Albian Research Articles

Uppermost Jurassic to Lower Cretaceous benthic foraminiferal faunas of the Weimei and the Bandingsi localities of northern and southern parts of South Tibet – A preliminary analysis

Diverse foraminiferal assemblages from the Weimei–Gyabula, and the Menkadun–Gucuo formations have been recorded based on the study of two Upper Jurassic to Lower Cretaceous successions, respectively located in the northern and southern parts of South Tibet. Each section contains three different foraminiferal assemblages. Due to the poor state of preservation and the occurrence of long-ranged cosmopolitan species, these foraminiferal assemblages do not allow a precise age assignment for the fossil bearing strata. However, the identification of the Globulina prisca assemblage indicates a Cretaceous age for the Shale Unit of the Gucuo Formation, although the Jurassic/Cretaceous (J/K) boundary was traditionally delineated above this unit. On the other hand, the occurrence of Dorothia oxycona indicates that the uppermost Gyabula and Gucuo formations cannot be older than Aptian and middle Albian age, respectively.During the Late Jurassic to Early Cretaceous, the northern part of South Tibet was located in a deep marine environment, probably at bathyal to abyssal depths, whereas the southern part of South Tibet was part of the outer neritic shelf environment. Typical foraminiferal associations of mildly oxygen-deficient deep-water environment and increased surface productivity have been recorded during the late Early Cretaceous. The biofacies succession indicates that the late Early Cretaceous was associated with a deepening of the palaeobasin, probably associated with a global Albian transgression.

Reappraisal of the latest Albian (Mortoniceras fallax Zone) cephalopod fauna from the classical Salazac locality (Gard, southeastern France)

The Salazac locality (Gard, southeastern France) is renowned for the richness of its cephalopod fauna (especially ammonites) from the Mortoniceras fallax Zone (uppermost Albian, Lower Cretaceous). However, most ammonite species have paradoxically been scarcely illustrated up to now. Furthermore, the rare assessments of ammonite taxonomic diversity are presumably inaccurate, as they either result from a drastic typological approach or could not benefit from the most recent advances in modern concepts of ammonoid intraspecific and ontogenetic variations. In this work, we document an original cephalopod assemblage from Salazac represented by abundant, well-preserved specimens (564 studied ammonites, including ca. 50% of heteromorphs) constituting a high diversity. The sample size and quality of this new material allowed some extensive morphological and biometric analyses whenever possible (i.e., for subdatasets in which a significant number of measurements is available) and to thoroughly assess intraspecific and ontogenetic variations for a few species. This led to determine the diagnostic value of various shell characters commonly used to characterize both well-documented and poorly-defined species. In particular, we show that a significant part of the variation in the number of ribs per whorl within the heteromorphic genera Mariella and Turrilitoides is directly related to shell size and that the strength of tubercles covaries negatively with the number of ribs in Mariella, therefore challenging the diagnostic value of these characters. We further suggest that rib density covaries with whorl shape in Mariella, following Buckman’s first rule of covariation. In total, one species of nautilid and 38 taxa (25 genera) of ammonites are described, among which five species are documented from Salazac for the first time. In turn, this study provides valuable data for future phylogenetic, biostratigraphical, biogeographical and broad-scale diversity studies.

The Iorokhan Complex of Minor Intrusions in the Eastern Part of the Bureya Massif: Geology, Age, and Gold Mineralization

