Conodont chronostratigraphical resolution and
Declinognathodus
evolution close to the Mid-Carboniferous Boundary in the Barcaliente Formation type section, NW Spain
Abstract:The Barcaliente Formation in its type section provides significant conodont occurrences in the Mid‐Carboniferous Boundary interval (between the Mississippian and Pennsylvanian sub‐periods). A sequence of Declinognathodus morphotype appearances (considered here as species) is recognized from the uppermost Serpukhovian to the lower Bashkirian. These morphotypes belong to Declinognathodus noduliferus (Ellison & Graves) sensu lato, the primary marker for the worldwide correlation of the Mid‐Carboniferous Boundary.… Show more
“…The predominantly shallow‐water facies of theValdediezma Limestone are not the best facies for the record of conodonts, and thus, many samples are barren or show a low diversity compared to those of the ammonoid‐bearing nodular limestones (Sanz‐López & Blanco‐Ferrera, ). Continuous records and complete phylogenic lines are not recognized yet in this shallow‐water platform to be compared with those recorded in deep‐water facies of the region, such as those in Sanz‐López, Blanco‐Ferrera, and García‐López (), Sanz‐López et al (), and Sanz‐López, Blanco‐Ferrera, Sánchez de Posada, and García‐López ().…”
Section: Resultsmentioning
confidence: 99%
“…Upper Serpukhovian siliciclastic deep sea fan deposits above the Alba Formation are considered the first Variscan synorogenic deposit at the inner margin of the Cantabrian Zone (Julivert, ; Reuther, ). Dark limestones enriched in organic matter were deposited in most parts of the foreland basin in the late Serpukhovian and early Bashkirian times (Barcaliente Formation after Wagner, Winkler Prins, & Riding, ; see also Sanz‐López, Blanco‐Ferrera, & Sánchez de Posada, ). Progradation of the Variscan deformation associated with the emplacement of nappes caused high sedimentation rate and migration of the subsidence depocentre along the Cantabrian Zone (Marcos & Pulgar, ).…”
A new Mississippian to early Bashkirian shallow‐water carbonate platform, the Valdediezma Limestone, is identified in the central–eastern part of the Picos de Europa tectonic unit of the Cantabrian Mountains. The oldest beds (probably late Tournaisian or early Viséan) are faulted above middle Cambrian rocks. Biostratigraphy based on conodont and foraminiferal faunas allows to differentiate the Viséan–early Bashkirian Valdediezma Limestone from younger Bashkirian and Moscovian shallow‐water platforms previously described in the same area (Valdeteja and Picos de Europa formations). The Valdediezma Limestone recorded the rapid growth of a carbonate platform contemporaneous to the extended sedimentation of the Mississippian condensed, cephalopod‐bearing, nodular carbonates of the Alba Formation in the adjacent deep‐water basin. The growth of the platform continued during the late Serpukhovian and early Bashkirian, when deep‐water carbonates of the Barcaliente Formation were deposited in a geographically restricted foreland basin, and siliciclastic deposits filled the foredeep in the south‐western margin of the Cantabrian Mountains. A sedimentary hiatus from the early Bashkirian to the late Moscovian occurs above the Valdediezma Limestone. The exhumed and eroded platform was buried by late Moscovian to Kasimovian strata when the Variscan deformation affected the Picos de Europa unit. The Valdediezma Limestone was deposited on an isolated platform that rarely is preserved in South Europe, where contemporary shallow‐water carbonates were eroded and reworked into the synorogenic siliciclastic deposits of flysch‐type facies.
“…The predominantly shallow‐water facies of theValdediezma Limestone are not the best facies for the record of conodonts, and thus, many samples are barren or show a low diversity compared to those of the ammonoid‐bearing nodular limestones (Sanz‐López & Blanco‐Ferrera, ). Continuous records and complete phylogenic lines are not recognized yet in this shallow‐water platform to be compared with those recorded in deep‐water facies of the region, such as those in Sanz‐López, Blanco‐Ferrera, and García‐López (), Sanz‐López et al (), and Sanz‐López, Blanco‐Ferrera, Sánchez de Posada, and García‐López ().…”
Section: Resultsmentioning
confidence: 99%
“…Upper Serpukhovian siliciclastic deep sea fan deposits above the Alba Formation are considered the first Variscan synorogenic deposit at the inner margin of the Cantabrian Zone (Julivert, ; Reuther, ). Dark limestones enriched in organic matter were deposited in most parts of the foreland basin in the late Serpukhovian and early Bashkirian times (Barcaliente Formation after Wagner, Winkler Prins, & Riding, ; see also Sanz‐López, Blanco‐Ferrera, & Sánchez de Posada, ). Progradation of the Variscan deformation associated with the emplacement of nappes caused high sedimentation rate and migration of the subsidence depocentre along the Cantabrian Zone (Marcos & Pulgar, ).…”
A new Mississippian to early Bashkirian shallow‐water carbonate platform, the Valdediezma Limestone, is identified in the central–eastern part of the Picos de Europa tectonic unit of the Cantabrian Mountains. The oldest beds (probably late Tournaisian or early Viséan) are faulted above middle Cambrian rocks. Biostratigraphy based on conodont and foraminiferal faunas allows to differentiate the Viséan–early Bashkirian Valdediezma Limestone from younger Bashkirian and Moscovian shallow‐water platforms previously described in the same area (Valdeteja and Picos de Europa formations). The Valdediezma Limestone recorded the rapid growth of a carbonate platform contemporaneous to the extended sedimentation of the Mississippian condensed, cephalopod‐bearing, nodular carbonates of the Alba Formation in the adjacent deep‐water basin. The growth of the platform continued during the late Serpukhovian and early Bashkirian, when deep‐water carbonates of the Barcaliente Formation were deposited in a geographically restricted foreland basin, and siliciclastic deposits filled the foredeep in the south‐western margin of the Cantabrian Mountains. A sedimentary hiatus from the early Bashkirian to the late Moscovian occurs above the Valdediezma Limestone. The exhumed and eroded platform was buried by late Moscovian to Kasimovian strata when the Variscan deformation affected the Picos de Europa unit. The Valdediezma Limestone was deposited on an isolated platform that rarely is preserved in South Europe, where contemporary shallow‐water carbonates were eroded and reworked into the synorogenic siliciclastic deposits of flysch‐type facies.
