Supradetachment Basin Research Articles

Geometry and origin of folding in the Neogene sediments of the Gediz Graben, western Anatolia, Turkey

A close relationship between formation of approximately upright folds with axes normal to the extension direction and ramp/flat extensional geometries is established for well exposed Neogene syn-extensional rocks on the presently low-angle Gediz detachment fault, along the southern margin of the Gediz Graben region of western Anatolia, Turkey. Three unconformity-bounded sedimentary sequences and several metamorphic extensional allochthons were mapped in the upper-plate of the Gediz detachment. The oldest sedimentary sequence consists of deformed and folded strata of sandstones and conglomerates that are regarded as being deposited in a supra-detachment basin during the Miocene-Early Pliocene. This unit rests unconformably on the extensional allochthonous, but directly in fault contact with the lower-plate mylonitic rocks. The younger slightly tilted Late Pliocene-Pleistocene sedimentary sequences are post-detachment units that are controlled by EW-trending high-angle normal faults. The youngest alluvium comprises the undeformed present-day basin fill of the Gediz Graben. The supra-detachment sedimentary rocks contain a number of kilometric-scale longitudinal folds that are nearly parallel to the east-west-trending fault system of the Gediz Graben. The folds have a steeply inclined bisecting surface, an interlimb angle of 130–150°, and a plunge of <10°. These folds may be interpreted to form as a result of bending in the underlying Gediz detachment fault. The bending may have an alternation of ramp and flat geometries on which a hanging-wall syncline and rollover anticline formed, respectively. This study again shows the importance of local geology in understanding of some spectacular structures of the extensional basins. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Geometry and origin of folding in the Neogene sediments of the Gediz Graben, western Anatolia, Turkey

A close relationship between formation of approximately upright folds with axes normal to the extension direction and ramp/flat extensional geometries is established for well exposed Neogene syn-extensional rocks on the presently low-angle Gediz detachment fault, along the southern margin of the Gediz Graben region of western Anatolia, Turkey. Three unconformity-bounded sedimentary sequences and several metamorphic extensional allochthons were mapped in the upper-plate of the Gediz detachment. The oldest sedimentary sequence consists of deformed and folded strata of sandstones and conglomerates that are regarded as being deposited in a supra-detachment basin during the Miocene–Early Pliocene. This unit rests unconformably on the extensional allochthonous, but directly in fault contact with the lower-plate mylonitic rocks. The younger slightly tilted Late Pliocene–Pleistocene sedimentary sequences are post-detachment units that are controlled by EW-trending high-angle normal faults. The youngest alluvium comprises the undeformed present-day basin fill of the Gediz Graben. The supra-detachment sedimentary rocks contain a number of kilometric-scale longitudinal folds that are nearly parallel to the east-west-trending fault system of the Gediz Graben. The folds have a steeply inclined bisecting surface, an interlimb angle of 130–150°, and a plunge of <10°. These folds may be interpreted to form as a result of bending in the underlying Gediz detachment fault. The bending may have an alternation of ramp and flat geometries on which a hanging-wall syncline and rollover anticline formed, respectively. This study again shows the importance of local geology in understanding of some spectacular structures of the extensional basins.

Structural and Sedimentologic Evolution of a Miocene Supradetachment Basin, Silver Peak Range and Adjacent Areas, West-Central Nevada

The Silver Peak region of west-central Nevada provides a unique opportunity to study the history of a supradetachment basin, its deformed basement, and the detachment fault itself. The region experienced Late Cretaceous to Paleogene plutonism and stretching of a Neoproterozoic through Ordovician miogeoclinal section. Upper-crustal thinning above the Mineral Ridge pluton was accommodated by development of gently dipping schistosity in Neoproterozoic strata, and a mosaic of low-angle attenuation faults in overlying Cambrian strata. Middle and Late Miocene detachment faulting accommodated approximately 8-15 km of northwest transport of hanging-wall strata. The Mineral Ridge detachment fault apparently reactivated the basal décollement of the Late Cretaceous to Paleogene attenuation faults. The Esmeralda basin evolved in the hanging wall of the detachmentfault system, and represents subsidence over a significantly broader region than modern extensional basins. The supradetachment basin fill consists of three interfingering lithofacies assemblages: (1) an east-derived, conglomeratic, sedimentaclastic, alluvial-fan assemblage deposited adjacent to the breakaway; (2) mudstone and coal deposited in lacustrine and paludal environments; and (3) a westderived, sandy, volcaniclastic assemblage deposited in braidplain/braiddelta environments. Geometric relations indicate that the detachment fault dipped gently while active, and was the sole fault for a stack of listric-normal growth faults. Late Miocene arc volcanism within the Silver Peak region postdated cessation of detachment faulting. Present physiography is controlled by Pliocene to Holocene normal and strike-slip faulting associated with volumetrically minor basaltic volcanism. This complex history of late Mesozoic and Cenozoic deformation, magmatism and sedimentation in the Silver Peak region may be analogous to other parts of the Basin and Range Province, suggesting broad applicability of the model developed herein.

