What is the difference between jeevatma and kaarana sareera (causal body)?
Jivatma is the self dwells inside the body and experiences fruits of Karma:
द्वा सुपर्णा सयुजा सखाया समानं वृक्षं परि षस्वजाते।
तयोरन्यः पिप्पलं स्वाद्वत्त्यनश्नन्नन्यो अभि चाकशीति॥ १.१६४.२०
Two birds of beautiful plumage, who are inseparable friends, reside on the self-same tree. Of these, one eats the fruits of the tree with relish while the other looks on without eating.
Whereas Karana Sharira is one of the three Sharira explained in other answers. It is the cause of other (Shtula and Sukshma) Shariras and experienced in the state of Sushupti (deep sleep), Anandamaya Kosha.
As explained in Viveka Chudamani:
अव्यक्तमेतत्त्रिगुणैर्निरुक्तं तत्कारणं नाम शरीरमात्मनः ।
सुषुप्तिरेतस्य विभक्त्यवस्था प्रलीनसर्वेन्द्रियबुद्धिवृत्तिः ॥ १२०॥
- This Undifferentiated, spoken of as the compound of the three Gunas, is the causal body of the soul. Profound sleep is its special state, in which the functions of the mind and all its organs are suspended.
So, these Shariras are bodies of Jivatma (the individual self) and Jivatma (who is actually the Atman according to Advaita) dwells inside it. Following verse of Vivekachudamani verily differentiate the self from three bodies/states and five Koshas (and directly deals with your question I think):
योऽयमात्मा स्वयञ्ज्योतिः पञ्चकोशविलक्षणः ।
अवस्थात्रयसाक्षी सन्निर्विकारो निरञ्जनः ।
सदानन्दः स विज्ञेयः स्वात्मत्वेन विपश्चिता ॥ २११॥
- This self-effulgent Atman which is distinct from the five sheaths, the Witness of the three states, the Real, the Changeless, the Untainted, the everlasting Bliss - is to be realised by the wise man as his own Self.
Visit following related posts for clear understanding of Shariras, Koshas and relation with Jivatma: