Extraction of fossils from carbonates is affected by using different techniques depending on the composition and preservation of the fossils and the hardness of the enclosing sediment (matrix). Preparation consists of the following steps: 1) breaking up the sample (disaggregation) by chemical and physical means; 2) removing the fine fraction through sieving; 3) drying the residue; and 4) hand-picking the fossils. The harder the sample is, the harsher the preparation treatment required (Green 2001). For uncemented, slightly consolidated sediments, treatment by wet sieving is generally sufficient. If the fossils are embedded in more firm sediments, such as chalk, sieving will be useless without proper pre-treatment. The sample must be subjected to a procedure of disaggregation (without damaging the fossils) prior to wet sieving. The simplest way of disaggregating indurated calcareous sediments, such as the Upper Cretaceous White Chalk, is by saturating the samples with water and then placing them in a freezer. The formation of ice crystals in the pore system breaks up the matrix (Hanna and Church 1928; Pojeta and Balanc 1989). This freeze-thaw method can be repeated several times until the sediment (matrix) is fully disaggregated. Another freeze-thaw method is Glauber's Salt method (Na2SO4 10H2O, hydrated sodium sulphate) that also requires repetition of the procedure to function properly (Surlyk 1972).
The purpose of this paper is to document the combination of two methods that are more efficient and less time-consuming than freeze-thaw methods but have received little attention. These are called the acid-hot water method and the waterblasting technique. They have been applied separately and in combination on samples from two localities: Lower Campanian skeletal sands at Ivö Klack, Sweden; the Maastrichtian White Chalk at Stevns Chalk Quarry, Denmark; the Danian Bryozoan Limestone at the sea cliff Stevns Klint, Denmark; and the Danian Bryozoan Limestone at the Fakse Limestone Quarry, Denmark.