Turonian Research Articles

Cretaceous biostratigraphy and lithostratigraphy of the Glinzendorf Syncline based on well Gänserndorf UeT3 (Vienna Basin, Austria)

Abstract The 2200 m thick Cretaceous units of well Gänserndorf UeT3 have been biostratigraphically analyzed based on cuttings from 3210 m to 5140 m. The deposits from the Tirolic Glinzendorf Syncline (a part of the buried Northern Calcareous Alps) can be largely correlated with the Lower Gosau Subgroup of the Grünbach Syncline. An exception is the basal unit, which has no equivalent in the Grünbach Syncline. This lower unit is subdivided into a non-marine lower and a largely marine upper part. No age constraints are available for the lower part, whereas the upper part has a possible age range from middle Turonian to Coniacian. For this unit, which is documented for the first time from the Glinzendorf Syncline, we propose Glinzendorf Formation as new lithostratigraphic term. The Glinzendorf Fm. is overlain by the Grünbach Fm., which is intercalated by a thick unit of conglomerates. These are interpreted as equivalents of the Dreistetten Conglomerate Mb. The calcareous nannofossils of these units suggest a latest Santonian to early Campanian age. Non-marine conditions prevailed during deposition of the Grünbach Fm., but marine incursions are indicated for parts of the Dreistetten Conglomerate Mb. The top of the Grünbach Fm. is formed by an about 50-m-thick unit of coal, rich in Characeae oogonia, which, together with the Dreistetten conglomerates serve as marker layer for correlation with the outcrops in the Grünbach Syncline. The Grünbach Fm. is overlain by marls and silty shales of the Piesting Fm. for which a late Campanian and Maastrichtian age is documented. Marine conditions predominated during this interval. The topmost unit in well Gänserndorf UeT3 is overthrusted on the Maastrichtian Piesting Fm. and represents Campanian sandstones and conglomerates of the Grünbach Fm. This Gänserndorf Thrust is detected and biostratigraphically constrained for the first time.

Paleoenvironment of the Late Cretaceous (Late Touronian–Early Campanian) Ostarcoda in the Kometan Formation, Dokan Area, Kurdistan region, NE-Iraq

In the present study, selected the Kometan Formation (Late Turonian - Early Campanian) from the Dokan area, NE-Iraq. In this formation studied Ostracoda and identified fifteen open Ostracoda species belonging to ten genera (Bairdia, Bairdiacypris, Bythocypris, Bairdoppilata, Cavellina, Cypridina, Cytherella, Haplocytheridea, Pterygocythereis, and Paracypris). The goal of the present study is to identify Ostracoda species under polarizing microscopes for the first time in the Kometan Formation in the Dokan area. The Ostracoda assemblage such as Bairdia, Bairdiacypris, Cytherella, Cypridina, and Paracypris with foraminifera species Globotruncana linneiana, Globotruncanita stuartiformis, Marginotruncana schneeansi, and Dicarinella asymetrica indicate the Kometan Formation deposited in the deep marine environment.

A fish-parasitic isopod (Cymothoidae) on the pachyrhizodont Goulmimichthys roberti from the lower Turonian (Upper Cretaceous) Vallecillo plattenkalk, NE Mexico

The platy limestone (plattenkalk) deposit of Vallecillo in northeastern Mexico is widely known for its well preserved and diverse fish and marine reptilian assemblage dated to the early–middle Turonian (Late Cretaceous). A single specimen of the pachyrhizodont G. roberti revealed the first Cretaceous isopod (Crustacea, Arthropoda) attached to a fish host. Preservation allows for the interpretation of the entire body and most appendages. A parasitic lifestyle of the isopod is inferred based on the specimen's morphology including claw-like dactyli, but is also inferred based on the anoxic bottom conditions variously interpreted for the Vallecillo plattenkalk deposit, which excluded scavengers. The individual is here referred to the family Cymothoidae and described as Mothocya vallecillae n. sp.

