INORGANIC SILICA SOURCES CONTRIBUTING TO THE FORMATION OF NODULAR CHERTS WITHIN THE KITTATINNY SUPERGROUP CARBONATES, NORTHWESTERN NEW JERSEY

Cambro-Ordovician Kittatinny Supergroup cherts, Great Valley Sequence, northwestern New Jersey, are being investigated for evidence of inorganic silica sources. Cherts of the Cambrian Limeport and Upper Allentown and Ordovician Stonehenge, Rickenbach, Epler and Ontelaunee Formations, bear evidence of silica sources other than siliceous spicules.

Mapping of the Epler (Big Springs Member) and Ontelaunee (Harmonyvale Member) Formations show clay-rich seams at chert contacts. The clays are interpreted as cratonically-derived sediments deposited on the Laurentian carbonate margin. XRD and SEM analyses of these cherts show clay platelets preserved within the silica matrix.

A secondary silica source is available with the presence of quartz sand in cherts of the Limeport, Upper Allentown, Stonehenge, Rickenbach and Epler Formations. Quartz sand lenses have been mapped in close spatial association with these cherts, lining unconformities, porous zones, karst sequences, algal structures and various types of pressure solution surfaces. Examination of the quartz sand grains by optical petrography and SEM show dissolution along quartz grain boundaries.

Bentonitic ashes within the Epler Formation (Big Springs Member) represent a third inorganic silica source. The volcanic ash has been mapped in close spatial association with the Big Springs cherts, affecting not only the genesis of, but also the rheological properties of the cherts. Big Springs cherts are deformed into box folds, with bentonite forming a local detachment along which ductile deformation progressed. SEM examination of this chert has identified novaculitic triple point structures associated with high Titanium peaks; a signature of bentonitic ashes. Titanium peaks associated with novaculitic triple points provides evidence of a volcanic origin for the Big Springs chert.

Microbial bacteria have been identified (7000 x SEM magnification) in the Limeport and Ontelaunee Formations. The microbes occur in stromatactis mounds and algal structures within the cherts, suggesting the universal presence of microbes in extreme environments, where cherts usually form. Microbial bacteria may represent a biological catalyst in an inorganic sulfide complexing reaction, yielding the precipitation of inorganic silica for the formation of nodular chert.