ENDOLITHIC BORINGS IN HYALOCLASTITE SHARDS FROM THE HAWAII SCIENTIFIC DRILLING (HSDP) #2 PHASE 1 CORE: DISTRIBUTION, TIMING, AND BEHAVIOR

Endolithic tubular borings are common features in sideromelane shards in many samples of submarine hyaloclastite in the HSDP #2 Phase 1 core. Elongate tubules extend into sideromelane and palagonite from shard margins, cracks, vesicles, and patches of smectite that replace shard margins.

A common variety of tubules is about 1 mm in diameter and a few mm to 10's of mm long, straight to gently curving, and rarely bifurcating. Most tubules appear to be empty. This form resembles endolithic tubules of microbial or fungal origin described in soils and carbonate rocks. Points where tubules intersect the surface of thin sections take a DAPI stain, indicating the presence of DNA. Rigorous sample preparation and control exclude contamination as a source of this DNA. The structures are likely to be of biological origin.

The borings display aspects of behavior of the organisms that make them. Petrographic analysis demonstrates that the inception of the tubules is limited in time to a period after initial crushing of grains and coating of shards with smectite, but before any formation of palagonite. Boring activity may thus have occurred in buried hyaloclastites. Tubule-making organisms had the capability of dissolving silicate glass. The organisms, or parts of them, are drawn into the sideromelane, initially at high angles to the shard surface. Tubules very commonly curve toward olivine crystals in glassy shards, and then terminate at the crystal margin. We infer that the organisms respond to chemical signals in the glass substrate.

Tubules are highly associated with areas where smectite has replaced shard margins. The boring organisms may have effected alteration of the sideromelane in ways beyond their obvious ability to dissolve volcanic glass. On the other hand, formation of isotropic, apparently non-crystalline, palagonite alteration rinds on sideromelane shards is not demonstrably a microbial process.

Tubules are present in samples from the shallowest hyaloclastites encountered, at a depth of about 1100mbsl. Borings are most abundant in samples from about 1500mbsl. Hyaloclastites from deeper than 2200mbsl in the core are apparently free of borings, despite displaying the other features of alteration present in the samples containing tubules.