Lower Middle Devonian Research Articles

Paleomagnetic Study of Devonian and Carboniferous Rocks of the Southern Urals: An Independent Test of Collision between the Magnitogorsk Island Arc and the Passive Margin of the Continent of Laurussia

New paleomagnetic data on Devonian and Lower Carboniferous rocks of the Magnitogorsk Zone (Southern Urals) are presented. The paleomagnetic pole calculated for the Lower–Middle Devonian is quite close to the coeval pole of the Baltica Paleocontinent (Laurussia), which indicates that the Magnitogorsk island arc was probably located close to the continent, but not being accreted with it. Paleomagnetic data obtained for Lower Carboniferous rocks may indicate that the Magnitogorsk island arc was turned in the Early Carboniferous and collided with the continent of Laurussia forming a single continent.

Paleozoic gas potential in the Weald Basin of southern England

Abstract Gas has been found in Mesozoic reservoirs in the Weald Basin, particularly along the northern margin. Most of the gas is dry, with a high methane content and often associated nitrogen. Isotopic evidence indicates that the gas is from a thermogenically mature marine source. Although there is evidence of some shallow, biogenic gas, only the lowermost Lias is projected to have reached the thermogenic gas window before Tertiary uplift. Estimated maturities from isotopic data from the main gas accumulations indicate significantly greater levels than those projected for Liassic shales: thus, the gas is thought to have originated from Paleozoic rocks. Data on the distribution of Paleozoic rocks subcropping the Variscan unconformity is limited. However, available data suggest that their distribution owes more to Acadian erosion than to Variscan. It is thought that the Upper Devonian and Lower Carboniferous transgressed over a thick, folded Tremadocian shale sequence in the west, and over folded Silurian and Lower–Middle Devonian rocks in the central Weald. There is some evidence for the presence of isolated late Carboniferous or early Permian clastics but no significant coals have been encountered to date. Regional source studies suggest that the only Paleozoic rocks with potential are post-Acadian-aged Devonian shales.

TECTONOSTRATIGRAPHIC ANALYSIS OF THE UPPER CAMBRIAN – DEVONIAN SEDIMENTARY SUCCESSION IN THE CENTRAL DARLING BASIN, SE AUSTRALIA: AN INTEGRATED INTERPRETATION OF SEISMIC, GRAVITY AND WELL DATA

This paper presents a tectonostratigraphic interpretation based on seismic, gravity and well data of the Upper Cambrian through Devonian sedimentary succession in the central part of the Darling Basin, New South Wales (SE Australia). A composite roughly north‐south trending 2D seismic section through this area, tied to two exploration wells, defines four unconformity‐bound second‐order seismic megasequences. The megasequences are: A, Upper Cambrian – Middle Ordovician (Llanvirnian?); B, uppermost Silurian – Lower Devonian (Emsian); C, upper Lower Devonian – lower Middle Devonian (Givetian); and D, upper Middle Devonian – Upper Devonian (Famennian). The megasequences are bounded by prominent seismic marker horizons which represent phases of regional‐scale orogenic activity.The composite 2D section studied is about 150 km long and traverses from north to south the Pondie Range sub‐basin, the inverted Wilcannia High and the Blantyre sub‐basin. Along the section, the Upper Cambrian to Devonian succession is deformed into a series of large‐scale, fault‐associated anticlines and synclines including the Avon High, an asymmetric anticlinal fold associated with several high‐angle reverse faults. Major faults extend into, and flatten within, the basement. The top‐basement surface is characterized by broad highs and lows which are represented on a gravity map of the study area. The map shows that the Wilcannia High defines the northern margin of the Blantyre sub‐basin and the southern margin of the Pondie Range sub‐basin. These sub‐basins are in general defined by gravity lows.The development of the Blantyre and Pondie Range sub‐basins can be divided into five tectonostratigraphic phases during which there were distinct patterns of fault activity and regional subsidence. These phases are investigated using a restoration model which involves the successive removal of each seismic megasequence in turn, assuming simple vertical shear. The model provides new constraints on the distribution of structural and stratigraphic features which are relevant for future hydrocarbon exploration.