On the Composition and Age of Taphofloras of the Krivorechenskaya Formation (Upper Cretaceous) of the Anadyr River Left Bank, Northeast Asia

Chineiveem taphoflora from the Krivorechenskaya Formation of the Anadyr River left bank (Northeast Asia) is characterized by a relatively low diversity of plants represented by ginkgoaleans, conifers, and angiosperms. Judging by their systematic composition, this taphoflora is younger than the Grebenka flora from the Krivorechenskaya Formation of the Anadyr River basin. Its closest analog is the Penzhina flora of Northwestern Kamchatka and the Yelistratov Peninsula, the age of which is reliably defined as Turonian, excluding the beginning of the Turonian. Therefore, the age of the Chineiveem floristic assemblage is also Turonian, most probably late Turonian. Such dating of this taphoflora is in agreement with the late Turonian or Coniacian age of marine mollusks from the overlying Dugovskaya Formation layers of the Chineiveem River and with a conformable stratigraphic contact of these layers with the plant-bearing beds. A tectonic contact between these deposits is not supported by our paleobotanical data. The observed succession of taphofloras from the Krivorechenskaya Formation in the Ubiyenka–Chineiveem interfluve suggests that the upper age limit of the Grebenka flora is the beginning of the Turonian.

Stratigraphic distribution of the Codell Sandstone in the Denver Basin using wireline logs and core

Core data from five key wells spanning the Denver Basin were tied to wireline log data and used to interpret the distribution of the Middle Turonian Codell Sandstone Member of the Carlile Formation across the Denver Basin. The character of the Codell’s upper contact is sharp with a localized top-down truncation across the basin, which is consistent with an associated unconformity surface. In contrast, the Codell’s lower contact varies from being gradational in most of the southern Denver Basin to being unconformable in the northern basin. Log correlations reveal that the Codell is absent within an elongate northeast-trending swath up to 125 miles wide in northeastern Colorado. This elongate gap is herein referred to as the ‘No Codell Zone’ abbreviated as NoCoZo. Hypotheses to explain the absence of the Codell Sandstone in the NoCoZo include a lateral facies change from sandstone to shale, non-deposition of Codell-equivalent sediments across this area, post-depositional erosion, or a combination of these processes. Correlation of wireline logs across the northern and southern limits of the NoCoZo, combined with outcrop and core observations, suggest top-down erosion of the Codell increasing into the NoCoZo. However, the overlying Fort Hays Limestone is laterally continuous and has a relatively consistent thickness across the NoCoZo, suggesting two tenable hypotheses: 1) The NoCoZo represents an area of post-Codell erosion due to short-lived growth of a broad, low relief uplift that was no longer active during Fort Hays deposition; or 2) A stepped sea level fall and forced regression resulting in non-deposition of the Codell over this broad swath. North of the NoCoZo, the Codell thickens northward to more than 40 ft into adjacent parts of Wyoming and Nebraska. In this northern area, the Codell has two main lithofacies in three laterally correlative zones, in ascending order: a lower bioturbated siltstone to very fine-grained sandstone ranging from 2 to 20 feet thick, a middle 2 to 10-foot thick laminated to bedded siltstone to fine-grained sandstone, and an upper 5 to 20-foot thick bioturbated siltstone to very fine-grained sandstone. Southeast of the NoCoZo the Codell thickens to as much as 80 feet in an east-trending belt from Pueblo, Colorado, into west central Kansas. The southern Codell can be divided into two coarsening upward parasequences, from a basal muddy coarse siltstones to very fine-grained sandstones. The siltstones and sandstones in the southern Codell are mostly bioturbated with locally developed bedded facies at the top.

