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Titolo:
Chaetetid buildups in a westphalian (Desmoinesian) cyclothem in southeastern Kansas
Autore:
Suchy, DR; West, RR;
Indirizzi:
Univ Kansas, Kansas Geol Survey, Lawrence, KS 66047 USA Univ Kansas Lawrence KS USA 66047 sas Geol Survey, Lawrence, KS 66047 USA Kansas State Univ, Dept Geol, Manhattan, KS 66506 USA Kansas State Univ Manhattan KS USA 66506 pt Geol, Manhattan, KS 66506 USA
Titolo Testata:
PALAIOS
fascicolo: 5, volume: 16, anno: 2001,
pagine: 425 - 443
SICI:
0883-1351(200110)16:5<425:CBIAW(>2.0.ZU;2-U
Fonte:
ISI
Lingua:
ENG
Soggetto:
PENNSYLVANIAN CYCLOTHEMS; GROWTH FORM;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
41
Recensione:
Indirizzi per estratti:
Indirizzo: Suchy, DR Univ Kansas, Kansas Geol Survey, 1930 Constant Ave, Lawrence, KS66047 USA Univ Kansas 1930 Constant Ave Lawrence KS USA 66047 KS 66047 USA
Citazione:
D.R. Suchy e R.R. West, "Chaetetid buildups in a westphalian (Desmoinesian) cyclothem in southeastern Kansas", PALAIOS, 16(5), 2001, pp. 425-443

Abstract

Small buildups of chaetetids and associated biota in the Higginsville Limestone Member of the Fort Scott Formation (Desmoinesian, Middle Pennsylvanian) are well exposed in three dimensions in an abandoned quarry in Crawford County, Kansas. Regional studies indicate that the buildups were deposited during a relative sea-level highstand but within normal wave-base, on the southern flank of the Bourbon Arch. The chaetetid facies consists of a fusulinid wackestone to packstone that encloses the chaetetids. In the lower part of the chaetetid interval, chaetetids are small and tabular, but gradually upsection. they grade into larger domical forms that sometimes form tall,ragged columns. These, in turn, coalesce upward to form large masses (boundstone) up to 6 m across. At the top of the bed, the chaetetid masses and surrounding matrix are covered by intertidal to supratidal, coastal, and/or terrigenous facies, indicating a shallowing of sea level to the point that chaetetid growth was terminated. Attachment surfaces for individual chaetetids initially involved partiallylithified sediment or shell fragments, whereas within the columns they attached to underlying chaetetids, Multithecopora or algal overgrowths on underlying chaetetids, or thin sediment layers that define growth interruptionswithin the columns. Apparent maximum relief of chaetetids relative to the seafloor during growth was from 30 to 45 cm. Cross laminations in the matrix and some toppling of chaetetids indicate a moderately high-energy paleoenvironment. Ragged margins of the chaetetids accompanied by overlying thin sediment layers; a periodic overgrowths by the tabulate coral Multithecoporaand encrusting algae, indicate growth interruptions instigated by periodicinfluxes of sediment or other environmental factors. Abundant fossils are present on and among the chaetetids, including brachiopods, encrusting algae, ostracodes, and foraminiferids. Many of them are apparently in life positions, indicating a diverse, stenohaline biota living in this environment. Chaetetid masses are relatively evenly distributed throughout the quarry and, thus, give no indication of an end to the buildup in any direction, or of a windward or leeward orientation. Directional indicators within the rocks and linear trends of the buildups suggest a paleocurrent that moved in anortheasterly direction. Apparently the environment of deposition was relatively uniform, flat, shallow, well-aerated, and open marine, at some distance from shore.At the time of deposition, this area was within 10 degrees of the paleoequator. Changes in rainfall, ocean circulation, mixing, aeration, and nutrient input are reflected in the rocks and by their preserved biota. Black shale represents the least mixing and aeration, the phylloid algal limestone suggests low-turbidity and possibly low salinity but well-aerated and nutrient-rich marine conditions, and the chaetetid interval represents normal marine salinity and low nutrient input with the best circulation,mixing, and aeration. Recent studies of growth rates in extant coralline sponges suggest that the chaetetid bed of this study represents a minimum of 10,000 to nearly 20,000 years of deposition, and the largest individual chaetetid in this bed may have lived over 3,000 years. The relatively thin transitional bed betweenthe underlying phylloid algal limestone and the chaetetid bed represents several hundred years of deposition. The limestone bed overlying the chaetetid bed contains a few chaetetids that may have lived up to 400-800 years, and it contains evidence of a tidal cycle of strong and weak tides.

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Documento generato il 03/07/20 alle ore 22:34:36