Devonian Strata Research Articles

Role of Cenozoic fault reactivation in controlling pre-rift plays, and the recognition of Zechstein Group evaporite-carbonate lateral facies transitions in the East Orkney and Dutch Bank basins, East Shetland Platform, UK North Sea

The East Orkney and Dutch Bank basins are located to the north of the Moray Firth rift arm in the UK North Sea. The East Orkney Basin measures approximately 60 by 30 km and is bounded to the west, north and east by large normal faults. The West Fladen High consists of a series of horsts and grabens, and separates the East Orkney Basin from the Dutch Bank Basin, which is situated immediately to the north of the Witch Ground Graben and to the west of the Fladen Ground Spur. Although exploration well results for the limited penetrations of structural highs on the margins of the East Orkney Basin have been disappointing, geophysical and geochemical analyses all appear to indicate the presence of a mature source in the region. Integration of wireline data, core samples, and the interpretation of 2D seismic data within the area allow mapping of the main structures in the basins and correlation to the adjacent well penetrations, thus not only enabling a tectonic and stratigraphic history, but also a framework for prospectivity to be established. A pillow-shaped sedimentary package at approximately 3 seconds two-way traveltime within the centre of the East Orkney Basin represents the downdip equivalent of stratigraphy on the West Fladen High, and is interpreted to be a Zechstein Group salt body, underlain by a thick sequence of Lower Permian (Rotliegend Group) and Devonian strata. Cored intervals from well 14/2-1 on the West Fladen High contain carbonates, evaporite dissolution breccias and anhydrites, implying a lateral change in sedimentary facies between structural highs and lows. Rifting took place through the Triassic and Jurassic, followed by relative tectonic quiescence in the Cretaceous, but as in adjacent areas, the Cenozoic witnessed structural inversion related to plume-generated uplift in the North Atlantic and the activation/reactivation of underlying faults coupled with deformation of the basin fill adjacent to these structures. Regional tilting from the Paleocene to early Eocene led to an influx of siliciclastics into the Dutch Bank Basin. The main play type is thought to consist of Rotliegend Group and Devonian sandstone reservoirs on the West Fladen High, sealed by Zechstein Group anhydrites or Cretaceous/Tertiary mudstones and charged by a deeply buried Devonian (Orcadian) lacustrine source. Although hydrocarbons are interpreted to have utilized normal faults as migration pathways, comparison with adjacent areas and observations of numerous oil seeps on the sea surface suggest that reservoir breach through reactivation of these faults to the seabed poses the main exploration risk. This fault reactivation has resulted from differential uplift combined with synchronous extensional faulting that affected adjacent areas, including the Inner Moray Firth.

Stratigraphy, sedimentology, structure and tectonics of Lower Ordovician and Devonian strata of South Mootwingee, Darling Basin, western New South Wales

A small inlier of marine Bynguano Quartzite, of Early Ordovician age, was discovered in the eastern part of the mapped area, although most of the strata are Devonian in age. The mid‐Emsian to mid‐Eifelian Snake Cave Sandstone consists of seven informal units. In the west the Waverly Creek Formation (new) is unconformable on the Snake Cave Sandstone; it consists of The Rocky Tank Conglomerate Member (new) (?early Givetian in age), which is overlain by the Ramparts Creek Sandstone Member (new) (mid‐Givetian in age). In the west the late Givetian to Famennian Ravendale Formation is conformable on the Ramparts Creek Sandstone Member whereas further east where the Waverly Creek Formation is absent, the Ravendale Formation is largely paraconformable on Snake Cave Sandstone. The area is cut by the north‐northwest‐trending Mootwingee (in the west) and the Boorungie Faults (in the east). These faults were active during the Tabberabberan and the Kanimblan Orogenic Pulses of the Lachlan Orogen and they subdivide the area into West, Central and East Blocks. The West and the Central Blocks are an uplifted part of the Bancannia Trough (basin inversion) whereas the East Block is a southern part of the Wonominta Block.

