Red Clastics Research Articles

Rapid Late Quaternary denudation of the Karacasu Graben in response to subsidence in the Büyük Menderes Corridor: Insights from morphotectonics and archaeogeology

The timing and geomorphological consequences of high-angle normal faulting in the Büyük Menderes Graben (W Anatolia) is an essential yet poorly studied issue that has been evaluated mostly regarding detachment faulting in the Central Menderes Core Complex. However, this subject has direct concerns related to ongoing debates regarding the level of seismic risk and the response of surface process to active tectonics in the most rapidly extending region in the world. To approach this problem, an integrated scheme was followed that involves the study of late Quaternary stratigraphy, terraces, and ancient and modern civic structures in the Karacasu Graben located on the southern uplifted block of the Büyük Menderes Graben. Our stratigraphic observations coupled with the existing micro-mammalian fossils demonstrate the widespread occurrence of terrestrial coarse red clastics (Karacasu Formation) before the appearance of the narrow-faulted corridor. The onset of high-angle normal faulting started with gradual denudation through the axial Dandalas Creek and its confluences southward while alluvial sedimentation remained active in the more southern areas of the Karacasu Graben. Ages from surface dating techniques (mainly OSL and cosmogenic radionuclides) show that previous knickpoints determined by the incision/accumulation threshold reached the vicinity of the antique Greek city of Aphrodisias, 30 km from the Büyük Menderes Valley with a headward erosion rate of 75mky−1 by the end of Last Glacial Maximum (LGM).Incision rates derived from terraces and Roman aqueducts in the middle and upper reaches of the basin increased from 1 mmy−1 (background average geological rate for the last 65 ka) to 3 mmy−1in the last 2.3 ka, presumably due to increased population pressure in and around the vicinity of the city of Aphrodisias at the centre of the graben. Modern civic structures such as aqueducts and bridges constructed after the 1970's demonstrate the second wave of incision increased to as much as 10 mmy−1, likely due to increasing human pressure and the mechanisation of farming. On the other hand, inverse extrapolation of the knickpoint progression rate yields a surprisingly younger age of 400 ka for the birth of the new narrow tectonic corridor. This morphotectonic transformation exposed large depositional areas such as Karacasu and Bozdoğan grabens to erosion and should have resulted in a significant increase in the sediment supply to Büyük Menderes River. However, seismic investigations in the Aegean Sea have yet to identify the sedimentary record of this tectonic transformation.

Astronomical time scale of the Paleogene lacustrine paleoclimate record from the Nanxiang Basin, central China

The chronostratigraphy of the Paleogene succession of the Nanxiang Basin, a petroliferous basin in central China with a predominantly lacustrine fill, remains controversial due to the lack of an accurate geological time scale. In this work, high-resolution gamma-ray (GR) logs from the B270 and BS1 boreholes from depocenters in the Biyang Depression of the Nanxiang Basin were used to analyze the cyclostratigraphy. Paleocene floodplain facies of red clastics and purple mudstone is conformably overlain by Eocene through Oligocene lacustrine facies of gray mudstone, oil shale, and clayey dolomite interbedded with siltstone-sandstone. The multitaper method of spectral analysis and Gaussian bandpass filtering were used to identify Milankovitch cycles. Based on the recognition of 405-kyr long-eccentricity cycles, the series was tuned to establish a 46-Myr floating astronomical time scale (ATS), which was then anchored to the Paleogene/Neogene boundary age of 23.03 Ma. The ATS enables the assignment of the ages to non-marine biozones, depositional facies and rifting episodes within the Nanxiang Basin. The subsidence and rates of sediment accumulation within the rift basin of the Nanxiang Basin has an inverse relationship to the convergence rates between Pacific plates and the eastern margin of Eurasia. The middle Eocene slowing of the convergence rate at ~50 Ma, coupled with the onset of the collision of the Indian and Eurasian plate, corresponds to the beginning of the climax stage of rifting, the development of deep lakes and the deposition of oil shales in the Nanxiang Basin. The organic-rich 3rd member of the Hetaoyuan Formation (Eh3) during this middle Eocene interval preserved a range of climatic cycles from annual varves to a ~1.2-Myr modulation of obliquity cycles, indicating the importance of climatic oscillations on the development of those hydrocarbon source rocks.

