The word used is buried (qbr), but we should not assume that refers to only modern-style graves and not tombs. For example, in Genesis 23, Abraham offers to buy land to gbr Sarah (23:4). The people he is haggling with use the words sepulcher and bury together (23:6). He then entombs her in a cave on the field (23:19). Abraham was also entombed there upon his death (25:9, 10) using the same word in question.
I am a stranger and a sojourner with you: give me a possession of a buryingplace with you, that I may bury my dead out of my sight. (Genesis 23:4)
Hear us, my lord: thou art a mighty prince among us: in the choice of our sepulchres bury thy dead; none of us shall withhold from thee his sepulchre, but that thou mayest bury thy dead. (Genesis 23:6)
And after this, Abraham buried Sarah his wife in the cave of the field of Machpelah before Mamre: the same is Hebron in the land of Canaan. (Genesis 23:19)
And his sons Isaac and Ishmael buried him in the cave of Machpelah, in the field of Ephron the son of Zohar the Hittite, which is before Mamre; The field which Abraham purchased of the sons of Heth: there was Abraham buried, and Sarah his wife. (Genesis 25:9, 10)
The word does also mean to simply bury without a tomb, as seen in Genesis 35:8 when Rebekah's nurse dies.
But Deborah Rebekah's nurse died, and she was buried beneath Bethel under an oak: and the name of it was called Allonbachuth. (Genesis 35:8)
The word allows for entombed, and Jacob's raising of a pillar (35:20) there shows that even if it is a below-ground grave, he marked the place where his beloved lay.
KJV used. Emphasis added to all verses above. Bold shows the use of qbr. Italics show qbr being used in reference to an above-ground tomb or sepulchre.