Origin and age of the Manila high and associated Big Lake "sunklands" in the New Madrid seismic zone, northeastern Arkansas

Uplift of the Manila high and subsidence of the south-flowing Little River during the great New Madrid earthquakes of 1811-1812 formed the present lak e in Big Lake basin of northern Arkansas. This is the most recent deformati on of the 19-km-long Manila high that began between 11000 and 5400 yr ago a nd is time transgressive toward the south. At least 4 m of Holocene uplift occurred on the northern portion of the Manila high prior to initiation of the Little River distributary in mid-Holocene time. The distributary is def lected around the high, and overbank sediment derived from it thins and is Locally absent across the northern (highest) portion of the high. Deformati on along the southern end of the high began between 3500 and 2000 yr ago. S ince 3500 yr B.P., 2 m of uplift appears to have caused a reduction in grad ient, anastomosing upstream of the uplift, and incision of the Little River across the uplift. North of the Manila high, in the Big Lake basin, the Li ttle River has an increased aggradation rate similar to 10 times that of th e preuplift rate. Cores collected in and adjacent to Big Lake indicate that the Little River was ponded twice, apparently in response to deformation i n 1811-1812 and between 90 B.C. and A.D. 1640.