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Lower Aptian ammonite biostratigraphy and potential for further studies of OAE 1a in Bulgaria
Abstract
Sediments of Early Aptian age in Bulgaria can be assigned to four different facies: platform carbonates (Urgonian complex), shallow-water siliciclastics, hemipelagic and flyschoid siliciclastics. The taxonomic analysis of the ammonite faunas of 18 sections from these four different facies resulted in a revision of the existing ammonite zonation scheme so far applied in Bulgaria and adjoining areas. A new biostratigraphic scheme, which bridges the western and eastern Tethys, is thereby proposed for the Lower Aptian of Bulgaria.
... These sections have been studied extensively in terms of litho-and biostratigraphy (Nikolov and Stoykova, 1995) and a detailed biostratigraphical frame work based on ammonites has been established (Ivanov, 1995;Ivanov and Idakieva, 2013) (Fig. 1). The OAE 1a has also been indicated in the Butovo section (Ivanov and Idakieva, 2013), based on lithological data. ...
... These sections have been studied extensively in terms of litho-and biostratigraphy (Nikolov and Stoykova, 1995) and a detailed biostratigraphical frame work based on ammonites has been established (Ivanov, 1995;Ivanov and Idakieva, 2013) (Fig. 1). The OAE 1a has also been indicated in the Butovo section (Ivanov and Idakieva, 2013), based on lithological data. ...
... The obtained palynological assemblages are composed of dinoflagellate cysts, trilete spores, gymnosperm and early angiosperm pollen. The chronostratigraphical framework for the sections established by Ivanov and Idakieva (2013) was utilized in order to estimate the timing of the encountered dinocyst events. ...
Upper Barremian and lower Aptian dinoflagellate cyst assemblages have been documented for the first time from five ammonite-controlled sections in Central and Northeast Bulgaria. They include important biostratigraphical markers, such as Rhynchodiniopsis aptiana, Prolixosphaeridium parvispinum, Cerbia tabulata, Lithodinia stoveri and Ctenidodinium elegantulum. The distribution of taxa is generally consistent with published palynostratigraphical schemes, but some differences are noted in this study. The best global markers for the lowermost Aptian interval are represented by the LOs of R. aptiana and C. elegantulum; however, in the sections studied, these taxa consistently occur only within the upper Barremian. The recorded overwhelming dominance of the Classopollis group, together with persistent records of pteridophyte spores, is interpreted as indicative of extremely hot and humid climate, which caused and accompanied the deposition of the OAE 1a in this part of the Tethyan Realm. Pavlishina, P. 2017. Palynology of the upper Barremian and lower Aptian interval in parts of North Bulgaria. Geologica Balcanica 46 (2), 41-45.
... The lower Aptian includes the lower part of the formation, which is rich in ammonites. Recent studies of Ivanov and Idakieva (2013) provided full description of this section and extensive biostratigraphical study of the ammonite successions. The authors recognized the Deshayesites forbesi ammonite Zone, indicating early Aptian age for the succession in the section. ...
... The authors recognized the Deshayesites forbesi ammonite Zone, indicating early Aptian age for the succession in the section. The OAE 1a has also been indicated in the Butovo section, based on lithological data (Ivanov, Idakieva, 2013). Pavlishina (2017) reported dinoflagellate cyst successions from the upper Barremian-lower Aptian interval in North Bulgaria, including those from the Butovo section. ...
First record of early angiosperm pollen from the lower Aptian sediments in the Butovo section, Central North Bulgaria is documented. It is represented by monocolpate crotonoid grains attributed to the Stellatopollis genus and the species Stellatopollis barghoornii Doyle, Van Campo, Lugardon, 1975. The encountered sporomorph association also includes abundant gymnosperm pollen from the Classopollis and Araucariacites genera as well as a variety of pteridophyte spores from the Cretaceous genera Appendicisporites, Cicatricosisporites, Bikolisporites, Trilobosporites, Klukisporites and Deltoidospora. The palynological association indicates that the studied area was part of the ––Southern Laurasian floral province. The persistent record of pteriodophyte spores in the assemblages with the relatively abundant gymnosperm pollen from the Classopollis group suggests a warm and relatively less humid climate for this part of the province during the early Aptian. The results imply that early angiosperms still played minor role in lower Aptian Bulgarian floras.
... Thus, the stratigraphic correlation between Georgian sections and other parts of the Mediterranean Tethys remains unclear. Ivanov and Idakieva (2013) suggested that the heteroceratid assemblages of the "C." securiformis Zone of western Georgia and its equivalent, the "Colchidites" ratshensis horizon of the Turkmeniceras turkmenicum Zone of the Transcaspian region, are marked by a strong facies-controlled distribution that has caused it to be confused with the western Mediterranean M. sarasini Zone . These zones have been repeatedly correlated with one another, but no author have been put them in synonymy since the introduction of the standard late Barremian M. sarasini Zone (Reboulet et al. 2006).The current knowledge of the distribution of late Barremian ammonites shows that the ammonite assemblage of the M. sarasini Subzone is rather similar in the whole Mediterranean-Caucasian Subrealm and the adjacent part of the Boreal-Atlantic Subrealm, with consequent great potential for biostratigraphic correlation (Reboulet et al. 2014 with references). ...
... In the light of this study, there is no doubt that the peculiar heteroceratids faunas shared by the Podestat-Pouli and Tvishi sections correspond to the environmentally proximal assemblages of the base of the M. sarasini Subzone. Therefore, in our view, there is no doubt that the M. sarasini Subzone should be given preference in western and eastern Mediterranean settings, thus following the recommendation of Ivanov and Idakieva (2013). ...
Investigation of the late Barremian deepening succession of the Provence platform, cropping out south of Marseille (Bouches-du-Rhône, France), has yielded a new ammonite fauna belonging to the Martelites sarasini Subzone (Martelites sarasini Zone). The fauna is dominated by representatives of the Heteroceratidae Spath, characterized by different patterns of coiling, high intraspecific variabilities and dwarfism. These heteroceratids are distinctive and utterly different from all previously known taxa, and this justifies the introduction of the new taxa Heteroceras denizoti sp. nov., Heteroceras veratiae sp. nov., Calanquites gen. nov., based on Imerites katsharavai Rouchadzé; Giovaraites gen. nov., based on Giovaraites massiliae gen. et sp. nov., Barguesiella gen. nov., based on Barguesiella goudesense gen. et sp. nov. and the closely allied Barguesiella mantei gen. et sp. nov. The occurrence of the latter species at the top of the Maiolica Formation in Italy questions its early Aptian age assumed in the literature. The newly described fauna could be considered as the first case of micromorphy in the Heteroceratidae. Its biostratigraphy, palaeoenvironmental and palaeobiogeographical significance are discussed.
... Thus, the stratigraphic correlation between Georgian sections and other parts of the Mediterranean Tethys remains unclear. Ivanov and Idakieva (2013) suggested that the heteroceratid assemblages of the "C." securiformis Zone of western Georgia and its equivalent, the "Colchidites" ratshensis horizon of the Turkmeniceras turkmenicum Zone of the Transcaspian region, are marked by a strong facies-controlled distribution that has caused it to be confused with the western Mediterranean M. sarasini Zone . These zones have been repeatedly correlated with one another, but no author have been put them in synonymy since the introduction of the standard late Barremian M. sarasini Zone (Reboulet et al. 2006).The current knowledge of the distribution of late Barremian ammonites shows that the ammonite assemblage of the M. sarasini Subzone is rather similar in the whole Mediterranean-Caucasian Subrealm and the adjacent part of the Boreal-Atlantic Subrealm, with consequent great potential for biostratigraphic correlation (Reboulet et al. 2014 with references). ...
... In the light of this study, there is no doubt that the peculiar heteroceratids faunas shared by the Podestat-Pouli and Tvishi sections correspond to the environmentally proximal assemblages of the base of the M. sarasini Subzone. Therefore, in our view, there is no doubt that the M. sarasini Subzone should be given preference in western and eastern Mediterranean settings, thus following the recommendation of Ivanov and Idakieva (2013). ...
Investigation of the late Barremian deepening succession of the Provence platform, cropping out south of Marseille (Bouches-du-Rhône, France), has yielded a new ammonite fauna belonging to the Martelites sarasini Subzone (Martelites sarasini Zone). The fauna is dominated by representatives of the Heteroceratidae Spath, characterized by different patterns of coiling, high intraspecific variabilities and dwarfism. These heteroceratids are distinctive and utterly different from all previously known taxa, and this justifies the introduction of the new taxa Heteroceras denizoti sp. nov., Heteroceras veratiae sp. nov., Calanquites gen. nov., based on Imerites katsharavai Rouchadzé; Giovaraites gen. nov., based on Giovaraites massiliae gen. et sp. nov., Barguesiella gen. nov., based on Barguesiella goudesense gen. et sp. nov. and the closely allied Barguesiella mantei gen. et sp. nov. The occurrence of the latter species at the top of the Maiolica Formation in Italy questions its early Aptian age assumed in the literature. The newly described fauna could be considered as the first case of micromorphy in the Heteroceratidae. Its biostratigraphy, palaeoenvironmental and palaeobiogeographical significance are discussed.
... Zlatarski, 1886;Paquier, 1903Paquier, , 1905Tzankov, 1960;Atanassova-Deltcheva, 1969, 1974, 1978. The Urgonian formations were outlined by Khritschev (1966) and revised by Ivanov and Idakieva (2013) who precisely referred to ammonite zones the key rudist-bearing carbonates classically reported from the literature: i.e. the Emen, Stratech and Devetaki Formations which are currently mostly assigned to the Barremian. The western carbonate Urgonian belt of Northern Turkey (Pontides) is considered as the eastern extent of the Fore-Balkan . ...
... The Procheloniceras-Cheloniceras-Epicheloniceras lineage is characteristic of the Tethyan Realm and of the southern area of the Boreal Realm (Casey et al. 1998;Kakabadzé et al. 2004;Pictet 2012). In the late early Aptian, Roloboceras and Megatyloceras, closely-allied or possibly congeneric with Cheloniceras, are typically recorded during the early Aptian of the Mediterran-Caucasian Subrealm and southern area of the Boreal Realm (Casey 1961;Moreno-Bedmar et al. 2010;Ivanov and Idakieva 2013). Dauphin (2002) documented a complex turnover in the earliest late Aptian that led to the appearance of the widespread family Parahoplitidae. ...
... cornuelianum (Casey et al., 1998, p. 516). The conclusions of Casey (1961;Casey et al., 1998) have thereafter been globally accepted by authors, and C. cornuelianum is nowadays generally quoted from the D. forbesi Zone to the D. furcata Zone (Castro et al., 2001;Delanoy, 1997;Gauthier et al., 2006;Ivanov and Idakieva, 2013;Moreno-Bedmar et al., 2009;Pictet, 2012;Ropolo et al., 2009). Some authors have performed new revisions of this species with a "paleobiologic" approach: Dutour (2005), on the basis of material from the Argiles à Plicatules and the D. deshayesi and D. furcata zones of southeastern France, considered that C. cornuelianum occurs within a D. deshayesi-D. ...
The aim of the present work is to determine the morphological characteristics of the lower Aptian (lower Cretaceous) ammonite species Cheloniceras cornuelianum (d'Orbigny, 1841) (Douvilleiceratinae, Douvilleiceratidae) on the basis of 32 specimens from the Paris Basin (France), including the lectotype of the species and 23 topotype specimens. It is generally admitted that this species occurs in the Deshayesites forbesi-Dufrenoyia furcata zones interval (lower Aptian). Our study has lead to several unexpected results. First, the study sample of C. cornuelianum is very probably younger and has more primitive traits than expected: it is probably dated around the limit between the Deshayesites forbesi and Deshayesites deshayesi zones and is morphologically close to the earlier genus Procheloniceras Spath, 1923. Secondly, the lectotype is an extreme specimen with much derived traits compared to its original population. It constitutes an example of type-specimen not morphologically representative of its original population, responsible of a risk of misinterpretation of the species. Finally, the intraspecific variability and the proportion of asymmetric specimens of the study sample of C. cornuelianum are very important but there is no evidence of sexual dimorphism.
