3rd Order Cycles Research Articles

Astronomical timescale for the early Toarcian (Early Jurassic) Posidonia Shale and global environmental changes

Lower Toarcian sediments (Early Jurassic, c. 183 Ma) record the Toarcian Oceanic Anoxic Event (T-OAE), which represents a period of profound environmental changes. The event involved the widespread deposition of organic carbon-rich strata in oxygen-depleted paleo-shelf settings, global warming, and is characterized by a negative Toarcian carbon-isotope excursion (T-CIE). The T-CIE provides a global time-correlative chemostratigraphic marker; however, its age, duration and underlying causes remain uncertain in the absence of an accurate early Toarcian timescale. This article presents a cyclostratigraphic framework for the lower Toarcian Posidonia Shale Formation from the Dotternhausen Quarry (South German Basin), one of the best-studied sediment archives that record early Toarcian environmental and ecosystem changes. The Posidonia Shale in the study site was deposited in the deeper part of the epicontinental shelf sea, where sediment accumulation rates were relatively uniform and major hiatuses unlikely. These factors are rarely found in most sections, and favor obtaining accurate cyclostratigraphic results at the study site. Our astronomical timescale indicates that black shale deposition at the site lasted about ∼3.2 Myr, a remarkably long period for sufficient primary productivity in stagnant bottom-water conditions. The estimated durations of the tenuicostatum and falciferum ammonite zones, and the T-CIE are ∼0.9, ∼1.8 and ∼ 1.2 Myr, respectively. Early Toarcian global warming, accompanying the T-CIE, occurred over a period of ∼400 kyr. Early Toarcian 3rd-order sea-level cycles correlate to 1.2 to 1.6 Myr orbital cycles, reflecting long-term obliquity and eccentricity periods. Orbitally-forced 3rd-order sea-level cycles, in combination with 405 kyr long-eccentricity, and potentially 100 kyr short-eccentricity cycles, controlled sea-floor oxygenation and deposition of black shales. Short-term environmental changes (e.g., redox cycles), responding to long- and short-eccentricity cycles were most pronounced during 3rd-order sea-level lowstands, when the depositional environment was most susceptible to short-term environmental instabilities. Our results highlight orbital-forcing as a key driving mechanism for early Toarcian environmental conditions.

Depositional Architecture and Stratigraphic Framework of Albian Succession in Balad and Nasiyia Oil Fields

The Albian Carbonate-clastic succession in the present study is represented by the Mauddud and Nahr Umr formations were deposited during the Albian stage within the Wasia Group More than 200 thin sections of cores and cuttings in addition to well logs data for Nahr Umr and Mauddud formations from 4 boreholes within two oil fields (Ba-4, Ba-8, Ns-2 and Ns-4) were used to interpret the different associations facies as well as the facies architectures to describe the sedimentary framework of the basin and development the petrophysical properties. Seven major microfacies were diagnosed in the carbonate succession of the Mauddud Formation, while the Nar Umr Formation includes five lithofacies; their grain types characteristic and depositional textures enabled to recognize of paleoenvironments. These microfacies were deposited in restricted, shallow open marine, back-reef, slope and deep open marine for the Mauddud succession. While in Nahr Umr, the lithofacies were deposited in bay fill, back-shore and distributary channel. The studied succession in Balad oil field which represents two 3rd order and four 4th order cycles (A1, A2, A3 and A4). These cycles are asymmetrical and starts with cycle A1 where the Backshore facies in Lower Mauddud Formation represents the transgressive systems tract and then appear the hightstand systems tract bounded below by a transgressive surface which coinside with the unconformable surface with the underlying Shuaiba Formation. In Nasyria oil field the studied succession represents two 3rd order cycles and three 3rd order cycles (A1, A2 and A4) with absence of A3 cycle. These cycles are asymmetrical and starts with cycle A1 where the distributary channel in the lower part of Nahr Umr succession represents the transgressive systems tract bounded below by unconformable surface with the underlying Shuaiba Formation. The highstand systems tract of cycle A1 is reflected by shallowing upward for distributary channel, bay fill and back-sore facies of the Nahr Umr Formation. This relatively thick parasequence reflect time of sea level stillstand where tectonic subsidence is the major controlling factor on producing the necessary accommodation for thick aggregational to progradation clastic succession to deposit.

