Djupadal Formation

The Djupadal Formation is a geologic formation in Skåne County, southern Sweden. It is Early Jurassic (probably Pliensbachian-Toarcian, or Late Toarcian) in age. It recovers at various locations throughout Central Skane, know by the discovery of basalt tuff layers, including Sandåkra, Korsaröd and Djupadal. An original analysis of the location of Korsaröd led to a Toarcian-Aalenian age, a finding that was accepted in various papers in the 1980-90s but was dismissed in 2016, when a series of Palynogical samples recovered a Late Pliensbachian and probably Lower Toarcian age for the Korsaröd Outcrop. The same year this result was also challeged by an in-depth study of the Lilla Hagstad neck that yield a Late Toarcian Age. The formation was deposited in the Central Skane region, linked to the late early Jurassic volcanism. The Korsaröd member includes a volcanic-derived Lagerstatten with exceptional fern finds. The data provided by fossilized wood rings showed that the location of Korsaröd hosted a middle-latitude Mediterranean-type biome in the late Early Jurassic, with low rainfall ratio, delayed to seasonal events. Superimposed on this climate were the effects of a local active Strombolian Volcanism and hydrothermal activity.
Description.
Djupadalsmölla, the original location has been known due to its volcanic Tuff and other volcanoclastic-derived facies. It was originally described in 1826 as the local basalts where identified as coming from ancient volcanic eruptions. The exposure of Anneklev, located near Höör was where the first volcanic neck was discovered, with other volcanic remnants mentioned on Jällabjär and Rallate along with the tuff at Djupadalsmölla. These deposits were described as volcanic rocks composed mostly by tuff, that includes basaltic bombs (composed by Pyroxene and pseudomorphs from this, along with Olivine on adjacent pyroclastics), accidental lithics and occasional wood from conifers, in the form of small pieces to large logs. At Djupadal the Rönne River has cut a 20 m deep valley mainly in the Precambrian basement, where Lower Jurassic strata (including volcanic tuff) form part of the southern valley side, and also occur in the valley northwestwards, indicating that the valley is partly an exhumed sub-Jurassic depression. The modern strata of the Valley is over a Late Weichselian melt-water channel and it also contains eroded fluvioglacial deposits. A nearby roadcut shows kaolinized basement beneath the Toarcian sediments and a nearby boring has penetrated 44 m of kaolinized Gneiss. The Valley Bottom exposes small ridges and cupolas (in gneiss) and tors (mainly in Amphibolite). 
The "Djupadalsmölla" pyroclastic reaches almost 10 m high and 20 m wide, with pyroclastics appearing also through the west more than 100 m, along the valley of the Rönne River. The strata is composed by mostly small Lapilli (around 30–50% of the content) and ash (-10 mm), with some samples being red in patches. Tuff concretions are recovered locally composed mostly of coarse ash, with rich amounts of Calcite and Wood pieces. This composition indicates moderate explosivity on the genesis of the materials, relating the eruption products with short transport paths, as show little mechanical weathering, also corroborated by the thick layering and the low amount of basaltic bombs reported, while the correlation of wood and lapilli indicates a terrestrial deposition. All together shows local Strombolian Volcanism, linked probably to a coeval rift, as recovered by the presence of more than 100 coeval volcanic necks in central Scania. 
Dominating the "Djupadal formation" is moderately sorted lapilli tuff with abundant scoria, what indicates moderate explosivity, giving the eruption products short transport paths, preventing extensive mechanical weathering, that would create rounded fragments and large amounts of ash, that along thick layers and decimetre sized bsaltic bombs are clear signs of closeness to the volcanic source. The presence of wood, together with the moderately sorted lapilli tuff, indicate a terrestrial depositional environment, probably influenced by freshwater deposits.
On Snälleröd (65 m thick, 44 m saprolite) samples taken, compared with the ones from the bottom of the road cut at Djupadal at 1.5 km NNE of this last one showed massive, soft lumps of a white, fine-grained material lacking any visually detectable grains of primary minerals, where only chemical data showed that this material is highly depleted in Calcium, Potassium and Sodium with significant kaolinization. The kaolinized rock has Kaolinite content exceeding 85%. The samples taken at the NNE of Djudapal shows angular, gravel-sized material contains less altered granules of gneiss, remnant Feldspar and Quartz on a fraction dominated by Smectite, unlike the previous kaolinite-dominated ones, altrougth this last one is also abundant. 
