Fotini Pomoni-Papaioannou

Depositional environments and diagenesis of upper jurassic subsurface sponge- andTubiphytes reef limestones: Altensteig 1 well, Western Molasse Basin, Southern Germany

SummaryAn up to 300 m thick Kimmeridgian and Tithonian “reef sequence”, occurring in the Altensteig-1 well southwest of Augsburg, Bavaria, has been studied with regard to facies types, depositional environment and diagenesis. The reef sequence consists of oolitic sands and sand bars, stabilized by binding organisms and overgrown by siliceous sponges and the enigmatic organismTubiphytes. The biota consists of siliceous sponges, sclerosponges, bryozoans, brachiopods, molluscs, serpulid and terebellid worms, and echinoderms. Foraminifera exhibit no significant distribution patterns. Algae occur in samples of core 4 (Malm zeta 3). Four facies types (sponge/algal boundstones, tuberoid-peloid wackestone/packstone, ooid-intraclast grainstone andTubiphytes packstone/boundstone) can be differentiated. TheTubiphytes boundstones represent a particular reef type not yet described in detail from the Upper Jurassic. As can be deduced from subsurface samples and from surface samples (Graisbach quarry near Donauwörth),Tubiphytes formed an organic frame-work within a shallow subtidal environment. The diagenesis of most of the section is characterized by the existence of early marine-phreatic cements, except for the Malm delta/Malm epsilon interval. For this interval, an widespread subaerial exposure of Upper Jurassic carbonates is indicated by the absence of marine-phreatic cements, the occurrence of meteoric-vadose meniscus cements, meteoric-phreatic granular to blocky cements, and of asymmetric radiaxial-fibrous cements.

Sedimentological study of the triassic solution-collapse Breccias of the Ionian zone (NW Greece)

The Triassic Breccias of the Ionian zone are typical evaporite dissolution collapse breccias. Several features indicate the pre-existence of evaporites, while alternation of dolomites and evaporites consist a very common association in the subsurface.Brecciation took place in two principal brecciation stages. The first brecciation stage started soon after deposition, during a period of subaerial exposure due to periodic seasonal desiccation and small-scale meteoric removal of intrastratal evaporites. During this stage, the carbonate beds suffered in-situ breakage and carbonate mud infiltrated into fractures.Shortly after, a major brecciation event occurred, that affected the still non-well lithified carbonate fragments, due to progressive dissolution of evaporites by meteoric water. Carbonate mud continues to be infiltrated in-between the breccia fragments. In the same time, intensive calichification processes were responsible for further brecciation and reworking of the brecciated carbonate beds locally sediments, testifying a period of temporary regional emergence (paleosoil).The breccia matrix is characterized by microbreccioid appearance, resulting from internal brecciation of the coarser clasts. Due to early calichification, the matrix becomes enriched in oxidized clays and by pronounced calichification tends to assimilate the breccia clasts, being gradually transformed into a calcrete with floating texture.Clasts microfacies types include phytoclasts with strongly impregnated by Fe-oxides laminae (laminar calcrete), carbonized plant tissue, lime and dolomitic mudstones with evidence of former evaporites (dolomite/calcite pseudomorphs after gypsum and/or void-filling anhydrite cement, molds after evaporite nodules, euhedral quartz crystals etc.), carbonate fragments pseudomorphic after evaporites, pelsparites/ intrasparites, recrystallized dolomites and dedolomites.The predominance of shallow intertidal to supratidal carbonate fragments, indicates that the strata that gave birth to the breccia, formed in a very shallow, restricted, hypersaline, lagoonal setting, evolved into sabkha sequences in the frame of a lowstand episode. Sedimentation of dolomite and evaporite is considered that has taken place during arid periods, while meteoric water influx during the wetter intervals. During that lowstand episode, that resulted in a hiatus interval, the breccias have suffered intensive calichification. Circulating pore-fluid brines resulting from evaporation, provoked syngenetic to early diagenetic dolomitization of muds, by increase of molar Mg/Ca ratio and provided ions for evaporite nodules/crystal growth.Post-Pliocene to Recent subaerial exposure of the carbonate breccias, led to intensive soil-forming processes, active till today, that accentuated the brecciated appearance of the formation. These processes are responsible for the formation of porous carbonate breccias, the so-called “rauhwackes”.