Slope Stability of Darbendikhan Dam Site and Near Surroundings. A Reconnaissance Study, Kurdistan Region, NE Iraq

Darbendikhan Dam is constructed on the Sirwan (Diyala) River during 1955- 1961. The dam is of earth fill type with concrete spill ways and gates for electric power generation. The dam axis is almost E – W with both left and right abutments being constructed within the Gercus Formation, which consists of red clastics with more claystones. The Gercus Formation is overlain by the Pila Spi Formation that consists of hard to very hard, well bedded carbonates. The Pila Spi Formation is overlain by the Fatha Formation that consists of thick reddish brown claystones alternated with thin gypsum and limestone beds. Both Gercus and Fatha formations form steep to very steep slopes on upstream and downstream, respectively. All the slopes on the dam site and near surroundings suffer from different types of mass movements with different sizes. Some of them are old and dormant; others are recent and active exhibiting geological hazards, which may cause large loss of human life and the existing properties and infrastructure. We studied the slopes using different types of satellite images with different resolutions and conducted field trips to the dam site to collect data. We recommended some precautions to make the slopes more stable.

Association of rudists and red clastic facies in the upper part of Aqra Formation, Mawat area, Kurdistan Region, NE Iraq

In Mawat area, the Late Maastrichtian Aqra Formation (or lens) is located in the upper part of the Tanjero Formation (Lower–Middle Maastrichtian) and overlain by Red Bed Series (Paleocene–Eocene). This lens consists of about 10–100 m of massive biogenic and well-bedded detrital limestone with rich fossil content such as rudists, large forams (luftusia, omphalocyclus, and orbitoids) gastropods, pelecypods, and echinoderms. The present study discusses the geology of an association of rudists and red clastic facies in the upper part of the Aqra Formation. The tectonic and paleogeographic importance of the association are clarified and correlated with similar occurrence in Turkey and Iran. Sedimentologic and paleontologic evidence proved that all the rudists were preserved in their life position which shows that their orientations are in right side up and evidence of reworking or transporting was not found. The occurrence of these opportunistic rudists, in the red clastics, has one to three very important implications. The first is that it is possible that the red clastics belong to and occur in the Cretaceous (Maastrichtian). This occurrence is the first to prove paleontologically that red clastics are deposited during the Late Cretaceous in northern Iraq. This finding has tectonic implication as red clastics prove that the source area was active and soil development started on the recently uplifted Zagros orogenic belt. The second is that some opportunistic rudists were crossed the Tertiary/Cretaceous boundary and survived at the Early Paleocene. Since evidence from the over world put the age range of the rudists between the Late Jurassic and Late Cretaceous, this possibility is discounted by the present authors. Between the two possibilities, the authors prefer the first one. The third is that the extinction of rudists was due to prevalence of turbid red clatics in the northern Iraq.

Stratigraphy and some structural features of the İstanbul Paleozoic

Palaeozoic rocks crop out across large areas in the İstanbul region. The Palaeozoic sequence starts with the Lower Ordovician fluviatile and lacustrine deposits (Kocatöngel and Kurtköy formations). The area was transgressed by the sea during the Late Ordovician-Early Silurian, represented by the feldspathic quartzwacke and quartz-arenites of the Kınalıada and Aydos formations. The basin became progressively deeper and more stable during the Silurian and Devonian. In this period, micaceous siltstones and sandstones of the Yayalar Formation (Upper Ordovician (?)-Lower Silurian), shelf-type carbonates of the Pelitli Formation (Lower Silurian-Lower Devonian), fossil-rich micaceous shales with rare limestone intercalations representing a low-energy open shelf environment (Pendik Formation, Lower-Middle Devonian) and nodular limestones, formed in an open shelf to slope setting (Denizli Köyü Formation, Upper Devonian-Lower Carboniferous), were deposited. Lower Carboniferous black lydites, which form horizons within the Denizli Köyü Formation, and also constitute a marker horizon at the top of the formation, imply a source with a high silica content. The basin, which was tectonically stable from the Ordovician to the beginning of the Carboniferous, became a site of turbiditic flysch deposition (Trakya Formation) and tectonically active during the Early Carboniferous. Tectonic movements in the Carboniferous-Permian period resulted in the deformation and intrusion of the Permian Sancaktepe granitoid. The Variscan deformation probably involved east-west contraction resulting in north-south-trending asymmetric folds and thrusts, which resulted in the uplift of the region, followed by the deposition of Permian (?)-Lower Triassic fluviatile red clastics over large areas.

Palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest Permian- late Triassic Solway basin (U.K.)

The late Permian to late Triassic sediments of the Solway Basin consist of an originally flat-lying, laterally persistent and consistent succession of mature, dominantly fine-grained red clastics laid down in part of a very large intracontinental basin. The complete absence of body or trace fossils or palaeosols indicates a very arid (hyperarid) depositional environment for most of the sediments. At the base of the succession, thin regolith breccias and sandstones rest unconformably on basement and early Permian rift clastics. Overlying gypsiferous red silty mudstones, very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary, and their margins. These pass upwards into thick-bedded, multi-storied, fine- to very fine-grained red quartzo-felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter. Above, thick trough cross-bedded and parallel laminated fine-grained aeolian sandstones (deposited in extensive barchanoid dune complexes) pass up into very thick, multicoloured mudstones, and gypsum deposited in marginal marine or lacustrine sabkha environments. The latter pass up into marine Lower Jurassic shales and limestones. Thirteen non-marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures. The five associations can be compared with the desert pavement, arid ephemeral stream, sabkha, saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as Lake Eyre and Lake Chad. The accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent (caused by climatic change and local variation) and this promotes a large-scale layer-cake stratigraphy as exemplified in the Solway basin. Here, the dominant fine-grained mature sandstones above the local basal reg breccias suggest water-reworking of wind-transported sediment, as in the northern part of the Lake Chad basin. Growth faulting occurs in places in the Solway basin, caused by underlying evaporite movement, but these faults did not significantly affect pre-late Triassic sedimentation and did not expose pre-Permian units above the basal breccias. There is no evidence of post-early Permian rifting anywhere during deposition of the late Permian to middle Triassic British succession although the succession is often interpreted with a rift-basin model. The arid to hyperarid palaeoclimate changed little during deposition of the Solway basin succession, in contrast to Lakes Eyre and Chad: and this is attributed to tectonic and palaeolatitude stability. Unlike the later Mesozoic- Cenozoic, only limited plate movements took place during the Triassic in western Europe, palaeolatitude changed little, and the Solway Basin remained in the northern latitudinal desert belt from early to mid-Triassic times. However, the influence of the early Triassic impoverished biota on environmental interpretations needs further study.

Remarks on the Permian-Triassic transition in Central and Eastern Lombardy (Southern Alps, Italy)

The main lithological and petrographical characteristics of the Permian-Lower Triassic Orobic and Brescian successions in central and eastern Lombardy are briefl y recorded, especially with regard to the units cropping out below and above the P-T boundary. The lower formation is represented by the Verrucano Lombardo, which consists of continental, fluvial red clastics, barren of fossils, generally Late Permian (Lopingian) in age, whereas the overlying Servino Formation, which is represented by well-bedded clastic and carbonate polychrome sediments, generally rich in fossils, pertains to the Early Triassic (Induan-Olenekian). The sequences of the two above-mentioned areas differ at least in part, as proof of their regional division, probably because of an inherited paleotopography and syntectonic activity. Taking into account the units bracketing the P-T boundary, which represents the real topic of this work, the Verrucano Lombardo of the Orobic Alps is paraconformably covered by the conglomerates and sandstones of the Prato Solaro Member in the lower part of the Servino Formation, cropping out extensively, although discontinuously, from the eastern side of Lake Como to the upper Scalve Valley in the Camonica region. The shape of some quartz rock fragments, derived from the Variscan crystalline basement and its Upper Carboniferous siliciclastic cover, has been interpreted as due to relatively coeval aeolian activity, and testifi es to an arid climatic “event” probably late Dienerian-early Smithian in age. In contrast, in the Brescia province, the onset of the Servino is made up of wave and current rippled, fi ne clastics, 1-2 m thick, and a typical horizon of oolitic dolostones (“Praso Limestone” Auct.), continuous from the lower Camonica Valley to the western Trentino. This unit could laterally correlate towards east, in the eastern South-Alpine segment, with the famous oolitic Tesero Member at the base of the Werfen Formation of the Dolomitic and Carnic Alps. In the Brescian Prealps, the above oolitic deposits crop out below some Claraia beds yielding forms common to those present in the Siusi Member of the Dolomites, generally attributed to late Griesbachian-early Dienerian times. Their age could be ascribed to a slightly older Griesbachian, i.e. to early Induan. Therefore, the P-T boundary in central and eastern Lombardy seems substantially located between the fi nal part of the Permian and the very base of the respective Triassic successions, temporally and spatially ranging in different ways and generally affected by non-depositional and perhaps tectonic processes. In our opinion, however, the duration of the gap, based on correlations with the well-documented stratigraphical studies recently carried out in the nearby Dolomitic area and other European regions, should be considered as slightly longer than previously recognized: the maximum gap could be estimated at about 3-4 Ma. As a consequence, we thus point out that the Servino Formation of the Brescian Alps rests, itself, paraconformably on the Verrucano Lombardo red beds, even if the P-T gap was probably less for correlation with the well-known Dolomites sections. At the end of the paper, for a more comprehensible understanding of the late- to post-Variscan geological scenario, is a tentative synthesis of the regional evolution.

