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The identification and interpretation of drowning events in the geologic record can aid significantly to the reconstruction of the depositional, tectonic and eustatic history of a study area and often improve reservoir and seal prediction in carbonate rocks. The differentiation between drowned platforms showing a record of continuous deepening and those with a record of exposure followed by rapid deepening remains, however, problematic. The Zhujiang carbonate platform (Liuhua 11-1 field, South China Sea) study shown here provides an example of an integrated approach combining high-resolution geochemistry, microfacies analyses and foraminiferal biostratigraphy in order to improve the reconstruction of environmental conditions prior, during and after platform demise and drowning. The Zhujiang carbonate platform displays the following vertical succession of four facies types i) skeletal grain facies with a miogypsinid/lepidocyclinid-dominated fauna deposited in a moderately deep (< 50 m), oligotrophic back-reef setting; ii) in situ corals in patch-reef facies in an oligotrophic lagoon (< 10 m); iii) rhodoid facies with in situ red algal crusts, dominated by Heterostegina sp. and spiroclypeids, possibly capped by a subaerial exposure surface. Well-rounded rhodoids representing a mesotrophic lagoon dominate the upper portions of the rhodoid facies; iv) pelagic marine shales of the Hanjiang Formation burying the carbonate platform after drowning. This facies succession, in combination with geochemical evidence suggests a deepening-upward trend. This trend might have been interrupted by transient subaerial exposure but no evidence for meteoric diagenesis was found at the drowning unconformity topping the carbonate platform. Instead, microfacies analyses suggest that platform demise may be related to progressive changes in environmental conditions, including increasing nutrient-levels and/or decreasing temperature up-core towards the drowning unconformity. These findings are of significance for those concerned with Miocene carbonate factories and, more specifically, the demise of carbonate platforms in general. Crown Copyright © 2009.

The analysis of nine periplatform cores in the surrounding of the Pedro Bank carbonate platform showed the presence of characteristic depositional environments during the last 300 ky. This subdivision is based on mineralogical and grain size variations in space and time. Along the leeward, downcurrent transect the fine sediment fraction (< 63 μm) dominates the periplatform sediments during interglacial highstands in sea level, and no spatial variations in the fine sediment concentration could be observed within 100 km offbank distance. The sediments are mainly of neritic origin preferentially fine aragonite needles. With increasing distance from the margin (> 40 km) aragonite is still the most abundant mineral, but the percentage decreases, while the pelagic carbonate mineral content (LMC) increases. Within the subordinate coarse-fraction classes (> 63 μm) the very fine sand-fraction dominates at proximal sites (< 20 km) as a result of the influence of fine neritic sediments shed offbank. More distal sites (> 20 km) show a more bimodal distribution pattern in the coarse grain sizes with maximum percentages within the very fine and medium sand-fraction, indicating a mixed neritic/pelagic signal. During glacial lowstands in sea level a twofold division in the spatial distribution of the periplatform sediments is evident. A proximal environment (< 28 km) with enhanced coarse-fraction percentages vs. a distal environment (> 28 km) showing a strong dominance of the fine fraction (> 90%). The increased coarse-fraction percentage during glacials at proximal sites results from various interacting processes: (1) lower input of fine neritic sediments, (2) increased current winnowing, and (3) redepositional processes at the upper slope during lowered sea level, and the export of this material to “proximal basinal” sites (< 28 km). At upcurrent sites the mineralogy displays a similar spatial evolution as seen along the downcurrent margin, but with overall reduced percentages. This is the result of the lower export potential of the platform against the main direction of the Caribbean Current, the most important factor for neritic sediment dispersal in the study area. The coarse-fraction content is slightly higher during interglacials compared to the downcurrent margin. During glacials a similar reduction in the percentage of the coarse-fraction is evident in a spatial context. This also substantiates the reduced sediment export and redeposition potential at the upcurrent margin.

It is generally assumed that the effects of tectonism, sediment accumulation and compaction, and eustasy on accommodation change cannot be untangled on a regional scale. Hence, most reconstructions of past eustatic change have focused on global correlations. Here, this approach is questioned. In the time domain of few My and less, global cycle correlation is often unreliable and the effects of isostasy on sea level show strong provincial variations. In contrast, on a regional scale, cycle correlation is more precise and regional tectonism has predictable limitations. These considerations form the base for an assessment of the poorly understood causes of high-rate sea-level change in the Mesozoic. Three well-documented, regional, semi-quantitative sea-level curves are chosen here for reference (Jurassic of Britain, Cretaceous of Russia, Albian of Oman). The absolute numbers of amplitudes are open to question, but the order of magnitude (rates of several meters to tens of meters per My) is a robust property of all three curves even when considering large error bars. Variable mechanisms that cause these regressive-transgressive cycles are considered but rejected with exception of the controversial issue of glacio-eustasy or unknown mechanisms. Therefore, orbital forcing of glacio-eustasy is assessed. Freezing-melting cycles of higher-altitude ice shields can explain high-rate sea-level change with moderate amplitudes but conclusive evidence is buried beneath 3 km of East Antarctic ice. Thus, although several ambiguities of 'global' sea-level correlation are avoided by the regional approach, the causes of high-rate Mesozoic sea-level change remain poorly understood. © 2005 Elsevier B.V. All rights reserved.

