Morphological and structural relations in the Galilee extensional domain, northern Israel

The Lower Galilee and the Yizre'el Valley, northern Israel, are an extensional domain that has been developing since the Miocene, prior and contemporaneously to the development of the Dead Sea Fault (DSF). It is a fan-shaped region bounded in the east by the N–S trending main trace of the DSF, in the north by the Bet-Kerem Fault system, and in the south by the NW–SE trending Carmel Fault. The study area is characterized by high relief topography that follows fault-bounded blocks and flexures at a wavelength of tens of km. A synthesis of the morphologic–structural relations across the entire Galilee region suggests the following characteristics: (1) Blocks within the Lower Galilee tilt toward both the southern and northern boundaries, forming two asymmetrical half-graben structures, opposite facing, and oblique to one another. (2) The Lower Galilee's neighboring blocks, which are the Upper Galilee in the north and the Carmel block in the southwest, are topographically and structurally uplifted and tilted away from the Lower Galilee. (3) The southern half-graben, along the Carmel Fault, is topographically and structurally lower than the northern one. Combining structural and geological data with topographic analysis enables us to distinguish several stages of structural and morphological development in the region. Using a semi-quantitative evolutionary model, we explain the morpho-structural evolution of the region. Our results indicate that the Galilee developed as a set of two isostatically supported opposite facing half-grabens under varying stress fields. The southern one had started developing as early as the early Miocene prior to the formation of the DSF. The northern and younger one has been developing since the middle Pliocene as part of the extension process in the Galilee. Elevation differences between the two half-grabens and their bounding blocks are explained by differences in isostatic subsidence due to sedimentary loading and uplift of the northern half-graben due to differential influences of the regional folding.     

Late Alpine evolution of the central Menderes Massif, western Turkey

The central Menderes Massif (western Turkey) is characterized by an overall dome-shaped Alpine foliation pattern and a N-NNE-trending stretching lineation. A section through the southern flank of the central submassif along the northern margin of Büyük Menderes graben has been studied. There, asymmetric non-coaxial fabrics indicate that the submassif has experienced two distinct phases of Alpine deformation: a top-to-the N-NNE contractional phase and a top-to-the S-SSW extensional event. The former fabrics are coeval with a regional prograde Barrovian-type metamorphism at greenschist to upper-amphibolite facies conditions. This event, known as the main Menderes metamorphism, is thought to be the result of internal imbrication of the Menderes Massif rocks along south-verging thrust sheets during the collision of the Sakarya continent in the north and the Anatolide-Tauride platform in the south across the Gzmir-Ankara suture during the (?)Palaeocene-Eocene. Top-to-the S-SSW fabrics, represented by a well-developed ductile shear band foliation associated with inclined and/or curved foliation, asymmetric boudins, and cataclasites, were clearly superimposed on earlier contractional fabrics. These fabrics are interpreted to be related to a low-grade (greenschist?) retrogressive metamorphism and a continuum of deformation from ductile to brittle in the footwall rocks of a south-dipping, presently low-angle normal fault that accompanied Early Miocene orogenic collapse and continental extension in western Turkey. A similar tectono-metamorphic history has been documented for the northern flank of the dome along the southern margin of the Gediz graben with top-to-the N-NNE extensional fabrics. The exhumation of the central Menderes Massif can therefore be attributed to a model of symmetric gravity collapse of the previously thickened crust in the submassif area. The central submassif is thus interpreted as a piece of ductile lower-middle crust that was exhumed along two normal-sense shear zones with opposing vergence and may be regarded as a typical symmetrical metamorphic core complex. These relationships are consistent with previous models that the Miocene exhumation of the Menderes Massif and Cycladic Massif in the Aegean Sea was a result of bivergent extension.     

Active tectonics of the Yizre'el valley, Israel, using high-resolution seismic reflection data

We present a series of high-resolution seismic reflection lines across the Yizre'el valley, which is the largest active depression in Israel, off the main trend of the Dead Sea rift. The new seismic reflection data is of excellent quality and shows that the valley is dissected into numerous small blocks, separated by active faults. The Yizre'el valley is found to consist of a series of half grabens, rather than a single half graben, or a symmetrical graben. The faults are generally vertical and appear to have a dominant strike-slip component, but some dip-slip is also evident. A marked zone of compression near Megido is associated with the intersection of the two largest faults in the valley, the Carmel fault and the Gideon fault. Variable trend of the faults reflects the complexity of the local geology along the boundary between the wide NW–SE trending Farah–Carmel fault zone and the E–W trending basins and ranges in the Lower Galilee. This tectonic complexity is likely to result from a highly variable stress pattern, modified by the structures inside it. Normal faulting in the valley occurred at an early stage of its development as a tectonic depression. However, strike-slip motion on the Carmel fault, and possibly also on some of the other faults, appears to have started together with the onset of normal faulting. Earthquake hazard in the area appears to be uniform as faults are distributed throughout the Yizre'el valley.     