ABSTRACT: The Interaction Between Basin-Scale Extensional Folding and Sedimentation in a Supradetachment Basin

Hanging-wall deformation in extensional settings has the potential to create complex syntectonic sedimentary packages. These sediments record interplay between sedimentation and synextensional folding, as recorded in Grasshopper rift basin, SW Montana. As a result of this interaction, Grasshopper basin, has a complex, threedimensional stratigraphic and structural geometry. Large, basin-scale extensional folds developed in this north-trending Paleogene supradetachment basin during extensional deformation. A major N-trending anticline, 10 km long and 1.8 km in structural relief, occupies the western half of the basin. Approximately perpendicular to the anticline, a major syncline 8 km long and roughly 0.5 km in structural relief plunges 88 toward an antiform in the underlying listric detachment fault. Sedimentologically, we interpret the basin as a sediment starved lacustrine system dominated by southward axial infilling and lesser, yet significant, transverse sediment influx. The basin contains about 4 km of Tertiary basin fill. Stratigraphic and sedimentological analyses reveal that several basin-scale lacustrine transgressions, facilitated by slip on the eastern border-fault and increased accommodation space due to folding, laterally shifted depositional environments. Interruptions in the southward progradation of the fluvial-deltaic facies are marked by the north-northeast retreat of conglomerates and sandstones on the north limb of the transverse syncline. In the mid to late stages of basin deformation, current data suggests that the longitudinal anticline evolved. To help visualize the large-scale stratigraphic and structural features of this basin, we integrated seismic data and structural, stratigraphic, and sedimentological field data into three-dimensional structural models (2D/3DMove from Midland Valley Exploration) of the basin.

Multistage exhumation of the Menderes Massif, western Anatolia (Turkey)

Structural analyses along selected transects across the Menderes Massif and incorporation of existing data have resulted in a synthetic cross section across southwestern Turkey. The tectonic interpretation has been combined with 40Ar/39Ar laser-probe experiments on two syn-kinematic white mica populations, which, respectively, predate and overprint documented Early Miocene deformational fabrics. Our results indicate that the regional extension had initiated by Eocene–Oligocene times. A 36±2 Ma 40Ar/39Ar age derived from white mica which formed during a regionally observed, northward-directed tectonic transport suggests that the extension was contemporaneous with the tectonic emplacement of mid-crustal continental basement. Alternatively, the age may relate to the regional cooling of the basement sequence, and thus postdates the tectonic emplacement. In the latter scenario, the analysis fails to solve the present ambiguity on the Pan-African or Alpine affinity of the northward-directed transport. Further exhumation of basement rocks is characterized by a dominant displacement along the north-dipping Gediz Detachment at the northern margin of the massif, which developed under ductile conditions in the Early Miocene by partial exploitation of older zones of weakness, which originated from an earlier phase of basement emplacement. Youngest (semi)ductile activity along the Gediz Detachment has been recorded as having a 7±1 Ma 40Ar/39Ar age derived from syn-kinematic white mica in the top of the detachment. Following the initiation of the ductile Gediz Detachment, an antithetic, semibrittle, and south-dipping Buyuk Menderes Detachment had developed in the center of the massif, which, together with the Gediz Detachment, accommodated further doming of the central part of the Menderes Massif and controlled the architecture of the surrounding supradetachment basins.

Sedimentation in Supradetachment Basins: The Influence of Extensional Folds on Stratigraphic Architecture, Grasshopper Basin, Southwest Montana

Sedimentation in Supradetachment Basins: The Influence of Extensional Folds on Stratigraphic Architecture, Grasshopper Basin, Southwest Montana

Low-angle, range-flank faults in the Panamint, Inyo, and Slate ranges, California: Implications for recent tectonics of the Death Valley region

Research Article| June 01, 2000 Low-angle, range-flank faults in the Panamint, Inyo, and Slate ranges, California: Implications for recent tectonics of the Death Valley region Marek Cichanski Marek Cichanski 1De Anza College, 21250 Stevens Creek Boulevard, Cupertino, California 95014, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (6): 871–883. https://doi.org/10.1130/0016-7606(2000)112<871:LRFITP>2.0.CO;2 Article history received: 15 Jun 1998 rev-recd: 10 May 1999 accepted: 01 Nov 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Marek Cichanski; Low-angle, range-flank faults in the Panamint, Inyo, and Slate ranges, California: Implications for recent tectonics of the Death Valley region. GSA Bulletin 2000;; 112 (6): 871–883. doi: https://doi.org/10.1130/0016-7606(2000)112<871:LRFITP>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Four of the mountain ranges near Death Valley, California, display exhumed, low-angle normal faults on their flanks, features originally referred to as turtleback structures. These fault surfaces are smooth, planar to curviplanar, and defined by faceted spurs and coincident interfluve crests. The lowest parts of these faults are overlain in tectonic contact by poorly indurated fanglomerate, and locally by Quaternary volcanic rocks. Steep fault scarps in alluvium are present at the foot of each turtleback-type flank.Although these may be examples of active low-angle normal faults, it is difficult to establish the dip histories of these faults. The problem with constraining the dip histories is one of missing and concealed information, because the exposed hanging-wall rocks are some of the youngest material cut and displaced by the (currently) shallow-dipping faults. Another important relationship along these range flanks is the intersection between the low-angle faults and steep, scarp-forming faults that cut alluvium at the range fronts. Although this relationship remains unconstrained in most of the ranges, a shallow-dipping fault is cut by one of the steep faults in Panamint Valley, suggesting that, in one area at least, the low-angle faults are not active.The low-angle faults, and not the steep neotectonic faults, are probably responsible for most of the opening of the present valleys, because each low-angle fault intersects the valley floor at the range front. None of the low-angle faults are perched high in the ranges, as would be the case if the steep faults had uplifted them significantly. Therefore, even if there has been a geologically recent transition from low-angle normal faulting to steep normal (with or without strike slip) faulting, the modern topography still reflects the former regime. Strictly speaking, the Death Valley region may not be an example of active low-angle normal faults and supradetachment basins. You do not currently have access to this article.

