Aptian Research Articles

Turtle and pterosaur tracks from the Los Cayos Dinosaur Tracksite, Cameros Basin (Cornago, La Rioja, Spain): tracking the Lower Cretaceous bio-diversity

New fossil turtle and pterosaurian tracks have been found at the Los Cayos locality (Cornago township, La Rioja province, Spain). The Los Cayos tracksite is situated in the Cameros Basin, ant it is included in the Enciso Group, which is late Barremian-Early Aptian in age (Lower Cretaceous). The turtle tracks are formed by parallel isolated digit impressions. Digits show acuminate distal ends and relatively blunt proximal margins. Most of the tracks show three digits, and only two of them are pentadactyl. No trackways can be observed but only different track alignments suggesting some kind of direction of movement. Two track-bearing layers have yielded 5 pterosaur manus prints. No pes footprints or trackways have been discovered at these outcrops yet. These prints are tridactyl, with digit I, the shortest, and III, the longest. The angles between the digits are variable: angle I-II is significantly bigger than between II-III. These tracks from Los Cayos were the first discovery of pterosaur tracks in the Enciso Group.

Early Cretaceous charophytes from south Dobrogea (Romania). Biostratigraphy and palaeobiogeography

Eleven boreholes and one outcrop of the Lower Cretaceous in South Dobrogea (south-eastern Romania) were sampled for charophytes. Twenty species are described and illustrated in two non-marine rock units, the Zăvoaia Member and the Gherghina Formation. The Zăvoaia Member contains a charophyte assemblage dominated by Feistiella bijuescensis, aff. Mesochara harrisii, Nodosoclavator bradleyi, Clavator bilateralis, and Clavator grovesii var. grovesii, indicating a Berriasian age. Other less abundant species include Feistiella sp., Latochara sp., Mesochara dobrogeica sp. nov., Globator maillardii var. nurrensis, Atopochara trivolvis var. micrandra, Clavator grovesii var. discordis, Hemiclavator adnatus, and Hemiclavator neimongolensis var. posticecaptus. The occurrence of G. maillardii var. nurrensis in this assemblage suggests late Berriasian age. The Gherghina Formation is dominated by the species Atopochara trivolvis var. triquetra and Clavator grovesii var. jiuquanensis. Other less abundant species include Sphaerochara andersonii, aff. Mesochara harrisii, Globator maillardii var. trochiliscoides, Globator maillardii var. biutricularis, Clavator harrisii var. reyi, and Clavator ampullaceus var. latibracteatus var. nov. This assemblage indicates a late Barremian–early Aptian age. This study sheds new light on the palaeobiogeographical distribution of Lower Cretaceous charophytes in the Tethyan realm. Well-known western European charophyte species such as F. bijuescensis, S. andersonii, G. maillardii var. trochiliscoides, H. adnatus, and H. neimongolensis var. posticecaptus are herein described for the first time in eastern Europe. Very significantly, this is the first report in Europe of the hitherto North American taxon C. bilateralis, while the species C. ampullaceus has previously been reported only from the Middle East and eastern Africa.

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.

New Protocytheridae and Mandocytheridae Ostracods from the Aptian of the Crimean Mountains

Two new Ostracoda species are described from Aptian sediments of the Crimean Mountains, Protocythere whatleyi Karpuk, sp. nov. (Protocytheridae Lyubimova, 1955) and Homocythere spinasphaerica Karpuk, sp. nov. (Mandocytheridae Grundel, 1969).

Osteohistology and microanatomy of a new specimen of Cearachelys placidoi (Testudines: Pleurodira) a side-necked turtle from the lower Cretaceous of Brazil.

Pelomedusoides had a recognised diverse Early Cretaceous fauna of turtles in Northeast Brazil. Within them, the bothremydid Cearachelys placidoi has a relatively abundant record. This diversity contrasts with the scarcity of osteohistological studies in this group. The relatively well-preserved shell of C. placidoi (UFRPE 5600), from the Aptian age of Araripe Basin, is studied here for the purpose of filling this gap. We performed the osteohistological description of the plastron of a new specimen of C. placidoi. Also, to conduct a comparative study, we carried out histological sections in bones of the recent chelid Phrynops sp. Our histological findings indicate similarities between the histological pattern of freshwater turtles and the coastal marine C. placidoi. Moreover, osteohistological features imply metaplastic incorporation of dermal interwoven structural fiber bundles. Lastly, the xiphiplastron of C. placidoi shows an increase of bone compactness over its craniocaudal axis. This microanatomical feature is exclusive to Cearachelys so far.

Influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the Lower Cretaceous Bayingebi Formation of the Yin’e Basin, China

The lacustrine black shales of the Lower Cretaceous Bayingebi Formation are an important hydrocarbon source rock in the Yin’e Basin. It is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the Early Cretaceous in northwestern China and search for potential oil and gas resources. Based on petrological, elemental geochemical and organic geochemistry analyses of typical field profile samples, the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units (Unit I, II and III) is revealed. Unit II has the highest total organic matter abundance (TOCavg = 5.95%), mainly type I kerogen (lamalginite), which is in the immature to low mature stage. Organic carbon isotope data (δ13Corg), element ratios (Sr/Cu and C-value) and weathering indexes (including CIA, CIW and PIA) together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the Early Cretaceous. The increase in rainfall in Unit II enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level, which contributed to adequate sources and favourable preservation conditions for organic matter accumulation. Several lines of evidence, including high sulfur contents, the combination of vein pyrite and micritic dolomite, positive Eu anomalies, and element geochemical correlations, confirm the existence of intermittent low–temperature white smoker–type hydrothermal activity. The decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid, which provided necessary nutrient elements for biological productivity. According to palaeontological and radioisotope dating data, it can be inferred that the black shales of the Bayingebi Formation are the product of the combined effect of global palaeotemperature rise in the early Aptian stage of the Early Cretaceous and intermittent low–temperature hydrothermal activity.

Chronostratigraphic constraints and paleoenvironmental interpretation of the Romualdo Formation (Santana Group, Araripe Basin, Northeastern Brazil) based on palynology

The Santana Group of the Araripe Basin is a major paleontological unit in Brazil, incorporating two important Cretaceous Konservat-Lagerstätten. The lower formations are Aptian, but the age of the uppermost Romualdo Formation has been extended into the Albian. The precise chronostratigraphic position of this upper unit is of considerable significance because the Romualdo Formation records the Cretaceous marine ingression into the interior of Northeastern Brazil, thus playing a significant role in understanding the paleogeography of Gondwana. The main objective of this paper is to establish the chronostratigraphy of the Romualdo Formation based on its most complete section in the Araripe Basin, by determining the occurrence of palynomorphs, in particular establishing the vertical range of the species Sergipea variverrucata, a guide fossil of the Aptian in Brazil. Based on the presence of S. variverrucata, the Romualdo Formation is almost entirely Aptian in age. The palynological assemblage confirms the presence of at least three intervals with marine palynomorphs (dinoflagellate cysts and foraminiferal linings); and a typical regressive pattern towards the top of the Romualdo Formation, evidenced by progressive increase in inaperturate pollen grains (Araucariacites, Uesuguipollçenites and Inaperturopollenites). The palynological data presented herein indicate that the entire Santana Group is of Aptian age because of the conspicuous presence of Sergipea variverrucata and the absence of indisputably Albian forms. Precise dating of the Romualdo Formation signifies that the marine transgression into the interior of northeastern Brazil occurred in the late Aptian, thereby enabling correlation with the sedimentary events recorded in the Brazilian marginal basins.

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

Stratigraphy, detrital zircon geochronology and provenance of the Morita formation (Bisbee Group) in northeastern Sonora, Mexico

