60 research outputs found
Paleogeographic evolution of the Parnassus-Ghiona carbonate platform in the interval Late Maastrichtian-Paleocene (Greece)
No full textPomoni-Papaioannou F. Paleogeographic evolution of the Parnassus-Ghiona carbonate platform in the interval Late Maastrichtian-Paleocene (Greece). In: Géologie Méditerranéenne. Tome 21, numéro 3-4, 1994. Perimediterranean carbonate platforms. First International Meeting. Marseille – France (5-8 septembre 1994) sous la direction de Jean-Pierre Masse. pp. 153-154
SABKHA-RELATED EVAPORITIC CYCLES IN THE “MIDDLE CRETACEOUS” LIMESTONE OF THE MONTEFORTE AREA (SOUTHERN APENNINES, ITALY).
No full textDuring the mid-Cretaceous times significant climatic-oceanographic changes are recorded. In the same time interval, both the eustatic oscillations and the tectonic events of the peri-Adriatic region produced localized emersions and deep physiographic alterations of the Apenninic carbonate platforms. Emersive phases that affected the Peri-Adriatic carbonate platforms resulted in reduced and discontinuous Albian-Cenomanian records in central-southern Italy. Exposure surfaces are often associated with palaeokarst networks and discontinuous bauxite covers. This supports the evidence of warm and humid climatic conditions. However, recent preliminary data suggest that dry and warm climatic conditions were active in the same time interval in different areas of the peri-Adriatic region (e.g.: Cilento area in southern Apennines, Tripolitza subzone of the External Ellenides, see Pomoni-Papaioannou F. and Zambetakis-Lekkas A., 2007; Bravi et alii, 2008). Detailed time and space constrains are needed in order to clarify their relationships with the hot and humid climatic conditions causing the intensive karst and bauxite development solving the above climatic discrepancy.
The detailed analysis of a shallow-water carbonate succession cropping in the Campania Apennines (Southern Italy), has shown recurrent evidence of evaporitic depositional conditions. The related limestone has been dated early Albian up to late Cenomanian in age on the base of the presence of microfossil as Paracoskinolina tunesiana Peybernes and Sellialveolina viallii Colalongo in the lower part, and Cisalveolina fraasi (Gumbel) and Pseudolituonella reicheli Marie in the upper part. In-depth facies analyses of the basal interval of the succession, pointed out to a cyclic sedimentary pattern with shallowing upward cycles. The basal intervals of the cycles are made up of shallow water subtidal limestone followed by evaporitic levels (containing silica pseudomorphs after anhydrite/gypsum crystals), which in turn pass upward to marly layers including limestone nodules, barren or bearing a very poor biotic contain, few centimeters in diameter. Resting over this first interval, a middle Cenomanian “Platy Dolomite” interval occurs, in which remains of xerophytic megaflora (e.g. Sapindopsis sp., Frenelopsis sp.) have been found (Bravi et alii, 2004; Bartiromo et alii, 2008). Finally upper Cenomanian bioturbated limestone follows partly consisting of rudist coarsely grained biodetrital material and rapidly passing upward to thin muddy layers bearing planktonic microfauna.
All the above suggests a deepening trend into an inner platform-restricted setting subject to dry climatic conditions. Palaeobotanical evidences both in the studied succession and in other carbonate sequences of the Campania region belonging to the same time span, further testify and confirms the prevailing dry and warm climatic conditions. In this frame, the evaporitic cycles witness repeated episodes of salinity shifting in paralic depositional settings. Salt, brackish or schizohaline ponds along with sabkha areas alternated in time and space repeatedly in the area likely following short-term climatic variations
Arid versus wet climatic evidence in the "middle Cretaceous" calcareous successions of the Southern Apennines (Italy)
No full textAn upper Albian-lower Turonian shallow-water carbonate succession cropping out near the village of Monteforte Cilento (Campania Apennines, southern Italy) was analyzed in detail within the framework of studies showing contrasting climatic evidence from the "middle" Cretaceous peri-Mediterranean carbonate successions. The full succession covers a time span in which there was a major global transgression, superimposed by fluctuating sea levels, coupled with a significant increase in temperature. There is also evidence of repeated climatic shifts from humid to dry with seasonal contrasting conditions. Restricted peritidal facies dominate the section and demonstrate the general characteristics associated with restricted brackish/schizohaline up to hypersaline depositional settings in which mesotrophic to mildly eutrophic conditions largely prevail. However, an opening and/or deepening trend of the depositional areas is recorded upward in the succession by deeply bioturbated plankton-rich strata at the Cenomanian-Turonian transition. This trend stopped with the inception of new shallow-water depositional settings which radiolitid rudists repopulated or from which shallow-water skeletal remains were supplied. This transient drowning event was anticipated and then marked by the occurrence of sediments bearing low-oxygen tolerant planktonic assemblages adapted to mesotrophic conditions. This suggests ecological conditions that were unfavourable to the main carbonate-producing shallow-water assemblages at the Cenomanian/Turonian boundary. Conditions of stress in the reconstructed shallow-water settings correlate with the deterioration of the water mass that culminated in deep-water domains with the well-known OAE2 anoxic crisis. The uppermost Albian-lower Cenomanian interval is characterized by intertidal to supratidal, partially dolomitized limestone with abundant silica pseudomorphs after evaporites. The silicified evaporite nodules and layers are evidence of episodes of highly evaporitic conditions in very shallow subtidal to supratidal settings in which salty to hypersaline ponds and areas of sabkha occurred. The occurrence of xerophytic megafloral remains also suggests that an arid, evaporite-promoting climate obtained in the depositional areas of the Albian Cenomanian succession studied. Within the framework of the climatic evolution of "middle" Cretaceous time, the evaporite cycles of the Monteforte Cilento section are of particular interest. The different peri-Mediterranean carbonate successions record widespread karst phenomena and bauxite, which are expressions of hot/humid climates. Accurate biostratigraphic analyses and published geochemical data constrain the evaporitic episodes recorded in the Monteforte Cilento section. The related arid/semiarid climatic conditions fall within a time interval in which different coeval Apennine successions show shallow-water deposits (from stromatolitic/loferitic peritidal cycles of restricted inner shelf areas to more open, subtidal deposits of an open shelf) sandwiched between two tectonically uplifted surfaces marked by humid climate-related mature soils (bauxite) and/or karst phenomena. This suggests that dry climatic episodes post-dated the hot/wet intervals in which the bauxite and karst systems developed but, in turn, predated more recent hot/wet climatic conditions that resulted in the karst systems which occur at the top of the upper Cenomanian limestone. (C) 2012 Elsevier Ltd. All rights reserved
Microfacies and cycle stacking pattern in Liassic peritidal carbonate platform strata, Gavrovo-Tripolitza platform, Peloponnesus, Greece
No full textFacies analysis of Lofer cycles (Upper Triassic), in the Argolis Peninsula (Greece)
No full textThe Upper Triassic carbonate sediments of Argolis Peninsula are part of the Upper Triassic-Lower Jurassic extensive and thick neritic carbonate formations (Pantokrator facies) that formed at the passive Pelagonian margin and are considered as Dachstein-type platform carbonates. Facies analysis of the Upper Triassic "Lofer-type" lagoonal-peritidal cycles in the Dhidimi area, proved that cycles, although mostly incomplete, were regressive shallowing-upward. The ideal elementary cyclothems are meter-scale in thickness and begin with a subtidal bed (Member C), represented by a peloidal dolostone with megalodonts (wackestone or packstone), being followed by a stromatolitic intertidal dolomitic mudstone and/or fenestral intertidal dolomitic mudstone (Member B) that is overlain by dolocrete (terrestrial stromatolites or pisoidic dolomite) or a supratidal "soil conglomerate" in red micritic matrix (Member A). Lofer-cycle boundaries are defined at the erosional surfaces and accordingly the Lofer cyclothems are unconformity-bounded units. Due to common post-depositional truncation of the subtidal and intertidal facies, the supratidal members prevail, being developed, in places, directly upon subaerial exposure surfaces (erosionally reduced cyclothems). Peritidal layers are characterized by a well-expressed lamination, sheet cracks, tepee structures, fenestral pores and karst dissolution cavities. The studied lagoonal-peritidal cycles are considered to have been deposited in a tidal-flat setting (inner platform), repeatedly exposed under subaerial conditions, in the context of a broader tropical rimmed platform. Although the studied area was tectonically active due to rift-activity and the autocyclic processes should also be taken in consideration, the great lateral correlatability of cycles, the facies shifting and the widespread erosion that resulted in superposition of supratidal-pedogenic facies directly upon subtidal members (subaerial erosional unconformity), indicating a sea-level drop, reflect allocyclic control via high-frequency eustatic sea-level oscillation (orbital forcing). Sediment deposition occurred during low-stand system tract (LST), that probably continued also in the transgressive system tract (TST) and reflects an overall sea-level fall. Under these conditions dissolution and cement precipitation episodes, as well development of paleosols and karsts, were triggered, during a relatively less arid interval. © 2008 Elsevier B.V. All rights reserved
Sedimentological study of the Triassic solution-collapse Breccias of the Ionian zone (NW Greece)
No full textThe 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 pronounched calichification tends to assimilate the breccia clasts, being gradually transformed into a calcrete with floating texture. Clasts microfacies types include phytoclasts with strongly impregnanted 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'
Microfacies and cycle stacking pattern in Liassic peritidal carbonate platform strata, Gavrovo-Tripolitza platform, Peloponnesus, Greece
No full textPlatform carbonate sediments of Liassic age cropping out in the area of the Pigadi-Fokianos Gulf (SE of Leonidion, Peloponnesus) have been investigated in order to determine their depositional environment. Facies analysis allowed the recognition of several microfacies types and their cyclic stacking pattern. The carbonates were deposited in a restricted inner platform environment (lagoon-peritidal domain) and are arranged into small-scale shallowing-upward cycles. Palaeosol horizons containing typical pedogenic features are developed on the top of the peritidal facies or are directly superimposed on subtidal deposits, forming diagenetic caps. This implies repeated sea-level fluctuations and periodic emersion episodes. The presence of orbitally forced cyclicity though is mostly probable, cannot be clearly documented by the available data. The studied carbonates are comparable with other coeval analogous peritidal cycles of the same age along the southern margin of the Tethys. © Springer-Verlag 2008
Chlorozoan VS foramol carbonate sedimentary systems in an Upper Jurassic-Cretaceous Pelagonian margin: Rhodiani area (West Macedonia, Greece)
No full textFacies analysis of the Trypali carbonate unit (Upper Triassic) in central-western Crete (Greece): an evaporite formation transformed into solution-collapse breccias
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