Fenestrate Bryozoa of the Moniello Formation (Lower-Middle Devonian, NW Spain)

Fenestrate Bryozoa of the Moniello Formation (Lower-Middle Devonian, NW Spain)

Earth\u2019s oldest \u2018Bobbit worm\u2019 \u2013 gigantism in a Devonian eunicidan polychaete

Whilst the fossil record of polychaete worms extends to the early Cambrian, much data on this group derive from microfossils known as scolecodonts. These are sclerotized jaw elements, which generally range from 0.1–2 mm in size, and which, in contrast to the soft-body anatomy, have good preservation potential and a continuous fossil record. Here we describe a new eunicidan polychaete, Websteroprion armstrongi gen. et sp. nov., based primarily on monospecific bedding plane assemblages from the Lower-Middle Devonian Kwataboahegan Formation of Ontario, Canada. The specimens are preserved mainly as three-dimensional moulds in the calcareous host rock, with only parts of the original sclerotized jaw walls occasionally present. This new taxon has a unique morphology and is characterized by an unexpected combination of features seen in several different Palaeozoic polychaete families. Websteroprion armstrongi was a raptorial feeder and possessed the largest jaws recorded in polychaetes from the fossil record, with maxillae reaching over one centimetre in length. Total body length of the species is estimated to have reached over one metre, which is comparable to that of extant ‘giant eunicid’ species colloquially referred to as ‘Bobbit worms’. This demonstrates that polychaete gigantism was already a phenomenon in the Palaeozoic, some 400 million years ago.

Lower–Middle Devonian rocks at junction of the Volga–Ural anteclise, Ural foredeep, and North Caspian basin: Lithology and perspectives of petroleum potential

New data on the stratigraphy and lithology of the Lower–Middle Devonian rocks at junction of the Volga–Ural anteclise, Ural foredeep, and North Caspian basin are reported. Facies maps are also presented for the Takatinian, Koiva–Vyazov, Eifelian, and Givetian stages of the region evolution. The paleogeographic evolution and structural zonation of the basin in the Early–Middle Devonian are discussed. The evolution of carbonate buildups (Akbulak and Saraktash) in connection with their possible petroleum potential is examined.

Seismic stratigraphic interpretation of megasequence and sequence framework in the Upper Cambrian through Devonian formations in the central part of the Darling Basin, western New South Wales, Australia

Upper Cambrian through Devonian formations in the central part of the Darling Basin, western New South Wales were investigated using seismic data, complemented by well and outcrop information. Detailed seismic stratigraphic interpretation of four main second-order seismic megasequence buildups in the central-northern Blantyre and southern Pondie Range sub-basins, shows that they are constructed of seventeen principal third-order seismic sequences. The four seismic megasequences are characterized as follows: Seismic megasequence A corresponds to the Upper Cambrian through Middle Ordovician strata and is equivalent to the Scropes Range Formation or Mutawintji Group, Seismic megasequence B corresponds to uppermost Silurian through Lower Devonian strata and is equivalent to the Winduck Interval, Seismic megasequence C corresponds to upper Lower Devonian through lower Middle Devonian strata and is equivalent to the Snake Cave Interval and Seismic megasequence D corresponds to upper Middle Devonian through Upper Devonian strata and is equivalent to the Ravendale Interval. Five regional seismic-stratigraphic boundaries have been identified in the three seismic sections to show the continuity of the Upper Cambrian through Devonian formations throughout the central-northern Blantyre and southern Pondie Range sub-basins. All seismic-stratigraphic boundaries are based on good continuous markers, with strong amplitudes throughout the whole sub-basins.Detailed sedimentological analysis was applied using lithologic samples, wireline-log and limited biostratigraphic information, to aid in the development of a paleodepositional environment for the Upper Cambrian through Devonian sequence which displays ten different sedimentary facies successions. Seismic facies analysis was also applied to some of the seismic lines, comparing well log observation with reflection configuration and other seismic characteristics for the Upper Cambrian through Devonian successions. The seismic facies patterns show continuous, semicontinuous and discontinuous reflections with moderate amplitude and high to moderate frequency. The sedimentary sequence from the well data can also be recognized in the seismic lines, with features such as subparallel to divergent high amplitude reflections, parallel to subparallel medium to low amplitude reflectors with high-amplitude and high-continuity reflections, sediment waves with hummocky clinoforms and sometimes high-angle clinoforms, indicating fluvial channels complex and shallow channel-fill complex. As a result, a sequence stratigraphic framework was constructed successfully, consisting of nine seismic sequences. Six of these contain three systems tracts (lowstand, transgressive to highstand) and two sequence surfaces (transgressive surface and marine flooding surface). Another seismic sequence is composed of two systems tracts, a transgressive systems tract and a highstand systems tract separated by a maximum flooding surface. The other two, within the Blantyre 1 well and the Pondie Range 1 well, consist of one stratal pattern that has a highstand systems tract capped by a seismic sequence boundary.