Permian to Triassic sequences from selected continental areas of southwestern Europe

Abstract This contribution is a tentative reconstruction of the still-debated geological history in the primarily continental domains now represented in various parts of southwestern Europe, between the end of the Variscan diastrophism and the beginning of the Alpine sedimentary evolution. Data and interpretations vary from one region of terrestrial rocks to another. Despite this, we have tried to highlight the most typical and significant geological features. From the Carboniferous to Triassic, palaeontological investigations of the macroflora, microflora and tetrapod footprints, as well as radiometric data, generally point out the presence of three main ‘tectono-stratigraphic units’ (TSUs), separated by marked unconformities and gaps of as yet uncertain duration. The most important geological episode generally started about the Early/Middle Permian boundary and later spanned discontinuously and intensely throughout Middle Permian (Guadalupian) time. It was characterized by specific tectonic, magmatic, thermal and basinal features, which could mark the presumed change suggested by some authors from a Pangaea B to a Pangaea A. In this context, it is worth mentioning that the unconformable Middle?-Upper Permian higher TSU in Spain consists of ‘Buntsandstein’-type red beds, sometimes yielding a Thuringian flora; differently, in southern France, such as in the Lodève area, the Buntsandstein is Anisian and thus constitutes a later Triassic sequence, which rests unconformably above the as yet undefined (Mid-Late) Permian age assessment of the ‘La Lieude fossil site’; in the Southern Alps, the ‘Second tectono-sedimentary Cycle’ emphasized from the recent literature, which is initially made up of the Verrucano Lombardo-Val Gardena Sandstone red clastics, is in part laterally and upwardly replaced, east of the Adige Valley, by the sulphate evaporite to shallow-marine Bellerophon Formation. It is thus represented by continental and marine sediments generally pertaining to Late Permian (post-‘Lower Tatarian’) time and can be interpreted, in the light of the geological context of the region, as an Upper Permian and Lower Triassic TSU of a slightly younger numerical order (i.e. TSU 3 in place of TSU 2).

Environmental geological and geotechnical investigations related to the potential use of Ankara clay as a compacted landfill liner material, Turkey

Clay-bearing Upper Pliocene red clastics and Quaternary alluvial deposits occupy the Ankara basin. The clayey levels of the Upper Pliocene deposits, referred to as Ankara clay, is considered as a source for compacted clay liners due to their low coefficients of permeability and widespread distributions throughout Ankara. This study investigates the geological, geotechnical and mineralogical properties of the founding clayey soils at two sites of the Ankara region. The geotechnical index properties along with the hydraulic conductivities of the clayey soil samples collected from these sites were determined. A mathematical relation between the clay mineralogical content and hydraulic conductivity was established. The results of this investigation show that, from a geotechnical point of view, Ankara clay may be regarded as a highly suitable material for a compacted clay landfill liner given that its mineralogical compatibility with leachate is confirmed.

