Table 2 Summary of characteristics of all lithofacies observed in the Zeglingen Formation in the study area
LF No | Name | Sedimentary structures | Mineralogy | Bed thickness | Distinction from other LF |
|---|---|---|---|---|---|
Layered sulfates and carbonates | |||||
1a | Wavy laminated sulfates | Wavy to crinkly lamination (Fig. 4A); sometimes with desiccation cracks or fenestrae. In some cases, lamination is chaotically deformed ('elephant skin' and 'upturned margin' structures). Domal structures are rare. Pseudomorphs of selenitic gypsum may occur in single layers. Isolated layers with flat pebbles or other intraclasts are not recorded separately | Gypsum or anhydrite, often dolomitic and/ or argillaceous. Single dolomitic or argillaceous beds within successions are not recorded separately | Mostly laminae < 1 cm | LF 1b is predominantly dolomitic LF 2 (laminated sulfates) does not show any signs of tidal flat environment (fenestrae, flat pebbles, elephant skin, desiccation cracks, etc.) |
1b | Wavy laminated to thin-bedded dolomite | Wavy to crinkly lamination (Fig. 4B); sometimes with desiccation cracks. Flat pebbles and other intraclasts may be intercalated. Only few thin clay layers occur. Chert or anhydrite nodules occur within single layers. Dolomite often shows millimeter-sized pores and fenestrae. Occasionally the dolomite has a somewhat nodular appearance | Dolomite | Mostly laminae < 1 cm and some thin beds up to 5 cm | LF 1a consists mainly of sulfates |
2 | Laminated sulfates | The mainly planar lamination can be folded (slumping, Fig. 4C, 8A). Individual layers indicate transport (ripples, graded layers of transported nodules or individual intraclasts). Occasionally single horizons show dipping, probably indicating cross-lamination. In some levels, fractured clay layers occur, in others flame structures. Selenitic ghosts are rare | Gypsum or anhydrite, often dolomitic and/ or argillaceous. Single dolomitic or argillaceous beds within the successions are not recorded separately. Within the upper part of the «Obere Sulfatzone» in some boreholes, anhydrite laminae occur intercalated with thin-bedded clay | Mostly laminae < 1 cm | LF 3a is mainly thin bedded LF 1a shows more wavy to crinkly lamination with signs of tidal flat environment (fenestrae, flat pebbles, elephant skin, desiccation cracks, etc.) |
3a | Thin bedded sulfates | Commonly, the mostly planar layers show no primary structures (Fig. 4D; probably due to recrystallization) and appear massive. Occasionally normal grading is recognized. Flame structures occur in some levels and can easily be mistaken as selenite ghosts. The layers may be folded (slumping) | Gypsum or anhydrite, occasionally argillaceous. Single layers of differing lithology (dolomite, clay or marl) are not recorded separately | Mostly thin bedded | LF 2 is predominantly laminated LF 3b consists mainly of dolomite |
3b | Thin to medium bedded dolomite | Commonly, layers have no recognizable internal structure. Rarely, individual layers with normal grading or intraclasts as well as layers with flaser stratification indicate sediment transport. Some dolomite layers with mm-sized anhydrite nodules but without signs of transportation are ascribed to this LF if they are not laminated. Mudcracks may appear in some levels and indicate temporary desiccation. (Fig. 4E, F) | Dolomite, often argillaceous. Single layers of sulfates are not recorded separately | Thin bedded to medium bedded | LF 3a consists mainly of sulfates LF 1b show wavy lamination |
4 | Selenitic sulfate layers | Due to recrystallization more or less clearly recognizable selenite crystals (often only ghosts), partly ripples or other laminated layers in between, which were repopulated by crystals after deposition. Rarely single clasts are intercalated (Fig. 4G) | Gypsum or anhydrite. Single dolomitic or argillaceous beds within the succession are not recorded separately | Layering is blurred due to recrystallization to selenitic crystals but is likely to have been mostly thin bedded | If selenite ghosts are recognizable as such clearly distinguishable from other LF |
