Crustal structure of the Indian subcontinent

Studies carried out by various investigators up to 1971 to delineate the Indian crustal structure using body wave travel times, surface wave dispersion and gravity methods are summarised and reviewed. The average crustal thickness is found to be 35–40 km in the Indian peninsular shield, 30–35 km in the Indo Gangetic plains and 60–80 km in the Himalayas and the Tibetan plateau region. The limitations of the various methods used and the errors in the estimation of crustal thickness by them are discussed. As no deep refraction work for crustal studies has been carried out so far in India, this topic is not covered in this study.     

Tectonic implications of the earthquakes in the Indian subcontinent

The Bhuj earthquake (26 January 2001) in India and the Ghori earthquake (8 October 2005) in Pakistan, both occurred close to the Indian-Iranian plate boundary related to the activity along the intercontinental Chaman transform fault. It is suggested that the seismic activity along NNW — NNE trending weak zones or faults is more intense in the sub-continent than along the WNW trending zones. Since the stress along the former is less compressive but more of the shear or translational type. The devastative Koyna (1967) and Latur (1993) earthquakes both occurred along faults or weak zones that were close to the meridional rather than the equatorial trend. The Indian plate is moving to the north or NNE or NNW, along a rotational trajectory and hence the force tends to be more compressive along the equatorial weak zones. In contrast, it tends to be less compressive and more of the shear or translational along the weak zones that are close to meridional trend. The seismic activity is therefore more intense along the weak zones with NNW to NNE trend than along the ENE to EW trending zones.     

Stromatolites and sabkha cycles from the Lower Fars Formation (Miocene) of Iraq

Stromatolites and cryptalgal laminites are described from the Lower Fars Formation of Middle Miocene age from northern Iraq. The Lower Fars is comprised of many cycles of the sequence marl, limestone, gypsum. The microstructures of the stromatolites are described and compared with those of Recent algal mats. An intertidal depositional environment is indicated by the features of the cryptalgal limestones and by the presence of calcite pseudomorphs after gypsum. The significance of this interpretation in terms of Lower Fars sedimentation is discussed. It is concluded that the sulphate horizons formed in a supratidal setting and that the cycles resulted from repeated sabkha progradation.

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Zusammenfassung Charakteristisch für die untere Fars-Formation (Mittel-Miozän) im Nord-Irak sind Stromatolithe und kryptoalgische Plättchen. Das untere Fars wird aus zahlreichen Zyklen von Mergel, Kalk und Gips aufgebaut. Die Mikrostrukturen der Stromatolithe werden mit heutigen Algenrasen verglichen. Ein Ablagerungsraum in der intertidalZone ist durch die Merkmale des kryptoalgischen Kalkes und die Kalzit-Pseudomorphosen nach Gips angedeutet. Der Schluß folgt, daß die Sulphat-Horizonte im Supratidal entstanden und daß die Zyklen durch wiederholtes Sabkhawachstum entstanden sind.

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Résumé Sont décrites ici les stromatolites et les laminites cryptalgaires de la formation du Fars Inférieur d'âge Miocène Moyen du nord de l'Irak. Les Fars Inférieur comprend beaucoup de cycles formés de marne, calcaire, gypse. Les microstructures des stromatolites sont décrites et comparées avec celles des mattes algaires récentes. Un milieu de depôt intertidal est indiqué par les caractères des calcaires cryptalgaires et par la présence de pseudomorphoses de gypse en calcite. On discute l'importance de cette interprétation en termes de sédimentation du Fars Inférieur. En conclusion: les horizons sulfatés sont formés dans un emplacement supratidal et les cycles sont le résultat d'une progradation répétée de sabkha.

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High resolution numerical weather prediction over the Indian subcontinent

In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields (analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization (a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution physical initialization applied at the regional model level. Higher skills in wind and precipitation forecasts over the Indian summer monsoon region are achieved using this version of the regional model with physical initialization. A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon region.     