The type section of the Codell Sandstone

We formally assign, describe and interpret a principal reference section for the middle Turonian Codell Sandstone Member of the Carlile Shale near Codell, Kansas. This section, at the informally named Pumpjack Road, provides the thickest surface expression (9 m, ~30 ft) of the unit in Ellis County. The outcrop exposes features that typify the Codell throughout the southern Denver Basin and vicinity. At this reference section, the Codell conformably overlies the Blue Hill Shale Member of the Carlile Shale and is unconformably overlain by the Fort Hays Limestone Member of the Niobrara Formation or locally by a thin (<0.9 m, <3 ft) discontinuous mudstone known as the Antonino facies. The top contact of the Codell is slightly undulatory with possible compaction features or narrow (<30.5 m, <100 ft), low-relief (0.3-0.6 m, 1-2 ft) scours, all of which hint that the Codell is a depositional remnant, even at the type section. At Pumpjack Road, the Codell coarsens upward from a recessive-weathering argillaceous medium-grained siltstone with interbedded mudstone at its base to a more indurated cliff-forming muddy, highly bioturbated, very fine-grained sandstone at its top. The unit contains three informal gradational packages: a lower Codell of medium to coarse siltstone and mudstone, a middle Codell of muddy coarse siltstone, and an upper muddy Codell dominated by well-sorted very fine-grained sandstone. The largest grain fractions, all <120 mm in size, are mostly quartz (40-80%), potassium feldspar (7-12%), and albite (1-2%), with some chert (<15%), zircon, and other constituents such as abraded phosphatic skeletal debris. Rare fossil fish teeth and bones also occur. Detrital and authigenic clays make up 9 to 42% of the Codell at the reference section. Detrital illite and mixed layer illite/smectite are common, along with omnipresent kaolinite as grain coatings or cement. As is typical for the Codell, the sandstone at the type section has been pervasively bioturbated. Most primary structures and bedding are obscured, particularly toward the top of the unit where burrows are larger, deeper and more diverse than at its base. This bioturbation has created a textural inversion in which the larger silt and sand grains are very well sorted but are mixed with mud. Detrital zircons from the upper Codell are unusual in that they are mostly prismatic to acicular, euhedral, colorless, unpitted, and unabraded, and have a near-unimodal age peak centered at ~94 Ma. These characteristics suggest they were reworked mainly from Cenomanian bentonites; their ultimate source was likely from the Cordilleran orogenic belt to the west and northwest.

Cibolaites petraschecki sp. nov., a new collignoniceratine ammonite from the Brießnitz Formation of Saxony (Turonian, Elbtal Group, Germany)

Cibolaites petraschecki sp. nov., a new collignoniceratine ammonite from the Brießnitz Formation of Saxony (Turonian, Elbtal Group, Germany)

Testing the persistence of Carcharodontosauridae (Theropoda) in the Upper Cretaceous of Patagonia based on dental evidence

The deposits corresponding to the Upper Cretaceous Neuquén and San Jorge Gulf basins from northern and central Patagonia have provided two of the most complete sequences of terrestrial vertebrate faunas of all Gondwanan landmasses. Among the carnivorous components, the carcharodontosaurid theropods appeared as common elements during the Early Cretaceous and the earliest Late Cretaceous in northern and central Patagonia. Although recorded mostly in the lower Turonian, isolated teeth suggest their presence in younger strata in northern and central Patagonia, reaching the clade in the region as late as the early Maastrichtian. Here, we verify the assignment of such isolated teeth previously identified as belonging to Carcharodontosauridae from the Upper Cretaceous strata of northern and central Patagonia. Using three different methods, namely a cladistic analysis performed on a dentition-based data matrix, and discriminant and cluster analyses conducted on a large dataset of theropod crown measurements, we assign a tooth from Candeleros Formation to carcharodontosaurid theropods and teeth from Cerro Lisandro, Bajo Barreal, Portezuelo, Plottier and Allen formations to abelisaurid theropods. These new reappraisals provide additional evidence about the extinction of Carcharodontosauridae in South America at about the late Turonian–earliest Coniacian as part of a general faunistic turnover event, with the last clear evidence of this lineage in Patagonia coming from the early–middle Turonian.

