Our comparison of magnetic susceptibility with the lithology reveals that the high values of magnetic susceptibility are in the strata of sand and silt in the interglacial periods, whereas they are low in the strata of silty clay in the glacial periods.
In about 1980 Alvarez helped his son, the geologist Walter Alvarez, publicize Walter's discovery of a worldwide layer of clay that has a high iridium content and which occupies rock strata at the geochronological boundary between the Mesozoic and Cenozoic eras (i.e., about 65.5 million years ago).
There is a weak confined aquifer in the fifth stratum, which is consisted of clay with large amount of lime concretions.
This stratum is covered with silt composed of clay, sand and flints and Roman pottery pieces, of the late Neogene age.
The Paleozoic sediments are composed mostly of beds of shales (laminated sediments consisting mostly of particles of clay) and sandstones in which strata of limestone occur in places.
The Neogene strata (average thickness 49.84 m) are predominantly composed of clay and gravels and disconformably overlie the Shengli Formation.
In details, from the bottom to upwards, the stratigraphic series is formed by Numidian Flysch Fm. (alternation of brown clay and thick strata of yellowish quartz-arenite; Upper Oligocene-Burdigalian), followed by grey-blue and brown marly clays with foraminifera fauna (Terravecchia Fm. - Upper Tortonian).
"Bivalves can live in saltwater or freshwater and biologically, clams can live in different regions as they only need a stratum of sand or clay," he says.
The Cretaceous Paleogene boundary of 66 million years ago, marking the temporal border between the Cretaceous and Paleogene periods of geological time, was identified by a thin stratum of iridium-rich clay.
He studied the Old Red Sandstone (Devonian strata), the boulder clay of Caithness, and the Carboniferous plants (about 299 million to 359 million years old) of Scotland.