The Morita Formation is a Lower Cretaceous unit of the Bisbee Group that crops out in northern Sonora and southeastern Arizona where it was deposited within the Altar-Cucurpe, and Huachuca sub-basins of the Bisbee basin, respectively. In northern Sonora it either overlies strata of the Upper Jurassic Cucurpe Formation, the Glance Conglomerate, or strata of the Lower Cretaceous Cerro de Oro/Rancho La Colgada formations, and it grades upward into the Mural Limestone. In this contribution we characterize the stratigraphy, petrography and detrital zircon geochronology of the Morita Formation along a ca. 60 km-long northwest-southeast transect that includes the complete columns of the Mule Mountains in southeastern Arizona and the sierras San José, Anibacachi and Rancho Búfalo area in northeastern Sonora. Thickness of these sections varies from a minimum of 555 m in Sierra Anibacachi to a maximum of 855 m in Rancho Búfalo. In most sections, the lower half of the Morita consists of reddish siltstone and mudstone with pedogenic calcareous nodules with interbeds of mostly single-storey sandstone bodies, which changes to isolated multi-storey sandstone bodies in its upper half. In contrast, the lower part of the Rancho Búfalo column consists of reddish mudstone/siltstone with isolated, fining-upward, clast-supported, fine-pebble conglomerate beds that grades into reddish to purple, brown and green mudstone/siltstone with isolated, single-storey to multi-storey sandstone beds of its upper part. Lithofacies association in the Morita Formation suggest it is of fluvial origin but ichnofossils and local herringbone- and flaser-cross bedding in its upper part indicate intermitent marginal marine sedimentation preceding the transgression that deposited the overlying Mural shelf.Sandstone composition of the Mule and San José mountains is dominantly feldspatho-quartzose indicating dominant provenance from basement uplift and transitional continental areas, while composition at Sierra Anibacachi and Rancho Búfalo ranges from feldspatho litho-quartzose to litho-quartzose, indicating provenance from recycled orogen. Detrital zircon grains dated from samples of all the studied sections share very similar populations of Proterozoic to Mesozoic ages, but the Mesoproteozoic and Triassic grains compose ca. 64% of the total grains. Detrital zircon grains of Lower Cretaceous age that are only present in samples from the bottom of the Mule and San José Mountains help to constrain a maximum depositional age of 125.5 ± 0.8 Ma for inception of sedimentation of the Morita Formation in this region. According to this age and to observed stratigraphic relationships, we interpret that the lower contact of the Morita Formation is a disconformity with the underlying Glance Conglomerate, or with the Cerro de Oro Formation in northeastern Sonora. Similarly, according to regional stratigraphic relationships and age data known from the Cucurpe-Tuape region, in north-central Sonora, the age of this unit may be constrained to the Aptian stage, in Sonora, from ca. 125 to 115 Ma. Regional isopach curves confirm merging of the sub-basins in northeastern Sonora, continuous sedimentation of the Morita Formation, and presence of the Cananea high separating them.

The ‘coprolite’ bearing Woburn Sands Formation, Lower Greensand Group (Aptian) at Upware, Cambridgeshire, UK

Upware, about 15 km north of Cambridge, eastern England, was heavily involved in the ‘Coprolite’ Industry during the 19th century. Rich phosphate deposits especially at the base of the Lower Greensand (Early Cretaceous) were dug by hand and after processing supplied the Victorian agricultural industry with fertiliser. They were also a source of abundant reworked and indigenous fossils which feature in the original accounts and descriptions of the geology and palaeontology of the area including those in the classic award-winning Sedgwick Prize essays of Harris Teall in 1873 and Walter Keeping in 1879. Today, however, there are no permanent exposures of the Lower Greensand in the area. The sites of the original commercial excavations have been returned to agricultural land and traces of phosphatic lithoclasts and bioclasts may only be encountered in ploughed fields and the debris from animal burrows. In 2015 temporary trenches were dug by the authors in the base of the Lower Greensand Group, Woburn Sands Formation (Late Aptian). Much poorly bedded and phosphate depleted Woburn Sands was exposed which is attributed to backfilled ‘Coprolite’ workings. However, one site provided exposure of undisturbed Woburn Sands resting unconformably upon the Upware Limestone Member, West Walton Formation (mid-Oxfordian, Late Jurassic) and the feather edge of the Ampthill Clay Formation (mid-Late Oxfordian). The sand contains rich concentrations of reworked phosphatised fossiliferous concretions of original Jurassic-Cretaceous boundary to mid-Aptian age and indigenous calcitic fossils, of Late Aptian age. This is the first time that in situ Woburn Sands have been exposed in the Upware area since the time of the coprolite workings and are documented photographically for the first time. A detailed stratigraphic succession has been recorded and new geological and palaeontological collections have been made from accurately known levels at a precisely known site. New observations allow us to re-evaluate the early geological accounts and provide the opportunity to discuss more closely the relationships of the reworked faunas of Oxfordian to Aptian age, and in particular we draw attention to those faunas with affinities to the Jurassic-Cretaceous boundary deposits of the Spilsby Basin to the north. This work confirms the basic accuracy of Keeping’s earlier seminal account.