Palaeoenvironments and sequence development of the Upper Palaeogene-Lower Neogene Succession in Kirkuk, Bai Hassan and Khabaz oil Fields, Northern Iraq

Microfacies analysis of the Upper Palaeogene-Lower Neogene succession which include Jaddala, Palani, Sheikh Allas, Shurau, Tarjil, Baba, Bajwan, Ibrahim, Azkand, Anah and Jeribe formations within Kirkuk area led to the recognition of many microfacies. They were grouped into nine facies associations ranging from supratidal to basin setting. These facies associations were deposited within a rimmed shelf with a barrier reef during the Palaeogene and a steepened ramp setting with fringing patch reef during the Neogene. The digenetic imprints on the recognized microfacies are prominent and dominated by cementation, neomorphism, dolomitization, precipitation of authigenic minerals, dissolution (leaching), compaction, mechanical degredation, micritization and geopitalstractures.
 The Upper Palaeogene-Lower Neogene succession is represented by a 2nd order cycle, It includes five 3rd order cycles within the shallowing upward upper part (The highstand systems tract) of this cycle. Cycles A and B were deposited during the Oligocene and present in the wells of Kirkuk oil field and bounded below by a transgressive surface and above by Type1 sequence boundary, Cycles C and D were deposited during the Aquitanian Early Miocene and found in Khabaz Field only and bounded below and above by a Type1 sequence boundary. These cycles were formed where the tectonic component was the major controlling factor on their development, This have caused successive episodes of relative sea level rises and stillstands, followed by sea level fall. Another 3rd order cycle within the Jeribe Formation was identified at Bai Hassan and Khabaz fields, this cycle is bounded below and above by a Type1 sequence boundary and also represent a brief episode of relative sea level rise followed by a major fall eroding most of the formation.
 The development of the Upper Palaeogene-Lower Neogene succession went through three main stages. The first stage was represented by the deposition of the basinal Jaddala and Palani formations (Eocene-Early Oligocene) all over the study area. The second stage was characterized by the basin trend being to the south toward the Khabaz Field and the reef buildup was located near Kirkuk Field and an interfingering took place between the Sheikh Allas and Palani formations deposited as a 3rd order cycle (A) therefore the fore reef and reef of Sheikh Allas and the back reef Shurau were deposited as a second 3rd order cycle (B) in Kirkuk Field only whereas the deposition of the basinal facies of the Palani Formation continued in both Bai Hassan and Khabaz areas. The third stage took place during the Aquitanian Early Miocene where a positive area developed as the Baba Dome and the Bai Hassan Field were uplifted with Avanah and Khurmala domes in Kirkuk Field; therefore the Bajwan and Baba formations (Late Oligocene) became subject to erosion, and the Khabaz Field represent the area of reef buildup, and the depositional system was changed from the shelf to ramp setting. During the Langhian new transgression took place where the Bai Hassan and Khabaz areas represent a tidal flat and the Jeribe Formation was deposited, whereas the Kirkuk Field was a positive area.

Paleoenvironmental and Bio-Sequence Stratigraphic Analysis of the Cretaceous Pelagic Carbonates of Eastern Tethys, Sulaiman Range, Pakistan

The Cretaceous pelagic carbonate succession, i.e., Goru Formation was studied in the Chutair Section, Sulaiman Range, representing part of the eastern Tethys for the paleoenvironment and bio-sequence stratigraphy. Eight planktonic foraminiferal biozones are identified which include: 1. Muricohedbergella planispira Interval Zone; 2. Ticinella primula Interval Zone; 3. Biticinella breggiensis Interval Zone; 4. Rotalipora appenninica Interval Zone; 5. Rotalipora cushmani Total Range Zone; 6. Whiteinella archeocretacea Partial Range Zone; 7. Helvetoglobotruncana helvetica Total Range Zone; and 8. Marginotruncana sigali Partial Range Zone representing Albian-Turonian age. The petrographic studies revealed five microfacies: 1. Radiolarians-rich wacke-packestone microfacies; 2. Radiolarians-rich wackestone microfacies; 3. Planktonic foraminiferal wacke-packestone microfacies; 4. Planktonic foraminiferal wackestone microfacies; and 5. Planktonic foraminiferal packestone microfacies; indicating deposition of the Goru Formation in outer-ramp to deep basinal settings. Based on the facies variations and planktonic foraminiferal biozones, the 2nd and 3rd order cycles are identified, which further include six transgressive and five regressive system tracts. The sea level curve of the Goru Formation showed fluctuation between outer-ramp and deep-basin, showing the overall transgression in the 2nd order cycle in the study area, which coincides with Global Sea Level Curve; however, the 3rd order cycle represents the local tectonic control during deposition of the strata.

