Early Cambrian coastal dunes at Vassbo, Sweden
Coastal eolian deposits have been distinguished in the Groveldalen Member of the Vassbo Formation (Lower-Middle Cambrian) at Vassbo, Sweden. The sandstone is characterized by abundant cross-bedding and is divided into two parts, a lower medium-grained part (lower facies) and an upper fine-grained part (upper facies). The lower part, which is dominated by trough cross-bedding, is interpreted as a nearshore aqueous deposit of a seaward-prograding beach. The upper part, containing large-scale planar cross-bedding, translatent climbing ripples, and sandflow toes, represents eolian deposits. Compared to the medium-grained facies, the fine-grained facies is characterized by negative skewness and better sorting. Additional evidence supporting an eolian origin of the upper facies is a wind-abraded pattern, characterized by "upturned plates," which have been observed on the quartz grain surfaces from the same facies. Structural as well as textural parameters, together with the uniform paleocurrent pattern, suggest deposition of coastal dunes within the interpreted Cambrian trade-wind belt in a Southern Hemisphere position of the Baltic Shield.