The Korsaröd Lagerstatten is located also on central Scania, and represents the best outcrop of the formation, leading to exquisitely preserved (with fossilized nuclei and chromosomes) specimens of ferns of the extant genus "Osmundastrum". This location was linked by Ulf Sivhed in 1984 with the "Dajupadal Formation". What was corroborated by recent studies. It is also composed by volcaniclastic deposits, located at 380 m WNW of the nearest basaltic volcanic plug. It is composed by mafic clasts agruped with agglomerates, oriented to this volcanic plug, coming probably from it or nearby ones. It´s clasts are angular and poorly sorted, recovered on a series of layers whose timing is uncertain, as there is no probe if represent discrete episodes separated by intervals of non-deposition or is result of variations due to a high-energy depositional setting. Like in the Dajupadalsmölla type deposit, there is a great abundance of ash/mud content of the deposit filled with chaotic distributed wood fossil, what leds to the interpretation that this was a lahar deposit. This location has been compared with modern Rotorua, New Zealand, considered an analogue for the type of environment represented in southern Sweden at this time.
Eneskogen, Bonnarp and Säte volcanic necks are the main coeval of the Formation. While Bonnarp (5-6 m height and covers roughly 5,000 square meters, covered by Jurassic sediments) is calculated to have at least 185.4+4.6 Ma (Middle Pliensbachian), Säte (Comprise two basalt pipes, each roughly 6–10 m high and some 10,000 square meters in area) yielded 180.0+0.7 Ma and Eneskogen (A large hill covered by quaternary sediments. Some few boulders and basalt pillars were exposed) 182.1+0.6 Ma, both Lower Toarcian in age. It recovers one of the tree major mesozoic volcanic events on Skåne. Säte & Bonnarp volcanic strata is composed by Basanite, being the first Glassy Facies, and the second microcrystalline, while Eneskogen also microcrystalline, is dominated by Melanephelinite. Bonarp has a very special character, which differed considerably from the normal cone of a Stratovolcano. Bonarp hosts At Bonarp between the crystalline basement and the basalt tuff, a sedimentary layer sequence intervenes, alternating sandy and clayey layers. The layers linked to the volcano consists of sand and clay stones with thin coal seams, with bottom redistributed disturbed layers of kaolin. The overall appearance of the Bonarp volcano suggests that local tectonic movements were more or less complete when the eruption began. The pre-basaltic weathering process was also a deep kaolinization of the crystalline basement (Knutshög, Djupadal). At Bonarp the basement is also deeply decomposed.
Age.
Tralau (1973) measured the age for the local deposits, stablishing that where typical Middle Late Triassic to Lias strata, with absent Middle Jurassic sediments, with the exception of the volcanic event ejecting the tuffs in Korsaröd, stating that they took place in the Middle Toarcian. Radiometric ages obtained by using K–Ar techniques scatter in a wide range between 171 and 179 Ma. Following works on the 80s and 90s recovered also this original datation, putting this and the Dajupadalsmölla outcrop on the Toarcian-Aalenian boundary, as example of latest lower jurassic volcanism on the region. In 2011 a depth study of the Volcanic Plugs led to stablish a range 191 –178 Ma based on 40Ar/39Ar whole-rock ages for samples derived from eight basanite–nephelinite plugs. The Palynological studies on the 2014 tougth, changed the perspective of the age of the location, proposing a more fitting Late Pliensbachian. In 2016 an in depth palynological study of the Korsaröd section led to stablish a Pliensbachian–early Toarcian(?) age, based on the high presence of the genus "Perinopollenites elatoides" (Pinales) and "Eucommiidites troedsonii" (Erdtmanithecales). Other more recent works support that the outcrop is Toarcian in age. With a more recent work recovering a high-precision 40Ar/39Ar anorthoclase feldspar age of 176.7 ± 0.5 Ma (2-sigma), Late Toarcian. This confirmed Tralau Original palynology results and the Paleomagnetic Studies done in 1993.
The formation overlies the Höor Sandstone Formation, and is time-equivalent with the Rydebäck and Katslösa members of the Rya Formation on NW Skane, the Röddinge Formation of the Vomb Trough and the Sorthat Formation of Denmark, with which it shares the abundance of Fern-derived material. The formation also correlates with the Fjerritslev Formation of the Danish Basin, and the Gassum Formation of the Øresund Basin.