Global Eustatic Curve Research Articles

Integrated biostratigraphy and chemostratigraphy of the Maastrichtian–Danian succession at Abu Minqar, Egyptian Western Desert: Implications for sequence stratigraphy and tectonic influence

We investigated the Maastrichtian–Danian succession at the Abu Minqar section in the Western Desert of Egypt (part from the southern Tethyan margin) using an integrated analysis of biostratigraphic (calcareous nannofossils, foraminifers, macrofauna) and chemostratigraphic data to determine the controlling factors on depositional history. The integrated microplankton biostratigraphic framework identified two prolonged hiatuses at the lower/upper Maastrichtian and the Maastrichtian/Danian boundaries. Four depositional sequences were identified and subdivided into systems tracts based on paleodepth variation evidenced by foraminiferal investigations and the comparable response of the various geochemical indices. The study also highlighted the presence of two alternated depositional styles in the study area, influenced by relative sea level, with the first style involving the deposition of aluminosilicate-enriched intervals that yield non-calcareous foraminifers in lagoonal and coastal depositional settings induced by relative sea-level fall and river rejuvenation, and the second one involving the deposition of calcareous intervals containing abundant megafossils, calcareous foraminifers, and nannofossils during a sea-level rise. Despite the occurrence of certain resemblances to the global eustatic curves, the inferred relative sea level pattern suggests that regional tectonics had a substantial role in developing the depositional history and paleoenvironmental circumstances of the southern Tethys margin. These findings help build a more comprehensive picture of the geological evolution of the southern Tethyan margin during the Late Cretaceous to Paleogene.

Astronomical pacing of third-order sea-level sequences during the middle miocene in the northern south China sea

The Miocene Hanjiang Formation of the Pearl River Mouth Basin (PRMB) forms one of the most productive hydrocarbon reservoirs in China. Sparse biostratigraphic age control and limited dating hinder a thorough understanding of sea-level change and its sedimentary expression through this formation. To establish the relationship between third-order sea-level changes, their expression in the lithological record and astronomical forcing, a sequence stratigraphic and cyclostratigraphic analysis has been conducted through the Hanjiang Formation in the LF14 borehole. One second-order sequence and six third-order sequences are recognized based on gamma ray (GR) data, vertical lithofacies changes and sedimentary stacking patterns. Time series analysis of the GR data and subsequent interpretation allows recognition of approximately eighteen 405 kyr long eccentricity cycles. Based on this cyclostratigraphy, we constructed a ∼7.22-Myr floating astronomical time scale (ATS) for the Hanjiang Formation. We anchored this timescale to globally significant biostratigraphic events preserved in the basin to build an absolute ATS spanning 17.423 ± 0.4 to 10.221 ± 0.4 Ma. A prominent ∼1.2-Myr periodicity is identified in the amplitude modulation (AM) envelope curves of ∼41-kyr obliquity cycles preserved in the record. This ∼1.2-Myr periodicity shows good agreement with our sequence stratigraphic analysis and global eustatic curves. Our results suggest that ∼1.2-Myr obliquity AM was the main driver of third-order sea-level change and sequence development in the PRMB. Combined application of cyclostratigraphic and sequence stratigraphic analysis (utilizing INPEFA and wavelet transform methods) are demonstrated to be useful for understanding the drivers and subdivisions of third-order sequence evolution on a regional scale.

Paleomagnetism, magnetostratigraphy, provenance, and tectonic setting of the Lower Cretaceous of nuclear southern Mexico