Paleoenvironment, sequence stratigraphy and source rock potentiality of the Cenomanian-Turonian boundary sediments of Southern Tethys

The Abu Qada Formation is a reference interval for the Cenomanian–Turonian boundary event in the northeastern margin of Africa. In this paper, geochemical, biostratigraphical, and carbon isotope ratio studies are presented using high-resolution well data yielded from the Gulf of Suez, Egypt to evaluate the paleoenvironmental condition, sequence stratigraphy and source rock potential of the Upper Cenomanian/Lower Turonian Abu Qada Formation. A total of 12 core samples and 4 ditch cuttings were collected from OCT-A8St1 well in the October Oil Field for geochemical, palynological and calcareous nannoplankton analyses. Cyclostratigraphic analysis was prepared to characterize the electrofacies change along the Cenomanian/Turonian boundary interval including the Oceanic Anoxic Event 2 (OAE2). The Predictive Error Filter Analysis (PEFA) patterns and Integrated Predictive Error Filter Analysis (INPEFA) curves found 3rd order cycle of the OAE2 within the global third-order cycle Ce5. A stable carbonate isotope analyses with total organic carbon (TOC) resulted in a remarkable positive excursion δ13Ccarb (3.67‰) associated with change in the TOC content. The quantitative analysis of calcareous nannofossils indicates the high productiveness of nannoplankton around the Cenomanian/Turonian boundary interval. The high abundance of the Discorhabdus genus proves the paleoenvironmental change during the OAE2 interval. The palynofacies interpretation indicates the lower part of Abu Qada Formation to be deposited in a slightly reducing conditions at the inner neritic setting, while the upper part of Abu Qada to lower part of Wata formations were deposited in deeper marine setting under anoxic conditions. These changes in the overall depositional conditions are documented by the remarkable change in palynofacies and organic carbon content (TOC). Dark gray shale and carbonate sediments are interpreted to be a good source rock potential by kerogen quantified palynofacies analysis indicating oil and gas prone producing materials (Kerogen types II and II/III). The best source rock quality is associated with the Abu Qada Formation's OAE2 record. These criteria allow us to identify the occurrence of OAE2 record in the Gulf of Suez petroleum province as a useful tool for high-resolution chronostratigraphic analysis.

Microfacies architecture and depositional history of the Upper Jurassic (kimmeridgian) Jubaila Formation in central Saudi Arabia

The Upper Jurassic Jubaila Formation in central Saudi Arabia exhibits laterally coeval environments from the southwest to the northeast. These coeval environments involve inner, mid-, and outer ramps. The inner ramp occurs at the Al Haddar section in the extreme southwest and consists of mixed clastic-carbonate facies and are represented by intercalations of ferruginous calcareous quartz arenite, ferruginous sublitharenite, and burrowed dolomicrite. In the mid-ramp setting, there were changes from lateral facies in the Riyadh and the Wadi Huraymila areas to carbonates characterized by sandy lime-mudstones, dolosparie, peloidal olitic packstones, and coralline bioclastic wackestones to packstones. These are intercalated with sandy lime-mudstones that might be deposited in highly agitated environments. The outer-ramp setting occurred in the farther northeast Al Uyaynah area. It is characterized by reduced thickness and is composed of lime-mudstones, dolomitic marls, and pelletal bioclastic wackestones with thin beds of dolomitic marls. The lateral and vertical microfacies distribution in the Jubaila Formation are arranged vertically into four 3rd-order cycles that are correlate laterally overall the studied area, which are overprinted by oscillations in eustatic sea-level during the deposition of Jubaila Formation.

Synchrony evolution of two contradictory prograding Gilbert-type deltas at the margins of the foreland basin (case study from the Neogene Western Carpathian Foredeep)

The study concerns about two Miocene deltas located along the opposite margins of the Western Carpathian Foredeep (peripheral foreland basin), their architecture and evolution. Three synchrony phases of development of the Gilbert-type deltas were recognized based on 3D and 2D seismic data, well logs and cores. Individual phases are separated by seismic stratigraphy surfaces. The base of the deltas is formed by the erosional discontinuity (seismic stratigraphy surface 1), which is the sequence boundary of the 3rd order cycle. During the first phase, the sediment supply exceeds accommodation space creation and progradation of deltas and the normal regression regime dominates. The first phase is terminated by the maximum regressive surface/transgressive surface (seismic stratigraphy surface 2) and interpreted as the lowstand systems tract. In the second phase, the aggradation and retrogradation regime of deltas reveals the acceleration of the accommodation space creation and the deposits are interpreted as the transgressive systems tract. The third phase is bounded by the maximum flooding surface (seismic stratigraphy surface 3) and shows progradation of the delta in the normal regression regime, then the sediment supply exceeds the accommodation space. The maximum regressive surface (seismic stratigraphy surface 4) terminates this phase and allows to interpret it as the highstand systems tract. The synchrony evolution of deltas is explained by the tectonic activity along the fault system oriented perpendicular to the basin axis. Position of the deltas is also responsible for continuous sediment supply and its variations. The tectonic activity of the transverse fault system across the entire basin hidden the signals of the reciprocal activity of the opposite basin margins directed by flexural tectonics. • Two Gilbert-type deltas prograding contradictory at margins of foreland basin. • Ruling factors of synchronous Gilbert-type delta evolution – eustasy vs. tectonics. • Role of fault activity in reciprocal stratigraphy of foreland basin depozones. • Phases of the delta evolution in the concept of sequence stratigraphy.