Middle and upper Devonian chitinozoan biostratigraphy of the paraná basin in Brazil and Paraguay

Chitinozoans from Middle and Upper Devonian strata have been investigated from the Paraná Basin in southern Brazil and eastern Paraguay. These sequences are present in the Alto Garças (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in eastern Paraguay. Marine communication between the sub‐basins was established during the early Givetian. Of the 49 chitinozoan species encountered, 28 species are retained in open nomenclature, and Ancyrochitina simplex is newly described. A chitinozoan biozonation, with five zones, is proposed for the investigated interval. The zones are from oldest to youngest: concurrent range zone of Alpenachitina eisenacki and Spinachitina biconstricta (late Eifelian?‐early Givetian); the interval range zone of Ancyrochitina taouratinensis (latest early‐middle Givetian); concurrent range zone of Fungochitina pilosa and Ancyrochitina langei (late Givetian); concurrent range zone of Hoegisphaera glabra and Ramochitina derbyi (early Frasnian); and total range zone of Lagenochitinaavelinoi (early late Frasnian).

Upper Silurian and Devonian Chitinozoa from central and southern Bolivia, central Andes

A study of chitinozoans from Upper Silurian and Devonian strata from south central Bolivia has provided new stratigraphic information and improved correlations with adjacent basins in Argentina, Paraguay, Uruguay, and Brazil. The investigated succession extends from late Ludlow (upper Kirusillas Formation) to late Frasnian (upper Iquiri Formation). Unconformities in the section or condensed intervals occur in latest Pragian to early Emsian and for most of the Eifelian. Two early Givetian chitinozoan species, Ancyrochitina postdesmea and Ramochitina boliviensis, are newly described.

MIDDLE AND UPPER DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF THE PARANA BASIN IN BRAZIL AND PARAGUAY

Abstract Chitinozoans from Middle and Upper Devonian strata have been investigated from the Parana Basin in southern Brazil and eastern Paraguay. These sequences are present in the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in eastern Paraguay. Marine communication between the sub‐basins was established during the early Givetian. Of the 49 chitinozoan species encountered, 28 species are retained in open nomenclature, and Ancyrochitina simplex is newly described. A chitinozoan biozonation, with five zones, is proposed for the investigated interval. The zones are from oldest to youngest: concurrent range zone of Alpenachitina eisenacki and Spinachitina biconstricta (late Eifelian?‐early Givetian); the interval range zone of Ancyrochitina taouratinensis (latest early‐middle Givetian); concurrent range zone of Fungochitina pilosa and Ancyrochitina langei (late Givetian); concurrent range zone of Hoegisphaera glabra and Ramochitina derbyi (early Frasnian)...

Comparison of the Ordovician-Carboniferous Boundary Between Korea and NE China: Implications for Correlation and Tectonic Evolution

There is a great hiatus between Ordovician and Carboniferous strata in the Northeast China and Korean Peninsula. In order to understand geology and tectonic evolution, and to find out the similarities and differences in both regions, two sections in the Western Hill near Beijing in NE China and several sections in the Korean Peninsula were selected to examine their geologic boundaries between Lower and Upper Paleozoic strata to compare their characteristic features. At four sites in the two sections in the Western Hill near Beijing were examined their contact relations. The Hui Yu section is the same horizon where one site is top of a quarry hill and the other of down hill. Mid-Carboniferous Qingshuijian Formation rests on the Ordovician Majiagou Formation. Limestone beds are more commonly intercalated with shale and sandstone at site 2 of the Hui Yu section, while at site 1, conglomerate beds are dominant. Site 1 of the Se Shu Fen section shows eroded and concealed karst topography and conglomerate beds are intercalated within shale beds. Silurian and Devonian strata are absent in these areas. In the Korean Peninsula, most O-C contacts occur between Ordovician limestone formation and Carboniferous strata, although Silurian strata occur beneath the Carboniferous strata in the Jeongseon area and Pyeongnam Basin. Most contact relations are parallel unconformity and angular unconformity is rarely seen. The O-C relations in both regions are similar to each other, and these indicate that the Korean Peninsula was located near or belonged to the Sino-Korean paraplatform during Paleozoic time.