Palynological-age determination of Early Cretaceous vertebrate-bearing beds along the south Victorian coast of Australia, with implications for the spore-pollen biostratigraphy of the region

Palynology is used to provide new age controls for the coastal exposures yielding Early Cretaceous vertebrate faunas in the Otway and Gippsland basins, southeast Australia. This work shows all vertebrate-bearing deposits in the Otway Basin are Albian in age. On the eastern margin of Cape Otway, vertebrate-bearing deposits are attributed to the early Albian Crybelosporites striatus Zone, except for one in the younger Coptospora paradoxa Zone. To the west of Cape Otway, the sampled deposits range from the oldest zone in the Albian, the C. striatus Zone, to the C. paradoxa and Phimopollenites pannosus zones, providing a complete section of the Albian stage. In the Gippsland Basin, the structural setting of vertebrate deposits is more complicated and large portions of the coastal exposures consist of repeated sections controlled by small-scale faults. Sites in this region lie below or above the Barremian/Aptian boundary. However, owing to the paucity of age indicator species, some sampled deposits remain undated. In this basin, the ranges of certain key palynomorph species (e.g., Pilosisporites notensis and Pilosisporites parvispinosus) differed from those outlined in some previously published biostratigraphic schemes. The discovery of the angiosperm pollen Clavatipollenites hughesii in the lowermost Aptian deposits of the Gippsland Basin is consistent with its first occurrence elsewhere in Australia and shows it is a reliable indicator for the Aptian stage. This study shows that there is currently a collection bias towards vertebrate assemblages that are latest Barremian and early Albian in age.Barbara E. Wagstaff [wagstaff@unimelb.edu.au], The School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia; Stephen J. Gallagher [sjgall@unimelb.edu.au], The School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia; W. Michael Hall [mike.hall@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia; Vera A. Korasidis [korasidisv@si.edu], Smithsonian Institution, National Museum of Natural History, Department of Paleobiology, NHB121, 10th and Constitution Avenue, NW, Washington, DC20013-7012, USA; Thomas H. Rich [trich@museum.vic.gov.au], Melbourne Museum, 11 Nicholson Street, Carlton, Victoria 3053, Australia; Doris E. Seegets-Villiers [doris.seegets-villiers@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia; Patricia A. Vickers-Rich [pat.rich@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia and Swinburne University of Technology, Department of Chemistry and Biotechnology, Faculty of Science, Hawthorn, Victoria 3122, Australia.

Terrestrial and marine palynomorphs from deposits of the pull-apart rift of West Gondwana (Parnaíba Basin, northern Brazil): Biostratigraphy and relation to tectonic events

The thick, predominantly siliciclastic deposits of the Itapecuru Formation cover a large geographical area. Their deposition was controlled by strong tectonism in the rift stage of the Gondwana separation and by the evolution of the Atlantic Ocean, with the Cretaceous section of the Parnaíba Basin being related to the development of the Equatorial Segment. The age assignment for the Itapecuru Formation is based on the chronostratigraphic positioning of its exposed deposits along the Itapecuru River, in the eastern area of the Parnaíba Basin. Due to their high biostratigraphic resolution in both continental and marine sections, palynomorphs were chosen to accurately assess relative age. Palynofloras are mixed and dominated by terrestrial palynomorphs and aquatic plant spores, with rare marine and Paleozoic reworked palynomorphs. Based on species of biostratigraphic value recorded in the palynological assemblages, the Complicatisaccus cearensis Zone was characterized, thus attributing the upper Aptian age to the deposits. The stratigraphic ranges of Elaterosporites protensus, Elaterosporites verrucatus, Elaterosporites klaszi and Elaterosporites spp. small forms, Cavamonocolpites punctatus, Quadricolpites reticulatus and Elaterocolpites castelainii (A and B forms) are here extended, invalidating the definition of the boundary between the Complicatisaccus cearensis and Elateropollenites jardinei zones. These results allowed the correlation of the studied deposits with depositional sequences. The compositional variation and abundance of Afropollis, Araucariacites and elaterate complex in the palynofloras allowed their correlation with three palynofloristic provinces: Afropollis, Lower Cretaceous Dicheiropollis/Afropollis and Albian-Cenomanian Elaterates, suggesting a wet equatorial climate near the paleo equator.

