A discontinuity in the zone of shock metamorphism in the Charlevoix (Quebec, Canada) structure corresponds with a major fault separating an irregularly uplifted crown area from a depressed inner zone. The displacement along this circular fault is inverse to the normal displacement of the layers of this structure, that is to say, a broad collapsed area of terraces and grabens on the outside, and a gradual central build-up in the inner zone. This phenomenon can be explained as a consequence of the formation of a crater of excavation through impact, where a force of expansion tends to raise the edges of the crater, as insertion continues to the bottom of the crater. An essentially similar model for small and large craters is inferred in the first phase of formation. The readjustment that follows depends on the size of the crater and the material impacted. Started by decompression, the readjustment tends to continue until balance occurs along the fracture slip surfaces that initially formed on impact. The fractures are filled by impact fault breccias, particularly by mylolisthenites. This readjustment also depends on the speed of the meteorite at impact, as suggested by the central prominences found in the Charlevoix and the bassin form for the Ries (Germany).

Significance of microhabitat heterogeneity in the spatial pattern and size-class structure of Anastatica hierochuntica L.

Abstract Anastatica hierochuntica L. (Brassicaceae) is a desert monocarpic annual species characterized by a topochory/ombrohydrochory type of seed dispersal. The hygrochastic nature of the dry skeletons (dead individuals) permits controlling seed dispersal by rain events. The amount of dispersed seeds is proportional to the intensity of rainfall. When light showers occur, seeds are released and remain in the site. Seeds dispersed in the vicinity of the mother or source plant (primary type of seed dispersal) resulted in clumped pattern and complicated interrelationships among size-classes of the population. Following heavy rainfall, most seeds are released and transported into small patches and shallow depressions which collect runoff water. The dead A. hierochuntica skeletons demonstrate site-dependent size-class structure, spatial pattern and spatial interrelationships in different microhabitats. Four microhabitat types have been sampled: runnels, patches and simple and compound depressions in two sites (gravel and sand). Ripley's K-function was used to analyze the spatial pattern in populations of A. hierochuntica skeletons in the study microhabitats. Clumped patterns were observed in nearly all of the study microhabitats. Populations of A. hierochuntica in the sand site were more productive than in the gravel site and usually had more individuals in the larger size-classes. In the compound-depression microhabitat, the degree of clumping decreased from the core zone to the intermediate zone then shifted into overdispersed pattern in the outer zone. At the within size-class level, the clumped pattern dominated in small size classes but shifted into random and overdispersed patterns in the larger size classes. Aggregation between small and large size-classes was not well-defined but large individuals were found closer to the smaller individuals than to those of their own class. In relation to the phytomass and the size-class structure, the outer zone of the simple depression and the outer and intermediate zones of the compound depression microhabitats were the most productive sites.

Room Temperature Plasticity of Zr<sub>65</sub>Al<sub>7.5</sub>Ni<sub>10</sub>Cu<sub>17.5-x</sub>Pd<sub>x</sub> Bulk Metallic Glasses

Monolithic Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5 hardly had plastic deformability in tension at room temperature, although Zr65Al7.5Ni10Pd17.5 showed a large plastic strain in compression. A depressed zone that is the evidence of viscous flow deformation (so-called viscous flow depression zone; VFD-zone) was observed for Zr65Al7.5Ni10Pd17.5 around the edge at the point of failure on its specimen surfaces. However, no VFD-zone was seen for Zr65Al7.5Ni10Cu17.5. Thus, a clear difference in tensile plastic behavior was found between Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5. A structural change in the vicinity of the fracture surface of Zr65Al7.5Ni10Pd17.5 was measured by micro-beam X-ray diffractometry (MB-XRD). We may be able to discuss the room temperature plasticity of Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses correlating with the phase stability of the amorphous and icosahedral quasi-crystalline phases.