Depositional and tectonic evolution of a supradetachment basin: 40Ar/39Ar geochronology of the Nova Formation, Panamint Range, California

The Nova Basin contains an upper Miocene to Pliocene supradetachment sedimentary succession that records the unroofing of the Panamint metamorphic core complex, west of Death Valley, California. Basin stratigraphy reflects the evolution of sedimentation processes from landslide emplacement during basin initiation to the development of alluvial fans composed of reworked, uplifted sections of the basin fill. 40Ar/39Ar geochronology of volcanic units in middle and lower parts of the sequence provide age control on the tectonic and depositional evolution of the basin and, more generally, insights regarding the rate of change of depositional environments in supradetachment basins. Our work, along with earlier research, indicate basin deposition from 11.38 Ma to 3.35 Ma. The data imply sedimentation rates, uncorrected for compaction, of ~100 m Myr−1 in the lower, high‐energy part to ~1000 m Myr−1 in the middle part characterized by debris‐flow fan deposition. The observed variation in sediment flux rate during basin evolution suggests that supradetachment basins have complex depositional histories involving rapid transitions in both the style and rate of sedimentation.

Sedimentation and deformation in a Pliocene-Pleistocene transtensional supradetachment basin, Laguna Salada, north-west Mexico

This study examines a thick section of Pliocene–Pleistocene sedimentary rocks exposed in the footwall of an active normal fault (Canon Rojo fault) near its intersection with the dextral-normal Laguna Salada fault in north-western Mexico. These rocks are situated in the upper plate of an inactive strand of the Canada David detachment fault, which is cut on the north-east by the Laguna Salada fault. The stratigraphy is divided into three unconformity-bounded sequences: (1) marine mudstone of the Pliocene Imperial Formation; (2) nonmarine Pliocene–Pleistocene redbeds, consisting of sedimentary breccia, conglomerate, conglomeratic sandstone (all un-named) and fine-grained sandstone and mudstone of the Palm Spring Formation; and (3) uncemented Pleistocene boulder gravel. Coarse deposits of the redbeds sequence were deposited in fault-bounded, high- and low-gradient alluvial fans that passed laterally into a low-energy fluvial plain of the ancestral Colorado River (Palm Spring Formation) which occupied the present-day Laguna Salada. Detailed mapping reveals convergence and lap-out of bedding surfaces in the redbeds sequence onto the west limb of a large anticline cored by Imperial Formation. These geometries, combined with fanning dips and thickening of stratigraphy into the flanking syncline, indicate that the anticline grew during deposition of the redbeds. Fold axes of the growth anticline and smaller related folds trend N to NNE, parallel to the strike of associated normal faults and perpendicular to the extension direction. Based on its orientation, large size and relationship to neighbouring structures, the anticline is interpreted to be a fault-bend fold that grew in response to slip of the upper plate over a bend in the Canada David detachment fault during deposition in a transtensional supradetachment basin. Localized subsidence in the flanking syncline resulted in deposition of >1000 m of alluvial sediments near its intersection with the Laguna Salada fault. Sedimentary detritus is derived exclusively from the north-east (footwall) side of the dextral-normal Laguna Salada fault, indicating that topographic relief was high in the Sierra Cucapa and was subdued or negligible in the footwall of the coeval Canada David detachment. Following deposition of the redbeds and grey gravel units, the northern part of the detachment fault was abandoned and the modern Canon Rojo fault was initiated, producing rapid footwall uplift and erosion of previously buried stratigraphy. Slip rate on the Canon Rojo fault is estimated to be ≈2–4 mm yr−1 since middle Pleistocene time, similar to the late Pleistocene to Holocene rate determined in previous studies.

