Middle cambrian trilobites and biostratigraphy of the Almbacken drill core, Scania, Sweden

Sammanfattning: A core drilling at Almbacken in Södra Sandby, Scania, southern Sweden, penetrated a c. 30 m thick succession of Middle Cambrian-upper Lower Cambrian strata. The Middle Cambrian of this core is the most complete one so far documented in Scania. The core contains a stratigraphical sequence from the Lejopyge laevigata Zone (upper Paradoxides forchhammeri Stage) to the Holmia kjerulfi-group Zone (upper Lower Cambrian). The Acadoparadoxides oelandicus Stage is probably missing. The Middle Cambrian is c. 28.3 m thick and consists of dark grey to black mudstones and shales (alum shale) with stinkstone and limestone beds. Three major limestone beds can be identified: the "Fragment Limestone", the Exsulans Limestone, and the Andrarum Limestone. The Middle Cambrian is richly fossiliferous and the faunas are dominated by agnostid trilobites. Polymerid trilobites and indeterminate lingulate brachiopods are common at some levels. The succession of trilobite species are used for a biostratigraphical subdivision of the succession. The preservation is generally good and 31 trilobite species were identified. The excellent preservation in the stinkstones allowed a description of growth stages in pygidia of Ptychagnostus punctuosus (Angelin, 1851). Only the upper part of the Lower Cambrian (Gislöv Formation) was recovered, comprising c. 1.5 m of siltstones and a thin limestone bed at the base of the core.