At Site 897 Early Cretaceous sediments (Fig. 2) were first sampled at the base of the designated Subunit IIIB (Shipboard Scientific Party, 1994a). In both Holes 897C and 897D, Subunit IIIB consists of gravity-flow deposits of poorly sorted, poorly cemented granule-to-pebble clayey conglomerate that grades upsection to granule conglomerate and very coarse-grained, lithic, ferruginous clayey sandstone, to sandy claystone. This fining-upward sequence occurred over an interval of about 20 m in Hole 897C and over 10 m in Hole 897D, and in both holes the sequence was dark reddish and variegated. Resedimented clasts included in the conglomerate have diverse lithology and facies: white limestone, micritic limestone, marlstones, dolomite, and varied turbiditic arkosic-to-lithic sandstones. Minor clasts of shallow carbonates included in conglomerates of Subunit IIIB are interpreted as reworked from a previous debris-flow deposit at the source area. Clasts and granules of basalt and serpentinized peridotites are present as minor components in the conglomerate and coarse sandstone. Because samples at the base of this conglomerate yield an early late Aptian age (see nannofossil assemblages below), and gravity flows accumulate over a very short time span, we consider the entire Subunit IIIB to be of early late Aptian age.
At Site 899, analogous reddish-variegated ferruginous conglomerate and coarse sandstone, including basalt pebbles, were sampled in one interval of about 1 m (Shipboard Scientific Party, 1994b). Although at Site 899 these lithologies are barren of nannofossils, the close correspondence between these facies and their counterpart sampled at Site 897, together with their similar position within the drilled sedimentary sequence, strongly suggests that they pertain to the same early late Aptian debris-flow event (Fig. 2).
Older Cretaceous sediments (Unit IV, Fig. 2), sampled down-section at Sites 897 and 899, consist of heterogeneous discrete sediment bodies mixed or intercalated with mafic and ultramafic rocks. Sediments in Unit IV yield an early Aptian age (see below). Unit IV was recovered in an interval of 28.6 m in Hole 897C, 38.6 m in Hole 897D and 188 m in Hole 899B (Sawyer, Whitmarsh, Klaus, et al., 1994). Our post-cruise biostratigraphy indicates the same age—early Aptian—for the complete sequence at both sites, which differs from those considered by the Shipboard Scientific Party (1994a, 1994b).
Major lithofacies present at both sites correspond to pelagic/hemipelagic marlstones; clayey limestone and claystones, dark gray/green in color; and distal-bathyal calcareous and siliciclastic thin-bedded microturbidites (Pl. 1). Minor isolated elements with more exotic lithologies, black chert or brecciated marly limestones, also occur. Some thicker and continuous, homogeneous sediment intervals were recovered from Unit IV: 80 cm in Hole 897C (Core 149-897C-64R), 3 m in Hole 897D (Core 149-897D-8R) and less than 25 cm in Hole 899B.
Although the lithotypes are not particularly illustrative, some features of these rocks, such as degree of consolidation, synsedimentary deformation, resedimentation and reworking, provide insights into the behavior of the source area and coeval sedimentary processes. Most of the sediments of Unit IV were already structured, cemented, or consolidated before accumulation, and preexisting pervasive microfaulting is evident in cemented or semiconsolidated microturbidites. Signs of reworking also exist (e.g., the reversed microturbidite shown in Fig. 26 of the "Site 899" chapter, Shipboard Scientific Party, 1994b). Sediments and serpentinite gouges (referred to as serpentinite "sand" by the Scientific Shipboard Party, 1994b) are intimately mixed, stretched, and sheared together (Pl. 1, Figs. 1, 4). Slump and contorted structures are common in softer lithologies. These characteristics, together with the joining of facies from different sedimentary environments, confirm the allochthonous origin of the sedimentary rock assemblage, and, in turn, of the elements of igneous rock that it includes.
Our most noteworthy conclusion from these data is that during the Aptian, coeval or nearly coeval gravity-flow and gravity-sliding deposits reached Sites 897 and 899, located about 20 km apart. This probably implies a near-flat Aptian paleotopography—basin plain setting—between these sites, and that, at this time, the "Iberia Abyssal Plain" (Fig. 3) was a slope-controlled sedimentary environment in which broad areas were covered by deposits derived from adjacent slopes. The absence of these deposits (Subunit IIIB and Unit IV) on the basement at Site 900 (Sawyer, Whitmarsh, Klaus, et al., 1994) indicates that in the Aptian paleogeography, the seafloor at Site 900 was higher than at Sites 897 and 899.
Because the sediments involved in the gravity-deposits are mainly of pelagic or bathyal facies, the source area for the Aptian deposits (Subunit IIIB and Unit IV) is thought to be a broad pelagic high or Seamount adjacent to the basin plain that exposed, among other rocks, older basinal sediments (Fig. 3).
