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Paleoenvironmental significance of the monospecific biostromes in the Campanian-Maastrichtian Duwi Formation (Eastern Desert, Egypt)
... It is underlain by the Quseir Formation and overlain by the Dakhla Formation (El-Younsy et al., 2017), both of which also yielded terrestrial vertebrates, including dinosaurs (see above and below). The formation mainly consists of shales, limestones and phosphates and several massive oyster layers (Abdelhady et al., 2020;El-Ayyat & Kassab, 2004). The sediments were deposited in a shallow marine setting and marked the onset of fully marine conditions in Egypt following the late Cretaceous marine transgression of the region (El Ayyat, 2015; El-Ayyat & Kassab, 2004). ...
... The terrestrial vertebrates (theropod dinosaurs and the semi-aquatic goniopholid crocodyliforms) were likely washed into the sea and thus offer insights into the faunal composition of the nearby coast. The low faunal diversity of the Duwi Formation and the occurrence of autochthonous oyster beds probably are the result of stressed environmental conditions (Abdelhady et al., 2020); additionally, the oyster shell layers are indicative of repetitive storm events (Abdelhady et al., 2020). The palaeoclimate was probably humid and tropical as evidenced by the palynomorph assemblage (El Beialy, 1995). ...
... The terrestrial vertebrates (theropod dinosaurs and the semi-aquatic goniopholid crocodyliforms) were likely washed into the sea and thus offer insights into the faunal composition of the nearby coast. The low faunal diversity of the Duwi Formation and the occurrence of autochthonous oyster beds probably are the result of stressed environmental conditions (Abdelhady et al., 2020); additionally, the oyster shell layers are indicative of repetitive storm events (Abdelhady et al., 2020). The palaeoclimate was probably humid and tropical as evidenced by the palynomorph assemblage (El Beialy, 1995). ...
Egypt has yielded some of the richest and most spectacular records of Mesozoic terrestrial vertebrates from Africa. Certainly, the best-known and most diverse of these are the vertebrate assemblages of the Upper Cretaceous Bahariya Formation (Cenomanian), which includes numerous different taxa of fishes, abundant remains of turtles and crocodyliforms, as well as several different theropod and sauropod dinosaurs. Originally discovered early in the twentieth century by famous German palaeontologist Ernst Stromer von Reichenbach and fossil collector Richard Markgraf, most of the material has subsequently been destroyed during the Second World War. Aside from the high diversity, the Bahariya Formation also yielded some of the most bizarre and iconic dinosaurs such as the giant theropods Spinosaurus and Carcharodontosaurus or the enormous sauropod Paralititan. Although the Bahariya Oasis has yielded by far the most diverse and extensive remains of Mesozoic terrestrial vertebrates from Egypt, other localities from the Turonian, Campanian and Maastrichtian offer additional important—albeit much less complete—insights into the composition and evolution of African Late Cretaceous terrestrial ecosystems. Some of these assemblages, especially the latest Cretaceous Quseir Formation, have just begun to reveal the richness and diversity of their vertebrate fauna, often with spectacular results, and certainly have the potential to yield further significant insights into the evolution of the Cretaceous life on land. In this chapter, we provide a summary of the terrestrial Mesozoic vertebrate record of Egypt and thus an overview of these remarkable dinosaur faunas.KeywordsEgyptDinosauriaCrocodyliformesTestudinataBahariya FormationQuseir Formation
... The basic geological knowledge of this part of Egypt can be found in the synthetic works by Issawi et al. (2009), Tawadros (2011), Said (2017, and Hamimi et al. (2020). The articles by Stern (1981), Khalil andMcClay (2009), El Kammar (2015), Yousif et al. (2018), and Abdelhady et al. (2020) also shed light on some issues of the local geology. The latter attracted attention already in the times of Ancient Egypt (Harrell and Brown, 1992), and, thus, the history of the regional geological exploration counts thousands of years. ...
... The Upper Cretaceous-Lower Eocene sedimentary rocks crop out there, and, particularly, this is the type locality of the Campanian-Maastrichtian Duwi Formation including phosphate lenses. This locality exhibits broad spectrum of geological phenomena, and it has become a subject of international-class geological research projects (e.g., Abdelhady et al. 2020). One should note the presence of notable natural and human-modified landforms (Fig. 7a), cross-bedding in the Nubian sandstones indicating their fluvial origin (Fig. 7b), abundant chert nodules in the Thebes Formation (Fig. 7c), phosphate-rich deposits of the Duwi Formation (Fig. 7d) that were exploited (Fig. 7e, f), and various elements of stratigraphic architecture like angular unconformities (Fig. 7g). ...
... Currently, the proposed geosites are used chiefly for geological research (Abdelhady et al. 2020;Afify et al. 2020;Mohammad et al. 2020) and occasional, professionally guided excursions for university students (Fig. 9). ...
The Golden Triangle economic zone of eastern Egypt stretching between the Nile Valley and the Red Sea coast is a historical mining area, which is vast and rich in geology. Although none single study can comprehend the entire geoheritage of this area, field investigations and literature analysis permit to identify the eight most notable localities, which are interpreted as geosites (Sukari gold mines, Al-Fawakhier gold mine, Um Greifat polymetallic ore quarry, Gebel Abu Sha’ar El-Qibli manganese quarry, White Sand quarry, Gebel Duwi (including phosphate mines), Sodmein cave, and Meatiq dome). These geosites represent broad spectrum of unique phenomena. The latter are assigned to the stratigraphical, palaeontological, palaeogeographical, tectonic, igneous, sedimentary, metamorphic, mineralogical, geomorphological, economical, and geohistorical geoheritage types. Semi-quantitative assessment of these geosites indicates on the biggest value of Gebel Duwi, the Sodmein cave, and the Al-Fawakhier gold mine. The identified geoheritage of the Golden Triangle requires geoconservation and exploitation for the purposes of science, education, and tourism (some experience has already been accumulated), and the relevant initiatives can be managed within a geopark framework. This preliminary assessment proves geoheritage richness of the study area, and it establishes frame for geoconservation activities, and, particularly, search for more geosites. The presence of similar geologically rich areas in the other parts of Egypt makes urgent development and implementation of the national approaches of geoheritage management.
... Egypt was located at the southern rim of the Neo-Tethys during the Late Cretaceous time [1]. A major transgressive phase characterized the Campanian-Maastrichtian time in northern Egypt [2], resulting in the deposition of carbonate and marly facies [3]. The upper Campanian-Maastrichtian carbonate deposits are extensively exposed in Sinai, Gulf of Suez, north Eastern Desert, and northern and central Western Desert. ...
... During the Late Cretaceous, Egypt was situated at the southern edge of the Neo-Tethys [16,32,33], and an extended carbonate platform covered North Africa due to the sea-level rise [2,34]. Hemipelagic sediments of deep carbonate platform, consisting of carbonate and marley facies, were developed in northern Egypt during the Campanian-Maastrichtian time [3]. ...
The Upper Cretaceous deposits are widely distributed and well exposed in northern Egypt. Important upper Campanian-Maastrichtian carbonate deposits outcrop at the Northern and Southern Galala Plateaus, north Eastern Desert, represented by Sudr Formation. Sudr Formation is lithologically investigated, sampled, and the included fauna are collected for taxonomic and paleobiogeographic studies. Four gastropod species, belonging to three genera and three families, as well as twelve bivalve species, representative of twelve genera and nine families, are identified. Two gastropod species; Cerithium buddha Noetling, Potamides temalacaensis Perrilliat et al., and four bivalve species; Gryphaeostrea canaliculata (Sowerby), Venilicardia truncata (Sowerby), Calva (Egelicalva) buttensis (Anderson), Lyriochlamys dentata (Nilsson), are recorded for the first time from the Upper Cretaceous deposits of Egypt. The microfacies analysis of the carbonates of Sudr Formation revealed four distinct microfacies types, each with characteristic bioclasts and textural features. These microfacies types suggest open-marine, high-energy shallow subtidal shoal to low-energy deep subtidal environments. The paleobiogeography of the recorded bivalve taxa is highlighted, revealing two endemic species to Egypt; Nucula chargensis Quaas and Meretrix rohlfsi (Quaas). On the other hand, the other identified bivalve species show wide distribution over a broad geographical area, including North Africa, East and West Africa, Middle East, Asia, Europe, South America, and North America. The bivalve distribution in the present study suggests a strong affinity to the southern Tethyan Province. potential applications in various fields, such as pharmaceuticals, and materials science. Additionally, the synthesis of fluorescent sensors and potential inhibitors for enzymes is discussed.
... fair-weather and storm waves, tidal, long-term, storm-induced and turbidity currents), a reduced rate of sedimentation and a high biological production (e.g. Kidwell 1991;Fürsich and Oschmann 1993;Kondo et al. 1998;Fürsich and Pandey 2003;Stoica et al. 2007;Abdelhady et al. 2020). Their use for the reconstruction of depositional environments and palaeoecological conditions and characterising sequence stratigraphic units and boundaries has been documented in many studies (e.g. ...
... Their use for the reconstruction of depositional environments and palaeoecological conditions and characterising sequence stratigraphic units and boundaries has been documented in many studies (e.g. Kidwell 1991;Abbott 1997Abbott , 1998Kondo et al. 1998;Cantalamessa et al. 2005;Fürsich et al. 2009Fürsich et al. , 2018Fürsich et al. , 2021Sharafi et al. 2012Sharafi et al. , 2021aSharafi et al. , 2022bVelde et al. 2019;Mandic et al. 2019;Abdelhady et al. 2020). In this context, the accurate identification of the biofabric of shell beds and of the taphonomic signatures of their components play a crucial role in evaluating the environmental conditions and prevailing sedimentary processes that led to their formation, especially in homogeneous successions with little facies changes (e.g. ...