... Ce schéma biostratigraphique est également celui suivi dans le cadre des dernières études chimiostratigraphiques du secteur stratotypique (Stein et al., 2012 ;Lorenzen et al., 2012). Parallèlement, d'autres travaux effectués sur l'Aptien inférieur des marges du domaine méditerranéen (Moreno-Bedmar et al., 2009Pictet, 2011 ;Najarro et al., 2011 ;Gaona-Narvaez et al., 2013 ;Ivanov & Idakieva, 2012) situent la Sous-zone à Roloboceras hambrovi au sommet de la Zone à D. forbesi, un positionnement stratigraphique d'ailleurs comparable à celui des Roloboceras et Megatyloceras dans les Lower Greensands en Angleterre (Crakers et Upper Lobster beds de la Zone à Deshayesites forbesi) (Casey, 1961 ;Casey et al., 1998). Selon Ropolo et al. (2008b), la divergence sur le positionnement de la Sous-zone à Roloboceras hambrovi sur le secteur de Cassis-La Bédoule s'expliquerait par l'existence d'une barrière écologique ayant retardé la colonisation du milieu par les représentants des genres Roloboceras Casey, 1961et Megatyloceras Humphrey, 1949. ...
New account on the zonation of the historical early Aptian stratotype.- A population of Macroscaphites striatisulcatus (d’Orbigny) is described from the Unit 4 of the historical area of the “Bedoulian” (early Aptian) at Cassis-La Bédoule (Bouches-du-Rhône, France). The systematic analysis sheds new light on this misunderstood taxon and confirms the dimorphism between the genera Macroscaphites Meek and Costidiscus Uhlig. From a stratigraphical point of view, the study of the associated Deshayesites of the Unit 4, and the revision of the ammonite assemblage so far reported in the Deshayesites deshayesi Zone, lead us to reconsider the biostratigraphic scheme in this reference area. We suggest to fix the upper boundary of the Deshayesites forbesi Zone at the top of the Roloboceras hambrovi Subzone in accordance with the current Mediterranean zonation of the early Aptian.
... The Procheloniceras-Cheloniceras-Epicheloniceras lineage is characteristic of the Tethyan Realm and of the southern area of the Boreal Realm (Casey et al. 1998;Kakabadzé et al. 2004;Pictet 2012). In the late early Aptian, Roloboceras and Megatyloceras, closely-allied or possibly congeneric with Cheloniceras, are typically recorded during the early Aptian of the Mediterran-Caucasian Subrealm and southern area of the Boreal Realm (Casey 1961;Moreno-Bedmar et al. 2010;Ivanov and Idakieva 2013). Dauphin (2002) documented a complex turnover in the earliest late Aptian that led to the appearance of the widespread family Parahoplitidae. ...
This paper is a first approach to the distribution through space and time of the midCretaceous ammonite faunas of the Arabian plate. It is based on new collections made in Iran (Lurestan, Khuzestan and the coastal Fars area) and data from the literature (Oman, Lebanon, Jordan, Israel and Egypt). On the Arabian plate itself there is a marked difference between the diversity and abundance of the taxa present in intra-shelf basins from those on drowned platforms. Their comparison with faunas from Maghreb (Tunisia and Algeria mainly) enhances the validity of a premise concerning the existence of a South Tethyan endemic region that is well expressed during the Lower and Middle Albian, for it is marked by the success of highly distinctive faunas of Engonoceratidae ("Platiknemiceraś, Knemiceras and Parengonoceras) developed on drowned platforms. This endemism is less obvious during the remainder of the period studied and appears to be limited mainly to aberrant ranges: the early occurrence of some taxa (such as Neolobites in the Middle Cenomanian) or the persistence of others (such as Epicheloniceras in the middle of the Upper Aptian).
... The Procheloniceras-Cheloniceras-Epicheloniceras lineage is characteristic of the Tethyan Realm and of the southern area of the Boreal Realm (Casey et al. 1998;Kakabadzé et al. 2004;Pictet 2012). In the late early Aptian, Roloboceras and Megatyloceras, closely-allied or possibly congeneric with Cheloniceras, are typically recorded during the early Aptian of the Mediterran-Caucasian Subrealm and southern area of the Boreal Realm (Casey 1961;Moreno-Bedmar et al. 2010;Ivanov and Idakieva 2013). Dauphin (2002) documented a complex turnover in the earliest late Aptian that led to the appearance of the widespread family Parahoplitidae. ...
Ammonites are often dominant elements of Early Cretaceous marine faunas. Many species are important index fossils, in some cases with worldwide distribution. We review the paleobiogeography for the Early Cretaceous. We recognize three major faunal phases in the distribution of ammonites during that interval. The first phase, directly inherited from the Late Jurassic distribution patterns, extends from the Berriasian to the earliest Barremian, when the faunas of the Boreal Realm are clearly distinguished from the Tethyan Realm. From the late early Barremian to the late Aptian, a second phase is characterized by rather uniform faunas marked by the dominance of Tethyan-derived heteromorphs in the Boreal Realm. The last phase, covering most of the Albian stage, displays a more distinctive differentiation between Boreal and Tethyan faunas. The late Barremian marks the onset of the Austral Realm, originating from faunas that originally evolved in the Indo-Pacific Subrealm of the Tethyan Realm.
... Находки V. schilovkensis и V. sp. были сделаны в разрезах Болгарии (нижний апт, зона Deshayesites forbesi, подзона Roloboceras hambrovi : Ivanov, Idakieva, 2013), где они встречаются выше и ниже интервала битуминозных сланцев, напоминая тем самым фациальную приуроченность данных аммонитов в разрезах Поволжья. ...
New material of the ammonite subfamily Cheloniceratinae Spath, 1923 is described from the Aptiansuccessions of the Maghara area. We record Cheloniceras cornuelianum as well as Epicheloniceras tsch-ernyschewi from the lower and upper Aptian, respectively. These very widely distributed and commonspecies are important for the supraregional correlation, and we establish their stratigraphic range for theGabal Lagama and Gabal Abu Ruqum key sections. A short account is given about the palaeobiogeographicsignificance of both species.
Microstructures of belemnites are still poorly understood for many species, which may have wide-ranging implications for their palaeobiology and geochemical application. We acquired microscopical and geochemical data of taxonomically distinct co-occurring belemnites from the lower Aptian of Bulgaria and Germany. The rostra display consistent macroscopical, microscopical, and geochemical differences. Belemnopseid specimens (Mesohibolites sp., Neohibolites ewaldi) are well-preserved, apart from an originally porous, primarily organic-rich, and fine-grained section in the anterior part of the rostra, which was recrystallized and cemented during diagenesis. The results of the Aptian taxa are compared to data from Hauterivian Hibolithes jaculoides. Dissolution/erosion of these anterior sections is known to form a pseudoalveolus. In contrast to the belemnopseids, major parts of Duvalia grasiana specimens are recrystallized due to an originally high content of organic matrix.
