Meaning of てなわけで at the start of a sentence

Question

This sentence is the start of a new paragraph. The ellipses are as written:

...てなわけで、まる子は、カブトムシの幼虫を廊下のすみに置いたプラスチックの水槽で飼っていたのだったが...。それから一か月。
??? Maruko was raising the Rhinoceros Beetle grubs in a plastic fish tank that she'd put in the corner of the hallway, but... . A month went by.

I don't understand what てなわけで means. I read this question, but was unenlightened since I can't understand というわけで either.

My guess is that the わけ part together with the のだった part later on suggest that the narrator is explaining the reason for something. Later sentences got on to say that she forget to look after them for a month.

Answer 1

「てな」 comes from 「というような」

It is a rather drastic phonetic change, but you have already encountered the と-to-て change before, correct? So, we know we are dealing with quotative particles (と & て).

「てなわけで」＝「というようなわけで」（≒「というわけで」）

Both phrases mean "with that being said". Depending on the context, "for that reason" would fit better as 「わけ」 can mean "reason". A freer and more informal TL would be "so", believe it or not.

It seems to me that "so" might not be such a bad TL for the context in question, but it is really your choice.

In very informal situations in real life, people often start a conversation with 「てなわけで」 or 「というわけで」 without barely explaining what it is that they want to talk about. This is what I was talking about in my comment above.