Silurian and lower devonian chitinozoan biostratigraphy of the paraná basin in brazil and Paraguay

The taxonomy and distribution of Chitinozoa from Silurian (Llandovery) and Lower Devonian strata are reported from the Paraná Basin in southern Brazil and eastern Paraguay. The pre‐Carboniferous sequences of the Paraná Basin in this area are present in three sub‐basins viz., the Alto Garças (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in east Paraguay. There is more similarity in the lithology between the Alto Garças and “East Paraguay”; sub‐basins, than between the former and the Apucarana sub‐basin. Llandoverian and Lochkovian to Pragian beds are present in all sub‐basins. So far, no Emsian beds have been found in outcrops from the north‐northwest margin of the Alto Garças Sub‐basin, and no early Emsian beds in the outcrops on the northeast margin. Furthermore, Emsian beds could not be identified from the “East Paraguay Sub‐basin”; in the present study. The Early Devonian sequence is more complete in the Apucarana Sub‐basin. It seems that the Apucarana Sub‐basin endured a different evolution compared to the two other sub‐basins during the Ordovician, Silurian and lower Devonian. Of the 39 chitinozoan species encountered, 24 species are left in open nomenclature, and the following five species are newly described: Ancyrochitina paranaensis, Angochitina daemoni, Sphaerochitina silurica, Spinachitina harringtoni, and Spinachitina wolfarti. A chitinozoan biozonation, with five zones and three subzones, is proposed for the investigated interval, and compared with the spore zonation. In addition we infer that the Furnas Formation could correspond to two chitinozoan zones found in Bolivia and Argentina (zones of Urochitina loboi and Angochitina aff. A. comosa), ranging in age from late Lochkovian to earliest Pragian. The zones are, from oldest to youngest: total range zone of Belonechitina postrobusta (upper Rhuddanian); total range zone of Conochitina elongate (Aeronian); concurrent range subzone of Spinachitina wolfarti n. sp. and Plectochitina sp. A (lower Aeronian); concurrent range subzone of Conochitina proboscifera and Spinachitina harringtoni n. sp. (upper Aeronian s.l.); concurrent range subzone of Conochitina proboscifera and Desmochitina cf. D. densa (lower Telychian s.l.); concurrent range zone of Salopochitina monterrosae and Conochitina proboscifera (upper Telychian‐lower Sheinwoodian); total range zone of Urochitina loboi (upper Lochkovian); total range zone of Angochitina aff. A. comosa (lowermost Pragian); total range zone of Ramochitina magnifica (Pragian s.l.), and total range zone of Ancyrochitina parisi (upper Emsian).

SILURIAN AND LOWER DEVONIAN CHITINOZOAN BIOSTRATIGRAPHY OF THE PARANA BASIN IN BRAZIL AND PARAGUAY

Abstract The taxonomy and distribution of Chitinozoa from Silurian (Llandovery) and Lower Devonian strata are reported from the Parana Basin in southern Brazil and eastern Paraguay. The pre‐Carboniferous sequences of the Parana Basin in this area are present in three sub‐basins viz., the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in east Paraguay. There is more similarity in the lithology between the Alto Garcas and “East Paraguay”; sub‐basins, than between the former and the Apucarana sub‐basin. Llandoverian and Lochkovian to Pragian beds are present in all sub‐basins. So far, no Emsian beds have been found in outcrops from the north‐northwest margin of the Alto Garcas Sub‐basin, and no early Emsian beds in the outcrops on the northeast margin. Furthermore, Emsian beds could not be identified from the “East Paraguay Sub‐basin”; in the present study. The Early Devonian sequence is more complete in the Apucarana Sub‐basin. It seems that the Apucarana ...

ABSTRACT: Conodont Biostratigraphy of Devonian Strata of West Texas and Eastern New Mexico

ABSTRACT: Conodont Biostratigraphy of Devonian Strata of West Texas and Eastern New Mexico

Syngenetic Au on the Carlin trend: Implications for Carlin-type deposits

A new type of gold occurrence recently discovered in the Carlin trend, north-central Nevada, is clearly distinct from classic Carlin-type gold ore. These occurrences are interpreted to be of sedimentary exhalative (sedex) origin because they are stratiform and predate compaction and lithification of their unaltered Devonian host rocks. They contain barite that exhibits δ34S and δ180 values identical to sulfate in Late Devonian seawater and sedex-type barite deposits. Abrupt facies changes in the host rocks strongly suggest synsedimentary faulting and foundering of the carbonate shelf during mineralization, as is characteristic of sedex deposits. Gold occurs both as native inclusions in synsedimentary base-metal sulfides and barite, and as chemical enrichments in sulfide minerals. The absence of alteration and lack of δ13C and δ180 isotopic shift of primary carbonates in these rocks is strong evidence that this gold was not introduced with classic Carlin-type mineralization. Collectively, these features show that the Devonian strata were significantly enriched in gold some 300 m.y. prior to generation of the mid-Tertiary Carlin-type deposits. These strata may have been an important, perhaps even vital, source of gold for the latter. Although gold is typically low in most Zn-Pb-rich sedex deposits, our evidence suggests that transport of gold in basinal fluids, and its subsequent deposition in the sedex environment, can be significant.

Recognition of fine-scale imbricate thrusts in lower Paleozoic orogenic belts—An example from the Roberts Mountains allochthon, Nevada

Dating of lower Paleozoic cherts is now possible through advancements in radiolarian biostratigraphy, permitting greater refinement of structural and stratigraphic models than has previously been possible. A detailed study of the type section of the Ordovician Vinini Formation, Vinini Creek, Roberts Mountains allochthon, Nevada, has yielded anomalously young Devonian ages. These ages were unanticipated and indicate that structural imbrication exists in a classic and previously well dated section of basinal strata. Previous ages of cherts were inferred from their stratigraphic position relative to graptolite-bearing shales. New mapping and biostratigraphy reveal considerable structural interleaving of Ordovician and Devonian strata within the allochthon, and many of the cherts appear to have structural bases. The Roberts Mountains allochthon, considered to be allochthonous but not far traveled, displays a highly complex structural history, including out of sequence thrusting and/or overprinting by later contractional deformation having a similar transport direction. This deformation was previously unrecognized because of the lack of overlap sequences in critical areas and the paucity of internal age control. Because the Roberts Mountains allochthon is not considered to be exotic, but rather has undergone only a modest amount of transport, this study shows that convergent margins with high degrees of structural imbrication do not require large amounts of transport. A biostratigraphic approach that examines all lithologies, coupled with detailed observations of field relations, is required for the construction of detailed and accurate structure sections in early Paleozoic orogenic belts.

Stratigraphy and Operational Palynology of the Devonian System in Saudi Arabia

ABSTRACT Surface and subsurface Devonian rocks of Saudi Arabia are correlated using a combination of palynology and sequence stratigraphy. Recent exploratory drilling in eastern Saudi Arabia has confirmed that sweet gas and condensate-bearing Devonian strata are preserved on the flanks of high-relief Hercynian structures such as Ghawar field. This Devonian succession is composed of three homogeneous litho-stratigraphic units, the Tawil, Jauf and Jubah formations that cannot be imaged seismically nor readily discerned with conventional wireline logs. An operational palynological zonation was consequently devised based on first down-hole occurrences (i.e. extinctions) of encountered palynomorphs. This zonation was calibrated with the standard European spore zonations of Streel et al. (1987) and Richardson and McGregor (1986), and further controlled by mega-fossil data from outcrops in northwestern Saudi Arabia. Six palynozones, and four subzones, have been recognized. A particularly reliable late Early Devonian zone is based on the acme of an endemic Leiosphaeridia species. This palynosubzone coincides stratigraphically with the upper part of the gas-bearing Jauf Reservoir.

Tectonics and sedimentation in the hangingwall of a major extensional detachment: the Devonian Kvamshesten Basin, western Norway