Timing of amalgamation of the Alxa Block and the North China Block: Constraints based on detrital zircon U–Pb ages and sedimentologic and structural evidence

Detrital zircon LA-ICP-MS U–Pb ages of the Paleozoic strata in the southeastern Alxa Block indicate that the primary provenance did not change between the Devonian and the Early Carboniferous. Except for a sample from the Cambrian strata, the Early Paleozoic North Qilian Orogenic Belt may have been a major source of Paleozoic sediments in the study area. The main source of Lower–Middle Devonian sediments was the Early Paleozoic North Qilian Orogenic Belt. The source of the Upper Devonian sediments was the Alxa Block, while the North China Block was a minor contributor. The deformation of the Cambrian and Devonian Systems in the southeastern Alxa Block indicates that a strong east–west compression event occurred in the study area before the Early Carboniferous. The paleocurrents of the Upper Devonian in the southeastern Alxa Block indicate that the source was located to the north and was not the North Qilian Orogenic Belt to the south. Moreover, the deposition of the Upper Devonian in the southeastern Alxa Block was a response to a strong deformation event that occurred along the eastern boundary of the Alxa Block during the Late Devonian and Early Carboniferous. The North China Block became the primary source during the Early Carboniferous, and the Alxa Block was a minor source. A regional stratigraphic comparison also indicates that similar depositional environments were present until the Carboniferous and Permian on the Alxa Block and North China Block. All of these data indicate that amalgamation of the Alxa Block and the North China Block occurred between the Late Devonian and the Early Carboniferous.

Studies on plant cuticles from the Lower–Middle Devonian of China

Numerous plant cuticles were collected from five sections in the Lower–Middle Devonian of Yunnan and Sichuan provinces, China. Based on these cuticles and published data, we recognize five types of stomata or stoma-like pores in Devonian plants, i.e., anomocytic, rosette and complex types of stomata, pores like in Nematothallus, and pores within thick cuticle. Anomocytic and/or rosette types of stomata are more common in some horneophytopsids, rhyniopsids, renalioids, zosterophyllopsids, lycopsids and a progymnosperm. Complex type found only in the Middle Devonian likely occurred in Orestovia and Schuguria. Pores like in Nematothallus and pores within thick cuticle are documented in both the Lower and Middle Devonian and are usually observed on dispersed cuticles which have relationship with non-vascular plants. The various plant species share only five types of stomata and stoma-like pores. It is difficult to understand the exact affinities of epidermises without other macrofossil information.

An investigation of the genus Mesacanthus (Chordata: Acanthodii) from the Orcadian Basin and Midland Valley areas of Northern and Central Scotland using traditional morphometrics.

Mesacanthus is a common and speciose genus of acanthodian fish from Lower Old Red Sandstone and Middle Old Red Sandstone assemblages (representing the Lower Devonian and Middle Devonian respectively) and is well represented in many palaeoichthyology collections in the UK. Based upon descriptions given during the 19th century, specimens of the genus Mesacanthus from the Orcadian Basin and Midland Valley areas of Northern and Central Scotland have historically been referred to a number of different species; of these, the most frequently discussed in the literature are M. mitchelli, M. peachi and M. pusillus. In order to test the validity of these three species, traditional morphometric analyses were carried out on over 100 specimens of Mesacanthus, from both the Lower Devonian and the Middle Devonian, that cover the full range of known localities for these taxa in Northern and Central Scotland. Based upon morphological and morphometric comparisons, this investigation has found that at least two species of Mesacanthus are valid (M. mitchelli and M. pusillus) as specimens from the Lower Devonian and Middle Devonian have been shown to differ significantly in a number of important ways. However, no evidence has been found for the validity of the second and distinct Middle Devonian species, M. peachi.

