The Cilento Group (Langhian-to-Tortonian) is a thick turbiditic succession (1200-2500 m) of the Southern Apennines foreland region that unconformably overlain the Lucanian oceanic terranes. It has been divided into four formations from NW to SE: the Pollica, San Mauro, Torrente Bruca and Albidona formations. Here, the post-depositional history of the upper portions of the Cilento Group, the San Mauro Formation (SMF), is discussed. The SMF consists of 1400-1600 m thick succession characterized by three main turbidite facies associations: outer-fan, middle-fan, and inner-fan. The outer-fan facies association characterizes the lower part SMF and is made by 300-500 m of thin-bedded sandstones and thick mudstones and marlstones. Numerous intrabasinal carbonate turbidite beds paired with a coarse-grained volcaniclastic layer are interbedded with the outer-fan deposits. The middle-fan facies association define the middle part of the SMF and is represented by a section of about 700 m thick sandstone-lobe turbidite beds and thin fan-fringe deposits. Two impressive intrabasinal carbonate megaturbidite beds, 65 m and 35 m in thickness, respectively, are interbedded with sandstone-lobe strata. The inner-fan facies association typify the upper part of the SMF and is characterized by 400-500 m thick succession of channelized coarse-grained sandstone and conglomerate turbidite beds. Sandstones are generally characterized by quartzolithic, volcanolithic and quartzofeldspathic composition, whereas hybrid arenites and calcarenites characterize the carbonate megabeds. Several diagenetic processes reducing porosity and permeability, such as compaction and cementation, occurred within the SMF. In particular, framework grains result deeply compacted, as testified by the common deformation of ductile grains (mainly micas) and detrital matrix. Cementation occurred through the precipitation of different minerals. The main cements are: 1) carbonate, such as calcite and less dolomite, playing an important occluding role along intergranular space, even running a quite replacement in quartz and feldspar grains ; 2) authigenic quartz occurring as little overgrowths or as minor mosaic quartz; 3) phyllosilicates, mainly developing in the upper part of SMF as pore filling chlorite cement or as small and incomplete illite coatings on skeletal grains; 4) Fe-oxides occuring as pathchy or pore-filling cements. The pore system consists of inter-intra-granular pores with a small pore radius and fractures. The relationship between the compactional porosity loss (COPL) and the cementational porosity loss (CEPL) testifies that compaction is the main reduction porosity process for SMF sandstones. Burial analysis suggests two phases of intense subsidence, interpreted as the result of syn-orogenic extension at shallow crustal levels intermitted by periods of low sedimentation rates, linked to gravitational instability of a vertically growing orogen.
Diagenetic destruction of porosity in Quartzofeldspathic sandstones, Miocene Cilento group, Southern Apennines foreland basin system
Massimo Civitelli;Sara Criniti;Mario Borrelli;Salvatore Critelli
2021-01-01
Abstract
The Cilento Group (Langhian-to-Tortonian) is a thick turbiditic succession (1200-2500 m) of the Southern Apennines foreland region that unconformably overlain the Lucanian oceanic terranes. It has been divided into four formations from NW to SE: the Pollica, San Mauro, Torrente Bruca and Albidona formations. Here, the post-depositional history of the upper portions of the Cilento Group, the San Mauro Formation (SMF), is discussed. The SMF consists of 1400-1600 m thick succession characterized by three main turbidite facies associations: outer-fan, middle-fan, and inner-fan. The outer-fan facies association characterizes the lower part SMF and is made by 300-500 m of thin-bedded sandstones and thick mudstones and marlstones. Numerous intrabasinal carbonate turbidite beds paired with a coarse-grained volcaniclastic layer are interbedded with the outer-fan deposits. The middle-fan facies association define the middle part of the SMF and is represented by a section of about 700 m thick sandstone-lobe turbidite beds and thin fan-fringe deposits. Two impressive intrabasinal carbonate megaturbidite beds, 65 m and 35 m in thickness, respectively, are interbedded with sandstone-lobe strata. The inner-fan facies association typify the upper part of the SMF and is characterized by 400-500 m thick succession of channelized coarse-grained sandstone and conglomerate turbidite beds. Sandstones are generally characterized by quartzolithic, volcanolithic and quartzofeldspathic composition, whereas hybrid arenites and calcarenites characterize the carbonate megabeds. Several diagenetic processes reducing porosity and permeability, such as compaction and cementation, occurred within the SMF. In particular, framework grains result deeply compacted, as testified by the common deformation of ductile grains (mainly micas) and detrital matrix. Cementation occurred through the precipitation of different minerals. The main cements are: 1) carbonate, such as calcite and less dolomite, playing an important occluding role along intergranular space, even running a quite replacement in quartz and feldspar grains ; 2) authigenic quartz occurring as little overgrowths or as minor mosaic quartz; 3) phyllosilicates, mainly developing in the upper part of SMF as pore filling chlorite cement or as small and incomplete illite coatings on skeletal grains; 4) Fe-oxides occuring as pathchy or pore-filling cements. The pore system consists of inter-intra-granular pores with a small pore radius and fractures. The relationship between the compactional porosity loss (COPL) and the cementational porosity loss (CEPL) testifies that compaction is the main reduction porosity process for SMF sandstones. Burial analysis suggests two phases of intense subsidence, interpreted as the result of syn-orogenic extension at shallow crustal levels intermitted by periods of low sedimentation rates, linked to gravitational instability of a vertically growing orogen.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