Tectonic and eustatic impact on depositional features in the upper Cretaceous Austin Chalk Group of south-central Texas, USA

The upper Cretaceous Austin Chalk Group in south-central Texas, USA, displays vertical and lateral variations in thickness and facies resulting from an irregular paleotopography of the seafloor and variable preservation of 3rd-order sea-level cycles. During the Coniacian to early Campanian, the tectonic evolution of the San Marcos Arch, a prominent basement feature in the study area, impacted facies and sequence architecture within the Austin Chalk Group. Outcropping sections of the Austin Chalk Group along the margin of the Edwards Plateau in south-central Texas stratigraphically transition between inner and outer ramp environments. The cyclic stacking pattern of facies is recorded in vertical stratigraphic succession as 3rd-order cycles separated by discontinuity surfaces and condensed deposits. Inner ramp facies consist of Thalassinoides-burrowed bivalve wackestone to packstone with minor occurrences of skeletal grainstone. Outer ramp facies comprise Planolites-burrowed foraminiferal chalk and marl with fine skeletal debris. Condensed facies associated with transgressive re-working are characterized by glauconitic packstone with high concentrations of coarse skeletal debris and lithoclasts. Gamma-ray profiles of outcrops investigated in the study area are correlated to subsurface wireline logs of wells drilled along the outcrop and subsurface trend, in order to construct a stratigraphic framework across the San Marcos Arch. This stratigraphic framework is biostratigraphically well constrained and correlated to the type section of the Austin Chalk Group farther north in the vicinity of Austin. The integration of sedimentological and stratigraphic information enables the identification of four regional 3rd-order depositional sequences within the Austin Chalk Group. Thickness maps of each depositional sequence illustrate the tectonic evolution of the San Marcos Arch and its influence on the deposition of the Austin Chalk Group, which is judged as negligible during most of the lower Austin Chalk Group (Coniacian), and started to trigger lateral thickness variations and pinch-outs in the Santonian and early Campanian. Syndepositional tectonic movement played an active role in the geometry of Austin Chalk depositional sequences and should be accounted for in sequence stratigraphic models developed in chalk depositional settings to explain the occurrence of coarser and cleaner facies.

High frequency (4th order) sequence stratigraphy of Early Miocene deltaic shorelines, offshore Texas and Louisiana

Abstract Well logs and 3D seismic reflection data are integrated to image Lower Miocene depocenters of the upper Texas and westernmost Louisiana coastal and offshore areas. Although previously interpreted at a large scale (3rd order cycles), the detailed stratigraphy and depositional history of the early Miocene succession has not been fully developed. The upper lower Miocene interval from Robulus L (MFS10) to Amphistegina B (MFS9) has been further subdivided into five 4th order cycles (each 200–300 m thick) to provide finer scale stratigraphic detail and interpretation of depositional environments. Results of the finer scale correlations are presented in a series of sandstone percent maps. Overall, the maps display a strike-elongate (sub-parallel to the present day coastline) orientation for the sandstone bodies which thin to the southeast (basinward). Net sandstone thickness is relatively low in older cycles and increases in younger cycles suggesting an overall progradation of the deltaic system into the mapped area through time. Continued marine regression and southward movement of the shoreline are also confirmed by seismic amplitude maps. After a major transgression associated with Robulus L deltaic progradation occurred under rising sea level conditions. Deltaic sediments prograded southward and sandstone brought to the upper Texas coast was distributed laterally by longshore currents to form strandplain coast lines. Maximum regression occurred during the interval MFS9_2 to MFS9_3 when a deltaic depocenter formed offshore Texas in east High Island area. However, sandstone thickness progressively decreased laterally to the east (offshore Louisiana) where more shale was present and marine processes reworked deltaic derived sandstones into shore parallel bars. There was a clear retreat of the shoreline during the youngest cycle marking the beginning of transgression associated with Amphistegina B. Detailed stratigraphic interpretation (at a 4th order scale) shows more variability in the dominant shoreline processes during early Miocene than previously thought. Recognition of sedimentary systems variability at a 4th order scale is critical for improved hydrocarbon exploration and in understanding potential future CO2 storage in the area.

