Memory arrays comprising strings of memory cells and methods used in forming a memory array comprising strings of memory cells

A memory array comprising strings of memory cells, comprising:

• a conductor tier comprising conductor material;
• laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers directly above the conductor tier, channel-material strings of memory cells extending through the insulative tiers and the conductive tiers, conducting material of a lowest of the conductive tiers directly electrically coupling together the channel material of individual of the channel-material strings and the conductor material of the conductor tier;
• intervening material laterally-between and longitudinally-along immediately-laterally-adjacent of the memory blocks, the intervening material comprising insulating material;
• and horizontally-elongated lines in the conductor material between the laterally-spaced memory blocks, the horizontally-elongated lines being of different composition from the conductor material that is laterally-between the horizontally-elongated lines;
• and
• wherein an uppermost portion of the horizontally-elongated lines comprises conductively-doped semiconductive material having one of a primary n-type or p-type conductivity-producing dopant therein, at least the uppermost portion of the horizontally-elongated lines comprising a secondary dopant of different composition from that of the primary dopant.