Sr-Nd isotopes constrain on the deposit history of the basins in the Gulf of Mexico

Abstract:

The Brazos-Trinity Basin IV and Ursa Basin are situated on the northern slope of the Gulf of Mexico. The Ursa basin lies in the center of late Pleistocene Mississippi River deposition, received the sediment deposition during Marine Isotope Stage (MIS) 2- 4. The Brazos-Trinity Basin IV belongs to a part of the Brazos-Trinity fan, it recorded the turbidite deposition and hemiplegic deposition during MIS1- 5. The Sr and Nd isotopic composition of the detrital composition of the sediment in both basins indicates the change of the sediment provenance during the basin-filled process. In the Ursa basin, The difference of ⁸⁷Sr/⁸⁶Sr ratio and ε_Nd of the detrital component between MIS1,2 (⁸⁷Sr/⁸⁶Sr ~ 0.7219 - 0.7321, ε_Nd ~ -12 - -13.4) and MIS3,4(⁸⁷Sr/⁸⁶Sr ~ 0.7310 - 0.7354, ε_Nd ~ -16 - -17.9) is suggested to be related with the provenance change of the detrital particles since LGM. The addition of detrital particle from Appalachians with less radiogenic ⁸⁷Sr/⁸⁶Sr and positive ε_Nd altered the character of the sediment of the Mississippi River during the last glaciation and deglaciation. In the Brazos-Trinity Basin IV, the narrow range of ⁸⁷Sr/⁸⁶Sr and ε_Nd indicate that the sediment source of Brazos-Trinity Basin IV had not changed obviously during MIS5e to MIS2, mostly from coastal rivers such as Brazos River, Trinity River and Sabine River. The pre-fan with ⁸⁷Sr/⁸⁶Sr ~0.735 and ε_Nd ~ -14.5 to -16.9, which is very similar to the deep sediment in the Ursa Basin with ⁸⁷Sr/⁸⁶Sr ~0.733 to 0.735 and ε_Nd ~ -16 to -18. It is suggested that sediments of the pre-fan of the Brazos-Trinity Basin IV were supplied from the ancestral Mississippi River Delta during the low sea level (MIS 6). During the MIS5, the discharge of Mississippi River is thought switched to its present course, ~300 km to the east.