ISSN 08695938, Stratigraphy and Geological Correlation, 2012, Vol. 20, No. 2, pp. 211–229. © Pleiades Publishing, Ltd., 2012. Original Russian Text © M.A. Rogov, D.B. Gulyaev, D.N. Kiselev, 2012, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2012, Vol. 20, No. 2, pp. 101–121. Biohorizons as Infrazonal Biostratigraphic Units: An Attempt to Refine the Jurassic Stratigraphy Based on Ammonites M. A. Rogova, D. B. Gulyaevb, and D. N. Kiselevc aGeological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017 Russia email: [email protected] bScientific–Industrial Center “Nedra”, ul. Svobody 8/38, Yaroslavl, 150000 Russia email: [email protected] cYaroslavl Ushinskii State Pedagogical University, ul. Respublikanskaya 108, Yaroslavl, 150000 Russia email: [email protected] Received February 8, 2011; in final form, June 7, 2011 Abstract—The biohorizons (faunal horizons) as infrazonal units are the smallest correlatable biostratigraphic units. Their main features are: (1) potential indivisibility based on taxonomic differentiation of guide fossils; (2) determinancy of both lower and upper boundaries in the geological section; (3) identification by a single index species/subspecies. First such units were defined at the end of the 19th century and since the 1980s have been widely used in biostratigraphic investigations of Jurassic and, later, Cretaceous systems. The biohorizons are characterized by phylogenetic or immigrational paleobiological nature and geologically they are con nected with depositional and postdepositional transformation (and, consequently, structure) of the sedimen tary succession. Based on parallel sequences of phylogenetic and separate immigrational biohorizons, they are integrated into different zonal scales and an integrated regional scale. The problems related to the lack of universal criteria for defining and using biohorizons are discussed. The basic nomenclature rules, which are aimed at regulation of the use of these units in practical stratigraphic investigations, are suggested for their recognition and description. Keywords: infrazonal biostratigraphy, biohorizons, faunal horizons, ammonites. As the middle system of the middle (Mesozoic) group of fossiliferous rocks, the Jurassic is as good a sample as any that could be chosen to find out what light can be thrown on geological prob lems by the study of a single system all over the world (Arkell, 1956, p. 3). DOI: 10.1134/S0869593812010066 INTRODUCTION 1 taceous systems. Similar to many other innovations Despite the 150yearlong development history of in stratigraphy, paleobiology, and paleogeography, the the zonal method in stratigraphy, its basic theoretical infrazonal biostratigraphic units were first proposed by principles concerning biostratigraphic zones were for the experts engaged in study of the Jurassic System and mulated only in the second half of the 20th century. At are now most widely used in the Jurassic stratigraphy. the end of the 19th century, it became clear that Until recently, the biohorizons (in the sense consid smaller (infrazonal) biostratigraphic units may also be ered in this work) are defined by stratigraphers only for useful for subdivision and correlation of sedimentary 1 sections. Some researchers (Page, 1995; and others) use in this sense the term “intrasubzonal” units. Nevertheless, inasmuch as the sub zones represent stratigraphic units of the zonal rank (similar to Now, these smallest infrazonal biostratigraphic subgenera, which are taxa of the generic rank), the use of the less units (biohorizons, faunal horizons) are widely used in cumbersome adjective “infrazonal” seems a better choice for biostratigraphic investigations of the Jurassic and Cre biohorizons. 211 ing. Theapplicationofthe infrazonalapproachmade graphic rangeoftheirapplication isgraduallyincreas asforwidening thestrati stratigraphic unitsaswell the numberoffossilgroups usedfordefiningsuch the Mesozoicbasedmainly onammonites,although 212 Fig. 1. Thegrowthofresolutionstra Erathems and systems Series and stages Substages, zone, and subzones Biohorizons (after Kiselev, 2001; Lamberti Gulyaev et al.2002) Tithonian Lamberti Cenozoic Henrici Kosmoceras “Spinosum” medea medea Kimmeridgian Athleta Proniae STRATIGRAPHY AND GEOLOGICAL CORRELATION ANDGEOLOGICAL STRATIGRAPHY 20 Vol. No.2 2012 Catasigaloceras Cretaceous Phaeinum enodatum aeeta Upper Grossouvrei Oxfordian Coronatum Obductum Catasigaloceras enodatum enodatum tigraphic scalesdependingonthe Jurassic Jason Mesozoic Jason Callovian Medea Catasigaloceras enodatum planicerclus etal. ROGOV Triassic Enodatum Calloviense Bathonian Calloviense Catasigaloceras pagei graphic units is frequently ambiguous and even slightly graphic unitsisfrequently ambiguous andeven between biostratigraphicscales(Fig. 