The flood was worldwide. At the time of the flood, the earth was one land mass. After the flood, in the days of Peleg, the earth was divided.
Genesis 10:25
25 And unto Eber were born two sons: the name of one was
Peleg; for in his days was the earth
divided; and his brother’s name was Joktan.
1 Chronicles 1:19
19 And unto Eber were born two sons: the name of the one was Peleg; because in his days the earth was
divided: and his brother’s name was Joktan.
The genealogy of Peleg:
Noah
→ Shem
→ Arphaxad
→ Salah
→ Eber
→ Peleg
From this we see that it was after the flood that the earth was divided. Thus the kangaroo theory does not apply.
When Christ makes his second appearance, the earth will be turned back to the way it was before it was divided.
Doctrine and Covenants 133:20-25
20 For behold, he shall stand upon the mount of Olivet, and upon the mighty ocean, even the great deep, and upon the islands of the sea, and upon the land of Zion.
21 And he shall utter his voice out of Zion, and he shall speak from Jerusalem, and his voice shall be heard among all people;
22 And it shall be a voice as the voice of many waters, and as the voice of a great thunder, which shall break down the mountains, and the valleys shall not be found.
23 He shall command the great deep, and it shall be driven back into the north countries, and the islands shall become one land;
24 And the land of Jerusalem and the land of Zion shall be turned back into their own
place, and the earth shall be like as it was in the days before it was divided.
25 And the Lord, even the Savior, shall stand in the midst of his people, and shall reign over all flesh.