We analyze and generalize new data inferred from the geological, geochronological, and metallogenic studies performed in recent decades on igneous rocks of the Iorokhan gold-bearing complex in the eastern Bureya Massif. It is shown that four phases are determinative of the structure of the Iorokhan complex of minor intrusions whose rocks are referred to hypabyssal and subvolcanic intrusive facies. Specific features of their rock composition and structural tectonic conditions of localization are described and geological and geochronological (103 ± 1.0-97.4 ± 6.5 Ma) data on their Late Albian–Early Cenomanian age are presented. Based on the alumina, calcium, and alkali ratio, the major part of their compositions corresponds to the I-type (A/CNK < 1.1) high-alumina magnesia and magnesia–ferruginous varieties with decreased HFSE concentrations, including HREE. Melts formed due to amphibolite source melting might have been the deep sources of the Iorokhan diorites. The Noni deposit is briefly described and the main localization factors of the gold-ore mineralization are considered. The Iorokhan magmatite areals of the East Bureya Volcano–Plutonic Zone may be considered as one of the fragments of the structure bordering between the continental margin of the Bureya Massif and the accretionary prisms of the Sikhote Alin Orogenic Belt. The Iorokhan complex of minor intrusions is assumed to be a small fragment of an extensive band of Late Albian–Early Cenomanian magmatites developed in southern Far East Russia that originated under the transform continental marginal setting, and a combination of synstrike–slip compression and extension zones typical of such margins with further development of the pull-apart depressions.

ИОРОХАНСКИЙ КОМПЛЕКС МАЛЫХ ИНТРУЗИЙ ВОСТОЧНОЙ ЧАСТИ БУРЕИНСКОГО МАССИВА: ГЕОЛОГИЯ, ВОЗРАСТ, ЗОЛОТОНОСНОСТЬ

In this paper we analyze and summarize some recently acquired data coupled with the findings of previous geological, geochronological and metallogenic studies on igneous rocks of the Iorokhan gold-bearing complex in the eastern part of the Bureya massif. Four phases, whose rocks are of hypabyssal and subvolcanic intrusive facies, are shown to define the structure of the Iorokhan complex of minor intrusions; characteristic features of their composition and structural and tectonic settings of localization are given; geological and geochronological data are reported on their age (103 ± 1.0–97.4 ± 6.5 Ma), i.e. late Albian–early Cenomanian. By the ratio of alumina, calcium and alkalis, most of their compositions correspond to I-type high-alumina magnesia and magnesia-ferruginous varieties (A/CNK &lt; 1.1) with low concentrations of HFSE, including HREE. Melting of an amphibolitic source rock produced a melt that could be a deep source of the Iorokhan diorites. A brief description of the Noni deposit is given and the main factors contributing to the localization of gold mineralization are considered. The ranges of the Iorokhan magmatites in the East Bureya volcano-plutonic zone can be considered as one of the fragments of the boundary structure between the continental margin of the eastern part of the Bureya massif and the accretionary wedges of the Sikhote-Alin orogenic belt. The Iorokhan complex of minor intrusions is assumed to be a small fragment of the wide belt of Late Albian–Early Cenomanian magmatite occurrence in the southern Far East of Russia, which formed in a setting of transform continental margin and zones of compression associated with extension resulting in the development of pull-apart basins typical of such margins.

New Data on Stratigraphy and Distributions of Glendonites from the Carolinefjellet Formation (Middle Aptian\u2013Lower Albian, Cretaceous), Western Spitsbergen

The Aptian deposits on Spitsbergen Island are poorly studied. Moreover, there were no published data on fossil distribution in the Aptian and Albian in the vicinity of the town of Longyearbyen. This article provides new data on ammonite-based biostratigraphy of the Carolinefjellet Formation, indicating the presence of Beds with Tropaeum arcticum (middle Aptian) and Beds with Grantziceras (lower Albian). The age of the formation was verified and the presence of lower Albian strata was justified. The results of microscopic and isotope studies of five samples of glendonites collected from the middle Aptian of the Carolinefjellet Formation section are presented. Glendonites from the Carolinefjellet Formation are composed of three calcite phases: ikaite-derived calcite and two successive types of cement, which fill cavities and develop partially after the first-phase calcite. The O and C isotope compositions of glendonites were measured in five bulk samples from the middle Aptian interval of the section. The δ18O isotope composition of glendonites is significantly different from that of seawater, indicating the input of diagenetic fluids; the δ13C values are characteristic of sedimentary organic matter and methanotrophy. For the first time, findings of ammonites allowed us to clarify the stratigraphic intervals of glendonite occurrence and associated cold-climate episodes and prove the early Albian age of glendonites from the top of the Carolinefjellet Formation.