Testing models of rift basins: structure and stratigraphy of an Eocene–Oligocene supradetachment basin, Muddy Creek half graben, south‐west Montana

We examine the basin geometry and sedimentary patterns in the Muddy Creek half graben of south‐west Montana by integrating geological mapping, structural and basin analysis, 40Ar/39Ar geochronology, biostratigraphy and reflection seismic data. The half graben formed in late Middle Eocene to early Oligocene (?) time at the breakaway of a regional, WSW‐dipping detachment system. Although the structure of the half graben is that of a supradetachment basin, facies patterns and basin architecture do not conform to a recent model for extensional basins above detachment faults. The border fault, the Muddy Creek fault system, consists of three en echelon, left‐stepping normal faults separated by two relay ramps. The fault steepens southward toward each en echelon step, ranges in dip from 8 to 60° near the surface, but flattens at depths between 0 and 3 km. A broad ENE‐plunging displacement‐gradient syncline defines the central part of the half graben and is flanked by narrow SE‐and NE‐plunging anticlines to the north and south. Fine‐grained deposits of the syntectonic basin‐fill are thickest in the central syncline and interfinger with footwall‐derived conglomerate near the adjacent anticlines. These facies patterns suggest that folding was coeval with extension and sedimentation in the half graben. Pre‐extensional volcanic rocks and interbedded conglomerate filled a major ESE‐trending palaeovalley along the future axis of the Muddy Creek half graben. Synextensional sedimentary deposits include lacustrine and paludal shale, mudstone and sandstone ponded in the centre of the half graben, and a narrow (typically &lt;1.5 km wide) fringe of coarse alluvial‐fan and fan‐delta conglomerate and sandstone derived from the footwall. Angular unconformities and rock‐slide deposits occur only locally within the syntectonic sequence. These facies patterns agree well with the half‐graben depositional model of Leeder &amp; Gawthorpe but not with a more recent supradetachment basin model of Friedmann &amp; Burbank despite the demonstrably low dip‐angle of the basin‐bounding normal fault. These data show that it may not be possible to differentiate between supradetachment basins and half graben with steeper border faults using the architecture of the associated basin‐fill deposits.

Late Cenozoic extension of the Alpine collisional orogen, northeastern Greece: Origin of the north Aegean basin

The Rhodope metamorphic core complex, exposed beneath the Strymon Valley detachment in northeastern Greece, comprises a platform carbonate sequence >5000 m thick intruded by Tertiary calc-alkaline plutons. The final thickening of the north Aegean Alpine collisional orogen in Paleogene time and its Neogene-Quaternary extensional dismemberment in the backarc of the Hellenic subduction zone produced structures within and above the Rhodope core complex that are related here to four successive deformations. In early–middle Eocene time (D1), the Falakron marble series was subducted northeastward beneath the Serbo-Macedonian–West Thracian gneiss complex, a heterogeneous ophiolite-bearing high-grade metamorphic terrane that was accreted to southeastern Europe in Cretaceous time. The orogen began to extend on a northeast-southwest axis in earliest Miocene time, evidenced in the Rhodope core complex by the emplacement of the Symvolon granodiorite ca. 21 Ma within a northwest-trending midcrustal coaxial rupture of the Falakron slab (D2). The Strymon Valley detachment system succeeded the D2 Symvolon rupture and related structures, facilitating unroofing of the core complex and a transition from ductile to brittle deformation ca. 16–3.5 Ma (D3). The Serbo-Macedonian gneiss complex, the island of Thasos, and a supradetachment basin were translated relatively southwestward as much as 80 km in the D3 hanging wall. Balanced reconstructions of D2 and D3 displacements predicate two new hypotheses concerning the Cenozoic tectonic evolution of northeastern Greece. First, the southwest-vergent Thasos detachment and northeast-vergent low-angle normal faults in the Olympos region may both have rooted in the coaxial Symvolon rupture zone to form a bivergent early Miocene extensional system. Second, the Olympos and Falakron carbonate platforms may be correlative remnants of the subducted eastern margin of the Apulian microcontinent, implying that the “Vardar zone,” the putative Alpine suture, is a rootless ophiolite belt, and that segments of the Alpine suture are actually exposed over a zone as wide as 200 km, including the Rhodope province. Cumulative D2 and D3 stretching of greater than or equal to 100% created the north Aegean basin. The North Anatolian fault, which accommodates the westward escape of Anatolia from the Pontide suture, propagated into the north Aegean region in late Pliocene time. Its offshore continuation, the North Aegean Trough, transfers dextral strike-slip displacement into extension to the north, principally expressed in northern Greece by the Thermaikos, Strymon, and Drama half grabens (D4).