Nodular to layered sulfates | |||||
5 | Chicken-wire | 'Chicken-wire' nodules (Fig. 4H), in some cases indistinct due to gypsum–anhydrite transformation. Partly, this LF overprints existing textures (for instance nodules in algal mat sediments) | Sulfate nodules surrounded by clayey seams | Some cm to few dm | Sulfate nodules of LF 6 are isolated in a clay matrix Transitions to LF 7 are possible; pure nodular layers are described as LF 5, partly ductile-deformed nodules as well as transitions to enterolithic layers are classified as LF 7 |
6 | Nodules in clay | Single sulfate nodules in clayey or marly sediments (Fig. 4I). The nodules can occur isolated or clustered in layers. Individual nodules may be ductile-deformed. Layered nodules can be strongly elongated | Sulfate nodules in clay or marl | Some cm to few dm | If the sulfate content increases and individual (ductile-deformed) nodules form a completely disordered sulfate-clay mixture, such sediments are described as LF 7 Once strongly elongated nodules coalesce to form enterolithic layers in clayey sediment, they are ascribed to LF 8 |
7 | Contorted to disrupted nodular anhydrite | Disrupted or contorted lamination of sulfates and clay. Enterolithic layers and (often ductile-deformed) nodules appear within completely irregular to chaotic sulfates and/ or clay. Unlike other similar LF LF 7 shows at least weak subhorizontal layering. Sulfates and clay are often completely intermingled. Figure 4J, K) | Sulfates and clay | Some cm to few dm | Transitions to various other LF exist: LF 6 shows only individual sulfate nodules in clay If only sulfate nodules occur without chaotically intermingled clay and without ductile deformation, they are classified as LF 5 LF 8 shows only enterolithic folded sulfate layers without intercalated disrupted nodules LF 14 shows the most similarities; distinction is based primarily on the lack of subhorizontal layering and pronounced vertically oriented deformation of LF 14 sediments, which, unlike LF 7, indicates substantial dissolution |
8 | Enterolithic sulfate layers | Wrinkled, enterolithic and nodular layers in clay or marl (Fig. 4L). Rarely, such layers can also be found in sulfatic matrix | Sulfate layers in clay or marl | Some cm to few dm | The transition from continuous layers to strongly elongated nodules is gradual. If individual nodules dominate, the sediment is classified as LF 6 |
Conglomerates, breccias and chaotic deformed sulfates | |||||
9 | Fractured beds (packbreccia) | Particulate crackle (to mosaic), monomictic packbreccia with the former layering still recognizable (Fig. 5A). The brittle deformation indicates lithification before brecciation | Components are sulfates or carbonates, matrix is mostly clayey or marly, rarely sulfatic | Some cm to few dm | Single layers within layered sulfates and/or carbonates may be disturbed due to synsedimentary faulting. If these layers were not completely brecciated by this process, they were recorded as layered sulfates/carbonate (LF 1–4) |
10 | Fractured beds (floatbreccia) | Particulate mosaic (to rubble), mainly monomictic floatbreccia with the former layering still recognizable (Fig. 5B). Brittle deformation indicates lithification before brecciation | The components are sulfates or carbonates, the matrix is mostly clayey or marly, rarely sulfatic Some floatbreccias with ductile-deformed anhydrite matrix associated with synsedimentary faulting were also described for this LF | Some cm to few dm | Floatbreccias of LF 13 are mostly polymictic and do not indicate former layering |
11 | Conglomerates and flat pebbles | Conglomerates and layers with (partly rounded) flat pebbles and chip conglomerates. Flat pebbles are usually monomictic, conglomerate layers can be polymictic. In some cases, normal grading occurs, mostly combined with an argillaceous matrix. Rarely, conglomerates show imbrication. Conglomerates are mostly clast-supported; flat pebbles can also be matrix-supported (Fig. 5D, E) | Sulfates or dolomite, matrix is in some cases argillaceous | Flat pebbles layers are mostly very thin bedded, conglomerates can reach medium bed thicknesses | All other conglomerate or breccia LF show no evidence of lateral transport but either indicate in-situ formation by swelling and shrinking (LF 12), show clear evidence of dissolution breccia (LF 13), or show fractured and tilted layers but still with the former layering recognizable (LF 9 and 10) |