We studied the sedimentology, provenance, and paleomagnetism of Lower Cretaceous strata in nuclear southern Mexico deposited in continental, marginal and marine settings in order to better understand their tectonic setting and paleographic correlations. The studied units have been assigned to the Zicapa, Atzompa, Caltepec, Xonamanca, and Jaltepetongo formations, which are interpreted as an eastward-deepening paleogeography (in present day coordinates) deposited between Valanginian and Aptian time in a system of extensional basins contemporaneous with arc magmatism. Provenance interpreted from sandstone petrology, conglomerate clast counts, and detrital zircon U–Pb geochronology indicates that these successions consist of polymictic conglomerate, quartz-lithic metamorphoclastic and feldspathic-quartz lithic volcaniclastic sandstone, and mudstone. These were sourced from the underlying Precambrian and Paleozoic basement rocks, as well as from proximal suites of mafic to acid Jurassic (∼182-145 Ma), and Cretaceous volcanic rocks (∼140-123 Ma). The remanent magnetization in the Atzompa and Caltepec formations is multivectorial, and the characteristic remanent magnetization resides in hematite. For the Atzompa the grand mean is Dec = 335.3° and Inc = 25.4° (k = 15.4, α95 = 12.7°; N = 10 accepted sites). For the Caltepec the grand mean is Dec = 354.3°, Inc = 27.9° (k = 29.15, α95 = 6.1°, N = 20 accepted sites). Magnetizations in both units predate folding and pass reversal tests. For the uppermost Zicapa the magnetization is nearly univectorial and resides in a soft magnetic phase; the grand mean is D = 275.2°, I = 36.0° (k = 34.4, α95 = 10.1°, N = 7 accepted sites). For the Caltepec and Atzompa formations, I/E corrected directions indicate a paleolatitude of ∼20° to 23°N which is indistinguishable from that expected assuming stability with respect to the North America craton (∼24°), implying only minor tectonic motions since Early Cretaceous deposition, and demonstrating that the present distribution of units studied resembles their paleographic relations. The magnetostratigraphy of these units can be correlated with some confidence to the M10-M0r sequence of the geomagnetic polarity time scale, suggesting that the formations record late Valanginian and early Aptian marine transgressions that might correlate with global eustatic curves. The temporal and paleogeographic distribution of magmatism in southern Mexico is consistent with the presence of a continental arc formed by eastward subduction under the North American plate continuously from Early Jurassic to Aptian time, and extension in a back-arc setting during the Hauterivian-Barremian driven by slab rollback. We assign the system of extensional basins to the “southlands rift”, a short-lived event that predates amalgamation of oceanic terranes in the west and Albian carbonate platform development.

РЕЛЬЕФ И ОТЛОЖЕНИЯ ПОЗДНЕКАЙНОЗОЙСКОГО ВРЕМЕНИ СЕВЕРО-ЗАПАДНОЙ ЧАСТИ ЦЕНТРАЛЬНО-ЯКУТСКОЙ РАВНИНЫ И СОПРЕДЕЛЬНОЙ ТЕРРИТОРИИ ВОСТОЧНО-СИБИРСКОГО ПЛОСКОГОРЬЯ (ЛИСТ Q-51)

The so-called “watershed coarse gravels” of the Neogene were preserved within the development of heterochronous denudation peneplanation planes. Based on the comparison of paleontological data with the global eustatic Hague-Weil curve, a ladder of denudation levels is constructed. According to the latter, the age of alluvial are determined. Correlation of the deposits of erosion-accumulative terraces in the conditions of the Munsky neotectonic uplift with alluvium in the valley of the Lena is realised. For the latter, the Late Neo-Pleistocene-Holocene age is substantiated and separate geomorphological unit is proposed. The conclusion is made about the weak notion substantiation on the dammed origin of the Mavrinskaya Formation and its age range, the significant role of subaeral processes in its formation in the interval of the Samarovo-Muruktinskoye time is assumed.

Relative depth reconstruction method using marine ostracods: A case-study from the upper Barremian–Aptian of the Crimean Mountains

A method of reconstruction of outer sublittoral relative depth using ostracods has been suggested. The new method is based on an increasing percentage of ostracods with distinct eye tubercle with water depth rising. The proposed method was developed and checked on late Barremian–Aptian ostracods of the Crimea; the results are similar to those obtained from oxygen isotope analysis and principal component analyses. The combined curve of the depth changing in the Crimean sea during late Barremian–Aptian aligns with the global eustatic curve.