Oligocene and Early Miocene coral faunas from Iran: palaeoecology and palaeobiogeography

 Oligocene and Early Miocene coral assemblages from three sections of central Iran are investigated with respect to their palaeoecological and palaeobiogeographic implications. These corals are compared with faunas from the Mediterranean Tethys and the Indopacific. Associated larger foraminifers are used for biostratigraphy and to support the palaeoecological interpretation. The studied sections are situated in the foreland basins of the Iranian Plate which is structured into a fore-arc and a back-arc basin separated by a volcanic arc. The coral assemblages from Abadeh indicate a shallowing-upward trend. Infrequently distributed solitary corals at the base of the section indicate a turbid environment. Above, a distinct horizon characterised by a Leptoseris-Stylophora assemblage associated with lepidocyclinids and planktonic foraminifers is interpreted as maximum flooding surface. Small patch reefs with a Porites-Faviidae assemblage are a common feature of Late Oligocene to Early Miocene coral occurrences and indicate water depths of less than 20 m. The diversity of the coral faunas shows marked differences. Oligocene corals from the Esfahan-Sirjan fore-arc basin comprise more than 45 species of 32 genera and occur in a wide range of environments. Early Miocene corals from the Qom back-arc basin are less frequent, show a lower diversity (13 genera with 15 species) and occur in single horizons or small patch reefs. Received: 4 December 1998 / Accepted: 3 June 1999     

Cyclostratigraphic dating in the Lower Badenian (Middle Miocene) of the Vienna Basin (Austria): the Baden-Sooss core

The scientific borehole Baden-Sooss penetrates a succession of Badenian (Langhian, Middle Miocene) sediments at the type locality of the Badenian, the old brickyard Baden-Sooss in the Vienna Basin. The sedimentary succession of the 102-m-cored interval consists of more than 95% bioturbated, medium-to-dark gray marly shales with carbonate contents between 11 and 25% and organic carbon contents between 0.35 and 0.65%. Biostratigraphic investigations on foraminifera (mainly lower part of Upper Lagenid Zone) and calcareous nannoplankton (standard zone NN5) indicate an early Badenian (Langhian) age. Cycles in carbonate content, organic carbon content, and magnetic susceptibility have been identified by power spectra analysis. Correlations between the three variables are extremely significant. Using cross-correlation, periods around 40 m correlate significantly with the 100 kyr⁻¹ eccentricity cycle, the ∼20 m periods with the obliquity cycle, and the 15 to 11-m periods with both precession cycles. Wavelet transformation and decomposition of composite periodic functions were used to obtain the position of the cycle peaks in the profile. Cross-correlation with orbital cycles (La2004) dates the Baden-Sooss core between −14.379 ± 1 and −14.142 my ± 9 kyr.     

Numerical simulation of present day tectonic stress across the Indian subcontinent

International Journal of Earth Sciences - In situ measurements of maximum horizontal stress (SHmax) in the Indian subcontinent are limited and do not present regional trends of intraplate stress...     

Ionospheric disturbances with the time of occurrence, magnitude and location of the earthquake (M6.5) near the Indian subcontinent

The present study purports the analysis of total electron content (TEC, which is one of the major ionosphere anomalies during the earthquake), sea surface temperature (SST) and outgoing long-wave radiation (OLR) during the earthquake event recorded on 10 March 2013 (M = 6.5). Global assimilative ionosphere modelled output TEC values have been used for this present study; the clear signature of TEC during the recorded earthquake has been noticed (i.e. increase in TEC 60–70 TECU during the event). The correlation between the magnitude and location of earthquake with TEC is around 0.9, and the least correlation between SST and OLR is due to concerned atmospheric effects; we tried to study the variations of SST and OLR prior during and after the event from Kalpana satellite image products archived by IMD.     

Regional geoelectric structure beneath Deccan Volcanic Province of the Indian subcontinent using magnetotellurics

