The 'Infracambrian System' in the southwestern margin of Gondwana, southern South America

Abstract

The classical definition of 'Infracambrian' that refers strictly to sequences of Proterozoic age is not applicable in southwestern Gondwana. In this paper the term 'Infracambrian' is used to define the sequences deposited during the Pampean orogenic cycle, which extends until the Cambrian period.A classification of Infracambrian basins is proposed based on location, level of preservation and perceived petroleum potential. Only the eastern basins of the South American plate have potentially significant exploration potential.Two Neoproterozoic petroleum systems have been identified in the eastern basins: a Riphean system, developed on the western margin of the San Francisco Craton, in the San Francisco Basin of Brazil; and a Vendian system, developed on the eastern margin of the Amazonia -Río de la Plata cratons, in the Corumbá Basin of Brazil and Paraguay. The Riphean system is reportedly proven by a well test drilled by Petrobras. An active Vendian petroleum system is proven by the presence of oil seeps within fractured limestones. A Vendian petroleum system is proposed for the Claromecó Basin of Argentina based on the correlation of the Vendian and Riphean sequences.

Glaciogenic reservoirs and hydrocarbon systems: an introduction

“…Indeed, there are several areas of the world where organic-rich, Neoproterozoic black shales with good hydrocarbon source rock characteristics are either interbedded with, and/or directly overlie, Neoproterozoic glacial diamictites. For example, in the Neoproterozoic 'Sturtian' glacial sequence in the Saõ Francisco Basin in SE Brazil, black shales interbedded with glacial diamictites within the Vazante Group have a total organic carbon (TOC) content that is, locally, in excess of 3% (Olcott et al 2005(Olcott et al , 2006Hlebszevitsch et al 2009). Similarly, the melting of the Sturtian ice sheets in South Australia resulted in deposition of an extensive blanket of shale (the Tindelipina Shale Member) which is enriched in organic material and could form a potential source of hydrocarbons .…”

Global Neoproterozoic petroleum systems: the emerging potential in North Africa

“…Benshati et al 2009;Hlebszevitsch et al 2009;Le Heron et al 2009;Lü ning et al 2009), to represent sequences of undefined, but most probably Late Precambrian -earliest Cambrian age, which occur below the lowest definitively dated Cambrian successions and above igneous or metamorphic basement. The terms Tonian, Cryogenian and Ediacaran are preferred, but are only applied where dating is sufficiently robust to allow them to be used with some confidence (e.g.…”

“…The Gondwana supercontinent formed through the collisional amalgamation of the African, South American, Indian, Australian and Antarctic terranes during the late Precambrian (see, e.g. Hlebszevitsch et al 2009;Scotese 2009;Smith 2009) and consisted of the old stable cratonic blocks (including the West African and Chad cratons) separated by Pan-African mobile belts, which in North Africa have a dominant north -south structural grain (Fig. 7).…”

“…Elsewhere, the cap carbonates themselves pass either upwards and/or laterally into black shales. In one example, from the older Neoproterozoic glacial sequence in the Saõ Francisco Basin in SE Brazil, post-glacial black shales within the Vazante Group have a TOC content that is, locally, in excess of 3% (Olcott et al 2005(Olcott et al , 2006Hlebszevitsch et al 2009). In addition to their hydrocarbon potential, these organic-rich post-glacial shales represent attractive targets for Re -Os geochronology because they provide a minimum age constraint for the end of the associated glaciation (see Kendall et al 2009).…”