A COMPARISON OF MAGNETIC FABRIC IN ORIENTED PALEOMAGNETIC CORES TO OTHER CURRENT INDICATORS PRESERVED IN THE SAME ROCK SEQUENCE: PRESERVATION OF GRAIN ALIGNMENT AS AN INDICATOR OF PAST DEEP SEA CURRENTS AFTER LITHIFICATION AND SUBSEQUENT TECTONIC ACTIVITY

Can we use anisotropy of magnetic susceptibility (AMS) of a lithified and tectonically influenced sedimentary rock to indicate paleocurrent direction where no other indicators of current are present? In sedimentary deposits, paramagnetic minerals, such as a clays, as well as iron-bearing non-isometric minerals, can align themselves in specific directions relative to current flow; the resulting magnetic fabric can reflect that grain alignment and therefore current direction. Is this fabric still preserved after lithification and tectonic influence?

Studies indicate that a well-developed magnetic fabric is observed in sediment deposits resulting from turbidity currents. Turbidite deposits are end member examples of extreme current flow in a depositional environment and thus a meaningful test of the utility of AMS to discern depositional flow-related magnetic fabrics in sedimentary rocks as well.

The Hamburg Klippe - a Taconic allochthon primarily composed of trench deposits - has recognizable turbidite sequences. We recorded orientations of paleocurrent indicators and took oriented paleomagnetic cores, sampling different depths of an individual turbidite deposit within the Hamburg Klippe at Lenhartsville, PA. To compare the orientation of the magnetic fabric to extant paleocurrent indicators, we then measured the AMS signature in the paleomagnetic cores on a KLY-4 KappaBridge. The orientations of the principal magnetic axes preserved in the cores are consistent with flow directions of other paleocurrent indicators preserved in the rocks at the outcrop. However, one must take care to discriminate between sedimentary and tectonic fabrics; at this outcrop, the restored paleocurrent direction is subparallel to the direction of the emplacement of the allochthon there. Additional analysis of this and potentially other sites may help delineate between these two factors that may both influence the magnetic fabric and clarify the efficacy of this method in determining paleocurrent directions in lithified rock.