Understanding deep continental structure and the seismotectonics of Deccan trap covered region has attained greater importance in recent years. For imaging the deep crustal structure, magnetotelluric (MT) investigations have been carried out along three long profiles viz. Guhagarh–Sangole (GS), Sangole–Partur (SP), Edlabad–Khandwa (EK) and one short profile along Nanasi–Mokhad (NM). The results of GS, SP and NM profiles show that the traps lie directly over high resistive basement with thin inter-trappean sediments, where large thickness of sediments, of the order of 1.5–2.0 km, has been delineated along EK profile across Narmada–Son–Lineament zone. The basement is intersected by faults/fractures, which are clearly delineated as narrow steep conducting features at a few locations. The conducting features delineated along SP profile are also seen from the results of aeromagnetic anomalies. Towards the southern part of the profile, these features are spatially correlated with Kurduwadi rift proposed earlier from gravity studies. Apart from the Kurduwadi rift extending to deep crustal levels, the present study indicates additional conductive features in the basement. The variation in the resistivity along GS profile can be attributed to crustal block structure in Koyna region. Similar block structure is also seen along NM profile.Deccan trap thickness, based on various geophysical methods, varies gradually from 1.8 km towards west to 0.3 km towards the east. While this is the general trend, a sharp variation in the thickness of trap is observed near Koyna. The resistivity of the trap is more (150–200 Ω m) towards the west as compared to the east (50–60 Ω m) indicating more compact or denser nature for the basalt towards west. The upper crust is highly resistive (5000–10,000 Ω m), and the lower crust is moderately resistive (500–1000 Ω m). In the present study, seismotectonics of the region is discussed based on the regional geoelectrical structure with lateral variation in the resistivity of the basement and presence of anomalous conductors in the crust.     

The drift of the Indian subcontinent; an interpretation of recent palaeomagnetic data

The Precambrian and Phanerozoic drift of the Indian subcontinent is discussed on the hand of available palaeomagnetic data.Hard secondary magnetization components of Early Tertiary Deccan Trap origin were found in a number of red beds studied. Incompatabilities in some previously published red beds data of mainly Early Gondwana age are presumably due to incompletely cleaned results. A modified apparent polar wander curve is proposed after rejecting certain data on the grounds, that they reflect a later Deccan Trap remagnetization.The spatial and temporal relations between the Early Cretaceous Rajmahal Trap- and the Early Tertiary Deccan Trap effusions does not accord with a mantle fixed hot spot model. The Indian palaeomagnetic data when compared with data from the other Gondwanaland continents favour the hypothesis of an early fragmentational movement of Gondwanaland before Penno-Triassic times. Implications of available palaeomagnetic data on the convergence of India and Asia are discussed in relation to some recent plate tectonic models.

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Zusammenfassung Die präkambrische und phanerozoische Drift des Subkontinentes Indien wird anhand bisheriger paläomagnetischer Daten diskutiert. Harte sekundäre Remanenzkomponenten von frühtertiärer Deccan-Trap-Herkunft wurden in einer Anzahl der untersuchten red beds festgestellt. Unvereinbarkeiten in bisher publizierten red bed-Daten von meist Frühgondwana-Alter sind anscheinend die Folge störend überlagernder und nur zum Teil durch die Entmagnetisierung beseitigter sekundärer Remanenzkomponenten. Eine modifizierte Polwanderungskurve wird vorgeschlagen nach Ausschluß bestimmter Daten wegen nicht völlig eliminierter sekundärer Deccan-Trap-Remanenzkomponenten.Die räumliche und zeitliche Beziehung zwischen den frühkretazischen Rajmahal-Trap- und den frühtertiären Deccan-Trap-Effusionen stimmt nicht überein mit den mantelfixierten hot spot-Modellen. Ein Vergleich der paläomagnetischen Daten Indiens mit Daten der anderen Gondwana-Kontinente stützt die Hypothese einer fragmentierenden Bewegung Gondwanas vor der Permotrias. Folgerungen der bisherigen paläomagnetischen Daten für die Konvergenz von Indien und Asien in Beziehung zu rezenten plattentektonischen Modellen werden diskutiert.

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Résumé La dérive précambrienne et phanérozoique du subcontinent indien est discutée à partir des données paléomagnétiques connues aujourd'hui. Des composantes rémanentes secondaires dures, issues de l'activité volcanique du Deccan Traps au début du Tertiaire, ont été identifiées dans des couches rouges.Des contradictions entre quelques données paléomagnétiques, notamment des couches rouges permiennes et triassiques, sont probablement dues à des données issues d'une désaimantation insuffisante. Il a été proposé une courbe des pôles paléomagnétiques modifiée, après exclusion de certaines données d'où l'influence de cette aimantation sécondaire du Deccan Traps n'a pas été complètement éliminée.Les rélations dans le temps et dans l'espace entre les effusions des Rajmahal Traps (crétacé inférieur) et des Deccan Traps (début du tertiare) ne concordent pas avec le modèle d'un point chaud fixé dans le manteau. Les données paléomagnétiques Indiennes, comparées avec les données des autres continents gondwaniens, viennent à l'appui de l'hypothèse d'une ancienne phase de fragmentation du Gondwana avant l'époque permotriassique. Certaines implications des données paléomagnétiques disponibles sur le rapprochement de l'Inde et de l'Asie sont actuellement discutées, car elles ne semblent pas en accord avec de nouveaux modèles récemment présentés sur la tectonique des plaques intéressant cette partie du globe.