Deformation-Induced Nanoscale Dynamic Transformation Studies in Zr-Al-Ni-Pd and Zr-Al-Ni-Cu Bulk Metallic Glasses

Nanoscale dynamic transformations during tensile and compressive deformation of Zr65Al7:5Ni10Cu17:5 and Zr65Al7:5Ni10Pd17:5 bulk metallic glasses have been investigated. Although no apparent differences are observed in the stress-strain curves in the tensile deformation between the two alloys, fine striations and depression zones with viscous flow appear at the fracture surface near the edge in the Zr65Al7:5Ni10Pd17:5 alloy. Unlike the Zr65Al7:5Ni10Cu17:5 alloy and other bulk metallic glasses, the Zr65Al7:5Ni10Pd17:5 bulk metallic glass exhibits a large plastic strain of approximately 7% during compressive deformation. By detailed examination of the microstructure, we provide direct evidence for nanoscale multistep shear band formation in the Zr65Al7:5Ni10Pd17:5 metallic glass. A novel nanoscale structure where fcc Zr2Ni nanocrystalline particles are arranged in ‘‘bandlike’’ areas in the glassy matrix is observed near the compressive fracture tip. The suppression of the propagation of the shear bands due to dynamic nanocrystallization causes this structure. Furthermore, the results are recognized as a novel phenomenon, a nanoscale dynamic structural change by shear band propagation, and provide a new method for improving the mechanical properties of bulk metallic glasses. [doi:10.2320/matertrans.MF200615]

Seismic Anisotropy in the Crust in Northwestern Capital Area of China

AbstractSeismic anisotropy is obtained in the crust in northwestern capital area by shear‐wave splitting analysis, using the SAM technique. The seismic data was recorded at the Capital Area Seismic Network from Jan. 2002 to Dec. 2003. The results at 14 stations in all, every of which has at least 3 records available or more, are statistically discussed in this paper. The statistical results show that the average polarization of fast shearwaves is NE69.9° ±44.5° and the time delay of slow shear‐waves is 4.44±2.93 (ms/km). The average polarization of fast shear‐waves of NE69.9° ±44.5° suggests the direction of maximum horizontal principal compressive stress in this area. The most predominant polarization direction of fast shear‐wave suggests the tectonic implication of horizontal principal compressive stress at the direction NWW or nearly E‐to‐W, which exposes the Zhangjiakou‐Penglai depression fault zones with strike NWW. According to the polarization of fast shear‐wave, this study verifies that the predominant polarizations of fast shear‐wave at stations on active faults are consistent with fault strike. Possibly, both the Nankou‐Sunhe fault and Xiadian fault are two active faults while the Babaoshan fault is possibly a less active fault. The polarizations of fast shear‐wave in the North China Basin show the complexity, consistent with the complicated pattern of regional principal compressive stress controlled locally, induced by many faults crossing in the depression zone within the basin. This study also suggests that the quick change of time delays of slow shear‐waves is possibly related to the temperature change in deep crust.

Rb-Sr Isochron and K-Ar ages of igneous rocks from the Samnua Depression Zone in Northern Vietnam

The Samnua Depresion Zone (SNDZ) extends NW-SE for more than 400 km from Northern Vietnam to Southwestern China. It represents the northern edge of the Indochina block and is separated from the South China block by the Songma fault. The zone is occupied mainly by Paleozoic sedimentary rocks and Mesozoic volcano -sedimentary successions that are intruded by Mesozoic intrusives and extrusives and by Cenozoic extrusives. Representative igneous rocks of the SNDZ were geochronologically investigated by the Rb-Sr whole rock and K-Ar biotite methods. The Rb-Sr ages obtained are 222 Ma for the Nuichua gabbros, 213 Ma for the Songma granitoid (SMG), 203 Ma for the Piabioc granitoid (PBG), 138 Ma for the Banmuong subvolca- nic granite, 27 Ma for the Banchieng granitoid (BCG), 218 Ma for the Dongtrau felsic volcanics, 186 Ma for the Muonghinh felsic volcanics and 5.8 Ma for the Cenozoic basaltic rocks (CBR). The K-Ar methods give 252 Ma for the SMG, 237 Ma for the PBG and 24 Ma for the BCG. The groundmass fraction of the CBR yields an age of 1.9 Ma. Geochronological comparison and using fossil records suggest that the Rb-Sr ages of Mesozoic igneous rocks provide apparent young age, a pseudo isochron age. The major igneous activity of the SNDZ took place during Late Permian -Triassic time to form granitic and felsic volcanic rocks, which were related to the continental volcanic arc magmatism. Minor intraplate igneous activity occurred in the Paleogene. This suggests that the tectonic environment of the SNDZ changed from a convergent plate margin to a matured continental margin in the time span between the Triassic and Paleogene.