ST. PAUL — Gov. Mark Dayton said he lacks authority to impose a two-year moratorium on silica sand mining in southeastern Minnesota.

Mining opponents delivered a moratorium petition to St. Paul Tuesday as part of an Earth Day rally at the Capitol.

The petitions also call for creation of tough state-level regulations to protect air and water quality from the mining of silica sand, which oil and gas drillers use for hydraulic fracturing.

But Dayton’s spokesman issued a statement saying the governor “lacks the authority to unilaterally impose his own moratorium.”

The Land Stewardship Project launched the petition drive in January. The group contends Dayton has executive authority to enact a regional moratorium.

Dayton previously has expressed reservations about silica sand mining in the geologically fragile karst region of southeastern Minnesota.