Short Paper: A standardized model for Tethyan Tertiary carbonate ramps

Abstract

Low latitude carbonates in massive and clinoform bedded sheets, termed ramps, occur throughout the Tertiary Tethyan realm, and are characterized by recurring biofacies usually including large foraminifera, rhodolithic algae, coralgal patch-reef and gastropod dominated sequences. All can be interpreted broadly within a standardized Tertiary carbonate ramp model. Biota can be used to define precise palaeobathymetric zones which have a predictive utility in palaeoenvironmental modelling, especially where data are limited. The carbonate ramp model of earlier authors, has been elaborated by Read (1982) and ramp formation occurs mostly in passive margin and extensional tectonic settings. Ramps are characterized by slope gradients of less than 1 degree and, once established, are conservative to change. Much use has been made of the ramp model for Palaeozoic and Mesozoic lithofacies modelling. In contrast, published work on Cenozoic ramps is limited, however, Tethyan ramps are particularly widespread and extend tens to hundreds of kilometres along strike and occupy tens of kilometres of slope. Many studies have dealt with Cenozoic ramp associations and sequences (e.g. Pedley 1983 ; Reiss & Hottinger 1984; Purser 1973 ) and have demonstrated the diversity of biotal and sediment detail, but without ascribing them to a ramp model. Biota were quick to adapt to the Tertiary environments left vacant after the K–T boundary extinction events. New genera of Foraminifera, Mollusca, Bryozoa and Echinoder-mata rapidly replaced the extinct forms in bursts of innovative opportunism. Codiacean algae, Rhodophyta and marine angiosperms were equally adaptive colonizers of the carbonate platforms. Novel biofacies associations were derived from

Early Eocene orthophragminids (Foraminifera) from the type-locality ofDiscocyclina ranikotensisDavies, 1927, Thal, NW Himalayas, Pakistan: insights into the orthophragminid palaeobiogeography

“…suggest a shallow-marine depositional setting, most probably in inner-shelf setting for the Patala Formation. This interpretation follows the distribution model of larger foraminifera in fossil record from ancient ramps and shelves (Buxton & Pedley, 1989;Hottinger, 1997;Sinclair et al, 1998;Beavington-Penney & Racey, 2004). This is also supported by the common occurrence of discocyclinids and lack of orbitoclypeids and asterocyclinids in Patala Formation in Thal, which is in accordance with our previous observations on the distribution of orthophragminids from the western Tethyan platforms where discocyclinids chiefly occur in nummulitid-alveolinid facies and orbitoclypeids and asterocyclinids in comparatively deeper marine marls deposited in outer shelf Ben İsmail-Lattrache et al, 2013).…”

Circum-Tethyan carbonate platform evolution during the Palaeogene: the Prebetic platform as a test for climatically controlled facies shifts

“…A long-term sea level rise during the Early Palaeocene created new shelf areas and vacant biological niches (Buxton & Pedley 1989). The created vacant niches were occupied by larger benthic foraminifera and corals, which became a major part of shallow benthic assemblages (first phase of the global community maturation cycle; Hottinger 2001).…”

“…New larger benthic foraminifera emerged that were more tolerant to the cooler climate of the Late Palaeogene. This Oligocene-Miocene larger benthic foraminifera chronofauna is dominated by lepidocyclinids, smaller nummulitids, and miogypsinids (Buxton & Pedley 1989;McGowran & Li 2001). Increasing oligotrophic conditions during the Early Oligocene favoured the proliferation of larger coral communities throughout the Tethys.…”

Evolution and Geological Significance of Larger Benthic Foraminifera

“…They became the most common constituents of Late Paleocene-Early Eocene carbonate platforms, filling the empty niches left by the decline of the Cretaceous rudist-coral assemblages. They thrived on shallow, oligotrophic, circum-Tethyan carbonate platforms (Buxton and Pedley, 1989). By the Late Paleocene, nummulitids (Nummulites, Assilina and Operculina), orthophragminids (Discocyclina) and alveolinids (Alveolina) became important components of the carbonate Tethyan platforms.…”