Chronology and Eccentricity Phasing for the Early Turonian Greenhouse (∼93–94 Ma): Constraints on Astronomical Control of the Carbon Cycle

AbstractThe Early Turonian interval represents a unique confluence of climatic and oceanographic conditions including peak surface temperatures, high greenhouse‐gas concentrations, and maximum Phanerozoic sea level. The susceptibility of this climate mode to astronomical insolation forcing remains poorly understood partly due to a limited time control and unknown phasing of astronomical cycles in this interval. Here, we offer a refined astrochronology of the Early Turonian based on laterally consistent precession signals preserved in offshore strata of the Bohemian Cretaceous Basin (central Europe). Pristine amplitude modulation verified through interference patterns in depth‐frequency plots provides a robust indication of ∼100 and 405‐kyr eccentricity phases (maxima and minima) that are pinned to ammonite biozones and new carbon‐isotope data from two cores. The Early Turonian is estimated as 885 ± 41 (2σ) thousand years (kyr) in duration, with the Cenomanian/Turonian boundary predating the first Turonian 405‐kyr maximum (no. 232 in the Geological Time Scale 2020) by 82 ± 70 (2σ) kyr. The results support a possible link of the recovery from Oceanic Anoxic Event II to increasing magnitude of seasonal insolation extremes due to rising eccentricity on 405‐kyr and million‐year (Myr) time scales. Superimposed upon this trend are small‐scale carbon‐isotope anomalies the pacing of which passes from ∼110 kyr, resembling short eccentricity, to ∼170 kyr, possibly related to obliquity modulation. This eccentricity‐to‐obliquity transition, paralleling the rising phase of Myr‐scale eccentricity, suggests decoupling of the carbon‐cycle perturbations from low‐latitude seasonal insolation. Mid‐latitude to high‐latitude carbon reservoirs became involved toward the Middle Turonian.

A New Assemblage of Plant Mesofossils (Late Turonian–Middle Santonian; Upper Cretaceous) from the Tamagawa Formation, Kuji Group, in Northeastern Japan

A preliminary description is provided of a new assemblage of small, three-dimensional and charcoalified mesofossils from the Tamagawa Formation (late Turonian–middle Santonian; Upper Cretaceous) of the Kuji Group in northeastern Japan. The new mesofossils yield excellent structural details and include well-preserved circinate shoots of ferns together with conifer leafy-shoots, seeds and probable pollen cones, and variety of angiosperm fruits and seeds, including fruits of Cornales and seeds of Nymphaeales. The new mesofossil assemblage is complementary to the previously published macrofossil flora from the Kuji Group.

Trace fossils and depositional environments of the middle Turonian sandstones in the Upper Nysa Kłodzka Graben (Sudetes, Poland) revisited

We provide the first reports of some rare trace fossils from the middle Turonian (Upper Cretaceous) of the Sudety Mountains (SW Poland, Upper Nysa Kłodzka Graben, Długopole Górne Quarry). These include burrows ? Ancorichnus isp., Asterosoma cf. ludwigae Schlirf, 2000, Asterosoma isp., cf. Phycodes isp., Dactyloidites ottoi (Geinitz, 1849), Funalichnus strangulatus (Fritsch, 1883), Phycodes cf. palmatus Hall, 1852, cf. Phycodes , Phycosiphon incertum Fischer-Ooster, 1858, ? Phycosiphon isp., Planolites beverleyensis (Billings, 1862) and borings Entobia isp. Some body fossils, bivalves ? Brachidontes sp., Lima canalifera Goldfuss, 1836, Pinna ( Pinna ) cretacea (Schlotheim, 1813) and Rhynchostreon suborbiculatum (Lamarck, 1801) are also reported. The trace fossil assemblage indicates a distal Skolithos ichnofacies and proximal Cruziana ichnofacies, which characterize a proximal and distal lower shoreface setting respectively. Sedimentation of the middle Turonian sandstones took place in a shallow epicontinental sea of normal salinity and a soft substrate, which was well-oxygenated under low-moderate hydrodynamic conditions. The presence of the oyster Rhynchostreon in the deposits studied suggests the influence of a warm Tethys Ocean.