Phosphatic hardgrounds and stromatolites from the limestone/shale boundary section at Prossilion (Maastrichtian-Paleocene) in the Parnassus-Ghiona Zone, Central Greece

Abstract Sedimentological analysis of the limestone/shale boundary section (Upper Maastrichtian-Upper Paleocene) at Prossilion, Parnassus-Ghiona Zone, revealed that the Upper Maastrichtian sediments represent a shallowing pelagic sequence. Towards the top the sequence becomes highly condensed and owing to interruption of deposition at the Cretaceous/Tertiary boundary, culminates in a hardground through early lithification, boring and mineralization of the substratum by phosphates and iron-oxides. Several sedimentological features led us to assume that cementation-lithification of the sediments took place in a shallow submergent to periodically emergent setting. Stratiform and columnar laminated phosphatic stromatolitic crusts have developed on the bored pavements, during the late Early Paleocene, trapping the pelagic sediments deposited. Phosphate is considered to be supplied to the sediment by a bacterially controlled precipitation from interstitially circulated solutions. Both the uppermost Maastrichtian layers and stromatolitic crusts, are cross-cut by a system of thin slightly sinuous sheaths or tubular structures, interpreted as calcified filaments or rhizolitic structures. This fact suggests prolonged subaerial exposure, as a result of which pedogenic alteration of the already lithified sediments began. By progressive reorganization of the substrata by soil-forming processes, crusts of cryptocrystalline phosphate formed corresponding to phoscrete formations.

Palaeoenvironmental reconstruction of a condensed hardground-type depositional sequence at the Cretaceous-Tertiary contact in the Parnassus-Ghiona zone, central Greece

Abstract Phosphatic hardgrounds at the K/T boundary in the Parnassus—Ghiona zone reflect a major stratigraphic break. The hardgrounds developed on top of the uppermost Maastrichtian beds, which represent a condensed pelagic carbonate sequence of seamount type. Synsedimentary lithification and hardground formation took place on shallow, periodically emerged, seafloors. Phosphate cementation includes fillings of intra- and inter-particle porosity and occludes passive framework open spaces, as well as rim cement fabrics, developed through mineralization by non-phototropic microbial communities. Within the hardground superstructure a highly condensed phosphate sediment was precipitated, post-dating the hardground formation. Phosphate cementation was developed under well-oxygenated conditions, involved in a “low-productivity” phosphogenic system. Phosphate ions were released into pore waters through bacterial decomposition of organic matter. Glauconite developed due to prolonged contact of lithified chalk with seawater. The irregular, bored, impermeable and phosphate-cemented pavements are covered by stratiform and columnar laminated phosphatic stromatolitic crusts trapping Early Paleocene pelagic sediments, deposited during the subsequent Danian transgression. The source of phosphorus was external, either marine or continental. Phosphatization occurred during the bacterial degradation of the organic sheaths. Pyrite crystals within the stromatolitic laminae suggest a sulphidic environment beneath the mat-forming communities. Successive phases of intraformational reworking resulted in “mature” hardground development. Lags from eroded subjacent hardgrounds were accumulated in neighbouring submarine depressions. Marly material rich in quartz has been concentrated along discontinuities. On former topographic heights both the phosphatic hardground and stromatolites have been assimilated by a cryptocrystalline phosphatic material, rich in clay-iron oxides and quartz, considered to originate from subaerial weathering (phoscretization).

Neogene non-tropical carbonate sedimentation in a warm temperate biogeographic province (Rethymnon Formation, Eastern Crete, Greece)

The Apostoli Basin, in the central-west part of Crete, was formed as a fore-arc type basin related to the convergent plate boundary between the African and the Eurasian plates. Most of the Neogene sediments filling the basin were deposited in a terrestrial to shallow marine environment. The succession is a transgressive cycle, which culminates in the alternation of Rethymnon bioclastic limestones with marls, documenting the important Tortonian marine transgression. The Rethymnon limestones are classified as a typical non-tropical carbonate lithofacies. Two particular lithofacies have been recognized: (a) a rhodalgal-type lithofacies, characterized by predominance of encrusting coralline algae and bryozoans, and (b) an echinofor-type lithofacies, characterized by predominance of echinoderms and/or benthic foraminifera. The coralline algae occur mostly as in situ spheroidal or branched rhodoliths, whereas benthic foraminifera are mainly represented by larger foraminifera. In both lithofacies, typical tropical carbonate elements are lacking. Skeletal elements consisted of low- and high-Mg calcite. Although the observed lithofacies possess many similarities with facies of non-tropical carbonates, the presence of large benthic foraminifera suggests development in a warm temperate biogeographic province. The depositional environment corresponds to a shallow ramp, the sediments being deposited in a nearshore environment and under conditions analogous to those prevailing in the present-day circalittoral bottoms of the Mediterranean Sea. The main carbonate accumulation area is located at the factory area itself (rhodalgal-type sediments), and downslope from the factory area (echinofor-type sediments). In the classic zonation of Mediterranean benthic assemblages of Peres and Picard [Rec. Trav. Stn. Mar. (1964)], the rhodalgal-type sediments of the Rethymnon Fm correspond to the ‘‘Facies a Pralines’’, developed in areas strongly controlled by currents (e.g., tops of plateaus), and the echinofor-type sediments to the ‘‘Detritique Cotier’’ bioclastic deposits, derived mostly by bioerosion and fragmentation of local and adjacent calcareous benthic communities. D 2002 Published by Elsevier Science B.V.

Post-Pliocene calichified solution-collapse breccia from eastern Crete, Greece

SummaryPost-Pliocene caliche deposits of eastern Crete resulted from an intensive calichification of dolomitic and dedolomitic solution-collapse breccias. The solution-collapse breccias were formed by dissolution of gypsum, from the upper Triassic gypsum-rauhwacke formation of the Phyllite nappe.The carbonate necessary for calichification was mainly provided by dissolution of dedolomitized source rocks. Calichification seems to have been controlled by distribution and amount of vegetation. The microfacies types of the caliche rocks correspond with an ideal sequence (exhibiting different maturity stages of the caliche).

The carbonate-flysch transition (late Maastrichtian-late Palaeocene) in the Arachova sequence of the Parnassus-Ghiona Zone, central Greece

The transition from the carbonate to the flysch facies in the Arachova sequence of the Parnassus-Ghiona Zone is represented by argillaceous limestone beds with flaser structures deposited during latest Maastrichtian-Palaeocene time in a pelagic carbonate environment with a periodic clastic influx. Deposition was continuous except for a short interruption during the K/T boundary interval and the earliest Palaeocene when the area was subaerially exposed. This interruption gave rise to the development of a brecciated carbonate horizon through soil-forming processes. The mineralogical composition of the clastic influx (i.e. quartz, feldspars, clay minerals, amorphous iron oxides, amorphous phosphatic compounds), in particular the clay mineral assemblages (i.e. illite, chlorite, irregularly interstratified illite-vermiculite), shows that the clastic supply represents erosional material that originated from a tectonically active continental setting of both carbonate and clastic rocks, presumably the Pelagonian Zone, as for the flysch of the Beotian and Sub-Pelagonian Zones. The arrival of the first clastic material in the Arachova area as early as latest Maastrichtian time, its Pelagonian origin and the persistence of pelagic conditions of sedimentation throughout the Palaeocene, indicate that the Arachova area was situated along the northeastern margin of the Parnassus platform and that it subsided into the Beotian basin. While the central areas of the platform remained tectonically stable during middle Palaeocene times and there was an extensive development of stromatolites, the northeastern marginal areas transitional to the Beotian basin continued to subside allowing pelagic carbonate sedimentation with periods of clastic influx. The total collapse of the platform in the late Palaeocene gave rise to the deposition of the flysch over the entire zone.