New insights into the genesis of the Miocene collapse structures of the island of Gozo (Malta, central Mediterranean Sea)

Abstract

The large palaeosinkholes located in the NW of Gozo (central Mediterranean Sea, Malta) offer excellent exposures that provide information on the geometry and kinematics of large karst-related collapse structures. Detailed geological analysis of these peculiar palaeosinkholes indicates that deep-seated evaporite dissolution is the most feasible hypothesis to explain their formation, according to the following evidence. (1) Several structures have been formed by progressive foundering of cylindrical blocks with limited internal deformation as revealed by the synsedimentary subsidence recorded by their Miocene sedimentary fill. This subsidence mechanism is more compatible with interstratal dissolution of evaporites than karstification and cave development in limestone formations. (2) The dimensions and deformation style of the palaeosinkholes are similar to those of other collapse structures related to deep-seated dissolution of salt-bearing evaporites. (3) The arcuate monocline associated with some of these collapse structures is also a characteristic feature of subsidence related to dissolution of evaporites.\ud However, no major evaporite formations have been documented so far in the subsurface of the Malta Platform

Late Quaternary coastal landscape morphology and evolution of the Maltese Islands (Mediterranean Sea) reconstructed from high-resolution seafloor data

“…The bottom of these depressions, at present covered by a Posidonia oceanica mat of vegetation, is peppered by rocky blocks, or draped by medium-fine sand appearing as a flat and smooth surface. Considering their regular shape, their dimensions, their fill and the presence of radial fractures, these presumed sinkholes seem to correspond fairly well to those described by Coratza et al (2012), Soldati et al (2013) and Galve et al (2015) in Gozo. Thus, they could share a similar origin and, perhaps, age, but this hypothesis still requires further investigation (Fig.…”

“…The NE part of Gozo is dominated by an alternation of boulder scree ('rdum' in Maltese) and shore platforms, while, in the SW part, plunging cliffs comprise the prevailing type of coast (Said & Schembri 2010). The western coastline of Gozo is marked by largescale sinkholes Galve et al 2015). In NE Malta, the coast comprises a succession of plunging cliffs and shore platforms (Paskoff & Sanlaville 1978;Said & Schembri 2010;Biolchi et al 2015).…”

“…The Maltese Islands are marked by karst features of different size, from dolines to palaeosinkholes (especially in Gozo: Coratza et al 2012;Soldati et al 2013;Galve et al 2015), karst limestone pavements (especially on Lower and Upper Coralline Limestone) and pits (Alexander 1988;Pedley et al 2002;Magri 2006). The archipelago is also incised by a fluvial system consisting of several 'widien' (wadis) that are orientated SW-NE and that have formed narrow valleys from the 'hinterland' to the coastline (Alexander 1988;Anderson 1997).…”

“…Based on the assumptions of Pedley (1974), these depressions have been interpreted as caprock collapse palaeosinkholes by Soldati et al (2013) and Galve et al (2015). Soldati et al (2013) asserted that the first stage in the formation of these sinkholes is due to karst dissolution of the Lower Coralline Limestone Formation or, potentially, of the underlying evaporites.…”

“…These depressions could originate from the same processes responsible for the formation of the Gozitan sinkholes described in the previous section Galve et al 2015), but more in-depth investigation is required to determine their cause and age of formation (Fig. 7).…”