From extension to tectonic inversion: Mid-Cretaceous onset of Andean-type orogeny in the Lhasa block and early topographic growth of Tibet

AbstractRecent studies have indicated that an Andean-type orogen (Lhasaplano) developed on the Lhasa block in the Cretaceous during northward subduction of Neo-Tethyan oceanic lithosphere. When and how uplift of the Lhasaplano began, however, has remained controversial. This article integrates stratigraphic, sedimentological, tectonic, and provenance data from the latest marine to nonmarine strata in the Linzhou Basin to pinpoint the early topographic growth in southern Tibet. The Takena Formation mainly consists of lagoonal carbonates and mudstones yielding foraminiferal assemblages of Early Aptian age (ca. 123–119.5 Ma). The conformably overlying lower member of the Shexing Formation, mainly deposited in fluvial environments, was fed by volcanic and sedimentary rock fragments from the north Lhasa terrane. Clasts of the Gangdese arc to the south firstly appeared in the middle member and became dominant in the upper member of the Shexing Formation. By contrast, coarse grained, braided river facies occur in the uppermost part of the Shexing Formation, where detritus was mostly recycled from Paleozoic strata of north Lhasa, with minor volcaniclastic contribution from the Gangdese arc. Basin analysis indicates accelerating subsidence and sedimentation rates during deposition of Takena to middle Shexing strata (ca. 125–108 Ma), followed by steady subsidence during deposition of upper Shexing strata (ca. 108–96 Ma). Given this regional tectonic and sedimentary evidence, such an evolution is interpreted to reflect tectonic extension followed by thermal subsidence. Basin inversion and regional compression initiated during deposition of the uppermost Shexing strata (ca. 96 Ma), as indicated by active thrust faults and widespread accumulation of syntectonic conglomerates in the western part of the Lhasa block. This event marked the beginning of the Andean-type orogeny in southern Tibet. Such a paleotectonic evolution, from extension to tectonic inversion, is also documented in the Andes mountain range. It may be typical of the early stage growth of Andean-type active continental margins.

Dinocyst stratigraphy of the Valanginian–Aptian Rurikfjellet and Helvetiafjellet formations on Spitsbergen, Arctic Norway

AbstractIn order to improve the understanding of how the high northern latitudes responded to the escalating warming which led to the middle Cretaceous super greenhouse climate, more temperature proxy records from the High Arctic are needed. One of the current obstacles in obtaining such records is poor age control on the Lower Cretaceous strata in the Boreal region. Here, we provide a biostratigraphic framework for the Rurikfjellet and Helvetiafjellet formations representing the lower part of the Lower Cretaceous succession on Spitsbergen. We also attempt to date the boundary between the Agardhfjellet and the Rurikfjellet formations. This study is based on dinoflagellate cysts (dinocysts) from three onshore cores (DH1, DH2 and DH5R) and three outcrop sections (Bohemanflya, Myklegardfjellet and Ullaberget). Relatively abundant and well-preserved dinocyst assemblages from the Rurikfjellet Formation date this unit as early Valanginian – early Barremian. The dinocyst assemblages from the Helvetiafjellet Formation are significantly impoverished and are characterized by reworking, but collectively indicate a Barremian–Aptian age for this formation.

Age of the earliest transgressive event in the Krishna-Godavari Basin, India: evidence from dinoflagellate cysts and planktonic foraminifera biostratigraphy

A combined biostratigraphic study of dinoflagellate cysts and foraminifera was carried out on Early Cretaceous subsurface well cutting sediments from well A (DNG) (2800–2746 m depth) from the Krishna-Godavari Basin, India. The last appearance datum of marker species of dinoflagellate cysts and planktonic foraminifera was considered for the construction of the biostratigraphic framework. The study shows dominance of Early Cretaceous marker dinoflagellate cysts Cassiculosphaeridia magna, Cribroperidinium perforans, Hystrichodinium voigtii, Kleithriasphaeridium eoinodes, and planktonic foraminifera Hedbergella aptiana, Hedbergella mitra, Hedbergella praelippa, Hedbergella tardita, Microhedbergella miniglobularis and Hedbergella mitra species. In addition to this, the dinoflagellate cyst data were compared with the dinoflagellate biozones of Austral and Tethyan provinces. Based on earlier micropalaeontological records from the Krishna-Godavari Basin and the present study, a latest Barremian-early Aptian age has been determined for the earliest marine transgression in the Krishna-Godavari Basin. The early marine incursion during late Barremian-earliest Aptian in the Krishna-Godavari Basin compared to Albian age in Cauvery Basin suggests the opening of east coast from north to south.