Extensional tectonics in the Caledonides of southern Norway, an overview

The extensional collapse of the Scandinavian Caledonides resulted in rapid tectonic denudation of the orogen, exhumation of high- and ultra-high-pressure metamorphic rocks and provided a structural template for the formation of Devonian supra-detachment sedimentary basins. The geometry and intensity of the extensional deformation show considerable variation vertically in the crustal section as well as horizontally from east to west across the orogen. The most prominent structural feature related to the extension in central-south Norway is the change in the direction of tectonic transport, from the easterly directed nappe translation during the Silurian Scandian Orogeny, to top-westerly directed sense of shear during the extension. The Fennoscandian basement was little affected by extension in the eastern Caledonides. In the west, however, top-to-the-west shear zones are commonly observed in basement windows. Deformation affecting the Cambrian to Late Silurian rocks in the Caledonian foreland developed a typical of foreland fold and thrust belt geometry. Deformation in the foreland was apparently contemporaneous with the extension-related decompression of the high-pressure rocks in the hinterland. Thrusting in the foreland may thus have been driven by gravitational collapse, and as such have important similarities to the foreland-hinterland relationships of the Himalayan-Tibetan region. The basal contacts of the Jotun and other major nappes constitute prominent shear zones in which fabrics related to thrusting have been mostly destroyed by extensional shearing. The high structural levels of the Western Gneiss Region, adjacent to the western margin of the Jotun Nappe, were only moderately affected by the extensional deformation. Consequently, the Proterozoic orthogneiss complexes are generally well preserved in this area. The westernmost and structurally lowermost parts of the Western Gneiss Region have, however, been subjected to extreme overburden during the Caledonian continental collision. Initial, near-isothermal decompression of the high-pressure rocks occurred by non-rotational vertical shortening-horizontal stretching at eclogite- to amphilbolite-facies conditions; at a later stage, decompression and cooling from amphibolite to greenschist facies occurred by rotational deformation associated with the large-scale extensional detachments. The initial extensional deformation in the hanging wall of the detachments in western Norway commenced at greenschist-facies conditions, and became progressively more brittle and localised as the complexes were exhumed in the Late Silurian to Middle Devonian. Major syn-depositional normal faults in the hanging wall of the extensional detachments eventually controlled sedimentation in the Devonian supra-detachment basins.

Late Cretaceous-Paleocene Extensional Collapse and Disaggregation of the Southernmost Sierra Nevada Batholith

Geobarometric studies have documented that most of the metasedimentary wall rocks and plutons presently exposed in the southernmost Sierra Nevada batholith south of the Lake Isabella area were metamorphosed and emplaced at crustal levels significantly deeper (∼15 to 30 km) than the batholithic rocks exposed to the north (depths of ∼3 to 15 km). Field and geophysical studies have suggested that much of the southernmost part of the batholith is underlain along low-angle faults by the Rand Schist. The schist is composed mostly of metagraywacke that has been metamorphosed at relatively high pressures and moderate temperatures. NNW-trending compositional, age, and isotopic boundaries in the plutonic rocks of the central Sierra Nevada appear to be deflected westward in the southernmost part of the batholith. Based on these observations, in conjunction with the implicit assumption that the Sierra Nevada batholith formerly continued unbroken south of the Garlock fault, previous studies have inferred that the batholith was tectonically disrupted following its emplacement during the Cretaceous. Hypotheses to account for this disruption include intraplate oroctinal bending, W-vergent overthrusting, and gravitational collapse of overthickened crust. In this paper, new geologic data from the eastern Tehachapi Mountains, located adjacent to and north of the Garlock fault in the southernmost Sierra Nevada, are integrated with data from previous geologic studies in the region into a new view of the Late Cretaceous-Paleocene tectonic evolution of the region. The thesis of this paper is that part of the southernmost Sierra Nevada batholith was unroofed by extensional faulting in Late Cretaceous-Paleocene time. Unroofing occurred along a regional system of low-angle detachment faults. Remnants of the upper-plate rocks today are scattered across the southern Sierra Nevada region, from the Rand Mountains west to the San Emigdio Mountains, and across the San Andreas fault to the northern Salinian block. Batholithic rocks in the upper plates of the Blackburn Canyon fault of the eastern Tehachapi Mountains, low-angle faults in the Rand Mountains and southeastern Sierra Nevada, and the Pastoria fault of the western Tehachapi Mountains are inferred to have been removed from a position structurally above rocks exposed in the southeastern Sierra Nevada and transported to their present locations along low-angle detachment faults. Some of the granitic and metamorphic rocks in the northern part of the Salinian block are suggested to have originated from a position structurally above deep-level rocks of the southwestern Sierra Nevada. The Paleocene-lower Eocene Goler Formation of the El Paso Mountains and the post-Late Cretaceous to pre-lower Miocene Witnet Formation in the southernmost Sierra Nevada are hypothesized to have been deposited in supradetachment basins that formed adjacent to some of the detachment faults. Regional age constraints for this inferred tectonic unroofing and disaggregation of the southern Sierra Nevada batholith suggest that it occurred between ∼90 to 85 Ma and ∼55 to 50 Ma. Upper-plate rocks of the detachment system appear to have been rotated clockwise by as much as 90° based on differences in the orientation of foliation and contacts between inferred correlative hanging-wall and footwall rocks. Transport of the upper-plate rocks is proposed to have occurred in two stages. First, the upper crust in the southern Sierra Nevada extended in a south to southeast direction, and second, the allochthonous rocks were carried westward at the latitude of the Mojave Desert by a mechanism that may include W-vergent faulting and/or oroclinal bending. The Late Cretaceous NNW extension of the upper crust in the southernmost Sierra Nevada postulated in this study is similar to Late Cretaceous, generally NW-directed, crustal extension that has been recognized to the northeast in the Funeral, Panamint, and Inyo mountains by others. Extensional collapse of the upper crust in the southern Sierra Nevada batholith may be closely linked to the emplacement of Rand Schist beneath the batholith during Late Cretaceous time, as has been suggested in previous studies.

