Seagrass-Meadow Sedimentary Facies In A Mixed Siliciclastic-Carbonate Temperate System In the Tyrrhenian Sea (Pontinian Islands, Western Mediterranean)

Abstract

The paper presents the characteristics of surface sediments in a seagrass-dominated environment of the inner shelf of the Pontinian Islands (Tyrrhenian Shelf, Central Mediterranean). The aims of this work are to characterize the carbonate production and sedimentary processes of a representative high-latitude, temperate Posidonia oceanica-dominated area, to discuss the role of seagrass in the siliciclastic-carbonate mixing processes, which provide analogs for interpreting the occurrence and importance of these types of deposits in the rock record.The majority of sediments are poorly sorted siliciclastic skeletal sand. Based on grain type and abundance and carbonate content, these deposits include six subfacies. The different subfacies reflect environmental changes within the seagrass environment associated with variations in light penetration and hydrodynamic conditions.Additionally, the seagrass facies range from purely carbonate to mixed carbonate-siliciclastic, depending on the amount of siliciclastic input and on the capacity of seagrasses to trap allochthonous sediments while hosting carbonate-producing biota. The type of substrate and the erosion and transport processes control the siliciclastic input. In these Pontinian seagrass meadows, sedimentary facies contain abundant siliciclastic grains produced by erosion of the volcanic substrate and trapped by seagrass blades and rhizomes. This Pontinian example illustrates that in heterozoan-dominated seagrass settings, mudproducing green algae are not present or are not calcifying, and consequently, seagrass deposits are much more grainy than photozoan counterparts. Ancient heterozoan tropical seagrass deposits likely will be discriminated from their temperate or subtropical counterparts only by careful taxonomic analysis of skeletal grains.

Evidence for seagrass meadows and their response to paleoenvironmental changes in the early Eocene (Jafnayn Formation, Wadi Bani Khalid, N Oman)

“…Several lines of evidence suggest the presence of marine vegetation covering this inner platform setting (see section 5.2) and therefore this muddy, grainsupported facies, apparently representing low-energy settings, could result from the trapping and baffling action of seagrasses (e.g. Scoffin, 1970;Mateu-Vicens et al 2008, 2012. This shallow setting is characterized by an assemblage composed by photozoans (alveolinids, Nummulites and green algae) and heterozoans (encrusting acervulinids, echinoderms, small miliolids and rotaliids).…”

“…3 and 10 in Browne et al, 2013) and therefore are considered a reliable indicator of the existence of ancient seagrasses(Beavington-Penney et al, 2004;Mateu-Vicens et al, 2012;Sola et al, 2013;Reich et al, 2015). Nevertheless, adaptive as flat, concave-convex and folded-over, have been observed in recent epiphytic foraminifera (e.g.…”

Biogenic sediments from coastal ecosystems to beach–dune systems: implications for the adaptation of mixed and carbonate beaches to future sea level rise

“…The combined effects of anthropogenic and natural disturbance lead to a global decline in seagrass meadows, with loss rates estimated at 2 to 5 % per year (Waycott et al, 2009;Short et al, 2011). The decline in P. oceanica meadows has been reported in the Mediterranean Sea (Ardizzone et al, 2006;Boudouresque et al, 2009;Montefalcone et al, 2010), where many meadows have already been lost in recent decades (Bianchi and Morri, 2000;Leriche et al, 2006;Marbà et al, 1996). Figure 8.…”

“…For this reason, P. oceanica meadows are considered the main carbonate factory of the Mediterranean inner shelf (Canals and Ballesteros, 1997;Ahr, 1997, 2006;De Falco et al, 2008Mateu-Vicens et al, 2012).…”

The seagrass skeletal assemblage from modern to fossil and from tropical to temperate: Insight from Maldivian and Mediterranean examples

“…As seagrasses have a low preservation potential and records of exceptionally well‐preserved and plant material from marine settings are rare (Den Hartog, ; Ivany et al ., ; Beavington‐Penney et al ., ), these palaeoenvironments are difficult to identify in the rock record (Brasier, ; Reich et al ., ; Tomás et al ., ). Consequently, sedimentological and palaeontological proxies are the main indicators of the presence of seagrass‐dominated ecosystems (Pomar et al ., ; Beavington‐Penney et al ., ; James & Bone, ; Mateu‐Vicens et al ., , ; Reuter et al ., ; Reich et al ., ; Tomás et al ., ; Tomassetti et al ., ). Reich et al .…”