Luiz Carlos Veiga de Oliveira

Organic-Rich facies in the Sinemurian and Pliensbachian of the Lusitanian Basin, Portugal: Total organic carbon distribution and relation to transgressive-regressive facies cycles

The upper Sinemurian to Pliensbachian series of the Lusitanian Basin (Portugal) correspond to marly limestone sediments rich in benthic and nektonic macrofauna. This sedimentary record includes several intervals of organicrich facies, which are particularly well developed in the western sectors of the basin. They correspond to grey and dark marls locally showing strong lamination (black shale type) and are recognized as one of the most important potential oil source rocks. This study shows the vertical and lateral distribution of these organic-rich intervals, supported by over 550 total organic carbon (TOC) determinations. The results presented reveal two important intervals, with several black shale occurrences, in the Oxynotum(?)–Raricostatum (Polvoeira Member of Agua de Madeiros Formation) and at the top of the Ibex-upper part of Margaritatus zones (top of the Vale das Fontes Formation), showing in the distal (western) sectors up to 22% and 15% TOC, respectively. TOC values decrease progressively towards the proximal sectors, the youngest organic-rich interval being the most expressive at the basin scale. This lateral TOC distribution, the facies stacking patterns and the decrease observed in benthic macrofauna confirm that these intervals are related to 2nd-order transgressive phases. 2nd-order regressive phases, developed during the uppermost Raricostatum and Spinatum zones respectively, show lower TOC values. TOC distribution combined with other stratigraphic and sedimentological parameters enabled seven facies maps to be created for the time interval studied. At the regional scale, this study shows for the first time the good similarity between the upper Sinemurian-Pliensbachian sedimentary successions of the Lusitanian and Basque- Cantabrian basins.

AGES OF THE ONSET OF MARLY SEDIMENTATION AND OF THE BLACK SHALES IN THE TUSCAN BASIN (NORTHERN APENNINES, ITALY)

In this paper is for the first time dated the inception of the Lower Jurassic marly sedimentation and the lower Toarcian black shales in the Tuscan Nappe, based on semiquantitative analysis of the calcareous nannofossils recovered from the Calcare selcifero di Limano/Calcari e marne a Posidonia transition and the lower part of this latter unit. The boundary between these formations lies within the nannofossil NJT5 Lotharingius hauffii Zone (uppermost Pliensbachian to lower Toarcian), the lower portion of the Calcari e marne a Posidonia ranges from the nannofossil NJT5 Lotharingius hauffii Zone to the NJT7 Discorhabus striatus Zone (middle Toarcian) and the organic-rich interval lies in the nannofossil NJT6 Carinolithus superbus Zone (lower Toarcian). Consequently, the changes from carbonate-dominated to marly-dominated sedimentation (NJT5 Zone) and the black shales accumulation (NJT6 Zone) in the Tuscan and Umbria-Marche basins are two coeval sedimentary events.