Angiosperm diversification in the Early Cretaceous of Primorye, Far East of Russia

The Partizansk and Razdolnaya coal basins of Primorye, Far East of Russia, contain diverse early angiosperm fossils (pollen, leaves, and fruits). In this paper, we revise the previous data on early angiosperms of this region and summarize the results of our latest research. Age of the plant-bearing deposits was clarified using isotopic U-Th-Pb LA-ICP-MS and U-Pb ID-TIMS methods. Age of the upper part of the Lipovtsy Formation is 118 ± 1.4 Ma, which corresponds to the late Aptian. The early Albian age (109 ± 1 Ma) is assigned to the upper part of the Frentsevka Formation. The diversification of angiosperms in the Early Cretaceous of Primorye region and their systematic affinity are analyzed. Early representatives of Laurales, Ranunculales, Platanaceae, and probable Cercidiphyllaceae are revealed. New combination Pandanites ahnertii (Krysht.) Golovn., comb. nov. is created, and new species Araliaephyllum vittenburgii Golovn. et Volynets, sp. nov. is described. Reconstructions of herbaceous angiosperms from autochthonous locality Bolshoy Kuvshin are proposed.

Sedimentological and Biological indicators of oceanic anoxic events (1d) inside upper Balambo Formation, L. Albian, northeastern Iraq

The studydeals with succession from the upper part of the Late Albian Balambo Formation which are composed of fine-grained dark gray to black calcareous shale, limestone and marly limestone rich in sedimentary structures such as lamination, fissility and platy structures. Microfacies analysis revealed that mudstone, wackstone and few of packstone are the main facies in the studied succession. The studied rocks generally are rich in organic matter and pyrite in addition to dominance of radiolaria, sponge spicules and foraminifera with elongated champers maybe “Schackoina” genus. All these characters indicate deposition in marine conditions with reduced or absent-oxygen condition that relate to oceanic anoxic event (1d).

Palaeoecology and facies analysis of benthic communities in mid-Cretaceous successions in the Sinai platform, Egypt

Within the Aptian-Cenomanian formations of Sinai successions in Egypt, lateral and vertical changes occur in the numerous benthic communities. Microbenthos such as Orbitolina foraminifera and calcareous algae are widespread in the Aptian-Albian deposits in North Sinai, whereas oysters and gastropods are common in the Cenomanian siliciclastic deposits in South Sinai. In order to establish the biostratigraphy, 90 benthic and planktonic foraminifera species have been identified from the studied succession. Based on the stratigraphic distribution of the identified species the studied succession could be subdivided into three planktonic foraminiferal zones: Pseudothalmanninella ticinensis zone (Late Albian), Rotalipora cushmani zone (Middle-Late Cenomanian), and Whiteinella archaeocretacea zone (Late Cenomanian-Early Turonian). This work discusses the first record of the Albian dasycladalean alga Holosporella sugdeni (Elliott) from Sinai and reports on Montiella elitzae (Bakalova) from the Albian Risan Aneiza Formation. The occurrence of Orbitolina (Conicorbitolina) conica distinguished the Albian-Cenomanian boundary in the North Sinai sequences. The benthic communities of the studied successions indicated a faunal shift from an algal-orbitolinid foraminifera community around the Aptian-Early Albian to a rudist community during the Middle Albian and an oyster-gastropod community during the Cenomanian. This faunal shift coincided with the major sea transgression that covered North Sinai until the Middle Albian and reached South Sinai during the Cenomanian. The identified Cenomanian gastropods included Neoptyxis olisiponensis, Nerinea gemmifera, and Tylostoma bussoni. Many oyster species distinguished the Cenomanian deposits, such as Ceratostreon flabellatum, Rhynchostreon mermeti, Rhynchostreon suborbiculatum, and Costagyra olisiponensis. Identifying the benthic fauna and facies indicated a shallow inner to middle ramp environment. Stable carbon and oxygen isotope data from the Cenomanian oyster shells indicate an inner ramp environment. Comparing the carbon isotope values of the oysters with those previously recorded from the rudists may explain the different trophic levels of both groups.