Lithospheric folding in the southern North Sea: combined effects of Alpine compression and North Atlantic Ocean opening

Late Cretaceous to Palaeogene graben inversion in the southern North Sea is classically related to Alpine compression. Regional deformation analysis of Upper Cretaceous sediments based on seismic and well data reveals the existence of large-scale NW-SE folds. Folding patterns are interpreted as the result of lithospheric buckling during NE-SW shortening. We suggest that graben inversion at the scale of the southern North Sea is only a part of a more general process, involving lithospheric folding. Folding developed in response to two major plate boundary conditions, that is, E-W to NE-SW opening of the Atlantic Ocean constrained to the southeast by N-S Alpine collision. Lithospheric folding might have influenced both the oil generation process and reservoir properties in this area.     

Testing the case for a Middle Pleistocene Scandinavian glaciation in Eastern England: evidence for a Scottish ice source for tills within the Corton Formation of East Anglia, UK

The provenance of the Happisburgh Till and Corton Till of the Corton Formation is investigated using erratic clast lithologies and allochthonous palynomorphs to test whether the long held assumption that they were deposited by ice that originated in Scandinavia is valid. The results show a wide range of lithologies including Carboniferous Limestone and Coal Measures, and Permian Magnesian Limestone that are not found in Scandinavia, and an absence of distinctive Scandinavian material such as rhomb porphyry and larvikite. Lithologies found indicate deposition by an ice sheet which flowed southwards into north-east East Anglia from central and southern Scotland eroding and transporting materials derived from outcrops in these areas and from eastern England and the western margins of the southern North Sea Basin. It is concluded that the long held assumption that the Happisburgh Till and Corton Till of the Corton Formation were deposited by a Scandinavian ice sheet is erroneous and that they were instead deposited by Scottish ice.     

Late Cenozoic Sedimentary Evolution of Pagri‐Duoqing Co graben,Southern End of Yadong‐Gulu Rift,Southern Tibet

The north trending rifts in southern Tibet represent the E–W extension of the plateau and confirming the initial rifting age is key to the study of mechanics of these rifts. Pagri–Duoqing Co graben is located at southern end of Yadong–Gulu rift, where the late Cenozoic sediments is predominately composed of fluvio-lacustrine and moraine. Based on the sedimentary composition and structures, the fluvio-lacustrine could be divided into three facies, namely, lacustrine, lacustrine fan delta and alluvial fan. The presence of paleo-currents and conglomerate components and the provenance of the strata around the graben indicate that it was Tethys Himalaya and High Himalaya. Electron spin resonance (ESR) dating and paleo-magnetic dating suggest that the age of the strata ranges from ca. 1.2 Ma to ca. 8 Ma. Optically stimulated luminescence (OSL) dating showed that moraine in the graben mainly developed from around 181–109 ka (late Middle Pleistocene). Combining previous data about the Late Cenozoic strata in other basins, it is suggested that 8–15 Ma may be the initial rifting time. Together with sediment distribution and drainage system, the sedimentary evolution of Pagri could be divided into four stages. The graben rifted at around 15–8 Ma due to the eastern graben-boundary fault resulting in the appearance of a paleolake. Following by a geologically quiet period about 8–2.5 Ma, the paleolake expanded from east to west at around 8–6 Ma reaching its maximum at ca. 6 Ma. Then, the graben was broken at about 2.5 Ma. At last, the development of the glacier separated the graben into two parts that were Pagri and Duoqing Co since the later stages of the Middle Pleistocene. The evolution process suggested that the former three stages were related to the tectonic movement, which determined the basement of the graben, while the last stage may have been influenced by glacial activity caused by climate change.     