The Middle Devonian Kvamshesten Basin in western Norway is a late‐orogenic basin situated in the hangingwall of the regional extensional Nordfjord–Sogn Detachment Zone. The basin is folded into a syncline with the axis subparallel to the ductile lineations in the detachment zone. The structural and stratigraphic development of the Kvamshesten Basin indicates that the basin history is more complex than hitherto recognized. The parallelism stated by previous workers between mylonitic lineation below the basin and intrabasinal fold axes is only partly reflected in the configuration of sedimentary units and in the time‐relations between deposits on opposing basin margins. The basin shows a pronounced asymmetry in the organization and timing of sedimentary facies units. The present northern basin margin was characterized by bypass or erosion at the earliest stage of basin formation, but was subsequently onlapped and eventually overlain by fanglomerates and sandstones organized in well‐defined coarsening‐upwards successions. The oldest and thickest depositional units are situated along the present southern basin margin. This as well as onlap relations towards basement at low stratigraphic level indicates a significant component of southwards tilt of the basin floor during the earliest stages of deposition. The inferred south‐eastwards tilt was most likely produced by north‐westwards extension during early stages of basin formation. Synsedimentary intrabasinal faults show that at high stratigraphic levels, the basin was extending in an E–W as well as a N–S direction. Thus, the basin records an anticlockwise rotation of the syndepositional strain field. In addition, our observations indicate that shortening normal to the extension direction cannot have been both syndepositional and continuous, as suggested by previous authors. Through most of its history, the basin was controlled by a listric, ramp‐flat low‐angle fault that developed into a scoop shape or was flanked by transfer faults. The basin‐controlling fault was rooted in the extensional mylonite zone. Sedimentation was accompanied by formation of a NE‐ to N‐trending extensional rollover fold pair, evidenced by thickness variations in the marginal fan complexes, onlap relations towards basement and the fanning wedge geometry displayed by the Devonian strata. Further E–W extension was accompanied by N–S shortening, resulting in extension‐parallel folds and thrusts that mainly post‐date the preserved basin stratigraphy. During shortening, conjugate extensional faults were rotated to steeper dips on the flanks of a basin‐wide syncline and re‐activated as strike‐slip faults. The present scoop‐shaped, low‐angle Dalsfjord fault cross‐cut the folded basin and juxtaposed it against the extensional mylonites in the footwall of the Nordfjord–Sogn detachment. Much of this juxtaposition may post‐date sedimentation in the preserved parts of the basin.Basinal asymmetry as well as variations in this asymmetry on a regional scale may be explained by the Kvamshesten and other Devonian basins in western Norway developing in a strain regime affected by large‐scale sinistral strike‐slip subparallel to the Caledonian orogen.

The Frasnian/Famennian boundary at the Sessacker Trench section near Oberscheld (Dill Syncline, Rheinisches Schiefergebirge, Germany)

The section excavated by the reopening of the famous Sessacker Trench in Late Devonian strata of the Dill Syncline yields unique sedimentological phenomena and a distinct position of the Frasnian/Famennian (F/F) boundary. Detailed analysis of the condont development across the F/F boundary allows to pinpoint the boundary for the first time in rocks above Kellwasser type strata in hemipelagic cephalopod limestones, deposited on submarine rises. The depositional history, including synsedimentary slumping, can be demonstrated applying extremely detailed conodont biostratigraphy in this time interval. The conodont faunas allow to separate several steps in their evolutionary development during times of the F/F mass extinction and tied to the end-Kellwasser Crisis (main Kellwasser Event).

Provenance of Paleozoic sedimentary rocks in the Canadian Cordilleran miogeocline: a Nd isotopic study

Nd isotopes and trace elements in sedimentary rocks of the Yukon, the Northwest Territories, and northern British Columbia are used to examine the source of sediments in the Canadian Cordilleran miogeocline. Previous Nd isotope studies in southern Alberta demonstrated that strata of Neoproterozoic to Late Ordovician age were derived from Archean and Proterozoic Canadian Shield sources, whereas by the Late Devonian, a shift of 6 εNd units to younger crustal sources (εNd (T) = −6 to −9) had occurred. In this study, we found that the shift to younger crustal Nd isotopic signatures in the Yukon and Northwest Territories occurred much earlier than in southern Alberta. Cambrian and older strata have εNd(T) values of −10.0 to −21.1, consistent with derivation from Canadian Shield sources. Lower Ordovician through Permian strata in the Yukon and Northwest Territories, including the Innuitian-derived Imperial Assemblage, have εNd(T) values of −5 to −11.4. In northern British Columbia, the shift to a younger source reflects a wider range of εNd(T) values, from -−8.7 to −14.6 in Middle Ordovician through Middle Devonian strata, suggesting continued input from Canadian Shield sources. By the Middle Devonian, a complete shift to younger crustal signatures (εNd(T) = −5.9 to −10.5) had occurred in northern British Columbia. Several sources for the more juvenile sediments include (1) a mixture of locally erupted volcanic rocks with Canadian Shield sources, (2) a Grenville source, and (3) an Innuitian source. We propose that Ordovician to Lower Devonian strata were derived from a mixture of locally erupted, juvenile volcanics and pre-Cambrian Canadian Shield sources, and post-Middle Devonian strata were sourced from the Innuitian orogen in the Canadian Arctic.