Age constraint for the Moreno Hill Formation (Zuni Basin) by CA-TIMS and LA-ICP-MS detrital zircon geochronology.

The “mid-Cretaceous” (~125–80 Ma) was punctuated by major plate-tectonic upheavals resulting in widespread volcanism, mountain-building, eustatic sea-level changes, and climatic shifts that together had a profound impact on terrestrial biotic assemblages. Paleontological evidence suggests terrestrial ecosystems underwent a major restructuring during this interval, yet the pace and pattern are poorly constrained. Current impediments to piecing together the geologic and biological history of the “mid-Cretaceous” include a relative paucity of terrestrial outcrop stemming from this time interval, coupled with a historical understudy of fragmentary strata. In the Western Interior of North America, sedimentary strata of the Turonian–Santonian stages are emerging as key sources of data for refining the timing of ecosystem transformation during the transition from the late-Early to early-Late Cretaceous. In particular, the Moreno Hill Formation (Zuni Basin, New Mexico) is especially important for detailing the timing of the rise of iconic Late Cretaceous vertebrate faunas. This study presents the first systematic geochronological framework for key strata within the Moreno Hill Formation. Based on the double-dating of (U-Pb) detrital zircons, via CA-TIMS and LA-ICP-MS, we interpret two distinct depositional phases of the Moreno Hill Formation (initial deposition after 90.9 Ma (middle Turonian) and subsequent deposition after 88.6 Ma (early Coniacian)), younger than previously postulated based on correlations with marine biostratigraphy. Sediment and the co-occurring youthful subset of zircons are sourced from the southwestern Cordilleran Arc and Mogollon Highlands, which fed into the landward portion of the Gallup Delta (the Moreno Hill Formation) via northeasterly flowing channel complexes. This work greatly strengthens linkages to other early Late Cretaceous strata across the Western Interior.

Kurucaşile – Cide Dolayının Jeolojisi

Cide-Kurucaşile area on the İstanbul Zone is an important region for understanding the geological evolution of NW Anatolia and the Black Sea. The lowest visible unit of the region is the Carboniferous coal-bearing terrestrial sediments. Permian aged terrestrial Çakraz Formation and the overlying Triassic lacustrine Çakrazboz Formation unconformably overlie the Palaeozoic sequence. Dogger aged Himmetpaşa Formation represents a short-period marine invasion. The transgression that started in the Kimmerician on the Dogger and older units has led to the development of a carbonate platform, which has risen and demised after the Berriasian. A second carbonate platform, much more limited than the previous one, developed in the Late Barremian, and then the whole region deepened. The Cenomanian is a period of regional uplift and erosion. The first effective volcanic activity in the region started in the Middle Turonian. During this period, extensional faults coeval with the deposition of volcanic and volcanogenic clastics, and colluvial wedges developed in front of them, and the region gained an irregular topography. In the Middle-Late Santonian, the volcanism became silent for a while, the region rapidly subsided and became a completely deep marine environment. These events indicate that the continental crust of the region was totally broken up and the oceanic crust began to develop in the Western Black Sea back arc basin. In the Campanian, the volcanism reactivated much more intensely, but ceased after a short time, leaving its place to pelagic sediments forming the southern passive continental margin deposits of the Black Sea. In the Maastrichtian, the region was tectonically compressed and uplifted and provided turbiditic material to the Black Sea in the north and the Devrek Basin in the south. Siliciclastic turbidites have been deposited in the region until the Middle Eocene. At the end of the Middle Eocene, following uplifting of the entire region and the destruction of marine environments, the north-vergent thrusts were developed due to intense compression and the region became a fold-thrust belt. This compressional tectonic regime is probably still active.