Salinization and dilution history of ground water discharging into the Sea of Galilee,the Dead Sea Transform,Israel

The mechanism governing salinization of ground water discharging into the Sea of Galilee in Israel has been the subject of debate for several decades. Because the lake provides 25% of the water consumed annually in Israel, correct identification of the salt sources is essential for the establishment of suitable water-management strategies for the lake and the ground water in the surrounding aquifers. Existing salinization models were evaluated in light of available and newly acquired data including general chemistry, and O, H, C and Cl isotopes. Based on the chemical and isotopic observations, the proposed salt source is an ancient, intensively evaporated brine (21- to 33-fold seawater) which percolated through the valley formations from a lake which had formed in the Rift Valley following seawater intrusion during the late Miocene. Low Na:Cl and high Br:Cl values support the extensive evaporation, whereas high Ca:Cl and low Mg:Cl values indicate the impact of dolomitization of the carbonate host rock on the residual solution. Based on radiocarbon and other isotope data, the dilution of the original brine occurred in two stages: the first took place ∼30 000 a ago by slightly evaporated fresh-to-brackish lake water to form the Sea of Galilee Brine. The second dilution phase is associated with the current hydrological regime as the Sea of Galilee Brine migrates upward along the Rift faults and mixes with the actively circulating fresh ground water to form the saline springs. The spatially variable chemical and isotopic features of the saline springs suggest not only differential dilution by fresh meteoric water, but also differential percolation timing of the original brine into the tectonically disconnected blocks, registering different evaporation stages in the original brine. Consequently, various operations to reduce the brine contribution to the lake may be differentially effective in the various areas.     

Quaternary tectonics in the Gulf of Patras, western Greece

Air gun seismic and 3.5 kHz profiling data from the Gulf of Patras, western Greece, show that it is occupied by a small asymmetric graben with several geometric similarities to the larger-scale graben in the Gulf of Corinth to the east. Major listric faulting characterizes the southern flank of the graben whilst the northern flank represents an associated rollover structure affected by antithetic and synthetic faulting. The present phase of subsidence is of Holocene age, but buried growth faults suggest earlier subsidence in the Gulf. The average rate of subsidence through the Holocene is estimated to be 10 mm/year.The Gulf of Patras graben, together with the Gulf of Corinth graben and the Megara basin, represent a continuous system of WNW-ESE trending grabens in a broad zone of intense seismicity within the Aegean domain. Individual grabens are offset and are interconnected by NE-SW trending fault systems.     

The late Quaternary limnological history of Lake Kinneret (Sea of Galilee), Israel

The freshwater Lake Kinneret (Sea of Galilee) and the hypersaline Dead Sea are remnant lakes, evolved from ancient water bodies that filled the tectonic depressions along the Dead Sea Transform (DST) during the Neogene-Quartenary periods. We reconstructed the limnological history (level and composition) of Lake Kinneret during the past ∼40,000 years and compared it with the history of the contemporaneous Lake Lisan from the aspect of the regional and global climate history. The lake level reconstruction was achieved through a chronological and sedimentological investigation of exposed sedimentary sections in the Kinnarot basin trenches and cores drilled at the Ohalo II archeological site. Shoreline chronology was established by radiocarbon dating of organic remains and of Melanopsis shells.The major changes in Lake Kinneret level were synchronous with those of the southern Lake Lisan. Both lakes dropped significantly ∼42,000, ∼30,000, 23,800, and 13,000 yr ago and rose ∼39,000, 26,000, 5000, and 1600 yr ago. Between 26,000 and 24,000 yr ago, the lakes merged into a unified water body and lake level achieved its maximum stand of ∼170 m below mean sea level (m bsl). Nevertheless, the fresh and saline water properties of Lake Kinneret and Lake Lisan, respectively, have been preserved throughout the 40,000 years studied. Calcium carbonate was always deposited as calcite in Lake Kinneret and as aragonite in Lake Lisan-Dead Sea, indicating that the Dead Sea brine (which supports aragonite production) never reached or affected Lake Kinneret, even during the period of lake high stand and convergence. The synchronous level fluctuation of lakes Kinneret, Lisan, and the Holocene Dead Sea is consistent with the dominance of the Atlantic-Mediterranean rain system on the catchment of the basin and the regional hydrology. The major drops in Lake Kinneret-Lisan levels coincide with the timing of cold spells in the North Atlantic that caused a shut down of rains in the East Mediterranean and the lakes drainage area.     

