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Lithocodium aggregatum and Bacinella irregularis are now extinct, shallow marine life forms of unknown taxonomic origin. Forming part of the tropical platform biota during much of the Mesozoic, these organisms experienced bloom periods and temporarily replaced rudist–coral assemblages during parts of the Early Aptian. Within the limitations of time resolution, this ‘out‐of‐balance’ facies is coeval with the Oceanic Anoxic Event 1a‐related black shale deposition in oceanic basins but the triggering factors remain poorly understood. Here, a platform‐wide comparison of Lithocodium–Bacinella geobodies and morphotypes from the Sultanate of Oman is presented and placed in its environmental, bathymetric and physiographic context. Lithocodium–Bacinella geobodies reach from kilometre‐scale ‘superstructures’ to delicate centimetre‐sized growth forms. Clearly, scale matters and care must be taken when drawing conclusions based on spatially limited observational data. Whilst the factors that cause Lithocodium–Bacinella expansion should probably be considered in a global context, regional to local factors affected growth patterns in a more predictable manner. Here, the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of Lithocodium–Bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment. Acknowledging these limitations, the following tentative patterns are observed: (i) Lithocodium–Bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings (margin, intrashelf basin, inner platform) by obtaining characteristic growth forms. (ii) Lithocodium–Bacinella favoured low‐sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth; a feature perhaps pointing to a phototrophic metabolism. Circumstantial evidence for continuous growth within the upper‐sediment column is debated. (iii) The availability of accommodation space had a direct influence on the maximum size of geobodies formed. (iv) Fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of Lithocodium–Bacinella. Understanding the relationship between Lithocodium–Bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments. This study might represent a useful first step in this direction.

Ocean‐wide anoxic events represent intensively investigated anomalies in the global carbon cycle. Most previous research has focussed on hemipelagic and pelagic settings and on the relationship between black‐shale deposition and carbon‐isotope excursions. The study of ocean‐wide anoxic events and coeval shallow‐water settings is now increasingly seen as an interesting complementary approach, but one that is not without problems. Whereas platform drowning characterizes the Early Aptian of the northern Tethyan margin, Lithocodium–Bacinella‐rich facies and ongoing shoal‐water sedimentation at the southern Tethyan margin (Oman) bears important information on potential causes of carbon‐cycle perturbations. The present paper seeks to test the supra‐regional relevance of the Oman data by investigating coeval central Tethyan limestones. Three Lower Aptian shoal‐water sections in Istria (Croatia), deposited on the isolated Adriatic Carbonate Platform, are investigated applying chemostratigraphy (carbon and strontium) and detailed sedimentological analysis. The focus is on peritidal to lagoonal facies characterized by mass occurrences of Lithocodium–Bacinella, an enigmatic microencruster community. Lithocodium–Bacinella facies occurs predominantly in layers ranging from one to several centimetres in stratigraphic thickness, with several layers merging to metre‐thick packages. Growth fabrics within the layers include oncoidal morphotypes, lumps, interconnected patches and columns, layers and rare nodular to massive bindstone facies. These growth patterns show a remarkable regional extent and consistency over study sites distributed several kilometres apart. This widespread distribution suggests that specific Lithocodium–Bacinella morphotypes might serve as regional stratigraphic markers. The high‐resolution carbon‐isotope chemostratigraphy presented here is based on pristine rudist shells and matrix micrite samples and calibrated against strontium‐isotope data obtained from screened rudist low‐Mg calcite. The chemostratigraphic data are consistent with existing biostratigraphic data and place the studied strata at the onset of Early Aptian oceanic anoxic event 1a. Moreover, results indicate the near‐coeval nature of Lithocodium–Bacinella bloom facies in Istria and Oman. The outcomes of this study point to latitudinally different responses of Tethyan shoal‐water carbonate systems (platform drowning versus Lithocodium–Bacinella blooms) to the ocean‐wide anoxic event 1a.

