Petrographic and geochemical characterization of the early formative stages of Northern Adriatic shelf rocky buildups

Fulvio Franchi, Andrea Bergamasco, Cristina Da Lio, Sandra Donnici, Claudio Mazzoli, Paolo Montagna, Marco Taviani, Luigi Tosi, Massimo Zecchin

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2 Citations (Scopus)

Abstract

A peculiar type of marine rocky outcrops is generated under temperate conditions through the cementation of carbonate and siliciclastic sediments on the northwestern Adriatic shelf. The lithification process results into the genesis of punctiform outcrops (tegnùe) that serve as substrate to substantial coralligenous epibenthic growth. These buildups have been often described as beachrock. More recently, an alternative genetic mechanism, implying precipitation of carbonate cements in the marine phreatic zone, has been hypothesized for the rocky outcrops off the coast of Chioggia (south of Venice). These rocky outcrops are settled along the levee of meandering channels inherited from Pleistocene fluvial systems. Petrographic analyses of the Chioggia rocky outcrops allowed distinguishing three (3) main lithofacies: 1) biofouled sandstone blocks; 2) cross-stratified slabs and 3) bioclastic carbonates. These lithofacies have a common substrate mainly made by allochemic sandstone and sandy allochem limestone consisting in rounded grains of limestones and dolostones. The host sediments are cemented by a thin micrite coating followed by isopachous rims of scalenohedral and bladed calcite. Geochemical analyses revealed a sensible decrease in Mg contents between the early and late generations of isopachous cements. Vadose cements are missing suggesting that the precipitation of calcite cements occurred in marine phreatic zone without supra-tidal exposure. The lack of aragonite cements suggests that seawater was mixing with meteoric groundwater. The mixing of groundwater induced a partial dissolution of high-Mg calcite and precipitation of a later stage low-Mg calcite. The lithification of the morphologies inherited from Pleistocene fluvial systems provided the nucleus for the development of the coralligenous buildups observed in the North Adriatic Sea shelf. It is possible that diagenetic processes, other than those normally responsible for the formation of beachrocks worldwide, have been active in the northern Adriatic Sea starting from the post-Last Glacial Maximum transgression. It is therefore likely that these processes are more relevant for the coralligenous epibenthic growth in temperate siliciclastic shelves than previously thought.
Original languageEnglish
Pages (from-to)321-337
Number of pages17
JournalMarine and Petroleum Geology
Volume91
DOIs
Publication statusPublished - 2018

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outcrops
cements
shelves
cement
calcite
outcrop
Adriatic Sea
beachrock
lithification
carbonates
phreatic zone
limestone
sandstones
ground water
lithofacies
carbonate
sediments
sandstone
Pleistocene
substrate

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Franchi, Fulvio ; Bergamasco, Andrea ; Da Lio, Cristina ; Donnici, Sandra ; Mazzoli, Claudio ; Montagna, Paolo ; Taviani, Marco ; Tosi, Luigi ; Zecchin, Massimo. / Petrographic and geochemical characterization of the early formative stages of Northern Adriatic shelf rocky buildups. In: Marine and Petroleum Geology. 2018 ; Vol. 91. pp. 321-337.
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author = "Fulvio Franchi and Andrea Bergamasco and {Da Lio}, Cristina and Sandra Donnici and Claudio Mazzoli and Paolo Montagna and Marco Taviani and Luigi Tosi and Massimo Zecchin",
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Petrographic and geochemical characterization of the early formative stages of Northern Adriatic shelf rocky buildups. / Franchi, Fulvio; Bergamasco, Andrea; Da Lio, Cristina; Donnici, Sandra; Mazzoli, Claudio; Montagna, Paolo; Taviani, Marco; Tosi, Luigi; Zecchin, Massimo.