The infill of a supradetachment(?) basin: the continental to shallow-marine Upper Permian succession in the Dolomites and Carnia (Italy)

In the Dolomites and Carnia (eastern Southern Alps), the Upper Permian succession is represented by red beds of Val Gardena Sandstone, grading upwards and eastwards into the evaporitic and carbonate deposits of the Bellerophon Formation. An overall transgressive pattern is shown by the general trend of the depositional setting, which evolved from flashy alluvial fans, through multiple-channel bedload rivers, mixed-load sinuous rivers, terminal fans, coastal sabkha and evaporitic lagoon, to a shallow, low-gradient marine ramp. The inferred fluvial regime was subject to rapid and erratic fluctuations in discharge. Palaeosols are represented by calcic soils, and suggest a warm to hot, semi-arid or dry subhumid climate with strongly seasonal rainfall. Vertic features are associated with more inland alluvial complexes: they are missing in the terminal-fan deposits, suggesting greater aridity in lowland (coastal) areas. The Bellerophon Fm. consists of two units: a lower evaportte-bearing unit, deposited in a barred basin, and an upper shallow-marine carbonate unit, laid down on a very low-energy, low-gradient ramp. Five third-order sequences and the lower part of a sixth sequence, collectively showing a backstepping pattern, have been identified in the succession. Due to the presence of a very low-gradient ramp margin, and the consequent ineffectiveness of relative sea-level falls in producing large-scale erosion in coastal areas, it is suggested that, rather than eustatic changes, degradational episodes marking sequence boundaries in the red-bed succession reflect changes in the climate-modulated intrinsic variables of discharge and sediment supply, and/or tectonic uplift. Base level rises in, red-bed sequences are recorded by upward change from thick channel-belt sandstone bodies with an often high connectedness ratio, to progressively thinner channel deposits, ranging from isolated ribbons to channel-belt sandstone bodies potentially reaching high width/thickness ratios, encased in a comparably greater volume of overbank fines. This trend is thought to reflect the change from a confined geomorphic setting, with a limited area of potential avulsion, to an unrestricted setting with rivers free to move extensively; in addition, it documents the transition from an inland fluvial system with laterally migrating perennial or semi-perennial channels, to an ephemeral network of randomly migrating and frequently avulsing small terminal-fan distributaries, through a drastic downstream decrease in channel depth and discharge. Identification of key sequence-stratigraphic relationships within the red-bed succession was mostly aided by the presence of easily recognizable and regionally correlated marine and marginal marine bed packages, traceable landwards into alluvial deposits showing faint traces of tidal activity, interpreted as the equivalent of marine maximum-flooding sediments. They may grade upwards into progradational fluvial packages showing basinward increase in thickness. The Upper Permian deposits of the Southern Alps are considered part of an Upper Permian-Lower Triassic, second-order, structurally controlled sequence. The location of the basin on a thickened, previously active crust, affected by thermal perturbance after the last stages of the Variscan orogeny, the relatively reduced thickness of the basin fill, and predominantly long, transverse drainage networks, mostly derived from the denuded Insubric footwall, all suggest that sedimentation took place in a supradetachment basin, with a major detachment fault located in the palaeo-Insubric belt.

The Trobriand Basin, SE Papua New Guinea, as a Supradetachment Basin and Its Implications for the Crustal Dynamics of Highly Extended Terranes : ABSTRACTS

The Trobriand Basin, SE Papua New Guinea, as a Supradetachment Basin and Its Implications for the Crustal Dynamics of Highly Extended Terranes : ABSTRACTS

Subduction, mega-shear systems and Late Palaeozoic basin development in the African segment of Gondwana

Basins within the African sector of Gondwana contain a Late Palaeozoic to Early Mesozoic Gondwana sequence unconformably overlying Precambrian basement in the interior and mid-Palaeozoic strata along the palaeo-Pacific margin. Small sea-board Pacific basins form an exception in having a Carboniferous to Early Permian fill overlying Devonian metasediments and intrusives. The Late Palaeozoic geographic and tectonic changes in the region followed four well-defined consecutive events which can also be traced outside the study area. During the Late Devonian to Early Carboniferous period (up to 330 Ma) accretion of microplates along the Patagonian margin of Gondwana resulted in the evolution of the Pacific basins. Thermal uplift of the Gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and 330 Ma. At the end of this period the Gondwana Ice Sheet was well established over the uplands. The period 260–300 Ma evidenced the release of the Gondwana heat and thermal subsidence caused widespread basin formation. Late Carboniferous transpressive strike-slip basins (e.g. Sierra Australes/Colorado, Karoo-Falklands, Ellsworth-Central Transantarctic Mountains) in which thick glacial deposits accumulated, formed inboard of the palaeo-Pacific margin. In the continental interior the formation of Zambesi-type rift and extensional strike-slip basins were controlled by large mega-shear systems, whereas rare intracratonic thermal subsidence basins formed locally. In the Late Permian the tectonic regime changed to compressional largely due to northwest-directed subduction along the palaeo-Pacific margin. The orogenic cycle between 240 and 260 Ma resulted in the formation of the Gondwana fold belt and overall north-south crustal shortening with strike-slip motions and regional uplift within the interior. The Gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened marginal crustal belt subject to dextral transpressive motions. Associated with the orogenic cycle was the formation of mega-shear systems one of which (Falklands-East Africa-Tethys shear) split the supercontinent in the Permo-Triassic into a West and an East Gondwana. By a slight clockwise rotation of East Gondwana a supradetachment basin formed along the Tethyan margin and northward displacement of Madagascar, West Falkland and the Gondwana fold belt occurred relative to a southward motion of Africa.