Aptian–Albian deposits of the Ait Ourir basin (High Atlas, Morocco): New additional data on their paleoenvironment, sedimentology, and palaeogeography

AbstractThis sedimentological and palaeontological analysis of the Aptian–Albian sedimentary succession of the Ait Ourir basin in the High Atlas Mountains of Marrakesh in Morocco provides new data from a previously poorly understood basin. The palaeoenvironmental evolution is deduced based on a facies analysis allowing the restoring of depositional environments and their stratigraphic architecture. Within the Aptian–Albian succession, we distinguish two sedimentary sequences separated by a major discontinuity. The first sequence is composed of calcareous and dolomitic marls with the rudistPseudotoucasia catalaunicaof the Tadhart formation (upper Aptian in age) and of strongly dolomitized limestones with corals (Eugyrasp.,Thalamocaeniopsissp., andHolocystissp.) of the Lemgo formation (uppermost Aptian in age). These two formations were formed in an internal carbonate platform (the intertidal zone to the subtidal zone). The second sequence, Albian in age, is composed of sandy limestones of the Oued Tidzi formation and is represented by sediments showing terrigenous influence, with deposits of silt, sandstone, dolomitic sandstone, and limestone.

Sequences, discontinuities and water stratification in a low-energy ramp: the Early Albian sedimentation in central Tunisia

Based on a precise biostratigraphic framework stated previously, the detailed sedimentological study of eight sections of the early Albian succession of Central Tunisia made possible to refine the modalities of the Albian transgression and the related behavior of sedimentary system on the Tunisian margin. Major early Albian transgressive pulses occurred (i) at the base of the L. tardefurcata standard ammonite zone, (ii) around the top of the same zone, (iii) during the D. mammillatum standard zone, and (iv) near the top of the latter ammonite zone. They resulted in the progressive flooding of the Tunisian margin emergent since the Aptian boundary, in the disappearance of emergence evidences through time, in the southward backstepping of the carbonate shelf facies, and eventually in the homogeneization of the outer shelf marly sedimentation in the study area. The low energy of deposition of the early Albian sediments in this part of the South-Tethyan margin may be due to the deflection of winds and storms by the Coriolis forces toward the North-Tethyan margin, creating a clockwise gyre in this part of the ocean. This circulation may have enhanced upwelling currents likely responsible for phosphate mineralization, and for the oxygen depletion of deep waters, which progressively invaded the Tunisian margin, giving way to organic-rich deposits of late early Albian age. The early Albian sedimentation is then interrupted by a major hiatus of middle Albian to early late Albian age.

Methane-derived carbonate formation triggered by the latest Albian anoxia in northwestern Tunisia basins