Depositional cycles of the Lower Miocene Rudeis Formation (southwestern offshore margin of the Gulf of Suez, Egypt): Implications for reservoir evaluation

The Lower Miocene Rudeis Formation in the Zeit Bay Field (Gulf of Suez, Egypt) has been studied by analysis of cores from six boreholes. The objective was to detail the sedimentary cycles in the formation and their implications for the reservoir characteristics, as well as to obtain a more detailed insight into the precise age by establishing a foraminifer zonation. The formation, which was found to be some 60–191 m thick, is composed almost exclusively of various types of carbonates. These contain foraminifers that prove a Burdigalian age, and that also provide insight into the depositional environments, which turned out to form three belts. These belts represent an intertidal lagoon, barrier shoals, and a reef complex, respectively, indicating a down-dip depositional profile of a shallow marine rimmed carbonate shelf. Analysis of the cyclicity pattern of the Rudeis Formation, supported by facies analysis and CycloLog curves, makes it possible to distinguish three superimposed 3rd-order depositional cycles, which are subdivided into several higher-order cycles that are strongly controlled by eustatic sea-level fluctuations. A set of lithofacies isopach maps has been constructed for these cycles with the objective to facilitate interpretation of the spatial distribution of the reservoir quality for hydrocarbons. The maps show that the reservoir quality of the Rudeis Formation is heterogeneous because of the highly variable characteristics of the various lithofacies types.

Cyclo-sequence stratigraphy of the Miocene syn-rift succession, Al Amir and Geyad fields, southwestern part of the Gulf of Suez rift

A cyclostratigraphic analysis is performed using high-resolution well data to study the facies development, characteristics, and patterns of the Miocene syn-rift succession in the Gulf of Suez. The impact of syn-depositional tectonics on the distribution of reservoir units is also highlighted. The study area is in Al Amir and Geyad fields, which are located in the southwestern onshore part of the Gulf of Suez rift. The Cyclolog® software workflow has been applied on nine wells from these two fields using the Gamma Ray log of the Miocene sequences. The Predictive Error Filter Analysis (PEFA) patterns and Integrated Predictive Error Filter Analysis (INPEFA) curves support the definition and distinction of seven 3rd order cycles. These cycles are numbered as 1.4, and 1.5 for Nukhul Formation, 2.1, 2.2, and 2.3 for Rudeis Formation, 2.4 for Kareem Formation, and 2.5 for Belayim Formation. The Kareem Formation is represented by cycle 2.4 and could be divided into higher order subcycles 2.4 (a, b (u and l), c, d and e). The oil reservoir units occur in subcycle 2.4.b (u and l), whereas subcycle 2.4.b (l) is missing in Geyad field and subcycle 2.4.b (u) is missing in Al Amir SE-1X St well. Correlation profiles and isochore maps of the Upper Rudeis and Kareem formations (cycles 2.3 and 2.4 respectively) indicate the relationship between sediment supply and accommodation space which are related to tectonic subsidence of the West Zeit Basin and sediment supply from the Esh El Mellaha range.

Composite sequence stratigraphic patterns in alluvial to shallow-marine successions: Examples from the Piacenzian of the Valdelsa Basin (Central Italy)

The sequence-stratigraphic analysis of continental and shallow marine successions is a helpful tool for investigating the cyclicity of the sedimentary record. A similar approach is adopted in the present study to illustrate the composite cyclothemic facies architecture that characterizes the Piacenzian strata of the southern Valdelsa Basin (Central Italy). Specifically, we integrated facies analysis, paleopedology, paleobiology of marine mollusk assemblages and biostratigraphy to assess the response of geomorphic, sedimentary and biotic systems to Piacenzian multifrequency relative sea-level fluctuations. This integrated approach resulted in the definition of a composite sequence-stratigraphic framework that includes a hierarchy of units ranging from the elementary to the composite depositional sequences, referred to the 5th to 3rd order cycles of sea-level fluctuations, respectively. A correlation with the Piacenzian oxygen isotopic signature of glacial and interglacial stages and related sea-level fluctuations associates the cyclic development of fluvial, coastal and shallow marine depositional systems to the mid-Piacenzian Warm Period and to the subsequent transition to the Gelasian. Thus, the glacio-eustatic control prevailed on the development of the described multi-scale cyclical pattern of sedimentation, compared to the role played by the deformation of the Northern Apennines orogen.