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Hydrochemical and isotopic investigation of a tropical wetland system in the Indian subcontinent

The study reported here is a part of an attempt to establish a comprehensive hydrochemical and isotopic baseline for a tropical wetland system as background data for a range of applications. Surface water samples of Vembanad Lake were collected from 20 stations in three seasons during the period 2007–2009. The analytical results were subjected to different chemical classification techniques to understand processes affecting the chemical concentration of waters. The Piper diagram classified the water samples as 100% alkali group in pre-monsoon followed by 15% in monsoon and 85% in post-monsoon, and for anions 100% samples were of strong acids followed by 90% in monsoon and 100% in post-monsoon season. The plot to decipher the mechanism controlling water chemistry placed the Vembanad Lake in the region of precipitation and rock dominance in the monsoon season and in the field of saline water dominance in pre-monsoon and post-monsoon season. The positive values for the chloro-alkaline indices in pre and post-monsoon season promoted cation exchange in the system. The stable isotopes of water samples ranged from ?20.21 to +17.0‰ and ?5.6 to +3.34‰ for δ ²H and δ ¹⁸O, respectively. The most depleted δ values observed in the monsoon are due to the amount effect. The high enrichment observed in pre-monsoon is primarily due to evaporation and salinity mixing. The variation of isotopes in the whole system point toward the fact that salinity mixing can be indicated by the δ ¹⁸O variation and δ ²H indicates the evaporation effect. The plot of δ ¹⁸O with chloride concentration showed precipitation dominance in the monsoon season, mixing of saline water and evaporation in pre-monsoon season, whereas the post-monsoon samples plot in both fresh and saline region.     

印度陆块新生代两次仰冲事件及其构造驱动机制:论印度洋、特提斯和欧亚板块相互作用

印度陆块与欧亚大陆的碰撞是印度洋扩张和特提斯洋闭合综合作用的结果。本文通过综合分析和研究提出这3个板块的相互作用致使印度陆块发生过2次向北的仰冲:早期(古新世末-始新世初,~57Ma)仰冲受其超高速运动(140mm/yr)的驱动,与特提斯之间产生的速度差致使两者间的边界发生破裂,密度小的印度陆块沿印度洋东经90°海岭和马尔代夫岛链向北仰冲到特提斯洋壳之上,两者的叠加导致印度陆块北缘——特提斯喜马拉雅地壳增厚(~70km)并且沉积了一套造山磨拉石——柳曲砾岩;晚期(渐新世-中新世之交,~25Ma)仰冲发生在碰撞后,由于高喜马拉雅结晶岩系沿主中央冲断带和藏南拆离断裂发生的垂向挤出,位于上盘的特提斯喜马拉雅沉积盖层同时发生重力垮塌,沿大喜马拉雅反冲断裂仰冲到冈底斯岩浆岩带之上并且造成后者的隆升和前陆下陷,其北缘充填了一套造山磨拉石沉积——大竹卡砾岩。这两次构造事件均受印度陆块的快速运动驱动。此外,在印度陆块超高速运动的挤压下,特提斯洋可能在早白垩世之后就停止了扩张,而老的洋壳不是俯冲消减了就是被仰冲的印度陆块掩盖了,这解释了为什么雅鲁藏布江缝合带只存早白垩世蛇绿岩。印度洋内东经90°海岭和马尔代夫岛链构成印度陆块的南东和南西边界,前者呈右行走滑,后者呈左行走滑,两者勾画出印度陆块向北漂移的轨迹。     

Glauberite–halite association of the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain)