The enigma of fine-grained alluvial basin fills: the Permo-Triassic (Cumbrian Coastal and Sherwood Sandstone Groups) of the Solway Basin, NW England and SW Scotland)

The late Permian to Triassic sediments of the Solway Basin consist of a layer-cake succession of mature, predominantly fine-grained red clastics laid down in semi-arid alluvial plain to arid sabkha and saline marginal marine or lacustrine environments. The Cumbrian Coastal Group consists of Basal Clastics and Eden Shales. The Basal Clastics are thin regolith deposits resting unconformably on all-underlying units and are composed of mixtures of angular local gravel and far-transported fine to very fine-grained sands deposited as basal lag. The Eden Shales are predominantly gypsiferous red silty mudstones, with thin very fine-grained sandstone beds, and with thick marine gypsum beds at the base, deposited at a saline lake margin. The overlying Triassic Sherwood Sandstone Group consists of the Annan and Kirklinton Sandstones. The Annan Sandstones are predominantly thick-bedded, multi-storied, fine-grained mature red quartz sandstones in which coarse sand is practically absent despite channels with clay pebbles up to 30 cm in diameter. The overlying, predominantly aeolian, Kirklinton Sandstones consist of festoon cross-bedded and parallel-laminated fine-grained sandstones, almost identical to the Annan Sandstones except that mica and clay are absent. The Stanwix Shales, located above, consist of interbedded red, blue and green mudstones, siltstones, and thin very fine-grained sandstones, with gypsum layers. Although the entire succession can plausibly be interpreted as deposited in a large desert basin opening into a hypersaline marine or lacustrine embayment to the southwest, the uniformly fine-grained nature of the succession is unusual, as is the absence of paleosols, and body and trace fossils. There is almost no coarse sand even in the river channel units, and it seems likely that the basin was not only extremely arid but supplied predominantly by wind rather than water.

Shyok Suture Zone, N Pakistan: late Mesozoic–Tertiary evolution of a critical suture separating the oceanic Ladakh Arc from the Asian continental margin

The Shyok Suture Zone (Northern Suture) of North Pakistan is an important Cretaceous-Tertiary suture separating the Asian continent (Karakoram) from the Cretaceous Kohistan–Ladakh oceanic arc to the south. In previously published interpretations, the Shyok Suture Zone marks either the site of subduction of a wide Tethyan ocean, or represents an Early Cretaceous intra-continental marginal basin along the southern margin of Asia. To shed light on alternative hypotheses, a sedimentological, structural and igneous geochemical study was made of a well-exposed traverse in North Pakistan, in the Skardu area (Baltistan). To the south of the Shyok Suture Zone in this area is the Ladakh Arc and its Late Cretaceous, mainly volcanogenic, sedimentary cover (Burje-La Formation). The Shyok Suture Zone extends northwards (ca. 30km) to the late Tertiary Main Karakoram Thrust that transported Asian, mainly high-grade metamorphic rocks southwards over the suture zone.The Shyok Suture Zone is dominated by four contrasting units separated by thrusts, as follows: (1). The lowermost, Askore amphibolite, is mainly amphibolite facies meta-basites and turbiditic meta-sediments interpreted as early marginal basin rift products, or trapped Tethyan oceanic crust, metamorphosed during later arc rifting. (2). The overlying Pakora Formation is a very thick (ca. 7km in outcrop) succession of greenschist facies volcaniclastic sandstones, redeposited limestones and subordinate basaltic–andesitic extrusives and flow breccias of at least partly Early Cretaceous age. The Pakora Formation lacks terrigenous continental detritus and is interpreted as a proximal base-of-slope apron related to rifting of the oceanic Ladakh Arc; (3). The Tectonic Melange (<300m thick) includes serpentinised ultramafic rocks, near mid-ocean ridge-type volcanics and recrystallised radiolarian cherts, interpreted as accreted oceanic crust. (4). The Bauma–Harel Group (structurally highest) is a thick succession (several km) of Ordovician and Carboniferous to Permian–Triassic, low-grade, mixed carbonate/siliciclastic sedimentary rocks that accumulated on the south-Asian continental margin. A structurally associated turbiditic slope/basinal succession records rifting of the Karakoram continent (part of Mega–Lhasa) from Gondwana. Red clastics of inferred fluvial origin (‘molasse’) unconformably overlie the Late Palaeozoic–Triassic succession and are also intersliced with other units in the suture zone.Reconnaissance further east (north of the Shyok River) indicates the presence of redeposited volcaniclastic sediments and thick acid tuffs, derived from nearby volcanic centres, presumed to lie within the Ladakh Arc. In addition, comparison with Lower Cretaceous clastic sediments (Maium Unit) within the Northern Suture Zone, west of the Nanga Parbat syntaxis (Hunza River) reveals notable differences, including the presence of terrigenous quartz-rich conglomerates, serpentinite debris-flow deposits and a contrasting structural history.The Shyok Suture Zone in the Skardu area is interpreted to preserve the remnants of a rifted oceanic back-arc basin and components of the Asian continental margin. In the west (Hunza River), a mixed volcanogenic and terrigenous succession (Maium Unit) is interpreted to record syn-deformational infilling of a remnant back-arc basin/foreland basin prior to suturing of the Kohistan Arc with Asia (75–90Ma).