Cenomanian–Turonian facies, sequence stratigraphy and sea–level changes from east–central Sinai (Egypt)

The widely exposed Cenomanian–Turonian successions in east–central Sinai display well–marked vertical and lateral changes in lithology, biofacies and depositional sequences. Three sections were studied (from northeast to southwest: Gebel Themed, Sheikh Attiya and Gebel Shiti, respectively) to document sequence stratigraphy. Twenty–four microfacies types grouped into nine lithofacies associations ranging from peritidal to mid– to outer ramp settings were identified. These microfacies reveal a general shallowing trend towards the southwest (Gebel Shiti section) in a mixed siliciclastic/carbonate ramp, whereas the northwest (Gebel Themed section) is marked by a deeper carbonate–dominated regime. The Cenomanian–Turonian succession is divided into six third–order depositional sequences (SD1 to SD6) that are bracketed by basin–wide sequence boundaries (SB AIB to SB Tu3) of varied time span and marked by vertical changes in lithofacies, microfacies and faunal content. Within these depositional sequences, six maximum flooding surfaces are also recorded. In most depositional sequences, the absence of lowstand and falling systems tract are marked, possibly as a result of the lack of accommodation space due to the proximal position of the studied sections. The identified sequence boundaries are also compared with those identified in Egypt, Jordan, Tunisia and the Arabian Plate. The present sequence boundaries match with those documented from the Arabian and African plates as also with the eustatic sea–level falls. However, for those noted across the Cenomanian/Turonian boundary and during the early–middle Turonian transition, there is discordance, possibly due to the influence of regional tectonics, that caused major hiatuses and amalgamated several of them. The chronostratigraphic assignment followed in the present study is based on ammonites, enabling the recognition of five zones, upper Cenomanian Neolobites vibrayeanus and Vascoceras cauvini, lower Turonian Choffaticeras (Choffaticeras) segne and Wrightoceras munier and the middle–upper Turonian Coilopoceras requienianum Zone.

Late Cretaceous palaeogeography of NE Bohemian Massif: diachronous sedimentary successions in the Wleń Graben and Krzeszów Brachysyncline (SW Poland)

This paper provides a new sedimentological and palaeogeographic interpretation of the Late Cretaceous (late Cenomanian to early Coniacian) shallow-marine succession exposed in the Wlen Graben and in the Krzeszow Brachysyncline (NE Bohemian Massif, Sudetic Block). These two tectonic subunits are outliers of the North Sudetic and Intra-Sudetic synclinoriums, respectively, and contain relics of the diachronous sedimentary succession of a seaway linking the Boreal and Tethyan marine provinces during the Late Cretaceous. Results of sedimentological study and facies analysis show that the late Cenomanian sedimentation within this corridor was dominated by strong in situ reworking of the pre-Cretaceous bedrock driven by storm waves and possibly tidal currents. In the latest Cenomanian, siliciclastic sedimentation was followed by the deposition of offshore-transition to offshore muddy calcareous facies in the Krzeszow area, while the deposition of coarse-grained siliciclastic facies continued in the Wlen area. The nearshore clastic belt in the latter area changed into a wider strait dominated by offshore sedimentation in the early Turonian, whereby the interconnected Wlen and Krzeszow passages evolved into a uniform strait of fully-marine sedimentation. In the middle Turonian, the southern part of the strait became progressively filled with coarse-grained siliciclastic material supplied from the east. At the end of the late Turonian and in the early Coniacian, the strait funnelled bi-directional tidal currents along its axis. The youngest Cretaceous strata in the Wlen area comprise erosional relics of the early Coniacian shoreface to offshore-transition deposits. The younger Cretaceous deposits are unpreserved, probably eroded during the post-Santonian(?) tectonic inversion of the Wlen–Krzeszow strait. Despite the relatively small distance between the two relic parts of the strait, the shallow-marine succession reveals distinct diachroneity on a regional scale, reflecting an interplay of eustatic changes, differential tectonic subsidence and clastic sediment supply. This paper presents the first detailed sedimentological logs from the two study areas, with new findings of fossil fauna and flora, proposes a new palaeogeographic interpretation and discusses the influence and development of the source areas for the Cretaceous Sudetic Wlen–Krzeszow marine strait at the NE fringe of the Bohemian Massif.