In: Marine and Petroleum Geology, Vol. 91, 2018, p. 321-337.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Petrographic and geochemical characterization of the early formative stages of Northern Adriatic shelf rocky buildups

AU - Franchi, Fulvio

AU - Bergamasco, Andrea

AU - Da Lio, Cristina

AU - Donnici, Sandra

AU - Mazzoli, Claudio

AU - Montagna, Paolo

AU - Taviani, Marco

AU - Tosi, Luigi

AU - Zecchin, Massimo

PY - 2018

Y1 - 2018

N2 - A peculiar type of marine rocky outcrops is generated under temperate conditions through the cementation of carbonate and siliciclastic sediments on the northwestern Adriatic shelf. The lithification process results into the genesis of punctiform outcrops (tegnùe) that serve as substrate to substantial coralligenous epibenthic growth. These buildups have been often described as beachrock. More recently, an alternative genetic mechanism, implying precipitation of carbonate cements in the marine phreatic zone, has been hypothesized for the rocky outcrops off the coast of Chioggia (south of Venice). These rocky outcrops are settled along the levee of meandering channels inherited from Pleistocene fluvial systems. Petrographic analyses of the Chioggia rocky outcrops allowed distinguishing three (3) main lithofacies: 1) biofouled sandstone blocks; 2) cross-stratified slabs and 3) bioclastic carbonates. These lithofacies have a common substrate mainly made by allochemic sandstone and sandy allochem limestone consisting in rounded grains of limestones and dolostones. The host sediments are cemented by a thin micrite coating followed by isopachous rims of scalenohedral and bladed calcite. Geochemical analyses revealed a sensible decrease in Mg contents between the early and late generations of isopachous cements. Vadose cements are missing suggesting that the precipitation of calcite cements occurred in marine phreatic zone without supra-tidal exposure. The lack of aragonite cements suggests that seawater was mixing with meteoric groundwater. The mixing of groundwater induced a partial dissolution of high-Mg calcite and precipitation of a later stage low-Mg calcite. The lithification of the morphologies inherited from Pleistocene fluvial systems provided the nucleus for the development of the coralligenous buildups observed in the North Adriatic Sea shelf. It is possible that diagenetic processes, other than those normally responsible for the formation of beachrocks worldwide, have been active in the northern Adriatic Sea starting from the post-Last Glacial Maximum transgression. It is therefore likely that these processes are more relevant for the coralligenous epibenthic growth in temperate siliciclastic shelves than previously thought.

AB - A peculiar type of marine rocky outcrops is generated under temperate conditions through the cementation of carbonate and siliciclastic sediments on the northwestern Adriatic shelf. The lithification process results into the genesis of punctiform outcrops (tegnùe) that serve as substrate to substantial coralligenous epibenthic growth. These buildups have been often described as beachrock. More recently, an alternative genetic mechanism, implying precipitation of carbonate cements in the marine phreatic zone, has been hypothesized for the rocky outcrops off the coast of Chioggia (south of Venice). These rocky outcrops are settled along the levee of meandering channels inherited from Pleistocene fluvial systems. Petrographic analyses of the Chioggia rocky outcrops allowed distinguishing three (3) main lithofacies: 1) biofouled sandstone blocks; 2) cross-stratified slabs and 3) bioclastic carbonates. These lithofacies have a common substrate mainly made by allochemic sandstone and sandy allochem limestone consisting in rounded grains of limestones and dolostones. The host sediments are cemented by a thin micrite coating followed by isopachous rims of scalenohedral and bladed calcite. Geochemical analyses revealed a sensible decrease in Mg contents between the early and late generations of isopachous cements. Vadose cements are missing suggesting that the precipitation of calcite cements occurred in marine phreatic zone without supra-tidal exposure. The lack of aragonite cements suggests that seawater was mixing with meteoric groundwater. The mixing of groundwater induced a partial dissolution of high-Mg calcite and precipitation of a later stage low-Mg calcite. The lithification of the morphologies inherited from Pleistocene fluvial systems provided the nucleus for the development of the coralligenous buildups observed in the North Adriatic Sea shelf. It is possible that diagenetic processes, other than those normally responsible for the formation of beachrocks worldwide, have been active in the northern Adriatic Sea starting from the post-Last Glacial Maximum transgression. It is therefore likely that these processes are more relevant for the coralligenous epibenthic growth in temperate siliciclastic shelves than previously thought.

U2 - 10.1016/j.marpetgeo.2018.01.012

DO - 10.1016/j.marpetgeo.2018.01.012

M3 - Article

VL - 91

SP - 321

EP - 337

JO - Marine and Petroleum Geology

JF - Marine and Petroleum Geology

SN - 0264-8172

ER -