2). between times(Fig.1)andtheaccuracyof correlation several it possibletoincreasethe biostratigraphicresolution Galilaeii At thesametime,use Koenigi Curtilobus Middle Bajocian Sigaloceras micans Gowerianus Lower Middle Upper Kamptus Aalenian Herveyi Terebratus Sigaloceras calloiense lower rankofstratigraphic units. lower Paleozoic Keppleri Toarcian Kepplerites galilaeii Pliensbachian of infrazonalbiostrati Lower Sinemurian Hettangian BIOHORIZONS AS INFRAZONAL BIOSTRATIGRAPHIC UNITS 213 Boreal Atlantic realm East Mediterranean–Caucasian Realm European province Submediterranean province (European Russia) (mainly central and southern France, Portugal) (Fig. 7) (after Biostratigraphie …, 1997) Biochoremas Biohorizons Subzone (tints show biohorizons of Biohorizons Subzone Zone Zone different subprovinces) Substage Substage Collotia collotiformis “Spinosum” K. kuklikum Collotiformis Orionoides piveteaui F. funiferus K. rowlstonense Sublunuloceras trezeense Proniae F. patruus Trezeense K. proniae Pseudopeltoceras leckenbyi “F. sp. nov.” Upper (pars) “Pseudopeltoceras” Upper (pars) Phaeinum K. phaeinum Rota F. allae Rehmannia rota K. grossouvrei Choffatia waageni Grossouvrei Leuthardti K. posterior Erymnoceras leuthardti K. crassum Erymnoceras baylei Coronatum Athleta Obductum L. stenolobum Baylei K. obductum Flabellisphinctes villanyensis CallovianL. praestenolobum Stage K. jason jason Rehmannia richei Middle Middle Jason Tyranniformis K. jason sedgwickii Rehmannia blyensis Chanasia turgida Jason Coronatum Athleta K. medea magnum R. milaschevici Stuebeli Medea milaschevici K. medea medea Chanasia bannensis C. enodatum aeeta ? R. milaschevici C. enodatum Hecticoceras posterius Enodatum khudyaevi enodatum Patina C. enodatum (pars) . i A. difficilis Collotia pamprouxensis R in planicerclus fk ef Lower (pars) Gracilis (pars) Anceps Lower (pars) Calloviense h tc P. cracoviensis C. pagei Hecticoceras boginense Fig. 2. Correlation of biohorizons in regional (provincial) stratigraphic scales for the Middle Callovian in different paleobiogeo graphic realms. Here and in Figs. 3–7, names of conditional (preliminary) biohorizons are given in quotes. The dark and light gray colors indicate sequences of biohorizons based on cardioceratids and perisphinctids, respectively. chaotic. In this work, we consider critically the devel zonal units, for example, the Ammonites calloviensis opment history of the infrazonal biostratigraphy, ana and A. bullatus horizons in the A. macrocephalus Zone lyze the main features and nature of biohorizons, (Oppel, 1856–1858, p. 2009). Slightly later, Waagen assess their correlation potential, and formulate prin (1869), who established the first phylogenetic lineage ciples of their recognition and application. In addi of Bathonian and Callovian ammonites, formulated a tion, we propose a code of rules, which should concept of evolutionary mutations (quantitative mor decrease, if not eliminate, ambiguity inherent now in phological transformations) through time and the infrazonal biostratigraphy. described the zone as an interval corresponding to the existence period of a single mutation. This concept was further developed by Neumayr (1878, p. 40), who A DEVELOPMENT HISTORY OF INFRAZONAL noted that the Oppel’s zones of the Jurassic System BIOSTRATIGRAPHY chronologically correspond to the average existence In his famous work dedicated to the Jurassic Sys period of a single mutation among most widespread tem of England, France, and southwestern Germany, marine animals primarily such as cephalopods. Oppel (1856–1858), who formulated the basics of the Already at that time, the inconsistency between the zonal stratigraphy, described the zone as a horizon, historical continuity of zonal scales and their resolu which is characterized by the same fossil assemblage tion became clear for many researchers of the Jurassic even in remote areas of its development. He empha System. The zones that became generally accepted at sized that the accuracy in defining zones depends on that time could be divided into smaller units. Thus, the number of well described species (especially guide two different approaches to the zonal stratigraphy taxa), in addition to other factors. In the same work, existed at the end of the 19th century. The zones were this author defined the socalled horizons as intra accepted either as smallest biostratigraphic units or as STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 20 No. 2 2012 214 ROGOV et al. some stable stratigraphic “framework,” which implied the Bathonian–Callovian boundary interval of Scot the possibility of defining smaller stratigraphic units. land (Buckman, 1920), he subsequently increased The further development of views on detailed their number to eleven