... Depositional conditions were oscillated from low energy, dysoxic-anoxic, and high organic matter influx (non-fossiliferous fissile black shale) to high energy and oxic conditions (fossiliferous phosphatic sandstone, marl, and sandy limestone beds; Fig. 2) (cf. El Ayyat and El Ayyat, 2015;Abdelhady et al., 2020). ...
The palaeoenvironments of the Campanian‒lower Palaeocene composite succession in the Dakhla Oasis, Egypt, are interpreted based on the integration of sequence-stratigraphy, macrobenthic associations, and trace fossils. This succession comprises six rock units, corresponding to several transgression-regression cycles. These rock units include the Quseir Formation, the Duwi Formation, and the Mawhoob, Beris, Lower Kharga, and Upper Kharga members of the Dakhla Formation. Six unconformities delineate seven 3rd-order depositional sequences, including the lower‒middle Campanian DS-Q1, the upper Campanian DS-D1 and DS-D2, the lower Maastrichtian DS-Dk1, the upper Maastrichtian DS-Dk2 and DS-Dk3, and the lower Danian DS-Dk4. The invertebrate macrobenthic elements sporadically occurred throughout the studied succession, representing three bivalve associations: the late Campanian Nicaisolopha-Plicatula association, the late Maastrichtian Exogyra overwegi association, and an early Danian Venericardia association. At least 12 ichnotaxa have been identified, representing two ichnoassemblages: the late Campanian Thalassinoides-Psilonichnus and the latest Maastrichtian‒early Danian Rhizocorallium jenense-Tisoa siphonalis, both belonging to the Glossifungites Ichnofacies. Sequences characteristics indicate palaeoenvironments ranging from brackish, littoral, and near-shore to inner and outer neritic settings, reflecting the influence of syn-sedimentary tectonics combined with sea-level fluctuations, which resulted in varied depositional features. The distribution and the trophic structure of the body and trace fossil assemblages confirm the role of several environmental parameters, such as substrate characteristics, bathymetry, water energy, productivity level, sedimentation rates, and oxygen availability, in shaping the occurrence of different elements within these faunal assemblages.
... In terms of mineralogy, it contains a variety of minerals including montmorillonite, kaolinite, calcite, gypsum, quartz, and pyrite 59 . Lastly, analyses by Abdelhady et al. 60 focused on sedimentary analysis to understand the influence of environmental conditions on paleoecosystems. Their research underscores the economic significance of the Duwi formation within the Middle East phosphorite belt, emphasizing its potential as a valuable geological resource as it comprises three distinct facies: organic carbon-rich shales, phosphatized pack/grainstones, and biofloat/rudstones 60 . ...
Uranium exploration plays a pivotal role in meeting global energy demands and advancing nuclear technology. This study presents a comprehensive approach to uranium exploration in the Gebel Duwi area of the Central Eastern Desert of Egypt, utilizing remote sensing and airborne gamma-ray spectrometric data. Multispectral remote sensing techniques, including Principal Component Analysis (PCA), Minimum Noise Fraction (MNF), and Band Ratioing (BR), are employed to identify lithological units and hydrothermal alteration zones associated with uranium deposition, such as iron oxides, argillic, propylitic, and phyllic alterations. Additionally, airborne gamma-ray spectrometry data provide insights into the spatial distribution of radioelements, including uranium (eU), thorium (eTh), and potassium (K), as well as radioelement ratios (eU/eTh, eU/K, and eTh/K). The uranium migration index map (eU-(eTh/3.5)) and the F-parameter map (K*(eU/eTh)) have been generated to investigate the movement of uranium within various geological zones and characterize anomalous uranium concentrations. Statistical analyses, including mean (X), standard deviation (S), and coefficient of variability (C.V.), are conducted to identify uranium-rich zones. The integration of these datasets enables the generation of a uranium potential map highlighting areas of elevated concentrations indicative of uranium mineralization. Field observations and mineralogical analyses of collected samples validate our findings, confirming the presence of minerals associated with uranium mineralization in mapped high-potential areas. The significance of minerals like Fe-Chlorite, Fe-Mg-Chlorite, ferrihydrite, goethite, calcite, muscovite, dolomite, actinolite, vermiculite, and gypsum in indicating potential uranium mineralization processes underscores the importance of our results.
... The faunal associations found in Blesa also suggest deposition in a low-energy stressed peritidal environment colonised episodically by opportunistic taxa (e.g., Flügel, 2010;Cuitiño et al., 2013;Abdelhady et al., 2020), possibly a carbonate mudflat. ...
Detailed facies and sequence stratigraphic analysis of an Aptian shallow-marine succession illustrates the evolution of sedimentary environments and their benthic faunal associations in a marginal bay developed in northeastern Iberia (Maestrazgo Basin, Oliete Subbasin). In this bay, marine circulation was hampered by wide stationary shoals located in the low-subsidence transitional areas between subbasins. The Aptian sedimentary record of this bay (Josa and Oliete formations) is composed of four transgressive-regressive (T-R) sequences bounded by major unconformities generated during relative sea-level falls. The Josa Fm (formally defined herein) encompasses an asymmetrical T-R cycle (sequence J). It comprises transgressive prodelta clays with episodic orbitolinid blooms, grading upwards to regressive freshwater-influenced littoral and delta-front sandstones and sandy limestones which yield diverse bivalve communities dominated by trigoniids. The Oliete Fm encompasses three T-R cycles (sequences O1-O3), mostly deposited in a protected lagoon. The transgressive hemicycle of each sequence is dominated by marls containing low-diversity faunal associations composed of ostracods and mm-sized gastropods and bivalves, indicating stressed (probably dysoxic) conditions in the deepest parts of the lagoon, related to a lack of water circulation. The regressive hemicycle of sequences O1 and O2 is characterised by low-energy intertidal to shallow subtidal deposits including sponge spiculites, mud-dominated accumulations of articulated bivalves and gastropods with low-diversity microfaunal associations composed mainly of Choffatella and few other textulariids, and marginal oyster-serpulid patches. The uppermost part of Sequence O2 is characterised by the development of siliciclastic tide-influenced coastal plains. Sequence O3 consists of massive intertidal to shallow subtidal glauconite accumulations related to the transgressive reworking of siliciclastic deposits. Foraminiferal associations in Sequence O3 show an increase in diversity (including miliolids, lageniids and diverse textulariids), which was probably fostered by a more stable connection with open seas, caused by tectonic activity in the bounding shoal areas. The analysis of these four sequences represents a comprehensive and detailed characterization of shallow-to-marginal marine benthic communities integrated in a sequence stratigraphic framework.
... Frequency histograms were plotted using a size-class interval, reducing empty spaces as much as possible. Sizefrequency distributions were compared to a normal distribution using a Shapiro-Wilk test and the QQ plot [57]. All morphometrics and statistical analyses were conducted using PAST V. 2.17c [58]. ...
Wetland ecosystems of the Nile Delta face severe threats due to natural climatic changes and anthropogenic activities. Life and death assemblage comparisons can be implemented as a historical record to detect anthropogenic-induced environmental changes in the past few decades. A geometric morphometric approach was applied to quantify the pollution-induced morphological variation between life and death populations of the gastropod Melanoides tuberculata. The results indicated that life populations differ significantly from the death ones, where the first tend to be much smaller, more globular, and with a depressed aperture and whorl section. In addition, the phenetic diversity of the life populations was also decreased, and the allometric growth was shifted. These morphological changes in the life populations are well-known adaptations for reducing the cost of shell maintenance in polluted water. No distinct morphospace was found between life populations from different habitats, suggesting that habitats have no significant role in the current pollution-induced evolution.
... Hallam (1989) indicated that regression may be only an indirect factor behind extinction, while the most significant factor is the anoxic bottom water. Anoxia can be associated either with transgression (deepening) and lowering hydrodynamics (e.g., Precht et al. 2004;Abdelhady and Mohamed 2017;Abdelhady et al. 2020a) or regression and associated terrigenous influx, eutrophication, and decay of terrestrial organic matter (Abdelhady and Fürsich 2014). ...
Based on the global occurrence dataset, the shift in taxonomic and functional diversity of bivalves at the Triassic/Jurassic transition was examined herein. There is a noticeable decline in diversity at many taxonomic levels (generic, family, and order) along the Triassic/Jurassic boundary. Test changes in the functional diversity (e.g., life habits, mobility levels, and feeding mode) revealed that the percentage of mobile exceeded stationary taxa after the end of the Triassic crisis, while no major changes were observed in the life habit or feeding mode. By the Sinemurian, diversity reached the pre-extinction levels. A significant difference was also found between survivors’ longevity and extinct taxa, where the Early Jurassic (Hettangian) fauna have a longer duration relative to those that became extinct. The Triassic/Jurassic boundary is marked by a marked sea-level fall and a decrease in the mean Sea Surface Temperature (SST), which is associated with increasing siliciclastic and decreasing carbonate rocks. The latter may also point to ocean acidification at the Triassic/Jurassic boundary. The geographic range size of bivalves is slightly changed by the end of the Triassic, where the taxa are slightly characterized by narrower ranges. Hence, the geographic range size, the result of ecophysiology, plays a major role in determining the extinction risk. The difference in the magnitude of the diversity loss (i.e., taxonomically vs. functionally) indicated that the shallower marine habitat destruction resulting from the sea-level fall is the primary cause of the Triassic/Jurassic mass extinction.