Submerged Pleistocene spodic horizon remnant exposed on the inner continental shelf off Guanabara Bay (Rio de Janeiro, Brazil)

A deposit dated from 40 cal ka bp is interpreted as a remnant of a spodic B horizon exposed on the seabed adjacent to Guanabara Bay at an average depth of 22 m. Bathymetric data, side scan sonar imagery, and underwater images were used to map the expressive feature, never informed before. It is a semi-consolidated muddy-sand deposit with an escarpment up to 4 m and 2.5 km in length (E-W) and 1.5 km in width (N-S). Grain size and geochemical analyses were carried out, and the hypothesis of being formed by podzolization was confirmed. The paleo sea level at the time of the pedogenesis was estimated to be above the maximum height of the global eustatic curves related to Marine Isotopic Stage 3. The feature exhibits a quartzose-sand constitution, defined as an erosion surface exposed at ca. 12 ka bp. The coastal retrogradation of upper unconsolidated sediment during the last transgression contributed to the settlement of a sandbank at the bay mouth.

РЕГИОНАЛЬНОЕ ЗНАЧЕНИЕ И ОБЪЕМЫ ПЕРЕРЫВОВ/НЕСОГЛАСИЙ В ПАЛЕОГЕНОВЫХ ОТЛОЖЕНИЯХ СЕВЕРНОЙ ТЕТИЧЕСКОЙ ОБЛАСТИ

РЕГИОНАЛЬНОЕ ЗНАЧЕНИЕ И ОБЪЕМЫ ПЕРЕРЫВОВ/НЕСОГЛАСИЙ В ПАЛЕОГЕНОВЫХ ОТЛОЖЕНИЯХ СЕВЕРНОЙ ТЕТИЧЕСКОЙ ОБЛАСТИ

Benthic foraminiferal response to relative sea-level changes in the Maastrichtian–Danian succession at the Dakhla Oasis, Western Desert, Egypt

AbstractThe Maastrichtian–Danian benthic foraminiferal diversity and assemblages through sequence stratigraphy were studied at Dakhla Oasis, Egypt. Benthic foraminifera numbers (BFN), high-flux species and characteristic benthic foraminiferal species and genera distribution are also incorporated to assess palaeobathymetry, palaeoenvironment and palaeoproductivity. All these proxies are then taken together to construct a sea-level curve and interpreted in terms of regional tectonics, climate and eustasy. Data suggest a remarkably highly equitable benthic environment deposited in a brackish littoral and/or marsh setting with moderate (?) to low oxygen conditions and reduced salinity (oligotrophic), possibly due to increased precipitation and terrestrial runoff. The interrupted dominance of calcareous forms and high-organic-flux species suggests occasional marine incursions and high palaeoproductivity, due to local upwelling. The inferred sea-level curve replicates the global eustatic curve and suggests that the curve is more influenced by the prevailing climate and global eustasy rather than by regional tectonics. The post-Cretaceous–Palaeogene boundary displays improvement in the environment in terms of diversity and number of species and specimens, with a marked reduction in the abundance of high-organic-flux species during early Paleocene (Danian) time, indicating a shift from a more mesotrophic open marine environment to much reduced oligotrophic conditions.

Last Glacial Cycle and seismic stratigraphic sequences offshore western Hainan Island, NW South China Sea