Such diverse belemnite microstructures must be considered in geochemical studies. Their palaeobiological background is discussed in terms of the modification of hydrostatic stability. Originally porous, primarily organic-rich anterior rostra might represent a synapomorphy of a group of belemnites containing at least some species of the Belemnopseidae as well as potentially further derived belemnite taxa.
A detailed planktonic foraminiferal biostratigraphic framework, associated with supporting ammonite data, is presented for Aptian–Albian intrashelf sedimentary succession (Kazhdumi Formation) at the Tang-e-Maghar section, Zagros Basin, SW Iran. Most of the identified planktonic foraminiferal species are reported for the first time from this region, and the fauna permits five biozones to be newly proposed from the upper Aptian Globigerinelloides aptiensis Zone to the middle Albian Ticinella primula Zone. Notably, we recognize a narrow interval of faunal turnover in the Microhedbergella miniglobularis Zone, the base of which is delimited by the highest occurrences of Aptian-representing taxa and the top by the lowest occurrence of the Albian Microhedbergella praeplanispira. The proposed Aptian/Albian boundary should lie within this interval accordingly. In addition, we report on 12 ammonite levels that can be used to constrain the Aptian–Albian Substages. The proposed planktonic foraminiferal biozonation of the studied section will be an important step toward better understanding of the nature of the biotic and global changes across the Aptian/Albian boundary on the Arabian Plate in the paleotropical southern Neo-Tethys.
The revision of Monopleura Matheron shows that the right valve of this genus has an asymmetrical myophoral arrangement. By contrast in Homopleura n. gen. the right valve myophores are nearly identical and located on transverse shell thickenings. In the group of Homopleura affinis the left valve posterior myophore is a bulge protruding into the opposite valve and is flanked by a perimyophoral depression. In the group of Homopleura rustrella n. sp. the left valve posterior myophore is flat and there is no perimyophoral depression. Homopleura n. gen. includes five species restricted to the upper Barremian and accordingly possess a significant biostratigraphic potential. Four species are recorded from SE France, Homopleura affinis, H. imbricata and H. coquandi, and a new species Homopleura rustrella n. sp. An additional species Homopleura balkanica n. sp. is described from Bulgaria. Homopleura n. gen. derives from Monopleura emend. Besides myophoral changes, the evolution of the Monopleura-Homopleura n. gen. lineage records morphometric changes, i.e. size increase. Homopleura n. gen. is the ancestor of the Polyconitidae and may also be the root of the Caprinulidae.
Some representative taxa of the Family Heteroceratidae from the Sarcheshmeh Formation are studied. These are: Heteroceras cf. colchicus Djanelidze, Heteroceras spp., Martelites cf. tenuicostatus (Kakabadze), Martelites securiformis (Simonovich, Bastevich and Sorokin), Martelites cf. tinae (Eristavi), Martelites sp.1, Martelites sp. 2, Argvethites sp., Imerites sparcicostatus Rouchadze and Paraimerites sp. These indicate a Late Barremian age. The Imerites giraudi and Martelites securiformis Biozones are proposed for the Upper Barremian Sub-Stage in the Koppeh Dagh Basin. The paleobiogeographic distribution of the Heteroceratidae during Late Barremian is discussed.
The Coleoidea are by abundance as well as diversity the dominant group of cephalopods in modern seas and an important component of marine ecosystems. They are characterized by an endoskeleton which is largely reduced in many recent taxa. This endoskeleton can be covered by secondary carbonate deposits forming a so-called rostrum. The rostra of the extinct belemnites represent the most common coleoid fossils of the Jurassic and Cretaceous. Due to their low-Mg calcite composition, which is relatively stable during diagensis, belemnite rostra have become one of the most frequently used geochemical archives for the marine paleoenvironment. Paleoenvironmental proxies commonly derived from the rostrum calcite are stable carbon and oxygen ratios (δ13C, δ18O), as well as the element ratios Mg/Ca and Sr/Ca. These proxy data have been predominantly applied to reconstruct paleotemperature and carbon cycle trends.
Despite this widespread application, there are several factors which restrict the use of belemnite rostra as paleoenvironmental archives. The primary microstructure of belemnite rostra is controversially debated, with reconstructions ranging from originally aragonitic, highly porous low- Mg calcitic, to mostly dense low-Mg calcitic. Many structural features of the rostra have not been investigated in detail in a comparative paleontological framework. The likely nektic, active lifestyle of belemnites makes interpretation of their geochemical data more complicated than that of benthic animals due to possible migration. Potential vital effects, formation of the rostrum calcite out of (isotope)chemical equilibrium due to biomineralization processes, are often neglected. Furthermore, all fossils are subject to different extents of diagenesis which might alter their geochemical composition. Screening for diagenetic alteration is difficult in belemnites, because no recent cephalopod provides a structure which is identical to the calcitic rostrum and could be used as a benchmark of perfect preservation.
This thesis consists of four studies which investigate different aspects of the structure and geochemistry of recent (argonauts; Argonauta argo) and fossil (belemnites; Belemnitida) calcitic skeletons of coleoid cephalopods. The first study deals with belemnite rostra of the Nusplingen Plattenkalk (Upper Jurassic, southwestern Germany). Oxygen stable isotope values of the rostra provide paleotemperatures inconsistent with their depositional setting. The predominant influence on their geochemical record was probably a locally or regionally increased evaporation rate. These findings highlight the importance of a critical interpretation of belemnite data in a sedimentological/paleontological framework.
III
The second study is the first to investigate geochemical data of the calcitic shells of the pelagic argonauts. High-resolution sampling of the shells reveals a complex combination of vital effects related to growth rate, as well as environmental influences acting on the shells’ δ18O, δ13C, Mg/Ca, Sr/Ca, and Ba/Ca ratios. Environmental influences are, nevertheless, only revealed if they are constrained by the potential drift/migration path and habitat of these cephalopods.
The third study presents microstructural and geochemical data derived from the belemnite Neohibolites minimus. The two growth stages of their rostra have distinct microstructures and geochemical compositions. These microstructures and cathodoluminescence patterns of the rostra are compared to those of argonaut shells. Development and evolution of the rostra is discussed and evidence for vital effects in these belemnites presented.