The late Albian exposures of northwestern Tunisia include authigenic carbonates typified by soft-sediment deformation (slumps) and doughnut-shaped concretions. Planktic foraminiferal biostratigraphy indicates a late Albian age (buxtorfi subzone). The carbonate bodies display veins and fractures partially filled with impsonite (bitumen). The microfacies analysis revealed multiple generations of fibrous and sparry calcite cements, pyrite, and clotted pelmicrite. Scanning electron microscope (SEM) analysis performed on clotted micrite shows the presence of pyrite spheroids and micrometer-sized calcified filamentous structures attributed to anaerobic methanotrophs. Depleted values of δ13C (ranging between − 36.88 and − 11.63‰ PDB) for these carbonates, suggested a thermogenic methane-derived carbon source with a contribution of crude oil to the carbon pool. The petrography and stable isotopes data provide unequivocal evidence that these carbonates are cold seeps–related. The cold seep features indicate that microbial communities have used ascending hydrocarbons and methane fluids and contributed to the precipitation of authigenic carbonates. The paleotemperature calculated from oxygen isotopes of early diagenetic micrite is indicative of parent fluids warmer (68 °C) than those of late Albian seawaters (~ 27 °C). We suggest that hydrothermal fluids linked to volcanic intrusions in the organic-rich lower Fahdene Formation beds may have triggered the release of thermogenic methane flux as cold seeps in the sedimentary basin. The accumulation of methane with other released gases in the water column is triggered by anoxic and stagnant water masses. The sluggish methane flux associated with the upwelling of deep anoxic waters contributes to the carbonate precipitation and the projection of carbonate bodies (e.g., chimney-like shape), induced by microbially mediated anaerobic oxidation of methane.

&lt;p&gt;&lt;strong&gt;New eremoneuran flies (Diptera: Eremoneura) from Cretaceous Charentese amber&lt;/strong&gt;&lt;/p&gt;

A new genus and two new species of Eremoneura are described from mid-Cretaceous amber of the Charentes region, in south-western France. Chimeromyia vulloi sp. nov., from early Cenomanian amber of Fouras, is the first record of Chimeromyiidae from France. It extends the geographical distribution of this family, which was hitherto known only from Cretaceous ambers of Lebanon, Spain, and Myanmar. A key to all known species of Chimeromyia is provided. Additionally, a specimen from latest Albian–earliest Cenomanian amber from Archingeay, which was studied using synchrotron imaging, is described as Francomyina incomparabilis gen. et sp. nov., and is left unassigned to family within Eremoneura. The affinities of both new species are discussed.

Sequence stratigraphy study of the Dariyan Formation in the Gadvan and Zana sections in the northeast and northwest of Shiraz, Zagros Basin, SW Iran

In the present paper, sequence stratigraphy and microfacies of the Dariyan Formation in the two sections of the Gadvan and Zana Mountains located were studied in NE and NW of Shiraz (Fars province, SW Iran). An area of 429.5 m of the Dariyan Formation sediments was studied through 187 thin sections. Also, the index microfacies were closely identified. Generally, index microfacies of the studied thin section were mudstone, wackestone, packstone, and grainstone microfacies. Received paleontological data confirm Aptian–lower Albian age of the Dariyan Formation. According to the lithostratigraphic aspect, the lower contact of Dariyan Formation with the Gadvan Formation in the Gadvan Mountain was described as a gradual type and in Zana Mountain; disconformity was found due to the sign of water withdrawal. Given the upper contact of the Dariyan Formation concerning the formation percentage, contact disconformity was observed due to the changes in the Allochem element and the situation of the entity from water and also according to the high percentage of iron nodules and Gluconate. According to the sequence, stratigraphic studies in the section of Gadvan Mountain, the lower border of the Dariyan Formation with Gadvan Formation was in the gradual form [type 2 Sequence Boundary (SB2)] and there was a disconformity in the upper border of this formation with Kazhdumi Formation [type 1 Sequence Boundary (SB1)]. Dariyan Formation included the system tracts (transgressive system tract, early highstand system tract, and late highstand system tract). There was a disconformity in its lower of the Gadvan Formation and disconformity in its upper boundary with the lower of the part Kazhdumi Formation (SB1) and it included the system tracts (highstand system tract, transgressive system tract, and lowstand system tract). Overall, lap sequence grade3 was seen in the two sections.

Interpreting character variation in turtles: Araripemys barretoi (Pleurodira: Pelomedusoides) from the Araripe Basin, Early Cretaceous of Northeastern Brazil.