Evolution of monolithological breccia deposits in supradetachment basins, Whipple Mountains, California

AbstractExtensive sheets of monolithological breccia (megabreccia) within detachment‐fault systems of the North American Cordillera have been identified as large landslides. Although the origin of the megabreccia deposits is controversial, their spatial and temporal association with detachment‐fault systems implies a causal relationship between the initiation of such landslides and motion along detachment faults. Emplacement may have been catastrophic following seismic activity, or slow, as the result of gravity gliding. Nevertheless, comprehensive analysis of these deposits provides important constraints on the evolution of supradetachment basins by detailing the unroofing history, palaeotopography and palaeoseismicity of detachment‐fault systems. An extensive Miocene landslide deposit, the War Eagle landslide, in the north‐eastern Whipple Mountains, provides an opportunity for such an endeavour to elucidate: (1) the cause and timing of its initiation; (2) mechanism for its emplacement; (3) nature of the apparent association of the landslide with detachment‐fault development; and (4) role of the megabreccia in the development of supradetachment basins. Cross‐sections were drawn through the deposit to determine the geometry and kinematic development of the landslide. Additionally, a simple mechanical model based on limit equilibrium force balance was designed to explore physical mechanisms that controlled its creation. The results of this model combined with field relationships suggest that the Whipple detachment fault was active at an angle of less than 30° with displacement most likely accompanied by the release of seismic energy. Continued extensional evolution of the Whipple detachment fault caused tilting of the upper‐plate strata and the formation of numerous half and full grabens as well as roll‐over structures. Rocks from the lower plate were brought to the surface during the later stages of detachment‐fault activity thereby producing sufficient topographic relief for large landslides to be seismically activated. Increased pore‐fluid pressure in the footwall subjacent to the Whipple detachment fault probably aided landslide initiation. The landslide was emplaced onto the upper plate of the detachment fault, providing a significant amount of material into the evolving supradetachment basin. Although the rate of emplacement of the megabreccia remains uncertain, penetrative fracturing throughout the breccia sheet is evidence that emplacement occurred catastrophically. The results of this study indicate that Tertiary megabreccias were emplaced during continued detachment‐fault evolution, implying oversteepened topography and seismicity of these low‐angle systems.

Rift basins and supradetachment basins: intracontinental extensional end‐members

AbstractTwo end‐members characterize a continuum of continental extensional tectonism: rift settings and highly extended terrains. These different styles result in and are recorded by different extensional basins. Intracontinental rifts (e.g. East Africa, Lake Baikal) usually occur in thermally equilibrated crust of normal thickness. Rift settings commonly display alkali to tholeiitic magmatism, steeply dipping (45–60°) bounding faults, slip rates &lt;1 mm yr‐1 and low‐magnitude extension (10–25%). Total extension typically requires &gt; 25 Myr. The fault and sub‐basin geometry which dominates depositional style is a half‐graben bounded by a steeply dipping normal fault. Associated basins are deep (6–10 km), and sedimentation is predominantly axial‐ or hangingwall‐derived. Asymmetric subsidence localizes depocentres along the active basin‐bounding scarp.Highly extended continental terrains (e.g. Colorado River extensional corridor, the Cyclade Islands) represent a different tectonic end‐member. They form in back‐arc regions where the crust has undergone dramatic thickening before extension, and usually reactivate recently deformed crust. Volcanism is typically calc‐alkalic, and 80–90% of total extension requires much less time (&lt;10 Myr). Bounding faults are commonly active at shallow dips (15–35°); slip rates (commonly &gt; 2 mm yr‐1) and bulk extension (often &gt; 100%) are high.The differences in extension magnitude and rate, volcanism, heat flow, and structural style suggest basin evolution will differ with tectonic setting. Supradetachment basins, or basins formed in highly extended terrains, have predominantly long, transverse drainage networks derived from the breakaway footwall. Depocentres are distal (10–20 km) to the main bounding fault. Basin fill is relatively thin (typically 1–3 km), probably due to rapid uplift of the tectonically and erosionally denuded footwall. Sedimentation rates are high (˜ 1 m kyr‐1) and interrupted by substantial unconformities. In arid and semi‐arid regions, fluvial systems are poorly developed and alluvial fans dominated by mass‐wasting (debris‐flow, rock‐avalanche breccias, glide blocks) represent a significant proportion (30–50%) of basin fill. The key parameters for comparing supradetachment to rift systems are extension rate and amount, which are functions of other factors like crustal thickness, thermal state of the lithosphere and tectonic environment. Changes in these parameters over time appear to result in changes to basin systematics.