From post-cruise studies we confirmed the presence of sediments in Sample 149-897C-70R-3, 26 cm. It is very important to verify the position of this sample. If correct, Unit IV would include an additional 31.5 m of peridotite breccia down to 713.4 mbsf, and the basement recovered at Hole 897C would be restricted to an interval of 31.8 m (Fig. 2).
Specific data on the abundance, preservation, and detailed range charts for the biostratigraphic distribution of Lower Cretaceous calcareous nannofossils are given in de Kaenel and Bergen (this volume).
In Hole 897C, the sequence below Core 149-897C-61R (Fig. 2) contains intervals barren of nannofossils; however, some other samples include many mixed nannofossil assemblages. At the base of Subunit IIIB, Samples 149-897C-62R-4, 38 cm, 62R-4, 50 cm, and 62R-4, 60 cm, lack the Aptian markers and contain a high percentage of reworked Hauterivian to lower Barremian species. The dominance of Nannoconus spp. and Micrantholithus spp. and the absence of upper Aptian species in Section 149-897C-62R-4 indicate that the entire assemblage was reworked from older sediments.
Sample 149-897C-62R-CC, 16 cm, is assigned to the upper Aptian R. angustus Subzone (CC7b). An early late Aptian age for this sample is indicated by the presence of Rhagodiscus pseudoangustus and Calcicalathina sp.
The interval from Samples 149-897C-63R-1, 1 cm, to 66R-1, 10 cm is placed in the Hayesites irregularis Subzone (CC7a). Assemblages of this Subzone indicate an early Aptian age for this interval.
Sample 149-897C-70R-3, 26 cm, contains Rhagodiscus achlyos-taurion, Zygodiscus elegans, Flabellites oblongus (early morphotype), and lacks Hayesites irregularis. This assemblage indicates the upper Barremian R. achlyostaurion Subzone (CC6b). This sample collected from the JOIDES Resolution, was from a dark, thin claystone interval mixed with serpentinite gouge, between massive serpentinite breccias. It is the only Leg 149 sample that yielded a late Barremian nannofossil assemblage. However, it is not clear from our data if these sediments are reworked.
Middle Aptian sediments were not present in Hole 897C.
In Hole 897D (Fig. 2) samples are barren or contain highly diverse, poorly to moderately well-preserved nannofossil assemblages.
Sample 149-897D-6R-3, 28 cm, at the base of Subunit IIIB, is assigned to Subzone R. angustus (CC7b). Nannofossil assemblages in this sample indicate an early late Aptian age. In Hole 897D, the base of the upper Aptian is placed in Sample 149-897D-6R-CC, 3 cm.
The underlying interval, down to Sample 149-897D-10R-4, 139 cm, is assigned to the lower Aptian H. irregularis Subzone (CC7a). The bottom of this interval (Sample 149-897D-10R-4, 139 cm) contains Rhagodiscus achlyostaurion and Flabellites oblongus (early morphotype) but lacks Rhagodiscus angustus. The latter species is observed 48 cm above this sample. Hayesites irregularis has an inconsistent occurrence in Hole 897D, since its first occurrence (FO) is recorded 170 cm above the FO of Rhagodiscus angustus. All these events are recorded in two cores and represent a very short period of time. Consequently, the base of this interval is placed in the same CC7a Subzone (lower Aptian), even though the zone marker (FO of H. irregularis) is not recorded at the same level.
As in Hole 897C, nannofossil assemblages of middle Aptian age are not present.
In Hole 899B (Fig. 2), the uppermost sedimentary sample from Subunit IIIB (Sample 149-899B-26R-1, 85 cm) has a nannofossil assemblage that includes the FO of Braarudosphaera bigelowii and Vagalapilla sp. This nannofossil assemblage lacks Eprolithus floralis and Palaeopontosphaera sp. and the markers of the upper Aptian. The FO of Rhagodiscus angustus is in Sample 149-899B-33R-1, 12 cm. Nannofossil assemblages from the base of this sedimentary interval, Sample 149-899B-35R-1, 99 cm, contain Hayesites irregularis, Flabellites oblongus, Rhagodiscus achyostaurion, and Zygodiscus elegans.
Below the 90 m thick main interval of serpentinized peridotite breccia (termed "Upper Breccia" by Shipboard Scientific Party, 1994b) sedimentary intervals are barren of nannofossils, or contain poorly to moderately well-preserved assemblages that allow us to assign these deposits to the lower Aptian H. irregularis Subzone (CC7a).
The succession of nannofossil events found at Site 899 correlates and confirms those determined at Site 897. The presence of Hayesites irregularis below the FO of R. angustus found at Hole 899B confirms the placement of the lowermost samples of Hole 897D in the lower Aptian.