Magnetostratigraphy of US paleogene depositional sequences : implications for dating sea level changes

Abstract

Results of a detailed magnetostratigraphic investigation of late Paleocene and early Eocene sediments from the US Atlantic and Gulf Coastal Plains are presented. In Virginia and Maryland, stratigraphic units from the Aquia, Marlboro Clay and Nanjemoy Formations were examined in outcrop and from core material which spanned calcareous nannofossil zones NP6 to NP13. In Alabama and Georgia sampling extended across the Nanafalia, Tuscahoma, Hatchetigbee and Tallahatta Formations (NP8 to NP14).

In sediments from the US Atlantic Coast a record of normal polarity magnetochrons C26n, C25n, C24n and C23n were identified. On the Gulf Coastal Plain records of magnetochrons C25n, C23n, C22n, and C21n were also recognised. Calcareous nannofossil data were used to correlate the polarity reversal sequence observed with that of the geomagnetic polarity timescale.

The palaeomagnetic results of this study are incorporated into a chronostratigraphic framework based on magnetostratigraphy, where the record of polarity reversal boundaries is linked across the Atlantic to those previously identified in similar-aged sequences in NW Europe. The correlation of polarity boundaries enables a high resolution comparison of depositional cycles between continental margins on both sides of the North Atlantic. The implications for dating and testing sea level cycles using this magnetostratigraphic framework are explored.

Finally, high quality palaeomagnetic data obtained from this study have been used to refine the North American palaeomagnetic pole position for the early Paleogene.

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