Observations nouvelles sur le Tithonique terminal et le Berriasien de la region de Luc-en-Diois (Drome)

Abstract

The upper Tithonian-Berriasian (uppermost Jurassic-lowermost Cretaceous) section of the Luc-en-Diois region (Drome, French Prealps) includes two conglomeratic sequences separated by marly limestones. Similar sections are known from several surrounding localities. The lower conglomerate at Luc-en-Diois is correlated with the upper Tithonian main breccia of Chomerac in the Ardeche region. The marly limestone contains microfauna of lower Berriasian ostracods. The upper conglomerate, with its associated red detrital limestone, may similarly be equivalent to the upper conglomerate of the Ardeche section; it is probably uppermost Berriasian, marking the Berriasian-Valanginian boundary.

Coarse carbonate breccias as a result of water‐wave cyclic loading (uppermost Jurassic – South‐East Basin, France)

“…More precisely, the ‘staircase’ geometry of the breccia base was interpreted as an erosional channel structure providing evidence for transport and erosion. Donze & Le Hégarat (1966), Remane (1966, 1970) and Beaudoin (1977) developed their ‘transport and resedimentation’ hypothesis from overall facies studies. Donze & Le Hégarat (1966; p. 358), even if they did not exclude in situ reworking (they interpreted the breccias as seismites), intended to demonstrate transport and redeposition based on the presence of well‐rounded clasts.…”

“…Donze & Le Hégarat (1966), Remane (1966, 1970) and Beaudoin (1977) developed their ‘transport and resedimentation’ hypothesis from overall facies studies. Donze & Le Hégarat (1966; p. 358), even if they did not exclude in situ reworking (they interpreted the breccias as seismites), intended to demonstrate transport and redeposition based on the presence of well‐rounded clasts. However, such evidence cannot be considered to be definitive because: (a) the extensive study of breccia presented in this paper shows that there is no preferred shape of the clasts; and (b) clasts can be either angular or well rounded in very different contexts including tempestites (Bernoulli & Kälin, 1984; Sami & Desrochers, 1992; p. 361).…”

“…considered that the missing material at Chateauneuf d’Oze does not account for the volume of breccia deposits (e.g. Donze & Le Hégarat, 1966; p. 358). Such hypotheses were advocated because gravity flow was the only process envisaged in the 1960s and 70s for interpreting marine breccias.…”

“…Further evidence for displacement and resedimentation was palaeontological. Donze & Le Hégarat (1966), Remane (1970) and Beaudoin (1977; p. 185–189, appendix, p. 19–21) proposed that the breccia bodies of the ‘Barre Tithonique’ included clasts with calpionellids older than those of the stratigraphically underlying lime mudstone beds. However, according to Beaudoin (1977 appendix), only eight of the 58 sections studied contain reworked calpionellids in the breccia bodies.…”