Late Cenomanian-Turonian isotopic stratigraphy in the chalk of the Paris Basin (France): a reference section between the Tethyan and Boreal realms

A chemostratigraphic study (δ13C and δ18O) of the Late Cenomanian and Turonian chalk succession from the “Craie 701” Poigny borehole (near Provins in the Paris Basin, France) provides new high-resolution stable carbon and oxygen isotope data. Correlation of the bentonite horizons and the isotopic trends from Poigny with its English Chalk equivalent allows the development of a precise stratigraphic framework. δ13C and δ18O variations are synchronous and widespread throughout the European epicontinental seas and Tethyan Ocean. In the Poigny borehole, the Oceanic Anoxic Event 2 (OAE 2) is marked by a large and brief positive excursion of carbon isotopes (a carbon isotope excursions: CIE of 3‰ amplitude) without any apparent anoxia in the Late Cenomanian Chalk. Comparisons between different key sections on a North-South transect from the Anglo-Paris Basin to the Umbria-Marche Basin (Gubbio Section, Italy) and the Vocontian Basin (South-East France), suggests that the OAE 2 is linked to an increase in marine organic matter production, modulated by a regional effect on the organic carbon burial rate. Thus, the large positive carbon isotope increase spanning the Middle Cenomanian through to the Middle Turonian, including the salient CIE associated with the OAE 2, reflects a global scale increase in marine productivity that would be concomitant with a major long-term sea level rise. The stratigraphic position of the Turonian-Coniacian boundary can also be better defined by this isotopic study. A comparison of δ18O data between the Anglo-Paris Basin and Tethyan Basin shows high-amplitude, long-term synchronous variations reflecting primary paleo-environmental changes which are independent of local facies, sediment thickness and diagenesis. In particular, a negative shift (−1‰ of amplitude) reflects a warmer climate regime, marking the onset of OAE 2. Two colder phases (+1‰ amplitude each) occurred in the Early Turonian and the beginning of the Late Turonian.

Storm‐flood‐dominated delta: A new type of delta in stormy oceans

AbstractStorms are increasingly identified as a key depositional process. Their deposits show unique sedimentary characteristics, distinct from deposits of fair‐weather wave processes, but are not currently separated in classic ternary deltaic classification schemes. The term ‘storm‐flood‐dominated delta’ is proposed for a new type of delta that more fully represents deltas dominated by storm‐flood processes. This study describes several outcrop cliffs of the Gallup Formation, deposited during the Late Turonian to Early Coniacian in north‐west New Mexico, that exemplify storm‐generated facies and provide examples that can be used to generate a facies model for storm‐flood‐dominated deltas. Key identification criteria include extensive sharp‐based planar to hummocky cross‐stratified sandstone beds, commonly presenting as large‐sized gutter casts. They are interbedded with mudstones that show low bioturbation intensity and normally and inversely graded beds, suggesting direct deposition from river plumes. Major types of gutter casts are classified based on geometry and dimension. The gutter casts are interpreted as storm channels of storm‐flood‐dominated deltas and formed by erosion and infill of submerged channels resulting from offshore‐oriented downwelling currents that may include localized rip currents. These amalgamated channels are likely linked to multiple feeding rivers and distributary channels that ensured high sediment supply rates and highly efficient offshore‐directed sediment transport through hyperpycnal flows. A four‐component pyramidal classification scheme of deltaic deposition is employed to emphasize storms as a distinct process in contrast to the traditional classification that lumps storm and fair‐weather processes in a single ‘wave’ end‐member. The four‐component depositional model can be readily applied to interpret storm‐dominated environments and provide new insights into depositional processes of the marine realm. Recognition of storm processes in deciphering depositional evolution will also help to better understand control mechanisms of sequence stratigraphy, such as relative sea‐level changes, and to analyze sedimentary processes governing sediment transport in ‘source to sink’ systems.