Abstract In order to investigate the relationship between sea-level changes during the Last Glacial Cycle (LGC) and seismic stratigraphic sequences on the NW continental shelf of the South China Sea, a sparker single-channel high-resolution seismic profiling was correlated with a sediment core taken offshore western Hainan Island. Interpretation of the seismic stratigraphy in relation to local and global sea-level changes could be refined. According to the age model, developed from AMS (accelerator mass spectrometry)- 14 C and OSL (optically stimulated luminescence) dates, and δ 18 O (oxygen isotope) stratigraphy, the 88.3 m sediment core reflects environmental change since 110 ka. Correlation with a sediment core in the adjacent basin based on stable oxygen isotope records allows a zonation of the top 15 m of the sediment core and the identification of marine isotope stages (MIS) 1–5e. Seven seismic reflectors interpreted as unconformities were identified. These erosional surfaces have been dated by interpolation using an age–depth model compared to global eustatic curves. The results indicate that seven sea-level cycles can be distinguished in the study area during the LGC, and these are correlated with regional and global sea-level change models. Further research confirms that seismic stratigraphy in the NW South China Sea can be intimately related to LGC sea-level changes associated with regional surface uplift and sediment supply.

Paleoenvironments, stratigraphic evolution and reservoir characteristics of the Upper Cretaceous Yingjisha Group, southwest Tarim Basin

The Upper Cretaceous Yingjisha Group in the southwestern Tarim Basin is an important host of hydrocarbons with the highest-quality reservoirs are a product of depositional environment, diagenesis and tectonics. The Yingjisha Group is composed, in ascending order, of the Kukebai, Wuyitak, Yigziya and Tuyiluok formations. Strata are thickest in the Kashgar Sag in the northwest and the Yecheng Sag (up to 635 m) in the southeast and thin over the central Qimugen Uplift (less than 70 m). Six facies associations (1–6) are interpreted, respectively, as braided fluvial, lagoon, nearshore-shelf, playa-lake, restricted carbonate platform and open carbonate platform to platform margin. Stratigraphic evolution of the Yingjisha Group, recorded in vertical changes in inferred depositional environments, is related to changes in water depth and climate. At least two transgressive (Kukebai and Yigziya formations) - regressive (Wuyitak and Tuyiluok formations) cycles are recognized that can be correlated with the global eustatic curve of Haq et al. (1988). Detailed paleoenvironmental analysis forms the basis for understanding and predicting the occurrence of reservoir rocks in this mixed siliciclastic-carbonate succession. High-energy, braided-fluvial sandstones and carbonate platform and platform-margin grainstones (locally dolomitized) comprise the best reservoirs. The most important diagenetic processes in sandstones that resulted in porosity and permeability changes are: 1) mechanical compaction, 2) cementation, and 3) replacement and dissolution of unstable clastic grains and cements, whereas in carbonate rocks the dominant diagenetic processes are cementation and dissolution. Fracturing played an important role in enhancing the quality of sandstone and especially carbonate reservoirs notably in terms of their permeability by connecting previously isolated pores. Stratigraphic evolution of the Yingjisha Group resulted in stacking of seal rocks above reservoirs during the late transgressive and regressive phases of sedimentation.

Sequence stratigraphy of the Gurpi Formation (Campanian–Paleocene) in southwest of Zagros, Iran, based on palynomorphs and foraminifera

The Gurpi Formation is a well-known source rock in the Zagros basin, which stretches from northeast to southwest Iran. Sequence stratigraphy was done based on the integration of evidence derived from palynological proxies and foraminiferal data. According to sequence stratigraphy, seven time lines including four sequence boundaries of type II and three maximum flooding surfaces with a resolution varying from 1 to 5 MY and three complete third-order sequences and one transgressive systems tract (TST) were differentiated. Maximum flooding surface of the first sequence in middle Campanian probably equates the 70-Ma maximum flooding surface (MFS) K175 of Sharland et al. (GeoArabia P: 371, 2001), and MFS of the second sequence in early Maastrichtian is correlated with the marked 68-Ma MFS (MFS K180) of Sharland et al. (GeoArabia P: 371, 2001) that is recorded in many parts of the Arabian Plate. Correlation with the Haq global eustatic curve, though uncertain because of the effect of local tectonics over the relative sea level changes, however, could be possible with the 69.5 Ma. Also, purple shales of the base of the Pabdeh Formation with a Thanetian age are defined as a MFS, correlation of which with the marked 58-Ma MFS (MFS Pg10) of Sharland et al. (GeoArabia P: 371, 2001) and with 56.5-Ma MFS of Haq seems likely. The relative sea level curve resulted in this study is not well in accord with the existing eustasy curves for the middle Campanian-late Paleocene indicating effect of tectonic on relative sea level changes during this period.

