Abstract The study examines a Lower Jurassic （late Liassic） cyclic lagoonal-peritidal stratigraphic unit outcropping in central western Crete （Tripolis unit）, which corresponds to the eastern （internal） part of ...Abstract The study examines a Lower Jurassic （late Liassic） cyclic lagoonal-peritidal stratigraphic unit outcropping in central western Crete （Tripolis unit）, which corresponds to the eastern （internal） part of the mainland Gavrovo-Tripotis platform, the most significant external platform of the Hetlenides. The studied Tripolis carbonate sequence consists of meter-scale, shallowing-upward successions of restricted inner- carbonate platform facies, including cyclically repeated subtidal, intertidal and supratidal facies, that are separated by erosion surfaces （elementary cycles）. Each cycle starts with relatively open-marine facies, which are overlain by shallower, more restricted facies （tidal fiat progradation）. The lithofacies association includes dotomitic intraclastic-peloidal-bioclastic wackestones-packstones/floatstones and grainstones/rudstones dominated by a restricted shallow-marine fauna （bivalves, gastropods, ostracods and seldom benthic fora- minifers）, representing a shaUow subtidal to intertidal, moderately high-energy environment within an inner- platform setting （peritidal environment to restricted lagoon）. This lithofacies association has been intermit- tently subaeriaUy exposed and has undergone diagenetic processes in an inter- or supratidal environment, exhibiting features of vadose diagenesis and pedogenesis due to long-lasting exposure along certain horizons. The peritidat facies are capped by dolocretes controlled by root-activities （laminar dolocretes, petoi- dat-pisoid dolocretes and massive dotocretes）, marking the end of each depositional cycle, and, thus, dis- tinguishing the successive episodes of a prolonged subaerial exposure period and birth of pateosol horizons. Dotocretes consist a diagenetic facies, characterized by several vadose and pedogenic fabrics, including fenestral cavities with geopetal structures, ＂flower spar＂ to blocky sparry cement in primary pores, micritic coatings, crudely pelleted watts, atveotar-septat texture, infilts of rootlet moulds, inter-granular micritic bridges, meniscus cement, sinuous desiccation cracks, circum-granular cracking and in-situ brecciation. The stratigraphic distribution of the cyclothems, suggests relative sea-level control on the peritidal cyclicity controlled by uniform tectonic subsidence and eustasy （attocyctic processes）, in an inner- ramp-to-shelf carbonate setting with tidal fiat and restricted lagoon depositional environment. However, a combination of attocyctic with autocyctic processes controtting accommodation space and sediment accumutation, shoutd be atso taken in consideration. The studied high-frequency cyctes are interpreted to have been formed during the fatting stage and correspond to towstand systems tract （LST） sediments, which consists part of a regressive peak of the Lower/htiddte Jurassic Transgressive-Regressive Facies Low Frequency Cycte （2nd order）. Due to the absence of massive evaporites, dolomitization has been attributed to reflux of stightly increased-satinity marine fluids （i.e. penesatine）, that are driven into the undertying tagoonat-peritidat carbonate sediments during periods of tong term sea-fever fatl in a marginal marine setting.展开更多
基金co-financed by the University of Athens Program KAPODISTRIAS/Special Account for Research Grants of the National and Kapodistrian University of Athens(S.A.R.G)
文摘Abstract The study examines a Lower Jurassic （late Liassic） cyclic lagoonal-peritidal stratigraphic unit outcropping in central western Crete （Tripolis unit）, which corresponds to the eastern （internal） part of the mainland Gavrovo-Tripotis platform, the most significant external platform of the Hetlenides. The studied Tripolis carbonate sequence consists of meter-scale, shallowing-upward successions of restricted inner- carbonate platform facies, including cyclically repeated subtidal, intertidal and supratidal facies, that are separated by erosion surfaces （elementary cycles）. Each cycle starts with relatively open-marine facies, which are overlain by shallower, more restricted facies （tidal fiat progradation）. The lithofacies association includes dotomitic intraclastic-peloidal-bioclastic wackestones-packstones/floatstones and grainstones/rudstones dominated by a restricted shallow-marine fauna （bivalves, gastropods, ostracods and seldom benthic fora- minifers）, representing a shaUow subtidal to intertidal, moderately high-energy environment within an inner- platform setting （peritidal environment to restricted lagoon）. This lithofacies association has been intermit- tently subaeriaUy exposed and has undergone diagenetic processes in an inter- or supratidal environment, exhibiting features of vadose diagenesis and pedogenesis due to long-lasting exposure along certain horizons. The peritidat facies are capped by dolocretes controlled by root-activities （laminar dolocretes, petoi- dat-pisoid dolocretes and massive dotocretes）, marking the end of each depositional cycle, and, thus, dis- tinguishing the successive episodes of a prolonged subaerial exposure period and birth of pateosol horizons. Dotocretes consist a diagenetic facies, characterized by several vadose and pedogenic fabrics, including fenestral cavities with geopetal structures, ＂flower spar＂ to blocky sparry cement in primary pores, micritic coatings, crudely pelleted watts, atveotar-septat texture, infilts of rootlet moulds, inter-granular micritic bridges, meniscus cement, sinuous desiccation cracks, circum-granular cracking and in-situ brecciation. The stratigraphic distribution of the cyclothems, suggests relative sea-level control on the peritidal cyclicity controlled by uniform tectonic subsidence and eustasy （attocyctic processes）, in an inner- ramp-to-shelf carbonate setting with tidal fiat and restricted lagoon depositional environment. However, a combination of attocyctic with autocyctic processes controtting accommodation space and sediment accumutation, shoutd be atso taken in consideration. The studied high-frequency cyctes are interpreted to have been formed during the fatting stage and correspond to towstand systems tract （LST） sediments, which consists part of a regressive peak of the Lower/htiddte Jurassic Transgressive-Regressive Facies Low Frequency Cycte （2nd order）. Due to the absence of massive evaporites, dolomitization has been attributed to reflux of stightly increased-satinity marine fluids （i.e. penesatine）, that are driven into the undertying tagoonat-peritidat carbonate sediments during periods of tong term sea-fever fatl in a marginal marine setting.
