Hard separation is not required.
The Silk Roads wound across central Asia for centuries providing a trickle of luxury goods but without making any major change to the economies of either the West (specifically, Rome and to a lesser degree, Persia) and the East (China). That as because an overland route could only transport relatively minor amounts of goods - a pack load for most animals was about 50 - 100 kg, so only high value, small volume goods could be transported at all.
Give Land trade routes similar restrictions in the game, and a 'soft' separation across deserts/mountains/passes/ et al could allow restricted Trade Routes by land while not allowing the lucrative cash flow of Treasure Fleets, which would require Exploration Age ships.
For example, a real in-game Silk Road across land might allow only the transport of any Resources you do not have at your end of the Trade Route. IF you have no Camels, then 'Camel' from the other end wold be a legitimate Silk Road good. Have any Camel anywhere on your 'side' of the continent/pangaea mass, and that Resource is not eligible to trade. Basically, this represents the fact that it has to be really, really exclusive to be worth transporting all that distance overland.
That would mean. effectively, mostly only Treasure Resources would be eligible, unless your side of the continent/pangaea is all one biome - like no Tropical areas to provide Elephant/Ivory or no Desert to provide Camels. That would also allow the sudden Upgrade in Exploration, when new ships allow the deep sea long-distance trade routes that historically could transport much greater tonnages of goods (even an average Carrack, for example, could haul 200 - 500 tons, the equivalent of several thousand camel pack-loads, and they wouldn't have to be divided up into 100 kg parcels)