Well Log Sequence Stratigraphic and Palynological Analysis of Late Miocene to Pliocene Agbada Formation, Southwestern Niger Delta Basin, Nigeria

Sequence stratigraphic interpretation of Chev-1, 2, and 3 wells offshore western Niger delta basin was carried out based on the vertical relationship of the lithofacies associations, electronic well-log, palynologic and foraminiferal data and the existing stratigraphic framework of the Neogene succession in the Niger delta basin. Each well was analyzed in terms of the system tracts, maximum flooding surfaces and sequence boundaries. The recovered palynomorphs together with planktonic foraminifera suggest Late Miocene to Pliocene age. The palynological assemblages exhibit cyclic changes which are here related to the sedimentary evolution.Eighteen depositional sequences were recognized; there are five in Chev-1, ten in Chev-2 and seven in Chev-3. Three of those in Chev-1 and Chev-2 are correlatable while one is correlatable between Chev-2 and 3. These sequence stratigraphic data are matched with existing global standard biostratigraphic zonation scheme and global eustatic curve in order to allow a correlation of sequence beyond local and regional scales.

Tectonic control on the sedimentary record of the central Moldavidian Basin (Eastern Carpathians, Romania)

AbstractThe sedimentary record of the Tarcău and Vrancea Nappes, belonging to the flysch accretionary zone of the Eastern Carpathians (Eastern Carpathian Outer Flysch), registered Cretaceous-Miocene events during the evolution of the Moldavidian Basin. Our biostratigraphic data indicate that the deposits studied are younger than previously reported. The comparison of sedimentary record studied with the Late Cretaceous-Early Miocene global eustatic curve indicates that eustatic factor played a secondary role, after the tectonic one. Four main stages of different processes influenced by tectonics are recognized in the sedimentary record: (1) Campanian-Maastrichtian-earliest Paleocene; (2) latest Ypresian-Lutetian; (3) late Chattian-earliest Aquitanian, and (4) late Aquitanian-early Burdigalian. The late Chattian- earliest Aquitanian and late Aquitanian-early Burdigalian records indicate a high tectonic influence. The first event was related to the foredeep stage of the sedimentary domain studied, and the second one to the deformation stage of the same domain. The sedimentary records of tectonic influence recognized during these stages are useful tools for geodynamic reconstructions. The stratigraphic correlation of Tarcău and Vrancea sedimentary records are used

Reply to the comment on “Sequence stratigraphy and onlap history of the Donets Basin, Ukraine: Insight into Carboniferous icehouse dynamics”

Ruban (this issue) raises two concerns regarding the onlap–offlap curve recently published by Eros et al. (2012) for the Donets Basin. One issue questions the use of the Carboniferous timescale presented in Eros et al. (2012) given that it differs from that of the Geologic Time Scale 2004 (Davydov et al., 2005). The second issue addresses three discrepancies between the Donets curve and “the available global eustatic curve” of Haq and Schutter (2008), bringing into question the degree to which the Donets onlap–offlap history might record regional tectonism to continental-scale mantle dynamics over glacioeustasy. The Carboniferous timescale (Davydov et al., 2010) used by Eros et al. (2012) incorporates new high-precision ID-TIMS U–Pb dates from tonsteins collected throughout the Donets Basin that are tied to stratigraphic sections and sequences referenced in Eros et al. (2012). This time-scale forms the basis of the Carboniferous interval in the latest edition of the Geologic Timescale 2012 (Davydov et al., 2012), which we consider the most appropriate for use in Carboniferous studies. Here we present a high-resolution correlation between the onlap and sea-level histories for the U.S. Midcontinent (Ross and Ross, 1987; Heckel, 2008), the Donets Basin, and the Pennine Basin (Waters and Condon, 2012) made possible by recently published chronostratigraphic constraints (Davydov et al., 2010; Schmitz and Davydov, 2012). This robust chronostratigraphically constrained comparison argues for a dominant eustatic driver on the observed hierarchy of stratigraphic cyclicity and inferred sea level variations on the 105 and 106-year scale in minimally the cross-Pangaean paleotropical regions. Existing discrepancies between these correlated records and the Late Paleozoic record of ‘modal mean of change in sea level’ (Haq and Schutter, 2008) awaits future inter-regional correlations of radiometrically and biostratigraphically well-constrained Carboniferous successions.

