Shales-with-‘beef,’ a Sequence in the Lower Lias of the Dorset Coast.

Abstract

Shales-with-‘beef’ was the name given to some 70 feet of Lias on the Dorset coast, lying above (53) Table Ledge and below (76 a) the Birchi-Tabular. The beds consist of paper-shales, marls, indurated bands, and limestone nodule-beds, with numerous, more or less impersistent, interbedded seams of fibrous calcite, called ‘Beef’ by the Officers of the Geological Survey. Descending to the beach at Charmouth, and there forming reefs on the foreshore, the Shales-with-Beef are the most accessible Lias of that place. Yet they are, perhaps, the least known of all the beds. This is doubtless because of the generally unsatisfactory condition of the fossils found in them, and their consequent worthlessness on the one hand to the native, who finds no sale for such fragmentary and friable remains as the fossils present; while, on the other hand, the geologist seldom finds specimens more than approximately identifiable, and generally obtains completely satisfactory examples from but three or four horizons. Sir Henry De la Beche described the Lias of this coast nearly a century ago; and, although he generally under-estimated their thickness, the subdivisions that he then made can be approximately correlated as follows, at any rate those five which lie above the Blue Lias limestones:— (5) Irregular bed of Limestone, with nodular concretions, frequently containing ammonites; 2 feet=Stellaris beds (87–89). (4) Slaty marls, with several thin beds of indurated marl; 67 feet = Black Marl series above Birchi-Tabular and below Stellaris beds (77–88). (3) Slaty marls containing small crystals of selenite; 32 feet Shales-with-Beef (54–76).

Early overpressuring in organic-rich shales during burial: evidence from fibrous calcite veins in the Lower Jurassic Shales-with-Beef Member in the Wessex Basin, UK

“…The Lower Jurassic Charmouth Mudstone Group consists of dark grey shales, paler grey blocky mudstone and marls, sporadic limestone concretions and tabular limestone beds (Simms 2004;Jenkyns & Weedon 2013), which were deposited in an extensive epicontinental sea during a major global sea-level rise (Anderton et al 1979). Fibrous beef veins and cone-in-cone structures are commonly observed in the black shales of the Lower Chamouth Mudstone, especially in the Shales-with-Beef Member (Lang et al 1923;Gallois 2008;Jenkyns & Weedon 2013;Zanella et al 2015).…”

“…The limestones commonly occur as decimetre-scale nodules, which often contain well-preserved ammonites (Simms 2004). The shales consist of numerous thin beds (<10 cm) of fibrous calcite veins, referred to as 'beef', which give the member its name (Lang et al 1923;Tarr 1933). The Shales-with-Beef Member is overlain by the Black Ven Marl, which consists of 43 m of dark grey thinly interbedded and organic-rich mudstone, with a few thin beds of muddy limestone (House 1989) (Fig.…”

Completeness of the fossil record and the validity of sampling proxies at outcrop level

“…2010) and ichnofossil fauna (Moghadam and Paul 2000). The Black Ven Mudstone is perhaps the most intensively sampled unit and is particularly rich in ammonites (Lang et al. 1923; Lang and Spath 1926; Simms 2004), as well as important fossils of marine reptiles (Martill 1995; McGowan and Milner 1999), the dinosaur Scelidosaurus (Martill et al.…”

“…The diverse fossil assemblages are well documented, including 14 type specimens of reptiles (Benton and Spencer 1995), many fishes (Dineley and Metcalf 1999) and a substantial number of invertebrate species. The section also benefits from exceptionally detailed stratigraphic accounts, especially by Lang (1924, 1936; Lang et al. 1923, 1928; Lang and Spath 1926) and Buckman (1910, 1917, 1922), who devised high‐resolution bed‐by‐bed stratigraphical frameworks for the Lias (Simms 2004; Lord et al.…”

The temporal and spatial development of landslides in the axmouth‐lyme regis undercliffs national nature reserve, Devon

“…The depths of the East Pinhay Bay slip, the Ware Cliffs slip, and the slip in the higher undercliff at Charton Bay have been determined by the position of the topmost unit of the Blue Lias, a thick bed of calcarenite called of Lang et al, 1923). Above this, in the Shales with Beef, the calcarenites die out, and the development of shear surfaces seems generally uninhibited withir.…”