12 | Ragged breccia to conglomerate | Particulate monomictic mainly rubble pack- to floatbreccias with comparatively low clayish matrix fraction (Fig. 5C). Components vary in roundness and sphericity and were at least partly lithified before brecciation. In some cases, the matrix consists of anhydrite. Typically, grading from small and isolated clasts or nodules in a clay matrix (floatbreccia) towards tightly coalescing clast aggregates (packbreccia) occurs | Sulfate or dolomite clasts in typically clay matrix | Some cm to few dm | In contrast to LF 11, breccias of LF 12 show no signs of transport and are always monomictic. The grading of floatbreccia into a packbreccia is typical for LF 12 Although the clasts of LF 12 often show some rounding, they also exhibit distinct signs of brittle deformation, which clearly distinguishes them from nodular sulfates (LF 5 and 6) |
13 | Rubble floatbreccia | Mostly polymictic rubble floatbreccias with clast content often increasing towards top. Sometimes a transition to a mosaic floatbreccia is observed. The clasts show varying roundness and sphericity. Some clasts show signs of brittle deformation whereas others have been ductilely deformed or show signs of superficial dissolution (Fig. 5F). Some may have a somewhat nodular appearance. The breccias show no signs of lateral transport rather than indicate sinking of the clasts into the clay matrix | Marl, sulfate or dolomite clasts in clay matrix | Some cm to few dm | LF 13 shows characteristics of dissolution breccias. This clearly distinguishes the breccias from other LF: Float breccias of LF 10 are mostly monomictic with still recognizable former layering Breccias and conglomerates of LF 11 are mostly packbreccias and show signs of transport LF 12 is monomictic and shows typical grading and signs of swelling and shrinking |
14 | Ductile-deformed anhydrite | Ductile-deformed sulfates, often mixed with clay, usually with signs of vertical displacement of some components. Primary layering is absent or only indistinctly recognizable. (Fig. 5G, H) If LF 14 is found near the base or top of the salt beds, halite crystals may occur in the mélange (Fig. 5I) | Anhydrite or gypsum and clay, rarely dolomite intermixed | Some cm to few dm, rarely > 1 m | LF 7 is very similar to LF 14; distinction is based primarily on the lack of subhorizontal layering and pronounced vertically oriented deformation structures in the LF 14 sediments, which, unlike LF 7, indicates substantial dissolution |
Halite | |||||
15 | Pure halite | (Almost) pure halite, sometimes cloudy or color-banded, may be fine to coarse crystalline. (Fig. 6 A) | Halite | Some cm to few dm | Clearly distinguishable from other halite LF, all other halite-LF are impure and contain either clay or anhydrite |
16a | Halite with thin seams | Halite, mostly coarse crystalline, containing impurities, mainly anhydrite in thin seams (which may be ragged, even ductile). Figure 6B | Halite with seams of anhydrite or clay | Some cm to few dm | Clearly distinguishable from other halite LF by the occurrence of thin seams consisting of clay or anhydrite |
16b | Halite with interlayers | Halite, fine to coarse crystalline, containing impurities of anhydrite or (more rarely) clay intercalations up to a few cm thick. Individual thicker layers are addressed separately (Fig. 6B). In this LF, salt successions with either single thin interlayers or multiple (repetitive) layers are combined. (Fig. 6C) | Halite with anhydrite and/ or clay | Some cm to few dm | LF 16a only shows thin seams and no layers of up to few cm thickness Single layers of several cm in thickness are addressed separately by their individual LF. As long as layering is clearly visible, the successions were ascribed to LF 16 b. If haloturbation due to recrystallization processes continues, the layering will eventually be completely destroyed, and the salt succession is then grouped into LF 19 (ductile disrupted anhydrite in halite) |