青藏铁路风火山段晚第四纪断裂活动分析

地表地质调查发现,第四纪期间在风火山逆冲-褶皱构造带以发生近东西向的伸展变形为特征。在该构造带中形成切割早期近东西向挤压变形构造带、指示近东西向伸展变形、整体沿北60°东向展布的二道沟断陷盆地。断裂活动的地质、地貌证据表明,控制该盆地晚第四纪断陷的主边界断裂位于其北缘,是一条断续延伸达24 km左右、可能兼具左旋走滑性质的正断层。根据该区晚第四纪沉积物的分布和时代,并对断裂所错动的晚第四纪地质-地貌体进行初步的年代学分析,可以初步断定该断裂的晚第四纪垂直活动速率应该介于0.2~0.4 mm/a之间。     

Proterozoic melting in the northern peridotite Massif, Zabargad Island: Os isotopic evidence

The geodynamic history of the three Zabargad peridotite bodies is the key to their significance as samples of the upper mantle. Currently, there are two main hypotheses that differ greatly in their implications for the origin and age of the peridotite complex as a whole. In the first, the Zabargad peridotite bodies all represent young asthenospheric mantle that was juxtaposed with ancient crustal gneisses during the opening of the Red Sea. In the second, the complex may represent a single package of residual mantle and lower crust of Pan-African age that was uplifted during the Miocene. In order to distinguish between these two models, we have analysed five samples of Zabargad peridotite and two pyroxenites for Os isotopes. The ¹⁸⁷Os/¹⁸⁸Os results range from 0.1198 to 0.1320 and correlate with Al₂O₃, allowing an age inference for the northern body, based on the Os isotopic evolution curve for the bulk Earth, of 1.4±0.3 Gyr. This is at least as old as the previously inferred Pan-African age and may be older, and agrees with previous suggestions that the northern and central peridotite bodies probably represent ancient continental lithospheric mantle, while the southern body represents recent asthenospheric mantle. Our results from both central and southern bodies are consistent with either crustal age hypothesis.     

Types,characteristics and implication for hydrocarbon exploration of the Middle Miocene deep-water sediments in Beikang Basin,southern South China Sea

The internal seismic architectures of the Middle Miocene in Beikang Basin, southern South China Sea, were investigated and described using regional 2D seismic data from Guangzhou Marine Geology Survey. In particular, five typical seismic facies were identified based on an integrated analysis of the amplitude, continuity, contact relationship, and morphologies of seismic reflections. Bathyal-abyssal fine-grained sediments, deltaic front sandy bodies, turbidites, and small-scale turbidite channels were developed in the Middle Miocene according to the tectonic-sedimentary evolution of the sedimentary basins in the southern South China Sea. The findings of this study suggest that deltaic front sandy bodies and turbidites can be considered as the two major types of deep-water clastic reservoirs for the depression stage of Beikang Basin. A well-developed source-reservoir-cap assemblage was composed by deep rift-stage source rocks, deep-water clastic reservoirs of the Middle Miocene, and bathyal-abyssal deep-water fine-grained sediments after the Middle Miocene, implying a good potential for hydrocarbon exploration.©2019 China Geology Editorial Office.     

Deep structure of the Danilovskii graben in Western Siberia: A geological interpretation of the density models

Gravimetric modeling is conducted for the Triassic Danilovskii graben. The model region may be an etalon for all of Western Siberia because of the nearby Danilovskoe and Severo-Danilovskoe oil deposits and representative geophysical and drilling data. The correctness of the gravitation model was checked by the magnetic model of the graben constructed on the basis of the gravitation model; the difference between the measured and model anomalous magnetic fields is less than 5%. The density models of the graben have shown that rocks with a significantly excess density of 0.3 g/cm³ and higher, which probably represent the Triassic mantle diapir, should be located under the axial part of the graben. Rhyolites, forming small irregular bodies on the geological map of the basement, are combined into the common lopolith-like subvolcanic body at depths. The graben is flattened toward the north, which explains the previously unclear presence of Carboniferous shales among the Triassic rocks.     