Carbonate platform tops are reliable but incomplete recorders of past sea-level fluctuations as they are riddled with hiatuses of various durations. Basinal sections represent a more complete record but fail to register regressive-transgressive events with small to moderate amplitudes. We seek to avoid these problems by combining information on past sea-level fluctuations from coeval platform top, slope and basinal sections. The outcome of this study is a semiquantitative Albian sea-level curve from the southern Tethyan margin in Oman. In subaerial exposure surfaces, the northern Oman margin recorded 4 high-amplitude (∼ 50 m); 6 intermediate-amplitude (∼ 30 m); and 26 low-amplitude (∼ 10 m) regressive-transgressive cycles. Hiatuses that cap the platform top depositional sequences might account for between 30% to 70% of the cycle duration. The resulting platform top depositional sequences have frequencies in the order of 230 ± 20 kyr; i.e. they are in the time range of orbital eccentricity cycles. It appears that at least some of these Albian regressive-transgressive cycles were rapid and punctuated, as opposed to sinus-shaped Milankovitchian sea-level oscillations. © 2002 Elsevier Science B.V. All rights reserved.

The Sorbas basin of SE Spain contains one of the most complete sedimentary successions of the Mediterranean reflecting the increasing salinity during the Messinian salinity crisis. A detailed cyclostratigraphic study of these successions allows a correlation of the sedimentary cycle patterns to astronomical target curves. Here, we present an astrochronological framework for the Messinian of the central part of the Sorbas basin. This framework will form a solid basis for high-resolution correlations to the marginal carbonate facies and to the Central Mediterranean area. The early Messinian Abad Member contains 55 precession induced sedimentary cycles marked by homogeneous marl-opal-rich bed alternations in the 'Lower Abad' and by homogeneous marl-sapropel alternations in the 'Upper Abad'. Astronomical tuning results in an age of 5.96 Ma for the transition to the Yesares evaporites and thus for the onset of the 'Messinian salinity crisis'. The marl-sapropel cycles of the 'Upper Abad' are replaced by gypsum-sapropel cycles (14) in the Yesares Member, indicating that the evaporite cyclicity is related to precession controlled oscillations in (circum) Mediterranean climate as well. As a consequence, gypsum beds correspond to precession maxima (insulation minima) and relatively dry climate, sapropelitic marls to precession minima (insolation maxima) and relatively wet climate. An alternative (glacio-eustatic) obliquity control for evaporite cyclicity can be excluded because the number of sedimentary cycles with a reversed polarity is too high. Sedimentation during the Abad, Yesares, and the overlying coastal sequences of the Sorbas Member, took place in a continuously marine environment, indicating that marine conditions in the Sorbas basin prevailed at least until 5.60-5.54 Ma. According to our scenario, deposition of the Yesares and Sorbas Member took place synchronously with deposition of the 'Lower Evaporites' in the Central Mediterranean. Finally, the continental Zorreras Member consists of 8 sedimentary cycles of alternating reddish silts (dry climate) and yellowish sands (wet climate) which correlates very well with the 'Upper Evaporites' and Lago Mare facies of the Mediterranean. © 2001 Elsevier Science B.V. All rights reserved.

Using recent advances in the stability analysis of current ripples, a new model for the calculation of duration of sediment deposition from decelerating high-density turbidity currents is proposed. The model, named TDURE, refines a duration model proposed by Allen (1991) (J. Sediment. Petrol. 61, 291-295) by calculating the accumulation time of the rippled T(c)-division separately from the massive and plane parallel-laminated T(ab)-divisions in Bouma-type turbidites. TDURE consists of three modules. In the first module, the accumulation time for the T(a)- and T(b)-divisions is approximated by assuming a linear decrease in sedimentation rate with height in the turbidite. As in the original model, a straight line is fitted through inferred sedimentation rates at the T(ab)- and T(bc)-boundaries. In the second module, angle of climb of ripples, thickness of the T(c)-division and grain size distribution are used in empirical relationships between ripple migration rate and a grain-related mobility parameter to estimate the accumulation time of the T(c)-division. In the third module, the expected development of ripple size across the T(c)-division is calculated using empirical relationships between rate of development of ripple height and grain-related mobility parameter, and subsequently compared with the observed development of ripple size in the turbidite. In this way, the accuracy of the accumulation time calculated in module 2 can be verified independently. TDURE was tested using Bouma-type turbidites from the Doheny Channel (Capistrano Fm., CA, USA) and the Flysch di Motta (Calabria, Italy). Accumulation times of 12 and 10.75 min for the T(c)-division, and 19 and 16 min for the T(abc)-sequence were calculated for the Doheny Channel and the Flysch di Motta turbidites, respectively. Although module 3 underestimates the rate of development of current ripples near the T(bc)-boundary in both beds, ripple size at the T(cd)-boundary is calculated accurately. The underestimation of development rate may be caused by differences between flow conditions in experimental flumes on which the model calculations are based and turbidity-current dynamics. (C) 2000 Elsevier Science B.V. All rights reserved.