Miocene paleogeography and biostratigraphy of the Slovenj Gradec Basin: a marine corridor between the Mediterranean and Central Paratethys

Abstract The Miocene evolution of the area transitional from the Eastern Alps to the Pannonian Basin System was studied through the paleogeographic evolution of the Slovenj Gradec Basin in northern Slovenia. It is based on mapping, section logging, nannoplankton biostratigraphy, and petrography. The results are correlated with the lithological column of the borehole MD-1/05. The evolution of the basin is connected with the development of the Pannonian Basin System, and the global 3rd order cycles, which influenced the connection with the Mediterranean Sea. Sedimentation started in the Karpatian in a fluvial to lacustrine environment and terminated at the end of the Early Badenian. During this period, three transgression–regression cycles were recorded. The first transgression occurred in the Karpatian and corresponds to the TB 2.2. cycle. The sediments reflect proximity of the hinterland. After a short break in sedimentation, the Early Badenian deposition followed. It marks the second transgression into the SGB, the first Badenian, correlated with the TB 2.3 cycle. There are signs of a transitional environment, which evolved to marine in advanced stages. At the high-stand system tract, the sea flooded the entire Slovenj Gradec Basin. Subsequent reduced quantity and diversity of the microfossils marks the onset of the second regression stage. It is followed by the third transgression, the second in the Badenian, correlated with the TB 2.4 cycle. The late Early Badenian deposition continued in the lower-energy, though occasionally still turbulent environment. Silty sediments with upward increasing content of organic matter indicate shallowing of the basin, until its final diminishing. Layers of fresh-water coal already bear witness to the existence of restricted swamps. After the Early Badenian, the area of the Slovenj Gradec Basin became dry land, exposed to erosion.

High resolution sequence stratigraphy of Middle Eocene Hazad Member, Jambusar-Broach Block, Cambay Basin, India

Abstract The Middle Eocene Hazad Member of the Ankleswar Formation in the Cambay Basin is characterized by 13 sandstone units (GS-0 to GS-12), representing progradational pulses within an overall fining-up 2nd order transgressive systems tract (TST). The overall facies architecture of the Hazad Member implies deposition in a tide affected marginal marine (deltaic) environment. High resolution sequence stratigraphic analysis based on core and electrolog data allows to subdivide the 2nd order TST into three 3rd order systems tracts, namely, (i) basal shaly transgressive systems tract (TST), followed by (ii) a highstand systems tract (HST) incorporating four intervening parasequence-sets (GS-0 to GS-2, GS-3, GS-4 to GS-6 and GS-7 to GS-9) separated by 4th order flooding surfaces, and (iii) a transgressive systems tract (TST) at the top consisting of parasequence-sets (GS-10 to GS-12) capped by the Kanwa Shale that includes the maximum flooding surface (MFS). The amalgamated sands of the 3rd order sequences found landward split basinward to form six coarsening-up 4th order cycles (parasequence-sets), which are further subdivided into twenty one 5th order cycles (parasequences), separated by minor events of marine flooding. The depositional model and paleogeographic maps using 3rd, 4th and 5th order cycles reveal a minimal sand supply at the beginning of 3rd order HST and a significant increase in fluvial sand supply thereafter, which resulted in progradation leading to constructive delta building till GS-9. The topmost transgressive parasequence-sets constituting GS-10 to GS-12 mark landward retreat due to a paucity of sand supply and/or a rise in relative sea-level, which resulted in back-stepping of the paleoshoreline and development of estuaries over the older deltaic system. The model helps to explain the extent of short-term transgressive-regressive cycles, improving elucidation of the hydrocarbon-bearing sand units of the Cambay Basin in future exploration.

Chemostratigraphy and palaeo-environmental characterisation of the Cambrian stratigraphy in the Amadeus Basin, Australia

The sedimentary succession of the central Australian Amadeus Basin consists of Neoproterozoic to Carboniferous sedimentary rocks and contains shallow marine, subtidal carbonates of Middle to Late (Series 2 to Furongian) Cambrian age. A combination of sequence stratigraphy, geochemistry and mineralogy shows a transgressive 2nd order cyclicity deposited between ~511–490Ma and a change from arid, low energy to humid, high energy depositional environments. This is reflected in an initially evaporitic sequence with upward decreasing halite and anhydrite abundance and transition from oxygenated to anoxic conditions, reflected by the Fe mineral species change from hematite to pyrite during transgression. Sequence boundaries of several 3rd order cycles consisting of HST carbonate rocks and LST siltstones, correlate with globally recognised sequence boundaries linked to the inferred eustatic sea level record for the upper two series of the Cambrian System. The carbon isotope record for this ~1400m thick succession in combination with biostratigraphic age correlation allowed the identification of the globally recognised Steptoean Positive Carbon Isotope Excursion (SPICE), Drumian Carbon Isotope Excursion (DICE) and Redlichiid-Olenellid Extinction Carbon Isotope Excursion (ROECE).