Finally, the fourth study compares two distinct belemnite taxa (Mesohibolites sp., Duvalia grasiana) which experienced the same diagenetic pathway. Differences in preservation of these taxa are reflected in their geochemistry and cathodoluminescence patterns. Diagenesis of the rostra was controlled by their different primary microstructure. The largely porous pseudoalveoli of Mesohibolites were cemented during diagenesis while large sections of the D. grasiana rostra recrystallized due to their high primary organic content. This results in an invariable loss of large sections of the ontogenetic geochemical record of the rostra and necessitates a precise taxonomic identification of the rostra.
In conclusion, these studies reveal that I) the exact environmental parameters which influence the skeletal geochemistry are often difficult to discern in recent and particularly in fossil coleoid cephalopods, II) vital effects might influence the geochemical data significantly, distorting environmental signals, and III) diagenesis of belemnite rostra is influenced by differential reaction of their microstructures, often leading to the loss of ontogenetic records and necessitating a precise taxonomical determination of analyzed rostra. All of these factors largely restrict the utility of belemnite rostra as environmental archives.
The Maiolica-type Gorgo a Cerbara section (Central Italy) was proposed as GSSP candidate for defining the base of the Aptian Stage with the base of the reverse magnetochron CM0r as the primary datum. Comparison with well-documented, ammonite-bearing successions of southeast France shows that the bio-, litho- and chemostratigraphic events recorded in Italy, below, at, and above this magnetochron fall within the Martelites sarasini ammonite zone. Since there is an agreement that the M. sarasini Zone is the last ammonite zone of the Barremian, the use of the base of magnetozone CM0r as a datum to define the Barremian/Aptian boundary is questioned.
The mid-Cretaceous was marked by emplacement of large igneous provinces (LIPs) that formed gigantic oceanic plateaus, affecting ecosystems on a global scale, with biota forced to face excess CO2 resulting in climate and ocean perturbations. Volcanic phases of the Ontong Java Plateau (OJP) and the southern Kerguelen Plateau (SKP) are radiometrically dated and correlate with paleoenvironmental changes, suggesting causal links between LIPs and ecosystem responses. Aptian biocalcifi cation crises and recoveries are broadly coeval with C, Pb, and Os isotopic anomalies, trace metal infl uxes, global anoxia, and climate changes. Early Aptian greenhouse or supergreenhouse conditions were followed by prolonged cooling during the late Aptian, when OJP and SKP developed, respectively. Massive volcanism occurring at equatorial versus high paleolatitudes and submarine versus subaerial settings triggered very different climate responses but similar disruptions in the marine carbonate system. Excess CO2 arguably induced episodic ocean acidifi cation that was detrimental to marine calcifi ers, regardless of hot or cool conditions. Global anoxia was reached only under extreme warming, whereas cold conditions kept the oceans well oxygenated even at times of intensifi ed fertility. The environmental disruptions attributed to the OJP did not trigger a mass extinction: rock-forming nannoconids and benthic communities underwent a signifi cant decline during Oceanic Anoxic Event (OAE) 1a, but recovered when paroxysmal volcanism fi nished. Extinction of many planktonic foraminiferal and nannoplankton taxa, including most nannoconids, and most aragonitic rudists in latest Aptian time was likely triggered by severe ocean acidifi cation. Upgraded dating of paleoceanographic events, improved radiometric ages of the OJP and SKP, and time-scale revision are needed to substantiate the links between magmatism and paleoenvironmental perturbations.
Early Cretaceous glauconitic sandstones form part of the well-established boulder association known in the German literature on glacial erratics as the “Ahrensburger Geschiebesippe”. Because ammonites are very rare in these sandstones, a small assemblage is described, based
on material mentioned in several classical papers. The following taxa are recognized: Hypacanthoplites elegans, Hypacanthoplites jacobi, Aconeceras sp. juv. cf. A. nisus, Sanmartinoceras (Sinzovia) stolleyi (based on the original material of
Oppelia (Adolphia) baltica Ernst, 1921, a nomen nudum) and Cheloniceras (Cheloniceras) cornuelianum. According to the ranges attributed to these taxa the stratigraphic interval represented is late Early Aptian to earliest Albian. This expanded
stratigraphic range is in contrast to that of the rich boulder fauna recently reported from Wolgast-Hohendorf in northeast Germany (essentially Early Albian, Leymeriella acuticostata Subzone, in age). The origin of both boulder associations is assumed to be the southern part of the
Danish-Polish Basin.
This work is a study of the ammonite record of a new stratigraphic section of Aptian age, at the Mina Texali (Puebla State, Central Mexico). A detailed biostratigraphic analysis was carried out on 309 specimens systematically sampled on a bed-by-bed basis. An Aptian ammonite zonation is proposed for the Mina Texali (= MT) section with two interval zones, Dufrenoyia justinae and Caseyella sp., and one informal biostratigraphic unit represented by the Huastecoceras trispinosoides beds. We also analyze the taxonomic composition, paleoecology and some systematic issues of the ammonite record of the MT section. The first record in Mexico of the genera Pseudosaynella, Xerticeras and the nautiloid Heminautilus is identified in this section. The ammonite assemblage is assigned to the proximal part of the outer neritic region of the continental shelf. The ammonite record of the studied section is diagnostic in establishing the lower-upper Aptian transition, and the local zonation of the MT provides important data for the development of an Aptian standard ammonite zonation for the Central Atlantic province.
Biostratigraphical and paleontological studies of lower Aptian material from the Eastern Iberian Chain (Spain) have revealed the presence of a new genus of micromorphic heteromorph ammonite: Xerticeras gen. nov. (type species: Xerticeras salasi sp. nov.). This new taxon comes from the Deshayesites deshayesi and Dufrenoya furcata ammonite zones. The size difference observed in the population is considered due to sexual dimorphism.