One of the most striking aspects of the Mediterranean "Messinian Salinity Crisis" as observed in landbased sections, is the basin-wide synchronicity in facies change (Krijgsman et al., 1999a). The Messinian succession of the Caltanisetta Basin on Sicily serves as the classical standard for these facies changes, which can also be recognised elsewhere in the Mediterranean, i.e. on Cyprus, Crete, northern Italy and southern Spain. It starts with an alternation of open marine marls and sapropels, passes via diatomites into evaporitic limestones, gypsum and halite of the "Lower Evaporites" (of marine origin) and, following an erosional unconformity, ends with the "Upper Evaporites" and associated fresh to brackish water deposits of the Lago Mare that are essentially of non-marine origin and contain a caspi-brackish ostracode fauna. The erosional unconformity between the "Lower and Upper Evaporites" is assumed to reflect the phase of most extreme sea level drawdown in the Mediterranean that caused significant erosion and localised channel entrenchment on the continental shelves and slopes.

The correlation of carbonate platform and slope sediments with biostratigraphically and radiometrically dated basinal successions in the Western Dolomites allows the reconstruction of the growth of a Middle Triassic carbonate platform (Schlern/Rosengarten) over a time interval of approximately five ammonoid zones (Reitzi, Secedensis, Curionii, Gredleri, Archelaus zones). The whole platform evolution had a total duration of

The reconstruction of the depositional events related to the Messinian Salinity Crisis (MSC) of the Mediterranean is generally hampered by an incomplete stratal record in the circum-Mediterranean basins. The sediments of the northern part of the Nijar Basin, however, provide an excellent and continuous record of Late Messinian sediments because features of severe erosion are lacking. Especially, the successions of the deeper part of the basin had sufficient accommodation space to warrant ongoing deposition and may thus serve as a testing ground for existing hypotheses regarding the MSC. Conformable contacts with the overlying Pliocene and good correlation possibilities with the adjacent, astronomically dated, Messinian of the Sorbas Basin provide the necessary age constraints.The main body of evaporites in the Nijar Basin (Yesares Formation) has been affected by local dissolution and erosion prior to deposition of the latest Messinian (Lago-Mare) facies. Pelitic float breccias show textures indicating flowage and/or mass transport and include slumped and slided stratal packets due to foundering of the mixed evaporitic-clastic margin. Increased runoff of meteoric waters probably played an important role as these packet slides are perfectly sealed by the hyposaline Lago-Mare strata. Field observations show that marginal sediments, commonly classified as the Terminal Carbonate Complex (TCC), are a lateral equivalent of the basinal Yesares evaporites.The latest Messinian deposits (Feos Formation) are characterized by a sedimentary cyclicity, related to fluctuating base levels, consisting of chalky-marly laminitic strata alternating with continental coarser clastic intervals. Despite considerable W-E facies changes and indications for discrete tectonic events, a persistent sequential pattern of eight Lago-Mare cycles is present, which are interpreted as precession-controlled variations in regional climate. Instead of one major desiccation event in the latest Messinian, the repeatedly fluctuating water levels of the Lago-Mare episode may have been the cause of the widespread vigorous erosion and canyon cutting in the "Lower Evaporites". Abrupt, non-erosional contacts with the normal marine Pliocene take place above the continental interval of the last Lago-Mare cycle, indicating that flooding took place during a period of lowered water levels.The paleogeographic configuration of the Nijar, Sorbas and Vera basins has changed considerably during the Messinian. Separation of the formerly interconnected basins is thought to have started in the late Yesares times by tectonic uplift of the basement complexes. In the latest Messinian of the Nijar Basin, two different coarse clastic supply areas can be distinguished which point to the partial emergence of the Sierra Cabrera and the Cabo de Gata block and activity of the Sierra Alhamilla and Carboneras faults. Concerning the overall regional tectonic activity, tectonics were probably also instrumental for the restoration of the Atlantic gateway in the basal Pliocene. © 2002 Elsevier Science B.V. All rights reserved.

The development of the Ediacaran Doushantuo Formation (635-551 Ma) on the Yangtze platform is studied to analyse the environmental changes on this platform accompanying the Ediacaran bioradiation. In this study we will present a detailed facies analysis and propose a tentative stratigraphic analysis of seven selected sections that are located predominantly on the platform shelf situated in the Hubei Province. The Doushantuo Yangtze platform displays two major depositional environments: a rimmed carbonate platform and an open shelf. The shift from one depositional model to another may be related to the paleotopography in horsts and grabens inherited from previous extensional movements. The strata observed in the shelf deposits of the Doushantuo Formation are organised in three stacked facies successions. These shallowingupward facies successions may be correlatable with other Ediacaran sections worldwide. © 2010 Elsevier B.V. All rights reserved.