SYNRIFT STRATIGRAPHY OF THE LAURENTIAN RIFTED MARGIN

Breakup of Rodinia and opening of the Iapetus Ocean produced the rifted margin of eastern Laurentia in the late Neoproterozoic to Early Cambrian. The irregular rifted margin includes orthogonally zigzag promontories and embayments distributed from Texas to Newfoundland. The Laurentian rifted margin subsequently was deformed by Appalachian orogenesis; however, along-strike correlations of synrift and rift-to-drift stratigraphy have supported palinspastic reconstruction of the Laurentian margin. Radiometric dating of rift-related igneous rocks along the margin displays a range in ages from 757 Ma to 530 Ma. Significant diachroneity documented by radiometric age data constrains timing of multiple episodes of rifting in specific locations along the margin.

An along-strike cross-sectional representation of synrift and rift-to-drift stratigraphy from the Pennsylvania embayment (southernmost Pennsylvania) through the St. Lawrence promontory (western Newfoundland) displays sedimentary accumulations with a range of thicknesses and facies. The synrift sedimentary units overlie Grenville basement rocks. Deposition during Iapetan rifting produced a synrift stratigraphy that may be correlated along the entire Laurentian margin. Significant lithologic variations in synrift stratigraphy along the northeastern part of the Laurentian margin include a range of rock types, for example, variegated mudstones, thick-bedded quartzose sandstone turbidites, and quartz-rich feldspathic sandstones with local to dominant shales. Sedimentary rocks are interstratified with volcanic rocks in some locations. Substantial variations in thicknesses of synrift successions are distributed along the rifted margin. A laterally continuous Early Cambrian quartzose sandstone of varying thickness represents the transition from rift-stage deposition to a passive-margin environment. Lateral variations in facies and thicknesses of the synrift stratigraphy are related to the promontories and embayments of the Laurentian margin.