Early diagenetic dolomitization is a common feature in cyclic shallow-water carbonates throughout the geologic record. After their generation, dolomites may be subject to dedolomitization (re-calcification of dolomites), e.g. by contact with meteoric water during emersion. These patterns of dolomitization and subsequent dedolomitization frequently play a key role in unravelling the development and history of a carbonate platform. On the basis of excellent outcrops, detailed logging and sampling and integrating sedimentological work, high-resolution sequence stratigraphic interpretations, and isotope analyses (O, C), conceptual models on early diagenetic dolomitization and dedolomitization and their underlying mechanisms were developed for the Upper Jurassic / Lower Cretaceous Jura platform in north-western Switzerland and eastern France. Three different types of early diagenetic dolomites and two types of dedolomites were observed. Each is defined by a distinct petrographic/isotopic signature and a distinct spatial distribution pattern. Different types of dolomites are interpreted to have been formed by different mechanisms, such as shallow seepage reflux, evaporation on tidal flats, and microbially mediated selective dolomitization of burrows. Depending on the type of dolomite, sea water with normal marine to slightly enhanced salinities is proposed as dolomitizing fluid. Based on the data obtained, the main volume of dolomite was precipitated by a reflux mechanism that was switched on and off by high-frequency sea-level changes. It appears, however, that more than one dolomitization mechanism was active (pene)contemporaneously or several processes alternated in time. During early diagenesis, percolating meteoric waters obviously played an important role in the dedolomitization of carbonate rocks that underlie exposure surfaces. Cyclostratigraphic interpretation of the sedimentary succession allows for estimates on the timing of early diagenetic (de)dolomitization. These results are an important step towards a better understanding of the link between high-frequency, probably orbitally forced, sea-level oscillations and early dolomitization under Mesozoic greenhouse conditions.

Discontinuity surfaces in shallow‐marine carbonate successions may represent significant time gaps in the geological record of ancient epeiric‐neritic seas. Understanding the hidden geological information contained in major discontinuities is thus of key significance in palaeo‐environmental analysis, sequence stratigraphy, reconstructions of sea‐level change and basin evolution. In the present paper, the Aptian top Lower Shu’aiba Formation discontinuity in the Sultanate of Oman is taken as a prominent example of a regionally extensive (>100 000 km2) surface with a long (up to 10 Myr) and complex geological history. The top Shu’aiba discontinuity formed on the topographically elevated domain of the Oman platform and represents in essence the Late Aptian time interval. Coeval carbonates in the intrashelf Bab Basin and oceanic rim indicate forced regression and sequence‐wise, gradual down‐stepping. Available regional, sedimentological, sequence‐stratigraphic, petrographic, palaeontological and geochemical evidence from outcrops and cored wells in Oman is summarized, in part complemented by new data, and reviewed in a process‐oriented context. In the field, the discontinuity is expressed as a low relief, stained surface with evidence for a marine hardground stage being dominant. Indistinct features that indicate a transient meteoric precursor stage (isotope shifts, meteoric cements, circumgranular cracks, etc.) are present but their interpretation requires careful and detailed work. This feature is remarkable, as a series of relative sea‐level falls with amplitudes of up to several tens of metres from the Early to Late Aptian boundary to the end of the Aptian are reported from the Middle East and elsewhere. Despite the palaeogeographic position of the study area in the tropical climate zone, evidence of deep‐cutting karst features, characteristic for many long‐term exposure surfaces worldwide is scarce. Acknowledging the fact that the modern world offers no genuine analogues for the Lower Aptian carbonate system in Oman, morphological similarities between actualistic, wave‐eroded coastal terraces and the top Shu’aiba discontinuity are discussed critically. This discussion may imply that, during an exposure time of several million years, the top Shu’aiba discontinuity experienced repeated stages of shallow flooding and emergence, with each transgression removing portions of the underlying rock record. The data shown here exemplify the complexity of hiatal surfaces in epeiric‐neritic carbonates and may serve as a case example for other major discontinuities.

Ammonite biostratigraphy plays a central role in the definition of Jurassic stratigraphy. Nevertheless, the strong provincialism of European ammonite species during the Kimmeridgian is a longstanding problem in correlation attempts between the boreal and Tethyan faunal realms. Moreover, the sequence-stratigraphic interpretations for northern and southern Europe given in the Jurassic chronostratigraphic chart of Hardenbol et al. in SEPM Publ. 60 (chart) (1998) are different. The present study aims to resolve this correlation problem in order to better understand the connections between the boreal and the Tethyan realms during the Kimmeridgian. A sedimentological and high-resolution sequence-stratigraphic interpretation is presented for two unpublished sections (Cras d'Hermont and Roche de Mars) in the northern Swiss Jura, where recently discovered ammonites display both boreal and Tethyan influences. Then, these sections are correlated with the same time interval in the central Swiss Jura and Vocontian Basin, which belong to the Tethyan realm. Lastly, a longdistance transect is constructed between the Vocontian Basin, Swiss Jura, northern France, and southern England, the last two areas being part of the sub-boreal realm. The main results of this work are that: (1) thirdorder depositional sequences, and also higher-frequency sequences, can be correlated from the Tethyan to the boreal realm; (2) the sequence-stratigraphic interpretation given by Hardenbol et al. in SEPM Publ 60 (chart) (1998) for northern Europe seems to be accurate and agrees with the sequence-stratigraphic framework established in the Swiss Jura; (3) the Late Kimmeridgian of the Swiss Jura displays boreal influences; (4) integrated high-resolution sequence-stratigraphic and cyclostratigraphic studies are a valuable approach for bridging the correlation gap between northern and southern Europe.

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