One method of splitting up calcareous sediments is Glauber's Salt method (Franke 1922; Wicher 1942; Herrig 1966; Surlyk 1972; Schmid 1974; Wissing and Herrig 1999). Following an idea from A.G.W. van Riemsdyk, Harting (1866) introduced the use of a saturated solution of crystalline sodium sulphate as a substitute for ordinary water. The method, using a solution prepared at about 40°C, was successfully used by Keilhack (1917) and Franke (1922) for extraction of foraminifers and other microfossils from chalk. The sodium sulphate crystals grow in the pore system initiated by placing the samples in a deep freezer (or a water-cooled container), and was an improvement in the water-based freeze-thaw process and decreased the cycles of treatment to 16 to 18 times (Wicher 1942; Surlyk 1972). Moreover, Wicher (1942) modified the Glauber's Salt method to involve heating of samples covered with anhydrous sodium sulphate and subsequent boiling in a concentrated solution of sodium sulphate. The method is destructive to the microfossils, and thus, Kirchner (1958; Green 2001) revised the method by maintaining the temperature of the solution below the boiling point. Although still widely used, the Glauber's Salt method has some disadvantages: 1) The samples have to be reduced to smaller pieces of walnut size prior to treatment with Glauber's Salt; 2) The method is time consuming; 3) The fossils are not generally free of adhering sediment particles, and therefore need to be cleaned in an ultrasonic bath.
Non-calcareous fossils are usually extracted from chalk and limestones by dissolving the matrix with a solution of acetic acid (Reid 1958; Müller 1962; Zankl 1965; Rudner 1972; Jeppsson et al. 1985, 1999). Because this process destroys the calcareous fossils, other methods must be used to extract such fossils. Improving the procedure by Bourdon (1956; 1962; Lethiers and Crasquin-Soleau 1988), Nötzold (1965) described a method for disaggregating calcareous and clayey calcareous sediments used to extract charophytes and gyrogonites. A sample is submerged partly (2/3) in a solution of 96% acetic acid (CH3COOH) and anhydrous copper II sulphate (CuSO4) for 12 to 20 hours. Then the sample is removed from the solution and covered by at least 10 litres of cold water. The formation of calcium acetate ((CH3COO)2Ca) and absorption of water within crystals leads to the breakdown of the sample (Nötzold 1965; Hansch 1994; Reich 1997; Wissing and Herrig 1999). The method requires the use of highly toxic components. Another drawback is that further treatment with hydrogen peroxide (H2O2) may be required to clean fossils (Wissing and Herrig 1999). Our acid-hot water method resembles a modified and much improved version of the method given by Nötzold (1965). However, there is a fundamental difference: the disaggregation is caused by carbon dioxide formation and not crystal-bound water as in Nötzold's (1965) method.