Mid-Cretaceous biostratigraphy (ammonites, inoceramid bivalves and foraminifers) at the eastern margin of the Anarak Metamorphic Complex (Central Iran)

Biostratigraphy of ammonite, inoceramid and orbitolinid foraminifer faunas from the mid-Cretaceous (Aptian–Turonian) succession at the eastern border of the Anarak Metamorphic Complex, a basement uplift in the north-western part of Central Iran, helped to understand complex lithostratigraphic patterns, to trace tectonic unconformities and to reconstruct the geodynamic significance of the succession. The basal continental Noqreh Formation can only be dated by stratigraphic superposition as pre-late early Aptian. An orbitolinid assemblage in the overlying shallow-marine Shah-Kuh Formation indicates a latest early Aptian age. The lower member of the overlying Bazyab Formation documents a considerable deepening in the early late Aptian (Epicheloniceras subnodosocostatum Zone). The boundary to the middle member of the Bazyab Formation is a conspicuous sedimentary unconformity, separating marly offshore strata below from shallow-marine, bioclastic sandstone above. The upper part of the middle member yielded ammonites of the upper lower Albian Douvilleiceras mammillatum Zone. In the upper member of the Bazyab Formation, ammonites of the upper Albian Mortoniceras rostratum Zone have been found. The base of the overlying Debarsu Formation is of earliest Cenomanian age (Mantelliceras mantelli Zone, Neostlingoceras carcitanense Subzone) and lower Cenomanian shallow-marine limestones range up to an intra-formational unconformity below the upper marl member of the formation, yielding early Turonian inoceramid bivalves and ammonites in the lower part. The Debarsu Formation is truncated along a major regional unconformity at the base of the Haftoman Formation. The erosional episode is correlated to a Coniacian tectonic event but further studies are needed to fully understand its geodynamic significance.

PRELIMINARY REPORT ON THE LACUSTRINE STRATA OF THE SANFRANCISCANA BASIN IN NORTHERN MINAS GERAIS, BRAZIL

We report new data on the geology and the fossil record of the Sanfranciscana Basin in sites to the north of the traditionally explored localities within Minas Gerais. The strata in the new explored area are formed by distinct lithologies, encompassing pelitic rocks with caliche levels and metric bodies of cross-bedded sandstone towards the top, similar to the fluviolacustrine beds of the Areado Group in the southern portions of the basin. Also similar to other regions of the São Francisco Craton, the deposits of the Sanfranciscana Basin studied herein lie discordantly to the rocks of the Bambuí Basin. We preliminarily report neopterygian fish scales, little informative archosaurian bones and an association of the ostracods Ilyocypris- Fossocytheridea. This ostracod association is registered for the first time in the Cretaceous of the Sanfranciscana Basin. The ostracods have been collected from the lacustrine, vertebrate-bearing rocks cropping out in Lagoa dos Patos and Coração de Jesus. The cytherideid Fossocytheridea assigns a minimal Aptian age to its bearing rocks. Its association with Ilyocypris was also reported in Upper Cretaceous oligohaline paleoenvironments in Brazil and Argentina, indicating similar depositional conditions to the strata reported in this paper. The putative affinities of the specimens of the Sanfranciscana Basin with F. ventrotuberculata, and their association with Ilyocypris, raise the hypothesis of a younger age for some levels of that basin in northern Minas Gerais, perhaps ranging into the Late Cretaceous.
 Keywords: Ostracoda, Archosauria, Areado Group, Cretaceous, Gondwana

WITHDRAWN: Evolutionary characteristics and controlling factors on Cretaceous deep-sea fans along a passive continental margin, Senegal Basin, Northwest Africa