... The encrustation, shell fragmentation, disarticulation, and orientation (e.g. convex-up vs. convex down) were quantitatively estimated (see Abdelhady et al., 2020b). Rock samples were collected for further analyses and preparation in the laboratory (e.g., thin sections). ...
The Cenomanian shallow marine succession in the Southern Galala Plateau of Egypt contains rich benthic fauna and preserves enormous information on how paleo-communities respond to fluctuating environmental conditions. Based on rock and fossil data, the Galala Formation was interpreted to be the result of deposition on a tide-dominated homoclinal ramp. Three main facies associations representing three depositional environments (intertidal, shallow subtidal, and deep subtidal) were recognized. Three distinct macroinvertebrate associations corresponding to these environments and dominated mainly by oysters were quantitatively identified. They show a gradational vertical increase in diversity as well as in the infaunal and mobile species. This trend can be attributed to the Cenomanian sea-level rise, where harsh marginal marine environments in the middle Cenomanian became more stable toward the latest Cenomanian. Sea flooding may have eliminated barriers, enhanced water circulation, and stopped hyperpycnal flow and/or terrigenous flux. Consequently, oxic mesotrophic conditions may have prevailed and siliciclastic starvation may have concentrated fossil materials, and therefore, diversity increased. Based on the vertical and lateral changes of the facies stacking pattern, two main parasequence types were recognized, the first includes deep subtidal deposits changed upwards to shallow subtidal and the second includes shallow subtidal deposits that pass upward into intertidal. Moreover, two and one-half third-order mixed sequences were identified and correlated to their regional and global counterparts.
In contrast to the Cenomanian-Turonian, the Coniacian-Santonian macroinvertebrates of the Middle East and North Africa are rarely investigated. Previous investigations indicated the occurrence of low diversity faunal associations, which can be attributed either to ecological (primary/biogenic) or taphonomic (secondary/ sedimentologic) factors. The poorly preserved macrofauna of the Hawashia Formation (north Eastern Desert, Egypt) has been quantitively analyzed resulting in the identification of fifteen macrofaunal species including five bivalve, seven gastropod, two ammonite taxa, and one echinoid taxon. The occurrence of the ammonites Metatissotia fourneli Bayle and Texanites (T.) texanus Roemer confirms the Coniacian‒Santonian age for the Hawashia Formation. Based on litho- and biofacies, this fauna likely lived in a normal oxygen tidal-influenced shallow subtidal environment under arid conditions. Taphofacies indicates a low-energy regime with low sedimentation rate. Most shells are highly damaged (encrusted, bioeroded, and fragmented) due to their long residence time in the Taphonomic Active Zone (TAZ). Few of the benthic species have a wide geographic distribution (e.g., Oscillopha dichotoma), which generally imply low sea-levels. In contrast, ammonites have been precariously recorded from Africa, Europe, and Asia in addition to South America, outlines a cosmopolitan attitude.
Environmental reconstruction can benefit from the interpretation of the postmortem history of shell remains. The molluscan death assemblages obtained from grab samples at forty-nine sites in the Manzala lagoon, the largest lagoon in the Nile Delta, were analyzed to infer the taphonomic alteration. The preservation of shells at each site has been semi-quantitatively ranked based on the taphonomic features formed by encrustation, bioerosion, abrasion, dissolution, precipitation, fragmentation, discoloration, and loss of sheen (low, moderate, high). A significant difference has been observed between sites of low and high environmental stress. Water depth and substrate type (hydrodynamics) correlate significantly to the percent number of altered shells. The southern parts of the lagoon, which are characterized by lower water energy and higher rates of sedimentation, are highly polluted by heavy metals (Cd, Pb, Zn) and organic pollutants. The southern parts receive much sediment from the agricultural drains, which increases burial of shelly material and decreases their time on the TAZ. The northern parts of the lagoon have slower rates of sedimentation, so that the molluscan shells remain longer at the sediment-water interface (Taphonomic Active zone; TAZ), where fragmentation is enhanced by winnowing under higher water-energy. The long residence in the TAZ also favored both bioerosion (Trypanites and Oichnus) and encrustation by bryozoan colonies, polychaetes, and oysters. Therefore, the taphonomic processes have the potential to cause severe damage and taphonomic loss of shell materials. Chemical dissolution and precipitation of shell remains may be related to acidic pore water. Moreover, high alkalinities in the southern polluted parts may also reduce the dissolution in contrast to the acidic water in the northern parts of the lagoon.
The present paper focuses on the phosphate-bearing deposits that represent promising geologic resources for mining and sustainable development in central Egypt. Phosphates are important for manufacturing fertilizers, elemental phosphorus and chemical industries. The Upper Cretaceous phosphate-bearing Duwi Formation (with grades of P 2 O 5 20-32 %) can be mined either by open cast or underground. Three main sites are promising for the phosphate mining, these are: 1) The Abu Tartour mine (with estimated reserves of 1 billion tons and up to 31% P 2 O 5); 2) The Sibaiya mine (with a reserve of < 500 million tons and grades of 28-30% P 2 O 5); and 3) The Red Sea mines (yielding reasonable reserves and grades of 25-33% P 2 O 5). Egypt holds 4% of global phosphate deposits (2.78 billion tones) and produces 3% of global phosphate production (6 million tones / year).
The last 8 Myr of the Cretaceous greenhouse interval were characterized by a progressive global cooling with superimposed cool/warm fluctuations. The mechanisms responsible for these climatic fluctuations remain a source of debate that can only be resolved through multi-disciplinary studies and better time constraints. For the first time, we present a record of very high-resolution (ca. 4.5 kyr) seasurface temperature (SST) changes from the Boreal epicontinental Chalk Sea (Stevns-1 core, Denmark), tied to an astronomical timescale of the late Campanian-Maastrichtian (74 to 66 Ma). Well-preserved bulk stable isotope trends and calcareous nannofossil palaeoecological patterns from the fully cored Stevns-1 borehole show marked changes in SSTs. These variations correlate with deep-water records of climate change from the tropical South Atlantic and Pacific oceans but differ greatly from the climate variations of the North Atlantic. We demonstrate that the onset and end of the early Maastrichtian cooling and of the large negative Campanian- Maastrichtian boundary carbon isotope excursion are coincident in the Chalk Sea. The direct link between SSTs and δ13C variations in the Chalk Sea reassesses long-term glacioeustasy as the potential driver of carbon isotope and climatic variations in the Maastrichtian.
About 20 billion tonnes of world-class, high-grade phosphorite resources occur in a small area of the eastern Mediterranean region, including Jordan, northern Negev (Palestine), northwestern Saudi Arabia, western Iraq, and southeastern Syria. Major deposits were formed during Campanian to Eocene times and contribute significantly to the economic development of these countries, particularly Jordan and Syria. The phosphorite deposits consist mainly of reworked granular material. The phosphate particles are peloids, such as pellets, intraclasts, nodules, coated grains and coprolites, and vertebrate fragments (bone and teeth). The phosphorite sequences are associated with extensive bedded chert, porcelanite, and organic-rich marls. The main phosphate mineral is francolite, a carbonate-rich variety of fluorapatite that has a relatively enhanced uranium content as a result of substitution for calcium in its crystal structure.
Two factors are deemed responsible for the deposition of the phosphorites and their associated chert, porcelanite, and marl within this relatively restricted area. The first was a compressional event associated with the initial collision of the oceanic forefront of the Afro-Arabian Plate with the subduction trench of Eurasia that began in Turonian times and continued into the Eocene. This event resulted in gentle folding that produced the Syrian Arc, the Ha’il, Rutba, and Sirhan paleohighs and the Ga’ara Dome, which were loci for the deposition of phosphorites. The second factor was the obstruction and consequent upwelling of oceanic currents by these tectonic highs, enhanced by winds blowing from east to west along the southern platform margin of the Neo-Tethys Ocean. The intense upwelling was associated with the Tethyan Circumglobal Current that flowed along the Afro-Arabian platform on the southern margin of the Neo-Tethys Ocean. In contrast, relatively minor phosphorite deposition took place to the north in southern Europe.
The upwelling spread cold, nutrient-rich oceanic water from the deep Neo-Tethys Ocean to the surface, thereby enhancing bioproductivity to produce organic-rich sediments. The subsequent authigenesis of phosphorites, their diagenesis and the reworking and winnowing of the phosphorite-rich sediments, concentrated the materials into economic deposits. Phosphorite deposition ended in the Late Eocene following the final collision of the Afro-Arabian Plate with Eurasia. The sub-aerial exposure of this formerly productive shallow-marine platform was the result of the separation of the Arabian Plate from the African Plate during the mid-Miocene.
Abstract The objective of this study is to assess the organic material for petroleum potential and characterize the relationships between organic material, thermal maturity, and the depositional environments. This is done using ‘‘14” samples from the shales of the Dakhla and Duwi formations in Abu Tartur area. The samples have been analyzed using the geochemical method of Rock–Eval pyrolysis. The analysis shows that the total organic carbon content lies between 0.56 and 1.96 wt%. It also shows that kerogen is a mixture of type II and III that is dominant, and is deposited in the shallow and restricted marine environment under prevailing reducing conditions. This type of kerogen is prone to oil and oil/gas production. The geochemical diagrams show that all the studied samples have good thermal maturation. The Dakhla and Duwi formations which have been divided into all zones are mature (have Tmax over 435 �C), and have organic carbon content located at the oil window (Tmax between 435 and 443 �C).
