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Ammonoid zonation in the Oxfordian of the Gondwanian Tethyan margin developed in Kachchh, India

Krishna J., Pandey B., Ojha J.

Volumina Jurassica

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2006

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Vol. 4, no. 1

181-181

EN

The Kachchh Basin in the extreme west of India has been considered the most prospective region of the Gondwanian Tethyan margin for the development of an independent Jurassic ammonoid zonal framework. In furtherance of our earlier realizations of independent ammonoid zonal schemes in the Kachchh of Callovian, Kimmeridgian and Tithonian stages, we here present the ammonoid zonal formulation in the Kachchh Oxfordian into a succession of 7 zones that is exclusively developed in Perisphinctidae. The older 3 zones (Bernensis Zone, Obliqueplicatum Zone, and Indogermanus Zone) are developed in the Lakhapur section in the distal exposed part of the basin with good density, diversity and frequency of ammonoids. The 4th zone – the Orientalis Zone which includes the 1st order MFS (maximum flooding surface) is the richest in ammonoids of the entire Kachchh Jurassic in the proximal most exposed part of the basin at Kantkote. The younger 3 zones (Subevolutum Zone, Kantkotensis Zone, and Wagurensis Zone) also developed in the Kantkote-Bharodia section in the proximal exposed part are ammonoid scarce in view of their location on the margin along with stratigraphic position above the 1st order MFS. All the Kachchh Oxfordian 7 zones are precisely correlated with the European Tethyan standard on the basis of common or similar Peltoceratinae (Peltoceratoides in Early and Gregoryceras in the Middle Oxfordian), Perisphinchinae (Properisphinctes and Alligaticeras in Early, Perisphinctes and Larcheria in Middle, Dichotomoceras in early Late, and Pseudorthosphinctes, Orthosphinctes and Idoceras in late Late Oxfordian). The geologically interesting and eventful Kachchh Oxfordian includes the 1st order MFS of the Toarcian-Albian sequence in the younger part of the late Middle Oxfordian Orientalis Zone (equivalent of the European Transversarium Zone, Schilli Subzone, Subschilli Horizon), which subdivides the Kachchh Oxfordian into two altogether contrasting sedimentation regimes with markedly revealing litho-biofacies and environmental frameworks. The Early and Middle Oxfordian until the close of Schilli Subzone time is in extremely slow sedimented, condensed to starved, fining, thinning and deepening upward in irregularly based, lensoidal, pebbly/nodular/conglomeratic, hard grounded, mixed carbonate-siliclastic ammonoid rich facies with increase in the share of carbonates and also in the reworking of pebbles/nodules. There is decrease in clastics, also in presence and size of physical structures and energy framework from margin to basin as also upward. Paleontologically, there is increase in the ammonoid density, diversity and frequency, share of European Tethyan elements, also of relatively deeper water sphaeroceratids, phylloceratids, lytoceratids upward and also from margin to the basin. In contrast, from the start of Rotoides Subzone time to near the close of Oxfordian, the ca 280 m thick sedimentary succession present only in the margin in relatively rapidly sedimented, coarsening, thickening and shallowing upward, is scarce to nearly devoid of ammonoids and other macro-invertebrates.

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Correlation of the zonal schemes at the Middle - Upper Oxfordian (Jurassic) boundary in the Submediterranean Province : Poland and Switzerland

Głowniak E.

Acta Geologica Polonica

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2006

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Vol. 56, no. 1

33-50

EN

Definition of the Oxfordian Elisabethae Subzone of the upper Transversarium Zone, and the Wartae Subzone, is provided. The Wartae Subzone has been absorbed into the overlying Bifurcatus Zone as a basal Subzone. The redefined base of the Bifurcatus Zone lies somewhat below the lower boundary of the Bifurcatus Zone of CARIOU and al. (1997). The boundary between the redefined Transversarium and Bifurcatus zones is now the boundary between the Submediterranean Middle and Upper Oxfordian. Correlation between the zonal schemes of Poland and Western Europe is established by means of the intermediate area of northern Switzerland, where the indexes of the zonal schemes co-occur. The lower boundary of the Wartae Subzone of the Bifurcatus Zone in Poland is approximately coeval with the lower boundary of the Schilli Subzone and Zone in Switzerland. The overlying Rotoides Subzone correlates with the upper part of the Wartae Subzone in Poland.Description of topotypes of Perisphinctes (Dichotomoceras) wartae from Czestochowa, and the accompanying macroconch species, is provided.

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The ammonites of the family Perisphinctidae from the Plicatilis Zone (lower Middle Oxfordian) of the Polish Jura Chain (Central Poland); their taxonomy,phylogeny and biostratigraphy

Głowniak E.

Acta Geologica Polonica

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2002

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Vol. 52, nr 3

307-364

EN

The Plicatilis Zone of the Submediterranean Middle Oxfordian is redefined and subdivided into three subzones; the Paturattensis Subzone, the Ouatius Subzone and the Arkelli Subzone. Their boundaries are defined by the appearance of the successive perisphinctid species referred to a Kranaosphinctes-Otosphinctes lineage. Correlation with other lower Middle Oxfordian zonations is provided. Classification of the studied ammonites is based on the morphological variability in the successive perisphinctid assemblages. The species are assigned to three genera: Perisphinctes, Liosphinctes and Neumannia gen. nov. Microconchs of Neumannia gen. nov. and of Perisphinctes trifidus (SOWERBY) are described for the first time. The type species of the subgenus Arisphinctes, P. ariprepes (BUCKMAN) is reassigned to the subgenus Kranaosphinctes BUCKMAN, and thus Arisphinctes is treated as a younger synonym of Kranaosphinctes; Perisphinctes plicatilis (SOWERBY) and Perisphinctes laevipickeringius ARKELL are reinterpreted and reassigned to the genus Liosphinctes BUCKMAN. Two new chronosubspecies, Perisphinctes ouatius ouatoides and Perisphinctes arkelli wysokae of the subgenus Otosphinctes, are described. The Kranaosphinctes-Otosphinctes lineage gives rise to the Perisphinctes-Dichotomosphinctes lineage at the boundary between the Plicatilis and Transversarium zones. The two other lineages, one of P. trifidus (a possible offshoot from the Kranaosphinctes-Otosphinctes lineage), and the other of the genus Liosphinctes, disappear in the upper Arkelli Subzone of the Plicatilis Zone. Mediterranean roots for all of the three lineages are suggested. The fourth lineage, of Neumannia gen. nov., appears in the upper Arkelli Subzone of the Plicatilis Zone as a consequence of an immigration event from the Mediterranean area.

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The Platysphinctes immigration event in the Middle Oxfordian of the Polish Jura Chain (Central Poland)

Głowniak E.

Acta Geologica Polonica

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2000

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Vol. 50, no. 1

143-160

EN

Ammonites of the subgenus Platysphinctes, represented by the species Perisphinctes (Platysphinctes) perplanatus (TINTANT, 1961), both microconchs, were recently found in the Middle Oxfordian of the Częstochowa Upland (Polish Jura Chain, Central Poland). Their appearance marks an invasion of ammonites of Mediterranean affinities into the Submediterranean Province. This episode is represented in the studied succession by a distinct horizon, named herein the Platysphinctes event - horizon, that is located in the upper part of the newly erected Arkelli Subzone of the Plicatilis Zone. An emended description of Perisphinctes (Platysphinctes) perplanatus and a description of a new species, Perisphinctes (Otosphinctes) arkelli sp. nov. are provided