Timing of Extension on the Büyük Menderes Graben, Western Turkey, and Its Tectonic Implications

Abstract The Büyük Menderes Graben is one of the most prominent structures of western Anatolia (Turkey) and borders the Aegean. New structural and stratigraphic evidence demonstrates that the (?)Miocene fluvio-lacustrine, coal-bearing red clastic sediments exposed along the northern margin of the graben are northward back-tilted, locally folded and overlain unconformably by horizontal terraced Pliocene-Pleistocene sediments. Also, there is no evidence that these red clastics at the base of the Neogene sequence were deposited during neotectonic extension. It is suggested here that these sediments cannot be regarded as passive neotectonic graben-fill deposits. This new evidence further indicates that the age of the modern Büyük Menderes Graben is Pliocene, younger than previously considered (Early-Middle Miocene) and that initiation of north-south neotectonic extensional tectonics in the graben, and thus in western Anatolia, is unlikely to have resulted from orogenic collapse. The Pliocene estimate of the start of extension is in close agreement with the start of slip on the North Anatolian Fault Zone. The north-south extensional tectonics, and associated east-west faulting and basin formation, commenced during the Pliocene due to the effect of westward tectonic escape of the Anatolian block along the North and East Anatolian Faults. New mammal evidence also constrains the start of slip on the younger faults which bound the present-day graben floor to c . 1 Ma. The Büyük Menderes Graben has experienced a two-stage extension. An initial extension (latest Oligocene-Early Miocene) along initially moderately, steeply dipping normal faults was superseded by movement on steeper normal faults during the (?)Pliocene. The two phases of deformation appear to reflect significant changes in the tectonic setting of western Anatolia and are attributed to orogenic collapse followed by tectonic escape.

Facies-Dependent Diagenesis of Shelf-Margin Sandstones and Siltstones, Yates Formation, Northern Margin of Delaware Basin: ABSTRACT

Shelf-margin sandstones and siltstones of the Permian (late Guadalupian) Yates Formation, continuously cored in the Gulf PDB-04 research well of the northern margin of the Delaware basin, have varying textures, compositions, and diagenetic histories. Gray, dolomitic, quartzose, very fine to fine-grained sandstones occur in the lower part of the formation; dark red (FeO/sub 2/-stained detrital clay-bearing), anhydritic, subarkosic to arkosic, very fine-grained sandstones/siltstones occur in the upper portions. Stratigraphic relations, associated carbonates, and ichnofossils suggest that the gray sands were deposited seaward of a pisolite shoal complex in an intertidal to marginally subtidal setting, whereas the overlying red clastics accumulated along the crest of the shoal in a supratidal environment. This interpretation is congruent with the progradational history of the Yates Formation as established by outcrop and subsurface studies. Depositionally updip sandstones, studied from outcrop and other wells, show that the source sandstones for the gray and red sandstones in the PDB-04 well have relatively uniform depositional textures and mineralogies (silty, fine grained, lithic, subarkoses to arkoses). This strongly suggests that the variations seen in the core are due to facies-dependent diagenesis.