La mise en corrélation des principaux signaux d'ordre sédimentaire, biologique et géochimique recueillis à l'occasion d'une révision du stratotype historique de l'Aptien inférieur dans la région de La Bédou-le-Cassis permet de mettre en évidence et de calibrer au sein de la série barrémo-bédoulienne un certain nombre de coupures ou discontinuités importantes ou même majeures : niveau "Taxy", niveau "Roch" (limite Barrémien-Aptien), niveau "Toucas", discontinuité A2 (majeure) (limite Bédoulien inférieur-Bédoulien supérieur), banc 158, banc 170, et de les replacer dans le contcxtc régional (SE de la France). Inversement des crises reconnues dans l'océan mondial ("crise des Nannoconus", événement anoxique AOE1a) ou la limite paléontologique entre Bédoulien et Gargasien ne sont pas clairement exprimées ou marquées à La Bédoule. Les coupures résultant d'une approche de stratigraphie intégrée ne coïncident aussi que très rarement avec les limites de séquences et autres événements de la récente charte séquentielle publiée par Hardenbol et al. (1998), pourtant en grande partie appuyée sur des données d'observation provenant du stratotype. Au strict point de vue biostratigraphique, la limite Barrémien-Aptien est précisément marquée par l'apparition du genre d'ammonites Deshayesites, dont les différentes espèces (D. tuarkyricus, D. weissi, D. deshayesi), relayées par un autre Deshayesitidé (Dufrenoya furcata) permettent également d'établir une biozonation de l'Aptien inférieur conforme au standard méditerranéen. Seul le Bédoulien supérieur est clairement caractérisé par des changements significatifs des Foraminifères planctoniques, avec l'apparition étagée de plusieurs espèces dont notamment Blowiella blowi et Schackoina (Leupoldina ) cabri. Aucun renouvellement marqué n'est observé à la limite Bédoulien-Gargasien. En revanche les Nannofossiles calcaires marquent la limite Barrémien-Aptien avec l'apparition d 'Hayesites irregularis, îa limite Bédoulien inférieur-Bédoulien supérieur avec celle de Rhagodiscus angustus et la base de la zone à D. furcata avec Eprolithus floralis. Chez les Dino-flagellés les bio-événements s'opèrent au sein des principales bio¬ zones d'ammonites, avec en particulier l'apparition de Tehamadinium tenuiceras, datum significatif à l'échelle au moins européenne, ici calibré au sein de la zone à D. furcata.
Detailed multidisciplinary analyses of several sections through the Barremian-Aptian interval resulted in the revision of the Aptian stage, including the Barremian-Aptian boundary. The Aptian Working Group (= AWG) established an integrated stratigraphy based on biostratigraphy (ammonites, belemnites, calcareous nannofossils, planktonic and benthic foraminifera, dinoflagellates, radiolarians), magnetostratigraphy, isotope stratigraphy (δ13C and 86Sr/87Sr), event stratigraphy, sequence stratigraphy, and cyclostratigraphy. Historical precedence was considered and the preliminary proposals made at the Copenhagen Symposium in 1983 were considered as starting point. The new information highlighted the difficulty of using the first appearance of Prodeshayesites for the definition of the base of the Aptian, and revealed the importance of biostratigraphy based on other fossil groups, especially micro- and nannofossils, as well as physical and chemical tools such as magnetostratigraphy, chemostratigraphy, sequence stratigraphy and cyclostratigraphy in global correlations. Following the discussions at and after the Second International Symposium on Cretaceous Stage Boundaries (Brussels, 8-16 September 1995), the majority of the AWG selected the base of magnetic chron MO as the event for the definition of the base of the Aptian stage. It must be emphasised that magnetostratigraphy must always be integrated with biostratigraphy and magnetic chron MO must be identified in relation to palaeontological events. After accepting the base of magnetic chron MO as the base of the Aptian stage, the AWG identified the Gorgo a Cerbara section (Umbria-Marche Basin, Central Italy) as possible GSSP for the base of the Aptian Stage. This section represents an excellent exposure of Barremian to Aptian pelagic carbonates, and offers a wide range of available stratigraphies including magnetostratigraphy, calcareous nannofossil and planktonic foraminiferal biostratigraphy, radiolarian biostratigraphy, dinoflagellate biostratigraphy, chemostratigraphy (δ13C) and cyclostratigraphy. Moreover, the Oceanic Anoxic Event 1a is represented by the black shales of the Selli level. The record of ammonites is not continuous; however, a few diagnostic layers have been detected. The Aptian substage subdivision was also discussed, but the AWG has not yet provided recommendations. While a two-fold subdivision is adopted for the Boreal Aptian, a three-fold subdivision is often applied to low-latitude sequences. The integrated stratigraphy elaborated by the AWG for the stage is still under revision and Aptian subdivisions will be the subject of further work.
This report is the synthesis of the discussions held during the 2nd W orkshop of the Lower Cretaceous Cephalopod Team of IGCP-Project 262: Tethyan Cretaceous Correlation (Mula, SE Spain, July 2-5, 1992). It presents a new proposition of zonal scheme fór the Lower Cretaceous of the M editerranean Region and justifications about the choice of the index-species fór somé biostratigraphical units. RESUMEN Se presentan las conclusiones dél " 2nd W orkshop of the Lower Cretaceous Cephalopod Team of IGCP-Project 262: Tethyan Cretaceous Correlation " , celebrado en M ula (SE de Espana) durante los días 2 al 5 de julio de 1992. Se incluye la propuesta de un nuevo esquem a zonal basado en am m onites para el Cretácico Inferior dél ámbito mediterráneo, así como notas aclaratorias sobre la elección de las especies índice de algunas unidades bioestratigráficas.