Abstract Deep-sea fan reservoirs on passive continental margins are one of the hottest fields in offshore petroleum exploration. Understanding deep-sea fan spatiotemporal evolution helps refine the geologic model enhancing exploration and development of related reservoirs. Seismic and drilling data are the basis of the analysis. Different types of deep-sea fans with characteristic lithology, shape, and size are identified along the passive continental margin of Senegal Basin. Factors such as sea level changes, sediment supply, and paleo-geomorphology, are integrated into the interpretation. The study shows that during the Cretaceous Age, the study area underwent three tectonic-sedimentary evolution stages, 1) carbonate platform build up stage, in Neocomian and Aptian Ages, 2) clastic deposition on a continental fault-slope stage, from Albian to Santonian Ages, and 3) clastic deposition on a gentle continental slope (slope-break) stage, in Campanian and Maastrichtian Ages. During this time, five types of deep-sea fans developed in the study area, with varying lithology, morphology, and size. The effect of each factor on the development and evolution of the deep-sea fan is different. Global sea level changes and terrestrial clastic supply had the greatest influence on the texture and size of the fan, while the geomorphology of the continental slope determines the shape and the distribution of the fan.

Lacustrine coquinas and hybrid deposits from rift phase: Pre-Salt, lower Cretaceous, Campos Basin, Brazil

This study presents a facies characterization, facies succession and conceptual depositional model of the Coqueiros Formation, Lower Cretaceous of Campos Basin, based on core analyses of two wells. WELL-1 is a shallow water drilling located at south of Campos Basin within the Badejo structural high, and WELL-2 is an ultra deep water drilling located at north, over the “External High”. Ten carbonate facies, three siliciclastic facies, two magnesium clay mineral rich facies and two hybrid facies were identified. The carbonate facies were defined as rudstone, grainstone, packstone and mud supported carbonate rock, composed of bivalves, ostracods, and rare gastropods. Bivalve shells, mostly disarticulated with distinct degrees of fragmentation, characterized the main components of the ten carbonate facies. The siliciclastic facies are sandstones and mudstones, which occur locally. The magnesium clay rich facies is composed by stevensitic claystone and arenites. The mixture of bioclasts, siliciclastic grains, stevensite ooids and peloids constitute hybrid facies. The depositional processes involved waves and storm currents, as well as storm refluxes and tectonically-driven gravitational deposits, which mixed particles from different basinal sites producing the hybrid facies. The conceptual depositional model for each geological setting were elaborated based on facies stacking pattern analysis. A hybrid ramp in rift setting, studied in WELL-1, is characterized by carbonate, argillaceous, siliciclastic and hybrid successions, suggesting a strong terrigenous influence and variation of the lake water chemistry. An isolated bioclastic high in a rift setting, studied in WELL-2, is basically constructed by bioclastic sequences with local occurrence of siliciclastic mudstones deposited from hypopycnal plumes in relatively deep water. The extraordinary dominance of bivalve mollusks occurred during the lower Aptian stage in Campos Basin, in an active rift basin, with robust bioclastic productivity within protected basement highs. In structures near to the lake border, predominated siliciclastic and hybrid rock sequences as a result of high structural gradients and terrigenous input. Isolated highs from lakeshores were protected from external terrigenous influence. In lacustrine deep water bioclastic and hybrid arenites were deposited as fans generated by gravitational flows triggered by destabilization of shallower water deposits during episodic storms and tectonic activities. This study of the coquina deposits constructional model within a nearshore and also in a offshore lacustrine system is a useful knowledge for the understanding of coquina reservoir distribution and is applicable in the exploratory investigation of new areas with correlate lacustrine systems.

New records of planktonic foraminifera in the Shuaiba Formation (Aptian Age), Mesopotamian plain, South of Iraq

Shuaiba Formation is an important formation in Iraq, because of their deposition in the important period during the geological history of Arabian plate. The study is focused on a number of selected wells from several fields in southern Iraq, despite the many of oil studies to Shuaiba Formation but it lacks to paleontological studies. Four selected wells are chosen for the current study, Zb-290, Ru-358, R-624, WQ1-353, the selected wells are located within different fields, these are Zubair, Rumaila and West Qurna Oil Fields. In this study fourteen species followed to genus Hedbergella were discovered for first time as well as three genera followed to genus Heterohelix in the Shuaiba Formation at the different oil fields, Hedbergella tunisiensis Range Zone is suggested biozone to the current study, the age of this biozone is Aptian, most of the other genera located within this zone.