The Cretaceous to Eocene succession in central and south Jordan is characterised by passive continental margin depositional sequences, which pass upward from alluvial/paralic to carbonate shelf and pelagic ramp settings. Detailed section logging and outcrop mapping have produced robust lithostratigraphic and lithofacies schemes that can be correlated throughout the region and in the subsurface. These schemes are set in a sequence stratigraphic context in relation to the evolution sedimentation on the Arabian and Levant plates. Three major megasequences are described (Kurnub, Ajlun and Belqa), and these are further subdivided into large-scale depositional sequences separated by regional sequence boundaries that represent maximum flooding surfaces. There is close correspondence between maximum flooding surfaces recording major sea-level rise with those derived for the Arabian and Levant plates, although there are some discrepancies with the precise timing of global sea-level fluctuations. An upward change from braided to meandering stream fluvial environments in central and south Jordan during the Early Cretaceous, reflects a decreasing geomorphological gradient of the alluvial plain, declining siliciclastic sediment flux, and increased floodplain accommodation, associated with a regional Late Albian (second-order) rise in relative sea-level. The Late Albian to Early Cenomanian marine transgression across the coastal alluvial plain marks a major sequence boundary. During Cenomanian to Turonian times a rimmed carbonate-shelf was established, characterised by skeletal carbonates showing small-scale, upward-shallowing cycles (fourth-to fifth-order parasequences) ranging from subtidal to intertidal facies, arranged into parasequence sets. Rimmed carbonate shelf sequences pass laterally to coeval coastal/alluvial plain facies to the south and east. Eustatic (third-order) fluctuations in relative sea level during the Cenomanian and Early Turonian resulted in deposition of ammonite-rich wackestones and organic-rich marls, during high sea-level stands (maximum flooding surfaces). Progradational sabkha/salina facies passing landwards to fluvial siliciclastics were deposited during an Early Turonian sea-level low stand, marks a regional sequence boundary, above which a highstand carbonate platform was established.
The Late Cretaceous 'greenhouse' world witnessed a transition from one of the warmest climates of the past 140 million years to cooler conditions, yet still without significant continental ice. Low-latitude sea surface temperature (SST) records are a vital piece of evidence required to unravel the cause of Late Cretaceous cooling, but high-quality data remain illusive. Here, using an organic geochemical palaeothermometer (TEX86), we present a record of SSTs for the Campanian-Maastrichtian interval (~83-66 Ma) from hemipelagic sediments deposited on the western North Atlantic shelf. Our record reveals that the North Atlantic at 35 °N was relatively warm in the earliest Campanian, with maximum SSTs of ~35 °C, but experienced significant cooling (~7 °C) after this to <~28 °C during the Maastrichtian. The overall stratigraphic trend is remarkably similar to records of high-latitude SSTs and bottom-water temperatures, suggesting that the cooling pattern was global rather than regional and, therefore, driven predominantly by declining atmospheric pCO2 levels.
A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
Anoxic conditions prevailed on the Late Cretaceous seafloor beneath a long-term upwelling system situated across the southern Tethys. In Israel, the acme of this system was during the Campanian, when a suite of characteristic lithofacies (organic-rich carbonate, phosphorite, porcelanite, and chert) was broadly distributed over at least a 250 km wide zone encompassing the paleotopography of the Syrian Arc fold belt and beyond. Stressed faunal associations developed all across this belt. While more ventilated horizons supported molluscan assemblages, laminated sediments with oxygenation levels below 0.1 ml O2/l were macroscopically sterile but were found to support rich foraminiferal microfaunas. These faunas, apparently adapted to near anoxia, are dominated by two highly specialized buliminid species, Neobulimina canadensis and Praebulimina prolixa, in five assemblages that define different levels of oxygen stress. The foraminifera presumably lived below the sediment surface in the pore-water microenvironment, where habitat partitioning depended on food and oxygen resources rather than the nature of the sediment particles. They therefore do not correlate to the sediment type or lithofacies from which they were recovered.
Paleoecology has a dual relationship with sequence stratigraphy. On one hand, body and trace fossils, together with their taphonomy, may provide sensitive indicators of environmental parameters, including depth, substrate consistency, sedimentation rate/turbidity, and benthic oxygenation, which are critical in recognizing and interpreting parasequences and sequences. Fossils may provide some of the best guides to identifying hey surfaces and inferring sedimentation dynamics within sequences. Conversely, the sequence stratigraphic paradigm and its corollaries provide a predictive framework within which to examine biotic changes and interpret their probable causes. Such changes include ecological epiboles (short-term, widespread proliferation of normally rare species), outages (absence of normally common species), ecophenotypic changes, and longterm (tens to hundreds of Ka) community replacement. Community replacement should be carefully distinguished from short-term (10 to a few hundred years) ecological succession, rarely resolvable at the scale of single beds, although replacement series through shallowing-to-deepening cycles may display some features that parallel true succession. Replacement in marine communities may he relatively chaotic, but, more commonly in offshore settings, it appears to involve lateral, facies-related shifting of broad biofacies belts, or habitat tracking. Tracking patterns may be nearly symmetrical in areas of low sediment input. However replacement cycles are commonly asymmetrical. The asymmetries involve both apparent and real effects; deletion of portions of facies transitions at sequence boundaries or condensed sections leads to artifactual asymmetries. Alternatively, in areas proximal to siliciclastic sources, tracking asymmetries arise from the markedly higher sedimentation rates during regressive (late highstand) than transgressive phases. Replacements may also involve immigration of species into a sedimentary basin, either as short-lived events (incursion epiboles) or as wholesale faunal immigrations. The latter will typically follow intervals of extinction/emigration of the indigenous faunas. Both large and small immigration events appear most commonly during highstands (transgressive peaks), which may be associated with altered water-mass properties, and may open migration pathways for nekton and planktonic Larvae. At least in isolated basins, allopatric speciation may also occur during fragmentation of habitats associated with regressions. Finally, there are predicted and empirical correlations between sequence-producing sea-level fluctuations and macroevolution. Major extinctions may be associated with habitat reduction during major regressions (lowstands), or with anoxic events during major transgressions, Generally, rising sea level may be correlated with evolutionary radiations. Hence, some ecological-evolutionary unit boundaries may correlate either with sequence boundaries or maximum flooding surfaces. However in other cases, no correlation has been found between macroevolutionary patterns and sequence stratigraphy. The situation is obviously complex, but sequence stratigraphy at least provides a heuristic framework for developing and testing models of macroevolutionary process.
WILMSEN, M. & VOIGT, T. 2006. The middle-upper Cenomanian of Zilly (Sachsen-Anhalt, northern Germany) with remarks on the Pycnodonte Event. Acta Geologica Polonica, 56 (1), 17-31. Warszawa. A detailed stratigraphic log of the 28 m thick Cenomanian succession at Zilly (Sachsen-Anhalt) is presented. The suc- cession is composed of 11 m of middle Cenomanian hemi-pelagic marl-limestone alternations ('Pläner Limestones') grad- ing into 15 m of upper Cenomanian calcareous pelagites ('Poor rhotomagense Limestones') unconformably overlain by 1.5 m of red-coloured marly clays and limestones ('Rotpläner'). The proof of the interregional marker beds of the Pycnodonte Event at the 11 m level, the Facies Change at 26 m, and the base of the plenus Bed at 26.9 m allow a bio-/chronostrati- graphic correlation of these levels with the middle/upper Acanthoceras jukesbrownei Zone (upper middle Cenomanian), the Calycoceras (Proeucalycoceras) guerangeri/Metoicoceras geslinianum Zone transition, and the lower Metoicoceras ges- linianum Zone, respectively (middle upper Cenomanian). Litho-/microfacies and sequence stratigraphic analyses indicate an overall increase of pelagic influence up to the Facies Change. This retrogradational trend was shortly interrupted by the Pycnodonte Event, the base of which correlates with the late middle Cenomanian sequence boundary SB Ce IV and the succeeding transgressive surface. The Facies Change indicates a significant mid-late Cenomanian sea-level fall (sequence boundary SB Ce V), followed by more shallow water Rotpläner deposition. The Pycnodonte Event is very thick and prox- imal in character at Zilly. Its monospecific oyster fauna consists of small pycnodonteines assigned to Pycnodonte (Phygraea) vesicularis (LAMARCK) vesiculosa (J. SOWERBY), a secondarily free-lying oyster which lived as a 'cup-shaped recliner'. The patchy occurrence of the oysters, the sorting and partial damage of valves prior to final burial along with significant supply of terrigenous materials suggest episodically elevated water energy and strong environmental stress during deposition of the Pycnodonte Event. This situation promoted colonization of the sea-floor by, and reproductive success of the inferred eurytopic oyster. The Pycnodonte Event is a classic example of an 'onlapping bioevent', the formation of which was con- trolled by different factors such as sea-level rise, terrigenous influx, environmental stress, and preferential preservation.
Skeletal concentrations are ubiquitous in Bathonian Oxfordian shallow water sediments of the pericratonic basins of Kachchh and Rajasthan, western India. By analysing the biofabric of the concentrations and the taphonomic signatures of individual components, it is possible to distinguish between the final concentration process (recorded by the biofabric) and events taking place prior to final deposition (recorded by taphonomic signatures). The skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations. They mainly reflect biological and hydraulic processes, and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient. Plotted against the stratigraphic sections, the skeletal concentrations show, in accordance with other sedimentological data, three orders of bathymetric trends. The first two orders are shallowing-deepening cycles which possibly correspond to eustatic changes in sea level; the third order represents parasequences with a strongly asymmetric sedimentary record. Skeletal concentrations are a useful additional tool in basin analysis, but are best used in combination with other data.