Glauberite is the most common mineral in the ancient sodium sulphate deposits in the Mediterranean region, although its origin, primary or diagenetic, continues to be a matter of debate. A number of glauberite deposits of Oligocene–Miocene age in Spain display facies characteristics of sedimentologic significance, in particular those in which a glauberite–halite association is predominant. In this context, a log study of four boreholes in the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain) was carried out. Two glauberite–halite lithofacies associations, A and B, are distinguished: association (A) is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite; association (B) is made up of laminated to thin‐bedded, clear macrocrystalline, massive, clastic and contorted lithofacies of glauberite, and small amounts of bedded cloudy halite. Transparent glauberite cemented by clear halite as well as normal‐graded and reverse‐graded glauberite textures are common. This type of transparent glauberite is interpreted as a primary, subaqueous precipitate. Gypsum, thenardite or mirabilite are absent in the two associations. The depositional environment is interpreted as a shallow perennial saline lake system, in which chloride brines (association A) and sulphate–(chloride) brines (association B) are developed. The geochemical study of halite crystals (bromine contents and fluid inclusion compositions) demonstrates that conditions for co‐precipitation of halite and glauberite, or for precipitation of Na‐sulphates (mirabilite, thenardite) were never fulfilled in the saline lake system.     

Lower Miocene sediments of central and western Ciscaucasia

The composition, structure, and geochemical properties of the thickest, relatively deep-water Lower Miocene sediments developed in western Ciscaucasia are considered. Of particular interest are materials from the Kuban superdeep borehole SG-12000 that recovered the uppermost layers of the Maikop Group at 3148–3961 m in the central Indol-Kuban Trough west of Krasnodar. However, the borehole did not penetrate the whole Lower Miocene section of the Maikop Group. Therefore, characteristics of the Maikop Group are supplemented with new materials from several other boreholes drilled in the eastern Kuban region. Thus, the typical (reference) Lower Miocene section of central and western Ciscaucasia has been sufficiently well described.     

Lower Miocene oyster shells from the Southeast Zagros Basin (Zade Mahmud area, Iran) and their paleoecology

The Guri limestone Member of the Mishan Formation in the Zagros Basin consists of thick bedded limestone bearing benthic foraminifera and oyster shells. Seven species of Ostreidae and Gryphaeidae were identified as belonging to four genera (Crassostrea, Cubitostrea, Ostrea, and Hyotissa), i.e., Cubitostrea frondosa, Ostrea (Cubitostrea) dubertreti, Cubitostrea digitalina, Crassostrea gryphoides, Hyotissa virleti, Ostrea vesitata, and Ostrea plicatula. These fossils are reported for the first time from Iran. Miocene deposits in the studied area contain a rich benthic foraminiferal fauna dominated by Pseudotaberina, Meandropsina, Miogypsina, Flosculinella, Borelis, and other larger benthic foraminifera. We assign these sediments to a Burdigalian age based on Borelis melo curdica–Borelis melo melo Assemblage Zone. Paleoecological considerations also revealed that the beds were deposited in a near-shore non-agitated and shallow-water environment with moderate to low sedimentation rate. The studied oysters are located in one of more important paleogeographic settings in the world and very similar to many other Tethyan regions. The presence of these oysters suggests that the Zade Mahmud area located at margins of a sea way that connected the north and south of Zagros Basin during Burdigalian.     

Plant-Arthropod Associations from the Lower Miocene of the Most Basin in Northern Bohemia(Czech Republic):A Preliminary Report

<正>Terrestrial plants and insects currently account for the majority of the Earth's biodiversity,and approximately half of insect species are herbivores.Thus,insects and plants share ancient associations that date back more than 400 Myr.However,investigations of their past interactions are at the preliminary stages in Western Europe.Herein,we present the first results of our study of various feeding damage based on a dataset of nearly 3500 examined plant specimens from the Lower Miocene of the Lagerstatte Bilina Mine in the Most Basin, Czech Republic.This site provides a unique view of the Neogene freshwater ecosystems.It has long been studied by scientists working in different branches of sedimentology,paleobotany,and paleozoology.The fossils are preserved in three characteristic horizons overlaying the coal seam(Clayey Superseam Horizon,Delta Sandy Horizon,and Lake Clayey Horizon),reflecting paleoenvironmental changes in a short time period of development The trace fossils are classified as functional feeding groups or"guilds",without searching for a direct cause or a recent analog host relation.Approximately 23%of specimens of dicotyledonous plant leaves were found to be damaged and associated with some leaf"morphotypes".Deciduous plant-host taxa,and those with a chartaceous texture typical of riparian habitats,were frequently damaged,such as Populus,recorded with two species Populus zaddachii and Populus populina(57.9%and 31%herbivory levels,respectively),followed by Acer,Alnus,and Carya,averaging almost 30%of damaged leaves/leaflets.There has been evidence of 60 damage types(DT) representing all functional feeding groups recorded at the Bilina Mine,including 12 types of leaf mines and 16 gall- type DT.In total,Lower Miocene of the Lagerstatte Bilina Mine exhibits a high level of external foliage feeding types(23.7%),and a low level of more specialized DT,such as galls(43%)and leaf mines(1%).A broader comparison based on DT of the main sedimentary environments shows significance supporting different biomes by frequency of damage levels and DT diversities.     

