BLACK, GREEN, AND RED: EARLY PALEOZOIC SLATE COLORS, CORRELATIONS, AND PASSIVE MARGIN-EARLY OROGENIC HISTORY ON THE OUTER MARGINS OF THE TACONIAN ALLOCHTHONS, EASTERN LAURENTIA

Break-up of the Rhodinia supercontinent included latest Proterozoic–earliest Cambrian rifting on the northeast Laurentian margin and deposition of thick lithic arenites. Succeeding passive-margin continental-slope deposits are mudstone dominated. The condensed (ca. 600 m) passive-margin successions on the outer margins of the Taconian allochthons from New Jersey to western Newfoundland have macroscale color alternations that are extend along depositional (and tectonic) strike. Alternations of green (and laterally equivalent purple and red) mudstones, locally with shelf-derived carbonate blocks, and black mudstones with bedded and nodular carbonates are linked redox-carbonate alternations (low vs high organics and carbonate). Black mudstone intervals in the allochthons include the upper Lower Cambrian (Olenellus Zone); a long uppermost Lower Cambrian–lower Tremadoc interval; the upper Tremadoc; lowest, middle and uppermost Arenig; and lower Caradoc. The latter intervals correlate with major eustatic rises and deposition of carbonate-dominated lithosomes on the platform. Climate maxima due to higher insolation with widespread shallow seas, limited deep-water circulation with reduced storminess, and increased carbonate sediment production/margin progradation explain the high organic content and bedded carbonates of black mudstones. Intervening green mudstones reflect eustatic fall (e.g., the Hawke Bay regression), climate minima, enhanced slope-water circulation, and platform margin collapse. Convergence with the Taconic island arc and the end of passive-margin deposition is marked by arc-derived flysch in the Taconian allochthons. However, the first synorogenic deposit in the Taconian allochthons is a diachronous Middle Ordovician red mudstone below the flysch. This burrow-mottled to –churned red mudstone reflects oxygenated bottom waters. Its thin ashes and radiolarites are the first evidence of the proximity of the volcanic arc, and its condensed nature (e.g., undiluted ashes and radiolatites) shows a reduction in background sediment (mud) accumulation. Rather than recording accumulation of laterites produced on a “Sauk sequence” unconformity as earlier proposed, Taconian Middle Ordovician red mudstones reflect condensed deposition as the peripheral bulge passed through the slope.