Röddinge Formation
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| Röddinge Formation | |
|---|---|
| Stratigraphic range: Late Sinemurian-Late Toarcian ~ | |
| Type | Formation |
| Unit of | Vomb Trough |
| Underlies | |
| Overlies | Unknown Hettangian deposits |
| Thickness | Up to 300 m (980 ft) |
| Lithology | |
| Primary | Limonite and Chamosite-cemented Quartz arenites containing abundant chamosite ooids. |
| Other | Berthierine, Siderite and Iron ooids. |
| Location | |
| Region | East Skåne County |
| Country | Sweden |
| Type section | |
| Named for | Röddinge |
  Röddinge Formation (Sweden) | |
The Röddinge Formation is a geologic formation in Skåne County, southern Sweden. It is Early Jurassic (Sinemurian-Toarcian) in age.[1] It is a unit with a limited degree of exposure, being identified mostly by its deposits on the Fyledalen Fault Zone, specially on Kurremölla, where the main fossil deposit is present.[2] It is a unit known mostly for large museum collections and estimated to have a thickness of several hundred meters.[3] It is also known for its large iron deposits.[2] It is correlated with the mostly marine Rya Formation of western Skåne County, the Volcanic deposits of the Djupadal Formation and specially the Sorthat Formation of Bornholm.[4][5] Most likely, the coarse-grained nature of the Röddinge Formation is linked to rapid erosion of a tectonically active hinterland.[6]
A profile up to 300 m thick was described in 1968 from the Eriksdal-Kurremölla area, dated Pliensbachian-Toarcian.[7] The Pliensbachian levels where dominated by sands and sandstones of marine origin, hosting a highly fossiliferous bed containing a rich mollusc fauna.[7] A Sinemurian layer assigned to the formation was also found on other works.[3] The Röddinge formation has a great abundance of Limonite and Chamosite quartz arenites, fine-to medium-grained, with subordinate thin conglomerates.[1] Sediments related to the unit are found consolidated by Berthierine or Siderite cement, with berthierine oolites being common in the layers.[1] These ooids are rather small in most of the successions, around 0.3 mm in diameter and ellipsoidal in shape, having cores composed of detrital quartz or heavy minerals.[1] The deposits of the formation evidence strong degradation by modern weathering and have a red, brown or yellow stain (iron hydroxides).[1] The deposits not affected by erosion are known from boreholes and host greyish dark green facies due to the content of berthierine and siderite.[1] The iron contents differ based on the weathering grade of the layers: on weathered sandstones is about 8–10%, then is in up to 20% in the oolites, and finally at the major fossiliferous deposit on Kurremölla a 1.7 m thick oolite bed has an iron content of up to 35%.[1] Owing to this high content in iron, the Kurremölla locality was mined from 1930 to 1937, although there was not enough iron supply and enrichments were too dispersed in the source rock, which led to it not being economically viable to maintain the mining process for very long.[8][9] The presence of mostly poor exposures has made mostly impossible to do detailed facies analysis, although it is suggested that the sediments come from prolonged reworking.[1]