The Araripe Basin (Northeastern Brazil) has yielded a rich Cretaceous fossil fauna of both vertebrates and invertebrates found mainly in the Crato and Romualdo Formations, of Aptian and Albian ages respectively. Among the vertebrates, the turtles were found to be quite diverse, with several specimens retrieved and five valid species described to this date for the Romualdo Formation. There were also records of turtles from Ipubi and Crato Formations, mainly fragmentary material which precluded proper specific identification; however, Araripemys barretoi is supposed to occur on both Crato and Romualdo Formations. Here we describe thirteen specimens of A. barretoi-including the first description of an almost complete individual, bearing a skull, from the Crato Formation. We report a great amount of morphological variation, interpreted as being essentially of intraspecific nature, including individual, sexual and ontogenetic variation.

A stagodontid mammal from the mid-Cretaceous of France confirms the Euramerican distribution of early marsupialiforms

The global palaeobiogeography of early marsupialiform mammals is still poorly understood due to a meagre fossil record outside western North America. Here, two isolated teeth of a marsupialiform mammal from the lowermost Upper Cretaceous (lower Cenomanian) of southwestern France are described and referred to Stagodontidae, a dentally specialized group whose unambiguous members are so far known exclusively from the Upper Cretaceous of North America. The occurrence of stagodontids in Europe represents additional evidence of faunal exchanges between the two landmasses during the latest Albian–early Cenomanian interval, around 100 million years ago, and shows that early (mid-Cretaceous) marsupialiforms were more widely distributed than previously thought.

The first Cretaceous megaspores from Ukraine

The first megaspores recovered from Ukrainian Lower Cretaceous strata are described and illustrated by reflected light and scanning electron micrography. Four lycopsid megaspore taxa are identified in core samples from north of Kherson (Khersons'ka Oblast), in the Black Sea Basin, southern Ukraine. Miospore assemblages recovered from the same samples reveal a slightly higher diversity of lycopsid microspores and, in conjunction with previous foraminiferal biostratigraphy, indicate an Aptian–Albian age for the strata. The megaspore suite shares genera with mid-Mesozoic assemblages from widely distributed parts of the world, but most of the Ukrainian specimens have subtle morphological differences from congeneric forms established in other regions. The megaspores accumulated in fluvial floodplain facies and highlight the potential of this region for investigating other Cretaceous mesofossils including early flowers.

Major and trace element characterization of Oceanic Anoxic Event 1d (OAE 1d): Insight from the Umbria-Marche Basin, central Italy

The Pialli Level in the Umbria-Marche Basin (central Italy) correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late Albian–early Cenomanian Oceanic Anoxic Event 1d (OAE 1d). High-resolution litho-, bio- and chemostratigraphic data from the Monte Petrano and Le Brecce sections allow for a bed-by-bed comparison of the two successions, and discriminate local from basin-scale signals. We present new X-ray fluorescence, ICP-MS and TOC data for both the limestones and the Pialli Level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices. Data indicate a homogenous background sedimentation dominated by pelagic carbonates, biogenic silica with little contribution by clays. The limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input. Higher Mn concentrations coupled with low enrichments in redox-sensitive elements, such as U, Fe, S, Re, Mo, Ag, suggest that the Pialli Level shales represent temporary suboxia without reaching anoxia. Furthermore, P, authigenic Ba, Cd and Ni enrichments, together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession, with only minor increases for some of the black-to-dark grey shales of the Pialli Level. The nannofossil temperature index highlights a warm climate during the OAE 1d, with the warmest conditions experienced during the deposition of the Pialli Level shales. During the late Albian, the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions. Such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late Albian interval in the Umbria-Marche Basin. As such, the Pialli Level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early Cenomanian.