Evolution of Permian Evaporite Basin in Texas Panhandle

Permian (Leonardian to Ochoan) evaporites in the Texas Panhandle were deposited in a range of marine shelf to supratidal environments along an arid coastline. Carbonates in these strata generally were deposited in inner shelf systems and include subtidal to supratidal facies. Landward of shelf environments, evaporites were deposited in brine pans and salt flats. Brine-pan facies are laminated anhydrite and banded salt that formed in shallow, hypersaline waters such as restricted lagoons or supratidal salines. Salt-flat facies are mainly chaotic mixtures of mudstone and halite possibly formed by salt deposition on and within mud flats that bordered brine pans, or in brine-soaked mud-flat depressions. Periodically, mud flats built across the evaporite systems and were suppl ed with red terrestrial clastics, mainly mud and silt. These facies occur together in at least three different types of lithogenetic units. Strata in the Clear Fork Group (Leonardian) are considered deposits of a coastal evaporite basin that was progressively filled by terrestrial clastics. These rocks exhibit regressive cycles of brine-pan, salt-flat, and mud-flat facies. In contrast, San Andres strata (Guadalupian) were deposited in a broad marine embayment with persistent brine-pan conditions, and contain cycles of inner shelf and brine-pan facies. Post-San Andres strata (late Guadalupian and Ochoan) were deposited in the inner reaches of a broad interior salt basin and are composed mainly of mud-flat, salt-flat, and halite-rich brine-pan facies.

Micro-Platform Carbonate Development and Facies in Mauch Chunk Formation (Chesterian) of Southwestern Pennsylvania: ABSTRACT

Through much of southwestern Pennsylvania, adjacent Maryland, and West Virginia, Upper Mississippian (Chesterian) strata are represented by intertonguing of red clastics of the Mauch Chunk Formation and carbonates of the Loyalhanna and Wymps Gap Limestones. The lower clastic wedge of the Mauch Chunk represents an episodic shoreline progradational event that buried the underlying Loyalhanna carbonates. The sea level rise concurrent with the Wymps Gap transgression resulted in nearly continuous deposition of clastics in nearshore areas while carbonates were being deposited on more offshore areas. This resulted in the development of a lobe of clastics (forming a small platform) that created significant topography to be transgressed by the deepening Wymps Gap sea. Facies development of the Wymps Gap carbonates was markedly influenced by this inherited topography. In areas where clastics are thin, the Wymps Gap is represented by a medium-bedded, dark-gray, petroliferous, clay-rich carbonate mudstone to wackestone. These sediments are represen ative of open shelf deposition, in moderate water depths below storm wave base. Along the margin of the thick clastic lobe, the Wymps Gap is represented by a light-gray, locally cross-bedded carbonate grainstone to packstone. These accumulations appear to represent a slope-break platform-edge shoal environment. Over the top of the thick lobe of clastics, highly argillaceous, nodular-bedded, variegated, bioturbated carbonate mudstone to packstone formed. These facies represent platform deposition landward of the shoal environment in an open-circulation shallow lagoon. End_of_Article - Last_Page 1916------------

Structural Aspects and Hydrocarbon Potentials of Basins on Continental Margins Off Labrador and Newfoundland: ABSTRACT

The continental shelf of Labrador and Newfoundland is underlain by several discrete subbasins. On the western margin of the Labrador Sea, north of the east-trending, east-plunging Cartwright arch, the continental shelf is underlain by up to 10 km of Upper Cretaceous to upper Tertiary marine clastics that constitute the Hopedale-Saglek basin. These sediments overlie a narrow rifted basin of early to middle Cretaceous age, informally called the Erik graben. Further south, between the Cartwright arch and the axis of the Avalon uplift, the continental shelf is more complex. This region contains the St. Anthony basin, an Appalachian successor basin with upper Paleozoic coal measures and red clastics; the somewhat sinuous, generally northeast-southwest trending Avalon basin containing mixed facies of Mesozoic and Tertiary age; and an unnamed, early Tertiary depocenter having a NNW-SSE trend which is infilled with mostly fine-grained marine clastic rocks. Hydrocarbon occurrences discovered can be explained in terms of the nature and thermal maturity of probable source rocks and the time of trap formation. Liquid hydrocarbons have only been found in significant amounts in the Avalon basin where traps are supra-adjacent to mature Upper Jurassic source rocks. However, in this basin Lower Cretaceous deltaic sequences can be expected to generate gas. In the remaining basins the sequences contain organic matter that is largely terrestrial and/or at a low level of thermal maturity. In these basins, a low potential for gas is likely. End_of_Article - Last_Page 1672------------

POSSIBLE DISPLACIVE HALITE IN THE PERMIAN UPPER EVAPORITE GROUP OF NORTHEAST YORKSHIRE1

ABSTRACTHalite lying above the potash‐rich interval of the Permian Upper Evaporite Group of northeast Yorkshire, England, is intimately associated with fine red clastics in such a way as strongly to suggest that the former originated by nucleation and growth within the latter. It is inferred that this process took place in distal sediments of a mature basin‐margin plain, probably in a belt subject to repeated inundation caused by periodic large‐scale expansions and contractions of an extensive basin‐centre playa. Such an environment is consistent with the generally shallow‐water to continental origin of the underlying Carnallitic Marl and the overlying Permian Upper Marls, and contrasts with the deep‐basin depositional model customarily applied to the Zechstein evaporites.