Macroinvertebrate fauna and depositional environment of the lower Upper Cenomanian Oberhäslich Formation in the Saxonian Cretaceous Basin (Germany)

In Saxony (southeast Germany), the global early Late Cretaceous transgression is reflected by the onlap of shallow-marine siliciclastics of the lower Upper Cenomanian Oberhäslich Formation (Calycoceras naviculare Zone) onto the eastern Erzgebirge, the central part of the emergent Mid-European Island. Based on detailed logging of sections south of Dresden and the study of extensive collection material, the depositional environment and macroinvertebrate assemblages of the Oberhäslich Formation have been reconstructed. This unit, with a mean thickness of 10–15m, usually shows a fining-upward trend that may become reversed towards the top, was laid down in a single 3rd-order sea-level cycle and is capped by an unconformity at the base of the overlying upper Upper Cenomanian Dölzschen Formation (sequence boundary Cenomanian 5; junction of the Calycoceras naviculare and Metoicoceras geslinianum zones). The macroinvertebrate assemblage of the Oberhäslich Formation, collected mainly from bioturbated, fine- or rarely medium-grained, quartz-rich sandstones, is fairly diverse, comprising nearly 50 taxa, predominantly bivalves (94.3%). Most conspicuous and abundant are relatively large forms such as Rhynchostreon (R.) suborbiculatum (25%) and Inoceramus pictus spp. (21%), eponymous taxa of the Rhynchostreon suborbiculatum/Inoceramus pictus assemblage. Non-bivalve benthic invertebrates are rare and represented by rather poorly preserved irregular and regular echinoids, siliceous sponges, a few gastropods, crustacean remains and a single starfish. Common Thalassinoides and Ophiomorpha burrows indicate that crustaceans were an important part of the infauna. Pervasive bioturbation resulted in a post-depositional homogenization of the sediments while all body fossils are preserved as (composite) internal moulds. The guild structure of the Rhynchostreon suborbiculatum/Inoceramus pictus assemblage shows a predominance of epifaunal and semi-infaunal suspension feeders (95.3%), suggesting eutrophic and unstable “green-water conditions” of an inner-shelf setting. Deposit-feeding biota are rare. The common occurrence of articulated bivalves and storm-induced shell beds indicate episodic rapid burial, most probably by tempestites. A current-influenced, well-oxygenated and nutrient-rich environment slightly below fair-weather base is inferred for the fine-grained sandy, fossiliferous sediments of the Oberhäslich Formation.

Lithostratigraphy of the Abrahamskraal Formation (Karoo Supergroup), South Africa

The Middle Permian Abrahamskraal Formation is the lowermost formation of the lower Beaufort Group (Adelaide Subgroup, Karoo Supergroup) in the main Karoo Basin. It has been amalgamated with the lithologically similar and age-equivalent Koonap Formation and now occupies the entire southern part of the main Karoo Basin. It consists of greenish-grey and less common reddish-brown mudrock and subordinate light grey fine-grained sandstone, arranged in fining-upward, 1st to 3rd order cycles that range in thickness from a few metres to a few tens of metres. It reaches a maximum thickness in the southwest part of the basin (2200 to 2565 m) and thins northeastward with younging of the lower contact with the underlying Ecca Group and overlap of the overlying Middleton Formation onto the Ecca Group in the vicinity of Petrusville. The Abrahamskraal Formation contains several arenaceous zones in the southwest part of the basin, which increase in thickness towards a source area located along the southwest margin of the basin. The sedimentary facies represent deposition on a vast alluvial plain with lateral and downstream accretionary sand bodies in fluvial channels and floodbasin and subordinate lacustrine muds and silts in the extensive interchannel areas. Biostratigraphically, the Abrahamskraal Formation falls within the Tapinocephalus Assemblage Zone. However, along the southwestern margin of the basin, this zone is underlain by the Eodicynodon Assemblage Zone.