A late Devonian (Frasnian) coral-bafflestone reef at Houshan in Guilin, South China

Givetian to early Carboniferous sediments of South China are characterized by carbonates. Middle and Late Devonian strata are best developed in the Guilin area. Reefs and organic shoals are recorded by various lithofacies types indicating the existence of an extended carbonate platform and a change of the composition of reef communities in time. Starting in the late Devonian, stromatoporoids and corals were replaced by algae that subsequently played an important role together with stromatoporoids, receptaculitids and fasciculate rugose corals in reef communities. In Houshan, 5 km west of Guilin, a coral-bafflestone reef occurs in the Frasnian strata, situated near an offshore algal-stromatoporoid reef. The coral reef was formed in a back-reef area adjacent to the inner platform margin. The coral-bafflestone reef is unique among the late Devonian reefs of South China with regard to the biotic composition. The reef is composed of fasciculate colonies ofSmithiphyllum guilinense n. sp. embedded within in packstones and wackestones. The height of colonies reaches 1 m. The community is low-diverse. The species ofSmithiphyllum occurring in the Frasnian reef complexes of Guilin exhibit a distinct facies control:Smithiphyllum guilinense occurs in or near to margin facies and formed bafflestone, constituting a coral reef whereasSmithiphyllum occidentaleSorauf, 1972 andSmithiphyllum sp.—characterized by small colonies with thin corallites—are restricted to the back-reef and marginal slope facies. The bush-like coral colonies baffled sediments. Algae and stromatoporoids (mainlyStachyodes) are other reef biota. Reef-dwelling organisms are dominated by brachiopods.

Evaluation of burial history, thermal maturity and source-rock assessment of the Upper Paleozoic succession of the eastern Taurus region, southern Turkey

The regional burial history pattern, thermal maturity variations and source rock assessment of the sedimentary succession in the eastern Taurus region, in the southern part of Turkey, have been studied on surface samples collected from the six different sections which represent the entire region. Organic petrography (Thermal Alteration Index) and geochemical data (TOC content, T max and HI values) were obtained from transmitted-light microscopy and Rock-Eval pyrolysis. The Lower Paleozoic (Cambrian, Ordovician and Silurian) strata were not investigated and modeled in terms of the maturity and hydrocarbon source rock potential, because of their poor organic matter content and their over maturity resulting from great burial depth (more than 7630 m). Other Paleozoic strata, except the Lower Devonian Ayitepesi Formation, generally have the values of more than 0.5% TOC. Organic matter of the Middle Devonian Safaktepesi sediments are composed of highly terrestrial organic material (type III kerogen), while samples from other three formations (Gumusali, Ziyarettepe and Yigilitepe Formations), while samples from other organic matter (type II and type III kerogen). The average TAI values are as high as 3.4 (equivalent to 1.42 of R 0%) for Ayitepesi and as low as 2.75 (equivalent to 0.77 of R 0%) for Yigilitepe Formations. Time-temperature index values (TTI) indicate that Ziyarettepe and Yigilitepe sediments are marginally mature to mature, while the Devonian strata are overmature. There are minor discrepancies between ΣTTI values and geochemical data in terms of the organic maturity for Devonian strata. In contrast, the e is a consistency between those values for the Ziyarettepe and the Yigilitepe Formations. The onset of oil generation time in the region was initiated from as early as the Norian (216 Ma) to as late as the Lutetian (45 Ma). Regional variations in the level of thermal and source-rock maturities of the Upper Paleozoic sediments in the eastern Taurus region largely depend on burial depth.

Early Paleozoic (Cambrian to Early Devonian) Tectonic Framework, Canadian Cordillera

