Unique clay assemblages in the Levant basin (Haifa Bay) subsurface reflect a land–sea transition zone and restricted environments throughout the last ~ 1 m.y.

Abstract

A subsurface sequence in Haifa Bay, the Levant basin, was studied for its clay mineralogy by X-ray diffraction (XRD) in order to examine the response of clay assemblages to sea-level changes and alternating environments over a long period, apparently longer than ever recorded before. The study was conducted on continuous cores of three boreholes that represent ~1m.y. of very shallow (<40m) and shallow (40–80m) water depths alternating with wetland and terrestrial sediments, including soils. Another aim of the current study was to evaluate the constancy of clay sources along this long record within a bay located at the northern end of the Nile cell. Marine samples, regardless of water depth, are characterized by low amounts of kaolinite+illite (<25%) and variable mix-layer illite-smectite (IS) compositions, in contrast to paleosols with high amounts of kaolinite+illite (30–60%) and illite-rich IS. The sandy permeable parent material of coastal paleosols enabled efficient leaching and major pedogenic clay transformations. Maximum soil development apparently occurred when glacial marine isotope stages were more humid (MIS 6 and MIS 26). When environmental changes were rapid previous clay assemblages were preserved, as indicated by wetland sediments that display pedogenic characteristics and coastal dunes that display marine characteristics. Closely-spaced boreholes yielded two unique marine clay provinces, not known before elsewhere in the Levant basin north of the Nile delta: 1. marine sediments from two boreholes on both sides of the Carmel fault are enriched by up to 90% palygorskite; 2. clean marine sand with a clay fraction dominated by discrete smectite or smectite-rich IS that occur within dark peloids, apparently fecal pellets. Two exotic minerals are occasionally present in trace amounts: clinoptilolite, derived from the nearby northeastern hinterland; and serpentine, derived from the remote Iskenderun Bay. Both unique clay provinces prevail throughout the sequence, indicating stable environmental conditions in south Haifa Bay for the last ~1m.y.