Studies are conducted on the ammonite sequences in cross-sections of the Lower Cretaceous on the basis of which two ammonite zones are separated in the Lower Aptian sediments: Procheloniceras pachystephanum and Deshayesites deshayesi. In the beds around the Barremian-Aptian boundary in a cross-section at Kacelovo village is established a rarely encountered joint development of the ammonite genera Colchidites and Procheloniceras. The precise dating of this stratigraphic level suggests that the representatives of Colchidites genus have continued their existence after this boundary in the beginning of the Aptian Age.-from Abstracts of Bulgarian Scientific Literature
The Lower Cretaceous deposits are widespread in North Bulgaria: in the Fore-Balkan, the Transitional Zone, and the Moesian Platform. The scheme of the formal lithostratigraphic units includes 37 Formations and has been elaborated for all this territory on the basis of outcrops and numerous boreholes. Four Groups (West-Balkan Carbonatic Group, Central-Balkan Flysch Group, Vraca Urgonian Group and Loveč Urgonian Group) consist of 19 Formations, and the other 18 Formations are independent. A total of 15 Members has been introduced within 9 of the Formations. The composition and interrelations of tbe lithostratigraphic units reflect the inhomogeneities and the different tendencies of the development of tile Early Cretaceous basin. The most expressive facies boundary in the west-east direction is the so-called Jablanica Line. West of it, carbonatic and marly deposits predominate in the Fore-Balkan. The carbonatic Formations belong to the West-Balkan Carbonatic Group and the Vraca Urgonian Group. The Salaš Formation is built up of clayey limestones and marls, and is widespread in the West Fore-Balkan, as well as in the western part of .the Moesian Platform. The asymmetry of the basin with a dry land as source region to the south of it, is clearly outlined to the east of the Jablanica Line, within: the Central and East Fore-Balkan and the adjacent Transitional Zone. This character of the basin controlled a facies differentiation with development of predominantly terrigeneous units in the south, and of carbonatic and marly units, to the north. This difference is expressed at its best at the lower levels of the Lower Cretaceous where units of the Central-Balkan Flysch Group are interfingering with units of the West-Balkan Carbonatic Group. The lateral transition takes place within the Transitional Zone. At higher stratigrapic levels (Hauterivian - Aptian) the asymmetry is expressed into a horizontal transition of terrigenous non-flysch deposits (Kamchija Formation and Roman Formation) with predominantly marly deposits (Gorna-Orjahovica and Trâmbeš Formations) to the north. A specific feature is the presence of Urgonian deposits in the Transitional Zone (Loveč Urgonian Group). At both sides of its development area, fans of the terrigeneous deposits of the Roman Formation are traced towards north. They are bounded to the Iskar (at the west) and Etar (to the east) depressions. Urgonian limestones occur also within the Moesian Platform in the area of Ruse (Ruse Formation). The highest (Albian) levels of the Lower Cretaceous section have been observed only in northwest Bulgaria. They are represented by the marls of the Sumer Formation, the glauconitic predominantly sandy deposits of Malo Peštene Formation, and the marls of Rabiša Formation.
Upper Barremian/lower Aptian (Bedoulian) ammonite faunas in the stratotypic area of Cassis-La Bédoule (SE France). Present knowledge status and proposal for an Ammonite zonation of the type-Bedoulian. On the basis of recent investigations, the ammonite inventory of the upper Barremian/lower Aptian beds in the historical stratotype area of La Bédoule leads to confirm that the Bedoulian substage (and thus the Aptian stage) lower boundary is determined by the first appearance of the genus Deshayesites. The Bedoulian/Gargasian boundary is drawn at the top of the Dufrenoya furcata zone (= Dufrenoya spp./Tropaeum bowerbancki zone sensu Conte, 1994). The ammonitic content of the stratotype leads also to a subdivision which conforms better to most of the recently proposed Mediterranean zones and permits to partly correlate the standard zonation with that of the Boreal realm.
Thanks to new discoveries, the stratigraphical position of "Emericicerus' collignoni Thomel is determined precisely but the examination of this new material reveals that this taxon is really a member of the genus Eristavia Kakabadze (Family Heteroceratidae). A Giraudi Zone is proposed in the Upper Barremian of the southeast of France. There is an abridged English version. -English summary
In the Mangyshlak Mountains, the lower Aptian deposits are represented by thin beds (0.5-1.5 m) of sandstone and conglomerate, and in the Kugusem anticline, this time range spans two conglomerate beds incorporating an intermediate clay member (up to 15 m thick). The lower Aptian beds rest with a hiatus on different horizons of the Cretaceous (Berriasian-Barremian), or on the Middle Jurassic rocks. The beds yielded diverse assemblages of various faunal groups: ammonites, belemnites, bivalves, brachiopods, Echinoidea, and others. The beds represent a condensed sedimentary sequence of the shallow-shelf type and are divisible into the lower Aptian Deshayesites weissi, Deshayesites deshayesi, and Dufrenoya furcata ammonite zones. The lower Aptian ammonite assemblages include 21 species from genera Deshayesites, Dufrenoya, and Cheloniceras, two of which (Deshayesites semenovi and Cheloniceras sinzowi) are new and described in the paper. The paper also presents images of 16 other species, including 11 forms discovered for the first time in the Mangyshlak Mountains.
The idea that monomorph Deshayesitaceae descended from heteromorph Heteroceratidae is confirmed. This transition from Heteroceras and further to Turkmeniceras is based upon a similar type of suture line morphogenesis and sculpture in late Colchidites and early Turkmeniceras. A zonal subdivision of Lower Aptian in areas of the eastern and also partially of the western hemispheres is suggested mainly in accordance with the development of the Deshayesitaceae. The Lower Aptian ammonite zones of the Middle Volga region, of the Northern Caucasus and of Turkmenistan are characterized. Biozones of Barremian and Aptian boundary deposits from the Mediterranean and Boreal realms are compared. Seven genera of the superfamily Deshayesitaceae (family Deshayesitidae) are described: Turkmeniceras TOVBINA, 1962; Deshayesites KAZANSKY, 1914; Paradeshayesites KEMPER, 1967; Obsoleticeras BOGDANOVA & MIKHAILOVA, 1999; Dufrenoyia KILIAN & REBOUL, 1915; Burckhardtites HUMPHREY, 1949, Neodeshayesites CASEY, 1964; diagnoses of known species are given and three new species are erected: Turkmeniceras tovbinae sp. nov., Deshayesites caseyi sp. nov. and D. kemperi sp. nov.
Correlation of the main sedimentary, biological and geochemical signals observed within the historical lower Aptian stratotype in the Cassis-La Bédoule area leads to discern and to calibrate several significant breaks or discontinuities. The "Taxy", "Roch" (Barremian-Aptian boundary) and "Toucas" levels, the Δ2 major discontinuity (lower/upper Bedoulian boundary), and bench-mark beds 158 and 170, all stratigraphically well-defined in the stratotype, can be recognized at least regionally (SE France). Conversely, some worldwide events as the "Nannoconus crisis" or the OAE1a anoxic event, as well as the paleontological Bedoulian-Gargasian boundary, are either poorly expressed or even not recorded in the stratotype. Sequence stratigraphy surfaces and boundaries from the recently published global chart (HARDENBOL et al., 1998) are also difficult to correlate with the integrated stratigraphy established in the stratotype. From a biostratigraphic point of view, the Barremian-Aptian boundary is precisely marked by the first appearance of the ammonite genus Deshayesites, whose different species (D. tuarkyricus, D. weissi, D. deshayesi), with the addition of another deshayesitid (Dufrenova furcata) are used as index of a biozonation better conform to the Mediterranean standard. The upper Bedoulian only is clearly characterized by significant foraminiferal changes, with the successive appearance of several planktonic markers among which Blowiella blowi and Schackoina (Leupoldina) cabri, whereas any important foraminiferal change is observed at the Bedoulian-Gargasian boundary. By contrast the first occurrence of the calcareous nannofossil species Hayesites irregularis coincides with the Barremian-Aptian boundary, that of Rhagodiscus angustus with the lower/upper Bedoulian boundary and that of Eprolithus floralis with the basal part of the D. furcata zone. The dinoflagellate bio-events occur within the main ammonite biozones, with of particular interest the first occurrence of Tehamadinium tenuiceras, regarded as a significant datum at the European scale and here calibrated within the D. furcata zone.