Lower Middle Devonian, Eifelian, crinoids from central Guangxi, South China

The extensive Devonian marine deposits of South China have yielded few articulated crinoid cups or theca. Two Eifelian specimens, from the Gupa Member, are the first ones reported from the Yingtang Formation, Eifelian, from the Ma’anshan section, Guangxi, South China. The new taxon Guangxicrinus xiangzhouensis n. gen. n. sp. is the first report of a marsupiocrinid in China, extending the paleogeographic range of the family into the Paleotethys and the stratigraphic range of the family upward from the upper Silurian into the lower Middle Devonian, Eifelian. The occurrence of Halocrinites sp. is the third occurrence of a cupressocrinitid in China and extends the paleogeographic range from Yunnan to Guangxi.

A cold supergene zinc deposit in Alaska: The Reef Ridge case

The Reef Ridge deposit is a typical supergene “nonsulfide” zinc mineralization, located in the Yukon-Koyukuk region of west-central Alaska (USA). It is hosted in sedimentary rocks of the Farewell terrane, a continental fragment sandwiched between the Siberian and Laurentian cratons during the early Paleozoic. The mineralization occurs in Lower–Middle Devonian shallow-water dolomite of a Paleozoic carbonate platform succession belonging to the Nixon Fork tectonic unit. The mineralization consists of oxidized minerals associated with minor remaining sulfides (pyrite/marcasite and sphalerite). In the oxidation zone, smithsonite is the predominant mineral, mixed with Fe-(hydr)oxides (goethite and hematite). A complete petrographic and mineralogical study was performed. Samples were analyzed by X-ray diffraction, inductively coupled plasma–mass spectrometry and emission spectrometry, energy dispersive scanning electron microscopy, and QEMSCAN ® (quantitative evaluation of minerals by scanning electron microscopy). The most abundant mineral in the nonsulfide ore is smithsonite. Similar to other nonsulfide Zn deposits worldwide, the first generation of smithsonite has replaced both primary sphalerite and the host carbonates. A second smithsonite generation precipitated as cement in vugs, cavities, and fractures. Minor zinc amounts also occur in the Fe-(hydr)oxides, and zinc traces have been identified in clay minerals. The carbon and oxygen isotope values of smithsonite at Reef Ridge vary from −0.7 to 2.1‰ relative to Vienna Peedee belemnite (VPDB) and 19.1‰ to 21.9‰ relative to Vienna standard mean ocean water (VSMOW). The δ 13 C values are similar to those of the host rock, suggesting that the predominant carbon source for smithsonite was the host carbonates, with only a limited contribution from organic carbon. The oxygen isotope ratios of Reef Ridge smithsonite are more depleted in 18 O compared to supergene nonsulfides from other parts of the world formed under warm-humid, temperate, or semiarid climates. The oxygen isotope fractionation between water and smithsonite, which relates the δ 18 O value of the mineralizing solution, the formation temperature of smithsonite, and its δ 18 O composition, indicates that the δ 18 O composition of Reef Ridge smithsonite is related to very low formation temperatures (~10 °C), and strong depletion in 18 O of the precipitating waters. The δ 18 O smithsonite composition, the strong 18 O depletion, and the relationship of the formation of the Reef Ridge nonsulfide deposit with the development of the Sleetmute upland surface (which started in the Late Tertiary and continues to the present) indicate that the formation of the Reef Ridge nonsulfide deposit is probably related to cold/humid weathering episodes during a period comprised between Late Tertiary and Holocene. The “traditional” interpretation on the genesis of Zn nonsulfide deposits in warm-humid, temperate, or semiarid conditions should be questioned where other climate zones are indicated.