Middle Jurassic-Lower Cretaceous tectonic-eustatic cyclites of the Southern East European Craton

A methodical approach to assessment of the role played by vertical tectonic movements in the of tectonic-eustatic cyclicity and the facial appearance of the Middle Jurassic-Lower Cretaceous deposits on the eastern part of the East European Craton has been suggested. Resulting from comparison between the global and regional eustatic curves, the modeling of probable versions of the lithological composition for sediments during eustatic oscillations, and the comparison of modeling results with the chronostratigraphic scheme, the global eustatic component and regional “tectonic noise” have been identified. It has been found that the vertical tectonic movements formed the boundaries of the most distinguished cyclites on the eastern part of the East European Craton. The spatial-temporal uniformity in the material composition of cyclites, related to the long periods of stable high-stand sea level, caused their mineralogenic specialization for a broad range of non-ore mineral resources.

Comment on “Sequence stratigraphy and onlap history of the Donets Basin, Ukraine: Insight into Carboniferous icehouse dynamics” by J.M. Eros, I.P. Montañez, D.A. Osleger, V.I. Davydov, T.I. Nemyrovska, V.I. Poletaev and M.V. Zhykalyak [Palaeogeography, Palaeoclimatology, Palaeoecology 313–314 (2012) 1–25

Each high-quality regional study of relative sea-level changes may contribute to the understanding of global eustatic mechanisms. In particular, it is intriguing to compare the Carboniferous sea-level changes established in the Donbass (a large domain in the southwest of Russia and the east of Ukraine) by Eros et al. (2012) with the available global eustatic curve. At least two significant discrepancies between these reconstructions are found. The long-term early Moscovian lowstand that is reported from the Donbass coincides with the global eustatic rise. In contrast, the early Bashkirian global sea-level lowstand occurred when the relative sea level did not experience any extraordinary fall in the Donbass. Sea-level fluctuations across the Mississippian/Pennsylvanian boundary also differed slightly. At other time intervals, the regional and global curves are comparable. It is possible to hypothesize that either the regional signatures of the global eustatic fluctuations were altered by tectonic activity (e.g., in the form of dynamic topography) or that the available eustatic curve is incorrect in some places. Only further broad inter-regional correlations of Carboniferous sequences will permit choosing between these hypotheses. And it is not excluded that some different conclusions would be drawn if the observed stratigraphy of the Donbass is instead caused by regional vertical tectonic motions.