The Cretaceous to Eocene succession in central and south Jordan is characterised by passive continental margin depositional sequences, which pass upward from alluvial/paralic to carbonate shelf and pelagic ramp settings. Detailed section logging and outcrop mapping have produced robust lithostratigraphic and lithofacies schemes that can be correlated throughout the region and in the subsurface. These schemes are set in a sequence-stratigraphic context in relation to the evolution sedimentation on the Arabian and Levant plates. Three major megasequences are described (Kurnub, Ajlun and Belqa), and these are further subdivided into large-scale depositional sequences separated by regional sequence boundaries that represent maximum flooding surfaces. There is close correspondence between maximum flooding surfaces recording major sea-level rise with those derived for the Arabian and Levant plates, although there are some discrepancies with the precise timing of global sea-level fluctuations.
An upward change from braided to meandering stream fluvial environments in central and south Jordan during the Early Cretaceous, reflects a decreasing geomorphological gradient of the alluvial plain, declining siliciclastic sediment flux, and increased floodplain accommodation, associated with a regional Late Albian (second-order) rise in relative sea-level. The Late Albian to Early Cenomanian marine transgression across the coastal alluvial plain marks a major sequence boundary. During Cenomanian to Turonian times a rimmed carbonate-shelf was established, characterised by skeletal carbonates showing small-scale, upward-shallowing cycles (fourth- to fifth-order parasequences) ranging from subtidal to intertidal facies, arranged into parasequence sets. Rimmed carbonate shelf sequences pass laterally to coeval coastal/alluvial plain facies to the south and east. Eustatic (third-order) fluctuations in relative sea level during the Cenomanian and Early Turonian resulted in deposition of ammonite-rich wackestones and organic-rich marls, during high sea-level stands (maximum flooding surfaces). Progradational sabkha/salina facies passing landwards to fluvial siliciclastics were deposited during an Early Turonian sea-level low stand, marks a regional sequence boundary, above which a highstand carbonate platform was established.
A second-order, regional rise in sea level and marine transgression during the Early Coniacian marks a Type 2 sequence boundary, and subsequent drowning of the rimmed carbonate shelf by Late Coniacian times. Sedimentation during the Santonian to Maastrichtian was characterised by a hemi-pelagic chalk-chert-phosphorite lithofacies association, deposited in shallow to moderate water depths on a homoclinal ramp setting, although thicker coeval sequences were deposited in extensional rifts. The marked change in sedimentation from rimmed carbonate shelf to pelagic ramp is attributed to Neo-Tethyan mid-oceanic rifting, tilting, intracratonic deformation and subsidence of the platform; this is reflected in changes in biogenic productivity and ocean currents. Oceanic upwelling and high organic productivity resulted in the deposition of phosphorite together with giant oyster banks, the latter developing within oxygenated wave-base on the inner ramp. Chalk hardgrounds, sub-marine erosion surfaces, and gravitational slump folds indicate depositional hiatus and tectonic instability on the ramp. In the Early Maastrichtian, deeper-water chalk-marl, locally organic-rich, was deposited in density-stratified, anoxic basins, that were partly fault controlled.
Pulsatory marine onlap (highstand sequences) during the Eocene is manifested in pelagic chalk and chert with a paucity of benthic macro-fauna, indicating a highly stressed, possibly hypersaline, and density-stratified water column. Comparison with global and regional relative sea-level curves enable regionally induced tectonic factors (hinterland uplift and ocean spreading) to be deduced, against a background of global sea-level rise, changing oceanic chemistry/productivity and climatic change.
Few organisms can live in harsh transitional water due to highly variable and rapid changeable physicochemical conditions. Fortunately, connecting the community structure of such fauna to specific environmental parameters can be used in tracing past and recent environmental changes. Herein, we analyzed the benthic communities in Manzala lagoon (Nile–Delta), a region very impacted by the construction of the High–Dam at Aswan, along the the inshore-offshore gradient. About three thousand specimens belonging to thirty–one species sampled in fifty–four sampling sites were identified. The environmental and biological data were subjected to multivariate data analyses. Hierarchical clustering and non–metric multidimensional scaling identified three biotopes along a gradient of water salinity and sediment grain–size. The epifaunal/infaunal ratio was negatively correlated with salinity (R2 = – 0.72, p <0.01). The low salinity–stations with a high content of silt and clay sediments were dominated by deposit-feeders, opportunistic gastropods. In contrast, the suspension–feeding bivalves dominated the more saline water and sand-sized sediments (R = 0.83, p <0.001) near the Mediterranean outlets. The general low diversity and high dominance in the lagoon indicate high environmental stress and biodiversity loss as the background freshwater species have been declined and only a few opportunistic taxa have been flourished. In addition, a specific salinity-range was estimated at both species and community level. The results confirm that salinity and substrate type are major determinants for the structure of the molluscan community (feeding habit and life–mode) in marginal marine environments. Consequently, the feeding habit and life–mode of the mollusks, which has a continuous and very complete fossil record, can be used as a robust indicator for paleosalinity and paleo-hydrodynamics.
Based on rock and fossil data from the Upper Cretaceous of the El Hassana Dome (Abu Roash, Egypt), factors controlling facies architecture and the nature of biotopes are highlighted. The succession formed on a non-rimmed shelf, the architecture of which varied from an inner to an outer shelf setting upsection. Macrobenthic biotopes are reconstructed and their palaeoecological significance assessed using a novel ternary plot. Based on diversity and community structure (770 specimens assigned to 28 bivalve and gastropod taxa), four paucispecific associations are identified. These are: 1. the ‘Cucullaea’ Assemblage, a low-energy, soft-substrate, oligotrophic outer shelf environment with reduced terrigenous input dominated by infaunal bivalves and hexactinellid sponges; 2. the ‘Plicatula’ Assemblage, a low-energy, restricted inner shelf lagoonal setting with soupy substrates and dysoxia below the sediment-water interface dominated by plicatulid and ostreid bivalves, 3. the ‘Durania’ Assemblage, a high-energy, high-temperature, shoal environment dominated by elevator rudists with minor numbers of echinoids, corals and bryozoans, which together form several biostromes. and 4. The ‘Trochactaeon’ Assemblage, which share the same characteristics of the ‘Durania’ Assemblage. The paucispecific nature of these biotopes is indicative of different stress factors. Consequently, the predominant taxa exhibit different degrees of adaptive strategies. In addition to global sea level, local tectonics have significantly affected facies distribution and biotope structure. The shallower facies during the early Turonian and the dysoxia spanning the Coniacian–Santonian were linked to synsedimentary tectonics, which formed many barriers and led to circulation restrictions.
In the Early Jurassic, the late Pliensbachian through early Toarcian interval exhibits significant environmental perturbations and biotic extinctions. This study documents the macrobenthic community during this interval in a region that has previously received comparatively little study: northeastern Panthalassa. The relicts of benthic communities from the Ya Ha Tinda Lagerstätte (Fernie Formation) in Alberta, Canada are primarily composed of bivalves and brachiopods, and exhibit taxonomic and ecological similarities with coeval black shale faunas from Europe.
Cretaceous-Paleocene organic-rich sediments in Egypt occur as an east-west trending belt extending from the Quseir-Safaga district (Red Sea) to the Kharga-Dakhla (Western Desert) region. They are associated with the Duwi Formation (phosphate-bearing) and the overlying Dakhla Formation (deeper epicontinental shale/marl). This study aims to reconstruct the paleo-redox conditions during deposition of these thermally immature organic-rich sediments using carbon-sulfur-iron systematics and trace metal proxies in two cores, one each from the Quseir and Abu Tartur areas. Paleoproductivity, based on P content, seems to have been higher in the Quseir section than in the Abu Tartur section. The Quseir section also records a relatively greater occurrence of anoxic conditions during the accumulation of these sediments than the Abu Tartur section. This difference is indicated by its markedly higher total organic carbon (TOC) content as well as higher contributions of redox-sensitive and sulfide-forming metals (Mo, U, Ni, V, and Co). A weak correlation exists between S and TOC, and a positive S intercept (>1) was observed in most of the rock units of the study sections. A high consistency between the TOC-S-Fe relations and trace metals findings was found. The uppermost Duwi and the lowermost Dakhla strata, which have the highest TOC and represent a maximum sea transgression during the Late Cretaceous, have the highest contents of redox-sensitive trace metals. The carbonate-dominated transgressive Baris and Beida members of the Dakhla Formation record relatively stronger oxygen-depleted conditions during their accumulation than others, which led to relatively higher TOC contents and redox-sensitive metal accumulations. A scenario for the environmental conditions that existed during the deposition of these organic-rich successions, based on compiled trace metals and TOC-S-Fe implications, is reconstructed here.
Three textural features seem especially useful in classifying those carbonate rocks that retain their depositional texture (1) Presence or absence of carbonate mud, which differentiates muddy carbonate from grainstone; (2) abundance of grains, which allows muddy carbonates to be subdivided into mudstone, wackestone, and packstone; and (3) presence of signs of binding during deposition, which characterizes boundstone. The distinction between grain-support and mud-support differentiates packstone from wackestone—packstone is full of its particular mixture of grains, wackestone is not. Rocks retaining too little of their depositional texture to be classified are set aside as crystalline carbonates.
