At Site 1216, we sampled a 62-m section composed of pelagic clay and chert (Fig. F3). Fifty meters of pelagic clay of Eocene and younger age overlies 12 m of interbedded pelagic clay and chert. The sedimentary section is divided into two lithologic subunits differentiated by the ratio of clay concentration vs. chert. The basal section is intensely affected by drilling disturbance with recovery largely limited to chert fragments. Only one core was recovered at Hole 1216B; therefore, the following lithologic description refers to the more complete sequence from Hole 1216A.
Unit I was divided into two subunits based upon the abundance of chert interbedded with clay.
Subunit IA is composed of pelagic clay. The first two sections of Core 199-1216A-1H contain sediments that alternate between dark brown (10YR 3/3) and brown (10YR 4/3). At the base of Section 199-1216A-1H-2, the color grades to very dark brown (10YR 2/2) and remains this color downcore. Subunit IA is also marked by thin accumulations of altered ash, zeolites, and zeolite clay layers that are yellowish brown (10YR 3/6) in color. Pronounced layers of zeolite accumulations are present in Sections 199-1216A-2H-2 (14 mbsf), 3H-1 (20 mbsf), and 3H-2 (22 mbsf). Zeolites are also abundant in burrow infillings in Core 199-1216A-4H. Both micro- and macromanganese nodules are present in the upper 20 m, and a discontinuous manganese hardground is present at 39 mbsf. Both iron oxide micronodules and black (N1) chert fragments are present in the basal portion of Subunit IA, beginning at 40 and 45 mbsf, respectively.
Subunit IB is differentiated from Subunit IA by the predominance of chert. The chert occurs as gravel-sized black (N1) fragments. Chert fragments result from brecciation of layers and/or nodules during drilling. Clay interlayered with the chert is not in situ because of drilling disturbance and in many instances is completely removed.
Site 1216 consists of a 62.2-m interval of pelagic brown clay and black chert, which have accumulated over the past 52 m.y. (see "Siliceous Microfossils" in "Biostratigraphy"). Core recovery was excellent in the upper four cores and decreases downcore because of the increasing frequency of chert. In contrast to Site 1215, there is no pronounced evidence for cyclical sedimentation or marked color changes representing critical transitions in Unit I.