Organic carbon burial rates,and carbon and sulfur relationships in coastal sediments of the southern Baltic Sea

Organic C burial rates and C–S relationships were investigated in the Holocene sediment sequences of 3 shallow polymictic coastal lagoons in the southern Baltic Sea to better understand the biogeochemical cycling of C and S in these environmental systems. The results show that these lagoons may have a considerable influence on the environmental status of the southern Baltic Sea area in having the potential to act as a temporary sink or source for heavy metals. High organic C accumulation rates (C_org-AR) can be observed in the sediments due to a high organic matter supply from land and a high productivity of the water bodies as a result of eutrophication. However, organic C burial does not increase as a result of increasing sediment accumulation rates (SAR). Even when high sedimentation rates do occur, there appears to be a thorough recycling and resuspension of the sediment enhancing the biological decay of organic matter before burial or the removal of organic matter from the system by transport. That is why high SAR in the coastal lagoons do not enhance pyrite formation, and thereby permanent fixing of heavy metals in the sediments, to the extent that could be expected from their magnitude. Initially there is a high potential for a temporary binding of heavy metals, but the latter are likely to be subject to mobilization and redistribution within the sediments and the water column. The patterns of burial of organic and mineral matter are different from those observed in the present-day Baltic Proper, implying possible important links in deposition between the central and coastal areas of the Baltic Sea and implications for C cycling in the ecosystem of the Baltic Sea.     

Quaternary faulting in the Upper Rhine Graben revealed by high-resolution multi-channel reflection seismic

A high-resolution multichannel seismic reflection river profiling campaign was completed in July 2002 in the southern Upper Rhine graben (URG), along the River Rhine. Preliminary results show apparent Quaternary vertical slip rates, on intra-graben faults that are relatively slow, of the order of a few thousandths to a few hundredths of mm/yr. Moreover, kinematical data from the Ludwigshafen area show decreasing vertical slip rates since the Middle Pleistocene and/or a migration of tectonic activity. While still preliminary, these data show inhomogeneous and relatively slow tectonic activity in the URG that could probably not alone have shaped the Quaternary graben morphology. To cite this article: G. Bertrand et al., C. R. Geoscience 338 (2006).     

Biological marker characteristics of oils and asphalts from carbonate source rocks in a rapidly subsiding graben,Dead Sea,Israel

A detailed GC/MS study of biological marker compounds in the saturated and aromatic hydrocarbon fractions of oils and asphalts from the Dead Sea area, Israel, provided decisive information to the solution of a long-lasting controversy by showing that the asphalts are products of early generation in an immature stage from the same type of carbonate source rock which generated more mature oils. The asphalts are not biodegraded residues of the oils.Oils from six different wells, and asphalts from wells, outcrops, and a floating block from the Dead Sea all have very similar sterane and triterpane patterns. They all lack rearranged steranes (diasteranes) indicating a carbonate source matrix and compare reasonably well with a sample of Upper Cretaceous bituminous chalk from Nebi Musa. The main difference between the oils and the asphalts is a significantly higher triaromatic to mono- plus triaromatic steroid hydrocarbon ratio in the former. This is explained as a result of rapid subsidence and heating of their source rock close to the deep parts of the Dead Sea graben. The oils thus were generated in the more deeply buried source rock blocks under the graben fill, whereas the asphalts either originate from an immature source rock section closer to the graben rims or represent an earlier phase of generation and expulsion.This study also provides general information on the evolution of biological markers in carbonate source rocks. Low-activation-energy processes, like isomerisation of steranes, appear to occur much faster at low temperatures than in shales. The high sulfur content and less cross-linking of the biogenic organic matter into a complex kerogen structure are suggested to be responsible for this. Care should be taken when using only sterane isomerisation to assess the maturity of hydrocarbons from carbonate rocks and of carbonate-derived oils.     

Micro- and macroseismicity of the Dead Sea rift and off-coast eastern Mediterranean

The seismicity of Israel has been evaluated from documented earthquake records of the present century and two years of routine monitoring of microearthquake activity by means of eleven stations spreading from the Gulf of Elat to northern Galilee.

The Dead Sea rift asserts itself as the tectonic feature that accounts for the seismicity of our region. The activity peaks at zones where the fault branches sideways or at a junction with other fault systems. In particular, the crescent fault of Wadi Faria seems to be a zone of high strain accumulation. This is probably the site of many historical earthquakes which caused inland and coastal damage. It is thus found that the most active fault today which constitutes the greatest seismic risk to Israeli metropolitan areas extends along the Dead Sea rift from 31.2°N to 33.4°N.

The seismicity around the Dead Sea conforms with the proposed movement along en-echelon faults. While the southwest segment is presently inactive, most of the seismic activity there is limited to the neighbourhood of its eastern shore with extreme seismicity at its southern tip near the prehistorical site of Bab-a-Dara'a. The seismicity of the Arava is much lower than the Jordan-Dead Sea section. The seismicity of the Israeli coast was found to be somewhat higher than that of the Arava.     