Sequence stratigraphy of Lower Cretaceous deposit on the eastern Russian Plate

The generalized eustatic and tectonoeustatic models developed by the author are tested on Lower Cretaceous deposits of the eastern part of the Russian Plate. The models are applicable to facies analysis of sections of epicontinental basins with mainly slope sedimentation. They demonstrate possible variations in section lithology depending on the rate of eustatic changes and the intensity and direction of epeirogenic movements. It has been revealed that the Lower Cretaceous sections in the east of the Russian Platform formed as a result of the synchronous global eustasy and regional epeirogeny. Superposition of the global eustatic curve onto the Lower Cretaceous chronostratigraphic chart of the eastern part of the platform showed that global eustasy, periodically concealed by regional epeirogeny, played a crucial role in the Early Cretaceous history of the study area. Regional epeirogenic and eustatic curves were constructed. The epeirogenic curve demonstrates the contribution of vertical tectonic movements to the overall eustatic-epeirogenic result recorded on a regional eustatic curve. The latter was constructed from the analysis of the spatial and temporal changes in the stratigraphic position of formations and strata and transgressive surfaces ranking. Eustatic cycles of different ranks, from elementary (systems tracts) to regional scale, have been recognized. In the rank of largest lithostratigraphic units, three sequences are revealed: Valanginian (RP-1K), Upper Hauterivian–Upper Aptian (RP-2K), and Albian (RP-3K), which reflect the crucial stages of the Early Cretaceous evolution of the eastern Russian Plate. The eustatic-epeirogenic processes during accumulation of formations and strata from Early Berriasian to Late Albian (145.5–99.6 Ma) are considered. It is shown that the division of the studied composite section into sequences permits precise prediction of diverse solid minerals.

Are global Phanerozoic marine diversity curves truly global? A study of the relationship between regional rock records and global Phanerozoic marine diversity

The consensus view that the amount of rock available for sampling does not significantly and systematically bias Phanerozoic marine diversity patterns has broken down. How changes in rock availability and sampling intensity affect our estimates of past biodiversity has been investigated with a variety of new approaches. A number of proxies for the amount of rock available for sampling have been used, but most of these proxies do not rely directly on evidence from large-scale geological maps (maps that cover small areas) and accompanying memoirs. Most previous map-based studies focused on single regions or relied on small-scale synoptic maps. We collected data from published geological maps and memoirs from western Europe, Australia, and Chile, which we combined with COSUNA data from the United States to generate the first multiregional data set for investigating whether the global Phanerozoic marine diversity record is a true global record, or is instead biased toward North America and Western Europe as has long been suspected. Both short and long-term trends in variation in the amount of outcrop display limited correlation among the regions studied. A series of diversification models obtained better matches to observed fossil diversity from the European and U.S. records than for the Chilean and Australian records, further supporting suspicions that the global Phanerozoic diversity curve is disproportionately influenced by European and U.S. fossil data. These results indicate that future research into Phanerozoic marine diversity patterns should not continue to apply global eustatic curves as a proxy for rock at outcrop, but should use regional data on rock occurrence.

The Monte Carrubba Formation (Messinian, Sicily) and its correlatives: New light on basin-wide processes controlling sediment and biota distributions during the Palaeomediterranean–Mediterranean transition

A little known marine Miocene (Messinian) succession in the Hyblean region of south eastern Sicily preserves a carbonate ramp sequence which developed on the tectonically stable foreland margins of the African Plate (Pelagian Block). The ramp (Monte Carrubba Formation) was distally steepened and contained a shoalwater barrier and lagoonal inner ramp complex. The outer ramp is poorly preserved though distal deep water ramp facies (Tellaro Formation) in the south Hyblean region preserve a full Globorotalia mediterranea Subzone and major part of the Globigerina multiloba Subzone succession. This ramp sequence faithfully records the subtle interplay between the global eustatic curve and internal Palaeomediterranean base-level signatures for the Late Miocene. The earliest second order Palaeomediterranean lowstand occurred in the Late Tortonian at about 7.3 Ma and a second occurred at about 6.75 Ma within the Early Messinian G. mediterranea Subzone. Both were in the order of 40 m and global sea-level was probably restored to the Palaeomediterranean after the lowstands. Although the overriding control at the time was the global eustatic curve, harmonic discrepencies between it and the Palaeomediterranean curve resulted from constriction of the Atlantic connection during the latest Tortonian. From about 6.4 Ma until about 5.96 Ma increasingly restricted conditions developed across the Monte Carrubba inner ramp. These faithfully reflect many second order, constriction-driven Palaeomediterranean sea-level oscillations which were superimposed on to the falling global signal as the connecting Atlantic seaways became constricted. These oscillations resulted in major reductions in planktonic faunal diversity within the outer ramp, followed by total emergence of the inner ramp by about 6.05 Ma. Marine deposition continued until about 5.96 Ma in the southern part of the Hyblean region. However, between 6.05 Ma and about 5.6 Ma the amplitude of successive Palaeomediterranean sea-level oscillations increased to over 100 m, causing prolonged periods of total Palaeomediterranean isolation. The Hyblean carbonate suite also contains post-Messinian Salinity Crisis (post-MSC) ‘Lago Mare’ highstand deposits which are developed unconformably above the Monte Carrubba Formation. The widespread distribution of hyposaline to near-marine Congeria faunas within the Lago Mare episode argues for high post-MSC Mediterranean water levels in the Central Mediterranean Late Messinian. In this article we draw together disparate regional evidence from this stable foreland setting and assimilate it with published data from regions lying on the European Plate in order to demonstrate that the tectonically stable Monte Carrubba succession provides an unambiguous record of Central Palaeomediterranean base-level change during the Messinian. Furthermore, the post-MSC sequence demonstrates a prolonged Mediterranean base-level rise throughout the Late Messinian, leaving little readjustment necessary in order to restore Mediterranean base-level to global water levels in basal Pliocene times.

