I don't think there is any tag that maps to a "pause" semantically. And there wouldn't be a way for a screen reader to see a margin-top as one, because there's no way it could understand intent like that. So basically, anything you do here would be kind of inherently unsemantic and possibly lost to screen readers. Hypothetically you could group paragraphs together into <section>s or something, but it sounds more like these are "let that sink in" type pauses rather than actual changes in topic, so that would also be incorrect semantically if that's the case.
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