Archaeological evidence for tectonic activity in the region of the Haifa-Qishon Graben, Israel

Thirty-five archaeological sites between Lebanon and Gaza on the Mediterranean shore of Israel were surveyed for evidence of relative changes of sea level; and published and unpublished data were compiled on a further 23 sites. Remains of occupation levels were classified into 13 archaeological periods from Neolithic to Crusader, giving a good dating scale over the last 9000 years. The Bronze Age shoreline (4000 years B.P.) is shown to be very close to the present shore along most of the coast, with vertical changes of less than 1.0 m at most sites. For later periods the accuracy of measurement of relative changes of level was improved to a root sum square error of 28 cm.The mean and modal sea levels derived from all sites of the same archaeological period were plotted against time to indicate the most probable “eustatic” sea-level curve, though it is accepted that hydro-isostatic adjustment and broad-scale slow earth movements cannot be separated statistically from eustatic changes on a 200-km stretch of coast. The relative sea level is shown to have been between −70 cm and present sea level for the last 4000 years, with no evidence for oscillations of amplitude more than ±30 cm at periodicities longer than 400 years, and no high sea level still stands.Relative vertical displacement between sites of the same archaeological age is attributed to tectonism. The sites on the alluvium of the Haifa—Qish on graben show no signs of vertical displacement, but there is maximum activity to north and south. Acco, on the north margin, shows submergence of nearly 2.0 m since A.D. 1300, with probable uplift preceding that date. Mount Carmel, south of the graben, shows signs of only very slight relative change, possibly attributable to eustatic change, in the immediate vicinity of the graben. But the southern flank of the mountain, 20–80 km south of the southern fault of the Graben, shows active vertical movements on the whole coast. Dor and Caesarea indicate multiple vertical movements ranging from 1.0 to 5.0 m in the last 2000 years, and a slump or fault has intersected the harbour area of Caesarea about 150 m offshore.These observations are related briefly to recent geodetic levelling of the coast and graben area; observations on the Dead Sea Rift, and hypotheses of fault control of the linearity of the Israel Mediterranean coastline.     

Paleo-environmental reconstruction of Lopingian (upper Permian) sediments in the Galilee Basin,Queensland, Australia

The recent review of the Lopingian (upper Permian) stratigraphic framework of the Galilee Basin, prompted a reconsideration of the paleo-environments of deposition. This study interpreted the distribution of sedimentary facies from geophysical logs across the basin complemented by detailed logging from four key wells (GSQ Tambo 1-1A, OEC Glue Pot Creek 1, CRD Montani 1 and GSQ Muttaburra 1). Seven facies associations were identified: terrestrial fluvial, floodplain, lacustrine and mire; and paralic to marine estuarine shoreline, delta and restricted marine. Coal measures (mire facies) are best developed in the northeastern margin of the basin, whereas the southern Springsure Shelf was dominated by marine conditions throughout the Lopingian, only developing terrestrial facies towards the very uppermost Lopingian. The ‘Colinlea Sandstone equivalent’ was deposited in a fluvial system, with tidal influence exhibited in the southern part of the basin, which decreases further north as lacustrine environments become common. The regional transgression represented by the Black Alley Shale can be mapped into the central part of the basin, but based on new exploration data its northern extent is more limited than previously thought. The ‘Burngrove Formation equivalent’ and Bandanna Formation represent a southerly prograding fluvial-deltaic system during the regional regression in the upper part of the Lopingian.     

Middle Miocene graben development in Crete and its possible relation to large-scale detachment faults in the southern Aegean

The linkage between the development of south-facing Cretan graben and large-scale detachment faulting in the southern Aegean is unknown. Widespread Serravallian deposits in the Ierapetra graben of Crete supply constraints to Middle Miocene graben development in the southern Aegean. The Ierapetra graben, and by inference the Cretan graben in general, were hitherto believed to have formed as a result of sinistral transpression during N–S shortening. We argue that the formation of the Cretan graben is due to N–S extension. The south-dipping, N–S-extending Kritsa normal fault served as the master fault controlling graben development in the Ierapetra graben. The Kritsa normal fault is either an antithetic fault related to the top-N Cretan detachment or a synthetic fault associated with the top-S Ios detachment. The overall geometry and timing relationships lead us to favour a connection with the Ios detachment, which in turn implies a large-scale displacement on the Ios detachment.