Chronostratigraphy and Ecostratigraphy of Cretaceous Formations Recovered on DSDP Leg 47B, Site 398

Abstract

Some sedimentary units (I to V) or sub-units will be discussed in the ecostratigraphy section of this report. The designation of sedimentary units and sub-units described in this report are unique to this study and do not apply to the designations provided by the shipboard sedimentologists. These sedimentary units comprise lithologic entities (here called lithoterms) which were partially described onboard ship and upon which we further elaborated at Lamont-Doherty Geological Observatory. The different lithoterms in a given unit roughly correspond to the successive intervals, which are usually distinguished in a sedimentary graded sequence. They have been designated differently, depending on the different units (1, 2, 3 . . . , I, II, III . . . , A, B, C. . .). In the caption of Column G of Chart 1A (back pocket, this volume), these letters and Arabic or Roman numbers have been inserted from one unit to 287

The Cenomanian/Turonian Boundary Event (CTBE) at Hole 641A, ODP Leg 103 (Compared with the CTBE Interval at Site 398)

“…Although none of the fossil groups was found through out Units A-E, we were able to restrict the age of the black shale to the Cenomanian/Turonian boundary interval, thereby proving that it virtually represents the Cenomanian/Turonian OAE (Schlanger and Jenkyns, 1976) at this locality. This is also confirmed by the biostratigraphic results from the CTBE at nearby Hole 398D, where a much better resolution was obtained (Sigal, 1979;Taugourdeau-Lantz et al, 1982;Masure, 1984;Thurow, this volume), and the Cenomanian/Turo nian boundary was fixed by the stratigraphy of several fossil groups. The prominent positive 6 13 C excursion also supports this age assignment.…”

“…Sampling of Hole 398D, including the CTBE interval, was based on the compilation of Sigal (1979), which provides an overview of the abundance, preservation, and skeletal mineral ogy of Lower to middle Cretaceous faunas found at Site 398, and Schaaf s (1985) list of radiolarian-rich intervals. The Upper Cretaceous brownish claystones (cf.…”

“…The first//, lueckei was found in Sample 103-641A-6X-7, 24-26 cm, which assigns a Turonian age to the sample (Figs. 12 and 15) and also to Unit B, just above the black shale layer of Unit C. Site 398 Sigal (1979) compiled the results of foraminiferal studies from the Lower to middle Cretaceous sequence drilled at Hole 398D. For the interval considered comprising the CTBE, he reported only a few occurrences, which were unfortunately obscured by redeposition.…”

Berriasian to Aptian Dinoflagellate Cysts from the Galicia Margin, Offshore Spain, Sites 638 and 639, ODP Leg 103

“…In Holes 400A and 402A, the first appearance of this characteristic form is reported in a sample dated as late Aptian from foraminifers (Dupeuble, 1979). The first occurrence of O. verrucosum in DSDP Hole 398D is correlated with the Hedbergella trocoidea Zone (Sigal, 1979); the last occurrence is in the Aptian (Masure, 1984). In DSDP Hole 545, offshore north west Africa, Below (1984) observed the first occurrence of O. verrucosum in Sample 545-52-2, 123-126 cm, and the last oc currence in Sample 545-47-6, 72-75 cm.…”

Introduction, Objectives, and Principal Results: Ocean Drilling Program Leg 103, West Galicia Margin

“…On the basis of foraminiferal data, the oldest dateable strata directly overlying the post-rift unconformity are early Albian, whereas the youngest dateable strata immediately below are late Aptian (Sigal, 1979). This indicates a small hiatus of little more than a substage or perhaps only a somewhat condensed section.…”