Uppermost Proterozoic to Lower Devonian rocks in the Cordillera of western Canada accumulated within two ancestral continental margin systems--the Canadian Cordilleran and southwestern Franklinian miogeoclines. These miogeoclines are separated by the Ogilvie Arch. Prominent features of the southwestern Franklinian Miogeocline are the Richardson Trough, a failed arm or aulacogen opening northward into the outer Franklinian Miogeocline, and, west and east of it, the Porcupine and Lac des Bois platforms. The Canadian Cordilleran Miogeocline formed in Late Proterozoic as the result of rifting, and although the newly formed margin was Atlantic-type, it continued to have distinct periods of rifting and extension with volcanism, throughout its history. The Canadian Cordilleran Miogeocline is divided by numerous northeast-trending linear features interpreted to reflect the position of ancestral strike-slip or transfer faults. More than six major block segments are recognized. From south to north they are: the Montana Block, bordered north by the Moyie-Dibble Creek fault systems; the Alberta Block, bordered north by the Hay River and Great Slave Lake fault systems, and divided into the Peace and Southern Prairies sub-blocks along the Rimbey Magnetic-Snowbird Tectonic zones; the Macdonald Block bordered north by the Liard Line; the Blackwater Block, bordered north by the Fort Norman Line; and the Mackenzie Block, bordered north by the southwestern Franklinian Miogeocline. Many facies changes occur across these blocks and their bounding ancestral transfer or strike-slip fault zones, and these or associated faults are likely keys to independent tectonic histories, such as that demonstrated by the Peace River Arch. The most prominent and well known northeast-trending lineament is the Liard Line. Apparent on geological maps of Canada, or the Canadian Cordillera, is a northeastward swing of structural trends north of this feature. The Canadian Cordilleran Miogeocline to the north shows extensive preservation of lower Paleozoic (to Lower Devonian) strata northeastward to the Canadian Shield, whereas to the south the same rocks are generally preserved in only the Cordilleran deformed belt. Although Lower Paleozoic rocks in the south have been substantially cut by younger erosional events, facies and thickness patterns, in fringing Lower Paleozoic strata, indicate that the pattern of erosion and nondeposition is as much due to Lower Paleozoic tectonics and paleogeography as it is due to younger exposure or erosion. This profound change, and the connection to the Franklinian, divides the Canadian Cordilleran Miogeocline into three fundamental parts. The Liard Line is interpreted to have been an ancient transfer fault zone across which there was a reversal in the direction of asymmetry within the master separation fault system that formed the ancestral continental margin in Late Proterozoic time. The wide area north of the Liard line has a large outer miogeoclinal basin (Selwyn Basin), discrete rift systems (Misty Creek Embayment, Mackenzie Trough, Root Basin), a peculiar zone of high crustal attenuation and sediment accumulation (Liard Depression). In addition, it is complicated by several different arches or highs (Mackenzie, Redstone, McConnell, Keele, Bulmer Lake, Niddery, etc.). This northern half of the Canadian Cordilleran Miogeocline has the characteristics of a lower plate margin and is here defined as the Northern Cordilleran Lower Plate Zone, comprising the Blackwater and Mackenzie blocks. The Canadian Cordilleran Miogeocline south of the Liard Line is narrowly preserved in the Cordillera and consists of the White River, Robson and Kechika troughs, and their marginal Macdonald and Bow platforms. The eastern miogeocline is dominated by Lower Paleozoic paleotopographic highs (Montania, West Alberta Ridge, Peace River Arch and Macdonald High). This southern zone has the characteristics of an upper plate margin and is here defined as the Southern Cordilleran Upper Plate Zone, comprising the Montana, Alberta and Macdonald blocks. A previous upper-lower plate model of the Canadian Cordilleran Miogeocline is reviewed and its criteria of width, structural complexity and uplift-subsidence are found to be useful as plate-type indicators. However, the use of gneisses to indicate lower crust, transitional gradients base on isopleths, and Cambrian zero edges are found to be equivocal. The Canadian Cordilleran Miogeocline non passive character is compared to that of Mesozoic-Tertiary continental margins, which are also fundamentally non passive, suggesting that models for plate tectonic drifting phases need to be revised.

Abstract: Subsurface to Surface: Use of Outcrop Gamma-ray Logs to Interpret Structurally Complex Exposures of Appalachian Devonian Strata 

Abstract: Subsurface to Surface: Use of Outcrop Gamma-ray Logs to Interpret Structurally Complex Exposures of Appalachian Devonian Strata 

The Devonian System in Iran: a review

AbstractUpper Devonian strata are distributed widely throughout Iran. A review of all available literature on the Devonian, together with information from recent studies in the Kerman region, provides a basis for correlation and description of facies successions for the whole country. In most sections the local base of the Upper Devonian sits disconformably on older rocks, whilst the upper contact with the Carboniferous is almost everywhere transitional. There is everywhere an apparent hiatus spanning a probable early and mid Devonian interval. Lower and Middle Devonian fossils have not yet been discovered, but for the Upper Devonian there are abundant fossil data indicating the widespread occurrence of Frasnian and Famennian shallow marine deposits. A palaeogeographical map for the Upper Devonian of Iran is constructed.