A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin

Oligocene–Miocene chronostratigraphic correlations within the Paratethys domain are still highly controversial. This study focuses on the late Early Miocene of the Swiss and S-German Molasse Basin (Late Burdigalian, Ottnangian–Karpatian). Previous studies have published different chronologies for this time interval that is represented by the biostratigraphically well constrained Upper Marine Molasse (OMM, lower and middle Ottnangian), Upper Brackish Molasse (OBM, Grimmelfingen and Kirchberg Formations, middle and upper Ottnangian to lower Karpatian, MN 4a–MN 4b) and Upper Freshwater Molasse (OSM, Karpatian–Badenian, MN 5). Here, we suggest a new chronostratigraphic framework, based on integrated magneto-litho-biostratigraphic studies on four sections and three boreholes. Our data indicate that the OBM comprises chrons 5D.1r and 5Dn (Grimmelfingen Fm), chron 5Cr (lower Kirchberg Fm) and the oldest part of chron 5Cn.3n (upper Kirchberg Fm). The OSM begins during chron 5Cn.3n, continues through 5Cn, and includes a long reversed segment that can be correlated to chron 5Br. The OMM-OSM transition was completed at 16.0 Ma in the Swiss Molasse Basin, while the OBM-OSM changeover ended at 16.6 Ma in the S-German Molasse Basin. As the lower Kirchberg Fm represents a facies of the Ottnangian, our data suggest that the Ottnangian–Karpatian boundary in the Molasse Basin is approximately at 16.8 Ma, close to the 5Cr–5Cn.3n magnetic reversal, and thus 0.4 Myr younger than the inferred age of 17.2 Ma used in recent Paratethys time scales. Notably, this would not be problematic for the Paratethys stratigraphy, because chron 5Cr is mainly represented by a sedimentation gap in the Central Paratethys. We also realise, however, that additional data is still required to definitely solve the age debate concerning this intriguing time interval in the North Alpine Foreland Basin. We dedicate this work to our dear friend and colleague Jean-Pierre Berger (8 July 1956–18 January 2012).     

Miocene echinoids from the Sadat area,south Gebel Ataqa,NW Gulf of Suez,Egypt: systematics,palaeobiogeography

The echinoid fauna from the Miocene sedimentary succession cropping out south Wadi Tweirig, and Wadi Hommath, south Gebel Ataqa, NW Gulf of Suez, has been examined with the aim to known their stratigraphic and paleogeographic distribution. The Miocene succession includes two formations: Sadat Formation, unconformably overlying the middle/upper Eocene rocks at the base and Hommath Formation at the top. Twenty-eight echinoid species (8 regular and 20 irregular) belonging to 18 genera, 13 families, and 7 orders have been identified, systematically described, and illustrated in this work. Eleven species are recorded for the first time from Egypt: ten of these came from the Hommath Formation (Schizechinus cf. serresii Desor (1856), Schizechinus pentagonus Kier 1972, Clypeaster cf. martini des Moulins 1837, Scutella checchiae occidentalis Desio 1934, Scutella melitensis Airaghi 1902, Echinodiscus desori Duncan and Sladen 1883, Echinolampas cf. zeitensis Fourtau 1920, Schizaster lovisatoi Cotteau 1895, Agassizia (Agassizia) powersi Kier 1972, and Hemipatagus ocellatus Defrance (1827)), and one from the Sadat Formation (Clypeaster campanulatus Schlotheim (1820)). The identified fauna shows a strong affinity with the Mediterranean bio-province.