The negative impacts of degradation in the coastal zone of the Red Sea are becoming well known in upper portions of the trophic web (e.g., humans and fish), but are less well known among the benthic primary consumers. In addition, the degree to which heavy metals are entering the trophic web can be better-quantified using macrobenthos. Two-gastropod genera encompassing Echinolittorina subnodosa and Planaxis sulcatus from three different localities on the Egyptian coast of the Red Sea were examined in order to deduce the impact of environmental deterioration on the morphology of shells. The examined sites include clean pristine, slightly polluted, and markedly polluted rocky shores. Phosphate/lead industry is the main source of pollution in this zone. Because landmarks on the rugose Echinolittorina are difficult to define and to ensure finer resolution of the analyses, a newly ‘grid-based’ landmarks was implemented. Both Canonical Variate Analysis (CVA) and Thin Plate Spline (TPS) were particularly capable to capture and terrace the minor morphological variations accurately. Two phenotypes portioned among the environmentally different populations were recognized and interpreted as ecotypes with many intermediate forms. The first ecotype has a higher spire and smaller aperture and dominating the pristine site North of Marsa Alam, whereas the second ecotype has a globular shell shape with big aperture and dominating the markedly polluted site. The intermediate forms dominating the slightly polluted site. The shape differences are interpreted as an adaptive differentiation to different metal concentrations. As the morphological variation between the two-ecotypes of both taxa is still minors, and both ecotypes occur together with many intermediate forms, the phenotypic divergence stage has not yet accomplished. The gradational shape change among the investigated populations was positively correlated with index of Pollution (IP). As the human activities were the main driver of the phenotypic changes, hence anthropogenic impact may shift the evolution and/or the extinction rates.
The Upper Cretaceous-lower Tertiary sedimentary rocks in central and southern Egypt are characterized by gradual facies differentiation of three main types--Nile Valley, Garra-El Arbain, and Farafra. These facies are present in three different basins within the marginal trough on the northern flank of the African shield. Two main parvafacies are recognized, one in the Maestrichtian and the other in the Paleocene; the Nubia Sandstone in southern Egypt represents a heterochronous magnafacies correlatable with several rock units in central Egypt.
The investigated exogyrine oysters are morphologically variable. Detailed investigations led to the detection of several morphological features that allow to separate these oysters into two species namely: Ilymatogyra (Afrogyra) africana (LAMARCK) and Rhynchostreon mermeti (COQUAND). Each species modifies its morphology and shell microstructure, including the umbo, attachment area, posteroventral margin, lenticular chambers and chalky layers as an ecological adaptation to the respective substrate.
Paleoecology has a dual relationship with sequence stratigraphy. On one hand, body and trace fossils, together with their taphonomy, may provide sensitive indicators of environmental parameters, including depth, substrate consistency, sedimentation rate/turbidity, and benthic oxygenation, which are critical in recognizing and interpreting parasequences and sequences. Fossils may provide some of the best guides to identifying key surfaces and inferring sedimentation dynamics within sequences. Conversely, the sequence stratigraphic paradigm and its corollaries provide a predictive framework within which to examine biotic changes and interpret their probable causes. Such changes include ecological epiboles (short-term, widespread proliferation of normally rare species), outages (absence of normally common species), ecophenotypic changes, and long-term (tens to hundreds of Ka) community replacement. Community replacement should be carefully distinguished from short-term (10 to a few hundred years) ecological succession, rarely resolvable at the scale of single beds, although replacement series through shallowing-to-deepening cycles may display some features that parallel true succession. Replacement in marine communities may be relatively chaotic, but, more commonly in offshore settings, it appears to involve lateral, facies-related shifting of broad biofacies belts, or habitat tracking. Tracking patterns may be nearly symmetrical in areas of low sediment input. However, replacement cycles are commonly asymmetrical The asymmetries involve both apparent and real effects; deletion of portions of facies transitions at sequence boundaries or condensed sections leads to artifactual asymmetries. Alternatively, in areas proximal to siliciclastic sources, tracking asymmetries arise from the markedly higher sedimentation rates during regressive (late highstand) than transgressive phases. Replacements may also involve immigration of species into a sedimentary basin, either as short-lived events (incursion epiboles) or as wholesale faunal immigrations. The latter will typically follow intervals of extinction/emigration of the indigenous faunas. Both large and immigration events appear most commonly during highstands (transgressive peaks), which may be associated with altered water-mass properties, and may open migration pathways for nekton and planktonic larvae. At least in isolated basins, allopatric speciation may also occur during fragmentation of habitats associated with regressions. Finally, there are predicted and empirical correlations between sequence-producing sea-level fluctuations and macroevolution. Major extinctions may be associated with habitat reduction during major regressions (lowstands), or with anoxic events during major transgressions. Generally, rising sea level may be correlated with evolutionary radiations. Hence, some ecological-evolutionary unit boundaries may correlate either with sequence boundaries or maximum flooding surfaces. However, in other cases, no correlation has been found between macroevolutionary patterns and sequence stratigraphy. The situation is obviously complex, but sequence stratigraphy at least provides a heuristic framework for developing and testing models of macroevolutionary process.
25 mollusc and 5 vertebrate species have been identified from the Duwi Formation exposed in the Nile Valley in the area between Idfu and Qift. One species, Cameliolopha pauciplicata, an early Maastrichtian oyster, is described as new. Within the Duwi formation, the late Campanian Scapanorhynchus texanus Range Zone, and the early Maastrichtian Lopha pomeli and Lopha villei range zones are established. The macrofaunas indicate deposition of the Duwi Formation in a shallow-marine environment and a strong connection with the Mediterranean Province of the Tethyan realm.
In contrast to the minor within-habitat improvements in shell shape and sculpture of primary soft-bottoms dwellers, the transition of fixosessile rock dwellers back to soft substrates has resulted in fast and drastic morphological changes. They were facilitated by the available ecologic stepping stones that caused morphogenetic programmes - first to 'derail' (rock habitats), then to be shortened (to fit the size of dead shell habitats), and finally to extend again (in order to increase mechanical stability on soft bottoms). The 3rd step allows only a limited number of adaptational strategies (flat, outriggered, and edgewise recliners; mud stickers; 'pickabacks') that led to convergent shell forms in different groups of bivalves. Within groups, however, phylogenetic and morphogenetic constraints, as well as the adaptational landscape, channel evolution to such a degree that it becomes difficult, at least in the fossil record, to resolve the multitude of parallel and iterative lineages. -Author
Includes a cyclic sequence of fine-grained sediments with numerous shell beds comprised of abundant, low diversity fresh- and brackish-water faunas. These record the initial marine transgressions of the Cretaceous in this region (Skull Creek-Kiowa tectono-eustatic cycle) and are interpreted as part of an extensive embayment with limited marine influence. Biostrationomic data suggest low rates of sedimentation, frequently shifting environments, and in the coquinas, reworking by storms to account for mixing of meso- to oligohaline and freshwater faunas.-from Authors
Wilmsen, M. 2012. Origin and significance of Late Cretaceous bioevents: Examples from the Cenomanian. Acta Palaeontologica Polonica 57 (4): 759-771. Palaeontological events, documented by widespread beds or thin intervals of strata with either unusual ("exotic") or acmes of common faunal elements are a characteristic feature of Upper Cretaceous epicontinental shelf sediments in NW Europe. Their importance in stratigraphic calibration has early been recognized and these "bioevents" are widely used as correlation tools. Furthermore, it appears that there is a genetic link between sequence and event stratigraphy as most of the "classic" bioevents developed during specific intervals of a 3rd-order depositional sequence. Early transgressive bioevents (ETBs) are subdivided into two subtypes, i.e., the lag and migration subtype. The lag subtype corresponds to the transgressive surface and develops in response to winnowing and relative enrichment of robust biogenic hardparts. Taphonomic alteration and time-averaging are important features. The migration subtype is related to the disappearance of physical or ecological barriers that triggered faunal migrations. Despite their onlapping character, most ETBs are quasi-isochronous, and their preservation potential is usually high. Thus, they are very useful stratigraphic markers. Maximum flooding bioevents (MFBs) represent autochthonous biogenic concentrations with relatively low shell densities. They are related to habitat stability and ecospace expansion, and develop by population blooms of taxa well adapted to the special maximum flooding conditions of the wide epicontinental shelf of NW Europe (e.g., low food availability). Cenomanian MFBs of NW Europe are not time-averaged and may comprise stratigraphically more expanded intervals with gradational lower and upper boundaries. Their often wide palaeogeographic extent associated with very high chances of preservation results in an excellent inter-basinal correlation potential. Late highstand bioevents (LHBs) are local to regional shell concentrations deposited as a result of increasing winnowing of fines and reworking by storms, currents and waves during late highstands. LHBs usually consist of paucior even monospecific skeletal concentrations with a high degree of fragmentation. Simple shell beds related to a single (storm) event, and composite (multiple-event) shell beds are recognized. LHBs share some features of ETBs, but lack of time-averaging, are laterally restricted and have low preservation potential. Thus, their importance in interbasinal correlation is poor. The time scales of Cenomanian bioevents range through several orders of magnitude (hours days in LHB storm event concentrations to similar to 100 kyr in MFBs). In terms of position within sequences, the three bioevent types correspond to shell concentrations recognized in Mesozoic-Cenozoic formations around the world. Shell beds with similar positions within cycles as well as comparable sedimentologic and taphonomic characteristics have also been described from high-frequency sequences and parasequences, suggesting that the formational processes of shell beds operate in base-level controlled sedimentary cycles of different hierarchies (i.e., 3rd-up to 7th-order).