Sequence stratigraphic analysis of fluvial deposits using facies characterization and wireline log correlation: case of the late Early-early Middle Devonian Snake Cave Interval, Darling Basin, Australia

In this article, we present the application of wireline log correlation for sequence stratigraphic analysis to the late Early to early Middle Devonian Snake Cave Interval in the Neckarboo Sub-basin (DM Kewell East DDH-1 well) and Hillston Trough (DM Mossgiel DDH-1 well), Darling Basin. The results of an integrated study using characterising wireline log signatures (gamma ray, sonic, resistivity shallow, long spaced neutron and limest neutron porosity) and core description data supplemented by limited palaeontological reports indicate that three major upper Lower to lower Middle Devonian cycles have controlled sedimentation of this stratigraphic succession. We distinguished seven core sedimentary facies, which were grouped into six electrofacies defined by wireline log signatures. The electrofacies were defined by describing and analysing the graphic gamma ray logs using basic geometrical shapes, such as bell, serrated bell, funnel, serrated funnel, cylinder (block) and linear. Six electrofacies informally named electrofacies SA, SB, SC, SD, SE and SF correspond to seven core facies (MS1-MS7), which have progressively greater sandstone/shale ratios and better electrofacies quality. These electrofacies are characterised as follows: electrofacies SA corresponds to the conglomeratic braided channel-fill, electrofacies SB corresponds to channel lag and point bar, electrofacies SC corresponds to crevasse splay sandstones and flood-plain fines, electrofacies SD corresponds to multistorey fluvial channel-fills, electrofacies SE corresponds to sandy braided channel-fills and electrofacies SF corresponds to distributary channel sands and local small delta-plain. The upper Lower to lower Middle Devonian sequence (Snake Cave Interval) of the Neckarboo Sub-basin and Hillston Trough is characterised by two major third-order sequences (Snake Cave sequence 1 and Snake Cave sequence 2) that consist of ten systems tracts and ten sequence surfaces. Snake Cave sequence 1 (SCS1) consists of two cycles with progradational to retrogradational trends (LST1 to TST1 and LST2 to TST2 separated by a marine flooding surface) divided into five sequence surfaces (SBSC1, TS1 MFS1, TS2 and MFS2, in ascending order) as defined by wireline log signatures. One cycle has progradational, retrogradational to aggradational trends (LST3, TST3 to HST1) and has seven sequence surfaces (e.g. MFS2, LST3, TS3, MFS3 and SBSC2, in ascending order). Snake Cave sequence 2 (SCS2) consists of one unit with progradational, retrogradational to aggradational trends (LST4, TST4 and HST2, in ascending order) with three sequence surfaces (e.g. SBSC2, TS4 and MFS4). No TST4 and HST packages were observed, and the MFS4 is poorly developed. The recognition of sedimentological sequence stratigraphic changes above and below marine flooding surfaces (MFS1-4), where deposition sequences have been defined without adequate biostratigraphic control, is easy since depositional sequence and bounding surface correlation can always be clearly demonstrated. A sequence stratigraphic architecture that can be used to accentuate and strengthen Darling basin exploration also documents significant changes in the local and regional tectonostratigraphic setting.

New data on Devonian Rhabdomesida (Bryozoans) from the Salair Ridge and Gorny and Rudny Altai

Members of the order Rhabdomesida (Bryozoa) are for the first time recorded in the Emsian Stage (Lower Devonian) and Eifelian Stage (Middle Devonian) of the Altai-Sayan Folded Area. The assemblage of Emsian Rhabdomesida of the Salair Ridge and Gorny Altai comprises three new species of the genera previously only known from the Lower-Middle Devonian deposits of Western Europe and West Africa: Paracuneatopora egregia sp. nov., P. kuvaschensis sp. nov., and Lenapora gurievensis sp. nov. In addition, this assemblage includes Nematopora rara sp. nov. and new species of a new genus, Salairella gen. nov.—S. petaloida sp. nov., S. variabilis sp. nov., and S. maculata sp. nov. Two new species, Salairella baskuskanensis sp. nov. and S. recta sp. nov., are described from the Eifelian Stage of the Salair Ridge and the Frasnian Stage of Rudny Altai, respectively.

Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey

Thin beds of tephra (K-bentonites) formed by the diagenesis of volcanic ash are exposed within the limestone-dolomitic limestone successions of the Yilanli formation at Zonguldak and Bartin in northwestern Turkey. They were deposited on the Middle Devonian-Lower Carboniferous shallow carbonate platform of the Zonguldak terrane. In this study, K-bentonite samples collected from Gavurpinari and Yilanli Burnu limestone quarries are investigated in order to reveal their mineralogical and geochemical characteristics and diagenetic evolution. Illite is the major clay mineral in the studied K-bentonites. Additionally, kaolinite and mixed-layer illite-smectite are identified in some samples. The nonclay minerals calcite, dolomite, quartz, gypsum, feldspar, pyrite, and zircon are also found. Crystal-chemical characteristics (Kubler index, d060 values, and polytypes of illites) from two different sampling locations do not show significant variations. Kubler index values for the Yilanli Burnu and Gavurpinari sampling locations, 0.47-0.93 (average: 0.71 $\Delta$°2$\theta$) and 0.69-0.77 (average: 0.72 $\Delta$°2$\theta$), respectively, indicate that illites were affected by high-grade diagenetic conditions. The swelling (or smectite) component (~5%), crystallite size (N = 10-20 nm), and polytype (2M1 > 1Md) data of illites support the same conditions. Illite d060 values of 1.491-1.503 A correspond to a range of octahedral Mg+Fe values of 0.27-0.51 atoms per formula, indicating a composition between end-member muscovite and phengite unit. Trace and rare earth element-based chemical classification of the K-bentonite samples revealed that composition of original volcanic ash is basaltic. Illitization took place by fixation of K from volcanic minerals and ash, and diffusion of elements (Mg+Fe) into and out of the beds during diagenesis. Mineralogical-chemical data point out that these K-bentonites evolved in high-grade diagenetic conditions (approximately 100-150 °C) from the products of volcanic eruptions of disputed sources and distances during the Late Devonian time.

Lower–Middle Devonian Fenestellidae (Bryozoa) of NW Spain: implications for fenestrate palaeobiogeography

The Emsian–Eifelian succession of NW Spain contains an abundant and diverse bryozoan fauna, fenestrates being the most outstanding group. The Fenestellidae of the Moniello Formation (upper Emsian–lower Eifelian, Asturias, NW Spain) comprise 13 species, four of which are new: Rectifenestella covae n. sp., Cavernella asturica n. sp., Hemitrypa adversa n. sp., and Hemitrypa terentei n. sp. The other species composing the assemblage studied are: Fenestella aff. parallela Hall, 1881, F. vera Ulrich, 1890, Rectifenestella pioneri (Krasnopeeva, 1935), Spinofenestella aff. antiqua (Goldfuss, 1826), S. estrellita (McKinney and Křiž, 1986), S. strigilla (McKinney and Křiž, 1986), Laxifenestella capillosa (Pocta, 1894), Hemitrypa aff. tubulosa (Nekhoroshev, 1948), and Ptylopora aff. nodosa Hall, 1883. Taking into account species reported in previous studies, the assemblage of Fenestellidae of the Emsian–Eifelian of NW Spain is composed of nine genera and 21 species. This fauna shows affinities with that of the Lower Devonian of Bohemia and also to those of the Middle Devonian of North America, Russia, and Asia. C. asturica n. sp. is the earliest and westernmost reported species of the genus, which was previously known to occur in the Carboniferous and Permian rocks from Hungary to Tibet. H. adversa n. sp. is the only known species of Hemitrypa with autozooecial apertures placed on the inner surface of the cone; some of the specimens of H. adversa n. sp. collected in the Moniello Formation developed unusually flat colonies.

Detrital zircon ages of Cambrian and Devonian sandstones from Estonia, central Baltica: a possible link to Avalonia during the Late Neoproterozoic

Detrital zircon U–Pb ages of Lower Cambrian and Middle Devonian have been determined for sandstone in Estonia through LA-ICP-MS (Nu instruments, Wrexham, UK). Both sandstones have a similar zircon age spectrum with distinct age clusters that reflect the basement geology of Baltica, i.e. 2800–2700 Ma (Kola–Karelia), 1900–1700 Ma (Svecofennian), 1600–1500 Ma (Rapakivi) and 1200–1000 Ma (Sveconorwegian). Noteworthy is a cluster at 750–550 Ma, because rocks of such age are absent within the core of Baltica. The present results suggest a possible link between Baltica and Avalonia/Cadomia during the Late Neoproterozoic.