On the basis of recent investigations, the ammonite inventory of the upper Barremian/lower Aptian beds in the historical stratotype area of La Bédoule leads to confirm that the Bedoulian substage (and thus the Aptian stage) lower boundary is determined by the first appearance of the genus Deshayesites. The Bedoulian/Gargasian boundary is drawn at the top of the Dufrenoya furcata zone (= Dufrenoya spp./Tropaeum bowerbancki zone sensu CONTE, 1994). The ammonitic content of the stratotype leads also to a subdivision which conforms better to most of the recently proposed Mediterranean zones and permits to partly correlate the standard zonation with that of the Boreal realm.
The morphostructural main features of the Balkanides and the evolution of the ideas on this alpine chain are firstly recalled. Then the most important stages are described: the structural units due to the Austrian phase (during the Albian) are obliterated by the Illyrian movements (later Mid-Eocene), at the origin of the present tectonic zones, that are briefly described. Finally, the Neogene to Quaternary phases are marked by various activities of the lineaments systems. The Rhodope zone, which is especially interpreted, reveals a pile of thick, nappes. The Balkanides arc is considered as a subduction-collision belt, marked by the sinking of the Arabia-Africa plate beneath the Eurasia one. -from English summary
The Early Aptian is marked by an event of widespread anoxia in the oceans, known as Oceanic Anoxic Event (OAE)1a. During this time the Lower Saxony Basin (LSB), constituting the southern extension of the Boreal-Arctic Sea, was affected by the deposition of finely laminated black shales
of the Fischschiefer (FS) considered to be the product of OAE 1a. This study focuses on Upper Barremian – Lower Aptian sediments from three different localities in northern Germany encompassing the FS. The proposed integrated litho-, bio-, and chemo-stratigraphy provides an accurate
time control for correlation and for detecting the timing of the processes that affected the LSB during the deposition of the FS. The paleoecological and paleoclimatic reconstructions based on calcareous nannofossils indicate that sedimentation during the Late Barremian was mostly depending
on regional conditions related to the paleogeography of the LSB. The deposition of the FS was instead mainly driven by mechanisms operating on a global scale and associated to OAE 1a: a warming event, also detected at low latitudes, was accompanied by high primary productivity and influx of
cosmopolitan taxa through new seaways opened to the Tethys. In the late Early Aptian local factors prevailed again on sedimentation although paralleled by a decrease in temperature documented at different latitudes which probably favoured the migration of Boreal species southwards.
A description is given of three new ammonite species: Matheronites brevicostatus, Turkrneniceras rarecostatum and T. tumidum from the top of the Tuarkyr and Malyy Balkhan Bar-remian. Ontogenetic studies have established that the initial whorls of Turkrneniceras were evolute to differing degrees and that there was a loosely coiled first whorl in members of the genus Math eronites. On the basis of the similarity between Matheronites and Crioceratites the family Hemi-hoplitidae has been placed in the superfamily Ancylocerataceae rather than in the Berriasellaceae. The upper horizons of the Barremian of Turkmenia contain a distinctive assemblage of ammo nites, the generic and specific composition of which was until recently practically unknown in the literature. Luppov (1936) described a number of species of ammonites from the Tuarkyr Barre mian, one of which, Matheronites turkmenicus Luppov, most probably originated from the top of the Barremian beds. Later, Tovbina (1963) described the new genus Turkrneniceras with three new species, T. turkmenicum, T. ge,pkderense and T. multicostatum. It has now been established that members of the genera Matheronites and Turkrneniceras are found together and characterize a definite part of the Upper Barremian beds which was initially dis tinguished as a Turkrneniceras turkmenicum horizon (Tovbina, 1963) and subsequently as a zone of the same name. The distinctive ammonite composition of this zone complicates comparison of this part of the profile with profiles of other regions. However, fragments of Matheronites ridzewskyi Karakasch found in the Bol'shoy Balkhan and Tuarkyr in these beds enable us to compare them with the part of the Lower Cretaceous of the Caucasus which is distinguished as a zone of Matheronites ridzewskyi, Tropaeum hillsi and Imerites densecostatus throughout the entire Greater Caucasus (Rcnngarten, 1951) or as a zone of Matheronites ridzewskyi and Acrioceras furcatum in Dagestan (Mordvilko, 1960, 1962; Drushits, 1963; Drushits and Mikhaylova, 1966) and as the corresponding Tropaeum hillsi zone in the North Caucasus (Mordvilko, 1960, 1962). These deposits are repre sented throughout the greater part of the territory by a thin band of phosphoritic sandstone contain ing fossils of different ages (Renngarten, 1931, 1946', 1947, 1961; Mordvilko, 1960, 1962; Drushits, 1963; Drushits and Mikhaylova, 1966). It is very difficult to distinguish an assemblage of fossils characteristic of only this zone. In the fullest Dagestanian profile (Akusha region), where the thick ness of the zone reaches several tens of meters, according to the data of I. A. Mikhaylova, V. V. Drushits and T. A. Mordvilko, the zona] ammonites are confined to its uppermost part and the over lying layers contain remains of Deshayesites. Elsewhere some beds containing Deshayesites rest disconformably on beds containing Colchidites ellipticus and C. rotundus in a number of profiles of the North Caucasus (near the town of Kislovodsk and in the Kuban' valley) (Drushits, 1963). In the correlation of profiles of Dagestan, the North Caucasus and other regions of the Caucasus, this zone of Deshayesites may evidently be regarded as a separate stratigraphic subdivision lying above layers containing Colchidites. Such a sequence of stratigraphic horizons is fully comparable to the ammo nite horizons of Turkmenia where deposits containing Turkrneniceras turkmenicum occur between layers containing Colchidites nicortsmindensis and Deshayesites.