Two‐phase evolution of the Shadow Valley Basin, south‐eastern California: a possible record of footwall uplift during extensional detachment faulting

AbstractMiocene strata of the Shadow Valley Basin rest unconformably on the upper plate of the Kingston Range ‐ Halloran Hills detachment fault system in the eastern Mojave desert, California. Basin development occurred in two broad phases that we interpret as a response to changes in footwall geometry. In southern portions of the basin, south of the Kingston Range, phase one began with near synchronous initiation of detachment faulting, volcanism and basin sedimentation shortly after 13.4 Ma. Between c. 13.4 and c. 10 Ma, concordantly bedded phase one strata were deposited onto the subsiding hangingwall of the detachment fault as it was translated 5–9 km south‐westward with only limited internal deformation. Phase two (c. 10 to 8–5 Ma) is marked by extensional dismemberment of the detachment fault's upper plate along predominantly west‐dipping normal faults. Phase two sediments were deposited synchronously with upper‐plate normal faulting and unconformably overlie phase one deposits, displaying progressive shallowing in dip and intraformational onlap.Northern portions of the basin, in the Kingston Range, experienced a similar two‐phase development compressed into a shorter interval of time. Here, phase one occurred between c. 13.4 and 12.8–12.5 (?) Ma, whereas phase two probably lasted for no more than a few 100000 years immediately prior to c. 12.4 Ma. Differences in the duration of basin development in and south of the Kingston Range apparently relate to position with respect to the detachment fault's breakaway; northern basin exposures overlie the upper plate adjacent to the breakaway (0–15 km) whereas southern basin exposures occur far from the breakaway (20–40 km).We interpret the phase one to phase two transition as recording breakup of the detachment fault's hangingwall during footwall uplift. We propose a model for supradetachment basin evolution in which early, concordantly bedded basin strata are deposited on the hangingwall as it translates intact above a weakly deforming footwall. With continuing extension, tectonic denudation along the detachment fault leads to an increasing flexural isostatic footwall response. We suggest that isostatic footwall uplift may drive internal breakup of the upper plate as the detachment fault is rotated to a shallow dip, mechanically unfavourable for simple upper‐plate translation. Additionally, we argue that continuing hangingwall thinning during phase two places geometrical constraints on the timing, amount and, thus, rate of footwall uplift. Kinematically determined footwall uplift rates (0.5–4.5 mm/yr) are comparable with rates determined independently by thermochronological and geobarometric methods.

Example of a supradetachment basin within a pull‐apart tectonic setting: Mormon Point, Death Valley, California

AbstractThe geological features now exposed at Mormon Point, Death Valley, reveal processes of extension that continue to be active, but are concealed beneath the east side of Death Valley. Late Cenozoic sedimentary rocks at Mormon Point crop out in the hangingwall of the Mormon Point low‐angle normal fault zone, a fault zone that formed within a releasing bend of the oblique‐slip (right‐normal slip) fault zone along the east side of Death Valley. The late Cenozoic sedimentary rocks were part of the valley when the low‐angle fault zone was active, but during late Quaternary time they became part of the Black Mountains block and were uplifted. Rocks and structures exposed at Mormon Point are an example of the types of features developed in a releasing bend along the margins of a major pull‐apart structure, and in this example they are very similar to features associated with regional detachment faults.The oldest sedimentary rocks in the hangingwall of the Mormon Point low‐angle fault zone dip steeply to moderately east or north‐east and were faulted and rotated in an extensional kinematic environment different from that recorded by rocks and structures associated with younger rocks in the hangingwall. Some of the younger parts of the late Cenozoic sedimentary rocks were deposited, faulted and rotated during movement on the Mormon Point low‐angle normal fault. Progressively, strata are less faulted and less rotated. The Mormon Point low‐angle normal fault has an irregular fault surface whose segments define intersections that plunge 18°‐30°, N10°‐40°W, with a maximum of 22°, N22°W that we interpret to be the general direction of slip. Thus, even though Death Valley trends north, movement on the faults responsible for its formation was at least locally north‐northwest. Gouge and disrupted conglomerates along the faults are interpreted to have formed either as adjustments to accommodate space problems at the corners of blocks or along faults that bounded blocks during their displacement and rotation.The younger units of the late Cenozoic sedimentary rock sequence and the geomorphic surfaces developed on them are rarely faulted, not rotated, and overlap the Mormon Point low‐angle faults. Active faults cut Holocene alluvium north of the late Cenozoic rocks and form the present boundary between Mormon Point and the Black Mountains. The distribution of active faults defines a releasing bend that mimics the older releasing bend formed by the Mormon Point low‐angle fault zone. Rocks and structures similar to those exposed above the Mormon Point low‐angle fault zone are probably forming today beneath the east side of Death Valley north‐west of Mormon Point.