The Jurassic succession at Gebel Maghara, North Sinai, Egypt, represents a mixed
carbonate-siliciclastic sequence. Combining information from both fossils and rocks allowed
a plausible reconstruction of the depositional environments and of the basin topography. The
Jurassic succession of Gebel Maghara was deposited on a ramp, and the architecture of the
ramp facies was strongly controlled not only by sea-level changes but also by extensional tectonics
in connection with rifting of the Tethys, North Gondwana. Seven tectonically modified
third-order sequences (DS 1-DS 7) have been recognized. The first three sequences (DS 1-DS
3), ranging from the Toarcian to the Bajocian, record sea invasion (intertidal to shallow subtidal
conditions) across an intracratonic area as a result of eustatic sea-level changes during a
quiescent rift stage. The remaining sequences (DS 4-DS 7) reflect open marine mid to outer
ramp settings. Non-marine conditions around the Bajocian-Bathonian boundary, documented
by caliche, represent the maximum regression of the sea. During an active extensional stage,
horsts, which formerly acted as barriers separating the Maghara sub-basin from the main
ocean, subsided. Subsequent rejuvenation and reactivation of faults shifted the homoclinal
physiography of the ramp to a distally steepened ramp during the early Bathonian, creating
a 200-m-thick deltaic wedge. Similar processes during the early Kimmeridgian created a calcirudite-
calcarenite succession of slope origin. The diversity of the stratigraphic pattern and
the epifaunal/infaunal percentage of the macrofauna display a cyclic pattern which coincides
more or less with the sequence stratigraphic architecture.
Peloids are considered as major constituents of modern and ancient sedimentary rocks, although their origins and pathways of formation are not yet comprehensively understood. Based on field and petrologic investigations, peloids have been recorded in the Duwi Formation (late Cretaceous) in both Eastern and Western deserts of Egypt. The Duwi Formation represents the first onset of fully marine conditions in Egypt accompanying the major late Cretaceous marine transgression. It comprises a heterogeneous suite of shallow marine sediments (phosphorites, oyster limestones, shales, glauconites and dolomite). According to the hosted rock, peloids are classified into two types: peloids in phosphorites and peloids in limestones, which are characterized by different shapes and sizes. Systematic study indicates that peloids resulted from the interplay between physico-chemical and microbial processes. Accordingly, the more important modes of origin are peloids derived from coprolites; by micritization of bivalve shells; fragmentation and abrasion of intraclasts; by phosphomicritization of bone fragments; peloids derived from internal molds; intraskeletal and interskeletal peloids; nucleated peloids; and peloids within matrices. The size and morphology of the studied peloids are mainly controlled by the parent material.
Detailed study of Middle Devonian trilobites from New York State indicates that taphonomic attributes are distributed nonrandomly among the strata and therefore may be used to characterize different taphofacies (ie facies defined on the basis of diagnostic taphonomic traits). Describes 4 Taphrofacies with Taphrofacies 3 and 4 further subdivided: all linked to stability of skeletal component and sedimentation rate. Taphonomic features provide criteria by which relative rates of sedimentation and bathymetry may be inferred. The taphofacies concept, therefore, constitutes a useful tool in the recognition and understanding of environmental processes and products.-after Authors
Sequence stratigraphy provides an integrated framework within which to examine historical patterns of paleontological phenomena. Biostratigraphy is a critical tool for relative age-dating and correlation of depositional sequences; in turn, sedimentological and depth-related variables exert a primary control on the occurrence of zonally significant fossils. The combination of refined graphic biostratigraphy, cycle-based ecostratigraphy, and sequence stratigraphy, sequence biostratigraphy, will ultimately permit extremely precise stratigraphic correlation and dating of marine strata. Taphonomic attributes of fossil assemblages also relate closely to sequence stratigraphy. Taphofacies vary predictably in depositional sequences because of the dependence of fossil preservation upon rates of burial and environmental energy. Close integration of paleontologic and sequence stratigraphic data should foster a greatly improved understanding of biases and relationships of biotic and abiotic processes in the accumulation of the stratigraphic record. -from Author
The late Kimmeridgian Tereñes Formation, exposed on the coast of Asturias, northern Spain, displays a complex pattern of directed changes of grain size, carbonate content, and skeletal concentrations. In its upper part, here investigated, the formation represents a protected shelf lagoon in which four major facies types are distinguished: The Nanogyra virgula mudstone (1) and the Corbulomima concentrations (2) are characterized by concentrations of small bivalves. The carbonate mudstone (3) contains pseudomorphs after gypsum crystals and thin crusts of gypsum, occasionally in connectionwith thinmicrobial layers. Finally, the silty to fine-sandy marlstone and micrite and marly silt (4) is highly bioturbated and contains amoderately diverse benthicmacrofauna. These facies indicate a generally quiet environment punctuated by brief episodes of high water energy. Two low-diversitymacrobenthic assemblages can be recognized, each of them strongly dominated by a single bivalve taxon. The Nanogyra virgula assemblage exhibits a higher diversity than the near-monospecific Corbulomima assemblage. The former lived inwell aerated waters of slightly reduced salinity, and the latter in dysoxic waters of more strongly reduced salinity. The environmental stress responsible for the extremely lowspecies richness and evenness is thought to be multifactorial, produced by reduced salinity, dysoxic conditions, and a soft substrate, and resulted in simple food chains. The eurytopic opportunist Corbulomima was the only element of the shelly macrobenthos that was able to thrive in the shelf lagoon under these conditions. It occurs in countless mm- to cm-thick pavements and shell beds which show evidence of winnowing, influence of weak currents, and occasionally of distal storms, as can be deduced from the orientation pattern of shells. These rhythmic Corbulomima concentrations are explained as reflecting small-scale climatic fluctuations between wetter, stormier conditions leading to mixing of the water masses and enabling colonization of the lagoonal floor by the bivalve, and drier, more tranquil conditions. The latter resulted in a stratified watermass and anoxia at the bottom. Superimposed on this rhythmic alternation are three higher orders of cycles which are partly climatic controlled, partly reflect changes in relative sea level.
Facies analyses and a sequence stratigraphical framework with regional correlation of the upper
Campanian phosphate province are presented, based on three main sections located in Egypt (Gebel
Duwi and Abu Tartur sections) and north Jordan (Umm Qais section). Fifteen facies types were grouped
into: phosphate (FT1–5), carbonate (FT6–11) and siliciclastic (FT12–15) facies associations. The main
component of phosphate rocks is pellets in situ and common reworked biogenic debris, especially in the
upper phosphate beds (e.g. fish teeth and bones), which along with abundant Thalassinoides burrows
suggests that the skeletal material was the main source for phosphates in Egypt; in contrast the common
authigenic phosphatic grains (pristine) in Jordan reflect an upwelling regime. Based on age assignment
as well as stratigraphical position, the phosphorite beds show great similarity that may suggests a
similar origin and proximity during the period of deposition of the Duwi Formation of the Red Sea coast
of Egypt and its equivalent, the Al-Hisa Phosphorite Formation in Jordan, which represents an early
transgressive system tract of a depositional sequence. On the Abu Tartur plateau, the presence of sandy
pyritic phosphatic grainstone (FT1) and glauconitic quartz arenite (FT12) in the middle part of the
studied section, along with the absence of chert facies (FT14), reflects a more shallow marine
depositional environment with increased fluvial sediment supply compared to those along the Red Sea
coast and north Jordan.
Macrobenthic palaeo-communities of the Middle and Upper Jurassic strata of G. Maghara, Egypt, were investigated to identify relationships with environmental parameters and to trace the temporal changes of the ecosystem associated with sea-level fluctuations. The quantitative analysis of a data matrix comprising 198 macrobenthic taxa in 138 samples collected from four sections identified nine associations and three assemblages, interpreted to be representative of their original environment. Non-Metric Multidimensional Scaling (NMDS) delineated the same degree of habitat partitioning as hierarchical clusters with very little overlap. Detrended Correspondence Analysis (DCA) identified water depth as the primary environmental gradient controlling the distribution of the fauna, while Axis 2 reflects substrate consistency. Community structure is related to the various ramp environments. Based on diversities, the associations and assemblages have been divided into two major groups, low-stress polyspecific associations and high-stress paucispecific associations. The low-stress polyspecific associations were interpreted to represent two different habitats, a high-energy, firm substrate habitat, in which epifaunal bivalves and brachiopods in addition to solitary corals dominated during advanced stages of transgression, and a low-energy, soft substrate habitat dominated by infaunal bivalves during the maximum flooding. The high-stress paucispecific associations are dominated by one or few taxa and occurred (1) in an oligotrophic setting that developed during episodes of sediment starvation in restricted inner ramp environments or during early transgression, (2) in a setting characterized by high sedimentation rates which developed during advanced regression, (3) in a distal prodelta setting with soft substrate and dysoxia during sea-level lowstand, and (4) in a high- energy shoal environment during peak regression. A combined stress involving a shortage in food supply, episodic dysoxia, in addition to a soupy substrate may have developed during maximum flooding episodes. Hydrodynamic conditions were most likely the main factor controlling the benthic communities. Hydrodynamic conditions influenced the substrate type, redistributed nutrients and were responsible for stratified water masses and hypoxia. Animal-sediment relationships in addition to replacement between bivalves and brachiopods are also discussed. Middle ramp settings were found to provide the best conditions for macrobenthos.
Cretaceous climate data of the long-lived Cretaceous Songliao Basin (SB) in eastern Asia is correlated and compared with the Western Interior Seaway (WIS) on the northern American plate, in order to understand better the dynamics of the Earth's past ‘greenhouse’ climates. Nearly continuous Late Cretaceous terrestrial deposition in the Songliao Basin is represented by two cores totaling 2431 m in length. The Turonian–Maastrichtian age of the section is based on integrated stratigraphy, and is comparable in age with Upper Cretaceous strata in the WIS. Being consistent with global trends, the dynamic Late Cretaceous climates of both the SB and WIS gradually cooled from the warmest Albian–Cenomanian time to the end of the Maastrichtian with several intervening warm periods as did the global climate. However regional differences existed, the Songliao Basin climate was humid to semi-humid, warm temperate–subtropical and the Western Interior Seaway was in the humid, warm temperate zone and experienced only moderate climatic changes. The shifts of oxygen isotope data in the Songliao Basin were frequent and abrupt, whereas WIS records more gradual change affected mainly by fresh-water runoff mixing with southern Tethyan and northern Arctic waters. Sedimentary cycles of eccentricity, obliquity and precession bands are recorded in both the SB and WIS basins. The sedimentary cycles in the WIS and SB are interpreted to be related to variations of the wet/dry runoff cycles, which indicate that orbital forcing played an important role in global climate change in Late Cretaceous. The most favorable condition for organic carbon burial in both the SB and WIS basin was bottom water anoxia regardless of the cause of the anoxia. But the organic carbon burial rate was usually much higher in the Songliao Lake than in the WI epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric CO2. In both basins organic-rich deposits formed during a rise in water level and incursion of saline waters. The integration of paleoclimate data from Cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the Cretaceous ‘greenhouse’ climate change and may provide insights for a future greenhouse world.
