In the following sloka from Kishkinda Kanda of Valmiki Ramayana, Sugriva narrates the celerity of Vali to Sri Rama.
समुद्रात् पश्चिमात् पूर्वम् दक्षिणाद् अपि च उत्तरम् |
क्रामति अनुदिते सूर्ये वाली व्यपगत क्लमः || ४-११-४
“Before the dawn of sun Vali unweariedly strides from western ocean to eastern, and even from southern to northern for offering water oblations to the rising sun.”
Please note the mention of 4th ocean, apart from 3 oceans in Eastern, Western and Southern directions, in the Northern direction to India.
We all know that there is no ocean available in Northern side of India right now, except the ocean beyond the present day Russia.
Thus, we can infer that
Either the incident of Vali performing Sandhyavandana in 4 oceans occurred before formation of Himalayas
Sage Valmiki was referring to another ocean might have existed in the Ramayana period, in Northern direction to India.
Sage Valmiki was referring to an ocean that is existing beyond the present day Russia
In my opinion, the ocean in the Northern direction to India, that Sage Valmiki was referring to, might be the Gobi desert.
The Gobi Desert is a large desert or brushland region in East Asia. It covers parts of Northern and Northeastern China and of Southern Mongolia.
It is interesting to note that the Gobi desert is composed of sediment from erosion of the volcanic rocks (granite, basalt, rhyolite) as well as from ocean sediments.
So the Gobi desert area might have been an ocean before the Continental drift was completed, but after the formation of Himalayas.
Valmiki Ramayana refers to existence of Himalayas.
After having been struck by Brahma’s missile released by Indrajit, Rama and Lakshmana became unconscious. Sixty-seven crores of monkeys fainted. Hanuma and Vibhishana, however in consciousness, roared about in the battle-front with torches in their hands, making a search of Jambavan. They find Jambavan.
Jambavan requests Sri Hanuma to proceed to Himalayas, by crossing over the ocean and to bring four important herbs, viz. Mrita Sanjivani, Vishalya karani, Suvarna karani and Sandhani; so as to bring succour to the fainted army of monkeys.
गत्वा परममध्वानमुपर्युपरि सागरम् |
हिमवन्तं नगश्रेष्ठं हनूमन्गन्तुमर्हसि || ६-७४-२९
“O Hanuma! You ought to go to Himalaya, the foremost of mountains, by traveling higher and higher over the large ocean.”
Ramayana might have occurred at the point of time, when an ocean was existing in the Northern direction to India.