Depositional framework and sequence stratigraphic aspects of the Coniacian–Santonian mixed siliciclastic/carbonate Matulla sediments in Nezzazat and Ekma blocks, Gulf of Suez, Egypt

Superb outcrops of mixed siliciclastic/carbonate rocks mark the Coniacian–Santonian Matulla Formation exposed in Nezzazat and Ekma blocks, west central Sinai. They are built up of various lithofacies that reflect minor fluctuations in relative sea-level from lower intertidal to slightly deep subtidal settings. Relying on the facies characteristics and stratal geometries, the siliciclastic rocks are divided into seven depositional facies, including beach foreshore laminated sands, upper shoreface cross-bedded sandstone, lower shoreface massive bioturbated and wave-rippled sandstones, shallow subtidal siltstone and deep subtidal shale/claystone. The carbonate rocks comprise lower intertidal lime-mudstone, floatstone and dolostone, shallow subtidal skeletal shoal of oyster rudstone/bioclastic grainstone, and shoal margin packstone. Oolitic grain-ironstone and ferribands are partially intervened the facies types. Deposition has taken place under varied conditions of restricted, partly open marine circulation, low to high wave energy and normal to raised salinity during alternating periods of abundant and ceased clastic supply. The facies types are arranged into asymmetric upward-shallowing cycles that record multiple small-scale transgressive–regressive events. Lime-mudstone and sandstone normally terminate the regressive events. Four sequence boundaries marking regional relative sea-level falls divide the Matulla Formation into three stratigraphic units. These boundaries are Turonian/Coniacian, intra-Coniacian, Coniacian/Santonian and Santonian/Campanian. They do not fit with those sequence boundaries proposed in Haq et al.’s global eustatic curves (1988) except for the sea-level fall associated with the intra-Coniacian boundary. Other sequence boundaries have resulted from regional tectonic impact of the Syrian Arc Fold System that has been initiated in north Egypt during the Latest Turonian–Coniacian. These boundaries enclose three well-defined 3rd order depositional sequences; their enclosing shallowing-upward cycles (i.e. parasequences) record the 4th order relative sea-level fluctuations. 34 and 20 parasequence sets, in the order of a few meters to tens of meters thick, mark the Matulla sequences in Nezzazat and Ekma blocks respectively. Each sequence shows an initial phase of rapid sea-level rise with retrogradational sets, followed by lowering sea-level and progradation/aggradation of the parasequence sets. The transgressive deposits display predominance of deep subtidal lagoonal facies, while highstand deposits show an increase in siliciclastic and carbonate facies with the progressive decrease of lagoonal facies. The sedimentary patterns and environments suggest that the regional, partly eustatic sea-level (i.e. intra-Coniacian) changes controlled the overall architecture of the sequence distribution, whereas changes in the clastic input controlled the variations in facies associations within each depositional sequence.