Ostracods from the marginal coastal Lower Cretaceous (Aptian) of the Central Tunisian Atlas (North Africa): Paleoenvironment, biostratigraphy and paleobiogeography

This work provides the first detailed taxonomic study of ostracod species from the Lower Cretaceous (Aptian) marginal coastal deposits of the Central Tunisian Atlas, the Kebar Formation, as well as biostratigraphic, paleoecological and paleobiogeographic implications. The ostracod fauna provides new insights into the depositional environment and biostratigraphic framework of the Kebar Formation, and is represented mainly by freshwater and brackish-water species among them, Perissocytheridea tunisiatlasica nov. sp., is newly described. The environmental setting of this formation comprises marginal-littoral conditions in its lower part, thus not exclusively non-marine/continental as assumed previously. The ostracod associations from the studied locality, Jebel Ksaïra, indicate a minimum age of Early Aptian as recently attributed to the lower member of the Kebar Formation based on charophytes (presence of Late Barremian to Early Aptian Globator maillardii var. biutricularis Vicente and Martín-Closas, 2012), whereas an Early Albian age had been previously assigned to the Jebel Kebar site. The relative sea-level fall documented in the lower member of the Kebar formation at Jebel Ksaïra might correspond to the 3rd order cycle major eustatic sea-level fall event starting at the base of the Aptian. Paleobiogeographically, the non-marine ostracod fauna newly discovered in the Kebar Formation shows some affinities to contemporaneous faunas of southern and western Europe, e.g. that of the uppermost Weald Clay Group of southern England (Cypridea fasciata subzone of Horne, 1995), West Africa, and possibly to eastern South America (Brazil). Hence, the studied ostracods further support the hypothesis of supraregional faunal exchange by passive ostracod dispersal during the Early Cretaceous – between Europe and Northern Africa on the one hand, and eastern South America/western Africa and North Africa on the other hand. This leads to the hypothesis that the Peri-Tethyan islands could have worked as effective bridges for non-marine ostracods to become widely dispersed passively by “island-hopping” of larger animals and thus, ultimately, facilitated intercontinental faunal exchanges between South America and Europe – potentially even Asia – via North Africa during the Early Cretaceous.

Deciphering the history of climate and sea level in the Kimmeridgian deposits of Bure (eastern Paris Basin)

Abstract An integrated stratigraphic study was conducted on a Kimmeridgian succession of 3rd-order cycles including marls and limestones in a shelf context at Bure (Paris Basin). The study was possible due to the exceptional opportunity provided by well-boring activities related to the construction of an underground laboratory of the French National Agency for Radioactive Waste Management (ANDRA). Studies of macrofossils, microfossils, sedimentology, clay mineralogy, isotopic composition (C, O) of shells and organic molecular geochemistry lead to a detailed description of the stratigraphic column, which allows us to address the history of sea-level and climate changes. Six transgressive–regressive cycles are recognised in the studied Kimmeridgian succession. In these 3rd-order cycles, the deepest environments are systematically represented by marls and organic-rich sediments whilst the shallowest are represented by limestones. These cycles do not correspond to changes in temperatures or carbonate production rates at a regional or global scale. On the contrary, long-term palaeontological, sedimentological, and geochemical changes during the Early Kimmeridgian are interpreted as climatically induced. These climatic changes are considered as responsible for bringing significant granular carbonate production to an end, in contrast to carbonate mud that was deposited in alternation with marls throughout the Late Kimmeridgian.

A hybrid approach for litho-facies characterization in the framework of sequence stratigraphy: A case study from the South Pars gas field, the Persian Gulf basin

The Upper Dalan and Kangan formations with dominant lithology of limestone and dolomite associated with anhydrite nodules and interbeds form the Permo-Triassic succession of South Pars gas field (SPGF) and host the largest none-associated gas reservoir in the world. The current study focuses on preparing a comprehensive litho-facies model in the framework of sequence stratigraphy. For this purpose, Self-Organizing Map Neural Network (SOM-ANN) and hierarchical cluster analysis (HCA) were utilized as effective tools to prepare the preliminary data for litho-facies mapping. Neural networks (self-organizing maps) and hierarchical clustering approaches were applied to characterize litho-facies in un-cored but logged wells. Particularly, the powerful visualization tools of the SOM-ANN which provide more information in comparison to HCA facilitate the task of establishing an order of priority between the distinguished electro-facies groups. The mentioned method of SOM-ANN clustering algorithm showed a good performance in petrophysical data clustering and litho-facies determination. Based on the porosity and permeability maps at different depth levels, the target reservoir is ranked and classified into four litho-facies and six electro-facies. They include litho-facies 3 with good reservoir quality (equivalent of electro-facies 4–6), litho-facies 4 with moderate reservoir quality (equivalent of electro-facies 2) and litho-facies 1 and 2 with poor to bad reservoir quality (equivalent of electro-facies 1 and 3). The main litho-facies assemblages are indicative of deposition within tidal flat, lagoon, shoal and off-shoal environments. The most shoal litho-facies with best reservoir quality occurs in the high energy sub-environment within upper transgression position (HST) of the 3rd-order cycle in K4 and K2 reservoir units. Distribution of the petrophysical characteristics was analyzed in detail in the framework of electro-facies and sequence stratigraphy. The methodology is illustrated by using a case study from SPGF, Iran.