[1] The Pacific Ocean is the largest water body on Earth, and circulation in the Pacific contributed significantly to climate evolution in the latest Cretaceous, the culmination of a period of long-term cooling. Here, we present new high-resolution late Campanian to Maastrichtian benthic and planktic foraminiferal stable isotope data and a neodymium (Nd) isotope record obtained from sedimentary ferromanganese oxide coatings of Ocean Drilling Program Hole 1210B from the tropical Pacific Ocean (Shatsky Rise). These new records resolve 13 million years in the latest Cretaceous, providing insights into changes in surface and bottom water temperatures and source regions of deep to intermediate waters covering the carbon isotope excursions of the Campanian-Maastrichtian Boundary Event (CMBE) and the Mid-Maastrichtian event (MME). Our new benthic foraminiferal δ18O and Nd isotope records together with published Nd isotope data show markedly parallel trends across the studied interval over a broad range of bathyal to abyssal water depths interpreted to reflect changes in the intensity of deep-ocean circulation in the tropical Pacific. In particular, we observe a three-million-year-long period of cooler conditions in the early Maastrichtian (72.5 to 69.5 Ma) when a concomitant change toward less radiogenic seawater Nd isotope signatures probably marks a period of enhanced admixture and northward flow of deep waters with Southern Ocean provenance. We suggest this change to have been triggered by intensified formation and convection of deep waters in the high southern latitudes, a process that weakened during the MME (69.5 to 68.5 Ma). The early Maastrichtian cold interval is closely related to the negative and positive carbon isotope trends of the CMBE and MME. The millions-of-years long duration of these carbon cycle perturbations suggests a tectonic forcing of climatic cooling, possibly related to changes in ocean basin geometry and bathymetry.
The Late Cretaceous was a period of long-term climate cooling succeeding the extreme warmth of the mid-Cretaceous greenhouse world. The cooling is mainly considered as a result of changes in ocean circulation due to plate movements resulting in progressive deep-water exchange between the deep oceanic basins and a parallel drop in atmospheric carbon dioxide concentrations. In Campanian - Maastrichtian times, pronounced climate cooling is documented between 71 - 69 Ma, when distinct changes in foraminiferal oxygen and carbon isotope data at a global scale indicate substantial deep-water cooling and reduced rates of organic carbon burial. The causal mechanisms of this cooling period, however, are poorly understood to date. While some authors suggest mainly oceanographic changes, others supposed an ephemeral glaciation related to a eustatic sea-level fall. Mainly, the relative timing of oceanic oxygen and carbon isotope changes to eustatic sea-level changes is not proven yet. Likewise, the influence of plate tectonic changes as the opening of gateways or the subduction of mid-ocean ridges and/or of orbital forcing is poorly understood. A principle objection beside the sparse available data is the low temporal resolution of biostratigraphic zonations. Here, we present carbon isotope stratigraphies from Campanian-Maastrichtian Boundary sites in the Boreal and Tethyan shelf seas of Europe and from Shatsky Rise in the tropical Pacific in order to improve the resolution of stratigraphic correlation. Prominent features at that time are two negative carbon isotope excursions (CIEs) in the late Campanian and earliest Maastrichtian, which are well documented in the Lägerdorf-Kronsmoor section in N-Germany and the Campanian-Maastrichtian Boundary Stratotype at Tercis in SW France. These new carbon isotope records correlate well with the carbon isotope reference curve from the English Chalk (Jarvis et al., 2002, 2006). The new carbon isotope record at Site 305 in the tropical Pacific shows the prominent negative CIE in the early Maastrichtian, which perfectly resembles the carbon isotope data of planktonic and benthic foraminifers (Barrera and Savin, 1999). Numerous stratigraphic details, represented only by single points in the foraminiferal record, are clearly resolved in the bulk-carbonate carbon isotope signal. Of special importance are several positive excursions, which are superimposed on the CIE. These detailed carbon isotope features can be correlated to the shelf-sea carbon isotope curves of Europe (Lägerdorf-Kronsmoor) in a surprisingly good precision supported by calcareous nannoplankton stratigraphy (Lees & Bown 2005). The possibility to correlate small-scale carbon isotope variations proves their robustness as significant signals. The carbon isotope variations seem to reflect minor changes in the global carbon cycle, possibly triggered by orbital forcing. The negative CIEs in the Campanian-Maastrichtian lasted about 0.8-1 million years and are associated with major regressions on epicontinental shelves. Intensified ventilation of the 12C enriched deep-water reservoir, lowering of the CCD and increased rates of terrestrial and marine organic matter oxidation during the sea-level fall could have caused an increase of 12C in the inorganic carbon reservoir. The associated change in the slope of seawater strontium isotopes possibly suggests an increased continental weathering flux as result of long-term (first order) sea-level fall and widespread continental shelf exposure. Activation of silicate weathering could have triggered enhanced atmospheric CO2 reduction, which again became a positive feedback for ongoing climate cooling at the end of the Cretaceous greenhouse climate.
The bivalve fauna from a late early Campanian rocky shore at Ivö Klack (southern Sweden), comprises just over sixty species, a very high diversity in comparison to other Late Cretaceous and modern rocky shore bivalve assemblages. This high diversity is here considered to represent a reliable census of the fauna; only in part can it be explained by the cumulative effect of generations of bivalves inhabiting this coastal environment. The high density and diversity and the wide range of shell morphologies allow interpretation of different modes of life in this variable environment with many contrasting habitats. Study of the functional morphology of bivalve shells and comparison with extant relatives has resulted in a subdivision of the fauna into seven guilds and five habitats. The bivalve fauna represents a within-habitat, time-averaged assemblage to which none of the species was introduced from adjacent environments. It includes some of the most northerly known, very small rudistid bivalves, in addition to the oldest known occurrences of Mytilus and Barbatia in association with rocky shores. Bivalves constituted the most important invertebrate group inhabiting the late early Campanian rocky shore at Ivö Klack, in terms of diversity, density and biomass.
The Late Cretaceous succession in Israel is part of an extensive high-productivity upwelling regime that persisted over ~ 20 m.y. in the southern margins of Tethys. The deposition of a ~ 40-m thick organic-rich carbonate (“oil shale”) sequence in the Negev, Israel, indicates a major change in the evolution of this high-productivity regime and reorganization of the marine ecosystem during the latest Campanian–early Maastrichtian time. The main objective of this study was to reconstruct changes in surface water productivity and seafloor oxygenation during the deposition of the Oil Shale Member (OSM) and transitions with the underlying Phosphate and overlying Marl Members using high-resolution records of planktic and benthic foraminifera and total organic carbon (TOC) content. The updated age of the OSM, determined by integrating planktic foraminifera, calcareous nannofossils and inoceramids, suggests that this sequence spans a maximum of 1.85 m.y. from 71.6 to 69.85 Ma, with a sedimentation rate of at least 2.4 cm/kyr.
The Toolebuc Formation (Late Albian) is a thin (<40m), very widely distributed unit marking the maximum deepening of the Cretaceous epicontinental sea recorded by the infill of the Great Artesian Basin, eastern Australia. It consists of organic-rich shale, with TOC ranging to 35%, and limestone as laminae and thin beds comprised of Inoceramus sutherlandi McCoy and, less commonly, Aucellina hughendenensis Etheridge. Finely interlayered organic-rich shale and coquina are typical of the formation, resulting in a distinctively black-and-white, thinly bedded to laminated rock. Inoceramus values are commonly disturbed by breakage, reorientation, and imbrication, and, in many cases, have disintegrated into prism horizons. Sedimentary laminae show that the sea floor was subject to some current activity, but benthic scavengers are considered to have been active agents of shell disturbance. Although shelly substrate suitable for encrusting epibenthos or colonization by endoliths was available in abundance, other benthic elements, inclusive of trace fossils, are very poorly represented. The formation contains diverse planktonic, pelagic, and nektonic fossil remains attesting to deposition beneath a water column of normal salinity, supporting a complex food chain. It displays a negative δ 13C org excursion, considered to relate to sea floor bacterial reworking of detrital organic material derived from plankton. In the context of the Toolebuc Formation, Inoceramus sutherlandi and Aucellina hughendenensis represent ecological specialists, with shell-growth strategies designed to cope with soft substrates and physiologies that were tolerant of oxygen-poor bottom conditions. Their intimate association with organic-rich shale suggests a trophic link with sea-floor bacterial productivity, supported from the organic-rich substrate. The lateral extent of Toolebuc coquinas suggests that Inoceramus sutherlandi and Aucellina hughendenensis were filter feeders rather than dependent on chemotrophic symbionts. Fine-scale interlayering of coquina and organic-rich shale attests to frequent alternation of sea-floor conditions conducive to colonization by bivalve communities and those that were not. Alternation is attributed in part to an autocyclic mechanism, with sea-floor accumulation of shelly debris having progressively isolated bivalve communities from trophic support, causing their episodic demise.