The record of tidal cycles in mixed silici–bioclastic deposits: examples from small Plio–Pleistocene peripheral basins of the microtidal Central Mediterranean Sea

Abstract

The Pliocene-Pleistocene peripheral marine basins of the Mediterranean Sea in southern Italy, from Basilicata and western Calabria to northern and eastern Sicily, represent tectonically formed coastal embayments and narrow straits. Here, units of cross-stratified, mixed silici-bioclastic sand, 25 to 80 m thick, record strong tidal currents. The Central Mediterranean Sea has had a microtidal range of ca 35 cm, and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out-of-phase reversal of the tidal prism in narrow straits linking the Tyrrhenian and Ionian basins. The siliciclastic sediment was generated by local bedrock erosion, whereas the bioclastic sediment was derived from the contemporaneous, foramol-type cool-water carbonate factories. The cross-strata sets represent small to medium-sized (10 to 60 cm thick) two-dimensional dunes with mainly unidirectional foreset dip directions. These tidalites differ from the classical tidal rhythmites deposited in mud-bearing siliciclastic environments. Firstly, the foreset strata lack mud drapes and, instead, show segregation of siliciclastic and bioclastic sand into alternating strata. Secondly, the thickness variation of the successive silici-bioclastic strata couplets, measured over accretion intervals of 2 to 3 m and analysed statistically, reveal only the shortest-term, diurnal and semi-diurnal tidal cycles. Thirdly, the record of diurnal and semi-diurnal tidal cycles is included within the pattern of neapspring cycles. Differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea, with the tidal currents locally enhanced in peripheral basins. It is suggested that this particular facies of mud-free, silici-bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub-tidal environment of straits and embayments and the shortest-term tidal cycles.

Deformed cross-stratified deposits in the Early Pleistocene tidally-dominated Catanzaro strait-fill succession, Calabrian Arc (Southern Italy): Triggering mechanisms and environmental significance

“…This migration resulted from the development of regional SE-and ESE-trending strike-slip fault zones and differently oriented normal fault sets (Knott and Turco, 1991;Tansi et al, 2007;Zecchin et al, 2015). From the Late Pliocene to Pleistocene, some parts of the back-arc zone were affected by extensional tectonic phase, WNW-ESE oriented, superimposed on strike-slip deformations, which resulted in the development of narrow transversal basins, such as the Catanzaro, Siderno and Messina straits, linking the Ionian Sea to the Tyrrhenian Sea with sublittoral sedimentation (Colella and D'Alessandro, 1988;Argnani and Trincardi, 1993;van Dijk et al, 2000;Chiarella et al, 2012aChiarella et al, , 2012bLonghitano, 2011;Longhitano et al, 2012;Longhitano et al, 2014;Chiarella, 2016) (Fig. 1B).…”

“…A tidal origin for these deposits has been extensively documented by several papers, and it is indicated by bimodal palaeocurrent pattern (i.e. herringbone cross-stratification), reactivation surfaces and tidal rhythmites composed of mixed siliciclastic-bioclastic couplets (Chiarella, 2011;Longhitano, 2011;Chiarella et al, 2012a;Longhitano et al, 2012;Longhitano, 2013;Longhitano et al, 2014).…”

“…The cross-stratified deposits contain a broad suite of tidally generated sedimentary structures (Chiarella, 2011;Longhitano, 2011;Longhitano et al, 2014). Cross-strata consist of a series of stacked bidirectional large-scale tidal dunes (40-60 cm thick) of mixed siliciclastic-bioclastic composition that accumulated in a narrow elongated basin (Chiarella, 2011;Longhitano et al, 2014).…”

“…Foresets show cyclical alternation of 10-20 cm thick thinning/fining-upwards and thickening/coarsening-upwards bed intervals characterized by heterolithic, moderately segregated siliciclastic/bioclastic lamina-scale couplets ( Fig. 3B; Longhitano, 2011;Chiarella and Longhitano, 2012). (ii) Facies association gravel/shell beds (Gsb) consists of clast-supported, rounded to well-rounded polymictic gravel (facies Gb), forming 20-60 cm thick tabular to lenticular layers.…”

“…The lack of wave-induced structures suggests sedimentation below the main wave base. Rhythmic alternations of segregated siliciclastic (thicker and coarser) and bioclastic (thinner and finer) foresets are considered to record diurnal to monthly tidal cycles in mixed sediments (Longhitano, 2011). Shell concentrations of FA Tsb show absence of encrusted and bored epibionts indicating a short time exposure of the shells on the sea floor during post-mortem reworking.…”