17 | Floatbreccia in halite-matrix | Halite, mostly fine crystalline, sometimes coarse crystalline, contaminated with mainly fractured anhydrite and—more rarely—clay components as floatbreccia (Fig. 6D, H). The clasts may still, but not necessarily have primary texture. Halite cubes may occur both between and within the anhydrite or clay components | Halite with anhydrite or clay, rarely dolomite | Some cm to few dm | Usually clearly distinguishable from other halite LF, no other LF shows floatbreccias Only to LF 19 exists partly a gradual transition. Differentiation is then based on the nature of the non-halite components: if these are clearly bounded without ragged edges, the sediment is assigned to LF 17. If the edges are clearly irregularly ragged, it is assigned to LF 19. Halite cubes tend to occur in LF 19 |
18 | Impure halite (intercrystalline anhydrite or clay) | Mostly coarse crystalline halite with anhydritic or clayey material in the intercrystalline space. The shape of the non-halite material is mainly controlled by the crystal shape of the halite. (Fig. 6E) | Halite with anhydrite and/ or clay | Some cm to few dm | The non-halite components of LF 17 and 19 do not show the angular shape typical of LF 18, dictated by halite crystal growth. However, some non-halite components seem to have been plastically deformed prior to coarse crystalline recrystallization of halite |
19 | Impure halite (ductile disrupted anhydrite or clay) | Fine to coarse crystalline halite with ductile-deformed and fractured clay and anhydrite fragments (Fig. 6F). The fragments are sometimes roughly layer-parallel and often still show internal structures. Salt cubes occur within the fragments as well as in between. The mélange may be completely chaotic, partly due to the growth of halite crystals (haloturbation) | Halite with anhydrite and/ or clay | Some cm to few dm | Non-halite clasts within the halite successions of LF 17 do not show ductile deformation and only rarely halite cubes within the clay or anhydrite The non-halite fraction of LF 18 shows a characteristic angular shape controlled by halite crystal growth There is a gradual transition to LF 20. As long as halite predominates or the non-halite fraction does not form semi-contiguous layers, the sediments are ascribed to LF 19 |
20 | Disrupted mélange | Halite in the form of fibrous salt or hypidiomorphic to idiomorphic single crystals between fragments of anhydritic marl (often with anhydrite nodules). The marl usually forms single layers. These are fractured and in the newly formed fissures fibrous halite crystalized (Fig. 6H), or have been further deformed by later growth of halite crystals (haloturbation, Fig. 6G) and show only weakly recognizable layering | Anhydritic marl with halite | Some cm to few dm | There is a gradual transition from LF 19 to LF 20. As long as halite predominates or the non-halite fraction does not form semi-contiguous layers, the sediments are grouped into LF 19 In some non-halite lithologies, fissures occur with fibrous halite, which is clearly and sharply distinguished (mainly by a distinctive red color) from surrounding salt layers. These fissures are considered to represent later events and, therefore, such layers are ascribed to the non-halite LF |
Clay-rich sediments | |||||
21 | Marl | Marl, partly with thin interlayers of other lithologies, which were not always outlined separately In some cases, anhydrite nodules occur (Fig. 6I). Occasionally mudcracks indicate desiccation | Dolomitic, argillaceous or anhydritic marl | Some cm to few dm | LF 3 has lower clay-mineral content, LF 22 is almost pure clay |
22 | Black clay | Black clay, layered (Fig. 6J) or structureless | Clay | Some cm to few dm | LF 21 has a lower clay content |