“…Similar problems with multiple morphotypes and subspecies are also observed in the marker for the Mid‐Carboniferous boundary, the conodont Declinognathodus noduliferus , which led to a revision of all those forms (Sanz‐López et al . ). Despite these inconsistencies in L. ziegleri that have been criticized by some authors (Herbig ), others have suggested to vote for an official boundary marker of the base of the Serpukhovian (Wang et al .…”
Section: Progress In Establishing the Viséan–serpukhovian Boundary Anmentioning
A detailed revision of foraminiferal zonal schemes in sections throughout Europe and North Africa for the Viséan–Serpukhovian boundary interval suggests that several foraminiferal taxa might have the potential to form reliable markers throughout the Palaeotethys. This would support the currently investigated boundary definition based on the First Appearance Datum of the conodont Lochriea ziegleri. However, correlation of these foraminiferal markers in the Western Palaeotethys region has encountered several problems, partly arising from taxonomic issues, but mainly because of apparent discrepancies between the First Occurrence Data (FOD). Analysis of the available foraminiferal data has revealed that some taxa show marked delays in their FODs, due to the timing of westward dispersal within the Palaeotethys, emanating from a probable source in eastern Russia. As a result of this investigation, two dispersal routes have been identified, a northern branch and a southern branch. In general, the displacements within the southern branch occurred more rapidly than in the northern branch. In addition to different dispersal routes, separation of the main foraminiferal markers in stratigraphical sections from different regions can result from isolation of shallow‐water facies of the inner platform from those of relatively deeper‐water settings in the outer platform, the latter showing more consistent foraminiferal FODs. The differences in palaeobathymetry and associated energy levels have enabled two foraminiferal zonal schemes to be distinguished for the Viséan–Serpukhovian boundary interval in the Western Palaeotethys, one for the inner platform and a second one for the outer platform.
“…1). For example, conodonts were a widely distributed group which suffered a marked reduction in diversity during this interval, followed by a renewed phase of evolution during Pennsylvanian time (Grayson et al 1990; Sanz-López et al 2006, 2013). The FAD of the conodont Declinognathodus noduliferus (Ellison & Graves, 1941) sensu lato , in its presumed evolutionary transition from Gnathodus girtyi simplex Dunn, 1966, was chosen to identify this important boundary (Fig.…”
Section: Introductionmentioning
confidence: 99%
“…D. praenoduliferus Nigmadganov & Nemirovskaya, 1992 and D. bernesgae Sanz-López et al 2006 were later described as early members of the D. noduliferus group (Sanz-López & Blanco-Ferrera, 2013). As a consequence of selecting the first occurrence datum (FOD) of a very broad species grouping as the biostratigraphic tool with which the GSSP of the mid-Carboniferous boundary was picked, the boundary elsewhere has been identified using the first occurrence of any member of the D. noduliferus plexus, regardless of whether it is now considered a species or subspecies (Sanz-López et al 2013). Figure 2. P 1 conodont element descriptive terminology.…”
Two stratigraphic sections spanning the mid-Carboniferous boundary were examined in the Clare Shale Formation of the Shannon Basin in Western Ireland. Calcareous nodules intermittently occur within these generally non-calcareous organic-rich shales, and these have yielded Serpukhovian and Bashkirian conodont elements. The biostratigraphic range of the Irish material is illustrated here for the first time. Results show that the mid-Carboniferous and Arnsbergian-Chokierian boundaries are coincident at Ballybunion. Gnathodus girtyi is restricted to the lower part of the Serpukhovian Stage (Late Mississippian), while G. bilineatus bollandensis persists into much younger strata, close to the first occurrence of Declinognathodus noduliferus s.l. One element belonging to G. postbilineatus is also present. These findings support the argument that D. noduliferus s.l. developed from G. b. bollandensis, rather than from G. girtyi. The biostratigraphical tool for the identification of the midCarboniferous boundary globally, and the suitability of the section at Arrow Canyon, USA as a GSSP, may therefore need to be reassessed.
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