Geology of Jurassic, Flomation-Jay Area, Alabama and Florida: ABSTRACT

Flomaton field, in Escambia County, is the first major gas condensate discovery from the Jurassic Norphlet Formation in Alabama. Structurally the field is a NW-SE trending low-relief salt anticline bounded on the north and east flanks by a major down-to-the-basin fault which is part of the Pickens-Gilbertown-Pollard regional fault system. The Norphlet sandstone reservoir is about 60 ft thick within the field and produces CO2 and sour gas with a high condensate yield. The paleostructural history of the area indicates that early Louann Salt movement and faulting occurred, probably as a result of gravity slide and basinward salt creep, forming structures necessary for trapping hydrocarbons. Jurassic deposition was affected by these early structural features and pre-salt topography. Norphlet clastics were derived from the northeast and deposited by braided stream systems. As the Smackover seas transgressed the area, the upper part of the Norphlet was partly reworked. In the Flomaton area, the Smackover Formation is a dark-brown, dense, micritic limestone. The overlying Haynesville Formation can be subdivided into an upper member consisting of predominantly red, coarse clastic material and a lower member consisting of fine, red clastics and evaporites. At Flomaton, over 300 ft of bedded salt has been drilled in the lower Haynesville causing many drilling and completion problems. The Cotton Valley Group marks the top of the Jurassic and consists primarily of coarse gravelly clastics. Exploration activity in southwest Alabama during 1969, 1970, and 1971 led to additional discoveries from the Jurassic. Among these is Jay field in Santa Rosa County, Florida, 7 mi southeast of Flomaton field. Jay produces oil from Smackover dolomite and is the first Jurassic discovery in Florida. The discovery well produced 1,710 BOPD and has resulted in one of the most active exploration plays in the United States. End_of_Article - Last_Page 1695------------

Jurassic Geology of Flomaton Field Area of Southern Alabama: ABSTRACT

Flomaton field, in Escambia County, Alabama, is the first major gas condensate discovery from the Jurassic Norphlet Formation in Alabama. Structurally the field is a NW-SE trending, low-relief salt feature bounded on the north and east by a major down-to-the-basin fault which is part of the Pickens-Gilbertown-Pollard regional fault system. The Norphlet sandstone reservoir is about 60 ft thick and produces CO2 and sour gas with a high condensate yield. The paleostructural history of the area indicates that movement of Louann salt and faulting occurred, probably as a result of gravity slide and basinward salt creep, forming structures capable of trapping hydrocarbons. Jurassic deposition was affected by these early structural features and by presalt topography that existed updip from the Flomaton area. Norphlet clastics were derived from the northeast and deposited by braided stream systems. As the Jurassic Smackover seas transgressed the area, the upper part of the Norphlet was partly reworked. In the Flomaton area, the overlying Smackover Formation is a dark-brown, dense, micritic limestone. Above the Smackover, the Haynesville Formation can be subdivided into upper and lower members with the upper Haynesville consisting of predominately red, coarse clastics and the lower member being fine, red clastics and evaporites. At Flomaton, over 300 ft of bedded salt has been drilled in the lower Haynesville causing many drilling and completion problems. The Cotton Valley Group marks the top of the Jurassic and consists primarily of coarse, gravelly clastics. End_of_Article - Last_Page 347------------

A New Interpretation of the Llandovery Sequence of North Connemara, Eire

AbstractThe historical development of the stratigraphic nomenclature of the Llandovery of north Connemara is described. The lowest beds are red sandstones and interbedding keratophyre passing up into a complex sequence of grey, green and red clastics with shelly facies fossils. Above this are red and green mudstones and siltstones with rare graptolites. In the east these are overlain by coarse sandstones and conglomerates. The conglomerates are probably allochthonous. In the west this coarse facies is developed earlier and laterally interfingers with the shelly facies clastics and overlying mudstones. The sub-Wenlock unconformity reported by McKerrow and Campbell from this region is reinterpreted as an appearance of this interfingering.