Taxonomic revision and phylogenetic affinities of the conodont Bipennatus montensis (Weddige 1977) from the Eifelian (Middle Devonian) of Poland

Conodont investigations of the tetrapod-bearing lower Middle Devonian strata in the Holy Cross Mountains (SE Poland) furnished new data on morphological variability and phylogenetic affinities of the early bipennatid form, B. montensis (Weddige 1977), the latter raised herein to species level. B. montensis, and the genus Bipennatus in general, probably developed near the Emsian-Eifelian boundary from ozarkodinids showing an incipient median trough on the upper surface of the blade. In turn, Bipennatus montensis gave rise to B. bipennatus by a gradual development of nodose ridges on both sides of the trough.

A prodeltaic system controlled by hyperpycnal flows and storm waves: reinterpretation of the Punta Negra Formation (Lower-Middle Devonian, Argentine Precordillera)

The Punta Negra Formation (FPN) constitutes a Lower-Middle Devonian sandstone unit located in the Argentine Precordillera. Based on detailed facies and ichnological analyses, this unit, which had been previously interpreted as a deep-water system, has been reinterpreted in this study as a prodelta system, in which the distribution and sedimentation of the clastic deposits were controlled by hyperpycnal flows associated with storms. Five lithofacies attest the deposition by unidirectional hyperpycnal flows combined with storm-generated oscillatory flows. Fossil traces testify variable energetic conditions of the depositional system with the colonization of opportunistic organisms immediately after the deposition of high energy combined flows and the colonization of more specialized organisms during the long low-energy periods. Three architectural elements, deposited from coastline to offshore, have been recognized: 1) Channelized sandstone, composed of the thickest and coarsest sandstone beds and interpreted as the proximal portion deposited close to the mouth of the distributaries of the delta system; 2) Tabular sandstone, which are composed of combined and oscillatory flow deposits with lesser thickness, grain size and spacing of the undulated bed forms; 3) Tabular sandstone interbedded to mudstone, which represents the most distal architectural element and is composed of thin sandstone and thicker mudstone strata, deposited by low-energy combined flows.

Comparison of Tidalites in Siliciclastic, Carbonate, and Mixed Siliciclastic-Carbonate Systems: Examples from Cambrian and Devonian Deposits of East-Central Iran

For the comparison of lithofacies in siliciclastic, carbonate, and mixed siliciclastic-carbonate tidal systems, three successions including Top Quartzite (Lower-Middle Cambrian), Deranjal Formation (Upper Cambrian), and Padeha Formation (Lower-Middle Devonian) in the north of Kerman and Tabas regions (SE and E central Iran) were selected and described, respectively. Lithofacies analysis led to identification of 14 lithofacies (Gcm, Gms, Gt, Sp, St, Sh, Sl, Sr, Sm, Se, Sr(Fl), Sr/Fl, Fl(Sr), and Fl) and 4 architectural elements (CH, LA, SB, and FF) in the Top Quartzite, 7 lithofacies (Dim, Dp, Dr, Ds, Dl, Dr/Dl, and Fcl) and 2 architectural elements (CH, CB) in the Deranjal Formation, and 17 lithofacies (Sp, St, Sh, Sl, Sr, Se, Sr(Fl), Sr/Fl, Fl(Sr), Fl, Dr, Ds, Sr/Dl, El, Efm, Efl, and Edl) and 5 architectural elements (CH, LA, SB, FF, and EF) in the Padeha Formation that have been deposited under the influence of tides. The most diagnostic features for comparison of the three tidalite systems are sedimentary structures, textures, and fabrics as well as architectural elements (lithofacies association). The CH element in siliciclastics has the highest vertical thickness and the least lateral extension, while in the carbonate tidalites, it has the least vertical thickness and the most lateral extension compared to in other systems.