scholarly journals Hiatuses and condensation: an estimation of time lost on a shallow carbonate platform

2015 ◽  
Vol 1 (2) ◽  
pp. 91-117 ◽  
Author(s):  
André Strasser
Keyword(s):  
Carbonate Platform ◽  
Shallow Carbonate Platform ◽  
Estimation Of Time

scholarly journals Onset of the Ordovician cephalopod radiation – evidence from the Rochdale Formation (middle Early Ordovician, Stairsian) in eastern New York

2008 ◽  
Vol 145 (4) ◽  
pp. 490-520 ◽  
Author(s):  
BJÖRN KRÖGER ◽  
ED LANDING
Keyword(s):  
New York ◽  
Community Structure ◽  
New Taxa ◽  
Intraspecific Variation ◽  
Carbonate Platform ◽  
Taxonomic Distinctness ◽  
New Information ◽  
Shallow Carbonate Platform ◽  
Depositional Setting ◽  
Rank Abundance

AbstractThe Rochdale Formation of eastern New York (= Fort Ann and lower Bascom formations, designations abandoned) is now recognized to record the earliest stages of the Great Ordovician Radiation of cephalopods. The earliest Bassleroceratidae, Tarphyceratidae and endoceridans on the east Laurentian shallow carbonate platform occur in the upper, thrombolite-bearing member of the Rochdale. This fauna demonstrates that the earliest radiation of Ordovician nautiloids took place in the late Tremadocian and is best recorded in tropical platform facies. Revision of this cephalopod fauna based on approximately 190 specimens collected along a 200 km, N–S belt in easternmost New York has provided new information on inter- and intraspecific variation of earlier described species. The ellesmerocerid Vassaroceras and the endocerids Mcqueenoceras and Paraendoceras are emended. New taxa include Bassleroceras champlainense sp. nov. and B. triangulum sp. nov., Mccluskiceras comstockense gen. et sp. nov., Exoclitendoceras rochdalense gen. et sp. nov. and Paraendoceras depressum sp. nov. A rank abundance plot of 146 specimens from a locality in the Lake Champlain lowlands provides information on the community structure of a nautiloid fauna in which the longiconic cyrtoconic Bassleroceras is shown to dominate strongly. The nautiloid community structure of the Rochdale Formation is similar to that of the underlying Tribes Hill Formation (late early Tremadocian) with respect to the depositional setting, diversity and evenness but displays a remarkably increased taxonomic distinctness.

scholarly journals Bioecostratigraphy of the Shu’aiba Formation, Shaybah field, Saudi Arabia

GeoArabia ◽  
2000 ◽  
Vol 5 (4) ◽  
pp. 545-578 ◽  
Author(s):  
Geraint Wyn Hughes
Keyword(s):  
Saudi Arabia ◽  
Depositional Environment ◽  
Carbonate Platform ◽  
Depositional Environments ◽  
Carbonate Reservoir ◽  
Reservoir Rocks ◽  
Paleoenvironmental Interpretation ◽  
Sequence Boundaries ◽  
Shallow Carbonate Platform ◽  
Reservoir Facies

ABSTRACT The Aptian Shu’aiba Formation forms a major carbonate reservoir in the Shaybah field of eastern Saudi Arabia. Lack of exposures and poor seismic data have forced the cored intervals to be fully exploited to provide evidence of the depositional environment and layering of the reservoir rocks and associated lithofacies. Rudist, foraminiferal and coccolith evidence indicates an Aptian age for the entire Formation, most of it being early Aptian. A major unconformity at the top of the Shu’aiba separates it from the overlying Nahr Umr Formation. Rapid biofacies variations suggest possible sequence boundaries within the Shu’aiba Formation. Semi-quantitative macropaleontological and micropaleontological analyses indicate significant paleoenvironmentally influenced lateral and vertical bioassemblage variations. Lagoon, rudist-associated back-bank, bank-crest and fore-bank, and upper-ramp depositional environments have been interpreted, of which the bank represents the gradual amalgamation of earlier isolated rudist shoals. Integrating the micropaleontological analyses with rudist assemblages has facilitated the prediction of rudist-associated reservoir facies. Variations in the micro- and macrofacies permit the Formation to be divided into three layers. (1) The “lower Shu’aiba” (without rudists) is dominated by a regionally extensive, moderately deep marine planktonic foraminiferal/algal association of Palorbitolina lenticularis-Hedbergella delrioensis-Lithocodium aggregatum and the benthonic foraminifera Debarina hahounerensis, Praechrysalidina infracretacea, Vercorsella arenata and rotalids. (2) The “middle Shu’aiba” shows the significant lateral and vertical differentiation of a rudist-rimmed shallow carbonate platform typically associated with a marine highstand. A predominance of rudist species Glossomyophorus costatus and Offneria murgensis occurs together with Lithocodium aggregatum, Palorbitolina lenticularis, Trocholina spp. and miliolid foraminifera. (3) The “upper Shu’aiba” represents an expansion of the lagoon (associated with a marine transgression), and a predominance of Agriopleura cf. blumenbachi and A. cf. marticensis rudists, together with Debarina hahounerensis, Praechrysalidina infracretacea and Vercorsella arenata. The localized distribution of the rudist Horiopleura cf. distefanoi in association with corals, is a feature of the eastern flank of the field. A coarse assemblage-based biozonation for the Shu’aiba has been proposed, but a detailed scheme is precluded by rapid diachronous biofacies variations across the Shaybah field. In addition to the major biocomponent assemblages, minor variations reveal high-frequency depositional cycles that may assist in the interpretation of the distribution and correlation of reservoir facies. The identification of bioassemblages, and the paleoenvironmental interpretation of formation micro-imager logs from vertical cores in exploration wells, has assisted the calibration of images from uncored horizontal development wells.

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