The First Occurrence of Ptychodus latissimus from the Codell Sandstone Member of the Carlile Shale in Kansas

Three teeth of the late Cretaceous shark Ptychodus latissimus (Agassiz) are described from the upper Middle Turonian Codell Sandstone Member of the Carlile Shale. These teeth are significant because they are the first documented occurrence of the species in Kansas, extending the paleobiogeographic range of species and adding a new paleoecological component to the Codell Sandstone fauna. Its association with various ammonite species living in different trophic levels with other ptychodontid sharks may be indicative of niche partitioning.

Foraminifera Biostratigraphy, Palynofacies and Paleoenvironment of deposition of the Albian to Santonian sediments in the Southern Benue Trough, Nigeria

The Albian-Santonian sedimentary sequence in the Ndeaboh-Nenwe area of Enugu, Southern Benue Trough, were analysed for foraminifera and integrated with ostracod and palynofacies analyses to comprehensively appraise the age and depositional environment of the sediments. This is paramount since the studied formations have intermittent series of non-marine sedimentary influences throughout the basin. The results of foraminifera evaluation indicate that the Abakaliki Formation is barren of foraminifera species, whereas the Eze-Aku and Awgu formations have preponderance of planktonic foraminifera assemblages over benthic forms. The Eze-Aku Formation records an abundance of species of Hedbergella and a peak for Heterohelix. The co-occurrence of Whiteinella archeocretacea, Hedbergella planispira, Heterohelix delrieonsis and the ostracod species Ovocytherida symmetrica, suggests a Late Cenomanian to Early Turonian age. Rare species of short-ranging and keeled planktonic taxa are present in Awgu Formation, which has a preponderance of Heterohelix reussi, Heteroheix globulosa, Heterhelix pulchra, Whiteinella baltica, and the ostracods Brachycythere ekpo and Cythereis sp. The Awgu Formation is Middle Turonian to Santonian. The percentage of amorphous organic matter and lithologic characteristics suggest a marine environment for the Abakaliki Formation, although the water depth cannot be ascertained. In the Eze-Aku Formation, the prevalence of Hedbergella and its co-occurrence with Whiteinella and associated palynofacies data (amorphous organic matter, black debris, few structured terrestrial phytoclasts) and dinoflagellate cysts suggest a fairly deep (200–300 m) marine environment with occasional terrestrial input. The low diversity of agglutinated benthic foraminifera assemblage in the Awgu Formation indicates deposition at a minimum paleo-water depth. The paucity of benthic foraminifera, rare occurrence of keeled planktonic species, and the dominance of Hedbergella and Heterohelix; low oxygen tolerant species, in the studied interval are attributed to anaerobic bottom conditions possibly caused by poor bottom water circulation and high organic productivity in the oceans and seas during the Cenomanian-Santonian.

Study of main planktonic foraminifera(Turonian-Santonian) in Kopeh-Dagh sedimentary environment, NE Iran

In order to study the fossil contents of the Abderaz Formation for biostratigraphical purposes the 500 meters thick section was sampled at type section. The sequence is mainly made up of grey shales and marls with two units of chalky limestone in upper part. The lower contact of the formation with Aitamir Formation is disconform while the upper contact with Abtalkh is continuous. Fifty six species belonging to 16 genera were identified and four biozones were differentiated. These are: Helvetoglobotruncana helvetica (Sigal)total range Zone, 2-Marginotruncana sigali - Dicarinella primitiva (Premoli Silva and Sliter)Partial range Zone, 3- Dicarinella concavata (Sigal)interval Zone and4-Dicarinella asymetrica (Postuma)total range Zone. Based on, these an age of Turonian-Late Santonian is quoted to the formation. Also it was shown that Helvetoglobotruncana helvetica, the index species for middle Turonian exists at the base of the formation while, in the samples immediately below this belonging to Aitamir Formation Rotalipora appenninica, the index for middel cenomanian was recorded. Therefore, lack of index species for late Cenomanian- early Turonian shows a gap spanning this period between the Aitamir and Abderaz formations. This could be a result of sub Hersinian orogeny.