Bromide Formation

The Bromide Formation crops out in the Arbuckle and Wichita Mountains and in the Criner Hills of Southern Oklahoma. == Stratigraphy ==

The Bromide Formation is the uppermost part of the Simpson Group, and originates from the Upper Ordovician (early Sandbian). This mostly carbonate succession is divided into the Mountain Lake and overlying Pooleville members. The Bromide Formation is a shallow water marine sediment. Much of the Mountain Lake Member comprises meter-scale, deep ramp cycles that overlie a lowstand systems tract of sandstones and sandy crinoidal grainstones. Cycle tops are starved surfaces with irregular, mineralized hardgrounds. The Pooleville Member consists of an early highstand interval of shallow subtidal carbonates and late highstand peritidal carbonates (Corbin Ranch Submember). Down-ramp, the Pooleville is represented largely by centimeter-thick shales and interbedded lime mudstones. == Economic use ==

The Bromide Formation has been a source of oil and gas, with exploration slightly north of the area where the formation is exposed. == Origin ==

The Bromide Formation was deposited in a shallow, storm-dominated epeiric sea that extended over part of the Laurentia continent, in what is today Southern Oklahoma. The sea spread into an area that sunk into a rift, that ultimately did not endure, a so-called aulacogen. Lying approximately at 30° Southern latitude, a low-land desert bordered much of the shallow sea from where well-rounded quartz sand blew in. This now represents the sandstone at the base of the Bromide Formation. Eventually, sea level rise caused by subsidence drowned the borderlands cutting off the supply of sand, and now the shales and limestones of the Middle Bromide (upper Mountain Lake Member) accumulated on a broad ramp. Gradually – primarily echinoderm – skeletons build up a carbonate shelf. Further eustatic sea level rise (transgression) cut off the supply of virtually all sediments from land, and remains of carbonate-producing organisms began filling the basin. This now forms the limestone of the upper Bromide (Pooleville Member). Finally, a drop in sea level (regression) exposed the entire platform, and became a broad, nearly featureless, hot, semi-arid sabkha. == Fossils ==

Fossils have been found in the Bromide Formation of green algae, sponges, corals, graptolites, lampshells, moss animals, trilobites, clam shrimps, molluscs, several groups of echinoderms, and teeth of jawless fish. === Green algae === • Ischadites iowensis === Sponges === • Dierespongia palla === Corals === • Saffordophyllum deckeri • Ancistorhyncha globularis (pooleville member) • Apianurus sp. ==== Edrioasteroids ==== • Cyathocystus oklahomae ==== Cystoids ==== • Amygdalocystites tribranchiatus • Traskocrinus sp. • Archaeocrinus subovalis • Calceocrinus longifrons • Carabocrinus treadwelli • Euptychocrinus skopaios • Hybocrinus crinerensis • Hybocrinus nitidus • Hybocrinus pyxidatus • Palaeocrinus hudsoni • Paracremacrinus laticardinalis === Chordates === ==== Teeth of jawless fish (conodonts) ==== • Ansella crassa Bauer 1994 • Ansella nevadensis (Ethington and Schumacher) • Baltoniodus gerdae (Bergström) • Bryantodina aequalis Bauer 1994 • Cahabagnathus sweeti (Bergström) • Cardiodus abbreviatus • Cardiodus densus • Cardiodus robustus • Cordylodus sp. • Curtognatus sp. • Curtognatus cordiformis • Curtognatus coronata • Curtognatus limitaris • Eoplacognathus elongatus (Bergström) • Erismodus typus Branson and Mehl • cf. Leptochirognatus sp. • Leptochirognatus extensa • cf. Microcoelodus sp. • Microcoelodus asymmetricus • Microcoelodus inornatus • Microcoelodus intermedius • Microcoelodus minutidentatus • Microcoelodus typuis • Oneotodus? ovatus (Stauffer) • Oistodus suberectus • Pharagmodus ambiguus Bauer 1994 • Phragmodus flexuosus • Plectodina edentula Bauer 1994 • Polycaulodus bidentatus • Polycaulodus tridentatus • Staufferella falcata (Stauffer) • Trichognatus obtusa • Trucherognatus distorta • Trucherognatus irregularis • Walliserodus declivis Bauer 1994 == References ==