Elasmobranch (Chondrichthyes) assemblages from the Albian (Lower Cretaceous) of Ukraine

Sampling of six horizons of quartz-glauconite sands in Kaniv dislocations in Ukraine yielded more than three thousand vertebrate specimens, including elasmobranch teeth, chimaera dental plates, actinopterygian and sauropsid teeth and bones. Our study represents the first illustrated and detailed description of elasmobranch teeth from Ukrainian Albian deposits since Rogovich (1861), whose specimens were still preserved in the collections of the Kiev National Natural History Museum of National Academy of Sciences of Ukraine. Twenty-three elasmobranch species belonging to eight orders were identified in our samplings and in some of Rogovich's material. This paper provides new data on the systematics of Cretaceous elasmobranchs and assesses the taxonomic status of Rogovich's species. Sampled assemblages include hybodonts, synechodontiforms, hexanchiforms, squaliforms, squatinifroms, orectolobiforms, heterodontiforms and lamniforms. The latter dominate the assemblages, both in terms of species and number of specimens with small odontaspidid species, early pseudoscapanorhynchids and archaeolamnids as well as large carnivorous sharks Cretoxyrhina and Cretolamna. Most importantly, Paraisurus macrorhizus and Cretoxyrhina vraconensis findings indicate a late Albian age for the sampled deposits, which were so far considered Albian–Cenomanian.

Quantification of a North American greenhouse hydrological cycle: using oxygen isotopic composition of phosphate from Early Cretaceous (Aptian–Albian) turtles

Quantification of a North American greenhouse hydrological cycle: using oxygen isotopic composition of phosphate from Early Cretaceous (Aptian–Albian) turtles

Ostracods as proxies for marginal marine to non-marine intervals in the mid-Cretaceous carbonate platform of the Central Tunisian Atlas (North Africa): Response to major short-term sea-level falls

Two non-marine to marginal-marine intervals have been identified by ostracod assemblages in the mid-Cretaceous carbonate platform of the Central Tunisian Atlas, the deposits of which belong to the Orbata Formation. The first non-marine interval has been recorded within member Unit 2b of the Orbata Formation which yielded the first lower Aptian ostracod fauna composed of Alicenula? leguminella, Vecticypris polita, Cypridea ventriosa, Perissocytheridea altesulcata sp. nov., Harbinia? cf. sinuata, Hourcqia aff. bateke, Ovocytheridea nuda, Bythocypris? pythagorasi sp. nov., Paracypris lusitanicus and Paracypris chekhmai sp. nov. The assemblages indicate continental to marginal-coastal environment and lower Aptian emergence of the Orbata Platform, and are interpreted as response to an earliest Aptian 3rd-order (0.5–3 myr) sea-level fall event of major amplitude. A second lowermost Albian ostracod fauna, recorded within members Unit 5b, 6 of the Orbata Formation, is composed of Candonopsis carthaginensis sp. nov., Cypridea quadrangulata, Virgatocypris kechoulaensis, Alicenula? leguminella, Vecticypris polita, Stenestroemia mosensis, Perissocytheridea kouminiensis sp. nov., Hourcqia aff. bateke, Dolocytheridea bosquetiana, Dolocytheridea donzei sp. nov., Ovocytheridea anterocompressa, Paracypris dubertreti, Paracypris mdaouerensis, Clithrocytheridea espichelensis, Bythocypris? multagracilis sp. nov. and Bythocypris dorsogibba sp. nov. The assemblages indicate another interval of non-marine to marginal-marine depositional settings as direct response to a prominent eustatic latest Aptian to earliest Albian sea-level fall event that enhanced the quasi-total emersion of the Central Tunisian Atlas palaeogeographic domain. Hence, the two studied faunas herein allow us to define two stratigraphic key surfaces of regional utility giving new insights into the chronostratigrahic subdivision of the Orbata carbonate platform, especially in supporting a previously neglected early Albian age of its upper part (Unit 5b, 6 and 7) and allow the regional stratigraphic correlation of these key surfaces in the Central Tunisian Atlas (CTA) domain. Accordingly, our results not only disprove the previous consideration of an uppermost Aptian–lower Albian hiatus but also implicate the necessity to redefine and review the previous palaeogeographic and tectono-sedimentary schemes of the CTA as suggested for almost fourty years.